UNIT 15 MAN-MACHINE SYSTEMS

Structure
15.1 Introduction
Objectives
15.2 Work Science - An Overview
15.3 Man-Machine System
15.4 Characteristics of Man-Machine System
15.5 Machine - As a Component of Man-Machine System
15.6 Man - As a Component of Man-Machine System
15.6.1 Functions of Man Element In Man-Machine System
15.6 2 Muscular Performance
15 6.3 Kinds of Muscular Actlvity
15 6 4 Nervous Control Movement
15.6.5 The Mechanism
15.7 Types of (Man-Machine) Systems
15.8 Man-Machine Relationships
15.9 Criteria for the Evaluation Man-Machine System
15.10 The Design Factors in Man-Machine System
15.11 Summary
15.12 Key Words
15.13 Answers to SAQs

15.1 INTRODUCTION
The recent researches in the field of industrial engineering are oriented to explore the
, various factors influencing the human efficiency while working on the machine. The
objective is to obtain maximum output of a worker. It has been defined as the
scientific study of the relationship between man, machine and the environment. The
word environment includes the tools, the materials, method of work, working etc. All
these are related to the nature of man himself, to his abilities and limitations. Today the
industrial working has become very complex because of rapid technological
development and increased demand of product. With the result the man has been
subjected to heavy stresses (mental and physical) and as such he either fails to get best
output out of himself or suffers operation break-down. These aspects have created the
interest in industrial engineers to understand the relationship between man and machine and
I
also with the environinent.
1
I Objectives
After studying this unit, you should be able to
understand the application of work science,
explain man-machine systems,
define man-machine relationship, and
suggest measures to reduce fatigue.
 15.2 WORK SCIENCE - AN OVER VIEW
Ergonomics

Work Science is the synonym of Ergonomics. The most important task to be done by
Work Science is to explore the human capacities of all the industrial tasks concerned with
all the factors of work and in the end it aimed at preventing the deterioration of efficiency,
and economically too. No doubt the tasks require consumption of energy and physique;
therefore, the outcome and costs of work depend on the efficiency. However, as discussed in
Unit 14, of this Block 4, the human efficiency is considered to be revolving around two basic
questions of work Science, viz. what technique is used and how the work is organised. Let us
review these quickly as these are the fimdamental concept. to describe a man-machine system.
Thus the work science can be studied under two heads :
(a) Techniques of Work, and
(b) Organisation of work.
Techniques of Work
These can be further divided into two major sections :
Biological Techniques
It deals with hygiene of work based on work psychology and work
pedagogies (Science of Training and Instruction.)
Mechanical Technique
It deals with time and motion study.
Organisation of Work
It concerns with disposition of work and the valuation of work (It may be based on
output of work and leading to work evaluation). It deals with how much a man may
be asked to do and how much rest he should be allowed to take. Further, the work
around the worker should be arranged in such a way that it can maximise the
efficiency of operator.
Thus on reviewing the concept of Work Science, we can conclude that it is a
combination of Methods Engineering, Ergonomics, Human Energy of Man-Machine
systems.

15.3 MAN-MACHINE SYSTEM

Ergonomics through the man-machine system aims to perfection of the system or to
improve the efficiency of human. According to Mr. C. T. Gould -"Ergonomics is also a
branch of I. E. such as 0, R., Work study, Organisation and Methods (0 & M). It is a
bridge between the social and human science on one side and engineer and manager on
the other side."
According to Dr. Franklin V. Taylor -Ergonomics has twin goals :
(a) To increase the efficiency of human operator obtained through giving
adequate attention to his comfort and to his needs as an organisation.

(b) To enhance the performance of the total man machine system.

All the researches in recent past in the field of industrial engineering, particularly, in the
field of man-machine systems are oriented to investigate the factors influencing the
human efficiency. The ultimate objective is to obtain maximum output of a worker with
causing minimum or no fatigue. This area of study is mostly covered by the Man-Machine
Systems under Ergonomics. In short, we can say that Ergonomics means the economics of
work in man-machine system.
Man-Machine System has been defined "As the scientific study of the relationship between Man-Machine Systems
man and his working environment. The word environment includes the tools; materials;
methods of work; organisation of his work. These are related to the nature of man himself to
his abilities, capabilities and limitations."
This subject of study took its birth after Second World War. During this period, there
was a tremendous development in the military equipment and hence became so complex
in operation (high speed operation) that the men were subjected to such stresses. This led
to two noteworthy consequences that they either failed to get the best output of
equipment or suffered operational break down. Thence, it became essential to learn
about the human performance, limitations or capacities.
Extensive research programmes were undertaken in UK and other countries to explore
such aspects of this field of work. Researches related to human performance were
continued even after the war and finally a decision was taken to form a society which
should bring industrial engineers, design engineers, anatomists, physiologists,
psychologists, etc. together. This society was later known as "Ergonomics Society."
The studies reviewed by the ergonomic society, in general and the man-machine systems in
particular significantly exhibited the technological development that could produce the
effects on operatives. There were two important findings :
(a) Stresses to which the human body is unwillingly subjected over a long period
may cause loss of efficiency or disability.
(b) Failure to match requirement of a task with the capabilities of the operator
may cause reduced output.
The importance or ergonomics is attributed because of three reasons :
(a) We, the human beings have the fallacy that we know all about ourselves.
But while we work, we lack or fail.
(b) We are rather conservative and unwilling to make changes, and the poor
designs are even accepted.
(c) The false notion that human body is very adaptable and can take any
amount of punishment.
In every sphere of the technology, there is involvement of human power and hence there
can be innumerable situations in which the human characteristics may conflict with the
characteristics of technical products and procedures. This relationship is not simple since
there are problems in discovering the characteristics and tolerances, of man since human
behaviour is very complicated. In simple words, the importance lies with the designing
of man-machine system as a whole.
Sir Wilfred Le Gros Clask, in the address to the Ergonomic Research Society at its
symposium on "Human Factors in Equipment Design" expressed, "A man and his
machine may be regarded as functional unit and the aim of ergonomics is the perfection
of this unit so as to promote accuracy, speed of operation and at the same time to ensure
minimum fatigue and thereby maximum efficiency."
A man-machine system is defined as an operating combination of one or more men with
one or more equipinents interacting to bring about from given inputs some desired output
with in constraints of a given environment.
A simple form of man-machine system can be a man with some common tools or device,
e.g. a data entry operator with a personal computer system; driver and a car or an
automobile; conveyor with the man unloading; a checkout counter of a grocery store and
the cashier; manned aircraft; A guided missile system, etc.
Reviewing these simple systems, it is obvious that a system must have some purpose and
the following components also necessary (Refer Figure 15. I ).
(a) Input
(b) Processing and Decision Making
Ergonomics (c) Output
(d) Feedback device for corrective action.

Input b Processing and Output

Decision Making

Feedback Device for

Corrective Action

Figure 15.1 :A Simple Model of Man-Machine System

Figure 15.2 : A Man-Machine System with Computer Operator - Computer

lnput of Information
It is the first and foremost feature and is very essential. The input information
consists of various ingredients which are necessary to achieve the desired out-
come. The input information may consist of physical objects or materials in the
form of information andlor energy. For example, in a system of sawmill, the input
is in the form of physical material, i.e. lumber where as the input at a data entry
operator on a personal computer is information.
Information Processing and Decision
This subsystem covers the functions of sensing (information receiving), storage,
processing and action. Sensing or receiving the information is a quite important
sub-component. If there is no proper sensing i.e. receiving of the information,
sometimes some information may enter from wrong direction from an outside
System. For example a virus may be sent to a computer by a hacker. Hence this
sub component (receiving information) becomes quite important. There are
various types of sensing devices such as electronic device mechanical device, etc.
Other subcomponent of this subsystem is the storage of information. Storage of
information is synonymous with memory of learnt material. Information can be
stored in many ways as on manually maintained record, punch cards, magnetic
tapes, floppy, compact diskettes, etc. Most of the information is stored in coded or
symbolic form, and the nature of the coding system can have bearing on the
efficiency of storage or other processing devices.
Information processing means, the sensed information along with stored
information undergo various types of operation. The identity and nature of such
information in the case of human mental processes are not yet clearly understood
and hence considered as a "BLACK BOX". But the information processing by
 machines must be programmed either by simple or complex method (computers). Man-Machine Systems
The result of information processing services is the basis of decision regarding
subsequent action. In man-machine system, a decision is a determination with
respect to a succeeding act.
Action function means the operations as result of subsequent decisions. These
actions can be classified into two broad categories :

(a) Physical control action or process equipments, movements, alterations,

etc.

(b) Communication action in the form of signals, records, etc.

Output
Output is the result of a system after processing. It may bring a change in product;
or a communication is transmitted; a service is rendered.
Feedback Device
It is not necessary that all man-machine systems should have a feedback device. It
is necessary only in the case of closed loop systems. It is essentially needed for
corrective action.

SAQ 1
(a) Explain the man-machine systems with suitable examples.

(b) State the objectives of man-machine system.

(c) Explain the features of man-machine system.

(d) Discuss the history and background of man-machine system.

(e) How do you use the man-machine system as tool to improvement of

productivity?

Activity 1
Fit the following works as a model of man-machine system. Describe its features.
(a) Driver - Bike : ........................................................................
............................................................................................
(b) An operator - Lathe Machine : ......................................................
............................................................................................
(c) Police - Gun : ........................................................................
Ergonomics
15.4 CHARACTERISTICS OF MAN-MACHINE
SYSTEM
The man-machine system, to that matter any system should have the following three
characteristics :
(a) System must have some purpose,
(b) System must have system components, and
(c) System should be designed to do some functions that suit the hurnan beings.
The function is indicator of the purpose of the system. Therefore, a\\ the data related to
purpose should be made available to the system designer. For example, in the case of
data entry operator and a personal computer system, the desired performance
characteristics, the type of computer. the stresses or load taken up by the computer, the
capabilities of its software, sitting and environmental conditions under which both have
to work, etc. should be known.
A system consists of number of components or sub-systems and each sub-system can be
considered as a system which may have all the requisites of a system. In order to analyse
any system, the various sub-systems should be considered as independent systems.
Output of a sub-system may become input to another sub-system.

15.5 MACHINE - AS A COMPONENT OF

MAN-MACHINE SYSTEM --

Machine receives instructions from the man and it carries them out and usually indicates
its progress to the man by a display of information. Therefore as many ergonomic
measures as possible should be introduced at the design stage of a building, appliance or
machine, or when equipment is being installed. A machine user should incorporate
ergonomic standards in the clauses of his contract with the machine manufacturer. It
must cover safety colours, warning signals and controls that have already been
standardised by International Organisation for Standardisation (ISO) and the
International Electro-technical Commission, in particular display panels and dials. It is,
therefore, obvious that machine is totally dependent on the understandability and
reliability of the operator. Thus, the information to be displayed must be clearly
understood and perceived by the operator for which universally acceptable, standard and
good display instruments must be attached to the machine.
The function usually best to allocate to a machine,
(a) For computing, differentiation, integration,
(b) When Response is required at great speed,
(c) Short-term information storage (memory), and
(d) For simple yeslno decision.
However, the man may introduce in the system delays, disturbance and noise because of
own limited capabilities. If the limitation data and capability - data of men are properly
known, .then the efficiency of work can be easily optimised considering man as an
element of system.

15.6 MAN - AS A COMPONENT OF MAN-MACHINE

SYSTEM
Man plays a vital role in the success of man-machine system. The sequence of events
generated from the receipt of the external stimulus to the completion of a response is
very complicated one. It involves the transduction of the external or internal stimuli, the
perception of the signals and their meaning, the making ofjudgment (mental process), Man-Machine Systems
the placing of information into temporary or permanent storage (memory) and recall as
and when necessary, finally leading to a decision making.
When a man is acting as a controller in a man-machine system, a large number of human
qualities play an important role, some of which make him outstandingly useful while
others put limitations on his performance. All these qualities should be considered in
relation to functions which are well done by man or not so well done by a machine. The
most exciting and useful quality of the man component is his flexibility and hence the
adaptability. Unlike a machine, which is designed for a specific purpose, a person can
change his role rapidly and frequently, moreover he has a multiplicity of channels which
he can select as and when required.
15.6.1 Functions of Man Element in Man-Machine System
Unless it is highly complex, Functions usually are done by a man better than a machine.
The main functions of man a component of man-machine system can be observed under
five sub-headings as follows :
As a Sensing Device
Man can act as a sensing device to minimal stimuli from a wide range of sources
and link up these signals together to project a complete picture of an event. In
carrying out this sensing, the man may respond to very dim lights or quiet sounds
and can relate these changes which are of infinite variety so as to arrive at a view
of their meaning. In this context, a term which is used to describe the means by
which data (signals) is conveyed to the central mechanism (efficiency of central
mechanism) is used known as reaction time. In simple words it is the time taken to
respond to a signal.
As an Amplifier, Flexibility, Switching Device
After receiving the signal, he may take-some action. The action would be in
reference to what he has perceived. In doing so he works as an amplifier. In
carrying, out this work, the man behaves in a. very flexible manner. Further, the man
can act as the switch also and use this information to any other relevant activity as and when
required.
Long Term Storage
The wonder of the God's creation is that the brain of human being has memory of
great capacity. The units that we use for measuring memory capacity such as
Megabyte (MB), Gigabyte (GB), Terabyte (TB) or Petabyte (PB) are not at all
sufficient to define the capacity of human brain. In addition to the memory space,
the memory duration is also very long. It can store the information for years and
decades also.
Perception of Depth and Pattern, Interpolation, Extrapolation, Translation
The Inan call perceive a signal in three dimensions and can also interpolate and
extrapolate. After receiving two pieces of data, as it happens in the case of
industrial measuring instruments, the man can interpolate satisfactorily between
these two limits of data and similarly he can extrapolate also. Man can do
prediction also on the basis of a signal data. Even if the data is spurious or
erroneous, the man can detect this and correct this in most situations. Suppose, a
sign-board at a road side was broken into pieces and a illiterate passerby joined
these kept them which read as 'SLOW BREAKER GO SPEED AHEAD'. A car
driver who notices this can understand the defect and correct and then interpolate
to read correctly as 'GO SLOW SPEED BREAKER AHEAD'. This Signal would
automatically cause the driver to decrease the speed and his judgement is fairly good.
Making Judgment and Predictions
Another magnificent function of man element in man-machine system is that
human brain can do the judgments and predictions efficiently and effectively. In
the entire system this phase is very important and vital for getting correct desired
output. However, most times the judgment is made by the man element only in this
Ergononiics system and hence the efficiency of the system is highly dependent on the man
element of the system.
15.6.2 Muscular Performance
Muscles influence man's working efficiency. About 45% of the body weight is constituted
by Muscles. The most interesting characteristic of muscle tissue is its ability to contract to
the extent of its half of the length. Each muscle - fibre contract with a certain force. The
maximum muscular-force in man amounts to about 4 kg/cm2 (cross section of the muscle).
The maximum force is exerted at the beginning of the contraction, when the muscle length is
still that of its relaxed state. As the muscle shortens, the force declines. These facts are
important, in the practical physiology of work.
The ~nuscularcontraction force depends on the number of actively contracting muscle
fibres. Fibre contraction is stimulated by incoming nervous impulses. Consequently the
amount of muscular work is determined by the number of nervous impulses and hence by the
number of excited motor neurons in the brain. The speed of a muscular contraction
depends upon the amount of force exerted within a fixed time. The speed of movement is
thus regulated by the number of fibres actively contracting during that time.
The mechanical energy due to muscular contraction is created from the chemical energy
reserves in muscle. The glucose in muscles becomes the most important source of energy of
muscular work. The presence of oxygen is necessary for the regeneration of glucose and of
high energy phosphate compounds and thus oxygen becomes the second most important
substance in the energies of the muscular system. Glucose and oxygen are stored only in
limited amount in the muscle and the continuous supply of glucose and oxygen to the
muscular system is maintained by the blood. So the supply of blood to the working muscle can
limit muscular performance.
15.6.3 Kinds of Muscular Activity
There are two kinds of muscular activities :
(a) Dynamic muscular work (Rhythmic work), and
(b) Static muscular work (Postural work).
Dynamic Muscular Work
In dynamic work, expansion (tension) and contraction (relaxation) of a muscle
follow one after the other rhythmically. Thus work be measured as a product of
shortening of the muscle and the force used (work = height of rising X weight).
During dynamic muscular work, a muscle operates like a motor pump for the
oirculation of the blood. Contraction causes an expulsion of blood and subsequent
relaxation allows a renewed flow of blood into the muscle. Thus the blood
circulation increases and a muscle receives the blood about fifteen to twenty five
times during dynamic work. So the muscle receives plenty of sugar and oxygen and
the waste products are readily removed. Because of this is the reason the dynamic
work on a suitable rhythm can be executed for a long time without fatigue.
The best example goes with the Heart muscles that work dynamically all through
life without 'fatigue'.
Cranking of wheel is another classic example of dynamic work. Therefore, it is
recommended that the work can be efficiently carried out if it is carried out on a
rhythmic scale.

Removal of waste by blood

Figure 153:DynamicMuseularWork: Relaxation Removal of Waste by Blood

 m -& Shoulder
Man-Machine Systems

Elbow---+A

Knee ---+A

d Ankle

Static Work
Holding of a weight with an extended arm can considered as static work where the
muscle remains in a state of contraction for sometime, and thus does not extend its
length. Hence, no visible work is achieved and it cannot be defined as force
multiplied by weight. During standing in a fixed posture, the muscles of legs, hips,
back and neck, etc. are in continuously in the state of contraction;so the blood
vessels are compressed by the rise of pressure within the muscles and this reduces
the blood supply. Thus a muscle which executes a long static contraction receives
neither sugar nor oxygen fiom the blood. As a result it has to consume its reserves.
Moreover, the waste products are not carried off but accumulate which in turn
produce acute muscular pain and fatigue. It also follows that static muscular stress.
Hence this type of work postures should be avoided or at least reduced to a
minimum (Figure 15.5).
Reduced blood & 02

Lactic acid and

Other waste

Length of contraction (static work )

100 %

" Max, duration of muscular

Contraction in minutes (effect of
Y

static work)
15.6.4 Nervous Control Movement
Every muscle of human body is connected to the brain and so the nervous system is the
controlling system upon the activities of organs of the body. When nerve cells are
stimulated, they transmit impulses along the nerve fibres to the concerned organs. The
neural impulses are of electrochemical in nature and so produce a very small potential
difference (few micro volts) which passes at a speed of 10-100 ms-' along the fibre. The
nerves are only able to conduct impulses and not a constant stream of direct current. The
number of impulses carried out by nerve fibre is regulated by the original
potassium-sodium equilibrium.
Each muscle is connected to brain by two types of nerves :
(a) Sensory, and
(b) Motor.
The microvolt potential difference (action potential) is transmitted to muscle fibre
through motor in the form of number of Pulses which controls the muscle movement, its
force and speed. The nervous impulses originate in spinal cord whereas a consequence of
reflex activity, action potentials is stimulated in the motor nerves.
The sensory nerves start in muscle spindles which are stimulated by change in length and
tension in the muscle and forward impulses through the sensory nerves into the spinal
cord. Finally, these sensory impulses are perceived in the brain as sensations of position,
tension and force. Thus they give information about the state of the muscular system
which is essential for the delicate control of muscular movement. Similarly, sight,
hearing, taste, etc. are connected by sensory nerves to the brain and the nervous impulses
received by the brain are interpreted as visual, acoustic and other forms of perception.

15.6.5 The Mechanism

The nervous controls are complex mechanisms particularly, directing the movements of
the body members according to the nature of the work perceived by the brain. For
instance let us consider the visual mechanism. Chiefly on the strength of visual
information, the nervous impulses travel from the retina (a part of eye) to the visual area of
the brain, where the sum of the incoming pulses is perceived as a picture or figure or
object. Suppose this object is to be grasped, then, from this visual area of the brain,
impulses are transmitted to other muscle control centres connected with voluntary
movement. This control center relays the signals to the fingers via hand to grasp. On the
strength of the visual information the brain thus controls the further sequence of
movements. When the object is grasped, new information reaches the brain from the
pressure sensitive nerves of skin and the brain alters the grip pressure accordingly, and
thus this process continues till the work is accomplished.
SAQ 2
(a) Explain the characteristics of man-machine systems.
(b) Explain the functions of machine element in man-machine system.
(c) Explain the functions of man element in man-machine system.
(d) Discuss Muscular performance and kinds of muscular activities.
Though, each man-machine system has got different characteristics, but can be
characterized in terms of major attributes. There are two major classifications of
man-machine systems we often consider. These are :

(a) Based on the importance of feedback.

(b) Based on the type of processing.

(c) Based on the number of men and machines.

Based on the Importance of Feedback
Under this category we have two types of systems. They are :
(a) Open Loop Systems, and
(b) Closed Loop Systems
Open Loop Systems
An open loop system is one which activates but needs no further control,
e.g. priming of a pump, a rocket firing system, i.e. after priming or firing, no
control is applied for tracking (Refer Figure 15.6).

Input Processing and Output

b Decision
b

Figure 15.6 :An Open Loop System

Closed LOODSvstems

which the continuous control is vossible (Refer Figure 15.7). I

Figure 15.7 :A Closed Loop System

Based on the Type of Processing

There are three types of systems under this category :
(a) Manual Systems,
(b) Semi-automatic Systems, and
(c) Automatic Systems.
Manual Systems
It is one in which all actions are performed by a human being using
non-powered devices.
Ergonomics Semi-Automatic Systems
In these systems certain functions are performed by a machine component
under human control. It may have a feed back information component, but it
is not always necessary. It is a relationship between some standards that
provide a basis for the operator to make appropriate adjustments or
corrections. The operator then makes the decision about the corrective
actions to be taken. The corrective action is taken by the operator through
certain control mechanism such as wheels, levers, switches, knobs, buttons,
etc.
Automatic Systems
It is essentially a closed loop system and is designed in such a manner that it
should perform all required operational functions. These systems must
possess two characteristics.
(a) A built in mechanism for sensing the existing state of affair,
i.e. the sensing function must be able to detect the error or
difference between the desired output and the actual output.
(b) A self-correcting mechanism, i.e. the error should be
minimised to have more accurate control in terms of desired
output.
Based on the Number of Men and Machines
Man-Machine System or One to One Type Man-Machine System
One man and one machine exist in this type of system, e.g. a driver with a car,
a data entry operator and a computer.
Men-Machine System or Many to One Type Man-Machine System
More number of people work on one machine in this type of system. For
example : people work at construction of a bridge or building.
Man-Machines System One to Many Type Man-Machine System
One man will be controlling more than one machine. It becomes easily
possible if some part or most part will be automated in such systems. For
instance : A man beating on a Jazz,A cook or housewife cooking more than
one dish simultaneously.
Meit-Machines System Many to Many Type Man-Machine System
More men and machines are involved here. The assembly lines and mass
production lines can be included under this category.

15.8 MAN-MACHINE RELATIONSHIPS

All the fields of man-machine systems deal with the relationship of men and machines.
As discussed above, the relationship may be referred to as open loop or close loop.
We understood that, when there is no link from output to input (i.e. feedback), the
system is said to be open loop, but when the output may have some influence on the input
then the system is said to be close loop. In the backdrop of this let us now understand
some relationships between the components (i.e. man and machine) of the man-machine
system.
Suppose that a housewife wants to wash her clothes in a washing machine. Now pressing
a start button on the washing machine, in response to the decision that the time has now
come to start, the machine starts. This operation can be considered as an example of
open loop system and the operator (i.e. housewife who is acting as the man component
of the system) is working as a link of open loop.
In the case of operation of a driver on a car, the speed and direction will depend on the Man-Machine Systems
information coming through the eyes from the nature of the process. In this case rate of
movement can be modified or adjusted according to the information coming. Here the
man is working as a link of dose loop system.
Most of the man-machine relationships are quite complex and multiple closed loop
systems where man serves as integral link of the system. Most of the tasks are tracking
tasks, i.e. man as controlling component. The tracking tasks are characterized by
following conditions :
(a) The operator actuates the control system so as to maintain the alignment of
the output signal with the input signal of the control system.
(b) An externally driven input signal defines an index of desired performance.
(c) The input signal is semi-based and independent of the operator's response,
i.e. the task is paced ( A paced task, is one in which the input stimulus is not
influenced by operator's response and defines the desired motor response of
the operator).
(d) The control system induces certain constraints that impose some transitional
courses of action on the human operator (The operator cannot move the
control from one possible condition to another directly such as from left to
right - without moving through all the intervening states of the control
system).
(e) The states of the input signal have the same transitional constraints as the
control system (The input signal must also change through the intervening
states).
Generalised illustration of a continuous closed loop man-machine system is referred to
as tracking system.
An essential feature of such a model is the relationship between desired output and
actual output, this error is, of course, being used. The essential feature of the task of the
operator is that of sensing this error and taking corrective action.
This error is the consequence of a number of contributing factors relating both to desired
output and to the man-machine system.
SAQ 3
(a) Explain the man-machine relationship.
(b) By what aspects the man-machine relationship can be deicribed? Explain.

Activity 2
Identify the man-machine systems in your organization or the organization with
which you are familiar, and write down here below. Examine if you can change a
one man - one machine system to a one man - 'n' machines, and so on to improve
the productivity.
One Man-One Machine Systems
............................................................................................
 Ergonomics One Man-'n' Machine Systems

............................................................................................
'n' Men-One Machine System

............................................................................................
'n' Men-'n' Machine Systems

15.9 CRITERIA FOR EVALUATION OF

MAN-MACHINE SYSTEM
It is based on the following two aspects. Depending on these two criteria, the system
can be evaluated orjudged :
(a) System Performance.
(b) System Reliability.
System Performance
Depending on the type of system, an effective parameter on which the system
can be evaluated is to be first established. Then a criterion is to be devised or
generated. Against it, for an individual system or subsystem, the system
performance is judged.
For example, in traffic system, the average waiting time of various vehicles at
interceptions could be effective a parameter and a criterion such as a suitable
queuing model can be used to judge the system performance.
For a data entry operator- computer system, speed or errors in typing etc. can be
powerful parameters to judge the system performance.
For generating a corresponding system, some information of existing system can
be useful. This evaluation is systematic and quantitative. Criterion in
man-machine systems is based on sub-systems and for this purpose
sometimes experimental model may be developed.
Sometimes, human parameter is taken as basis for the purpose of evaluation. It is a
well-known fact that human criterion is quite complicated. However, the
following four relatively distinct types of sub-criteria may be used to indicate
human behaviour.
(a) Human Performance Measurement

I
(b) Physiological Indices
(c) Subjective Responses
(d) Accident Frequency.
42
 We shall now discuss each of the sub-criteria. Man-Machine Systems

Human Peflormance Measurement

Strictly speaking, human performance measurement is not possible
particularly it is in terms of human activity, such as various sensory and
mental activities. For practical purposes, human performance can be rated
or compared under the conditions in which the task and associated
equipment conditions are uniform
Physiologrcal Indices
It is quite important index for evaluating man-machine systems. Few of the
indices are Consumption of oxygen, blood pressure, respiration rate, heart
beat rate, blood sugar, brain waves etc.
Subjective Respome
It includes quantitative rating, people opinion, etc.
Accident Frequency
Safety of human being is an important parameter in any man-machine
system. Thus, the number of accidents or injuries or deaths or amount of
loss, etc. can provide good criterion for transportation system.
System Reliability
Reliability is defined as the probability of not failing in given time under specified
conditions of operation. In other words, the term reliability means some measure
of dependability of the system or its component in performing its functions
satisfactorily. Simply speaking, the reliability of the system is the probability of
successful performance. It can also be expressed as function of mean time between
failures.
The basic relationship in such a case may be described as the reliability of the system or
the probability of successfbl operation as a function of time.
--t
R(t) = e

where t = operating time, and

m = mean life or mean time between failures.
In order to test the reliability of the system, its sub-systems could be tested.
Commonly the sub-systems may either be in series (sequence) or parallel or a
combination of both.
System with Series Components
If the components are in series then the system reliability is given by

'system = 'I . ' 2 .3' . . Rn

where R1,R2, R3 . . . R, are the reliabilities of individual sub-systems. It is
obvious that the reliability of the systems expressed as, percentage of
successful functioning is reducing.
If a system has 10 sub-systems and each sub-system has a reliability 0.95
then
Rlo = 0.95 x 9.5 x . . . 10 times = 0.5987

The reliability of a system would decrease exponentially and hence the rate of
failure is associated with time exponentially.
Ergonomics System with Parallel Components

= 1 - (1 - r)m . n

where r = reliability of subsystem,

m = number of components in parallel for each function, and
n = number of functions.

15.10 THE DESIGN FACTORS IN MAN-MACHINE

SYSTEM
The operator cannot be overlooked while designing any equipment. In fact, the design
shouId be oriented with a system approach and the operator should be considered an
integral part of the system. In this reference, designing means laying out the equipments
around the operator in such position which will ensure that his posture is adequate and he
can see what he has to do and can operate his controls in the most effective way and so on.
Most of the design considerationsrequired for a product are given in Unit 14, Ergonomics and
Product Design of this Block 4. The Design factors of inter-related aspects are focused here in
this unit. Further, some more aspects of design due to environmental effects are separately dealt
in the same Block 4, in the next unit, i.e. Unit 16, Environment and Human Productivity.
It is a minimum thing that any designer should think to see that the controls that the
operator uses are located at relevant positions within the reachable area easily for the
operator. Unfortunately this modest requirement is not always met perfectly in some
systems while not at all given a thought in some other cases. It seems that first the
equipment is designed and then the operator is asked to handle and adapt himself for the
existing design. This causes subjection of undue stresses and thereby operational
breakdown or some fault in operation. This situation may arise either because the
importance of designing equipment round the operator has not been realised. This change in
equipment design concept could be realised and better understood by looking at flash back
of the models of various machines and then the modifications made on them to bring them into
the relatively better design, which we presently are witnessing.
Arrangement of Machines Control/Assembly Work
In several systems, both the machine controls and assembly work have to be
dealt together because many principles can be applied on both. III such cases the
designer may require data regarding - laying out the areas for vision, for controls, for
sitting body dimensions etc. Another interesting point to be settled is whether the
operator will stand or sit or lay down so as to enable to do both. The designer also has
to think of number ofdesign factors such as design of a seat, foot pedals, foot rest, control
panel, handles, etc.
Control Panels
Control panels are needed in all types of systems. In almost all man-machine
systems, the man function is basically that of monitor. The importance ofthe
monitoring hnction will depend on the extent to which controllers have been installed.
Depending on the type of system such as open or closed, or automatic or manual
etc., and degree of control required, various principles have been laid down.
Design of Displays
A device or an insmment or event which gives information about a situation which is
likely to occur or occurring or has occurred, is called display. Instrumental
displays are of two types. These are :
(a) Visual Display, and
(b) Auditory Displays.
Visual Display Systems Man-Machlne Systems
These systems are most common and versatile displays in practice. These instruments
display the information either by means of an index or by means of light, shutters
which give data directly in numerical figures in certain designed units. The
relevant information measured by the instrument in the form of certain physical
quantity is converted by a transducer into suitable form of physical quantity to be
displayed or read. The choice of a display will depend on the nature of
information which is to be given, the type method of transduction and the
accuracy of information. Wrong information provided by displays can lead to disaster.
The commonly used visual display systems in practice are :
Systems with Dial Type Display
These are the most common type of visual displays with the graduated scale
on which the indication of a value is given by means of a pointer, called Dial
type displays, e.g. dial indicators of pressure meter, ammeter, voltmeter, etc.
Indicators
Pointer type instruments may have no graduated scale and may show state of
the system, e.g. A sign board showing the direction, traffic signals, LED
indicators for a particular value is open or closed, off or on.
Warning Devices
This type will call the attention operator of the operation to change in the
system. It may be a warning signal, caution signals, etc. are included in this
type.
Counter or Digital Display
This type of device gives direct display of information in numerals.
Applications of Visual Displays
The visual display systems can be applied in the following five different ways:
(a) For quantitative reading - e.g. clock or watch, ammeter.
(b) For check reading - indication for necessary action.
(c) For qualitative reading.
(d) For comparison.
(e) For warning.
Displays Used with Controls
In addition to the above, these display systems can also be used the following
three ways when they are extended with certain controlling devices :
(a) For controlling - to check if there is any deviation from a value (true
value or a predetermined fixed value).
(b) For setting - to set at a particular predetermined (static) point, for example
setting the generator to a desired voltage.
(c) For tracking - to follow continuously or to compensate for a changing
indication for a (dynamic) point - colmnon in military equipments
while not very common in industries.
Auditory Displays
These display systems play a significant role in our daily lives. The systems such
as telephone bell, motor horn, alarm clock, door bell, etc. are included under this
category.
Characteristics o f Controls
Controls are the integral parts of the man-machine systems and have their greater
utility in industries. It is a way in which a lnan conveys his instructions to a machine
in the man-machine system. The researches on the characteristics of the control
systems lead us to follow two lines.
Ergonomics Static Characterzstics
Shape, Size, Range, accuracy, precision, Inertia, Friction, etc.
Dynamzc Characterzstzcs
Control dynamics, Performance, etc.
While designing the controls system, it is required to consider the anatomy of limbs
used in operation in order to obtain the optimal static and dynamic characteristics.
The analysis is to be carried out for various possible alternatives. From this, we
determine the best type of limbs used in operation and hence, design the best type of
control for different uses.
Choice of Controls
The choice of control depends on various factors such as technical, managerial,
economic, and human aspects. However, the human factors are the imperative and
essential to consider while selecting a type of a control for a Inan - machine
system. The general principles of design can be derived from the anatomy and
physiology of the body. When a muscular movement is made, two or more groups of
muscles act in conjunction, and in this way fashion the control of muscular action is
obtained.
The choice of controls generally one of the following three types viz. Rotary control,
reciprocating control and press type controls :
Rotary Controls
Three principal types are crank, hand wheel and a knob, but greater accuracy
cannot be achieved.
Recprocatzng Controls
Levers and Joysticks. Levers give control in one dimension while Joysticks in two
dimensions. Both types of control can give speed and accuracy. Both can be
used in a no. of positions in relation to the body and to some extent their
operational characteristics depend on the position chosen.
Press Type Controls
The press buttons. push buttons, push pull buttons, mouse type buttons and with
the advent of the new technology in computers an electronics the touch - screen
display systems have come up. These are highly accurate and delicate.
Computerised Work Measurement
The contributions of F. W. Taylor in the field of scientific management and work
measurement have been the effective and basic tools for productivity improvement.
Unfortunately, the task of work-measurement needs considerable manual effort and
time in data collection, statistical analysis and generation of operational details to be
used by employees, etc. This time consuming tasks do not leave enough time for
analytical creativity, thus has an adverse effect on the accuracy of the work-
measurement. Therefore, to improve the accuracy of time standards, their own
productivity the application of computers in work-measurement has become
advantageous, and thus the complete process turns out to be more economic and
comprehensive.
The scope for application of computerization and automation in work-
measurement can be found in the following areas :

(a) Automatic data collection in time-study, work-sampling and so on.

(b) Statistical/mathematical analysis of work-measurement data including

rating factor, allowances, etc.

(c) Development and organisation of standard data.

 (d) Development and standard data using statistical/mathematical Man-Machlne Systems
techniques.

(e) Documentation of methods of operation & relevant information.

(9 Control of work measurement inputs, and other related information.

(g) Storage of data.

(h) Maintenance and updating of .work-measurement.

(i) Computation of index for optimisation of labour standard.

(j) Utilisation of work-measurement system.
Automation in data gathering is very important in this context. It consists of the
following basic steps :
(a) Designing the study,
(b) Observing activity,
(c) Recording observations,
(d) Analysing the data, and
(e) Reporting results.
All these steps of work measurement are being carried out by integrating
electronic data generating devices with computers. Automated data gathering
system however must have the following characteristics :

(a) Ability to accept inputs from stop watch time-study.

(b) High speed, accuracy, reliability of data acquisition.

(c) Portability.

(d) Ability to provide interface with a computer for data transfer, analysis
and storage.

(e) Ability to capture analyst's observations relevant to study.

(9 Capacity to prompt the observer, etc.

(g) Sufficient data storage capacity.

(h) Ability to audit the data being gathered.

After gathering the data automatically of manual elements of work, the data
regarding the rating factor and various allowances are to be fed to the computers
which ultimately deliver the standard time of manually controlled work elements
according to the instructions fed.

SAQ 4
(a) Explain the role of system performance in Man-Machine relationship.

(b) What do you understand by the term System Reliability? What is the role of
system reliability in Man-Machine relationship?

(c) Discuss the design factors in Man-Machine system?

(d) Write the types of the visual display systems and its applications?
Ergonomics Activity 3
Explain the mechanism of following sub-system activities in a car and driver
Man-Machine System
(a) Visual

.............................................................................................
(b) Audio

............................................................................................
(c) Brakes

.............................................................................................
(d) Clutch

15.1 1 SUMMARY
At the outset, the preliminaries of work science are reviewed as it forms the strong
background of the evolution of Man-Machine System. The basic model and
characteristics of Man-Machine System are explicated. Further, the functions of
Machine as a component of Man-Machine Systems are described. The Man's role as a
component Man-Machine System, the functions of Man element due to muscular
performance and the mechanism is narrated with suitable examples. Various types of
(Man-Machine) Systems and the Man-Machine Relationships have been discussed
exhaustively. The criteria and the design factors of Man Machine System are elucidated.

15.12 KEY WORDS

Man-Machine System : Operation of one or more men with one or more
machines.
Sensing Device : Device which minimizes stimuli from sources and
links these signals to project a complete picture.
Open Loop System : Open loop system is one, which activates but
needs no further control.
Closed Loop System : Closed loop system is one, which activates but
needs continuous control.
Manual System : A system in which all actions performed by Man-Machine Systems
human using non-powered devices.
Semi Automatic Systems : Certain functions of system are performed by a
machine component under human control.
Man-Machine System : A Machine working by a Man is called
Man-Machine system.
Men-Machine System : A Machine working by more number of humans is
called Men-Machine system.
Men-Machines Systems : Many Machines working by many number of
humans is Called Men-Machines system.
System Performance : Criteria which evaluate the performance of a
system.
System Reliability : The reliability of the system is the probability of
successful performance.

15.13 ANSWERS TO SAQs

Refer the preceding text for all the Answers to SAQs.