Series motor on-off speed control circuit having means for generating a complementary field current

Claim 2

A speed control circuit for a series motor comprising, periodically operable switching means connected in the motor armature circuit, means for deriving a complementary current and supplying same to the motor field winding during the intervals when the switching means is cut off, a sampling circuit connected to the terminals of the motor armature and synchronized with said switching means to sample the back emf of the motor only during said cutoff intervals of the switching means, an integrating circuit connected to the output of the sampling circuit to integrate the sampled pulses of back emf to derive a measuring signal indicative of the motor speed, a comparison member having a first input to which said measuring signal is applied, a second input to which a reference signal indicative of the nominal motor speed is applied and an output at which an error signal is produced that is indicative of the difference between the actual motor speed and the nominal motor speed, and means for regulating the on-off time of said switching means that includes means for coupling the error signal at the output of the comparison member to said switching means so as to regulate the on-off time thereof in a sense that tends to reduce the error signal.

Claim 3

A control circuit as claimed in claim 1 wherein said switching means comprises a thyristor having a control electrode to which the error signal is applied, and said complementary current deriving means comprises impedance means coupled to said field winding to supply thereto a current of the same amplitude during each sampling period and which is independent of the armature induced emf.

Claim 4

A control circuit as claimed in claim 1 wherein the integrating circuit comprises a resistor and capacitor connected to form a parallel RC-circuit having a time constant that is short in relation to the cycle period of the switching means so that the integrating circuit produces a voltage comprising a sawtooth voltage superimposed on a DC component of voltage of the same order of magnitude, and said comparison member comprises a trigger circuit having first and second inputs to which are applied the output voltage of the parallel RC-circuit and a reference voltage, respectively, and an output for supplying a signal that turns on the switching means upon equality of the voltages at said first and second inputs.

Claim 5

A control circuit as claimed in claim 2 further comprising a source of DC supply current for the motor, a resistor, and wherein the means for generating the complementary current comprises the supply source and the resistor connected to form a closed loop circuit with saId field winding.

Claim 6

A control circuit as claimed in claim 1 further comprising means for generating sampling pulses of a fixed duration that is shorter than one half period of the switching means cycle period, and means for coupling said sampling pulses to the sampling circuit to control the sampling of the motor back emf.

Claim 7

A speed control circuit for a series motor comprising, a source of AC supply current for the motor, periodically operable switching means comprising a semiconductor control device connected in the motor armature circuit between the field winding and the motor armature, means for deriving a complementary current and supplying same to the motor field winding during the intervals when the switching means is cut off, said current deriving means comprising a branch circuit connected to the terminals of the supply source and including, in series, a capacitor, a unidirectional conduction element and a first resistor, and means connecting one of the terminals of the field winding to an electrode of the capacitor and the other terminal to the other electrode of the capacitor via a second resistor, a sampling circuit connected to the terminals of the motor armature and periodically operable to sample the back emf of the motor only during said cutoff intervals of the switching means, an integrating circuit connected to the output of the sampling circuit to integrate the sampled pulses of back emf, and means for coupling the output of the integrating circuit to said switching means so as to vary the conduction period thereof as a function of the induced emf in the armature during the sampling period.

Claim 8

A speed control circuit for a series motor comprising, a source of AC supply current for the motor, periodically operable switching means comprising a semiconductor control device connected in the motor armature circuit between the field winding and the motor armature, means for deriving a complementary current and supplying same to the motor field winding during the intervals when the switching means is cut off, said current deriving means comprising a branch circuit connected to the terminals of the supply source and including, in series, a capacitor, a unidirectional conduction element and a first resistor, and means connecting one of the terminals of the field winding to an electrode of the capacitor and the other terminal to the other electrode of the capacitor via a second resistor, a sampling circuit connected to the terminals of the motor armature and periodically operable to sample the back emf of the motor only during said cutoff intervals of the switching means, an integrating circuit connected to the output of the sampling circuit to integrate the sampled pulses of back emf, and means for coupling the output of the integrating circuit to said switching means so as to vary the conduction period thereof as a function of the induced emf in the armature during the sampling period.

Claim 9

A control circuit as claimed in claim 6 wherein the unidirectional element comprises a diode and the components of said branch circuit are chosen so that the diode is cut off during the intervals when the switching means is cut off.

Claim 10

A speed control circuit for a series motor comprising, periodically operable switching means connected in the motor armature circuit, means for deriving a complementary current and supplying same to the motor field winding during the intervals when the switching means is cut off, a sampling circuit connected to the terminals of the motor armature and periodically operable to sample the back emf of the motor only during said cutoff intervals of the switching means, said sampling circuit including a voltage divider formed by two series-connected resistors connected to the terminals of the armature, means connecting the junction of said two resistors to a first electrode of a semiconductor control element having at least three electrodes, means for supplying to a control electrode thereof a periodic bias voltage, an integrating circuit connected to a third electrode of the semiconductor control element to integrate the sampled pulses of back emf, and means for coupling the output of the integrating circuit to said switching means so as to vary the conduction period thereof as a function of the induced emf in the armature during the sampling period.

Claim 11

A speed control circuit for a series motor comprising, periodically operable switching means connected in the motor armature circuit, means for deriving a complementary current and supplying same to the motor field winding during the intervals when the switching means is cut off, a sampling circuit connected to the terminals of the motor armature and periodically operable to sample the back emf of the motor only during said cutoff intervals of the switching means, said sampling circuit including a voltage divider formed by two series-connected resistors connected to the terminals of the armature, means connecting the junction of said two resistors to a first electrode of a semiconductor control element having at least three electrodes, means for supplying to a control electrode thereof a periodic bias voltage, an integrating circuit connected to a third electrode of the semiconductor control element to integrate the sampled pulses of back emf, and means for coupling the output of the integrating circuit to said switching means so as to vary the conduction period thereof as a function of the induced emf in the armature during the sampling period.

Claim 12

A control circuit as claimed in claim 8 further comprising a source of AC supply current for the motor, a circuit for converting the supply voltage into a periodic DC bias voltage of the same frequency, and means connecting the output of the converting circuit to the control electrode of the semiconductor control element of the sampling circuit.

Claim 13

A speed control circuit for a series motor comprising, periodically operable switching means connected in the motor armature circuit, means for deriving a complementary current and supplying same to the motor field winding during the intervals when the switching means is cut off, a sampling circuit connected to the terminals of the motor armature and periodically operable to sample the back emf of the motor only during said cutoff intervals of the switching means, an integrating circuit connected to the output of the sampling circuit to integrate the sampled pulses of back emf, said integrating circuit comprising a resisTor and capacitor connected to form a parallel RC-circuit that is arranged to produce a sawtooth voltage superimposed on a DC component of voltage proportional to the mean voltage of the sampled back emf pulses, and means for coupling the output of the integrating circuit to said switching means so as to vary the conduction period thereof as a function of the induced emf in the armature during the sampling period.

Claim 14

A speed control circuit for a series motor comprising, periodically operable switching means connected in the motor armature circuit, means for deriving a complementary current and supplying same to the motor field winding during the intervals when the switching means is cut off, a sampling circuit connected to the terminals of the motor armature and periodically operable to sample the back emf of the motor only during said cutoff intervals of the switching means, an integrating circuit connected to the output of the sampling circuit to integrate the sampled pulses of back emf, said integrating circuit comprising a resisTor and capacitor connected to form a parallel RC-circuit that is arranged to produce a sawtooth voltage superimposed on a DC component of voltage proportional to the mean voltage of the sampled back emf pulses, and means for coupling the output of the integrating circuit to said switching means so as to vary the conduction period thereof as a function of the induced emf in the armature during the sampling period.

Claim 15

A speed control circuit for a series motor comprising, periodically operable switching means connected in the motor armature circuit, means for deriving a complementary current and supplying same to the motor field winding during the intervals when the switching means is cut off, a sampling circuit connected to the terminals of the motor armature and periodically operable to sample the back emf of the motor only during said cutoff intervals of the switching means, said sampling circuit including a current control member having a control electrode to which said sampling pulses are applied, and means for coupling said sampling pulses to said switching means so that a sampling pulse simultaneously operates to turn the switching means off and the sampling circuit on, an integrating circuit connected to the output of the sampling circuit to integrate the sampled pulses of back emf, and means for coupling the output of the integrating circuit to said switching means so as to vary the conduction period thereof as a function of the induced emf in the armature during the sampling period.

Claim 16

A speed control circuit for a series motor comprising, periodically operable switching means connected in the motor armature circuit, means for deriving a complementary current and supplying same to the motor field winding during the intervals when the switching means is cut off, a sampling circuit connected to the terminals of the motor armature and periodically operable to sample the back emf of the motor only during said cutoff intervals of the switching means, said sampling circuit including a current control member having a control electrode to which said sampling pulses are applied, and means for coupling said sampling pulses to said switching means so that a sampling pulse simultaneously operates to turn the switching means off and the sampling circuit on, an integrating circuit connected to the output of the sampling circuit to integrate the sampled pulses of back emf, and means for coupling the output of the integrating circuit to said switching means so as to vary the conduction period thereof as a function of the induced emf in the armature during the sampling period.

Claim 17

A speed control circuit for a series motor comprising, periodically operable switching means connected in the motor armature circuit, means for deriving a complementary current and supplying same to the motor field winding during the intervals when the switching means is cut off, a sampling circuit connected to the terminals of the motor armature and periodically operable to sample the back emf of the motor only during said cutoff intervals of the switching means, an integrating circuit connected to the output of the sampling circuit to integrate the sampled pulses of back emf, and means for coupling the output of the integrating circuit to said switching means so as to vary the conduction period thereof as a function of the induced emf in the armature during the sampling period, said coupling means including a trigger circuit having a first input to which the output voltage of the integrating network is applied and a second input to which a reference voltage is applied, and said switching means comprises a semiconductor control device having a control electrode connected to the output of said trigger circuit.

Claim 18

A speed control circuit for a series motor comprising, periodically operable switching means connected in the motor armature circuit, means for deriving a complementary current and supplying same to the motor field winding during the intervals when the switching means is cut off, a sampling circuit connected to the terminals of the motor armature and periodically operable to sample the back emf of the motor only during said cutoff intervals of the switching means, an integrating circuit connected to the output of the sampling circuit to integrate the sampled pulses of back emf, and means for coupling the output of the integrating circuit to said switching means so as to vary the conduction period thereof as a function of the induced emf in the armature during the sampling period, said coupling means including a trigger circuit having a first input to which the output voltage of the integrating network is applied and a second input to which a reference voltage is applied, and said switching means comprises a semiconductor control device having a control electrode connected to the output of said trigger circuit.

Claim 19

A speed control circuit for a series motor comprising, periodically operable switching means connected in the motor armature circuit, means for deriving a complementary current and supplying same to the motor field winding during the intervals when the switching means is cut off, a sampling circuit connected to the terminals of the motor armature and periodically operable to sample the back emf of the motor only during said cutoff intervals of the switching means, an integrating circuit connected to the output of the sampling circuit to integrate the sampled pulses of back emf, said integrating circuit comprising a resistor and capacitor connected to form a parallel RC-circuit having a time constant in relation to the cycle period of the switching means such that the integrating circuit produces a sawtooth output voltage, and means for coupling the output of the integrating circuit to said switching means so as to vary the conduction period thereof as a function of the induced emf in the armature during the sampling period.

Claim 20

A speed control circuit for a series motor comprising, periodically operable switching means connected in the motor armature circuit, means for deriving a complementary current and supplying same to the motor field winding during the intervals when the switching means is cut off, a sampling circuit connected to the terminals of the motor armature and periodically operable to sample the back emf of the motor only during said cutoff intervals of the switching means, an integrating circuit connected to the output of the sampling circuit to integrate the sampled pulses of back emf, said integrating circuit comprising a resistor and capacitor connected to form a parallel RC-circuit having a time constant in relation to the cycle period of the switching means such that the integrating circuit produces a sawtooth output voltage, and means for coupling the output of the integrating circuit to said switching means so as to vary the conduction period thereof as a function of the induced emf in the armature during the sampling period.