Ergonomics 4

ERGONOMICS

What is Ergonomics?

ERGO=work

NOMICS= rules or laws

Ergonomics literally

means the laws of work

What is Ergonomics?

OSHA defines ergonomics as the

science of designing the job to fit

the worker, instead of forcing the

worker to fit the job.

What is Ergonomics?

Ideally, ergonomics:

Makes the job safer by preventing injury

and illness

Makes the job easier by adjusting the

job to the worker

Makes the job more pleasant by

reducing physical and mental stress

Saves money

Ergonomics

An applied scientific discipline concerned with how humans interact with the tools and equipment they use while performing tasks and other activities

Derived from the Greek words ergon, meaning work, and nomos, meaning laws

The word ergonomics was coined by British scientist K. F. H. Murrell and entered the English language in 1949

Earlier applications in fitting man to the job (1900s) Choose from the pool of job applicants who were best

suited to thr requirements (psychological tests)

Hawthorne experiments (1920s) Importance of social factors in work

Human Factors

Human factors is synonymous with ergonomics

Ergonomics emphasizes work physiology and anthropometry (individual at work)

Europe industrial work systems

Human factors emphasizes experimental psychology and systems engineering (the

human element in a system)

U.S. military work systems

History of Ergonomics

Taylor scientific management movement Critics against Taylorism

Frank and Lillian Gilbert- human factors Early 1900s: fitting the man to the job Late 1920s: The Hawthorne experiments social factors in the

workplace- human relations research 1900-1945: growth of use of machinery and mechanization End of WW II: Increased complexity of equipment human-

machine systems

K.F.H. Murrel: the term ergonomics emphasis on industrial work systems

1950: Ergonomics Research Society (UK) 1957: The Human Factors Society (US) 1960: consumer products and working class impact politically 1980 - current:

Advances in computer and automation technologies Disasters: critical importance of human in the operation of

human-machine systems

1949

July - "Ten scientists of differing background, but all interested in the study of human work, decided to form a group to enable research workers in different disciplines to meet and exchange ideas. They called themselves the "Human Research Society"" (K.F.H. Murrell, BPS Bulletin, No.22, January 1954).

Summer - "Ergonomics" defined by Murrell after consultation with Greek and Latin Scholars as "the study of the relationship between man and his working environment".

Autumn - meeting held in Oxford which decided to turn the group into a Society

27th September - Ergonomics Research Society formed - Queen Annes, Admiralty, London.

Objectives in Ergonomics

Main objective: to improve the performance of systems consisting of people and equipment.

Human-machine systems

Machine: a variety of objects aircraft, appliances, automobiles, chairs, computers,

hand tools, sports equipment

using knowledge of human abilities and limitations to design and build for comfort,

efficiency, productivity and safety The Ergonomics Society

Objectives in Ergonomics

Greater ease of interaction between user and machine

Avoid errors and mistakes

Greater comfort and satisfaction in use of the equipment

Reduce stress and fatigue

Greater efficiency and productivity

Safer operation

Avoid accidents and injuries

Ergonomics Application Areas

Work system design: interaction between worker and the equipment used in the workplace

Objectives: safety, accident avoidance, improved functional performance

Also includes environment such as lighting

Product design

Objectives: safety, comfort, user-friendly, mistake proof

Our focus: work systems (which in fact overlap with the product design)

Ergonomists What They Do

Research on human capabilities and limitations Discover the characteristics of human performance, e.g., how

much can an average worker lift?

Design and engineering applications Use the research findings to design better tools and work

methods

Engineering Design is concerned with the satisfaction

of human needs.

In many applications, human factors must be taken into

account in the design process.

Man-machine interface (MMI) is very important to be

considered in the design

process.

Human Factors in Engineering Design.

Human-Machine Systems

Basic model in ergonomics

Defined as a combination of humans and equipment interacting to achieve some desired result (e.g. external vs. internal work elements, levels of operator attention)

Types of human-machine systems:

1. Manual systems: a person using some (nonpowered) tool

2. Mechanical systems: one or more humans using powered equipment

3. Automated systems: automated system requiring occasional human attention

Human-Machine Interactions

A human-machine system has boundaries, that define what components are included within the scope of the system.

A worker-machine production cell is one component in the larger production department.

The ergonomist must decide where to draw the boundaries of the human-machine system of interest.

System Components

Setting the boundary matters because it identifies controllable / uncontrollable

it reflects what the human -machine system operation is assumed to be

The human

The equipment

The environment (both physical and social) Poor lighting may effect workers ability to perform an inspection

task

An unfriendly supervisor may reduce a workers motivation to work.

Human Components

Functions: (1) sensing the operation, (2) information processing, (3) actions

Human senses - to sense the operation Five basic human sense (vision, hearing, touch, taste, and

smell)

Related with sensory (+ nerveous) system of the body

Human brain - for information processing by the stimuli received from the senses

Thinking, planning, calculating, making decisions, solving problems

Related with the brain

Human effectors - to take action by the impulses from the nervous system

Fingers, hands, feet, and voice Related with the musculoskeletal system (+ nerveous)

system of the body.

Machine Components

The machine in a human machine-system can range from a simple hand tool to a complex and sophisticated system of equipment.

The process function or operation performed by human-machine system

Displays - to observe the process Direct observation for simple processes Artificial displays for complex processes (speedometer in a car)

Controls - to actuate and regulate the process Steering wheel, computer keyboard

A worker using a shovel to dig a hole in the ground. Process: digging, Displays: direct observation (no need for displays),

Controls: handle of the shovel

A worker monitoring the operation of an automated process. The worker should make sure that the process is within defined tolerances

Process: process itself, Displays: a digital monitor, Controls: buttons, levers

Human factors in man-machine relationship have the

following forms:

Anthropometric (Human interaction in static sense; dimensions of

body)

Ergonomic (Human interaction in dynamic sense; repeated

tasks)

Physiological (Human interaction with body characteristics)

Psychological (Human interaction with mental activities)

Man-Machine Interface

Man-Machine Interface

The Design Engineer can determine the relative

importance of human factors in his design

Environmental Components

Physical environment Location and surrounding lighting, noise, temperature, and

humidity

Social environment Co-workers and colleagues at work

Immediate supervisors

Organizational culture

Pace of work

Anthropometric Factors Anthropometric human factors are related to the

physical size of humans; it is man-machine

interaction in static sense.

One of the most common problems is that of driver accommodation in automobiles.

Some may have experienced difficulties in either getting in or out, reaching the controls or adequate

visibility.

These may have been due to inadequate attention to the nature of the physical dimensions of

humans.

Anthropometric Factors

Statistical distribution (relative frequency) diagram

for selected population-persons over 18 year's old

living in Saudi Arabia.


Cumulative distribution diagram is an alternative

method to present the same information.



The peak in the relative frequency diagram is often close to the average value.

By designing for the average person we often preclude 50% of the population.

An example which illustrates this concept is that of the forward visibility of a car driver.


For a car driver to be able to see an obstacle of height h

up to a minimum distance L from the front of the car.

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Ergonomic Factors

Importance when the human operator is involved with the machine in a dynamic sense.

A human is required to exert a force or perhaps supply work to the machine.

It should be obvious that the effective operation of a machine over long periods of time will depend

upon the matching of requirements to human

capability.

Ergonomic Factors

Ergonomic Factors

One simple example is that

when the brake operating

force is higher than can be

normally tolerated. The driver

will cope with the situation at

first, but if the brake operation

is frequent, muscle fatigue will

eventually occur and a

dangerous situation will

develop.

The capability for performing mechanical tasks of

this type depends upon:

The physical ability of the operator The range of movement required The speed of movement The duration of the activity The position of the operator The environmental condition.

Ergonomic Factors

The speed of movement consideration is important for assembly operations and also in control solutions.

It may be necessary to execute rapid movements to operate a control device such as a stop button.

There are two features of movement which are independent:

1. The acceleration and deceleration stage.

2. The constant velocity stage.

Ergonomic Factors

The designer of the system from an ergonomic point of view must commence with the

establishment of the system representation

showing the inter relationships and their relative

value.

A useful measure of the relative value of a relationship is the product of the importance of the

particular event by the frequency of occurrence.

If these can be established the designer has a logic available to assist in the planning of the layout.

Ergonomic Factors

An aircraft instrument panel can be considered as an example of this analysis.

The pilot devoted varying lengths of time to looking at a variety of instruments and at different frequencies of

observation. This data is as indicated in the following

table.

Ergonomic Factors

Instrument

Duration of

observation (sec)

No. of

observation per

min.

Relative

value

Cross pointer 0 0 0

Air speed 0.67 22 14.7

Directional Gyro... 0.51 24 12.2

Gyro. Horizon 0.59 26 15.3

Engine Instruments.. 1. 13 5 5.6

Altimeter, 0.47 10 4.7

Turn and Bank Indicator 0.39 5 2.0

Vertical Speed 0.17 12 5.6

Ergonomic Factors

we assume that all instruments are equally well designed so that the difficulty of reading is the same for each, then

the duration of observation may be regarded as a measure

of its importance.

The relative value is then the product of duration and frequency and is listed in the third column.

This indicates that the instruments of greatest importance are airspeed, directional gyro, gyro horizon.

Ergonomic Factors

Ergonomic Factors

These must be placed in the prime position of the instrument panel for ease of viewing.

The next are altimeter, vertical speed and turn and bank indicator.

Ergonomic considerations are important in the design of control buttons, handles, levers, etc.

There is an infinite variety of combinations of size, shape, surface texture, material and color which can

be chosen for control knobs as an example.

Physiological Factors

Physiological factors are of concern when the physiochemical characteristics of the body are

significant.

As far as body functions are concerned these involve the neurological, muscular, respiratory, vascular and

sensory systems.

The exterior manifestations can be grouped according to the response to various inputs such as:

Visual Auditory Tactile, kinesthetic and taste senses Environment.

Human operators receive a great deal of information visually.

The visual processes enable us to perceive from, color, brightness and motion and so read printed

instructions and instruments, observe moving objects

and react emotionally to combinations of shape and

color.

In order to achieve the discrimination necessary for correct interpretation it is necessary to achieve

satisfactory intensity and color discrimination and

resolution.


Color discrimination is impaired when illumination levels are low, and this can lead to unexpected difficulties in

comprehension.

An associated problem of illumination which has a critical effect on contrast is that of glare and shadow formation.

These can be controlled by careful design of lighting

systems and selection of materials and colors.



Another source of information is that which is transmitted audibly. This will range from spoken

information to the noise which machinery makes

when operating.

Spoken communication is, of course, very obvious, but the unusual sound is made by

malfunctioning equipment are often recognized as

such and lead to the taking of remedial action.

An excessive level of noise pollution is, in fact, undesirable for a number of reasons:

Leads to degradation of speech intelligibility. Will lead to physical damage to the human auditory system.

Hinders mental activity due to distracting influences. Can lead to psychological and mental disorders if sustained.


The speech interference level (SIL) is a measure of the destructiveness of noise.

It is determined by the level of noise in certain frequency bands.

High levels of sound intensity cause pain and even physical damage.

The usually accepted threshold of pain is at about 0.5 W/m2.



The following steps are available for the acoustic

treatment of working environments:

Control the noise at its source by changing the dynamic behaviors of the machine,

modifying fluid jet flow, etc. Create barriers between the source and the listener.

Provide personal protective devices. Modify operating procedures so that the exposure of personnel to noise is reduced.

Acoustic design can also take on a positive aspect when we are concerned with the quality of sound. This is

important in the design of concert halls, recording studios,

amplification equipment, to name a few areas.

In these cases it is necessary to consider the frequency analysis of the sounds and the reflection and absorptive

characteristics of surfaces over the appropriate frequency

range.

The geometric design is also of considerable importance since this determines the reflection of sound

waves and the possible interferences.


There are many sensory inputs to which the body responds and which must be taken into account, or

made use of in the man-machine relationship.

The sense of touch is one which is of great value in various recognition situations.

Braille printing of coded impressions is an example of the recognition process by the sense of touch.


The atmospheric environment in which the human performs his tasks may considerably affect his working

officially and accuracy.

When the temperature is below 10 oC, physical stiffness of the extremities begins.

Above 25C physical fatigue begins and above 30C the mental processes begin to slow down.

A temperature of 50C is tolerable for a short time but mental or physical effort is almost impossible.



Humidity has little effect on heat exchange for normal temperatures.

At high temperatures, however, humidity has an important effect on heat transfer, comfort and

physiological tolerance.

There is a relationship between temperatures and humidity which leads to similar degrees of comfort.

Psychological Factors

Psychological considerations in human factors analysis

are concerned with the mental activity relationship

between man and the machine. This involves:

Interpretation of information Motivation and fatigue Decision making Aesthetics


These factors are concerned with the manner of presentation to minimize the error of interpretation.

The design of visual displays such as control panels, instrument panels and other informative

displays is a typical example of psychological factors at

work.

There are a number of principles which have been developed. Some of these include:

1. Retain the usual method of operation (e.g., a

power switch is ON when the operating lever is DOWN

2. Use digital indicators for

precise numerical values with no

need for interpretation. That is

satisfactory only when values

are constant or not changing

rapidly.

3. For time variable readings not

requiring high accuracy use

moving pointers over a fixed

linear or circular scale.



4. Arrange control movement

to coincide with required

direction of instrument pointer

movement.

5. Color coding on dials are

useful in helping to recognize

conditions quickly e.g., green-

normal, yellow-caution, red-

danger.

The mechanism of the control device should be designed so that:

(i) Movements are easy.

(ii) Slackness is eliminated.

(iii) The operator is aware of a feedback response.

(iv) The system response is rapid.

If this cannot be achieved the controller should incorporate some restriction so that over reaction and

instability does not develop.


Decision making is sometimes a difficult task for people to carry out.

It is important that the incoming information be presented in a readily assimilated manner.

However, it is also necessary that this information be supplied in ample time for the operator to be able to

decide on his course of control action.


Cost of Ignoring Human Factors

is Poor Quality! Increased probability of accidents and errors

Less spare capacity to deal with emergencies

Increased labor turnover

Lower productive output

Increases in lost time

Higher medical costs

Higher material costs

Increased absenteeism

Low quality work

Injuries, strains

Ergonomic Products

There are a variety of ergonomic products available on the market, including:

Keyboards

Wrist rests

Mouse pads

Chairs

Adjustable desks

Glare screens

THANK YOU

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Ergonomics 4