A Theoretical Study for the Improvement of an Actuator Characteristics by the New Velocity Feedback Method

Abstract

This paper consists of three sections, the first section shows reciprocity problems for equivalent actuator circuits, the second section shows how to set up electric circuits having velocity feedback function without using velocity detectors. Lastly, a velocity feedback method is described, which has a new effect.
There are two kinds of equivalent circuits for an actuator which converts electric energy into mechanical energy, such as voltage and current into force and velocity. These equivalent circuits differ in their reciprocity.
Furthermore, the difference between reciprocity values for equivalent circuits depends upon physical actuator properties, such as those of electro-magnetic actuators and piezo-electric autuators.
The first section reports the reason for the difference between the electro-magnetic actuator, investigated from the view point of the circuit network theory, and the piezo-electric actuator is shown as the inverse relation between the internal resistance of electric power source and the damping condition of a control system.
The second section presents a construction method for an amplifier having the velocity feedback function without velocity detectors. This amplifier has the voltage feedback and current feedback function.
However, as shown in electro-magnetic actuators and piezo-electric actuators, the relation between the positive feedback and the negative feedback in these control systems is reversed.
The last section reports the two-terminalequivalent circuit expressing the control characteristics of a mechanical system, whose equivalent circuit always forms the reciprocity circuit. According to the study on this circuit, the elements that have been influenced by the velocity feedback are only electric circuit elements, not mechanical elements.
This paper proposes a new velocity feedback method which is equivalent to adding a viscous damping factor to the actuator. The method will be useful for improvement in linear control system characteristics and for linearizing the system with static friction.