A major advance in twentieth century manufacturing was the development of mass production techniques. Mass production refers to manufacturing processes in which an assembly line, usually a conveyer belt, moves the product to stations where each worker performs a limited number of operations until the product is assembled. In the automobile assembly plant such systems have reached a highly-developed form. A complex system of conveyer belts and chain drives moves car parts to workers who perform the thousands of necessary assembling tasks.
Mass production increases efficiency and productivity to a point beyond which the monotony of repeating an operation over and over slows down the workers. Many ways have been tried to increase productivity on assembly lines: some of them are as superficial as piping music into the plant or painting the industrial apparatus in bright colors; others entail giving workers more variety in their tasks and more responsibility for the product.
These human factors are important considerations for industrial engineers who must try to balance an efficient system of manufacturing with the complex needs of workers.
Another factor for the industrial engineer to consider is whether each manufacturing process can be automated in whole or in part. Automation is a word coined in the 1940s to describe processes by which machines do tasks previously performed by people. The word was new but the idea was not. We know of the advance in the development of steam engines that produced automatic valves. Long before that, during the Middle Ages, windmills had been made to turn by taking advantage of changes in the wind by means of devices that worked automatically.
Automation was first applied to industry in continuous-process manufacturing such as refining petroleum, making petrochemicals, and refining steel. A later development was computer-controlled automation of assembly line manufacturing, especially those in which quality control was an important factor.
History provides very early examples of automatic control, but they were little used in industry. Progress was slow until this century, but it received an important stimulus from the military needs of the last war and the pace has accelerated. Automatic control is most advanced in industries like chemicals, oil-refining and food-processing, where materials are easy to handle. Because of it these industries have become highly automatic without any of the well-known inventions, such as transfer-machines and electronic computers. Control is also largely automatic in the manufacture of goods so different as iron and steel, cement and paper.
A system of control usually consists of three basic units — one that measures, one that controls, and one that corrects. If, for example, the condition to be controlled is the temperature of a boiler, the measuring unit records what is happening to the 'temperature and tells the controlling unit, which compares the actual temperature with what it should be and then tells the correcting unit to adjust a steam valve and so correct the temperature.
Controlling instruments are pneumatic, mechanical or hydraulic, and electric. Electric or electronic units are fast and able to send signals over long distances so giving "remote" control.
Automatic control is perhaps best known in plants where production is continuous, such as oil-refineries, but it is also found in factories that produce in batches.