Step motor driving device

Patent metadata

Field	Value
Publication number	US-11378920-B2
Application number	US-201917254822-A
Country	US
Kind code	B2
Filing date	Jun 21, 2019
Priority date	Jul 2, 2018
Publication date	Jul 5, 2022
Grant date	Jul 5, 2022

Abstract

To reliably rotate a step motor while reducing power consumption, a step motor driving device includes a step motor that includes a rotor, stator, coil, driver circuit that outputs a measurement drive signal to the coil, phase detecting circuit that detects a counter-electromotive current that is generated in the coil after the output of the measurement drive signal and determines whether a phase of the rotor is a desired phase based on the detected counter-electromotive current, and a control unit that, if the phase is the desired phase, controls the step motor by a first driving method in which the drive circuit outputs a first drive signal for rotating the rotor by one step, and, if not, controls the step motor by a second driving method different from the first driving method so as to restrict the rotation of the rotor.

First claim

The invention claimed is:

1. A step motor driving device comprising:
a step motor that includes a rotor that is magnetized by two or more poles, a stator that transmits a magnetic force to the rotor and a coil that generates a magnetic force toward the stator;
a drive circuit that outputs a measurement drive signal to the coil;
a phase detecting circuit that detects a counter-electromotive current that occurs in the coil after the output of the measurement drive signal, and determines whether a phase of the rotor is a first phase based on the detected counter-electromotive current; and
a control unit that controls the step motor by a first driving method, in which the drive circuit outputs a first drive signal for rotating the rotor by one step, when the phase of the rotor is the first phase, and controls the step motor by a second driving method different from the first driving method so as to restrict the rotation of the rotor when the phase is not the first phase of the rotor.

2. The step motor driving device according to claim 1 , wherein
when the phase of the rotor is the first phase, the control unit controls the step motor by the first driving method in which the drive circuit outputs the first drive signal for rotating the rotor one step backward.

3. The step motor driving device according to claim 1 , wherein
in the first driving method, the drive circuit outputs the first drive signal including a first partial signal and a second partial signal, the first partial signal generating a magnetic force of a first polarity in the coil, the second partial signal generating a magnetic force of a second polarity opposite to the first polarity in the coil after the first partial signal.

4. The step motor driving device according to claim 3 , wherein
in the second driving method, the drive circuit outputs a second drive signal including a first partial signal, a second partial signal, and a third partial signal, the first partial signal generating a magnetic force of the first polarity in the coil, the second partial signal generating a magnetic force of the second polarity in the coil after the first partial signal, the third partial signal generating a magnetic force of the first polarity in the coil after the second partial signal.

5. The step motor driving device according to claim 3 , wherein
the drive circuit does not output a drive signal in the second driving method.

6. The step motor driving device according to claim 3 , wherein
in the first driving method, the drive circuit outputs the second partial signal without outputting the first partial signal.

7. The step motor driving device according to claim 3 , wherein
the control unit further includes a rank determining unit that detects a counter-electromotive current generated in the coil after the output of the first drive signal, determines a rotational force of the rotor based on the detected counter-electromotive current, and changes a rank indicating a strength of the first drive signal that is output by the drive circuit based on the determined rotational force.

8. The step motor driving device according to claim 7 , wherein
when the rank is a predetermined rank, the drive circuit outputs a signal for generating a magnetic force of the first polarity in the coil as the measurement drive signal, and outputs the second partial signal as the first drive signal, and
when the rank corresponds to a signal stronger than the predetermined rank, the drive circuit outputs the first partial signal and the second partial signal as the first drive signal.

9. The step motor driving device according to claim 7 , wherein
the rank determining unit changes the rank based on whether a period in which a signal exceeding a threshold value is detected after the first drive signal is output is shorter than a predetermined period, and
the rank determining unit changes the rank to a rank corresponding to a weaker signal when, in a period between the output of the first drive signal and the detection of the counter-electromotive current exceeding the threshold value, a counter-electromotive current having a polarity different from that of the counter-electromotive current exceeding the threshold value is detected.

10. The step motor driving device according to claim 7 , wherein
the rank determining unit detects a counter-electromotive current generated in the coil after the output of the first drive signal, and determines whether the rotor has made a predetermined rotation based on the detected counter-electromotive current, and
when it is determined that the rotor has not made the predetermined rotation, the drive circuit outputs a correction drive signal for rotating the rotor stronger than the first drive signal.

11. The step motor driving device according to claim 1 , wherein
after the measurement drive signal, the drive circuit connects a circuit for detecting a counter-electromotive current with the coil by a phase detection pulse including a plurality of intermittent first partial pulses, and after the first drive signal is output, connects the circuit for detecting a counter-electromotive current with the coil by a rotation detection signal including a plurality of intermittent second partial pulses, and
an output interval of the first partial pulses is smaller than the second partial pulses, or a period of applying each of the first partial pulse is longer than the second partial pulses.

12. The step motor driving device according to claim 1 further comprising a normal pulse generating circuit configured to generate and output a drive pulse.

Assignees

• Citizen Watch Co Ltd

Inventors

• Takyoh Yu

Classifications

• G04C3/143 Primary

  Means to reduce power consumption by reducing pulse width or amplitude and related problems, e.g. detection of unwanted or missing step · CPC title

• H02P6/182

  using back-emf in windings · CPC title

• H02P8/02

  specially adapted for single-phase or bi-pole stepper motors, e.g. watch-motors, clock-motors · CPC title