Pulse width modulated servo system

Claim 2

A CIRCUIT FOR DRIVING A D-C MOTOR FROM A D-C VOLTAGE SOURCE IN RESPONSE TO A COMMANDED VELOCITY SIGNAL COMPRISING: A. FOUR SWITCH ELEMENTS CONNECTED TO FORM A BRIDGE, THE MOTOR BEING CONNECTED ACROSS ONE DIAGONAL OF THE BRIDGE AND THE D-C VOLTAGE SOURCE BEING CONNECTED ACROSS THE OTHER DIAGONAL OF THE BRIDGE SO THAT WHEN ONE PAIR OF DIAGONALLY OPPOSED SWITCHES IS CLOSED THE VOLTAGE SOURCE WILL DRIVE CURRENT THROUGH THE MOTOR IN ONE DIRECTION AND WHEN THE OTHER PAIR OF DIAGONALLY OPPOSED SWITCHES IS CLOSED THE VOLTAGE SOURCE WILL DRIVE CURRENT THROUGH THE MOTOR IN THE OTHER DIRECTION; B. FOUR DIODES, EACH DIODE BEING CONNECTED IN PARALLEL WITH ONE OF THE SWITCH ELEMENTS AND POLED TO CONDUCT CURRENT INTO THE POSITIVE TERMINAL OF THE VOLTAGE SOURCE; C. MEANS FOR GENERATING A SIGNAL PROPORTIONAL TO THE ACTUAL VELOCITY OF THE MOTOR; D. CURRENT SENSING MEANS RESPONSIVE TO THE MOTOR ARMATURE CURRENT FOR GENERATING A CURRENT LIMIT SIGNAL HAVING A FIRST SIGNAL LEVEL WHEN THE MOTOR ARMATURE CURRENT IS LESS THAN A SELECTED VALUE AND HAVING A GOOD SIGNAL LEVEL WHEN THE MOTOR ARMATURE CURRENT IS GREATER THEN THE SELECTED VALUE; E. A SUMMING AMPLIFIER RESPONSIVE TO THE COMMANDED VELOCITY SIGNAL AND TO THE ACTUAL VELOCITY SIGNAL FOR GENERATING A VELOCITY ERROR SIGNAL THAT IS PROPORTIONAL TO THE DIFFERENCE BETWEEN THE COMMANDED VELOCITY SIGNAL AND THE ACTUAL VELOCITY SIGNAL; F. A CIRCUIT MEANS RESPONSIVE TO THE CURRENT SENSING MEANS SECOND LEVEL FOR CAUSING THE SUMMING AMPLIFIER VELOCITY ERROR SIGNAL TO BE MODIFIED SO THAT THE MOTOR ARMATURE CURRENT IS LIMITED; G. SWITCH CONTROL MEANS RESPONSIVE TO THE VELOCITY ERROR FOR OPERATING THE SWITCH ELEMENTS, THE POLARITY OF THE VELOCITY ERROR SIGNAL DETERMINING WHICH SWITCH ELEMENTS ARE TO BE CLOSED AND THE MAGNITUDE OF THE VELOCITY ERROR SIGNAL DETERMINING THE DURATION SAID SWITCH ELEMENTS ARE CLOSED, SAID MOTOR DRIVE CIRCUIT OPERATING TO MAKE THE ACTUAL VELOCITY OF THE MOTOR EQUAL THE COMMANDED VELOCITY.

Claim 3

A motor drive circuit as recited in claim 1 additionally comprising: a. circuit means connected to the d-c voltage source for generating a signal having a first level when the voltage of the d-c voltage source increases beyond a first predetermined value and having a second level when the voltage of the d-c voltage source decreases below a second predetermined value; b. energy dissipative means; and c. a switch responsive to the first level of the circuit means signal for Connecting the energy dissipative means across the d-c voltage source and responsive to the second level of the circuit means signal for disconnecting the energy dissipative means from the d-c voltage source.

Claim 4

A motor drive circuit as recited in claim 1 wherein each power switch comprises a plurality of transistors, said motor drive circuit additionally includes a bus fault detection circuit comprising: a. a resistor in series with each power switch transistor and the d-c voltage source; and b. circuit means responsive to the voltage developed across each series resistor for opening all of the power switches when one of the developed voltages exceeds a predetermined level.

Claim 5

A motor drive circuit as recited in claim 3 wherein the bus fault detection circuit includes a latch circuit for remembering that one of the developed voltages has exceeded a predetermined level and wherein the power switches are maintained open until the motor comes to a stop, said motor drive circuit additionally comprising: a. a stability network; and b. circuit means, responsive to the latch output for resetting the stability network so that the motor starts with zero commanded velocity.

Claim 6

A motor drive circuit as recited in claim 1 additionally comprising: a. a monitor circuit responsive to the d-c voltage source for generating an error signal when the d-c voltage source either exceeds a predetermined maximum value or is less than a predetermined minimum value; and b. circuit means responsive to the error signal for opening all of the power switches.

Claim 7

A circuit for driving a d-c motor from a d-c voltage source in response to a command velocity signal comprising: a. four switch elements connected to form a bridge the motor being connected across one diagonal of the bridge and the d-c voltage source being connected across the other diagonal of the bridge so that when one pair of diagonally opposed switches is closed the voltage source will drive current through the motor in one direction and when the other pair of diagonally opposed switches is closed the voltage source will drive current through the motor in the other direction; b. four diodes, each diode being connected in parallel with one of the switch elements and poled to conduct current into the positive terminal of the voltage source; c. means for generating a signal proportional to the actual velocity of the motor; d. current sensing means responsive to the motor armature current for generating a current limit signal having a first signal level when the motor armature current is less than a selected value and having a second signal level when the motor armature current is greater than the selected value; e. a summing amplifier circuit responsive to the commanded velocity signal, the actual velocity signal and the current limit signal for generating a velocity error signal that is proportional to the difference between the commanded velocity signal and the actual velocity signal when the motor armature current is less than the selected value and to the difference between the commanded velocity and the sum of the actual velocity signal and the current limit signal when the motor armature current is greater than the selected value; and f. switch control means responsive to the velocity error signal for operating the switch elements, the polarity of the velocity error signal determining which switch elements are to be closed and the magnitude of the velocity error signal determining the duration said switch elements are closed, said motor drive circuit operating to make the actual velocity of the motor equal the commanded velocity.

Claim 8

A circuit for driving a d-c motor from a d-c voltage source in response to a command velocity signal comprising: a. four switch elements connected to form a bridge the motor being connected across one diagonal of the bridge and the d-c voltage source being connected across the other diagonal of the bridge so that when one pair of diagonally opposed switches is closed the voltage source will drive current through the motor in one direction and when the other pair of diagonally opposed switches is closed the voltage source will drive current through the motor in the other direction; b. four diodes, each diode being connected in parallel with one of the switch elements and poled to conduct current into the positive terminal of the voltage source; c. means for generating a signal proportional to the actual velocity of the motor; d. current sensing means responsive to the motor armature current for generating a current limit signal having a first signal level when the motor armature current is less than a selected value and having a second signal level when the motor armature current is greater than the selected value; e. a summing amplifier circuit responsive to the commanded velocity signal, the actual velocity signal and the current limit signal for generating a velocity error signal that is proportional to the difference between the commanded velocity signal and the actual velocity signal when the motor armature current is less than the selected value and to the difference between the commanded velocity and the sum of the actual velocity signal and the current limit signal when the motor armature current is greater than the selected value; and f. switch control means responsive to the velocity error signal for operating the switch elements, the polarity of the velocity error signal determining which switch elements are to be closed and the magnitude of the velocity error signal determining the duration said switch elements are closed, said motor drive circuit operating to make the actual velocity of the motor equal the commanded velocity.

Claim 9

A motor drive circuit as recited in claim 6 additionally comprising: a. circuit means connected to the d-c voltage source for generating a signal having a first level when the voltage of the d-c voltage source increases beyond a first predetermined value and having a second level when the voltage of the d-c voltage source decreases below a second predetermined value; b. energy dissipative means; and c. a switch responsive to the first level of the circuit means signal for connecting the energy dissipative means across the d-c voltage source and responsive to the second level of the circuit means signal for disconnecting the energy dissipative means from the d-c voltage source.

Claim 10

A motor drive circuit as recited in claim 6 wherein each power switch comprises a plurality of transistors, said motor drive circuit additionally includes a bus fault detection circuit comprising: a. a resistor in series with each power switch transistor and the d-c voltage source; and b. circuit means responsive to the voltage developed across each series resistor for opening all of the power switches when one of the developed voltages exceeds a predetermined level.

Claim 11

A motor drive circuit as recited in claim 8 wherein the bus fault detection circuit includes a latch circuit for remembering that one of the developed voltages has exceeded a predetermined level and wherein the power switches are maintained open until the motor comes to a stop, said motor drive circuit additionally comprising: a. a stability network; and b. circuit means, responsive to the latch output for resetting the stability network so that the motor starts with zero commanded velocity.

Claim 12

A motor drive circuit as recited in claim 1 additionally comprising: a. a monitor circuit responsive to the d-c voltage source for generating an error signal when the d-c voltage source either exceeds a predetermined maximum value or is less than a predetermined minimum value; and b. circuit means responsive to the error signal for opening all of the power switches.

Claim 13

A circuit for driving a d-c motor from a d-c voltage source in response to a commanded velocity signal comprising: a. four switch elements connected to form a bridge, the motor being connected across one diagonal of the bridge and the d-c voltage source being connected across the other diagonal of the bridge so that when one pair of diagonally opposed switches is closed the voltage source will drive current through the motor in one direction and when the other pair of diagonally opposed switches is closed the voltage source will drive current through the motor in the other direction; b. four diodes, each diode being connected in parallel with one of the switch elements and poled to conduct current into the positive terminal of the voltage source; c. means for generating a signal proportional to the actual velocity of the motor; d. current sensing means responsive to the motor armature current for generating a current limit signal having a first signal level when the motor armature current is less than a selected value and having a second signal level when the motor armature current is greater than the selected value; e. first summing amplifier responsive to the commanded velocity signal and to the actual velocity signal for generating a velocity error signal that is proportional to the difference between the commanded velocity signal and the actual velocity signal; f. a second summing amplifier responsive to the error signal and to the motor armature voltage for generating a voltage command signal proportional to the difference between the error signal and the motor armature voltage; g. a circuit means responsive to the current sensing means second level for causing the voltage command signal to be modified so that the motor armature current is limited; and h. switch control means responsive to the voltage command signal for operating the switch elements, the polarity of the voltage command signal determining which switch elements are to be closed and the magnitude of the voltage command signal determining the duration said switch elements are closed, said motor drive circuit operating to make the actual velocity of the motor equal the commanded velocity.

Claim 14

A circuit for driving a d-c motor from a d-c voltage source in response to a commanded velocity signal comprising: a. four switch elements connected to form a bridge, the motor being connected across one diagonal of the bridge and the d-c voltage source being connected across the other diagonal of the bridge so that when one pair of diagonally opposed switches is closed the voltage source will drive current through the motor in one direction and when the other pair of diagonally opposed switches is closed the voltage source will drive current through the motor in the other direction; b. four diodes, each diode being connected in parallel with one of the switch elements and poled to conduct current into the positive terminal of the voltage source; c. means for generating a signal proportional to the actual velocity of the motor; d. current sensing means responsive to the motor armature current for generating a current limit signal having a first signal level when the motor armature current is less than a selected value and having a second signal level when the motor armature current is greater than the selected value; e. first summing amplifier responsive to the commanded velocity signal and to the actual velocity signal for generating a velocity error signal that is proportional to the difference between the commanded velocity signal and the actual velocity signal; f. a second summing amplifier responsive to the error signal and to the motor armature voltage for generating a voltage command signal proportional to the difference between the error signal and the motor armature voltage; g. a circuit means responsive to the current sensing means second level for causing the voltage command signal to be modified so that the motor armature current is limited; and h. switch control means responsive to the voltage command signal for operating the switch elements, the polarity of the voltage command signal determining which switch elements are to be closed and the magnitude of the voltage command signal determining the duration said switch elements are closed, said motor drive circuit operating to make the actual velocity of the motor equal the commanded velocity.

Claim 15

A motor drive circuit as recited in claim 11 additiOnally comprising: a. circuit means connected to the d-c voltage source for generating a signal having a first level when the voltage of the d-c voltage source increases beyond a first predetermined value and having a second level when the voltage of the d-c voltage source decreases below a second predetermined value; b. energy dissipative means; and c. a switch responsive to the first level of the circuit means signal for connecting the energy dissipative means across the d-c voltage source and responsive to the second level of the circuit means signal for disconnecting the energy dissipative means from the d-c voltage source.

Claim 16

A motor drive circuit as recited in claim 11 wherein each power switch comprises a plurality of transistors, said motor drive circuit additionally includes a bus fault detection circuit comprising: a. a resistor in series with each power switch transistor and the d-c voltage source; and b. circuit means responsive to the voltage developed across each series resistor for opening all of the power switches when one of the developed voltages exceeds a predetermined level.

Claim 17

A motor drive circuit as recited in claim 13 wherein the bus fault detection circuit includes a latch circuit for remembering that one of the developed voltages has exceeded a predetermined level and wherein the power switches are maintained open until the motor comes to a stop, said motor drive circuit additionally comprising: a. a stability network; and b. circuit means, responsive to the latch output for resetting the stability network so that the motor starts with zero commanded velocity.

Claim 18

A motor drive circuit as recited in claim 11 additionally comprising: a. a monitor circuit responsive to the d-c voltage source for generating an error signal when the d-c voltage source either exceeds a predetermined maximum value or is less than a predetermined minimum value; and b. circuit means responsive to the error signal for opening all of the power switches.

Claim 19

A circuit for driving a d-c motor from a d-c voltage source in response to a commanded velocity signal comprising: a. four switch elements connected to form a bridge, the motor being connected across one diagonal of the bridge and the d-c voltage source being connected across the other diagonal of the bridge so that when one pair of diagonally opposed switches is closed the voltage source will drive current through the motor in one direction and when the other pair of diagonally opposed switches is closed the voltage source will drive current through the motor in the other direction; b. four diodes, each diode being connected in parallel with one of the switch elements and poled to conduct current into the positive terminal of the voltage source; c. means for generating a signal proportional to the actual velocity of the motor; d. current sensing means responsive to the motor armature current for generating a current limit signal having a first signal level when the motor armature current is less than a selected value and having a second signal level when the motor armature current is greater than the selected value; e. first summing amplifier responsive to the commanded velocity signal, the actual velocity signal and the current limit signal for generating a velocity error signal that is proportional to the difference between the commanded velocity signal and the actual velocity signal when the current limit signal is at the first level and to the difference between the commanded velocity and the sum of the actual velocity signal and the current limit signal when the current limit signal is at the second level; f. a second summing amplifier responsive to the error signal and to the motor armature voltage for generating a voltage command signal proportional to the difference between the error signal and the motor armature voltage; and g. switch control means responsive to the voltage command signal for operating the switch elementS, the polarity of the voltage command signal determining which switch elements are to be closed and the magnitude of the voltage command signal determining the duration said switch elements are closed, said motor drive circuit operating to make the actual velocity of the motor equal the commanded velocity.

Claim 20

A circuit for driving a d-c motor from a d-c voltage source in response to a commanded velocity signal comprising: a. four switch elements connected to form a bridge, the motor being connected across one diagonal of the bridge and the d-c voltage source being connected across the other diagonal of the bridge so that when one pair of diagonally opposed switches is closed the voltage source will drive current through the motor in one direction and when the other pair of diagonally opposed switches is closed the voltage source will drive current through the motor in the other direction; b. four diodes, each diode being connected in parallel with one of the switch elements and poled to conduct current into the positive terminal of the voltage source; c. means for generating a signal proportional to the actual velocity of the motor; d. current sensing means responsive to the motor armature current for generating a current limit signal having a first signal level when the motor armature current is less than a selected value and having a second signal level when the motor armature current is greater than the selected value; e. first summing amplifier responsive to the commanded velocity signal, the actual velocity signal and the current limit signal for generating a velocity error signal that is proportional to the difference between the commanded velocity signal and the actual velocity signal when the current limit signal is at the first level and to the difference between the commanded velocity and the sum of the actual velocity signal and the current limit signal when the current limit signal is at the second level; f. a second summing amplifier responsive to the error signal and to the motor armature voltage for generating a voltage command signal proportional to the difference between the error signal and the motor armature voltage; and g. switch control means responsive to the voltage command signal for operating the switch elementS, the polarity of the voltage command signal determining which switch elements are to be closed and the magnitude of the voltage command signal determining the duration said switch elements are closed, said motor drive circuit operating to make the actual velocity of the motor equal the commanded velocity.

Claim 21

A motor drive circuit as recited in claim 16 additionally comprising: a. circuit means connected to the d-c voltage source for generating a signal having a first level when the voltage of the d-c voltage source increases beyond a first predetermined value and having a second level when the voltage of the d-c voltage source decreases below a second predetermined value; b. energy dissipative means; and c. a switch responsive to the first level of the circuit means signal for connecting the energy dissipative means across the d-c voltage source and responsive to the second level of the circuit means signal for disconnecting the energy dissipative means from the d-c voltage source.

Claim 22

A motor drive circuit as recited in claim 16 wherein each power switch comprises a plurality of transistors, said motor drive circuit additionally includes a bus fault detection circuit comprising: a. a resistor in series with each power switch transistor and the d-c voltage source; and b. circuit means responsive to the voltage developed across each series resistor for opening all of the power switches when one of the developed voltages exceeds a predetermined level.

Claim 23

A motor drive circuit as recited in claim 18 wherein the bus fault detection circuit includes a latch circuit for remembering that one of the developed voltages has exceeded a predetermined level and wherein the power switches are maintained open until the motor comes to a stop, said motor drive circuit additionally comprising: a. a stability network; and b. circuit means, responsive to the latch output for resetting the stability network so that the motor starts with zero commanded velocity.

Claim 24

A motor drive circuit as recited in claim 1 wherein the current limit signal generated by the current sensing means has a first signal level when the motor armature current is less than a first selected value, has a second signal level when the motor armature current is greater than the first selected value, and has a third signal level when the motor armature current is greater than a second selected value, said second selected value being greater than said first selected value.