Voltage mode drive for control circuit for an actuator using sampled back EMF control

An apparatus for controlling an actuator in response to a target speed voltage signal, said actuator having a moveable member and having a coil that influences movement of the member, comprising:

• a sample pulse generator for generating regularly occurring sample pulses;
• a voltage sense unit for sensing the voltage across said coil and providing a direction signal indicating whether said coil voltage is greater than, or less than, a reference voltage having a predetermined relationship to said target speed voltage;
• an up/down counter responsive to said sample pulses, counting at the rate of said sample pulses, and counting either up or down under control of said direction signal;
• a digital-to-analog converter responsive to the output of said up/down counter to provide a compensated voltage signal having a voltage corresponding to said up/down counter output, plus an incremental voltage;
• a voltage sensing and holding unit that senses the voltage across and coil in response to said sampling signal and holds said sensed voltage;
• a plus/minus indicator providing a plus/minus signal that switches between an indication of plus and minus in response to detecting that said up/down counter is counting down and that said up/down counter has reached a count of zero;
• a first switch, responsive to said voltage sensing and holding unit and to said digital-to-analog converter for adding said sensed voltage signal to said compensated voltage signal to produce a command voltage signal, and providing said command voltage signal with a polarity controlled by said plus/minus signal;
• a voltage amplifier, receiving said command voltage signal and providing a drive signal having a voltage magnitude that has a predetermined relationship to the voltage level of said voltage command signal;
• and
• a second switch, providing said drive signal to said coil in a direction determined by said plus/minus indicator output signal;
• such that when a substantially zero load is presented to said actuator, the contribution to said drive signal from said incremental voltage corresponds to the voltage of said target speed voltage signal.

An apparatus comprising:

• a control circuit including a move command signal input node to receive a move command signal and first and second control voltage signal nodes, the control circuit generating first and second control voltage signals based upon proportionally compensated signal, an integrally compensated signal and an inversely compensated signal, the first and second control voltage signals being presented at the first and second control voltage signal nodes;
• drive transistors coupled to receive the first and second control voltage signals;
• and
• an actuator driven by the drive transistors.