principles of motion

8/10/2019 Principles of Motion

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PRINCIPLES OF MOTION

ECONOMY

1.

Use of Human Body

1.1

Two hands should begin and complete their movements at the same time.

This first principle states that both hands should be used as equally as possible. Both hands will

reinforce the effectiveness of work and helps in minimizing the time for a particular task.

Method of work design must be evenly divided between two sides of the workplace which is the

right and left hand. This principle will organized according to the following principle.

According to the worker’s preferred hand

It is where the allocation of work should take advantage of the worker’s best or

preferred hand which is faster, stronger, and more practical.

1.2 Two hands should not be idle at the same time.

The design of this method of work is on the avoidance of having period wherein neither hand is

working. This method will at least avoid having both hands idle at the same time for it is

impossible to completely balance the workload between the right and left hands. Exceptions to

this principle are the following:

During rest breaks

Work cycle of a worker-machine system

It is monitoring the machine during its automatic cycle wherein monitoring

involves using cognitive senses rather than the hands

1.3 Motions of the arms should be balanced in opposite dir ection and should be made

simultaneously

Design of this method will minimize the amount of hand-eye coordination required by the

worker. At the same time, both sides of the hands are doing the same movements but less

concentration will be required than if both hands perform different and independent motions.

1.4 Hand and body motions should be made at the lowest classif ication at which i t is

possible to do the work satisfactori ly.



Table 1

Basic Body

Motions

1st class: finger motions,

Example: grasping small parts.

2nd

class: also wrist motions,

Example: positioning a part

3rd

class: also forearm motions,

Example: placing a small part in a bin

4th

class: also upper arm and shoulder motions,

Example: reaching object on high shelf

5th

class: whole body motions: leg, trunk,

Example: lifting a heavy box.

Class Pivot Body parts moved

1 Knuckle Fingers(F)

2 Wrist Hand (H)+ F

3 Elbow Forearm(FA) + H+F

4 Shoulder Upper arm(UA) + FA+H+F

5 Trunk Torso + UA+FA+H+F

HIGH SPEED &

PRECISION

LOW SPEED &

PRECISION

LOW FORCE

HIGH FORCE



1.5 Work shoul d be arr anged to permit an easy and natural rhythm wherever possible

Rhythm refers to motions that have a regular recurrence and flow from one to the next. Rhythm is

essential to the smooth and automatic performance of any operation. Rhythm, as in a regular sequence of

uniform motions, aids the operator in performing work. A uniform, easy, and even rate of work is aided

by proper arrangement of the workplace, tools, and materials. Proper motion sequences help the operator

to establish a rhythm that helps make the work a series of automatic motions where the work is performed

without mental effort.

Basically, the worker learns the rhythm and performs the motions without thinking, much like the natural

and instinctive motion pattern that occurs in walking.

1.6 Eye fixations should be as few and as close together as possible

Work should be arranged so that eye-movements are confined to a comfortable area, without the need for

frequent changes of the focus.

Where visual perception is required, it is desirable to arrange the task so that the eyes can direct

the work effectively. The workplace should be laid out so that the eye fixations are as few and as

close together as possible.

In work situations where hand-eye coordination is required, the eyes are used to direct the actions of the

hands. Eye focus occurs when the eye must adjust to a change in viewing distance.

For example: from 25 in. to 10 in. with little or no change in line of sight.

Eye travel occurs when the eye must adjust to a line-of-sight change.

For example, from one location in the workplace to another, but the distances from the eyes are the same.

Since eye focus and eye travel each take time, it is desirable to minimize the need for the worker to make

these adjustments as much as possible. This can be accomplished by minimizing the distances between

objects (e.g., parts and tools) that are used in the workplace.

Normal line of sight is 15 degrees below horizontal,

Visual field is defined by a cone,

Head movements are minimized if eye fixations are limited to a single cone.



Figure 1 Normal line of sight

1.7 The method should be designed to utilize the worker‟s feet and legs when appropriate:

The legs are stronger than the arms, although the feet are not as practical as the hands. The work method

can sometimes be designed to take advantage of the greater strength of the legs, for example, in lifting

tasks.

2. ARRANGEMENT OF THE WORKPLACE

2.1 Defi ni te and fixed positions/stations shoul d be provided for al l tools and material s to permit

habit formation.

There should be a definite and fixed place for all tools and materials. The operator should always have

tools and materials in the same location, and finished parts and assembled units should be placed in fixed

positions or locations. For example, in the assembly of mechanical hardware, the hand should move

without mental direction to the bin containing flat washers, then to the bin containing lock washers, then

Horizontal

15°

15°



to the bin containing bolts, and finally to the bin containing hex nuts. There should be no thinking

required on the part of the operator to do any of this.

As the saying goes, “a place for everything, and everything in its place.” The worker eventually learns

the fixed locations, allowing him to reach for the object without wasting time looking and searching.

2.2 Tools and materi als shoul d be pre-positioned to reduce searching.

In the horizontal plane, there is a definite and somewhat limited area that the worker can use with a

normal expenditure of effort. This includes a normal working area for the right hand and one for the left

hand for each working separately, and another for both hands working together. Figure 5 and 6 shows this

and the dimensions of normal and maximum working areas in the horizontal and vertical planes.

2.3 Containers shoul d be used to del iver the materials as close to the point of use as possible.

This can sometimes be accomplished by using parts bins with sloping bottoms that feed parts by gravity

to the front of the bin, eliminating the need for the assembly operator to reach down into the bin to grasp

parts. A gravity feed bin is a container that uses gravity to move the items in it to a convenient access

point for the worker. One possible design is shown in Figure (a). It generally allows for quicker

acquisition of an item than a conventional rectangular tray shown in Figure (b).



Figure 2 a) properly designed Gravity-feed, bins and containers b) poorly designed

Figure 3 Standard bins of the gravity-feed type

2.2.1 Tools, materials, and controls should be located within the „maximum working

area‟ and as near to the worker as possible.

This helps to minimize the distances the worker must move (travel empty and travel loaded) in the

workplace. In addition, any equipment controls should also be located in close proximity. This guideline



usually refers to a normal and maximum working area, as shown in Figure 2a. It is generally desirable to

keep the parts and tools used in the work method within the normal working area, as defined for each

hand and both hands working together.

If the method requires the worker to move beyond the maximum working area, then the worker must

move more than just the arms and hands. This expends additional energy, takes more time, and ultimately

contributes to greater worker fatigue.

Figure 4 dimensions of normal and maximum working area in the horizontal plane for

males



Figure 5 dimensions of normal and maximum working area in the horizontal plane for

females



Figure 6 Normal and maximum working space in three dimensions



Figure 7a) poor & b) Good arrangement of parts and tools in workplace

2.2.1 „Drop deliveries‟ or ejectors should be used wherever possible, so that operators

do not have to use hi s/her hands to dispose of the finished work.

The drop chutes should lead to a container adjacent to the worktable. The entrance to the gravity chute

should be located near the normal work area, permitting the worker to dispose of the finished work unit

quickly and conveniently. They are most appropriate for lightweight work units that are not fragile.

This requires configuring the work -place, for example, so that finished units may be disposed of by

releasing them in the position in which they are completed, delivering them to their next destination by



gravity. Besides the savings in time, this frees the two hands so that they may begin the next cycle

immediately without breaking the rhythm

2.2.2 Provision should be made for adequate lighting and, a chair of the type of

height to permit good postur e shoul d be provided.

The height of the workplace and seat should be arranged to allow alternate standing and sitting.

This usually means an adjustable chair that can be fitted to the size of the worker. The adjustments

usually include seat height and back height. Both the seat and back are padded.

Many adjustable chairs also provide a means of increasing and decreasing the amount of back support.

The chair height should be in proper relationship with the work height. An adjustable chair for the

workplace is shown in Figure 8.

Figure 8 Adjustable chair

2.2.3 The color of the workplace should contrast wi th that of the work and thus

reduce the eye-fatigue.



The issue of illumination is normally associated with ergonomics. However, illumination has long been

known to be an important factor in work design. Illumination is especially important in visual inspection

tasks.

Figure 9 working conditions

Working ConditionsTemperature &Humidity

Ventilation

Illumination Color

Noise & Vibration

Causes of AccidentsSafety

Work Breaks



3. DESIGN OF TOOLS & EQUIPMENT

2.2.4 The hands should be relieved of all work of “holding” the work -piece where this

can be done by a ji g, fi xture or foot-operated device.

principles of motion

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