CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No. PCT/JP2019/024760 filed on Jun. 21, 2019, which claims priority to Japanese Patent Application No. 2018-126055 filed on Jul. 2, 2018. The contents of each of the above documents are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a step motor driving device.

BACKGROUND ART

In an electronic watch with an analogue display means, for example, a step motor drives its hands. In a step motor having one coil and a rotor that is half-rotated in one step, a position where a magnetic pole of the rotor is stable when the coil is not energized and a position where the magnetic pole is stable when the coil is energized are different. This is to reliably make the coil rotate forward by applying only one pulse to the coil. In reversing the rotor, a first pulse to slightly rotate the rotor in the forward direction is applied to the coil, and then a second pulse of the potential in the opposite direction is applied to the coil so as to utilize the reaction to rotate the rotor in the reverse direction. Further, a third pulse having the same polarity as the first pulse is applied to the coil so that the rotor is more reliably stabilized at a desired position.

Patent Literature 1 discloses applying the repulsion pulse G1, the attraction pulse G2, and the repulsion pulse G3 to the coil in this order when reversing the step motor. The repulsion pulse G1 rotates the rotor in the forward direction, the attraction pulse G2 rotates the rotor in the reverse direction and pulls it back, and the repulsion pulse G3 pushes back the rotation of the rotor rotating in the reverse direction. Patent Literature 2 discloses, for rotating the step motor forward, swinging the rotor by applying the swing pulse after the drive pulse is applied, detecting whether the rotor is rotated based on the voltage generated by the swing of the rotor, and applying the correction drive pulse when the rotor is not rotated.

CITATION LIST

Patent Literature

Patent Literature 1:JP2016-3877A

Patent Literature 2:JPS63-73181A

SUMMARY OF INVENTION

Technical Problem

The inventors are considering not outputting the third pulse as much as possible in order to reduce the power consumption when reversing the step motor. On the other hand, external factors such as impact may cause the position of the rotor to deviate from the original position by half a rotation. If only the first pulse and the second pulse are output in such a case, the rotor rotates forward, and will also rotate forward in subsequent steps. The correction is very difficult in such a case, and thus the output of the third pulse could not be reduced.

One or more embodiments of the present invention have been conceived in view of the above, and an object thereof is to provide a step motor driving device capable of reliably reverse a step motor while reducing power consumption.

Solution to Problem

In order to solve the above described problems, the step motor drive device according to the present invention employs the configurations described below.

(1) A step motor driving device includes 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 desired 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 is the desired phase, and controls the step motor by a second driving method different from the first driving method so as to limit the rotation of the rotor when the phase is not the desired phase.

(2) In (1), when the phase is the desired 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) In (1) or (2), 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) In any one of (1) to (3), 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) In (3), the drive circuit does not output a drive signal in the second driving method.

(6) In any one of (3) to (5), in the first driving method, the drive circuit outputs the second partial signal without outputting the first partial signal.

(7) In any one of (3) to (6), 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) In (7), 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) In (7) or (8), 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) In any one of (7) to (9), 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) In any of (1) to (10), 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.

Effects of the Invention

According to the present invention, it is possible to reliably reverse the step motor while reducing power dissipation.

