STEPPER MOTOR CONTROL SYSTEM

• US 3,586,953 A
• Filed: 09/22/1967
• Issued: 06/22/1971
• Est. Priority Date: 09/22/1967
• Status: Expired due to Term

• Current Assignee: Carl O. Markkanen, Christian R. Kropac, Dale B. Blackwell, George A. Knaust, John M McCall
• Original Assignee: Carl O. Markkanen, Christian R. Kropac, Dale B. Blackwell, George A. Knaust, John M McCall
• Inventors: Markkanen, Carl O., Blackwell, Dale B., Knaust, George A., Kropac, Christian R., Mccall, John M.
• Application Number:
  US04/669,926
• Time in Patent Office: 1,369 Days
• US Class Current: 318/68
• CPC Class Codes: B41J 19/202 Drive control means for carriage movement
• CPC Class Codes: G05B 19/291 the positional error is used to control continuously the servomotor according to its magnitude
• CPC Class Codes: G05B 2219/34064 N+1 comparator
• CPC Class Codes: G05B 2219/42212 Rotation over, selection of smallest, shortest angle, distance
• CPC Class Codes: G05D 3/183 using stepping motor
• CPC Class Codes: H02P 8/32 Reducing overshoot or oscillation, e.g. damping

Abstract

A stepper motor drive system includes a shaft carrying an encoder which develops a binary-coded signal representative of 12 discrete shaft positions on either side of a reference position. Binary-coded signals representative of the desired position of the motor and the shaft position signals are applied to a digital comparator and direction logic circuit which develops output pulses until the motor advances to bring the shaft position signals and the input signals into coincidence. The comparator also develops CW or CCW signals indicating the direction of rotation of the motor in order to reach the desired position in the shortest direction. An electromagnetic detent on the motor shaft is controlled by the comparator to lock the motor shaft in the final desired position. To prevent overshoot of the motor past a desired position n and subsequent oscillation about that position, an auxiliary comparator responsive to the shaft encoder signals and the input signals develops a simulated coincidence signal when the motor reaches the n- 1 or n+ 1 position, depending upon whether it is rotating CW or CCW, respectively, and this latter signal is utilized to excite the motor momentarily in the reverse direction to check its momentum. Shortly before the motor reaches the final desired position, a forward direction pulse is applied to the motor to drive it to that position.

Claims

1. A system for operating a stepper motor to a preselected position in response to an encoded digital signal comprising:

a multichannel input circuit for supplying encoded groups of parallel digital control pulses for a motor to be controlled;

means adapted to be driven by a motor to be controlled for generating after each step an encoded group of parallel digital position-representative pulses;

a coincidence comparator coupled to said input circuit and to said generating means and effective to develop an output pulse upon each successive comparison of said pulse groups when said Two pulse groups do not correspond;

circuit means responsive to said output pulse for developing and applying a corresponding pulse to a stepper motor to be controlled; and

means responsive to correspondence between said two pulse groups for disabling said circuit means to stop the motor.

2. A system for operating a stepper motor to a preselected position in accordance with claim 1 in which said generating means includes a drum having a plurality of encoded position-representative holes and a photoelectric hole-sensing apparatus.

3. A system for operating a stepper motor to a preselected position in accordance with claim 2 in which said holes are arranged in angularly spaced axial rows of code groups.

4. A system for operating a stepper motor to a preselected position in accordance with claim 2 in which said drum also includes a peripheral ring of equally spaced timing holes and photoelectric sensing means therefor and in which said pulse-developing circuit means is controlled by said sensing means.

5. A system for operating a stepper motor to a preselected position in accordance with claim 1 which includes a source of timing signals and in which said pulse-developing circuit means is jointly responsive to said timing signals and to said comparator output signal.

6. A system for operating a stepper motor to a preselected position in accordance with claim 1 which includes a source of timing signals and a circuit jointly responsive to said timing signals and to said comparator output signal for controlling the application of said position-representative signal to said comparator.

7. A system for operating a stepper motor to a preselected position in accordance with claim 1 in which the motor is provided with a drive shaft and including an electromagnetic detent rigidly coupled to the motor shaft and having an angular positioning accuracy substantially greater than that of the stepper motor and means for energizing said detent only when the stepper motor has arrived at its preselected position, accurately to hold the motor in such position.

8. A system for operating a stepper motor to a preselected position in accordance with claim 1 in which the motor is provided with a drive shaft and including an electromagnetic detent rigidly coupled to the motor shaft and having an angular positioning accuracy substantially greater than that of the stepper motor and means responsive to said output signal to energize said detent and for energizing selected windings of the motor with direct current of a magnitude less than that of said pulses to lock the motor in the selected position.

9. A system for accurately positioning a stepper motor in a preselected position in response to a series of electrical pulses comprising:

an input circuit for supplying a series of electrical pulses to a stepper motor to be controlled;

a normally deenergized electromagnetic detent including a stator and a rotor rigidly connected to be driven by said controlled stepper motor and having an angular positioning accuracy substantially greater than that of the stepper motor; and

control means for energizing said detent substantially at the conclusion of said series of pulses to lock the motor in the selected position.

10. A system for accurately positioning a stepper motor in a preselected position in accordance with claim 9 in which said stator and said rotor have a plurality of complementary precision teeth which upon energization of the detent are locked in registering positions.