Electric motor controller

Apparatus for controlling the rate of rotation of a motor driving a load, the load having a predetermined mechanical resonant frequency, such apparatus comprising:

• means for generating a first signal having a magnitude corresponding to the rate of rotation of the motor;
• means for comparing said first signal with a reference signal, the reference signal having a predetermined magnitude corresponding to the selected speed of rotation of the motor, said comparing means generating a speed difference signal having a level representative of the difference between the magnitudes of the first signal and the reference signal;
• means, responsive to the electrical current flowing in said motor, for generating a second signal having a level corresponding to the magnitude of said current;
• means, responsive to the speed difference signal and the second signal, for producing an error signal having a level corresponding to the difference between the speed difference signal and the second signal;
• and
• means, responsive to the error signal, for switchably coupling current to and decoupling current from the motor in accordance with the error signal level at a frequency substantially higher than the mechanical resonant frequency of the load, said power coupling and decoupling means comprising:
• (a) means for generating a pulse train having a nominal frequency and duty cycle, such nominal frequency being selected to be substantially higher than the mechanical resonant frequency of the load;
• (b) means, responsive to said pulse train, for coupling current to the motor during each pulse of the pulse train and decoupling current from the motor between pulses;
• and
• (c) wherein the pulse train generating means modulates the duty cycle of the pulses in accordance with the level of the error signal.

Apparatus for controlling the rotational speed of motor, the motor driving a load having a predetermined mechanical resonant frequency, such apparatus comprising:

• means for generating a first signal having a level representative of the actual speed of rotation of the motor;
• means for generating a reference signal having a level corresponding to a selected speed of rotation of the motor;
• means for subtracting the first signal from the reference signal producing a speed difference signal and for integrating said speed difference signal;
• means, responsive to electrical current flowing through the motor, for producing a second signal having a level representative of the level of said current flow;
• means for comparing the levels of the speed difference signal and the second signal and for generating an error signal having a level corresponding to the difference between the second signal and the speed difference signal;
• means, responsive to the error signal, for generating a train of pulses of nominal frequency and pulse width and modulating said pulse width in accordance with the level of the error signal;
• wherein such nominal frequency is selected to be substantially higher than the mechanical resonant frequency of the load;
• and
• means, solely responsive to the train of pulses, for coupling voltage to the motor for the duration of each pulse and for decoupling voltage from the motor during the interval between each pulse of the pulse train.