Human is considered as an element in systems, the relationship of which is represented by human machine model. The simplest model of a human-machine unit consists of an individual operator working with a single machine. In any machine system, the human operator first has to sense what is referred to as a machine display, a signal that tells him something about the condition or the functioning of the machine. A display may be the position of a pointer on a dial, a light flashing on a control panel, the readout of a digital computer, the sound of a warning buzzer, or a spoken command issuing from a loudspeaker.
Having sensed the display, the operator interprets it, perhaps performs some computation, and reaches a decision. In so doing, the worker may use a number of human abilities, including the ability to remember and to compare current perceptions with past experiences, to coordinate those perceptions with strategies formed in the past, and to extrapolate from perceptions and past experiences to solve novel problems, which is altogether called ‘information processing’.
Having reached a decision, the human operator normally takes some action. This action is usually exercised on some kind of a control—a pushbutton, lever, crank, pedal, switch, or handle. The action upon one or more of these controls exerts an influence on the machine and on its output, which in turn changes the display, so that the cycle is continuously repeated.
A human-machine system does not exist in isolation but in an environment influencing the operator’s training, efficiency and performance. Humans make errors. An error is a difference between desired and actual performance. It is why the engineers often seek to design systems in such a way as to mitigate or preferably avoid the effects of error, whether unintentional or not. One type of error is human error for which systems engineering is applied to minimize this type of error by making systems more forgiving or error tolerant. Under training and Overtraining have been identified as major sources of errors in a system that go unnoticed for some time till the right set of circumstances arises that cause them to become active.
Some of the most challenging and complex human problems arise in the design of large man-machine systems and in the integration of human operators (having different calibers in terms of the level of training) into these systems. Examples of such large systems are a modern jet airliner, an industrial plant, a nuclear submarine, and a space vehicle launch and recovery system. In the design of such systems, human-factors engineers study, in addition to all the considerations previously mentioned, three factors: personnel, training, and operating procedures.
In large systems such as above, the specification of personnel requirements, particularly in training aspects is an integral part of systems design.
Personnel are trained; that is, they are given appropriate information and skills required to operate and maintain the system. System design includes the development of training techniques and programs and often extends to the design of training devices and training aids.
Instructions, operating procedures, and rules set forth the duties of each operator in a system and specify how the system is to function. Tailoring operating rules to the requirements of the system and the people in it contributes greatly to safe, orderly, and efficient operations. Reciprocally the bad effects (owing to lack of proper training) could be catastrophic.
Machine wear and tear is a critical element in any production environment that manufactures product where the product outcome or final assembly can be adversely affected by worn machines or tooling. There is a direct relationship between wear & tear and the level of operator training.
While manufacturers may deploy systems to monitor the quality of the product being produced which automatically rejects non-conforming items on the production line, this only ensures the item does not end up in the market resulting in consumer dissatisfaction. In these cases, the under trained operator may have contributed a greater part of tear and wear in the machines due to lack of knowledge in using the machines. An under trained operator may be responsible in making both errors of omission and errors of commission (incorrect handling).
Overtraining occurs when someone chronically over reach for months or years on end. This leads to performance regression. An over trained worker in a batch or row production may create bottleneck at the immediate front point of the production line since the rest of the workers are comparatively slow in progress. Vice versa, the under trained worker himself is a bottleneck in the production line that affects the overall system operation, both men and machine.
An over trained worker operates at a level of over confidence that might also create unexpected system failures. Under circumstances, both over training and under training in a given task can often create system failures in negligible to catastrophic magnitude.
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