CHARACTERISTICS AND DYNAMIC PERFORMANCE OF ELECTRICAL AND HYDRAULIC SERVO-DRIVES

Abstract

A brief review of the developments in the design and performance of electric d.c. motors suitable for servo systems is given, and graphs of power rate against angular velocity times the square root of the rotation inertia show how the designs have advanced rapidly in recent years. A comparison is made with the power rates of hydraulic motors, showing the latter to still have significant advantage. A basic, approximate mathematical analysis of the servo-loop for each case is presented, showing the similarities of the block diagram and transfer function for the case of velocity control. Obervations are made about the sensitivity to load disturbance and speed of response. The conclusion is that the hydraulic servo could still be a strong competitor, providing that care is taken with the shaping of the control loop. Overall cost is likely to be in favour of the electric drives.