Closed loop control for stepping motor drive

Claim 2

For use in a tape reader having a stepping motor driven sprocket for moving a tape having sprocket holes therein between successive read positions, a control circuit comprising: a. counting means having outputs connected to the stator windings of the motor for sequentially altering the energization of the windings to establish a rotating electromagnetic field. b. pulse generating means for driving said counting means through a repetitive counting sequence; and c. feedback means connected to the tape reader and said pulse generator, said feedback means being responsive to the presence and absence of sprocket holes for inhibiting the generation of a pulse unless the tape has been driven into a previously commanded read position by the stepping motor in response to the previously generated pulse.

Claim 3

A control circuit as recited in claim 1 wherein said counting means comprises a ring counter having a number of count states equal to the number of stator phase wiNdings of the stepping motor.

Claim 4

A control circuit as recited in claim 1 wherein said pulse generating means further comprises: a. a programmable unijunction transistor having anode, cathode and gate terminals with the cathode terminal being the output terminal; b. biasing means for maintaining the gate terminal potential at a substantially constant level; c. a charging circuit including a capacitor connected between the anode terminal and a first voltage bus and the series combination of a first diode and a resistor connected between the anode terminal and a second voltage bus.

Claim 5

A control circuit as recited in claim 3 wherein said feedback means includes: a. a second diode having its anode terminal connected to the anode terminal of the programmable unijunction transistor; b. a capacitor having one terminal connected to the anode of the first diode and the other terminal connected to the cathode of the second diode; c. means for applying a first voltage to the junction of said capacitor and said second diode when the tape is in a read position and a second voltage to said junction when the tape is in other than a read position.

Claim 6

A control circuit as recited in claim 4 wherein said last-named means comprises means for sensing whether a tape sprocket hole is in a read position.

Claim 7

A control circuit as recited in claim 5 further including inhibit means for preventing pulse generation independently of the position of the tape, said inhibit means including a diode having its anode connected to the anode of said unijunction transistor and its cathode adapted to be connected to the second voltage when inhibiting action is desired.

Claim 8

For use in a tape reader having a stepping motor for moving a tape having sprocket holes therein past a reading station, a control circuit comprising: a. counting means having outputs connected to the stator windings of the motor for sequentially altering the energization of the windings to establish a rotating electromagnetic field; b. sprocket hole sensing means for generating a signal indicating the presence and the absence of a sprocket hole at the reading station; and c. pulse generating means responsive to said signal for driving the counting means through a repetitive counting sequence, the pulse generating means driving the counting means after said signal indicates that a sprocket hole has left the reading station and that a next sprocket hole has arrived at the reading station.

Claim 9

For use in a tape reader having a stepping motor for moving a tape having sprocket holes therein past a reading station, a control circuit comprising: a. counting means having outputs connected to the stator windings of the motor for sequentially altering the energization of the windings to establish a rotating electromagnetic field; b. sprocket hole sensing means for generating a signal indicating the presence and the absence of a sprocket hole at the reading station; and c. pulse generating means responsive to said signal for driving the counting means through a repetitive counting sequence, the pulse generating means driving the counting means after said signal indicates that a sprocket hole has left the reading station and that a next sprocket hole has arrived at the reading station.

Claim 10

A control circuit as recited in claim 7 wherein said counting means comprises a ring counter having a number of count states equal to the number stator phase windings of the stepping motor.

Claim 11

A control circuit as recited in claim 7 wherein the sprocket hole sensing signal is a first voltage when a sprocket hole is at the reading station and a second voltage when there is no sprocket hole at the reading station and wherein the pulse generating means comprises: a. a programmable unijunction transistor having an anode, cathode and gate terminals, said cathode terminal being connected to the counting means; b. first circuit means connected to the programmable unijunction transistor gate terminal for providing a biasing voltage for the gate terminal; and c. second circuit means, connected to the anode terminal and responsive to the sprocket hole sensing signal so that the transition from said first voltage to said second voltage causes the programmable unijunction transistor to be non-conductive and the subsequent appearance of said first voltage causes the programmable unijunction transistor anode voltage to be greater than the gate biasing voltage whereby the programmable unijunction transistor becomes conductive and a pulse is generated for driving the counter means.

Claim 12

A control circuit as recited in claim 9 wherein the second circuit means comprises: a. a capacitor connected between the programmable unijunction transistor anode terminal and a first voltage bus; b. a first dIode having a cathode connected to the programmable unijunction transistor anode terminal; c. a resistor connected between the anode of the first diode and a second voltage bus; d. a second diode having an anode connected to the transistor anode terminal and a cathode connected to the sprocket sensing signal; and e. a capacitor connected between the anode of the first diode and the cathode of the second diode.