Basics of the Electric Servomotor and Drive

Abstract

This chapter discusses basic fundamentals concerning electric servomotors and drives. Motor control requires three basic elements: a motor, a drive, and one or more feedback devices. The drive controls current to produce torque; drives also commonly control velocity and sometimes control position. There are several control functions to be implemented for each axis of motion. First, a position profile, which is a sequence of position commands versus time, must be generated. Second, a position loop must be closed, and usually within that, a velocity loop is closed. Electronic motion control is a multi-billion-dollar industry. Servo motion is a fraction of that industry, sharing it with non-servo motion, such as stepper motors and variable-frequency systems. Servo systems must have feedback signals to close control loops. Often, these feedback devices are independent physical components mechanically coupled to the motor. When an object is formed as a complex shape, the effect of the geometry on reluctance is difficult to calculate. Most products that use magnetic circuits are composed of such complex shapes.