Circuit for shaping and making use of armature current ripple as generated by a D.C. motor, in particular for position control

A circuit for shaping ripple in D.C. motor armature current comprising:

• a phase locked loop including:
• a phase comparator having two inputs and an output;
• a first voltage controlled oscillator having a main input, a control input and an output, said output of the first voltage controlled oscillator being connected to a first input of the phase comparator;
• and
• a first low pass filter connected between the output of said phase comparator and the main input of said voltage controlled oscillator;
• said circuit further comprising:
• means for sensing armature current of a D.C. motor having a mean back electromotive force;
• a second lowpass filter having an input connected to the sensing means and generating an output signal to be applied to the second input of the phase comparator;
• and
• a second voltage controlled oscillator having a control input and an output;
• means connected to the sensing means for generating a signal proportional to the mean back-electro-motive force being applied to the control input of the second voltage controlled oscillator;
• and
• a switched capacitor filter controlled by the output from the second voltage controlled oscillator and connected between the output of the second lowpass filter and the second input of the phase comparator,
• wherein the output of the shaping circuit is the output of the first voltage controlled oscillator.