Actuating Mechanism

(also servomotor), a device designed to move a control member in automatic-control or remote-control systems and to be used as an auxiliary drive for units in servomechanisms and vehicular steering gear. A change in the position of the control member produces a change in the flow of energy or material to an object and thereby affects the operation of machines, mechanisms, and technological processes by eliminating the deviations of the controlled variable from its prescribed value. An actuating mechanism not only changes the state of the object being controlled but also moves the control member according to a specified control principle, with the minimum possible deviations. In most cases it is operated by external power sources, since direct control by means of an actuating mechanism consisting of primary control units such as relays and transducers is impossible because of their low power, which is insufficient to act on a control member.

An actuating mechanism usually consists of a motor, a transmission, and control units, as well as feedback, signaling, interlocking, and shutoff units. Actuating mechanisms to control the flow of fluids or gases consist of a valve, shutter, or gate, which is moved by hydraulic, pneumatic, or electrical drive. Diaphragm and piston drives are used in pneumatic automation systems. Electromechanical actuating mechanisms are extensively used in industrial automation; they are usually driven by an induction motor, but in some cases they are driven by an electromagnet (solenoid), the use of which is limited because of its abrupt (jerky) action on the member being controlled. Hydraulic mechanisms operate at pressures up to 3 mega-newtons per sq m (MN/m²), or 30 kilograms-force per sq cm (kgf/cm²); pneumatic mechanisms, at pressures up to 0.6 MN/m²(6 kgf/cm²). Most electric mechanisms have electric motors with powers ranging from 10 watts to 1 kilowatt or more.