Real-Time Control of a Multiple-Element Mechanical Linkage with a Microcomputer

In real applications, many devices are highly nonlinear and are difficult to control effectively. Variabilities within the systems and strong external influences make the problem more difficult. One example is the control of electric motors driving elements of a mechanical linkage system such as in an industrial manipulator. By adding a microprocessor to the system, however, the system can be made to operate as if it was linear with a time constant determined by the designer. A method of thus linearizing the system is the so-called ``sliding mode´´ control scheme in which the controller causes the system to follow a prescribed straight-line path in phase space. By applying two different control laws on opposite sides of this switching line, the system is said to be in ``sliding´´ mode between the two individual laws. Advantages of the method include insensitivity to plant parameter variations, applicability to highly nonlinear systems, and simplicity.