System and method for velocity control of a D.C. Motor

A method for controlling the velocity of a brush-commutated D.C. motor, comprising the steps of:

• applying an adjustable drive voltage to the D.C. motor;
• inhibiting the adjustable drive voltage, where the duration of said inhibition is constant and predetermined as a function of an electrical time constant of the motor expressed as L/R, where L is an inductance of the D.C. motor and R is a resistance of the D.C. motor, the duration of the inhibition being selected to be sufficiently long so that a motor current decays to substantially zero, and said inhibition is set to repeat at a predetermined, constant rate that is chosen to maximize available torque while maintaining a desired accuracy of motor speed control;
• sampling and storing during each said regularly repeated inhibit time interval a value proportional to an amplitude of a voltage across the D.C. motor, and after the motor current decays to substantially zero;
• comparing the stored value with a predetermined desired value;
• and
• controlling the magnitude of the adjustable drive voltage only in response to the comparison of the stored value and the desired value.

A system for controlling the rotational velocity of a brush-type, direct-current motor, wherein the stator of the motor produces a stationary magnetic field, and the rotor of the motor contains one or more windings which terminate in a rotating commutator, the commutator being contacted by conductive brushes connected to a unidirectional current source, the commutator being arranged to supply current to the windings in a manner which causes rotation of the rotor, comprising:

• (a) adjustable voltage means for applying voltage across the rotor windings of the D.C. motor wherein said adjustable voltage means is sufficient to cause rotation of the rotor of the motor;
• (b) means for inhibiting said adjustable voltage means, where the duration of said inhibition is constant and predetermined as a function of an electrical time constant of the D.C. motor expressed as L/R, where L is an inductance of the D.C. motor and R is a resistance of the D.C. motor, the duration of the inhibition being selected to be sufficiently long so that a motor current decays to substantially zero, and said inhibition is set to repeat at a predetermined, constant rate that is chosen to maximize available torque while maintaining a desired accuracy of motor speed control, thus inhibiting the voltage applied to the rotor windings of the D.C. motor where the duration of each such inhibition is such that the impact to the rotor velocity, of said D.C. motor, is negligible;
• (c) a back emf magnitude detector, comprised of a means for sampling and holding a voltage value proportional to the voltage detected across the rotor windings of the D.C. motor during each inhibition of said adjustable voltage means, and after the motor current decays to substantially zero;
• (d) means for comparing the voltage representing the magnitude of the sampled back emf, and thus representing the actual rotor velocity of the D.C. motor, with a value representing a desired rotor velocity to produce a velocity error signal;
• and
• (e) means for controlling, in real-time, said adjustable voltage means, in response to the velocity error signal, to adjust the voltage applied across the rotor windings of the D.C. motor to minimize the velocity error signal and achieve the desired rotor velocity of the D.C. motor.

A method for controlling the rotational velocity of a brush-type, direct-current motor, wherein the stator of the motor produces a stationary magnetic field, and the rotor of the motor contains one or more windings which terminate in a rotating commutator, the commutator being contacted by conductive brushes connected to a unidirectional current source, the commutator being arranged to supply current to the windings in a manner which causes rotation of the rotor, comprising the steps of:

• (a) applying an adjustable voltage across the rotor windings of the D.C. motor wherein the adjustable voltage is sufficient to cause rotation of the rotor of the D.C. motor;
• (b) inhibiting the adjustable voltage where the duration of said inhibition is constant and predetermined as a function of an electrical time constant of the D.C. motor expressed as L/R, where L is an inductance of the D.C. motor and R is a resistance of the D.C. motor, the duration of the inhibition being selected to be sufficiently long so that a motor current decays to substantially zero, and said inhibition is set to repeat at a predetermined, constant rate that is chosen to maximize available torque while maintaining a desired accuracy of motor speed control, thus inhibiting the voltage applied to the rotor windings of the D.C. motor, where the duration of each inhibition is such that the impact to the rotor velocity, of the D.C. motor, is negligible;
• (c) sampling and holding the magnitude of the back emf voltage detected across the rotor windings of the D.C. motor during each said inhibition such that the adjustable voltage is inhibited by said inhibiting step, and after the motor current decays to substantially zero;
• (d) comparing the stored, sampled voltage representing the magnitude of the sampled back emf, and thus representing the actual rotor velocity of the D.C. motor, with a value representing a desired rotor velocity to produce a rotor velocity error signal;
• and
• (e) controlling, in real-time, the adjustable voltage, in response to the rotor velocity error signal, to adjust the voltage applied across the rotor windings of the D.C. motor to minimize the velocity error signal and achieve the desired rotor velocity of the D.C. motor.

Apparatus for controlling angular velocity of a brush-commutated direct current motor operated by a single adjustable electric input, said apparatus comprising:

• means for inhibiting application of the adjustable electric input where the duration of said inhibition is constant and predetermined as a function of an electrical time constant of the D.C. motor expressed as L/R, where L is an inductance of the D.C. motor and R is a resistance of the D.C. motor, the duration of the inhibition being selected to be sufficiently long so that a motor current decays to substantially zero, and said inhibition is set to repeat at a predetermined, constant rate that is chosen to maximize available torque while maintaining a desired accuracy of motor speed control;
• means for sampling and holding the magnitude of the back emf of the motor during each said inhibition and after a sufficient delay from commencement of the said inhibition to permit decay of motor current to substantially zero and to permit the back emf to reach a steady-state level, wherein the delay is less than the predetermined duration of the inhibition;
• means for comparing the sampled and held back emf magnitude with a preset fixed value;
• and
• means for adjusting a magnitude of the single electric input proportional to any difference found by said comparing means between the sampled and held back emf magnitude and the preset fixed value.

A method for controlling angular velocity of a brush-commutated direct current motor operated by a single adjustable electric input, said method comprising the steps of:

• inhibiting application of the adjustable electric input where the duration of said inhibition is constant and predetermined as a function of an electrical time constant of the D.C. motor expressed as L/R, where L is an inductance of the D.C. motor and R is a resistance of the D.C. motor, the duration of the inhibition being selected to be sufficiently long so that a motor current decays to substantially zero, and inhibition is set to repeat at a predetermined, constant rate that is chosen to maximize available torque while maintaining a desired accuracy of motor speed control;
• sampling and holding the magnitude of the back emf of the motor during the inhibition but after a sufficient delay from commencement of the inhibition to permit decay of motor current to substantially zero and to permit the back emf to reach a steady-state level, wherein the delay is less than the predetermined duration of the inhibition;
• comparing the sampled and held back emf magnitude with a preset fixed value;
• and
• adjusting a magnitude of the single electric input proportional to any difference found by said comparing step between the sampled and held back emf magnitude and the preset fixed value.

A system for controlling the velocity of a brush-commutated D.C. motor, comprising:

• adjustable voltage means for applying a first voltage across said D.C. motor;
• means for periodically inhibiting, for regularly repeated time intervals of predetermined duration, the first voltage applied across the D.C. motor, where the duration of each inhibition is constant and predetermined as a function of an electrical time constant of the D.C. motor expressed as L/R, where L is an inductance of the D.C. motor and R is a resistance of the D.C. motor and where the duration of the inhibition is selected to be sufficiently long so that a motor current decays to substantially zero, and where the inhibition of the first voltage is set to repeat at a predetermined, constant rate that is chosen to maximize available torque while maintaining a desired accuracy of motor speed control;
• means for sampling and holding a voltage amplitude value proportional to a second voltage across said D.C. motor during each time interval that said first voltage is inhibited, and after the motor current decays to substantially zero;
• means for comparing the second voltage with a value representing a desired velocity;
• and
• means for controlling, in real-time, the adjustable voltage means only in response to the comparing means to adjust the first voltage to a value relating to the desired velocity.

A method for controlling the velocity of a brush-commutated D.C. motor, comprising the steps of:

• applying an adjustable drive voltage to the D.C. motor;
• periodically inhibiting, for a regularly repeated time interval of predetermined duration, the adjustable drive voltage, where the duration of each inhibition is constant and predetermined as a function of an electrical time constant of the D.C. motor expressed as L/R, where L is an inductance of the D.C. motor and R is a resistance of the D.C. motor, and where the duration of the inhibition is selected to be sufficiently long so that a motor current decays to substantially zero, and where the inhibition of the drive voltage is set to repeat at a predetermined, constant rate that is chosen to maximize available torque while maintaining a desired accuracy of motor speed control;
• sampling and storing during each said regularly repeated inhibit time interval a value proportional to amplitude of a voltage across the D.C. motor, and after the motor current decays to substantially zero;
• comparing the stored value with a predetermined desired value;
• and
• controlling the magnitude of the adjustable drive voltage only in response to the comparison of the stored value and the desired value.

A system for controlling the rotational velocity of a brush-type, direct-current motor, wherein the stator of the motor produces a stationary magnetic field, and the rotor of the motor contains one or more windings which terminate in a rotating commutator, the commutator being contacted by conductive brushes connected to a unidirectional current source, the commutator being arranged to supply current to the windings in a manner which causes rotation of the rotor, comprising:

• (a) adjustable voltage means for applying voltage across the rotor windings of the D.C. motor wherein said adjustable voltage means is sufficient to cause rotation of the rotor of the motor;
• (b) means for periodically inhibiting said adjustable voltage means at preset time intervals of predetermined duration, thus inhibiting the voltage applied to the rotor windings of the D.C. motor for each such time interval where the duration of each such interval of inhibition is such that the impact to the rotor velocity, of said D.C. motor, is negligible, and where the duration of each inhibition is constant and predetermined as a function of an electrical time constant of the D.C. motor expressed as L/R, where L is an inductance of the D.C. motor and R is a resistance of the D.C. motor, where the duration of the inhibition is selected to be sufficiently long so that a motor current decays to substantially zero, and where the inhibition of the voltage is set to repeat at a predetermined, constant rate that is chosen to maximize available torque while maintaining a desired accuracy of motor speed control;
• (c) a back emf magnitude detector, comprised of a means for sampling and holding a voltage value proportional to the voltage detected across the rotor windings of the D.C. motor during each time interval that said adjustable voltage means is inhibited by said inhibiting means, and after the motor current decays to substantially zero;
• (d) means for comparing the voltage representing the magnitude of the sampled back emf, and thus representing the actual rotor velocity of the D.C. motor, with a value representing a desired rotor velocity to produce a velocity error signal;
• and
• (e) means for controlling, in real-time, said adjustable voltage means, in response to the velocity error signal, to adjust the voltage applied across the rotor windings of the D.C. motor to minimize the velocity error signal and achieve the desired rotor velocity of the D.C. motor.

A method for controlling the rotational velocity of a brush-type, direct-current motor, wherein the stator of the motor produces a stationary magnetic field, and the rotor of the motor contains one or more windings which terminate in a rotating commutator, the commutator being contacted by conductive brushes connected to a unidirectional current source, the commutator being arranged to supply current to the windings in a manner which causes rotation of the rotor, comprising the steps of:

• (a) applying an adjustable voltage across the rotor windings of the D.C. motor wherein the adjustable voltage is sufficient to cause rotation of the rotor of the D.C. motor;
• (b) periodically inhibiting the adjustable voltage for regularly repeated time intervals of predetermined duration, thus inhibiting the voltage applied to the rotor windings of the D.C. motor for each such time interval where the duration of each such time interval is such that the impact to the rotor velocity, of the D.C. motor, is negligible, and where the duration of each inhibition is constant and predetermined as a function of an electrical time constant of the D.C. motor expressed as L/R, where L is an inductance of the D.C. motor and R is a resistance of the D.C. motor, where the duration of the inhibition is selected to be sufficiently long so that a motor current decays to substantially zero, and where the inhibition of the adjustable voltage is set to repeat at a predetermined, constant rate that is chosen to maximize available torque while maintaining a desired accuracy of motor speed control;
• (c) sampling and holding the magnitude of the back emf voltage detected across the rotor windings of the D.C. motor during each said time interval that the adjustable voltage is inhibited by said inhibiting step, and after the motor current decays to substantially zero;
• (d) comparing the stored, sampled voltage representing the magnitude of the sampled back emf, and thus representing the actual rotor velocity of the D.C. motor, with a value representing a desired rotor velocity to produce a rotor velocity error signal;
• and
• (e) controlling, in real-time, the adjustable voltage, in response to the rotor velocity error signal, to adjust the voltage applied across the rotor windings of the D.C. motor to minimize the velocity error signal and achieve the desired rotor velocity of the D.C. motor.

Apparatus for controlling angular velocity of a brush-commutated direct current motor operated by a single adjustable electric input, said apparatus comprising:

• means for periodically interrupting application of the adjustable electric input for a regularly repeated interval of a predetermined time duration, where the duration of each interruption is constant and predetermined as a function of an electrical time constant of the D.C. motor expressed as L/R, where L is an inductance of the D.C. motor and R is a resistance of the D.C. motor, where the duration of the interruption is selected to be sufficiently long so that a motor current decays to substantially zero, and where the interruption of the adjustable electric input is set to repeat at a predetermined, constant rate that is chosen to maximize available torque while maintaining a desired accuracy of motor speed control;
• means for sampling and holding the magnitude of the back emf of the motor during each said interval but after a sufficient delay from commencement of the interval to permit decay of motor current to substantially zero and to permit the back emf to reach a steady-state level, wherein the delay is less than the predetermined time duration;
• means for comparing the sampled and held back emf magnitude with a preset fixed value;
• and
• means for adjusting a magnitude of the single electric input proportional to any difference found by said comparing means between the sampled and held back emf magnitude and the preset fixed value.

A method for controlling angular velocity of a brush-commutated direct current motor operated by a single adjustable electric input, said method comprising the steps of:

• periodically interrupting application of the adjustable electric input for a regularly repeated interval of a predetermined time duration, where the duration of each interruption is constant and predetermined as a function of an electrical time constant of the D.C. motor expressed as L/R, where L is an inductance of the D.C. motor and R is a resistance of the D.C. motor, where the duration of the interruption is selected to be sufficiently long so that a motor current decays to substantially zero, and where the interruption of the adjustable electric input is set to repeat at a predetermined, constant rate that is chosen to maximize available torque while maintaining a desired accuracy of motor speed control;
• sampling and holding the magnitude of the back emf of the motor during the interval but after a sufficient delay from commencement of the interval to permit decay of motor current to substantially zero and to permit the back emf to reach a steady-state level, wherein the delay is less than the predetermined time duration;
• comparing the sampled and held back emf magnitude with a preset fixed value;
• and
• adjusting a magnitude of the single electric input proportional to any difference found by said comparing step between the sampled and held back emf magnitude and the preset fixed value.

A method for controlling an angular velocity of a brush-commutated direct current (D.C.) motor that is operated by a pulse width modulated (PWM) train of electric drive pulses, said method comprising the steps of:

• continuously generating PWM electric drive pulses for application to the D.C. motor;
• periodically asserting a constant pulse width signal to interrupt the application of the PWM train of electric drive pulses to the D.C. motor for a predetermined interval of time, where the duration of each interruption is the same and is predetermined as a function of an electrical time constant of the D.C. motor expressed as L/R, where L is an inductance of the D.C. motor and R is a resistance of the D.C. motor, where the duration of the interruption is selected to be sufficiently long so that a motor current decays to substantially zero, and where the interruption of the adjustable electric input is set to repeat at a predetermined, constant rate that is chosen to maximize available torque while maintaining a desired accuracy of motor speed control, and where a plurality of the PWM electric drive pulses are applied to the motor between assertions of the constant pulse width signal;
• during each interruption of the PWM train of electric drive pulses, waiting for the motor current to decay to substantially zero and then sampling and holding a magnitude of the back emf of the motor;
• deasserting the constant pulse width signal, thereby terminating the interruption of the PWM train of electric drive pulses;
• comparing the sampled and held back emf magnitude with a reference value that is indicative of a desired angular velocity of the D.C. motor;
• and
• adjusting the pulse width of the PWM train of electric drive pulses by an amount that is proportional to any difference found by said comparing step between the sampled and held back emf magnitude and the reference value.