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Ergonomics in Machine Design
Ergonomics (from the Greek word “ergon “meaning work,
and “nomoi” meaning natural laws), is the science of refining
the design of products to optimize them for human use. Human characteristics,
such as height, weight, and proportions are considered, as well as information
about human hearing, sight, temperature preferences, and so on.
The final objective of the ergonomics is to make the machine fit for user rather than to make the user adapt himself or herself to the machine aiming the decrease physical and mental stress to the user.
To achieve best
practice design, Ergonomists use the data and techniques of several
disciplines:
- anthropometry: body sizes, shapes; populations and variations
- biomechanics: muscles, levers, forces, strengt
- environmental physics: noise, light, heat, cold, radiation, vibration body systems: hearing, vision, sensations
- applied psychology: skill, learning, errors, differences
- social psychology: groups, communication, learning, behaviours.
Communication Between Man (User) and
Machine
The
ergonomic considerations in the design of the controls are as follows:
The
control devices should be logically positioned and easily accessible.
The control operation should involve
minimum and smooth moments.
The control operation should consume minimum energy.
The portion of the control device which
comes in contact with user's hand should be in conformity with the anatomy of
human hands.
The
proper colours should be used for control devices and backgrounds so as to give
the required psychological effect.
The shape and size of the control device should be such that the user is
encouraged to handle it in such a way as to exert the required force, but not
excessive force, damaging the control or the machine.
Working Environment
Lighting:
The
amount of light that is required to enable a task to be performed effectively
depends upon the nature of the task, the cycle time, the reflective
characteristics of the equipment involved and the vision of the operator.
The intensity of light in the surrounding
area should be less than that at the task area. This makes the task area the
focus of attention.
Operators will become less tired if the
lighting and colour schemes are arranged so that there is a gradual change in
brightness and colour from the task area to the surroundings.
The task area should be located such that
the operator can occasionally relax by looking away from the task area towards
a distinct object or surface.
The distinct object or surface should not
be so bright that the operator's eyes take time to adjust to the change when he
or she again looks at the task.
Glare often causes discomfort and also
reduces visibility, and hence it should be minimized or if possible eliminated
by careful design of the lighting sources and their positions.
Noise:
The noise at the work place causes
annoyance, damage to hearing and reduction of work efficiency.
The high-pitched noises are more annoying
than the low-pitched noises.
Noise caused by equipment that a person is
using is less annoying than that caused by the equipment, being used by another
person, because the person has the option of stopping the noise caused by his
own equipment, at least
intermittently.
The industrial safety rules specify the
acceptable noise levels for different
work places.
If the noise level is too high, it should
be reduced at the source by
maintenance, by the use of silencers and
by placing vibrating equipment on
isolating
mounts.
Further protection can be obtained by
placing the sound-insulating walls
around the
equipment.
If required, ear plugs should be provided
to the operators to reduce the
effect of noise.
Temperature:
When the heavy work is done, the
temperature should be relatively lower and when the light work is done, the
temperature should be relatively higher.
The optimum required temperature is
decided by the nature of the work.
The deviation of the temperature from the
optimum temperature required
reduces the efficiency of the operator.
Humidity and air circulation:
Humidity has little effect on the
efficiency of the operator at ordinary temperatures. However, at high
temperatures, it affects significantly the efficiency of the operator.
At high temperatures, the low humidity may
cause discomfort due to drying of throat and nose and high humidity may cause
discomfort due to sensation of stuffiness and over sweating in an
ill-ventilated or crowded room.
The proper air circulation is necessary to
minimize the effect of high temperature and humidity.
General Rules for Ergonomics in Machine Design:
- Distinguish between operational and maintenance touch points.
- Keep required amount of force consistent with purpose for force. For example, -the force to manually adjust the paper-guides in your printer should be small enough to let anyone slide them apart or together, but the guides must stay in place during use.
- Follow local conventions for up and down, rotation, color, and other stereotypical cues.
- For global products, make touch points flexible enough that local conventions can be used.
- Anticipate misuse. Design in means to prevent misuse or make the machine tough enough to withstand it.
For
Cabinets
- Prevent doors from closing completely if an internal component is improperly seated.
- Make door locations obvious and the method for opening them consistent with direction of opening, i.e., don't have users push in to have a door open outward.
- Make touch point appearance consistent with expected use.
- Falling covers are hazardous to fingers and heads. Ensure covers and doors stay up when opened. If held up by a mechanism, make sure it stays open despite wear and tear
- Doors should close and latch regardless of where users push on them. This is especially important for interlocked, hinged doors requiring a switch or sensor at the top or bottom.
For
Components and Consumables
- Avoid connections or situations where removing a component takes significant force. A sudden reduction in this force often causes the component to "eject" itself and fly out of the user's control or the user's hand to recoil onto a potentially dangerous surface.
- Inserting a component should not require exact positioning. If it does, make sure engagement points are clearly visible and obvious. And it should only be possible to insert the component one way, the correct way.
- Add an audible "click" or stop to signal a component is in its final position. And don't design in false cues.
- Ensure there's enough room for people with hands at least as large as those in the 95th percentile to grab handles and fit between components.
- Consider clothing users might wear. Ties, jewellery, and billowy blouses can get caught in rollers, pinch points, and other tight spots.
- Add an aid for removing a component if there is no way to grab it. AAA battery compartments, for example, often have small fabric straps under the batteries. Pulling on it lifts the batteries out of their spring-loaded compartment.
- Anticipate unintentional contact with hot or sharp surfaces and protect users from them. For example, think about where a user might put his left hand if the right hand is removing a component. If it takes enough force, he might put his left hand on an adjacent surface to provide leverage.
Labels
and Legends
- Include illustrations that show components in the same orientation as they would be seen by the user.
- Place labels next to areas they apply to.
- Use font size and style that is readable from where user will be when looking at labels.
- Assume there will be poor lighting and make sure there is high contrast between text, markings, and background. Unpainted, embossed lettering and markings are especially hard to read under such conditions.
- Put legends above the switches and buttons they identify. Putting legends below the controls mean they will often be obscured by the user's hand.
- Don't put legends directly on frequently used buttons. They will wear off.
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