SERVOMOTORS

  These motors are used in closed loop control systems in which work is the control variable, Figure 9. The digital controller directs operation of the motor by sending velocity command signals to the amplifier, which drives the motor. An integral feedback device (resolver) or devices (en-coder and tachometer) are either incorporated within the motor or are remotely mounted, often on the load itself.

  These provide position and velocity feedback that the controller compares to its programmed motion profile and uses to alter its velocity signal. The motion profile is a set of instructions programmed into the controller that defines the operation in terms of time, position, and velocity. The ability of the servomotor to adjust to differences between the motion profile and feedback signals depends greatly upon the type of controls and motors used. See the Controls and Sensors Product Department.

 Three basic types of servomotors are used in modern servosystems: ac, based on induction motor designs; dc, based on DC motor designs; and ac brushless, based on synchronous motor designs.