Lecture 1 Fundamentals of Mechanics and Mechanisms

8/10/2019 Lecture 1 Fundamentals of Mechanics and Mechanisms

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Technical University of Cluj-Napoca

Faculty of Mechanics

Department of Mechanisms, Precision Mechanics and Mechatronics

Lecture 1 Fundamentals of Mechanics and Mechanisms

ef lucr.dr.ing. Sergiu-Dan Stan

Lecture 1

Fundamentals of Mechanics andMechanisms

ef lucr. dr.ing. Sergiu-Dan STAN


B-dul Muncii 103-105, C 304


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References

Vistrian MTIE et al., Tehnologie i educaiemecatronic, Ed. Todesco, Cluj-Napoca, 2001.

Viorel HANDRA-LUCA, Introducere in teoria mecanismelor

Ed. Dacia, Cluj-Napoca, 1982.

Sergiu-Dan STAN, Optimizare cu algoritmi genetici

aplicaii n mecatronic, Ed. Todesco, Cluj-Napoca, 2007.


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Mechatronics is defined as the synergistic integration of mechanical engineering, with electronics and intelligent

computer control in the design and manufacturing of industrial products and processes.

Mechatronics

Mechanics

Information

technology

Electronicsmechanical elements

machines

mechanisms

precision mechanics

system theory

software

automation-technology

micro electronics

power electronics

sensors

actuators

Mechatronics


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Industrial Experience: Complexity is the Problem

Control (read software) is the largest cause of failure in complexmanufacturing machines

Failure to understand the consequences of complexity lead to

unreliable operation, poor performance

Mechanical engineersdont understand software

Software engineersdont understand machines

Mechatronics as Education Environment address all these issues.

Facts:Processor generation time18 months

Mechanical generation time520 years

A large portion of mechanical system value is in the software.

Mechatronics as education environment


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Integration


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Since the timing of the engine is dependent on the shape of the cam lobes and

the rotational velocity of the camshaft, engineers must make decisions early in

the automobile development process that affect the engines performance.

The resulting design represents a compromise between fuel efficiency and

engine power.

Since maximum efficiency and maximum power require unique timing

characteristics, the cam design must compromise between the two extremes.

Figure 1. Single Cam and Valve

New trend: camless engines!

IC_engine_4-stroke
http://localhost/var/www/apps/conversion/tmp/video%20mechanisms/IC_engine_4-stroke.wmvhttp://localhost/var/www/apps/conversion/tmp/video%20mechanisms/IC_engine_4-stroke.wmvhttp://localhost/var/www/apps/conversion/tmp/video%20mechanisms/IC_engine_4-stroke.wmvhttp://localhost/var/www/apps/conversion/tmp/video%20mechanisms/IC_engine_4-stroke.wmv


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Drive-by-Wirereplaces mechanical connectionspush rods,

rack & pinion, steering columns, overhead cams, cablesbymechatronic connectionssensors, actuators, embedded

microprocessors, control software

From mechanics, mechanisms toward mechatronics

drive-by-wire
http://localhost/var/www/apps/conversion/tmp/scratch_9/video%20mechanisms/drive-by-wire.flvhttp://localhost/var/www/apps/conversion/tmp/scratch_9/video%20mechanisms/drive-by-wire.flvhttp://localhost/var/www/apps/conversion/tmp/scratch_9/video%20mechanisms/drive-by-wire.flvhttp://localhost/var/www/apps/conversion/tmp/scratch_9/video%20mechanisms/drive-by-wire.flvhttp://localhost/var/www/apps/conversion/tmp/scratch_9/video%20mechanisms/drive-by-wire.flvhttp://localhost/var/www/apps/conversion/tmp/scratch_9/video%20mechanisms/drive-by-wire.flv


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h l f ld l f h d h


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Structural Analysis of Planar Mechanisms

Structural Analysis of Planar Mechanisms

Planar Kinematic Pairs (Joints) and Planar Mechanisms Kinematic Pairs (Joints)

Kinematic Chains and Mechanisms

The Kinematic Diagram of a Mechanism

Definition and Purpose

Representation of a Kinematic Pair

The Representation of a Link in the Kinematic Diagram Procedures for Drawing the Kinematic Diagram of a Mechanism

Degree of Freedom of a Mechanism

Definition

Structural Formula of a Mechanism

Condition for a Mechanism to have a Determined Motion

The Composition Principle and Structural Analysis Composition Principle of Mechanisms

Structural Analysis of Mechanisms


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Technical University of Cluj NapocaLecture 1 Fundamentals of Mechanics and Mechanisms


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Rigid mechanisms

Technical University of Cluj NapocaLecture 1 Fundamentals of Mechanics and Mechanisms


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MOTIONSTUDY

Study of position, displacement, velocity and

acceleration of different elements ofmechanism.

Given input Desired output

Motion study is important in Mechanisms and Machine Theory

Technical University of Cluj-NapocaLecture 1 Fundamentals of Mechanics and Mechanisms


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What is a linkage?



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Technical University of Cluj Napoca





Ubiquitous mechanical modules

http://en.wikipedia.org/wiki/Image:Nockenwelle_ani.gifhttp://en.wikipedia.org/wiki/Image:4-Stroke-Engine.gif


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http://en.wikipedia.org/wiki/Image:4-Stroke-Engine.gif


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y j p




Other mechanisms



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y j p




Engine 4 strike


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Linkage components



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Linkage classification



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Example: 4 bar door damper linkage



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F lt f M h i


f l d i S i D St


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Degrees of Freedom of a Rigid Body

Degrees of Freedom of a Rigid Body in Space

An unrestrained rigid body in space has six degrees of freedom: three translating

motions along the x, yand z axes and three rotary motions around the x, yand zaxes

respectively.

Degrees of freedom of a rigid body in space




ef lucr dr ing Sergiu Dan Stan


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TYPES OF KINEMATIC PAIRS

Based on nature of contact between elements

(i) Lower pair : The joint by which two members areconnected has surface contact.

Classification: types of kinematic pairs

Prismatic pair Revolute pair


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ef lucr dr ing Sergiu-Dan Stan


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Based on relative motion between pairing elements

(a) Sliding pair [DOF = 1]

(b) Turning pair (revolute pair)[DOF = 1]

Types of kinematic pairs




ef lucr dr ing Sergiu-Dan Stan


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ef lucr.dr.ing. Sergiu Dan Stan


(c) Cylindrical pair[DOF = 2]

(d) Rolling pair[DOF = 1]


BeltRolling bearings






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(e) Spherical pair [DOF = 3]

Eg. Ball and socket joint

(f) Helical pair or screw pair [DOF = 1]







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Based on the nature of mechanical constraint

(a) Closed pair

(b) Unclosed or force closed pair



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y


g g

Types of joints






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Types of joints






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Types of joints






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Kinematic joints, 1 DOF

Kinematic joints

f=6-k

f=degree of freedom

k=number of blocked motions

1 DOF (degree of freedom)






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f=6-k

f=1=degree of freedom

k=5=number of blocked motions

1 DOF (degree of freedom)

Symbol







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Example: Lead Screw, 1 DOF

Technical University of Cluj-NapocaFaculty of Mechanics

D f M h i P i i M h i d M h i

Lecture 1 Fundamentals of Mechanics and Mechanismsef lucr.dr.ing. Sergiu-Dan Stan


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Example: Gear mechanisms


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Department of Mechanisms Precision Mechanics and Mechatronics



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Symbol

2 DOF (degrees of freedom)

f=6-k





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Symbol


f=6-k







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f=6-k







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f=6-k




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p ,


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3 DOF Compliant Micro-motion Stages with Flexure Hinges





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New types of joints: compliant mechanisms (flexible joints)





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GRUBLERSCRITERION

Number of degrees of freedom of a mechanism is given by

F = 3(n-1)-2l-h

Where,

F = Degrees of freedom

n = Number of links in the mechanism.

l = Number of lower pairs, which is obtained by counting the

number of joints. If more than two links are joined together atany point, then, one additional lower pair is to be considered forevery additional link.

h = Number of higher pairs

Degree of freedom





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ExamplesDOF

Four-bar mechanism

F = 3(n-1)-2l-h

Here, n = 4, l = 4 & h = 0. F = 3(4-1)-2(4) = 1

i.e., one input to any one link will

result in definite motion of all the

links.

Examples - DOF


l = Number of lower pairs,

h= Number of higher pairs.





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ExamplesDOF

Five-bar mechanism

F = 3(n-1)-2l-h

Here, n = 5, l = 5 and h = 0.

F = 3(5-1)-2(5) = 2

I.e., two inputs to any two links are

required to yield definite motions in

all the links.

Examples - DOF


l = Number of lower pairs,

h= Number of higher pairs.


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Five-bar mechanism, realized at Dept. of Mechatronics, TU Cluj-Napoca

Five-bar mechanism, 2 DOF





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Five-bar mechanism, realized at Dept. of Mechatronics, TU Cluj-Napoca

Five-bar mechanism, 2 DOF


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Examples - DOF F = 3(n-1)-2l-h

Here, n = 6, l = 7 (at the

intersection of 2, 3 and 4, twolower pairs are to be considered)

and h = 0.

F = 3(6-1)-2(7) = 1

Examples - 1 DOF





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Homework!





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Homework!


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Types of links





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The Representation of a Link in the Kinematic Diagram

BA

A+ + B





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The Representation of a Link in the Kinematic Diagram

Cone Gears Drive Outer meshed cylindrical gear driveSpur gears





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Examples of rigid links

Examples of rigid links





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KINEMATIC CHAINS

Group of links either joined together or

arranged in a manner that permits them to

move relative to one another.

Kinematic chains





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LOCKED CHAIN OR STRUCTURE

Links connected in such a way that no relative

motion is possible.

Locked chains





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MECHANISM

A mechanism is a constrained kinematic chain.

Motion of any one link in the kinematic chainwill give a definite and predictable motionrelative to each of the others.

Usually one of the links of the kinematic chain isfixed in a mechanism.





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Kinematic chains and Mechanisms

Open kinematic chains Closed kinematic chains



http://upload.wikimedia.org/wikipedia/commons/0/05/Linkage_mobility.png


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Common 4-bar linkage types

MECHANISMS





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4-bar pin slider linkages


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Schematic representation





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Examples. Double slider-crank





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Example of a kinematic information chain





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Evolution from traditional mechanisms toward

mechanisms for mechatronics

AAmplifier, TrTransducer, Cmicrocontroller, Mdriving motor,

M1,M2DC servomotors





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PLANAR MECHANISMS

When all the links of a mechanism have planemotion, it is called as a planar mechanism. All

the links in a planar mechanism move in

planes parallel to the reference plane.





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Examples. Four bar mechanism



http://upload.wikimedia.org/wikipedia/commons/c/cf/Locking_pliers.jpg


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Example. Four bar mechanism. Type 1





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Example. Four bar mechanism. Linear trajectory







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http://en.wikipedia.org/wiki/Image:Nockenwelle_ani.gif


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Faculty of MechanicsDepartment of Mechanisms, Precision Mechanics and Mechatronics




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Differential


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Examples of trajectories obtained using different mechanisms

a) b)

c)






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Documents

Lecture 1 Fundamentals of Mechanics and Mechanisms