Method for detecting the position of a rotor of a DC motor and related circuit

• US 6,841,903 B2
• Filed: 10/30/2002
• Issued: 01/11/2005
• Est. Priority Date: 10/31/2001
• Status: Active Grant

• Current Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Original Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Inventors: Brambilla, Massimiliano, Galbiati, Ezio, Boscolo, Michele
• Primary Examiner(s): LE, DANG D
• Application Number:
  US10/285,362
• Publication Number:
  US 20030173972A1
• Time in Patent Office: 804 Days
• Field of Search: 310/68.B, 318/138, 318/254, 318/439, 318/720, 318/721, 318/722, 318/723, 318/724
• US Class Current: 310/68.00B
• CPC Class Codes: G11B 19/20 Driving; Starting; Stopping; Control thereof
• CPC Class Codes: H02P 6/182 using back-emf in windings
• CPC Class Codes: H02P 6/185 using inductance sensing, e.g. pulse excitation
• CPC Class Codes: H02P 6/22 in a selected direction of rotation

Abstract

A method for detecting the position of a rotor of a DC motor with N phases having a plurality of windings, comprising the steps of connecting two of the windings between first and second prefixed voltages through to a first current path for a prefixed time, allowing the current stored in the two windings to discharge through a second current path; comparing the voltage across one of the two windings with a reference voltage and providing a control signal when the voltage is smaller in absolute value than the reference voltage, performing the above steps for each of the winding pairs of the motor; detecting the position of the rotor on the basis of the control signals obtained.

Claims

1. Method for detecting the position of a rotor of a DC motor with N phases having a plurality of windings, comprising:

connecting two of said windings between first and second prefixed voltages through to a first current path for a prefixed time;

allowing the current stored in said two windings to discharge through a second current path;

comparing a voltage across one of said two windings with a reference voltage and providing a control signal when said voltage is smaller in absolute value than said reference voltage;

performing the above steps for each of plural winding pairs of the windings of said motor; and

detecting the position of said rotor on the base of the control signals obtained.

2. Method according to claim 1 wherein N equals three.

3. Method according to claim 1 wherein said first prefixed voltage is the supply voltage and said second prefixed voltage is ground.

4. Method according to claim 1 wherein said reference voltage is the supply voltage.

5. Method according to claim 1 wherein said second current path connects said two windings between said second and said first prefixed voltage.

6. Method according to claim 1 wherein the step of allowing the current stored in said two windings to discharge through a current path includes of setting the N phases at high impedance.

7. Method according to claim 1 wherein said first current path is formed by the activation of two transistors.

8. Method according to claim 1 wherein said second current path is formed by the activation of two transistors.

9. Method according to claim 1 wherein said second current path is formed by activation of a transistor and of a diode.

10. Method according to claim 1 wherein said second current path is formed by activation of two diodes.

11. Method according to claim 1 wherein the comparing step includes deriving a value of the control signal based on a length of time required for the voltage to drop below said reference voltage.

12. The method of claim 11 wherein the reference voltage is circuit ground.

13. Circuit for detecting the current of a DC motor with three phases, comprising:

three half-bridges for driving said motor;

a voltage comparator having a first input applied to a supply voltage and having a second input connected to a controlled selector, said controlled selector allowing the selective connection of said second input of the comparator to a central point of any one of said three half-bridges, in response to a control signal; and

a control logic that receives in input the output of said comparator, detecting the position of the rotor therefrom.

14. A method, comprising:

introducing a voltage across a pair of series connected motor windings for a period, Tact;

comparing, after the introducing step, a voltage over time across one motor winding of the pair of motor windings with the value of the voltage introduced across the pair of windings; and

determining, based on a result of the comparing step, the position of a motor rotor with respect to the pair of windings.

15. The method of claim 14 wherein the comparing step includes measuring the length of a period required for the voltage across the one of the pair of windings to drop below the value of the voltage introduced across the pair of windings.

16. A device, comprising:

a pair of motor windings;

means for selectively coupling a first end of the series connected windings to a supply voltage and a second end of the windings to a circuit ground for a selected period, T1; and

means for comparing a voltage across one of the pair of windings with the supply voltage, after the period T1.

17. The device of claim 16, further comprising detection means for determining a position of a rotor relative to the pair of windings based upon an output from the comparing means.

18. The device of claim 17 wherein the detection means determines the position of the rotor based upon the length of a period during which the voltage across the one of the pair of windings remains greater than the supply voltage.

19. The device of claim 17 wherein the detection means determines the position of the rotor based upon the relative values of the voltage across the one of the pair of windings and the supply voltage, after a selected period, T2.

20. A device, comprising:

a pair of motor windings;

means for selectively coupling a first end of the series connected windings to a supply voltage and a second end of the windings to a circuit ground for a selected period, T1; and

means for comparing a voltage across one of the pair of the pair of winding with a circuit ground.

21. The device of claim 20, further comprising:

a rotor; and

means for determining a position of the rotor based upon an output of the measuring means.

22. The device of claim 21 wherein the determining means includes means for measuring a period of time required for the voltage across the one of the pair of windings to reach the level of circuit ground.

23. A method, comprising:

introducing a voltage across a pair of series connected motor windings for a selected period;

comparing a voltage level, at a terminal of one motor winding of the pair of motor windings, with a reference voltage;

measuring a length of time until the voltage drops, in absolute value, below the reference voltage; and

determining, based on a result of the measuring step, the position of a motor rotor with respect to the pair of winding.

24. The method of claim 23 wherein:

the pair of motor windings is two of a plurality of motor windings;

the introducing step includes introducing the voltage, for respective selected periods, across pairs of the plurality of motor windings in a plurality of permutations;

the comparing step includes comparing a respective voltage level, at a terminal of one motor winding of each of the pairs of motor windings, with the reference voltage;

the measuring step includes measuring a respective length of time until the respective voltage level drops, in absolute value, below the reference voltage; and

the determining step includes determining, based on results of the measuring step, the position of the motor rotor with respect to all of the plurality of windings.

25. The method of claim 23 wherein the reference voltage is a supply voltage.