1. Field of the Invention
The present invention relates to servo systems and, in particular to a new and improved servo speed control circuit.
2. Prior Art
In the past, servo systems have been designed with linear gain to drive a servo motor at a fixed speed. In particular, such prior art servo systems having a feedback circuit for speed control employ a constant current generator to provide a linear ramp voltage for sampling purposes. The servo system is then tuned for the desired gain and phase margin at a selected speed.
A servo system tuned for operation at one speed may be unstable at other speeds since the gain required in the feedback circuitry is different for different speeds. Thus, if such prior art circuits are used to drive the servo motor at more than one speed, additional circuitry is required to control the speed of operation at each of the desired speeds.
Another approach to the above problem is to employ different current generators adjusted for each of the desired speeds, which generators are selectively switched into the feedback circuit so as to provide the different feedback gains for these different speeds. A problem with this approach is that the gain is correct only at those speeds having the appropriate gain. Other problems are that such circuitry is unreliable, cumbersome and complex.