55
ROAD VIBRATION SIMULATION EXPERIMENT: FINAL REPORT DESIGN AND DEVELOPMENT OF A ROAD VIBRATION SIMULATOR FOR THE MIAMI UNIVERSITY VIBRATIONS LABORATORY CAROLYN BASSETTI SARAH BRADY MANDY FREDERICK JESSICA IRONS MATT WINDON DR. SHUKLA DECEMBER 15, 2003 MIAMI UNIVERSITY SCHOOL OF ENGINEERING AND APPLIED SCIENCE DEPARTMENT OF MANUFACTURING AND MECHANICAL ENGINEERING

ROAD VIBRATION SIMULATION EXPERIMENT: FINAL REPORT Report3.pdf · road vibration simulation experiment: final report design and development of a road vibration simulator for the miami

Embed Size (px)

Citation preview

ROAD VIBRATION SIMULATION

EXPERIMENT: FINAL REPORT

DESIGN AND DEVELOPMENT OF A ROAD VIBRATION SIMULATOR FOR THE MIAMI UNIVERSITY VIBRATIONS LABORATORY

CAROLYN BASSETTI SARAH BRADY

MANDY FREDERICK JESSICA IRONS MATT WINDON

DR. SHUKLA

DECEMBER 15, 2003

M I A M I U N I V E R S I T Y S C H O O L O F E N G I N E E R I N G A N D A P P L I E D S C I E N C E

D E P A R T M E N T O F M A N U F A C T U R I N G A N D M E C H A N I C A L E N G I N E E R I N G

2

Road Vibrations Simulation EGR 448 SENIOR DESIGN FINAL REPORT

EXECUTIVE SUMMARY

The Road Vibration Simulation Team’s task is to design and develop a road vibration

simulator for the Vibration Laboratory at Miami University. This will test the vibration

response to various potential road conditions of a component of an automobile or an entire

automobile scaled down to 1/5 the size. The simulator must be able to generate input and

then measure the response of the specimen being analyzed. The vibration simulator will be

used primarily for educational purposes and three lab experiments will be developed to

coincide with the simulator. The final product will be posted to the internet so other smaller

schools can mimic the design created by the team here at Miami University. The design of

the vibration simulator includes many components. The simulator will be suitable for use

with a scale model of an entire car as well as individual car components. The sensors used

will be force and accelerometers. The actuator will be an electrodynamic shaker and the data

acquisition/analysis package used will be Matlab. The design team is closely following a

Gantt Chart written at the beginning of the project to stay on task. This vibration simulator

will be finished by mid-April of 2004. It will then be tested by EGR 315 students. Based on

their feedback and time remaining, changes will be made accordingly to improve the

experiments written for the simulator.

3

CONTENTS

1. Executive Summary 2

2. Introduction and Background 4

3. Research 8

4. Proposals 34

5. Conclusions and Future Work 50

6. References 53

7. About the Team 54

8. Appendix 55+

4

INTRODUCTION AND BACKGROUND

INTRODUCTION

Road vibrations simulators are very important in the automotive industry. Before

assembling any vehicles, the parts must be analyzed in order to determine their reaction to

road vibrations. Once constructed, the entire vehicle is often analyzed to determine

response to vibrations as well. There are many safety reasons and comfort factors to be

considered in road vibrations analysis. While there are theoretical ways to roughly estimate

the response these components will have to road vibrations, it is necessary to experimentally

measure the actual responses to get accurate information. This simulator should be able to

measure the responses as accurately as possible, and it should give students an intuitive,

hands-on experiment in which to learn about these vibrations.

PROBLEM DEFINITION

Problem definition is a critical step in engineering design. The problem statement

should include, “objectives and goals, the current state of affairs and the desired state, any

constraints placed on solution of the problem, and the definition of any special technical

terms [Dieter, 10].” The vibrations design team identified an overall objective, several

important constraints and some general tasks within their problem definition.

Objective

To design and implement a versatile device and corresponding classroom experiments

for use in the Miami University Vibration Laboratory to simulate road vibrations felt by

vehicles during normal operation.

5

Constraints

The constraints of the project include physical laboratory space, time, and funds. Kreger

is currently the home for the School of Engineering and Applied Science. Room 201 is used

as not only a classroom, but also as a laboratory for many engineering classes. Because of

this, the design team feels lack of space is a constraint. In initial meetings it was determined

that the space available for building, storing and running the experimental setup could only

be the size of a tabletop. The next constraint identified is limited time. EGR 448 and 449 is

a two semester series in which research and design should be completed within the first

semester, leaving the second for building and implementing the projects. With only a school

year, about 8 months, the design team must consider time throughout many aspects of the

project. Finally, taking on such a large project requires large funds. The design team has

identified funding as an important constraint limiting many aspects of design including the

components used, specifically the types of actuators and data analysis software.

Tasks

The four main tasks of this project include (1) design and build the vibration

experimental setup, (2) develop Matlab interface to acquire and analyze the data from the

vibration simulator, (3) develop a lab procedure and manual for students and instructors, and

(4) make all relevant documentation available to all of academia via Internet.

As mentioned, one aspiration of the road vibration simulator senior design is to enhance

the learning experience and future engineering curricula. Education cannot be limited to

learning solely from books, and because of this, the project team’s primary intentions for the

final device is that it be used by future engineering students and faculty at Miami University

to supplement the traditional vibrations courses. Following this idea, all four of the general

tasks identified in the problem statement have an end goal of enhancing education. The

6

road vibration simulator must have an experimental focus. Therefore, the first task classifies

the device as an experimental setup and designing and building it is of primary concern for

the design team. Engineering students use Matlab or other data acquisition devices to collect

and analyze data during experimental procedures, thus, it is important for the design team to

incorporate Matlab into the experimental setup. This allows students to use the simulator

and understand it with ease. The third task listed is also of vital importance when it comes

to the education process. The design team must develop a lab procedure for students to use

in supplementation of vibrations courses. In addition, the team would like to construct a

manual for students and instructors to refer to when using the road vibration simulator.

Finally, with a broader reach in mind, the project team would like to make all design

information, data, and documentation available to academia via Internet. The project team

hopes to not only enhance Miami University, but also allow other universities with limited

resources to improve the learning experience of their engineering students by taking ideas

from the team’s research and design to either duplicate or add to the experimental setup.

TEAM OBJECTIVE

With a problem definition focused on building equipment and designing experiments to

enhance the educational experience at Miami, the design team has created a team objective

to further clarify what this means to them. Education is fundamental to the conception of

the project in the team’s mind. They feel it is important to consider the enhancement of

education in every step of the design and later the implementation process. Because of this

an underlying, shared goal has been formed: To build intuitive, hands on experiments that

supplement vibrations courses to enhance the educational experience of the engineering

student. In order to achieve this goal, the team must constantly consider the future students

7

when making decisions about design. This will be referred to throughout the research and

proposal sections. A simple example comes when choosing the layout for the graphical user

interface (GUI). The team had to take the seat of the students when choosing this design.

They had to consider, as students without any previous experience in vibrations or use of the

software, what would make the interface easy to use and to understand. A more specific

discussion of what went into this process can be found in the research and proposal section

of GUI.

The team also shares a common drive for choosing this project and working hard at

providing intuitive educational aids. Throughout their educational experiences, the team

feels that they have experienced many different effective as well as ineffective teaching

techniques. It is well agreed upon that classes involving hands on experiences are the most

effective in terms of material learned. The team feels that the reason for this is that these

types of experiences force a student to apply the knowledge he or she has learned from a

book, which in turn reinforces what has been taught allowing for better absorption of the

material.

A final objective of the team is related more to functionality of equipment and

experiment. The team has made sure to keep in mind the goal of building a versatile device.

Because of this, they have taken steps to insure all pieces are mobile and independent. First,

this will be useful for when the new engineering building is built and the equipment will need

to be moved. And secondly, this is important so the equipment researched and purchased

can easily be used for future projects.

8

THE BIG PLAN

The design team developed the diagram below to show how they view the project as a

whole. The team feels there are three main interrelating tasks within their project: Hardware,

Software, and Classroom Experiments. As the tasks are interrelating, the team feels that

singling one out to start work on would be an inappropriate way to approach the project.

The team feels that moving forward in each task simultaneously is the best approach. This

allows for gaining feedback and dealing with troubleshooting early on. They feel that leaving

a category untouched until it is necessary to begin may cause problems in the other two

categories if a problem is encountered in the third. The design team keeps this diagram in

mind in determining goals as well as in determining how one category affects the rest of the

project. The Big Plan can be seen in Figure 1.

Figure 1

RESEARCH

IMPORTANCE OF VIBRATION IN DESIGN

Vibration is a very important issue to study and analyze when it comes to design because

it has many effects on the overall system and how the system performs. Safety, human

9

factors and ergonomics, and style are three primary issues that account for vibrations

considerations in their designs.

Safety

One of the primary reasons for analyzing a system’s vibrations properties is safety. Since

structural integrity and coupling are affected by changes in vibrations properties, if a system

is not designed to withstand the vibrations it is going to encounter, the structure could fail

and human lives could be in danger. A perfect example of when vibration was not properly

considered and analyzed in design is the Tacoma Narrows Bridge Disaster. According to the

Tacoma Narrows Bridge site, on November 7, 1940, at approximately 11:00 AM, the first

Tacoma Narrows suspension bridge collapsed due to wind-induced vibrations

[http://www.civeng.carleton.ca/Exhibits/Tacoma_Narrows/]. Situated on the Tacoma Narrows

in Puget Sound, near the city of Tacoma, Washington, the bridge had only been open for

traffic a few months.” The bridge had been designed for structural grace with slender

towers and shallow stiffening trusses. The bridge was so light that it behaved much like an

airplane wing, generating lift with significant enough winds. On the day that the bridge

failed, the wind speed was such that the bridge began to oscillate at its resonance frequency,

thus causing the bridge components to fail.

Until the Tacoma Narrows Bridge disaster, designing with resonance frequencies in

mind was virtually non-existent, and thus the study of design against resonance frequencies

is a fairly new field. Now, experiments in the field include placing tiny accelerometers all

over a structure to monitor how it is behaving and to be able to detect changes in the system

behavior. This way, if there is a significant change in the behavior of the structure, the

proper measures can be taken to ensure the safety of those using the structure.

10

Other safety considerations have to do with the modal properties of structures. Certain

physical quantities are characteristic of every structure; these properties are known as Modal

properties. Modal properties (resonance frequencies, mode shapes, etc.) of the structure are

very closely related to how vibrations affect the system and are functions of their physical

quantities; consequently, when damage in the system results in a change in the physical

properties of the structure, the outcome is a corresponding change in modal properties of

the structure. If these changes are too great, the integrity, and therefore the safety, of the

structure will be compromised. For this reason, it is very important to consider the modal

properties of all the materials to be used in a structure.

Human Factors/Ergonomics

Another important factor when it comes to vibrations in design is the consideration of

human factors and ergonomics. According to the Merriam Webster Online Dictionary

ergonomics is “an applied science concerned with designing and arranging things people use

so that the people and things interact most efficiently and safely -- called also human

engineering.” Therefore, vibrations is important to consider when it comes to ergonomic

designs because if the vibration of a structure that a human is using is causing the person to

become uncomfortable in someway, this may cause them to become less focused on using

the structure properly and could lead to safety hazards. A perfect example of the importance

of this issue is when it comes to driving a car. Vibrations in the structure of the car can

cause fatigue and decrease the safety of the driver. According to a study done by Australian

Transport Safety Bureau (ASTB), “Some studies identified vibration as a stimulant and

others as inducing drowsiness…random and stimulating vibration exposure can act to

increase alertness and that low frequency monotonous vibration has the opposite effect by

increasing drowsiness.” If there are many high frequency vibrations, this could keep the

11

driver awake as “vibration and noise exert a stimulating effect on the central nervous system,

however result in muscle fatigue in the back and arm muscles due to the strain of controlling

the car. Body chemistry changes due to the vibrations experienced when driving. According

to the ASTB study, “the increase in lactic acid is due to muscle activity in the spine directed

at maintaining posture under exposure to vibration.” This muscle fatigue could be due to

changes in the body’s metabolism. Despite the reason for increased fatigue due to

vibrations, this could be avoided if the car had been designed with vibrations and how they

affect ergonomics in mind. On the other hand, if there are too many low frequency

vibrations, more similar to a rocking motion, this can increase the driver fatigue and

drowsiness and also decrease the safety of the driver. Again this could have been avoided

had vibrations been considered in design. In general it was found that drivers became more

fatigued from a large amount of low frequency vibrations rather than a large amount of high

frequency vibrations, however, regardless of the type of vibrations induced on the driver by

the car, high and low frequency vibrations are both dangerous and therefore need to be

considered in the design of cars and any other structure where the user can be negatively

effected by the vibrations the structure causes just due to normal use.

Style

Another aspect when it comes to the importance of vibrations in design is the style of

the structure. It is possible to tune the engine such that it vibrates at a certain frequency to

give a desired sound. This is usually done for cosmetic reasons, such as the Ford Mustang,

which has what one would call a signature sound. Harley Davison has actually patented its

sound and now each new Harley Davison engine must be tuned to that desired, patented

frequency or it is not of acceptable quality for the Harley Davison Company.

12

REASEARCH INTO CURRENT VIBRATION SIMULATION EXPERIMENTS

In order to justify the cost and time expenses of designing a vibrations experiment from

scratch, the team obtained some catalogues and brochures from Dr. Ettouney for various

educational experiments. These companies included Armfield and Hampden, which are

leading companies in the field of educational experiments. Researching this information

showed that the companies do not currently make any type of vibrations simulation

educational experimental setups. The types of experiment packages available from Armfield

and Hampden companies are in subject areas such as fluid mechanics, heat transfer,

thermodynamics, unit operations, controls, and the like. As well as looking at the brochures

from Hampden and Armfield, the team contacted the companies to see if they knew of

other businesses that make vibrations experiments, as well as doing extensive research online

about whether such experiments are available. From this research, the team discovered that

there are currently no educational vibrations experiments available. Because of this, the team

needed to create an original vibration experiment to be used for education. Looking at the

booklets also gave the team an idea of what was needed in a laboratory set up description

that would be available to other universities interested in modeling the experimental set up.

For example, the Hampden brochures outline how well written experiments have a purpose,

description, and specifications in addition to the actual hardware and software associated

with the experiment.

TRIP TO UNIVERSITY OF CINCINATI VIBRATION LAB

One of the first steps in the team’s research was to visit the University of Cincinnati’s

vibrations laboratory in order to get an idea about what a vibrations simulator looks like and

how such a system works. The team was unable to go at a time where they could see the

13

simulator in operation; however, the team was able to get an idea about what types of

components go into such a the design of such a structure.

A picture of the simulator used at the University is shown in Figure 2.

Figure 2

http://www.eng.uc.edu/dept_min/research/

This simulator is very large scale. An entire car can be driven onto the simulator for

analysis and a separate controls room is used to monitor the forces going into the car, as well

as the vibrations effects which result on the system. Hydraulics are used as the force of

power for the simulator and each wheel is placed on one of the four hydraulically operated

shakers. A specially designed floor built on top of springs is used to isolate the experiment

from vibrating the rest of the building during the experimental testing.

The simulator is part of the SDRL (Structural Dynamics Research Laboratory) at

University of Cincinnati, which has a large list of corporate sponsors. The Boeing Company,

Ford Motor Company, General Motors Corporation, Hewlett Packard, Leuven

14

Measurements and Systems (LMS), The MathWorks, The Modal Shop, MTS. Noise and

Vibrations Division, PCB Piezotronics, Pemtech, Structural Dynamics Research Corporation

(SDRC) and Vold Solutions all cooperate with UC’s SDRL laboratory in some form.

DISCUSSION OF PRIMARY DESIGN COMPONENTS

Building a vibrations simulator like the one used at the University of Cincinnati would

require a much more space, funding, and time than the team has available for their project;

consequently, the goal is to be able to scale down UC’s design and create a table top

simulator that can be used to conduct an experiment with the same principles in mind.

Although the simulators will have obvious differences, the four major components needed

in the design remains the same: the physical structure, sensors, actuators, and data

acquisition and analysis software. The following section discusses some of the team’s

research and reflection on each of these components:

Structure

The first consideration the team debated was what physical structure to test using their

simulator. An entire car, an entire scaled model of a car, or individual car components were

all options for what object should be tested. Testing an entire car was eliminated

immediately on account of a lack of space and funding available. The next consideration

was the level of intuitiveness involved in the design. Since the simulator was designed with

the goal of being used for a beginner’s vibrations experiment, the team wanted to make the

design very intuitive in order for students to be able to readily see the real world applications

involved. The team believed that using an entire scaled down model of a car supported this

goal. Also, if individual car components were to be the subject of testing, the experiment

15

would want to eventually relate the effects on the individual components back to see the

entire ride of the car later in the experiment. A system of relating the two would have to be

developed, and consequently, by testing an entire scaled down model, this step can be

eliminated from the process.

As research showed, the world of scale model vehicles is vast including anything from

monster trucks to motor cycles at scales ranging from 1/36th to 1/4th. Dr. Fazeel Khan

spoke with the team specifically about 1/10th model cars and the realistic components found

on these cars. He brought in a car and the team was able to see the car’s size as well as its

many components. He also spoke with the team about what he felt would be a good model

size and type for the project at hand. He recommended a scale remote control car larger

than 1/10th. The team was able to agree with this recommendation prior to research due to

the shared desire for intuitive learning. The 1/10th scale was too small, allowing for little

variation in the placement of accelerometers or the actuator. Also, the addition of

accelerometers to a car weighing less than 5 pounds would add a substantial percentage of

mass to the system. The size also affected the acquisition of accurate data. It was found that

using a small scale car would produce frequency data consistently at high ranges, while a full

scale car would produce frequency data at low ranges. The problem here exists in that

analyzing data at either high or low ranges is not only difficult to do, but difficult to do

accurately. A car between 1/10th and full scale would produce data over a middle range

giving more consistent data that is easier to analyze. Again with the desire to make this

experiment applicable to the real world, the team chose a car as the remote vehicle as most

students drive cars in comparison with motorcycles or trucks.

16

Since a size between 1/10th and full scale was needed, the team started researching the

1/5th scales and 1/8th scales. The design team contacted a company, Technokit, who made

1/5th and 1/8th cars to determine whether one scale was more realistic than the other. Their

response suggested that their 1/5th scale cars were more similar to a real car in terms of

weight, engine, tires and response than their 1/8th cars. Upon discussing these results with

Dr. Shukla and Dr. Khan, the design team decided to focus their future research on

obtaining information and dealers of 1/5th scale cars.

Support Structure

An important part of the required hardware is a support structure for the car. There are

two main reasons for the structure. First, the car weighs approximately 23 lbs, and the shaker

can only support a payload of up to 10 lbs. Therefore, the structure will need to support the

weight of the car. Also, the support structure needs to prevent the car from being in contact

with the ground. Since the team does not have an isolated laboratory, outside vibrations may

be transmitted from the ground to the car. Also, the ground would dampen vibrations from

the shaker to the car. In order to fulfill these requirements, the team considered two possible

support structures. The first idea was to have the car suspended from the ceiling by 4 bungee

cords. This would be a simple and cost effective way to accomplish both requirements. The

other option was to build a separate support structure, and suspend the car from bungee

cords attached to the structure.

Sensors

Two types of sensors will need to be used in this experimental setup. These are force

sensors and accelerometers. Force sensors will be used to measure the input force applied to

17

the system by the actuator. The team will need to select their actuator before they can select

a force sensor that can be used in combination to accurately measure the impact. Miami

University already has three accelerometers available to be used in the experiment. The team

hopes to use these readily available accelerometers in order to cut back on some of the costs

involved with the project.

Load Cell

There are many options available to measure the force transmitted from the shaker to

the car. A good but potentially costly choice would be to use a load cell to measure the force

output from the shaker. One option would be to run an open loop experiment that would

not require a load cell. However, this would limit the data recorded, and reduce the accuracy

of the data. There are still other alternatives to using the load cell. If the team wanted to

achieve similar results at a cheaper price, they could use an accelerometer to measure the

input.

The team is using a load cell to incorporate the idea of force measurement (hence not

use an accelerometer) in the experiment. Force measurement is important in the experiment

because the team is attempting to create an intuitively obvious experiment. An important

aspect of this is to see the forces applied to the car by the road conditions. Theoretically, a

shaker would send the same signal as you generate in Matlab but using a load cell is more

precise. It also helps in detecting any loose connections between shaker and the car. The

voltage is input through Matlab, then amplified through the amplifier, so there will be many

chances for the data to differ from the predicted values. The load cell will record the actual

data, thus increasing the accuracy of the results. The team has not chosen a specific load cell

to purchase yet.

18

Actuators

The three primary types of actuators the team debated using in the design of the simulator

were hydraulic, electronic, and impact systems. The design team primarily investigated these

three types since they are the most commonly used techniques, and information on them is

readily available and accurate.

Hydraulic

Hydraulic actuators operate using Pascal’s Law, which states, “when a pressure is applied

to a liquid in a sealed container, the pressure is distributed across the liquid, and the pressure

is the same everywhere throughout the liquid.” In hydraulic systems, a power source must

supply pressure to the fluid. The pressure is the same throughout the fluid, which is

consequently used to push and pull a piston.

Hydraulic systems are lightweight and compact. Low compressibility of the medium and

low sensitivity to temperature are also advantages. Hydraulic actuators are best for heavy

loads and high speeds allowing for large forces and accuracy. The use of fluids allows for

inherent damping which results in no added vibration. The lightweight components in a

hydraulic system allow for quick acceleration and low heat generation. The vibrations

simulator used at the University of Cincinnati, as well as the Model 3.53.10 Multi-Axial

Simulation Table, both have impact forces powered by hydraulic systems.

Some disadvantages exist as well. These systems are typically complex and require

maintenance to numerous filters, fitting, valves and tubes. Maintenance must be performed

by someone with expertise in the hydraulic field and frequent testing of the hydraulic oil

must be done. Noise as well as leaking of oil are concerns, especially since the oil can be a

fire hazard. Costs can add up quickly as a separate power source is needed as well as

component replacements and energy to generate power.

19

Electric

Electrodynamic and electromagnetic are two different options for electric actuators.

These electric actuators use an electrical power supply as a drive. The electrodynamic uses

an electric motor, while the electromagnetic uses magnets and varying voltage to drive the

actuator.

Both offer low noise advantages as well as low power supplies which mean lower energy

costs. Electric actuators are excellent with light loads and low speeds. Electrodynamic

actuators are lightweight and do not use pipes or pumps. Without the use of flammable or

compressed fluids, the electric systems are environmentally safe. Neither unique nor

extensive maintenance is needed in electric systems. Electromagnetic systems have a quick

response time and can generate high forces.

The electromagnetic actuator is heavy and this can cause slow acceleration. Elements,

such as screws or gears, within the electrodynamic actuator may transmit vibrations to the

moving parts. As the parts of the system wear, the system may lose accuracy.

Impact/Manual

Impact testing is the third option the team has considered as the actuator for the applied

vibration force. In impulse testing, the input force to the system is a single impulsive force

applied by a specially designed impact device, such as an impact hammer.

There are several benefits to impact testing. It can be said that “the usefulness of the

impulse technique lies in the fact that the energy in an impulse is distributed continuously in

the frequency domain rather than occurring at discrete spectral lines as in the case of period

signals. Thus, an impulse force will excite all resonance frequencies within its useful

frequency range.” (Halvorsen) This basically means that impact testing can capture all of the

20

same results as the other two methods for system excitation, obtaining relatively accurate

representations of the system’s vibrations properties. Impact testing is also simple to setup

and take measurements for, as well as highly portable. Finally, one of the largest benefits to

impact testing is the relatively inexpensive

One of the largest downsides to impact testing is that it is not a very intuitive method of

testing, one of the primary goals for the team’s experimental design setup. It is doubtful that

vibrations beginners would believe that the force applied by an impact hammer can

represent a road vibration as accurately as an electrical motor. Also, impact testing is very

subject to human experimental error. In order to obtain the most accurate results, it is

desirable to average multiple hits on the system. In doing so, testers need to make sure that

they are striking the exact same place each time they repeat the experiment. They also must

strike the object being tested directly along a single axis of impact in order to obtain accurate

results. Finally, the tester must be sure to only strike the system twice, for if vibrations cause

a second impact to take place, the results on the system will not be accurate.

Electrodynamic Shaker Options

The group considered purchasing electromagnetic shakers from 3 different companies:

DataPhysics, Ling Dynamics, and MB Dynamics. After doing preliminary research, the

group discovered that MB Dynamics was the leading shaker supplier in the industry. Still, the

group wanted to consider all possible options before making a decision. Datasheets for the

shakers from these companies can be found in the Appendix.

Ling Dynamics, which distributes their products through the LDS (Ling Dynamic

Systems) Group, seemed to have exactly what was needed for the project. The shaker

considered by the group was the V406/8 – PA 500L. This was their 44lb sine force shaker.

21

Ling specified that their products could be used for laboratory experiments. They also

offered cooling fans and amplifiers in a package with their shakers. However, upon

contacting the LDS group, the team found that no academic discounts were available, and

the sales representative also made reference to MB dynamics as a reputable company that

may be able to suit our needs.

DataPhysics offered a 45 lb sine force shaker that produced a 31 lb random force, the

DP-V031. They also offered packages that included amplifiers and cooling systems.

However, DataPhysics was hard to contact, and did not seem to be willing to go out of their

way to fulfill the team’s needs.

MB Dynamics was very highly regarded by every shaker authority the team contacted,

and Dr. Shukla also felt that MB Dynamics was a reputable company that would be easy to

deal with. MB Dynamics offered a Modal 50A exciter that produced a 50 lb sine force. They

also offered amplifiers, cooling systems, amplifiers, and accessories kits. MB Dynamics also

responded quickly to any requests the team made, and offered an academic discount for any

items the team would purchase. MB had a great reputation for service, which the group

found to be very important due to the unique needs of our project.

Amplifier

The shaker requires an input voltage of up to approximately 20 volts. However, it is

dangerous to produce a voltage of much more than 5 volts through a software program,

such as Matlab. Therefore, an external amplifier is required to produce the necessary voltage.

Amplifier selection is a relatively simple process, since many shakers have recommended

amplifiers. The team also determined that they would need an accessories kit, or a similar

product, that would supply all of the necessary cables and attachments.

22

Cooling System

Cooling systems usually are necessary when the shaker is used at more than 50% of the

full performance force. To determine the necessity of a cooling system, the team asked many

representatives of the shaker suppliers their opinion, based on the projected uses for the

shaker. They also considered the requirements the experiments would have for the shaker,

and the possibility of future experiments that may have a greater force requirement from the

shaker and would therefore need a cooling system. The team decided that they will not be

using the shaker near its peak force, and the shaker experiments will be no longer than a few

seconds each. The alternatives they considered were as follows:

• No cooling system.

• Shop air cooling system. This would connect directly to the shop air supply. The

current vibrations laboratory has access to shop air, so this would be a feasible

option for us.

• Portable cooling system. This uses a vacuum cleaner type idea that can be used when

shop air is not easily accessible. This is a little more expensive than the shop air

cooling system, but because of its portability and air flow generation, it is a very good

option.

DATA COLLECTION & ANALYSIS

Matlab

Matlab is a software program designed to aid in the mathematical analysis of system

models and experimental analysis. Some of the capabilities of Matlab include technical

computing, control design, test and measurement, and image processing. In this experiment,

the goal will be to develop the capability to integrate Matlab into the experiment in order to

23

collect and analyze the experimental data. Matlab will also likely be used to obtain transfer

functions (graphs of the system output/ input with respect to time) and other relevant

vibrations graphs for the laboratory experiment.

LabVIEW

An alternative to MatLab is LabVIEW. LabVIEW is another software program that can

provide a graphical way for the group to acquire and measure the signal, analyze the

measurements, and present the data in an easy-to-use fashion. It is advertised to be easier to

use than other traditional development tools.

Selection

Primarily due to the fact that three of the students have had at least some previous

experience with Matlab, and two of the students have used Matlab in a vibrations-based

experiment for data acquisition as well as analysis, the team decided to use Matlab for the

software portion of the project. Information manuals and faculty expertise towards Matlab

is also more readily available, which would be helpful in troubleshooting problems that could

occur in learning this complicated and relatively new software program. Finally, research did

not concluded that LabVIEW’s data acquisition and analysis capabilities were superior to

Matlab’s in a way that would counteract the benefits of using Matlab.

DAQ

In order to measure and analyze physical phenomena, a data acquisition system is

necessary. This system typically provides the tools and resources necessary to perform the

24

aforementioned task. A data acquisition system is basically a connection between software

and hardware. Typically, a data acquisition system consists of:

• Data acquisition hardware

• Sensors and actuators

• Signal conditioning hardware

• Computer

• Software

The computer needs to read and analyze the data gathered by the accelerometers on the

car’s vibrations. The accelerometers read data in analog form. This data is then sent to a

signal conditioning box which also reads in analog. The signal conditioning box improves

accuracy with amplification, filtering, and allows for simultaneous sampling. From this signal

conditioning box, the data is sent to the computer. In the computer, there is a card that

converts analog data to digital data so it can be processed. Now, the data acquisition

software become important. The data acquisition software talks to this computer card and

brings in the digital data to Matlab. This software allows the user to read information from

the accelerometers. Data analysis begins once the GUI (Graphical User Interface) has been

initialized. Below is a diagram of the general flow of data:

There are not a wide variety of data acquisition software programs available to the design

team that are suitable. The Data Acquisition Toolbox in Matlab is the most suitable

NI Signal Conditioning Box: Analog

Analog Digital Converting Card inComputer

DAQ: Digital MATLAB Code To Analyze Data (GUI is used to initialize): Digital

Accelerometers: Analog

25

software because it is compatible with the already-owned signal conditioning hardware. It is

also built on the same platform as the GUI and analyzation code.

GUIDE To enable a user to initialize data collection and analysis through Matlab, a graphical user

interface has to be created. Creating one in Matlab is the most efficient option because this

will allow all parts of the design project program software to be built on the same platform.

In order to make use of a graphical user interface through Matlab, GUIDE has to be used.

GUIDE is an acronym for Graphical User Interface Development Environment. A set of

tools for creating GUIs is provided in GUIDE. When GUIDE is opened, the Layout

Editor appears. This Layout Editor is what contains the GUI as well as the control panel for

all GUIDE tools. Push buttons, pop-up menus, axes, and other components are available

from the component palette. They can be easily dragged into the layout area. Figure 3

shows an example of a GUIDE Layout Editor and its components.

Figure 3 Courtesy of www.mathworks.com

26

GUI

In order to make the road vibration simulation laboratory more user friendly, the design

team created a graphical user interface (GUI) in Matlab. A GUI is a program interface that

takes advantage of the computer’s graphics capabilities to make the program easier to use. If

designed appropriately, taking ergonomics into account, a GUI can free the user from

learning complex command languages. GUI’s can also make it easier to move data from one

application to another.

Some of the basic components of a GUI can be seen in Table 1. The design team used

some of these components, but not all of them, as the team wanted to keep their GUI as

simple and user friendly as possible.

GUI COMPONENTS

COMPONENT ACTION Pointer A symbol that appears on the display screen that

the users moves to select objects and commands.Pointing Device A device, such as a mouse, that enables the user

to select objects on the display screen. Icons Small pictures that represent commands, files, or

windows. Desktop The area on the display screen where icons are

grouped. Windows Areas into which the desktop is divided. Menus A way for the user to execute a command by

selecting a choice from a menu. Table 1

After reading manuals and documents about how to create a GUI using Graphical User

Interface Development Environment (GUIDE) command in Matlab, the team began

developing a GUI that they wanted to have be their final user interface that people using

their vibration simulator would use. After a short period, the team realized that the code

associated with the size of GUI that they wanted to use was quite large just for the different

components of the GUI such as pull down menus and graph windows. Once the team

27

starts adding code to make the GUI work with the Data Acquisition (DAQ) Toolbox and

other components of the simulator, the code will be quite complex, however, in order to add

this code in the right part of the GUI code, it is necessary for the team to understand the

code. When one large GUI is made at once, the code is too complicated for the team to

understand because of their relatively limited experience with Matlab. When developing a

GUI using Matlab, several lines of code are written for each element that is added to the

GUI. Because of this, the code behind the GUI can become quite complex very quickly. In

order to manage the amount of code they would have to work with, the team first developed

a simple example of a pull down menu. As can be seen in Figure 7, the team’s final GUI

contains several pull down menus, so it is import for the team to understand the code

associated with a pull down menu. Once they learn the basic code they will be able to add

more code and make the GUI do more complex operations. Similarly, because of the

amount of graphs on the team’s final GUI, the team first created a simple GUI that plots

just two functions of X based on a user input value. Understanding the code behind this

simplistic graph model will allow the team to make more complicated graph functions as

desired for the final GUI. The simple pull down menu and graph GUI’s can be seen in

Figure 4 and Figure 5 respectively. The code for these can be found in the Appendix for this

report.

Figure 4 Figure 5

28

Through research, the team found that when designing a GUI, it is very important to

consider ergonomics. Ergonomics is the study of designing for human safety and comfort.

The more ergonomically designed something is, the more likely the users are to use it

correctly without being injured. This is especially important when it comes to computers.

Some of the things that ergonomics focuses on in design are simplicity, consistency,

immediate feedback, and intuition.

Simplicity involves ease of use of the GUI. The simpler the GUI is to use, the more

easily the user will be able to figure out how to work the program, and thus gain more

benefits from it. According to congitivent.com, “the [GUI] designers attempted to

communicate with users more effectively by making the computer communicate in ways the

brain uses more readily; using icons for instance, because the visual part of the brain can

track their presence and state much better than words. They developed ways of organizing

information in patterns which the eye can track through more easily, drawing attention to

the work in progress. They developed the model of WYSIWYG (what you see is what you

get) to improve print proofing performance, and found through testing that the digital

representation of black text on a sheet of white paper increased information legibility and

retention.” Thus, including simplicity in the design of the GUI allows for users to use it

more effectively and learn more, which is exactly what the design team wants.

According to omnica.com, “there are a number of basic ergonomic guidelines which can

be incorporated into a product design that will eliminate or reduce learning curve times.”

Consistency, which is one of these guidelines, involves making sure everything on the GUI is

displayed in a consistent, almost repetitive manner. “Maintain consistency by making sure

similar or identical interfaces operate in a similar manner. Controls should also respond the

same way every time. While multifunctional buttons may conserve space and reduce cost,

29

they can also be a source of user aggravation.” The way the team achieved this in their GUI

is discussed further in the proposal section below.

Immediate feedback involves the ability of the user to perform an action with the GUI,

and them being allowed to see the results of their action immediately. According to

omnica.com, “if possible, the device should confirm to the user that input has been received

and is appropriate. Such feedback should be immediate, to prevent the user from repeating

the function. Some ways to accomplish this are to provide tactile, visual, or audio responses.

In addition, the designer can help prevent user confusion by giving different types of

feedback for dissimilar functions.” A perfect example of an item in a GUI is a pull down

menu. The user selects an item from the list in the pull down menu and they are

immediately able to see what they have selected. This makes the design much simpler and

the user is able to see whether they have performed a particular action correctly right away.

This improves productivity and learning. Again, according to omnica.com, immediate

feedback is an ergonomic guideline that, when incorporated into a design, will eliminate and

reduce learning curve times. The methods incorporated by the team in order to have

immediate feedback in their GUI are discussed in the following proposal selection.

Finally, intuition involves the idea that human tendencies can be incorporated into the

design of the GUI such that the actions that need to be performed by the user are very

intuitive in nature. According to mtnmath.com, “intuition is defined as knowing or sensing

without the use of rational processes.” It is important to incorporate this idea when

designing the GUI because if the GUI is designed such that students can just know or sense

what to do next, then it will be easier for them to perform the tasks required of them from

the GUI, perform the experiment and thus learn something from the whole simulation.

30

SIMULINK

Although the team would be unable to acquire the shaker as early in the design process

as was wanted, they did have the equipment to perform an impact hammer testing already

available in the vibrations laboratory. Because the team wanted to move forward on the

project in as many directions as possible early in the design process, it was decided that a

numerical experiment was needed that could analyze the differences in data resulting from

impact hammer excitation and shaker excitation. This would allow the team a larger portion

of time to develop analysis code and troubleshoot the problems that arose throughout the

process.

The team decided to use Matlab’s Simulink tool to develop the beginning model for the

numerical experiment. Simulink is a Matlab tool that can be used for modeling, simulating

and analyzing complex systems. Simulink’s ability to generate a wide range of signal types

made it fitting to the team’s objective for the numerical experiment.

Within the Simulink model, signal generators were used to create two different signals,

one to model the shaker excitation (a random signal), and one to model the impulse hammer

signal (two step signals added together, each with a different start time, such that the

addition results in an impulse force). These signals were then fed to a transfer function that

represents a general tendency for a system’s behavior, based on general trends for how the

output of the system results to input forces. The output response could be viewed through

the scopes placed at the end of the Simulink model. The Simulink model is shown in Figure

6.

31

Figure 6

The data from before and after the signals encounter the transfer function are outputted

to two separate files that can be loaded into a Matlab file. Within the Matlab file, the

function ‘fftmspec’ is used to take the Fourier transform of the input and output files and

convert them from time domain to frequency domain. From here, the signal output can be

divided by the signal input, and the transfer functions resulting from the two different forms

of excitation can be examined. The code developed so far for the corresponding Matlab file

is given in the appendix to this report.

For accurate results in this experiment, the team needed to ensure that the transfer

function used in the experiment was representative of a stable system. By making sure that

the poles (roots of the denominator of the transfer function equation) were negative, the

32

team made sure that the system model developed was indeed that of a stable system. Ideally,

the transfer function would be representative of the car; however, it was not necessary to

have that high of a degree of accuracy in the model to achieve the general purpose of

identifying differences in behavior.

The team is still working on the numerical experiment and hopes to use the data to

examine the affects which changing such experimental variables as windowing and averaging

have on the outcome of the transfer function.

CLASSROOM EXPERIMENTS

It is important to consider the importance of intuition in experiment and design, and as

previously mentioned, according to mtnmath.com, “intuition is defined as knowing or

sensing without the use of rational processes.” It is important to incorporate this idea when

designing an experiment because if the experiment is designed such that students can just

know or sense what to do next, then it will be easier for them to perform the experiment and

thus learn something from it. Continuing with this idea, the team wanted to use a car that

would respond much like a real size car since that is what students have had experience with.

Through research, the team found that 1/5th scale cars were more similar to a real car in

terms of weight, engine, tires and response than their 1/8th cars; which since students are

familiar with how a real car responds, using a 1/5th scale model increases the intuitiveness of

the experiment.

One important idea to consider when dealing with any type of experiment is the

accuracy of the data obtained from the experiment. This is important because there is no

point to doing the experiment and finding data from it if the data found is inaccurate and

therefore unable to be used. Because of this, it is important to look at ways of checking the

33

accuracy of data obtained from an experiment. There are several ways in which to

accomplish this with number of averages, cycle time, and windowing being some examples.

One technique for checking the accuracy of data taken from an experiment is changing

the number of averages taken when analyzing the data. The number of averages is going to

affect the accuracy of the data collection. Depending on the number of averages taken, the

outliers, high, or low points in the data, could be accentuated or diminished, thus affecting

accurate data collection. If your data remains consistent with many different numbers of

averages, then it can be considered that your data collection methods were accurate, but if

your data varies a lot depending on the number of averages taken, the data collection may

not have been too accurate. Once the data is sampled, then the Fast Fourier Transform is

computed to form graphs of the input excitation and output response. These functions are

averaged and used to compute the coherence function and the frequency response function;

both of which are important for modal data acquisition. The coherence function is used as a

data quality assessment tool which identifies how much of the output signal is related to the

measured input signal. The frequency response function contains information regarding the

system frequency and damping and a collection of frequency response functions contain

information regarding the mode shape of the system at the measured location.

Another technique for checking the accuracy of the data taken from an experiment is

sample time, which is going to affect the accuracy of the data because, as with any

experiment, a reasonable amount of time is needed in order to gather accurate data. In

general, it has been found that the more time the data is taken over, the more accurate the

results of the experiment. There does, however, reach a point, where increasing the cycle

time does not improve the accuracy of the taken data; which is something that is unique to

34

each individual experiment, and would therefore need to be analyzed and dealt with based

on the experiment being performed.

A third technique for checking the accuracy of your experimental data is a technique

known as windowing. Windowing is the process of adding a weighting function to the

measured data. This weighing function, or window, is used to force the data to better satisfy

the periodicity requirements of the Fourier Transform Process. This process minimizes the

distortion effects of leakage, which is a distortion in the data during the transformation of

time data to the frequency domain using the Fast Fourier Transform.

PROPOSALS

STRUCTURE

It was found that in America, the popular scale for remote control cars is like Dr. Khan

suggested, the 1/10th scale. The 1/5th scale cars were found primarily in Europe, so finding

retailers and information in the United States was quite difficult. After e-mailing companies

for information and getting little response, the design team determined that calling dealers

was the best way to get what they wanted. The team found that the best approach was to

explain the project at hand and then ask the companies for their opinion on what was

needed.

Upon discovering that a car with engine and electronics was nearly $1000, the team

decided they could make do with a realistic chassis and suspension system if it were less

expensive. After contacting several dealers, importers and race track companies explaining

the project and then asking if they could either sell the team parts or build the team

something, the team was given two options of put together machines, no electronics and no

35

engines. These two options were slightly over $500, which was the team’s maximum car

budget. While doing research focused on systems instead of cars, the team also came across

an offer from a company for a 1/5th scale car with engine and body, but no electronics, for a

discounted list price of $500 not including shipping. This was the only option that came

with a body, which added to the team’s intuitive initiative, making the test structure to look

more like a car than what a chassis and suspension system would look like. However, the

fact that the engine was included was the decision maker in determining which option the

team wanted. The team liked the idea of not having to add weight, which they would have

had to do with a chassis system since it would be missing key items like body, engine and gas

tank. The team also liked the fact that, for an extra $200 and a trip to the hobby shop,

future students or faculty could purchase the electronics to make the car run if research or

experiments warranted such a purchase. In order to fully justify their purchase decision, the

team constructed a selection matrix which can be seen in Table 2.

Selection Matrix (1-5)

Intuitiveness FunctionalityMetal Construction Suspension Cost Total:

Alro Racing- whole car 4 4 4 4 3 19

GB Direct-parts only 3 3 3 3 3 15

Victory Speedway-parts only

3 3 4 4 3 17

Build own-H frame & Suspension

2 2 4 3 4 15

Table 2

With the selection matrix, the design team weighed each option in several categories. A

discussion of the team’s definition of each category is necessary. The team considers

36

intuitiveness to be a measure of how much the car affects the students understanding of the

experiment. For example, with the whole car option, the team feels that this ranks highest

because the true to life appearance of the car will aid the student in understanding the

experiments application to a real car. With the built H frame option, the team felt that the

put together appearance of the structure would hinder the student in understanding that the

experiment was supposed to simulate a real car. Functionality is defined by the team as

opportunities for future use. The whole car option gets a four in this category because for

$200 someone could purchase the electronics to get the car to run if a running car was

needed for future senior design projects or other engineering classes. The suspension

systems built by GB Direct and Victory Speedway are rated with a three because there would

be a possibility that the companies supplying them could provide faculty with other parts to

enhance possible use. Therefore, the H frame option is rated with a two as there isn’t much

use outside of this project. Metal Construction is obvious in definition, but not so in

importance. The reason for using this category in the selection matrix is that metal

construction of the car affects the stiffness of the chassis and thus the realistic nature of the

model. All options were made with metal parts except there was some mention of older

plastic parts with the GB Direct offer. The team therefore rated this option slightly lower

than the rest. Suspension is used for obvious reasons as it is most important to the study of

vibrations in cars. The team rated the GB direct offer with a three because, although the

suspension system was made from realistic parts, the plastic used may affect the operation of

the system as a test structure. Also, the team rated the H frame option with a three because

the amateur construction of the system may affect the quality of suspension. And finally, cost

is another important aspect in determining selection. The only obvious savings came with

the H frame option as the team would be building most of it on their own. The other three

37

options were similarly priced at a little over $500, therefore all these options were rated the

same.

It was seen through the selection matrix, as well as the general team opinion, that the

entire car offer from Alro Racing, an importer of Technokit cars, was what the team wanted

for their experimental test structure. A picture of this car as well as its specifications can be

found in the Appendix. This car is made with metal parts and has four independent

suspensions. Each suspension system consists of 1/5th scale springs as well as hydraulic

shock absorbers. The car is 45 inches long, 14.5 inches wide and 10.5 inches high. Its

weight is 21 pounds. The car has been purchased and delivered to the team and they are

anxiously awaiting the first test with software and impact hammer.

SUPPORT STRUCTURE

The team’s two options for the support structure were:

• Suspend car from ceiling of vibrations lab

• Suspend car from independent support structure

As the team started looking into the feasibility of suspending the car from the ceiling, they

found that there was not a very good place to do this in the current vibrations lab. The team

also didn’t know what resources the vibrations laboratory would have in the new engineering

building. Finally, they agreed that they wanted to have the entire experiment be self-

contained and mobile. Therefore, the team chose to build an independent support structure

for the car. They will actually build the structure next semester in 449. A dimensioned Solid

Edge drawing can be found in the Appendix.

38

SHAKER

In order to achieve the desired results of the road vibration simulation, the design team

selected an electromagnetic shaker as the actuator for the experimental set up. This shaker

generates either a random or a sine force, and transmits the vibration force to the car

through the shaker’s stinger. For the 1/5 scale model car that is being used for the

experiment, many shaker companies that were contacted recommended a 50 lb sine force

shaker. A shaker that can produce a 50 lb sine force cannot generate as high of a force when

a random signal is generated, and the team determined that for the most accurate vibration

simulation, a random input force should be used. By looking at different shakers from

various companies, the team found that a 50 lb sine force shaker could generate

approximately 30 – 35 lb random force. However, a random signal force of 35 lbs will still

be enough to achieve a large enough amplitude for the experiments. Research also found

that a 50 lb shaker can usually only support a payload of 7 to 10 lb. By building a support

structure for the car this problem can be accounted for, even though the car weighs

approximately 21 lbs.

One of the first decisions that had to be made was the necessary size of the shaker. The

required size of the shaker had to correspond to the scale of the car. With a 1/5 scale model

car, a 50 lb sine force shaker could be used. If the car was any smaller, the team could

purchase a smaller shaker, but the results of the experiment would be less accurate. If the car

was any bigger, a bigger shaker would be required, which would be much more expensive.

The team contacted multiple shaker dealers, such as DataPhysics, Ling Dynamics, and MB

Dynamics. Although each company offered help in recommending equipment for the

project, MB Dynamics was the only company that submitted a price quote to the team. They

also offered an academic discount for the team. One of the benefits of this particular device

39

is its lightweight, compact design, which make it portable and easy to setup. Another

advantage is that the device is designed to excite small structures, making it applicable to the

team’s scaled-car testing setup. MB Dynamics has been extremely helpful in communicating

with us, and they are located in Cleveland, OH. This is a major advantage over some of the

other companies which were located overseas and thus would take a longer time to order

and would be harder to communicate with if problems were encountered with its

implementation into the team’s simulator design. None of the other companies felt they

could beat MB Dynamics’ price, and MB is a very reputable company that the team felt

comfortable dealing with. Therefore, the team chose to purchase the modal 50A exciter

from MB Dynamics. Specifications and a picture of this shaker can be found in the

Appendix.

Amplifier

MB Dynamics has a specific amplifier that is recommended for the modal 50A shaker.

Many of the other shaker companies such as DataPhysics and Ling Dynamics both

recommended purchasing an amplifier that was intended for the shaker that would be

purchased. Since no other alternative options are feasible for the project, the team chose to

purchase the amplifier from MB Dynamics.

Cooling System

The cooling systems are relatively cheap compared to the cost of a shaker and

amplifier, and by having a cooling system, the team will be able to use the shaker at its peak

force if necessary. To be safe, the team decided a cooling system would be a good

40

investment. The cooling system would also allow future experiments to be performed using

the shaker at whatever force was necessary. It was agreed that since the lab experiment was

supposed to be portable and self-contained, it would be best to purchase the portable

cooling system from MB Dynamics. Economically, this would also be the safest system to

buy, since it has not been determined if shop air will be available in the vibrations laboratory

in the new engineering building.

GUI

The design team’s final GUI for their vibration simulation laboratory can be seen in

Figure 7. As can be seen in Figure 7, the team’s GUI consists of three main areas; an area

for shaker input information, an area for the accelerometer output information, and an area

for the transfer function graphs.

Figure 7

41

The shaker input area has three pull down menus. One menu pull down menu is a

where the user can enter the number of averages. This is helpful information because the

number of averages taken during data collection can affect the accuracy of the data taken.

With this pull down menu option, the user can compare the data with different numbers of

averages taken, and make conclusions about how this affects the data. The second pull

down menu is for the sample time, which is the length of time during which the data is

taken. This can be input by the user, and will affect the outcome of the experiment, and can

therefore be changed to see how the output changes. The third and final pull down menu in

the shaker input area is for the force window. This will only have two options: on or off.

Windowing is one technique for checking the accuracy of experimental data. Windowing is

the process of adding a weighting function to the measured data. This weighting function,

or window, is used to force the data to better satisfy the periodicity requirements of the

Fourier Transform Process. This process minimizes the distortion effects of leakage, which

is a distortion in the data during the transformation of time data to the frequency domain

using the Fast Fourier Transform. The shaker input area on the GUI also includes a graph

window in which the shaker sine wave can be viewed by the user.

The accelerometer output area consists of a color key code to let the user know which

accelerometer is associated with which color on the graph and the actual graph output

window. The graph will show four different outputs, each one in a different color, that will

correspond to the data obtained from each respective accelerometer. Channel 0

corresponds to accelerometer 1 and is blue; channel 1 corresponds to accelerometer 2 and is

magenta; channel 2 corresponds to accelerometer 3 and is green; and channel 3 corresponds

to accelerometer 4 and is black. The accelerometer output area also includes two pull down

42

menus. The first menu is where the user can select the accelerometer number, then in the

second pull down menu the user selects the accelerometer location corresponding with the

chosen accelerometer number. The user then clicks the save button that is also located in

the accelerometer output area of the GUI. The save button saves the chosen accelerometer

number and corresponding location and the user can then choose more accelerometer

numbers and locations. This way, the user can view all the outputs from the accelerometer

in one graph.

The final area on the GUI is the transfer function area. This area contains a graph which

will output the transfer function of the data received from the Matlab Data Acquisition. The

user will not be able to input any information in this area, as it is only an area for the user to

view the results of the data collected.

As mentioned in the research section above, ergonomics in the design of many things

including GUIs. As the design team created their GUI, they kept the ergonomic ideas of

simplicity, consistency, immediate feedback, and intuition in mind. The team incorporated

simplicity into their design by making the number of input variables the user could change to

a minimum. This minimizes confusion on the part of the user and allows them to focus on

obtaining data from the program rather than entering it. Also, because the GUI is laid out

such that all the components line up at right angles, only the necessary information is

present, and much white space is used, the user isn’t confused by a lot of clutter or

randomness, which in turn enhances simplicity. Finally not many different types of

components are used, i.e. just pull down menus, push buttons, and graph windows, which

also helps add to the simplicity of the design. The simpler the design, the easier it is for the

user to use, which by definition is ergonomic design.

43

Consistency is shown in the team’s GUI because, as previously mentioned, all

components are in line, and appear in a logical order on the screen. First on the upper left

hand corner is the input information, followed by the output information in the upper right

hand corner, and finally there’s the transfer function graph area below these two and in the

middle. This makes sense because the transfer function is a combination of inputs and

outputs. The team’s GUI also shows consistency because all similar items have similar font

sizes for the headings; same sizes for each pull down menu, and the same size for the input

and output graphs. This makes the GUI easier to use as well as easier to look at, which

shows the team’s desire to design with ergonomics in mind.

Immediate feedback is achieved with this GUI design because it is created in Matlab and

the DAQ code as well as all other code associated with the vibration simulation is written in

Matlab, the GUI can immediately show the information obtained by the DAQ toolbox.

Also, pull down menus show immediate feedback because the user selects the desired option

and can immediately see what has been selected. The same is true for when the user selects

the accelerometer number and location and hits the save button; they can immediately what

combination they have chosen and what color the line on the graph will be. This is

important because if there wasn’t immediate feedback, then the user would have no way of

knowing what had been selected and whether or not they had selected the right option.

Immediate feedback is ergonomic design because the user doesn’t waste time looking for the

results, as they are created on the same screen as the inputs parameters are entered.

Finally, in order to enhance the ergonomic design of their GUI, the team incorporated

the concept of intuition when creating it. Because of the design of a pull down menu, as

well as the familiarity of pull down menus to most people, a pull down menu itself is very

44

intuitive. Most people know that the desired input needs to be selected from the pull down

list. As mentioned, the team incorporated several pull down menus in their GUI layout,

which makes the GUI intuitive. Also, the GUI area is laid out in a very logical order. With

the input area on the top left, the output area on the top right and the transfer function area

in the middle on the bottom, the order of flow of information follows the order in which

humans read. This is very ergonomic as well as the fact that the inputs are on the left, the

outputs on the right, and the transfer function, which is a combination the inputs and

outputs is in the middle.

Addressing all four of the aforementioned ergonomic issues makes the GUI much more

user friendly as well as limits the amount of confusion for the user. Both of these in turn

enhance the ability of the user to learn; which is the main focus of the team’s entire road

vibration simulation project. The code for these can be found in the Appendix for this

report.

DAQ

The design team chose to utilize the Data Acquisition Toolbox provided in Matlab because

no suitable systems for the team’s needs are available. These needs are based upon the signal

conditioning hardware already obtained (manufactured by National Instruments) as well as

the platform being used to design the experiments with. The Data Acquisition Toolbox in

Matlab is a collection of M-file functions as well as MEX-file dynamic like libraries built on

the Matlab technical computing environment. It allows for bringing in live, measured data

into Matlab. The Data Acquisition Toolbox within Matlab will be used because it is built on

the same platform as Matlab. This will allow for smooth transitions and less programming

conflicts. In order to test the Data Acquisition Toolbox, code was written in Matlab. This

45

code was tested by seeing if the computer could communicate with the accelerometers. The

code written can be found in the Appendix. The Data Acquisition Toolbox code that has

been written has been able to open up the lines of communication between the computer

and the accelerometers. Therefore, the Data Acquisition Toolbox in Matlab will be used to

talk to the computer card that converts analog to digital data and bring in the digital data

into Matlab.

FLOW OF INFORMATION

Figure 8

46

Figure 8 shown above demonstrates the flow of information between the software and

hardware of the team's experimental setup. The red lines show information that is being

sent from the computer to the car and the blue lines show information that is traveling back

as an input to the computer.

The information flow begins with a random signal generated by Matlab being sent from

the computer to the signal conditioning board. Because Matlab is only capable of generating

a signal on the order of 0-10 Volts and the necessary input voltage to the shaker is

sufficiently larger (on the order of 20 Volts) an amplifier is needed between the signal

conditioning board and the shaker. Once the signal reaches the shaker, the signal output

travels in two different directions. First, the shaker output is sent to the load cell in order to

measure the input force that is actually being sent to the car. This information is then

forwarded to Matlab by the load cell to be used in the data analysis. Second, the shaker

output is sent to the actual car, where the resulting output force of the car is measured by the

accelerometers. This information is then sent back to the signal conditioning board, where it

can also be used in Matlab for data analysis.

As a result of this information flow, both the input and output forces on the car are

being sent to Matlab. This information can be read from the Matlab GUI and analyzed by

the students according to the procedures developed in the corresponding labs.

CLASSROOM EXPERIMENTS

Because the goal of this entire project is to create a lab experiment that students taking

the vibrations class can use in the Miami University vibrations laboratory, the design team

had to keep in mind the experiments that they would write to go with their project. The

team wanted to focus on intuition when designing the experiments. The key objective of the

47

classroom experiments that the team is going to develop is intuitive learning. The team

wants to make sure that the students can perform the experiments such that a large amount

of intuition is involved on the student’s part. For example, as previously mentioned, the

GUI is designed with intuitiveness in mind. Also, the team chose the real 1/5th scale model

car because it looks and reacts the most like a real car. Because all the students would have

some idea as to how a real car performs, as they have certainly had much experience with

them throughout their lives, having a classroom experiment involving a car that very much

resembles a real car makes the experiment very intuitive, and by definition, the students will

learn more because the intuitiveness will allow them to perform the experiment more easily

and probably accurately.

The first classroom experiment the design team wants to develop and have the

vibrations students do in the laboratory is a basic experiment that introduces students to the

equipment as well as the basics of transfer functions. This experiment will involve a basic

introduction to the shaker and how to set it up with the amplifier, accessories kit, and

cooling system such that it performs in the correct manner. The students will also learn

about accelerometers and how to correctly connect them to the car and the signal

conditioning box. They will also learn how to connect the car properly to the support

structure. Not only will the students learn the basic hardware associated with this vibration

experiment, but they will also learn the basics of a transfer function. Because, at this point in

their schooling, students haven’t really had much experience with transfer functions, this

experiment will give them a basic idea of what a transfer function is and how they can use it

to analyze the data. This experiment will also involve learning how to use the GUI to input

data as well as run the experiment and get data. The overall point of this experiment will

48

only be to familiarize the student with all the components and steps involved in using this

road vibration simulator to gather data.

The second experiment the team will develop for the students to use perform in the

classroom is an experiment that involves changing the location of the shaker on the car and

comparing the different data acquired from the different shaker locations. The design team

would like to have a total of five preset locations at which the shaker can measure vibrations.

The team has currently selected the driver seat, front driver side wheel, rear driver side

wheel, front bumper, and rear bumper as locations to put the shaker. In order to make sure

the data taken by the students is consistent, the team will mark, using a permanent marker or

perhaps a paint pen, points on the aforementioned parts of the car so that the shaker is

placed in the same spot on that particular part of the car every time an experiment is

performed. Also, specifics in the Matlab code will pertain to these points, and thus it is

critical to place the shaker at the same point each time data is collected on that point.

With this experiment, the team hopes to allow the students to see how this model car

responds to vibrations in a similar manner as a real size car. The team wants to show the

students how the relationship between the vibrations felt in the driver seat as compared to

the driver side front wheel in the model car is similar to the relationship between vibrations

felt in those two spots on a real car. This will show students how vibrations are an actual

real world phenomenon that must be carefully analyzed and dealt with in the real world.

The team wants the students to be able to be able to see how vibrations they feel when

riding in a real car can be modeled by experiments and thus dealt with. The team hopes that

students will see that they are performing this experiment for a real reason, as it has real

world applications, and that this is not just a pointless experiment with no applications to

their lives. The team is certain that, since most students have undoubtedly had large

49

amounts of experience with cars in their lives that they will appreciate the work that goes

into making sure they have a comfortable ride when in a car.

Finally, a possible third experiment that the design team would like to develop for the

classroom is an experiment that teaches students about ways to analyze the accuracy of the

data collection technique they have used during the simulation. As can be seen in the GUI

discussion above, the shaker input area has three pull down menus; one for number of

averages, one for sample time, and one for windowing. These three items are all different

ways of analyzing and checking the accuracy of the data collection method.

The design team wants the students to be able to select the number of averages taken

when taking their data, and then see how changing the number of averages affects the data.

From this, they will be able to see whether they have collected the data accurately. The

team will have the students vary the sample time of the simulation to help them understand

the concept that increasing sample time will increase the accuracy of the data taken. Another

possibility with this experiment is to have the students analyze at what point it becomes

unnecessary to increase sample time in order to obtain more accurate data.

The final way the team will have the students check for the accuracy of their data is

through the technique of windowing. As discussed in the preceding research section,

windowing is adding a function to the data to make it easier to analyze and read. This

experiment will just be very basic when it comes to widowing, as windowing is a difficult

concept and can be very complicated. The team just wants the students to be exposed to the

idea of windowing and how it can help analyze the accuracy of the data collected.

The design team feels that if they have the students perform the above experiments that

they will gain a good insight into what goes into simulating road vibrations while learning

50

about how to interface hardware equipment with software, setting inputs and taking data,

then seeing how it applies to the real world.

CONCLUSIONS AND FUTURE WORK

CONCLUSIONS

The design and development of a road vibration simulator for the vibration laboratory

has many components to it. The initial component to be decided upon is the physical

structure to be used as the specimen being tested. The three preliminary ideas for this were

an entire car, an entire car scale model, or an individual car component. The design team

chose to design the simulator for use with a scaled model of a car, mostly based on

laboratory constraints and the team’s goal of intuitive learning. The next component to be

decided upon is the type of sensor to be used. The two main preliminary ideas for this were

force sensors or accelerometers. After performing some initial research, it was decided that

a force sensor would be used to measure the input while an accelerometer would be used to

measure output. The third component to be decided upon is the actuator. There were three

preliminary ideas for this: an electrodynamic shaker, a hydraulic shaker, or an impact tester.

The design team decided, after performing much research, that an electrodynamic shaker

would be the most suitable option for this simulator. The final component that needed to

be chosen was the type of data acquisition/analysis package to use. The preliminary ideas

were Matlab and Labview. Matlab was chosen as the type of data acquisition and analysis

package, primarily due to the fact a majority of the design team members have prior

experience with Matlab.

In terms of Hardware, once the team had decided to use a scaled model of a car, the

exact size and the particular model needed to be selected. After weighing the alternatives of

51

different scaled models and obtaining price quotes for several options, the team purchased

the TKT99 Junior 1/10 scaled model car from Alro Racing. The team also needed to select

a particular shaker to be purchased for the setup. The Modal 50A Exciter from MB

Dynamics was selected. This shaker was purchased along with the necessary corresponding

components (amplifier, cooling system, accessories kit) for this specific device. Finally, a

support structure was designed that could support the car from bungee chords during the

experimental testing.

In the software category, the team developed a mathematical experiment in Simulink that

would help them to understand the differences between shaker and impact hammer testing.

Code for data acquisition was also developed to allow the computer to communicate with

the data acquisition hardware. An overall goal for a GUI was designed, as well as individual

working GUI components that would allow for better understanding of development code.

Finally, three preliminary ideas were developed for laboratory experiments. These ideas

include an introduction to experimental testing and transfer functions lab, an analysis of

shaker location and relation to real world automobile lab, and a data collection and analysis

issues lab. The teams design goal of intuitive learning was a primary consideration in the

development of these designs.

FUTURE WORK

As can be seen in the Timeline, in Gantt Chart form, attached in the appendix, nearly

two-thirds of the project tasks have been either started or completed. All of the designs for

the system have been finalized during 448, leaving the only the remainder of the

implementation process to be completed during 449. For each of the major sections of the

52

project, (hardware, software, and experiments), specific tasks are described below that will

need to be completed during EGR 449. In addition, the team must constantly keep in mind

that it is the integrating of these three sections (hardware, software, and experiments) that is

key to the success of the road vibrations simulator.

Task Name Duration [Day] Start Date Finish Date

Test Components 45 days Mon 1/26 Fri 3/26

Assembly of Apparatus 15 days Mon 3/29 Fri 4/16

Develop Data Collection/Analysis Software 120 days Mon 11/3 Fri 4/16

Writing of Final Report 130 days Mon 11/3 Fri 4/30

Write Lab Manual 110 days Mon 11/17 Fri 4/16

Run User Test on EGR 315 Students 5 days Fri 4/16 Thu 4/22

Post Information to the Internet 3 days Mon 4/19 Wed 4/21

Table 3

53

REFERENCES

ALRO Racing: http://www.alroracingusa.com/ Technokit: http://www.technokit.it GB Direct: http://www.gbdirectusa.com/ Victory Speedway: http://www.victoryspeedway.com/ FG Modelsport: http://www.fg-america.com/site/lv1/productlines.htm RDP Corporation: http://www.rdp-corp.com/ MB Dynamics: www.mbdynamics.com Data Physics: http://www.dataphysic.co.uk/html/shakers.htm Random Vibration: http://www.algor.com/products/analysis_types/linear_dynamics/random_vibration.asp Modal Exciters: http://www.bksv.com/2329.htm Shaker Selection: http:/autotestreport.com/2002_articles/09_shaker.htm Ling Dynamics: http://www.lds-group.com/ Labworks, Inc: http://www.labworks-inc.com Derritron: http://www.derritron.com/ Quick Tech Hobby: http://www.quicktechhobby.com/prices/cars/5%20SCALE.htm# Ready-to-Run Modal Analysis: http://www.mecha.uni-stuttgart.de/Forschung/forschung_exp_meth/forschung_expmodal_en.htm Modal Analysis: http://www.gmi.edu/~drussell/GMI-Acoustics/Modal.html Modal Analysis: http://www.mts.com/nvd/PDF/1992_AMATLST.pdf Harm Racing: http://www.harm-racing.de/Cars_Street.asp?Lang=EN MCD Racing: www.mcdracing.com GUI Ergonomics: http://cognitivevent.com/gui.html Intuition Information: http://www.mtnmath.com/whatrh/node105.html GUI Ergonomics: http://www.omnica.com/omniview_industrial_design2.htm Math Works: www.mathworks.com National Instruments: www.nationalinstruments.com Mathworks. Data Acquisition Toolbox: For Use with Matlab User’s Guide. Version 2. 2001.

The Mathworks, Inc. Natick, MA.

54

ABOUT THE TEAM

There was a wide variety of engineering background within the group, with Manufacturing,

Management, Mechanical, and Environmental majors represented. This variety of

backgrounds has led to a wide array of skills, and many different approaches to problem

solving. Each member of the group shares the same feeling learning style. The group was

able to take advantage of the shared learning styles by taking a hands-on approach to the

project, for instance scheduling a trip to see a full scale road vibration simulator at the

University of Cincinnati. Two of the group members, Sarah and Mandy, have taken a

Vibrations class at Miami University, and Mandy spent last summer at Miami assisting in

vibrations research. Sarah and Jessica also had professional experience in the Engineering

Industry. Their prior knowledge and ability to share this knowledge with the rest of the team

has greatly benefited the group.

Each member of the group was interested in the subject matter behind this project, and the

team wanted to be able to help improve the Engineering Department at Miami University.

At first, small tasks were divided up between group members, and the main tasks were

accomplished as a group. As the semester progressed, the team decided that the main

sections of the project should be divided between subgroups within the team, so the team

divided into 2 sections. Due to their experience with Matlab, software development, and

vibrations software, Jessica, Mandy, and Sarah focused on software development for the

group. Due to their experiences as Engineering Management majors, Carolyn and Matt

worked primarily on the selection and acquisition of hardware for the experiment. Still, the

group met multiple times each week in order to ensure that all members of the group were

aware of what was being accomplished. By doing this, the group was able to maximize the

55

skills of each member as well as increasing the productivity of the group, while still ensuring

that each member was informed and knowledgeable of the overall progress of the project.

Appendix