The Design of Position and Velocity Servos for Multiplying and Function Generation

The design of position and velocity servos used in analog computation and simulation for multiplying and function generation is considered. The important characteristics of potentiometers, gear train, motor, amplifier, and tachometer are defined and discussed. Nonlinear performance requirement, such as velocity and acceleration limits, overshoot for large step inputs, and static resolution, are defined in terms of component parameters. A minimum gear reduction ratio is determined on the basis of acceleration, frictional torque ratio, overshoot for large step inputs, or static resolution. Linear system analysis is made and related to system components and nonlinear performance; in particular, it is shown that static resolution is limited by servo amplifier bandwidth for given motor, potentiometers, and gear train. The selection of damping methods and the reduction of steady-state errors is described. An example design is considered.