ERGONOMIC DESIGN OF WORKSTATIONS

BY: VISHAL SRIVASTAVA MECHANICAL ENGINEERING

VIII SEMESTER ROLL NUMBER: 10ESKME122

INDUSTRIAL ENGINEERING LAB

ERGONOMIC DESIGN OF WORKSTATIONS

What is Ergonomics?

Ergonomics (or human factors) is the scientific discipline concerned with the understanding of

interactions among humans and other elements of a system, and the profession that applies

theory, principles, data and methods to design in order to optimize human well-being and overall

system performance. Practitioners of ergonomics and ergonomists contribute to the design and

evaluation of tasks, jobs, products, environments and systems in order to make them compatible

with the needs, abilities and limitations of people.

In a broad sense, ergonomics is the applied science of workplace and equipment design with the

intention of maximizing productivity by reducing operator fatigue and discomfort.

Ergonomics in Workstation Design

In industrial workstation design the primary concern has usually been the improvement of the

performance of the equipment alone. Little consideration is given towards matching the abilities

of the operator with the task requirements.

Consequently, many industrial workstations are poorly designed, resulting in lost worker

productivity and unnecessary injury at the workplace. An ergonomics approach to the design of

an industrial workstation attempts to achieve an appropriate balance between the worker

capabilities and work requirements to optimize worker productivity and the total system, as well

as provide worker physical and mental well-being, job satisfaction and safety.

Proper industrial workstation ergonomics has a lot of advantages such as:

Reduction of many costs and increased profitability of operations.

Workers who use ergonomically correct industrial workstations experience more energy,

higher morale, less pain, and fewer days lost to sick time.

Additionally, by maximizing the efficiency of usable space for each workstation,

companies can reduce real estate holdings and increase income per square foot.

Basic Ergonomic Principles for Workstation Design and Work

Postures

“If it feels right, it probably is right. If it feels uncomfortable, there is probably something wrong

with the design, not the worker”

As mentioned above, with a properly designed workstation, a worker should be able to maintain

a proper and comfortable work posture, thereby preventing a variety of health problems such as

back injury, development of RSI and circulatory problems in the legs caused by poorly designed

seats, long period of standing, reaching too far and inadequate lighting. Below are some general

basic ergonomic principles for workstation design:

Head height

• Allow adequate space for the tallest possible worker.

• Position displays at or below eye level because people naturally look slightly downward.

Shoulder Height

• Control panels should be placed between shoulder and waist height.

• Avoid placing above shoulder height objects or controls that are used often.

Arm reach

• Place items within the shortest arm reach to avoid over-stretching while reaching up and

outward.

• Position items needed for work so that the tallest worker does not need to bend while reaching

down.

• Keep frequently used materials and tools close to and in front of the body.

Elbow height

• Adjust work surface height so that it is at or below elbow height for most job tasks.

Hand height

• Make sure that items that have to be lifted are kept between hand and shoulder height.

Leg length

• Adjust chair height according to leg length and the height of the work surface.

• Allow space so that legs can be outstretched, with enough space for long legs.

• Provide an adjustable footrest so that legs are not dangling and to help the worker change body

position.

Hand size

• Hand grips should fit hands. Small hand grips are needed for small hands, larger hand grips for

bigger hands.

• Allow enough work space for the largest hands.

Body size

• Allow enough space at the workstation for the largest worker.

NEUTRAL BODY POSITIONING

The Occupational Safety and Health Administration (OSHA) of the U.S. Department of Labor

designed a web-based e-tool that provides simple, illustrative and inexpensive principles on how

to create a safe and comfortable computer workstation. In setting up workstations, OSHA

emphasized that it is advisable to first understand the concept of neutral body positioning.

Neutral body positioning is when the joints are naturally aligned. The following are the principal

considerations in maintaining neutral body postures while working at the computer workstation:

• Hands, wrists, and forearms are straight, in line and roughly parallel to the floor.

• Head is level or bent slightly forward, forward facing, and balanced.

• Shoulders are relaxed and upper arms hang normally at the side of the body.

• Elbows stay in close to the body and are bent between 90 and 120 degrees.

• Feet are fully supported by floor or footrest.

• Back is fully supported with appropriate lumbar support when sitting vertical or leaning

slightly.

• Thighs and hips are supported by a well-padded seat and generally parallel to the floor.

• Knees are about the same height as the hips with the feet slightly forward.

CASE STUDY ON ASSEMBLY LINE WORKSTATION

ERGONOMIC DESIGN

Following is a case study conducted at an assembly workstation in at a motorcycle engine

manufacturing company. In this company, the assembly workers perform most of their assembly

tasks while in the standing position. The assembly tasks requires them to stand, bend their neck

and body and twisting their spines.

The worker performs the task while in the standing position. He needs to complete a job with a

standard time of 50 seconds or less. Normally, standing work is applied when the worker needs

to make frequent movements in a large work area, handling heavy or large objects or exert large

forces with their hands. In Company A, the workers’ needs to performed four types of awkward

postures while working at Station 3.

Based on the results of oral interviews, neck pain and leg pain were reported as the two major

MSDs complaints with respect to the task performed. After observing their activities, the authors

found these pains were due to their workstation and task design that requires them to stand, to

twist and bend their neck and bodies downwards.

Figure 1 shows the mean stature and elbow heights of the 20 subjects and the work surface of the

workstation. These measurements were taken while the workers are performing their tasks.

Basically, it covers the measurement from the head to the floor, the elbow to the floor, the height

of the table and the visual angle.

Now study is made, data collected and interpreted according to the standards of ergonomics

design. It is recommended the table height need to follow the workers’ mean elbow height with a

plus minus 10cm according to the type of jobs done on the table.

Principally, the task performed in this study can be categorized as medium class light work. The

recommended height of work benches is between 95cm to 114cm. The measurement shows the

current workbench height is 87cm from the floor, which is too low. That is, it lies outside the

range of recommended bench heights suitable for 90% of population data of elbow height taken

from the subjects in the sub assembly line. As a result of this, the worker’s needs to bend down

while performing their work task. As a result, this situation will develop into Musculoskeletal Disorders (MSDs) problems to the

worker as he carried 1 kilogram work piece with his right hand. The visual angle is about 60

degrees downwards and requires the worker to bend his neck and spine when locating the valve

to the fitting jigs

Recommendation on man-machine interface:

Figure 2 illustrates a recommended plan view of the workstation.

FIGURE 1

The following are recommended working distance for the arms: (Refer figure 3)

Set the table height according to 5th and 95th percentile that is suitable for 90% of population

elbow height with 95cm as the minimum dimension.

The worker should pick the cylinder head up with his left hand to avoid twisting of his spine,

carry the load with two hands and move one or two steps to accommodate with the picking up

and loading position

Assign the worker with a height between 160-170cm and elbow height as 95-110cm. The

objective is to avoid excessive pressure on the lumbar of the spinal column, if the worker is too

short and to avoid bending posture when he is too tall

Provide an adjustable table that can suit with any range of the workers’ height

Change the distance of support jig, so that it will be 20-30cm away from the body

Provide training and instructions to the operator on assembling the valve without bending his

neck and backbone. Also, modify the jig to make it easier to fix and hook the valve.

Provide a footrest to avoid muscular strain or cramp

FIGURE 2

Bring the table nearer to the rail to reduce the distance to carry the work piece and use left hand

to avoid twisting of the body

The work surface height should permit the upper arm and footrest in a relaxed position

Visual angle should be maintained within 30 degrees at all times

CONCLUSION

The findings from the case study indicate that the assembly workers had to use awkward

postures while working with an un-ergonomically designed workstation. An appropriate

workstation design is very critical in ensuring workers are safe and not exposed to

musculoskeletal disorders problems due to mismatches between workers anthropometrics data

with the tasks performed.

In other words, we can conclude from this over all discussion that a good workstation design that

incorporated ergonomic principles could ensure workers’ health and safety, while at the same

time able to improve their productivity. In summary, workstation design needs to incorporate

workers physical characteristics, working capabilities and limitations.

FIGURE 3