Parametric current control for microstepping unipolar motor

• US 5,015,937 A
• Filed: 10/26/1989
• Issued: 05/14/1991
• Est. Priority Date: 10/26/1989
• Status: Expired due to Fees

• Current Assignee: Siemens AG, Siemens-Bendix Automotive Electronics LP
• Original Assignee: Siemens-Bendix Automotive Electronics LP
• Inventors: Wiggins, Kregg S., Wright, Danny O.
• Primary Examiner(s): Shoop, Jr., William M.
• Assistant Examiner(s): BERGMANN, SAUL
• Application Number:
  US07/427,270
• Time in Patent Office: 565 Days
• Field of Search: 318/696, 318/685, 361/271, 310/68 C, 368/78.13
• US Class Current: 318/696
• CPC Class Codes: H02P 8/22 Control of step size; Intermediate stepping, e.g. microstepping

Abstract

A unipolar motor control system includes motor current regulation derived from monitoring battery voltage and motor temperature. The monitored battery voltage and motor temperature are inputs to a microprocessor control which has one or more look-up tables for developing an appropriate scaling factor that adjusts the voltage across the motor coils so that proper current magnitude is delivered to the motor.

Claims

1. A unipolar stepping motor control system comprising in combination:

a unipolar stepping motor comprising a two phase winding, each phase winding having two oppositely wound coils, said motor having a shaft that rotates a driven member;

present position sensor means effective to generate a signal indicating the present position of said driven member;

desired position generator means effective to generate a signal indicating the desired position of said driven member;

means, including a microprocessor, responsive to said signals for generating an error signal indicative of the difference between the present position and the desired position of said driven member to cause said stepping motor to drive said driven member to said desired position;

means for generating discrete sine and cosine values of a control current over a range of 360 degrees;

for each of said coils, a corresponding controlled conduction device for controlling the flow of current in the corresponding coil, the controlled conduction devices being under the control of said microprocessor;

said microprocessor serving to cause a first one of said controlled conduction devices to be conductive for only positive sine values of said control current, a second one of said controlled conduction devices to be conductive for only negative sine values of said control current, a third one of said controlled conduction devices to be conductive only for positive cosine values of said control current, and a fourth one of said controlled conduction devices to be conductive only for negative cosine values of said control current;

said system further including current regulating means for regulating the control current in each of said coils, said current regulating means comprising voltage sensing means, supplied to said microprocessor, for sensing the voltage of a D.C. supply that supplies the control current to said coils via said controlled conduction devices, and temperature sensing means, supplied to said microprocessor, for sensing motor temperature proximate said phase windings, and said microprocessor serving to operate said controlled conduction devices such that current to said coils is regulated in a manner causing motor operation to be substantially insensitive to fluctuations in motor temperature and in D.C. supply voltage.

2. A system as set forth in claim 1 in which said current regulating means includes a fifth controlled conduction device associated in circuit with two of the first four controlled conduction devices and their corresponding coils and a sixth controlled conduction device associated in circuit with the other two of said first four controlled conduction devices and their corresponding coils, the conductivities of said fifth and sixth controlled conduction devices being under the control of said microprocessor for regulating the magnitude of current flow to the motor when particular ones of said coils are selected by particular ones of said first through fourth controlled conduction devices.

3. A system for controlling a unipolar stepping motor comprising:

a unipolar stepping motor having a two phase winding and an output shaft connected to a driven member, said driven member operable to be rotated to a desired position;

position sensor means coupled to said driven member and operable to generate a signal indicating the present position of said driven member;

desired position signal generator means operable to generate a signal indicating the desired position of said driven member;

means responsive to each of said signals for generating an error signal indicative of the difference in said present and desired positions of said driven member;

means responsive to said error signal for generating a number of steps for said motor;

table look-up means responsive to said number of steps for generating one of a plurality of signals representing the pulse period for said motor;

means responsive to said signal from said table look-up means for supplying electrical power to said motor for rotating said driven member to said desired position;

wherein there is also included regulating means for regulating said means for supplying electrical power to said motor against fluctuations in motor temperature and in the magnitude of a D.C. supply voltage that powers said motor.

4. A system as set forth in claim 3 wherein said regulating means comprises a thermal sensor disposed in said motor proximate said winding.

5. A method for controlling a unipolar stepping motor having a two phase winding and an output shaft connected to a driven member operable to be rotated to a desired position comprising the steps of:

coupling a position sensor means to the driven member for generating a signal indicating the present position of the driven member;

generating a signal representing the desired position of the driven member;

calculating the difference between the desired position and the present position of the driven member;

responding to the magnitude of the difference for generating a stepping rate for the motor;

looking-up in a table in response to a stepping rate of the motor for a signal indicating an angular rotation of the motor; and

then

responding to said signal from the table look-up for supplying power to each winding of the motor for rotating the driven member to the desired position; and

wherein the step of looking-up, the table is N words of sine values for indicating the angular rotation of the motor; and

including

the step of regulating against fluctuations in the voltage of a D.C. supply that powers the motor and in the temperature of the motor, said regulating step comprising sensing the D.C. supply voltage, sensing the motor temperature, and then setting, in accordance with the sensed D.C. supply voltage and the sensed motor temperature, the duty cycle of a pulse width modulated current that is delivered from said D.C. supply to said motor.

6. The method as set forth in claim 5 in which the sensing of the motor temperature is conducted by a sensing device disposed proximate the motor windings.

7. A unipolar stepping motor control system comprising in combination:

a unipolar stepping motor comprising a two phase winding, each phase winding having two oppositely wound coils, said motor having a shaft that rotates a driven member;

present position sensor means effective to generate a signal indicating the present position of said driven member;

desired position generator means effective to generate a signal indicating the desired position of said driven member;

means, including a microprocessor, responsive to said signals for generating an error signal indicative of the difference between the present position and the desired position of said driven member for causing said driven member to be driven to the desired position;

controlled conduction devices in circuit relationship between said motor coils and a D.C. voltage supply that supplies current to said motor coils, said circuit from said supply being free of electrical devices other than said controlled conduction devices and said motor coils, said controlled conduction devices being under the control of said microprocessor for driving said driven member to said desired position;

said system further including current regulating means for regulating the control current in each of said coils, said current regulating means comprising voltage sensing means, supplied to said microprocessor, for sensing the voltage of said D.C. supply, and temperature sensing means, supplied to said microprocessor, for sensing motor temperature proximate said winding, and said microprocessor comprising means to operate said controlled conduction devices such that current to said coils is pulse width modulated so as to be substantially insensitive to fluctuations in motor temperature and in the voltage of said D.C. supply.

8. A system as set forth in claim 7 in which motor temperature is sensed by means of a temperature sensing device disposed in said motor proximate said winding.