Movement and electronic timepiece

A movement includes a driver having ON and OFF states, and outputting a drive signal to a coil of a motor, a lower limit detector detecting that a current flowing through the coil is less than a lower limit, a drive controller bringing the driver into the ON state based on a result of the lower limit detector, and bringing the driver into the OFF state based on an elapsed time from the ON state, a polarity switcher switching a polarity of the drive signal when an elapsed time from the OFF state of the driver satisfies a switching condition, and a drive stopper stopping driving of the driver when the OFF time satisfies a stopping condition.

The present application is based on, and claims priority from Japanese Patent Application Serial Number 2018-065940, filed Mar. 29, 2018, the disclosure of which is hereby incorporated by reference herein in its entirety.

BACKGROUND

1. Technical Field

The present disclosure relates to a movement and an electronic timepiece.

2. Related Art

There is a technique in which, in a case where a stepping motor driving a pointer of an electronic timepiece is controlled, the supply of a current to a coil of the motor is turned on such that the current is started to be supplied when the current flowing through the coil is equal to or less than a first threshold value, and is turned off such that the supply of the current is stopped when the current flowing through the coil is equal to or more than a second threshold value greater than the first threshold value, a position of a rotor of the motor is estimated on the basis of an ON time (current supply continuation time) or an OFF time (current supply stop time), and thus rotation of the motor is controlled (see, for example, JP-A-59-46575).

However, the ON time and the OFF time may change due to disturbances such as vibrations of the rotor caused by an external magnetic field or impact, and thus there is a problem in that accurate control cannot be performed in a case where a disturbance is received.

Particularly, in a stepping motor of an analog electronic timepiece in which current consumption is reduced to the minimum at which a motor is rotated, a drive force of the motor is small and is thus easily influenced by such a disturbance, and, as a result, there is concern that a problem such as an inaccurate hand position may occur.

SUMMARY

An advantage of some aspects of the present disclosure is to provide a movement and an electronic timepiece capable of being hardly influenced by a disturbance.

A movement according to an aspect of the present disclosure includes a drive unit that has an ON state and an OFF state, and outputs a drive signal to a coil of a motor so as to drive the motor; a lower limit detection unit that detects that a current flowing through the coil is less than a lower limit current value; a drive control unit that brings the drive unit into the ON state on the basis of a detection result in the lower limit detection unit, and brings the drive unit into the OFF state on the basis of an elapsed time from the ON state; a polarity switching unit that switches a polarity of the drive signal in a case where an OFF time which is an elapsed time from the OFF state of the drive unit satisfies a polarity switching condition; and a drive stopping unit that stops driving of the drive unit in a case where the OFF time satisfies a drive stopping condition.

According to the aspect of the present disclosure, the movement includes the drive stopping unit that stops driving of the drive unit in a case where the OFF time of the drive unit driving the motor satisfies a drive stopping condition. Here, the drive stopping condition is set to a condition which is not generated during a normal operation but is generated in a case where a disturbance such as an external magnetic field or impact is applied, and thus it can be detected that the influence of the disturbance is received. Therefore, driving of the drive unit driving the motor is stopped in that case, and thus it is possible to prevent the motor from being driven in a state of being influenced by the disturbance. Therefore, it is possible to prevent the occurrence of a problem that the motor is not accurately controlled due to disturbances, and thus a hand position is inaccurate.

A movement according to another aspect of the present disclosure includes a drive unit that has an ON state and an OFF state, and outputs a drive signal to a coil of a motor so as to drive the motor; a lower limit detection unit that detects that a current flowing through the coil is less than a lower limit current value; a drive control unit that brings the drive unit into the ON state on the basis of a detection result in the lower limit detection unit, and brings the drive unit into the OFF state on the basis of an elapsed time from the ON state; a polarity switching unit that switches a polarity of the drive signal in a case where an OFF time which is an elapsed time from the OFF state of the drive unit satisfies a polarity switching condition; and a drive stopping unit that stops driving of the drive unit in a case where an elapsed time from the time of starting driving or the time of switching a polarity satisfies a drive stopping condition.

According to the aspect of the present disclosure, the movement includes the drive stopping unit that stops driving of the drive unit in a case where an elapsed time from the time of starting driving or an elapsed time from the time of switching a polarity satisfies a drive stopping condition. Here, the drive stopping condition is set to such a long elapsed time which is not generated during a normal operation since driving is started by using the next drive signal of which a polarity is switched, and thus it can be detected that the influence of a disturbance is received. Therefore, driving of the drive unit driving the motor is stopped in that case, and thus it is possible to prevent the motor from being driven in a state of being influenced by the disturbance. Therefore, it is possible to prevent the occurrence of a problem that the motor is not accurately controlled due to disturbances, and thus a hand position is inaccurate.

A movement according to still another aspect of the present disclosure includes a drive unit that has an ON state and an OFF state, and outputs a drive signal to a coil of a motor so as to drive the motor; an upper limit detection unit that detects that a current flowing through the coil is more than an upper limit current value; a drive control unit that brings the drive unit into the OFF state on the basis of a detection result in the upper limit detection unit, and brings the drive unit into the ON state on the basis of an elapsed time from the OFF state; a polarity switching unit that switches a polarity of the drive signal in a case where an ON time which is an elapsed time from the ON state of the drive unit satisfies a polarity switching condition; and a drive stopping unit that stops driving of the drive unit in a case where the ON time satisfies a drive stopping condition.

According to the aspect of the present disclosure, the movement includes the drive stopping unit that stops driving of the drive unit in a case where the ON time of the drive unit driving the motor satisfies a drive stopping condition. Here, the drive stopping condition is set to a condition which is not generated during a normal operation but is generated in a case where a disturbance such as an external magnetic field or impact is applied, and thus it can be detected that the influence of a disturbance is received. Therefore, driving of the drive unit driving the motor is stopped in that case, and thus it is possible to prevent the motor from being driven in a state of being influenced by the disturbance. Therefore, it is possible to prevent the occurrence of a problem that the motor is not accurately controlled due to disturbances, and thus a hand position is inaccurate.

A movement according to still another aspect of the present disclosure includes a drive unit that has an ON state and an OFF state, and outputs a drive signal to a coil of a motor so as to drive the motor; an upper limit detection unit that detects that a current flowing through the coil is more than an upper limit current value; a drive control unit that brings the drive unit into the OFF state on the basis of a detection result in the upper limit detection unit, and brings the drive unit into the ON state on the basis of an elapsed time from the OFF state; a polarity switching unit that switches a polarity of the drive signal in a case where an ON time which is an elapsed time from the ON state of the drive unit satisfies a polarity switching condition; and a drive stopping unit that stops driving of the drive unit in a case where an elapsed time from the time of starting driving or the time of switching a polarity satisfies a drive stopping condition.

According to the aspect of the present disclosure, the movement includes the drive stopping unit that stops driving of the drive unit in a case where an elapsed time from the time of starting driving or the time of switching a polarity satisfies a drive stopping condition. Here, the drive stopping condition is set to such a long elapsed time which is not generated during a normal operation since driving is started by using the next drive signal of which a polarity is switched, and thus it can be detected that the influence of a disturbance is received. Therefore, driving of the drive unit driving the motor is stopped in that case, and thus it is possible to prevent the motor from being driven in a state of being influenced by the disturbance. Therefore, it is possible to prevent the occurrence of a problem that the motor is not accurately controlled due to disturbances, and thus a hand position is inaccurate.

A movement according to still another aspect of the present disclosure includes a drive unit that has an ON state and an OFF state, and outputs a drive signal to a coil of a motor so as to drive the motor; a lower limit detection unit that detects that a current flowing through the coil is less than a lower limit current value; an upper limit detection unit that detects that a current flowing through the coil is more than an upper limit current value; a drive control unit that brings the drive unit into the ON state on the basis of a detection result in the lower limit detection unit, and brings the drive unit into the OFF state on the basis of a detection result in the upper limit detection unit; a polarity switching unit that switches a polarity of the drive signal in a case where a relationship between an ON time which is an elapsed time from the ON state of the drive unit and an OFF time which is an elapsed time from the OFF state of the drive unit satisfies a polarity switching condition; and a drive stopping unit that stops driving of the drive unit in a case where the relationship between the ON time and the OFF time satisfies a drive stopping condition.

According to the aspect of the present disclosure, the movement includes the drive stopping unit that stops driving of the drive unit in a case where the relationship between the ON time of the drive unit and the OFF time of the drive unit satisfies a drive stopping condition. Here, the drive stopping condition is set to a condition which is not generated during a normal operation but is generated in a case where a disturbance such as an external magnetic field or impact is applied, and thus it can be detected that the influence of a disturbance is received. Therefore, driving of the drive unit driving the motor is stopped in that case, and thus it is possible to prevent the motor from being driven in a state of being influenced by the disturbance. Therefore, it is possible to prevent the occurrence of a problem that the motor is not accurately controlled due to disturbances, and thus a hand position is inaccurate.

In the movement according to the aspect of the present disclosure, the polarity switching unit may determine that the polarity switching condition is satisfied in a case where the OFF time is longer than a first switching determination time, and is shorter than a first stop determination time, and the drive stopping unit may determine that the drive stopping condition is satisfied in a case where the OFF time is equal to or longer than the first stop determination time.

In a case where a rotor is rotated by one step by turning on and off the drive unit such that a plurality of drive signals are input to the coil, a rotation angle of the rotor is in conjunction with an OFF time of the drive unit, the OFF time of the drive unit is short at the time of starting rotation of the rotor, and the OFF time is lengthened as rotation of the rotor comes close to an end. Therefore, in a case where the OFF time of the drive unit is longer than the first switching determination time, and is shorter than the first stop determination time, it can be determined that rotation of the rotor corresponding to one step is finished. Since a polarity of a drive signal is switched at this timing, the rotor can be further rotated by one step through the next-step driving of the motor.

A case where an OFF time is equal to or longer than the first stop determination time does not occur during a normal operation. Thus, the drive stopping unit can easily detect that the influence of a disturbance is received. Therefore, driving of the drive unit is stopped, and thus it is possible to prevent the motor from being driven in a state of being influenced by the disturbance.

In the movement according to the aspect of the present disclosure, the polarity switching unit may determine that the polarity switching condition is satisfied in a case where the elapsed time from the time of starting driving or the time of switching a polarity is shorter than a second stop determination time, and the OFF time is longer than a first switching determination time, and the drive stopping unit may determine that the drive stopping condition is satisfied in a case where the elapsed time from the time of starting driving or the time of switching a polarity is equal to or longer than the second stop determination time.

In the aspect of the present disclosure, in a case where the elapsed time from the time of starting driving or the time of switching a polarity is shorter than the second stop determination time, and the OFF time of the drive unit is longer than the first switching determination time, it can be determined that rotation of the rotor corresponding to one step is finished. Since a polarity of a drive signal is switched at this timing, the rotor can be further rotated by one step.

A case where the elapsed time from the time of starting driving or the time of switching a polarity is equal to or longer than the second stop determination time, that is, the next-step driving is not started even if the second stop determination time has elapsed does not occur during a normal operation. Thus, the drive stopping unit can easily detect that the influence of a disturbance is received. Therefore, driving of the drive unit is stopped, and thus it is possible to prevent the motor from being driven in a state of being influenced by the disturbance.

In the movement according to the aspect of the present disclosure, the polarity switching unit may determine that the polarity switching condition is satisfied in a case where the ON time is shorter than a second setting time after a first setting time elapses from the time of starting driving or the time of switching a polarity, and the drive stopping unit may determine that the drive stopping condition is satisfied in a case where the ON time is shorter than the second setting time before the first setting time elapses from the time of starting driving or the time of switching a polarity.

Typically, an ON time of the drive unit is shortened according to rotation of the rotor, and the ON time is shorter than the second setting time in a case where rotation of the rotor corresponding to one step (for example, 180°) is finished. On the other hand, excluding an exception such as the time right after driving is started, a case where an ON time is shorter than the second setting time from the time of starting driving to the time at which the first setting time elapses does not occur during a normal operation.

Therefore, in a case where an ON time of the drive unit is shorter than the second setting time after the first setting time elapses, it can be determined that rotation of the rotor corresponding to one step is finished. Since a polarity of a drive signal is switched at this timing, the rotor can be further rotated by one step.

In a case where an ON time of the drive unit is shorter than the second setting time after driving is started and before the first setting time elapses, the drive stopping unit can easily detect that the influence of a disturbance is received. Therefore, driving of the drive unit is stopped, and thus it is possible to prevent the motor from being driven in a state of being influenced by the disturbance.

In the movement according to the aspect of the present disclosure, in a case where the ON time is indicated by Ton, and the OFF time is indicated by Toff, in each cycle of the drive signal output from the drive unit, the polarity switching unit may determine that the polarity switching condition is satisfied in a case where Ton/(Ton+Toff) is equal to or less than a switching setting value, and the drive stopping unit may determine that the drive stopping condition is satisfied in a case where Ton/(Ton+Toff) increases during driving.

Typically, excluding an exception such as time right after driving is started, an ON time of the drive unit is shorted, and an OFF time thereof is lengthened, according to rotation of the rotor. Thus, in a case where a proportion (Ton/(Ton+Toff)) of the ON time Ton to one cycle of a drive signal, that is, a time obtained by adding the ON time Ton to the OFF time Toff is equal to or less than the switching setting value, it can be determined that rotation of the rotor corresponding to one step is finished. Since a polarity of a drive signal is switched at this timing, the rotor can be further rotated by one step.

Typically, Ton/(Ton+Toff) sequentially decreases, and a case where Ton/(Ton+Toff) increases during driving does not occur during a normal operation. Thus, the drive stopping unit can easily detect that the influence of a disturbance is received. Therefore, driving of the drive unit is stopped, and thus it is possible to prevent the motor from being driven in a state of being influenced by the disturbance.

The movement according to the aspect of the present disclosure may further include a timer that detects that an elapsed time from the drive unit being stopped by the drive stopping unit becomes a standby setting time, the drive control unit may resume driving of the drive unit in a case where the timer detects that the elapsed time becomes the standby setting time.

The drive stopping unit can stop driving of the drive unit by detecting the influence of a disturbance such as an external magnetic field. Thereafter, driving of the drive unit can be automatically resumed after a standby setting time (for example, one second) elapses. The standby setting time is set to a time for which it can be expected that the influence of the disturbance disappears, and thus it is possible to reduce a probability of receiving the influence of the disturbance after driving is resumed. Thus, after driving is resumed, the motor can be driven by a desired movement amount, and thus a pointer can be automatically moved to a desired indication position even in a case where the pointer is moved by the motor.

The movement according to the aspect of the present disclosure may further include a magnetic field detector that detects an external magnetic field, and the drive control unit may resume driving of the drive unit according to an output from the magnetic field detector in a case where the drive unit is stopped by the drive stopping unit.

According to the aspect of the present disclosure, driving of the drive unit can be resumed after the magnetic field detector detects that an external magnetic field disappears. Therefore, after driving is resumed, the motor can be reliably driven by a desired movement amount, and thus a pointer can be reliably moved to a desired indication position even in a case where the pointer is moved by the motor.

In the movement according to the aspect of the present disclosure, the magnetic field detector may include a control unit that brings at least one end of the coil into any of a high impedance state, a pull-down state, and a pull-up state, and a voltage detection unit that detects a voltage generated in one end of the coil.

Since the coil of the motor can be used as a part of the magnetic field detector, a configuration can be simplified compared with a case where a dedicated magnetic sensor is separately provided, and cost can also be reduced.

In the movement according to the aspect of the present disclosure, the magnetic field detector may include a chopper amplification circuit that subjects a voltage generated in at least one end of the coil to chopper amplification, and a voltage detection unit that detects the voltage.

Since the magnetic field detector can subject an induced voltage in the coil to the chopper amplification with the chopper amplification circuit, it is possible to improve the sensitivity of external magnetic field detection, to determine the presence or absence of an external magnetic field with high accuracy, and also to increase a certainty of driving at the time of resuming.

In the movement according to the aspect of the present disclosure, the drive control unit may output the drive signal in one step or a plurality of steps after a standby setting time elapses from the drive unit being stopped by the drive stopping unit, and resume driving of the drive unit in a case where a drive stopping condition for the drive unit is not satisfied at the time of outputting the drive signal.

After driving of the drive unit is stopped by the drive stopping unit, a drive signal is output in one step or a plurality of steps, for example, two steps, and thus it is possible to check whether or not the drive stopping condition is satisfied, that is, the influence of a disturbance is received. Therefore, it is not necessary to add a special detection unit such as a magnetic sensor detecting the influence of a disturbance, and it can be determined whether or not driving is resumed with a simple configuration.

Since the movement according to the aspect of the present disclosure can stop driving of the motor in a case where the influence of a disturbance is received, and can resume driving of the motor in a case where the influence of a disturbance is reduced, it is possible to implement the movement capable of increasing driving accuracy even in a case where a disturbance is present.

An electronic timepiece according to a still another aspect of the present disclosure includes the movement.

According to the electronic timepiece, a pointer can be moved with the movement having the motor control circuit, and thus it is possible to increase indication accuracy of the pointer. Particularly, even an analog electronic timepiece in which current consumption is reduced to the minimum for rotating a motor can be hardly influenced by a disturbance, and thus it is possible to improve indication accuracy of a hand.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, with reference to the drawings, embodiments of the present disclosure will be described.

First, a theory of a motor drive control to which the present disclosure is applied will be described.

In a case where control is performed such that, when a current flowing through a motor exceeds an upper limit current value Imax, a drive unit is turned off, and when the current is less than a lower limit current value Imin, the drive unit is turned on, assuming that a difference between Imax and Imin is sufficiently smaller than a current value of Imax or Imin, a voltage Vc of both ends of a coil, a coil resistance R, an inductance L of the coil, a drive current i, and an induced voltage V have a relationship of Vc=R*i+L*di/dt+V. In a case where an ON time Ton which is an elapsed time for an ON state of the drive unit and an OFF time Toff which is an elapsed time from an OFF state thereof are sufficiently short, this leads to i≅(Imax+Imin)/2. When the drive unit is in an ON state, a power source voltage is indicated by E, and thus Vc is E, so that E=R*i+L*di/dt+V (1) is obtained.

In a case where the ON time Ton is sufficiently short, di/dt=(Imax−Imin)/Ton (2) is obtained.

When the drive unit is in an OFF state, Vc is 0, and thus 0=R*i+L*di/dt+V (3) is given.

In a case where the OFF time Toff is sufficiently short, di/dt=(Imin−Imax)/Toff (4) is obtained.

A relationship of V=E*Ton/(Ton+Toff)−R*i (5) is obtained on the basis of the above (1) to (4). Since the induced voltage is correlated with a rotation position of a rotor, in a case where Imax and Imin are fixed according to Equation (5), a rotation position of the rotor can be estimated on the basis of a relationship between Ton and Toff, and thus phase switching, that is, polarity switching of a drive signal can be performed at a desired timing.

Here, in a case where Ton and Imin are fixed, and Ton is sufficiently small, Imax≅Imin≅i is obtained, and thus polarity switching of a drive signal can be performed at a desired timing by estimating a rotation position of the rotor on the basis of only Toff.

Here, in a case where Toff and Imax are fixed, and Toff is sufficiently small, Imax≅Imin≅i is obtained, and thus polarity switching of a drive signal can be performed at a desired timing by estimating a rotation position of the rotor on the basis of only Ton.

However, in a case where a magnetic field is applied from the outside, or a rotational speed of the rotor changes due to impact, such a relationship is not established, and thus polarity switching of a drive signal may not be performed at an optimal timing.

Thus, in the embodiments of the present disclosure, a novel function of stopping driving is added in a case where Ton and Toff have numerical values which are not present during normal times, or do not have expected numerical values for a predetermined time, and thus a wrong operation is prevented. Hereinafter, each embodiment of the present disclosure will be described.

First Embodiment

Hereinafter, with reference to the drawings, an electronic timepiece1according to a first embodiment of the present disclosure will be described.

As illustrated inFIG. 1, the electronic timepiece1is a wristwatch mounted on a user's wrist, and includes an outer case2, a disk-shaped dial3, a movement (not illustrated), a stepping motor13(refer toFIG. 2; and hereinafter, referred to as a motor13) provided in the movement, a second hand5, a minute hand6, an hour hand7which are driven pointers, and a crown8and a button9as operation members.

Circuit Configuration of Electronic Timepiece

As illustrated inFIG. 2, the electronic timepiece1includes a quartz crystal resonator11which is a signal source, a battery12which is a power source, a switch S1which is turned on and off in conjunction with an operation on the button9, a switch S2which is turned on and off in conjunction with an extraction operation on the crown8, and the motor13, and an IC20for the timepiece.

Configuration of Motor

As illustrated inFIG. 3, the motor13includes a stator131, a coil130, and a rotor133. Both ends of the coil130are electrically connected to output terminals O1and O2of a driver51which will be described later, and the rotor133is a magnet which is magnetized to two poles in a diameter direction. Therefore, the motor13is a bipolar single-phase stepping motor used for an electronic timepiece, and is driven by motor drive pulses (drive signals) output from the output terminals O1and O2of the IC20as will be described later.

The second hand5, the minute hand6, and the hour hand7are in conjunction with each other by a gear train (not illustrated), and are driven by the motor13so as to respectively display a second, a minute, and an hour. In the present embodiment, the second hand5, the minute hand6, and the hour hand7are driven by the single motor13, but a plurality of motors may be provided, such as a motor driving the second hand5, and a motor driving the minute hand6and the hour hand7.

As illustrated inFIG. 2, the IC20has connection terminals OSC1and OSC2connected to the quartz crystal resonator11, input/output terminals P1and P2connected to the switches S1and S2, power source terminals VDD and VSS connected to the battery12, and the output terminals O1and O2connected to the coil130of the motor13.

In the present embodiment, a positive electrode of the battery12is connected to the high potential side power source terminal VDD, a negative electrode thereof is connected to the low potential side power source terminal VSS, and the low potential side power source terminal VSS is set to be grounded (for example, a reference potential).

The quartz crystal resonator11is driven by an oscillation circuit21which will be described later, and generates an oscillation signal.

The battery12is configured with a primary battery or a secondary battery. In a case of the secondary battery, the battery is charged by a solar cell (not illustrated).

The switch S1is operated in conjunction with the button9located at the position of two o'clock of the electronic timepiece1, and is brought into an ON state in a state in which the button9is pushed, and is brought into an OFF state in a state in which the button9is not pushed.

The switch S2is a slide switch operated in conjunction with the crown8. In the present embodiment, the switch S2is brought into an ON state in a state in which the crown8is drawn out to the first stage, and is in an OFF state in the zero-th stage.

Circuit Configuration of IC

As illustrated inFIG. 4, the IC20includes the oscillation circuit21, a frequency division circuit22, a central processing unit (CPU, processor)23for control of the electronic timepiece1, a read only memory (ROM)24, an input/output circuit26, a bus27, and a motor control circuit30.

The oscillation circuit21causes the quartz crystal resonator11which is a reference signal source to oscillate at a high frequency, and outputs an oscillation signal having a predetermined frequency (for example, 32768 Hz) generated through high frequency oscillation, to the frequency division circuit22.

The frequency division circuit22frequency-divides the output from the oscillation circuit21, so as to supply a timing signal (clock signal) to the CPU23.

The ROM24stores various programs executed by the CPU23. In the present embodiment, the ROM24stores programs for realizing a fundamental timepiece function.

The CPU23executes the programs stored in the ROM24so as to realize the respective functions.

The motor control circuit30outputs a predetermined drive signal (that is, a drive pulse) in response to a communication which is input from the CPU23via the bus27.

Configuration of Motor Control Circuit

As illustrated inFIG. 5, the motor control circuit30includes a first timer31, a second timer32, a third timer33, a fourth timer34, a number-of-steps control circuit36, a first differentiation circuit371, a second differentiation circuit372, a decoder38, an SR latch circuit39, a flip-flop40, AND circuits41,42, and48, OR circuits43,44,45,46, and47, and a driver and detection circuit50.

The first timer31is a timer measuring a time t1for which a current is supplied to the coil130of the motor13. An output TM1from the first timer31is turned to an H level after the time t1elapses from the time at which a reset terminal R of the first timer31is turned to an L level such that a reset state thereof is canceled.

The second timer32is a timer measuring a determination time t2related to a condition for switching a polarity of a current flowing through the coil130of the motor13. In other words, the determination time t2is a first switching determination time. An output TM2from the second timer32is turned to an H level after the time t2elapses from the time at which a reset terminal R of the second timer32is turned to an L level such that a reset state thereof is canceled.

The third timer33is a timer measuring a time t3related to a condition for temporarily stopping driving of the motor13. In other words, the time t3is a first stop determination time. An output TM3from the third timer33is turned to an H level after the time t3elapses from the time at which a reset terminal R of the third timer33is turned to an L level such that a reset state thereof is canceled.

The fourth timer34is a timer measuring a standby time t4until driving of the motor is resumed. In other words, the standby time t4is a standby setting time. An output TM4from the fourth timer34is turned to an H level after the time t4elapses from the time at which a reset terminal R of the fourth timer34is turned to an H level such that a reset state thereof is canceled.

The driver and detection circuit50is a circuit which supplies a current to the coil130of the motor13and determines whether or not a value of the current flowing through the coil130exceeds a predetermined value. Details of the driver and detection circuit50will be described later with reference toFIG. 6.

The number-of-steps control circuit36includes a presettable down-counter, and outputs a drive period signal TD. The number-of-steps control circuit36sets the drive period signal TD in an H level until a preset value of the presettable down-counter set by a setting signal is counted down and becomes 0 by using a clock signal CL, and turns the drive period signal TD to an L level when the presettable down-counter becomes 0.

The setting signal which is input to the number-of-steps control circuit36is input from, for example, the CPU23via the bus27.

The decoder38receives a signal TON for switching ON and OFF of an drive signal output which will be described later, a drive polarity signal PL for switching a polarity of a drive signal, and a drive signal DON for controlling starting and stopping of the driver51, and outputs gate signals P1, P2, N1, N2, N3, and N4to the driver and detection circuit50depending on states of the signals as illustrated in timing charts inFIGS. 8 to 10which will be described later. Therefore, a drive control unit controlling driving of the driver51which is a drive unit is configured to include the decoder38.

The first differentiation circuit371outputs a differentiation pulse whenever the drive polarity signal PL rises and falls.

The second differentiation circuit372outputs a differentiation pulse whenever the timer signal TM3rises.

The AND circuit41receives a signal obtained by inverting an output DT1from the driver and detection circuit50and the output TM2from the second timer32.

The AND circuit42receives a signal obtained by inverting the output TM3from the third timer33, and the output TD from the number-of-steps control circuit36.

The OR circuit43receives an output from the AND circuit41and an output from the second differentiation circuit372.

The OR circuit44receives a signal obtained by inverting the output DT1from the driver and detection circuit50, and a signal obtained by inverting the output DON from the AND circuit42.

The SR latch circuit39has a set terminal S to which an output from the OR circuit44is input, and a reset terminal R to which the output TM1from the first timer31is input. The SR latch circuit39outputs an ON/OFF switching signal TON from an output terminal Q.

The flip-flop40has a clock terminal C to which an output from the OR circuit43is input. The flip-flop outputs the drive polarity signal PL from an output terminal Q.

The OR circuit45receives an inverted signal of the output DON from the AND circuit42, and the signal TON output from the SR latch circuit39. An output from the OR circuit45is input to the reset terminal R of the second timer32.

The OR circuit46receives an inverted signal of the output DON from the AND circuit42, an inverted signal of the output TON from the SR latch circuit39, and an inverted signal of the output DT1from the driver and detection circuit50. An output from the OR circuit46is input to the reset terminal R of the first timer31.

The AND circuit48receives the output TON from the SR latch circuit39, and an inverted signal of the output TM3from the third timer33.

The OR circuit47receives an output from the AND circuit48, and the output TM4from the fourth timer34. An output from the OR circuit47is input to the reset terminal R of the third timer33.

The output TM3from the third timer33is inverted to be input to the reset terminal R of the fourth timer34.

Configurations of Driver and Detection Circuit

The driver and detection circuit50includes the driver51and a current detection circuit61as illustrated inFIG. 6.

The driver51includes two Pch transistors52and53, four Nch transistors54,55,56, and57, and two detection resistors58and59. The respective transistors52to57are controlled according to the gate signals P1, P2, N1, N2, N3, and N4output from the decoder38, and supplies currents to the coil130of the motor13in both of a forward direction and a backward direction. Therefore, the driver51is a drive unit which outputs a drive signal to the coil130of the motor13and drives the motor13.

The current detection circuit61includes a first reference voltage generation circuit62, comparators641and642, and a complex gate68. The complex gate68is a single element having a function equivalent to a combination of AND circuits661and662and an OR circuit680as illustrated inFIG. 6.

The comparators641and642respectively compare voltages generated in both ends of the detection resistors58and59having resistance values R1and R2with a voltage from the first reference voltage generation circuit62.

Since the drive polarity signal PL is inverted to be input to the AND circuit661, and the drive polarity signal PL is input to the AND circuit662without being inverted, an output from one of the comparators641and642selected according to the drive polarity signal PL is output as the output DT1.

The first reference voltage generation circuit62is set to output a potential corresponding to voltages generated in both ends of the detection resistors58and59in a case where a current flowing through the coil130is the lower limit current value Imin.

Therefore, in a case where a current I flowing through the coil130is equal to or more than the lower limit current value Imin, voltages generated in both ends of the detection resistors58and59exceed an output voltage from the first reference voltage generation circuit62, and thus the detection signal DT1is turned to an H level. On the other hand, in a case where the current I is less than the lower limit current value Imin, the detection signal DT1is turned to an L level. Therefore, the current detection circuit61is a lower limit detection unit that detects that the current I flowing through the coil130is less than the lower limit current value Imin.

Control Process of Motor Control Circuit

Next, control performed by the motor control circuit30of the present embodiment will be described with reference to a flowchart inFIG. 7, and timing charts inFIGS. 8 to 10.FIG. 8is a timing chart illustrating an operation of the motor control circuit30of the present embodiment during normal times,FIG. 9is a timing chart in a comparative example showing a defect due to a disturbance such as an external magnetic field, andFIG. 10is a timing chart illustrating an operation of the motor control circuit30of the present embodiment in a case where a disturbance such as an external magnetic field occurs. The comparative example illustrated inFIG. 9corresponds to an operation example in a case where the third timer33and the fourth timer34are omitted from the motor control circuit30of the present embodiment.

Operation of Motor Control Circuit

In a case where drive control for the motor13is started, the CPU23of the IC20outputs a setting signal for setting a movement amount of a pointer to the number-of-steps control circuit36of the motor control circuit30. For example, in a case where the number of steps for moving the second hand5by one second is “5”, the CPU23outputs a signal for setting a setting value n of the number-of-steps control circuit36to “5” every second (SA1).

After the CPU23outputs the setting signal, and the setting value n of the number-of-steps control circuit is set, the following control is performed by each circuit of the motor control circuit30. In other words, the CPU23may only output a setting signal for setting a drive amount of the motor13to the motor control circuit30at a timing at which the motor13is driven.

In a case where the setting value n=5 is set in the number-of-steps control circuit36according to the setting signal, the drive period signal TD is turned to an H level, the output DON from the AND circuit42is turned to an H level, the decoder38turns on the driver51of the motor13by using the gate signals P1, P2, N1, N2, N3, and N4(SA2), and thus a forward current flows through the coil130. In the flowchart and the following description, turning on the driver51indicates that the driver51is controlled to be brought into an ON state in which a drive current can be made to flow through the coil130, and turning off the driver51indicates that the driver51is controlled to be brought into an OFF state in which a drive current cannot be made to flow through the coil130.

In the present embodiment, in the timing chart inFIG. 8, right after the output DON is turned to an H level, P1has an L level, and P2has an H level. Thus, the Pch transistor52is turned on, and the Pch transistor53is turned off. Since the N1to N3have an L level, and N4has an H level, the Nch transistors54,55, and56are turned off, and the Nch transistor57is turned on. Thus, a current flows through the Pch transistor52, the terminal O1, the coil130, the terminal O2, the detection resistor59, and the Nch transistor57. In the present embodiment, the current flowing through the coil130from the terminal O1toward the terminal O2is defined as a forward current. In the present embodiment, a drive signal (drive current) output to the coil130switches between a first polarity and a second polarity, and a forward current flows through the coil130in a case of the first polarity. Therefore, a state in which a forward current flows through the coil130is a state in which the driver51is controlled to be brought into an ON state such that a drive signal having the first polarity is output.

Next, the current detection circuit61determines whether or not the current I flowing through the coil130exceeds the lower limit current value Imin (SA3). The current detection circuit61continuously performs the determination process in SA3until voltages generated in the detection resistors58and59exceed a reference voltage from the first reference voltage generation circuit62(NO in SA3).

On the other hand, in a case where it is determined that a determination result in SA3is YES, the current detection circuit61turns the detection signal DT1to an H level, and thus the first timer31is operated. The first timer31is operated, and thus it can be determined whether or not the time t1has elapsed after the current I exceeds the lower limit current value Imin (SA4).

In other words, in a case where the detection signal DT1is turned to an H level, an output from the OR circuit46is turned to an L level from an H level, and thus a reset state of the first timer31is canceled. Thus, the first timer31starts to measure elapse of the time t1, continuously outputs a signal having an L level until the time t1elapses, and outputs a signal having an H level in a case where the time t1has elapsed, that is, a determination result in SA4is YES.

In a case where the output TM1from the first timer31is turned to an H level, and thus a determination result in SA4is YES, the SR latch circuit39is reset, and the output TON is turned to an L level. Therefore, the decoder38turns off the driver51by using the gate signals P1, P2, N1, N2, N3, and N4(SA5). Specifically, P1is turned to an H level, P2is turned to an H level, N1is turned to an H level, N2is turned to an L level, N3is turned to an H level, and N4is turned to an H level. Thus, both ends of the coil130are connected to the power source terminal VSS, so as to be short-circuited to each other, and thus the supply of the current I to the coil130from the driver51is also stopped. Therefore, a state in which a current does not flow through the coil130is a state in which the driver51is controlled to be brought into to an OFF state. In the present embodiment, a state in which the Pch transistors52and53and the Nch transistor55are turned off, and the Nch transistors54,56, and57are turned on is an OFF state of the driver51in the first polarity.

In this case, an output from the OR circuit45changes in conjunction with a level of the signal TON while the output DON has an H level since the output DON is inverted to be input. Therefore, in a case where the driver51is turned off, and thus the signal TON is turned to an L level, the output from the OR circuit45is also turned to an L level, so that the reset state of the second timer32is canceled, and thus the second timer32starts timer measurement. Therefore, in a case where the driver51is turned on, and thus the signal TON is turned to an H level, the output from the OR circuit45is also turned to an H level, so that the second timer32is reset, and thus measurement of the time t2is stopped. Consequently, it can be determined whether a turned-off time of the driver51which is a drive unit is equal to or smaller than the first switching determination time t2or exceeds the time t2by using the second timer32.

Next, it is determined whether or not the time t3measured by the third timer33has elapsed (SA6). The third timer33cancels a reset state thereof at a timing at which the output TON from the SR latch circuit39is turned to an L level from an H level, that is, a timing at which the driver51is turned off, and starts time measurement.

In a case where the motor13is normally operated, an elapsed time (an OFF time of a drive unit) from turning-off of the driver51until the current I is less than Imin is not equal to or longer than the first stop determination time t3, and thus a determination result in SA6is NO.

In a case where a determination result in SA6is NO, that is, the time t3has not elapsed from turning-off of the driver51in SA5, it is determined whether or not the current I flowing through the coil130is less than Imin (SA7). In a case where a determination result in SA7is YES, it is determined whether or not the OFF time of the driver51(an OFF time of a drive unit) exceeds the first switching determination time t2(SA8). In other words, in a case where a time (OFF time) from turning-off of the driver51until the current I is less than Imin is equal to or shorter than the time t2, a determination result in SA8is NO, and, in a case where the time exceeds the time t2, a determination result in SA8is YES.

In a case where a determination result in SA8is NO, polarity switching is not performed, and the flow returns to SA2, so that the driver51is turned on to drive the motor13.

In other words, when the output TON is turned to an L level, the second timer32cancels a reset state thereof, and starts measurement of the time t2, and the output TM2from the second timer32is turned to an H level at a time point at which the time t2has elapsed.

In a case where the current I is less than Imin, the detection signal DT1is turned to an L level. In this case, in a case where an OFF time measured by the second timer32is shorter than the time t2, since the output TM2from the second timer32has an L level, an output from the OR circuit43is maintained to have an L level, and thus the drive polarity signal PL output from the flip-flop40is maintained to have an identical level. Therefore, polarity switching is not performed, the detection signal DT1is turned to an L level, the output TON from the SR latch circuit39is turned to an H level, and thus the driver51is turned on.

In a case where the OFF time of the driver51exceeds the first switching determination time t2, and thus a determination result in SA8is YES, the flip-flop40performs polarity switching by turning the drive polarity signal PL to an H level (SA9).

In a case where a determination result in SA8is YES, the output TM2has an H level, and the detection signal DT1has an L level. Thus, since an output from the AND circuit41has an H level, and an output from the OR circuit43also has an H level, the clock signal is input to the flip-flop40, a state of the drive polarity signal PL is inverted, and the decoder38controls the driver51to switch between polarities of a drive signal. Since an OFF time of the driver51is correlated with a rotation angle of the rotor133, the time t2may be set on the basis of a value generated when the rotor133is rotated by about 180°.

Therefore, in the present embodiment, a polarity switching unit is configured with the second timer32, the third timer33, and the current detection circuit61respectively measuring the time t2, the time t3, and the current I related to polarity switching conditions, and that the current I is less than the lower limit current value Imin, and the flip-flop40and the decoder38controlling the driver51to switch a polarity of a drive signal on the basis of such measurement results.

In a case where a state of the polarity signal PL is inverted, and polarity switching is performed, a signal is output from the first differentiation circuit371to which the polarity signal PL is input, the signal is input to the number-of-steps control circuit36as a clock signal CL, and thus the remaining number of steps is reduced by one (SA10).

The number-of-steps control circuit36checks whether or not the remaining number of steps is 0 (SA11), and maintains the drive period signal TD in an H level in a case where a determination result in SA11is NO (n is not 0). Thus, the flow returns to SA2, and the driver51is turned on by using a signal from the decoder38. However, since the polarity signal PL is inverted, the decoder38outputs gate signals for setting a direction of a current flowing through the coil130to be opposite to a direction in the positive time. Specifically, P1is turned to an H level, P2is turned to an L level, N1, N2, and N4are turned to an L level, and N3is turned to an H level. Consequently, the Pch transistor52is turned off, and the Pch transistor53is turned on. The Nch transistors54,55, and57are turned off, and the Nch transistor56is turned on. Thus, a current flows through the Pch transistor53, the terminal O2, the coil130, the terminal O1, the detection resistor58, and the Nch transistor56. Therefore, a drive signal (that is, a drive current) output to the coil130has the second polarity, and a current in the backward direction opposite to the forward direction flows through the coil130. Therefore, a state in which the backward current flows through the coil130is a state in which the driver51is controlled to be turned on to output a drive signal having the second polarity.

As illustrated inFIG. 8, the gate signals P1, P2, N1, N2, N3, and N4are set such that directions of a current flowing through the coil130are different from each other, that is, polarities are different from each other, in a case of n=5, 3, and 1 and in a case of n=4 and 2.

In the present embodiment, in an OFF state of the driver51in the second polarity, P1has an H level, P2has an H level, N1has an L level, N2has an H level, N3has an H level, and N4has an H level.

In other words, a state in which the Pch transistors52and53and the Nch transistor54are in an OFF state, and the Nch transistors55,56, and57are in an ON state is an OFF state of the driver51in the second polarity. Also in the OFF state in the second polarity, both ends of the coil130are connected to the power source terminal VSS so as to be short-circuited to each other, and thus the supply of the current I to the coil130from the driver51is stopped.

In a case where a determination result in SA11is YES, the number-of-steps control circuit36turns the drive period signal TD to an L level, and thus the output DON is also turned to an L level such that the drive control for the motor13is finished.

Therefore, SA2to SA11are repeatedly performed, and thus the control as illustrated inFIG. 8is performed. In other words, in a case where the current I is less than the lower limit current value Imin, the driver51is turned on, and, in a case where an elapsed time from turning-on of the driver51exceeds the time t1, the driver51is turned off. In a case where an OFF time of the driver51does not exceed the time t2, the driver51is turned on again. Therefore, turning-on and turning-off of the driver51are repeatedly performed in an identical polarity.

The polarity is switched at a time point at which the OFF time of the driver51exceeds the time t2, the remaining number of steps is reduced by one, and, in a case where the number of steps is not 0, the same drive control as described above is performed as illustrated inFIG. 8except that a polarity differs. In a case where the number of steps becomes 0, the drive control for the motor13is finished.

Operation (Comparative Example) During Occurrence of Defect

Here, for comparison with the present embodiment, a description will be made of an example in which a defect occurs due to the influence of an external magnetic field or impact in a case where the third timer33and the fourth timer34are not provided, with reference to a timing chart inFIG. 9.

An ON time and an OFF time of the driver51depend on an inverse induced voltage generated in the coil130, but the inverse induced voltage changes due to the influence of an external magnetic field or impact, and thus a relationship between an ON time or an OFF time and a rotational position of the rotor133may not be established. For example, as illustrated inFIG. 9, in a case where a timing at which the rotor133is regarded to be rotated by 180° is ta, an OFF time is originally required to exceed the time t2before the timing ta.

However, in a case where an OFF time becomes shorter than the time t2due to the influence of an external magnetic field or impact, the driver51is turned on again. Thus, in a case where the driver51is turned off after the time t1elapses, detection of rotation is delayed, and thus the current I may be less than Imin after the rotor133greatly exceeds 180°.

In this case, when there is no control using the signals TM3and TM4in the present embodiment, polarity switching is performed at an abnormal timing, a step-output state occurs, and thus a relationship between a rotation angle and an ON time or an OFF time is not established. Thus, polarity switching is performed in an extremely short time as in a third step (n=3) inFIG. 9, and the rotor133is not rotated. Therefore, the next step (n=2) enters a suction state, and thus the rotor133is not rotated and is stopped even if a drive current is continuously supplied.

The example illustrated inFIG. 9is an example of defect occurrence patterns, and defects of other various patterns occur due to a disturbance.

Operation in First Embodiment During Occurrence of a Disturbance

A description will be made of an operation for preventing the defect in the present embodiment with reference toFIGS. 7 and 10.

In a case where the output TM4from the fourth timer34is maintained in an L level, and the output TON is turned to an L level, that is, the driver51is turned off, the third timer33cancels a reset state thereof, and starts to measure the time t3. In a case where the output TON is turned to an H level before the time t3elapses, and thus the driver51is turned on, the third timer33is reset.

In a case where an OFF period of the driver51exceeds the first stop determination time t3due to the influence of an external magnetic field or impact as in driving in a second step (n=4) in the timing chart inFIG. 10(YES in SA6), the driver51stops to be driven (SA12). Therefore, in the present embodiment, the third timer33and the decoder38configure a drive stopping unit which determines whether or not a drive stopping condition is satisfied, and stops driving of the driver51.

In other words, in a case where an OFF period of the driver51exceeds the time t3, the output TM3from the third timer33is turned to an H level, thus the output TM3is inverted to be input to the AND circuit42, and the drive signal DON which is an output from the AND circuit42is turned to an L level. Thus, the decoder38stops driving of the driver51. In a case where an OFF state of the driver51in SA5is compared with a stop state of the driver in SA12, in SA5, the decoder38turns off the Pch transistors52and53so as to control the driver51to be turned off, turns on one of the Nch transistors54and55, turns off the other, and turns on the Nch transistors56and57. On the other hand, in SA12, the decoder38turns off the Pch transistors52and53so as to control the driver51to be turned off, and turns on all of the Nch transistors54,55,56, and57as in a third step (n=3) inFIG. 10.

In SA12, in a case where the drive signal DON is turned to an L level, an output from the OR circuit44is turned to an H level, and the output TON from the SR latch circuit39is turned to an H level. Since the signal TON is a signal for switching turning-on and turning-off of the driver51, in a case where the signal TON is turned to an H level, typically, the decoder38turns on the driver51, but the drive signal DON has an L level, and thus the decoder38prioritizes a process of stopping driving of the driver51. In a case where the drive signal DON is turned to an L level, the Pch transistors52and53are turned off, and all of the Nch transistors54to57are turned on. In a case where all of the Nch transistors54to57are turned on, total ON resistance can be reduced such that short brake force can be increased, and thus stability for disturbance can be realized.

The outputs from the comparators641and642are constant, and thus it is possible to suppress an increase in unnecessary current consumption.

In a case where the output TM3from the third timer33is turned to an H level, an output from the second differentiation circuit372has an H level, a signal having an H level is input to the flip-flop40from the OR circuit43, the polarity signal PL is inverted, and a polarity is switched (SA13).

Since the polarity signal PL is inverted, a clock signal is output from the first differentiation circuit371, and the number-of-steps control circuit36reduces the remaining number of steps by one (SA14).

Since the output TM3from the third timer33is inverted to be input to the reset terminal R of the fourth timer34, the fourth timer34cancels a reset state thereof and starts to measure the time t4in a case where the output TM3is turned to an H level, and determines whether or not the time t4has elapsed after the drive signal DON for the decoder38is turned to an L level (SA15). The fourth timer34sets a standby time until drive control for the motor13is resumed, and the standby setting time t4is set to an OFF time having a length which is not normally generated. Since drive control is stopped until the time t4elapses, it can be expected that the influence of a disturbance such as an external magnetic field or impact is removed.

In a case where it is determined that a determination result in SA15is YES, the motor control circuit30returns to SA2, turns on the driver51, and performs the subsequent respective processes after SA2.

In other words, the fourth timer34turns the output TM4to an H level after the time t4elapses. Thus, the third timer33is reset, and the output TM3is also turned to an L level.

In a case where the output TM3is turned to an L level, the fourth timer34is reset. Therefore, the output TM4temporarily has an H level, and immediately returns to an L level.

In a case where the output TM3is turned to an L level, the drive signal DON is turned to an H level, and thus the driver51is turned on by using the gate signals from the decoder38. Consequently, driving of the motor13is resumed. In this case, since a polarity is switched, there is a low probability that the rotor133may be in a suction state, and thus the rotor133can be rotated.

Thereafter, as described above, SA2to SA11are repeatedly performed, driving of the motor13is performed until n becomes 0, and the driving is finished.

In a case where the time t3is measured again after driving is resumed in SA2(it is determined that a determination result in SA6is YES), the stopping processes in SA12to SA15are performed again.

The time t1to the time t4respectively measured by the timers31to34may be set according to characteristics or drive voltages of the motor13, and, for example, the time t1is set to 50 μsec, the first switching determination time t2is set to 100 μsec, the first stop determination time t3is set to 200 μsec, and the standby setting time t4is set to 1 sec.

Effects of First Embodiment

According to the motor control circuit30of the present embodiment, a case where the time t3or more elapses from turning-off of the driver51, that is, a case where the current I flowing through the coil130is not less than the lower limit current value Imin even if the time t3has elapsed from turning-off of the driver51is a situation which does not occur during a normal operation, and thus driving of the driver51is stopped. Consequently, it is possible to detect the influence of a disturbance such as an external magnetic field, and thus to prevent the motor13from being driven in a state of being influenced by the disturbance. Therefore, it is possible to prevent the occurrence of a problem that the motor13is not accurately controlled due to disturbances, and thus a hand position is inaccurate.

The motor control circuit30is provided with the timers31to34in addition to the current detection circuit which is a lower limit detection unit comparing the current I with the lower limit current value Imin, and can perform control by only measuring an elapsed time from turning-on of the driver51or an OFF time of the driver51. Thus, a configuration of the motor control circuit30can be simplified.

The motor control circuit30is configured with dedicated circuits using logic elements, and can thus realize low voltage driving and low power consumption so as to be appropriate for the portable electronic timepiece1such as, especially, a wristwatch.

First Modification Example

In the first embodiment, as illustrated inFIG. 7, in a case where an elapsed time from turning-off of the driver51exceeds the time t3, a determination result in SA6is YES, and the processes in SA12to SA15are performed. In contrast, in a first modification example, as illustrated in a flowchart inFIG. 11, in a process in SA16of determining a condition for transition to the processes in SA12to SA15, the number of steps is set in the number-of-steps control circuit36, and the processes in SA12to SA15are set to be performed in a case where an elapsed time from a time point of starting driving, or a time point of switching a polarity, that is, starting of driving in each step, is equal to or longer than a second stop determination time t13. The time t13such as 10 msec may be set to a condition which is not generated in a normal operation, and is generated in a case where the rotor133is in a suction state due to the influence of an external magnetic field or impact. In other words, as illustrated inFIG. 8, in a normal operation, a drive process in each step is finished within a predetermined time, a polarity is switched, and a drive process in the next step is started. On the other hand, as indicated by the step of n=4 inFIG. 9, in a case where the influence of a disturbance is received, a drive process in the step is not often finished within a predetermined time. Therefore, in a case where an elapsed time from a drive starting time point, that is, an elapsed time in an initial step (the step of n=5 inFIGS. 8 to 10) is equal to or longer than the time t13, or an elapsed time from switching of a polarity, that is, an elapsed time in the second and subsequent steps (n=4 to 1) is equal to or longer than the time t13, it is determined that the influence of a disturbance is received, and processes (SA12to SA15) of stopping driving of the driver51for a predetermined time may be performed.

Also in the first modification example, the same advantageous effect as in the first embodiment can be achieved. In the first embodiment, in a case where an OFF time of the driver51is shorter than the first stop determination time t3due to the influence of a disturbance, driving of the driver51cannot be stopped. In contrast, according to the first modification example, even in a case where an OFF time becomes shorter due to a disturbance, when an elapsed time from a starting time point of each step is equal to or longer than the second stop determination time t13, driving of the driver51can be stopped. On the other hand, in the first embodiment, there is an advantage in that, in a case where an OFF time of the driver51is longer than the first stop determination time t3, the driver51can be stopped early at that time.

Therefore, preferably, the first embodiment and the first modification example are combined with each other, and, in a case where a determination result in SA6is NO, determination in SA16is performed, and, in a case where a determination result of either of SA6and SA16is YES, a process of stopping driving of the driver51in SA12is performed.

Second Embodiment

Next, a second embodiment of the present disclosure will be described with reference toFIGS. 12 to 15. In the second embodiment, a constituent element equal or similar to that in the first embodiment is given the same reference numeral, and a description thereof will be omitted or made briefly.

Description of Configuration

The second embodiment is different from the first embodiment in that a motor control circuit30B illustrated inFIG. 12is used. The motor control circuit30B of the second embodiment also controls driving of the motor13of the electronic timepiece1in the same manner as in the first embodiment.

The motor control circuit30B is different from the motor control circuit30in terms of configurations of a driver and detection circuit50B and a decoder38B. The motor control circuit30B is different from the motor control circuit30in that the fourth timer34is not provided, and an AND circuit49is provided. The rest configuration is the same as that of the motor control circuit30.

Configurations and operations of the first timer31, the second timer32, and the third timer33of the motor control circuit30B are the same as those in the motor control circuit30. The third timer33is the same as that in the motor control circuit30in that the output TM3is input to the second differentiation circuit372and the AND circuit42, but is different from that in the motor control circuit30in that the output TM3is input to the decoder38B and the AND circuit49.

The decoder38B outputs the gate signals P1, P2, N1, N2, N3, and N4for the driver and detection circuit50B as illustrated in a timing chart inFIG. 15according to states of the ON/OFF switching signal TON for a current output, the drive polarity signal PL, the drive signal DON, the timer output TM3, and a clock signal SP.

Configurations and operations of the number-of-steps control circuit36, the first differentiation circuit371, the second differentiation circuit372, the SR latch circuit39, and the flip-flop40of the motor control circuit30B are the same as those in the first embodiment. Also in the second embodiment, a condition in which a polarity of a drive signal is switched or a condition for stopping the driver51by controlling the driver51with the decoder38B is the same as that in the first embodiment, and thus a drive control unit, and a polarity switching unit and a drive stopping unit are the same as those in the first embodiment.

The driver and detection circuit50B includes a driver51and detection circuits as illustrated inFIG. 13. The detection circuits include a current detection circuit and a magnetic field detection circuit71which is a magnetic field detector.

The configurations and operations of the driver and the current detection circuit61are the same as those in the first embodiment. In other words, the driver supplies a current to the coil130, and the current detection circuit61detects whether a current value of the current I flowing through the coil130is equal to or greater than the lower limit current value Imin or is smaller than the lower limit current value Imin.

The magnetic field detection circuit71is a circuit detecting the presence or absence of an external magnetic field. The magnetic field detection circuit71includes a clock generation circuit72, a latch circuit73, a fifth timer74, inverters751and752, and OR circuits77and78.

The magnetic field detection circuit71is operated in a case where the output TM3from the third timer33is turned to an H level.

Then, the decoder38B controls the driver51on the basis of a clock signal output from the clock generation circuit72of the magnetic field detection circuit71, and subjects electromotive force caused by an external magnetic field generated in the coil130to chopper amplification. Therefore, the magnetic field detection circuit71, the decoder38B, and the driver51configure a chopper amplification circuit. The magnetic field detection circuit71detects an external magnetic field depending on whether or not a voltage value subjected to chopper amplification exceeds threshold voltages of the inverters751and752.

In a case where the output TM3from the third timer33is turned to an H level, the clock generation circuit72is operated, and outputs the clock signal SP to the latch circuit73as a clock input and the decoder38B.

Operation in Second Embodiment

Next, a description will be made of control performed by the motor control circuit30B of the second embodiment with reference to a flowchart inFIG. 14and a timing chart inFIG. 15. Processes in SB1to SB14of the flowchart inFIG. 14are the same as the processes in SA1to SA14of the flowchart inFIG. 7in the first embodiment, and thus a description thereof will be made briefly.

Also in the second embodiment, in the same manner as in the first embodiment, in a case where a setting signal is input from the CPU23, the motor control circuit30B starts driving, and sets the number of steps (for example, five) in the number-of-steps control circuit36(SB1).

The number-of-steps control circuit36turns the drive period signal TD to an H level such that the drive signal DON is turned to an H level, and the decoder38B controls the gate signals P1, P2, and N1to N4so as to turn on the driver51, so that the current I is supplied to the coil130(SB2).

Thereafter, in the same manner as in the first embodiment, the processes in SB3to SB11are performed, during a normal operation as in a case of the number of steps n=5 inFIG. 15, the motor control circuit30B switches a polarity of a drive signal in a case where an OFF time of the driver51exceeds the first switching determination time t2, and continuously performs drive control.

On the other hand, as in a case of a second step (n=4) illustrated inFIG. 15, an OFF time of the driver51may change due to the influence of an external magnetic field, impact, or the like, and may thus exceed the first stop determination time t3set as an OFF time having a length which is not generated during normal times. In this case, in the same manner as in the first embodiment, since a determination result in SB6is YES, and the drive signal DON has an L level, driving of the driver51is stopped (SB12). In this case, since the output DT1has an L level in an H level of the output TM2, the polarity signal PL which is an output from the flip-flop40is inverted, and thus a polarity is switched (SB13). A clock signal CL is output from the first differentiation circuit371, and the number-of-steps control circuit36reduces the remaining number of steps by one (SB14).

Since the output TM3is turned to an H level, the magnetic field detection circuit71is operated, and thus a magnetic field detection process is performed (SB15). The magnetic field detection process in SB15is performed as follows.

In a period in which the output TM3has an H level, as illustrated inFIG. 15, the decoder38B controls each gate signal according to an output cycle of the clock signal SP such that the output terminal O1or the output terminal of the driver51is repeatedly brought into a high impedance state and a short state. The output terminal O1or the output terminal O2may be selected as a terminal side to which the current I is supplied through polarity switching. For example, in a third step (n=3) inFIG. 15, the Nch transistor54connected to the output terminal O1is turned on and off in synchronization with the clock signal SP, and thus an induced voltage generated in the coil130is subjected to chopper amplification.

In a case where a potential of the output terminal O1subjected to chopper amplification exceeds a threshold voltage of the inverter751, an output signal from the inverter751is turned to an L level, and thus an output from the OR circuit77to which the signal is inverted to be input is turned to an H level. Therefore, an output MD from the latch circuit73is turned to an H level in synchronization with the clock signal SP. Here, since the output MD from the latch circuit73and an inverted signal of the output TM3are input to the OR circuit78, in a case where the output TM3has an H level, an output from the OR circuit78also has an H level when the output MD from the latch circuit73has an H level. Thus, the fifth timer74is maintained in a reset state while an external magnetic field in the coil130is detected.

In the same manner for a case where the output terminal O2side is subjected to chopper amplification, in a case where a potential of the output terminal O2exceeds a threshold voltage of the inverter752, the output MD from the latch circuit73is turned to an H level in synchronization with the clock signal SP, and thus the fifth timer74is reset.

On the other hand, in a case where there is no external magnetic field, since respective potentials of the output terminals O1and O2do not exceed the threshold voltages of the inverters751and752, output signals from the inverters751and752are maintained in an H level, and an output from the OR circuit77to which the signals are inverted to be input is maintained in an L level.

Thus, the output MD from the latch circuit73is also maintained in an L level, and a reset state of the fifth timer74is canceled in a case where the output TM3has an H level. In other words, the fifth timer74starts time measurement at a timing at which the output MD from the latch circuit73is turned to an L level from an H level, that is, a timing at which a state in which an external magnetic field is detected changes to a state in which an external magnetic field is not detected.

The fifth timer74turns an output signal RM to an H level in a case where a reset cancelation state, that is, a state in which an external magnetic field is not detected last for a time t5or more. In a case where the output signal RM is turned to an H level, the third timer33is reset, the output TM3is turned to an L level, and the drive signal DON is turned to an H level. Thus, driving of the motor13is resumed.

Therefore, the time t5measured by the fifth timer74is an external magnetic field determination time, and is set to, for example, 30 msec. The time t5is preferably set to a period longer than a cycle of an AC power source (about 50 Hz) which tends to be a noise source.

Effects of Second Embodiment

According to the second embodiment, the same effects as those in the first embodiment can be achieved.

In other words, according to the motor control circuit30B, a case where the time t3or more elapses from turning-off of the driver51, driving of the driver51is stopped, and thus it is possible to prevent the motor13from being driven in a state of being influenced by a disturbance such as an external magnetic field.

Therefore, it is possible to prevent the occurrence of a problem that the motor13is not accurately controlled due to a disturbance, and thus a hand position is inaccurate.

The motor control circuit30B includes the magnetic field detection circuit71, and resumes driving of the driver51after the magnetic field detection circuit71detects that an external magnetic field disappears in a case where driving of the driver51is stopped. Thus, a probability that the driver51may be stopped again due to the influence of a disturbance after resuming driving of the driver51is reduced, and thus a pointer moved by the motor13can be reliably moved to a desired indication position after resuming the driving.

Third Embodiment

Next, a third embodiment of the present disclosure will be described with reference toFIGS. 16 to 21. In the third embodiment, a constituent element equal or similar to that in the first and second embodiments is given the same reference numeral, and a description thereof will be omitted or made briefly.

Description of Configuration

A motor control circuit30C of the third embodiment is different from the first and second embodiments in which driving of the motor13is controlled by comparing the current I with the lower limit current value Imin in that driving of the motor13is controlled by comparing the current I with an upper limit current value Imax.

As illustrated inFIG. 16, the motor control circuit30C includes a first timer31C, a second timer32C, a third timer33C, a fourth timer34C, a zeroth timer35C, a number-of-steps control circuit36C, a differentiation circuit371C, a decoder38C, SR latch circuits39and80, a flip-flop40, AND circuits41C,42C,46C,81, and82, OR circuits44C,45C, and47C, and a driver and detection circuit50C.

The first timer31C is a timer measuring a time (OFF time Toff) t31for which the supply of a current to the coil130of the motor13is stopped while the driver51is in an OFF state. An output TM1from the first timer31C is turned to an H level after a signal which is input to a reset terminal R of the first timer31C is turned to an L level such that a reset state thereof is canceled, and then the time t31elapses.

The second timer32C is a timer measuring a time (ON time Ton) t32for which a current is supplied to the coil130of the motor13while the driver51is in an ON state. The time t32is a second setting time, and is one of conditions for switching a polarity of a current or stopping driving of the driver51as will be described later. An output TM2from the second timer32C is turned to an H level after a signal which is input to a reset terminal R of the second timer32C is turned to an H level such that a reset state thereof is canceled, and then the time t32elapses.

The third timer33C is a timer measuring a first setting time t33serving as a condition for stopping driving of the motor13. An output TM3from the third timer33C is turned to an H level after a signal which is input to a reset terminal R of the third timer33C is turned to an L level such that a reset state thereof is canceled, and then the time t33elapses.

The fourth timer34C is a timer measuring a standby setting time t34until driving of the motor13is resumed. An output TM4from the fourth timer34C is turned to an H level after a signal which is input to a reset terminal R of the fourth timer34C is turned to an H level such that a reset state thereof is canceled, and then the time t34elapses.

The zeroth timer35C is a timer measuring a mask time t30for preventing a wrong determination of polarity switching when driving is started. An output TM0from the zeroth timer35C is turned to an H level after a signal which is input to a reset terminal R of the zeroth timer35C is turned to an H level such that a reset state thereof is canceled, and then the time t30elapses.

The driver and detection circuit50C is a circuit which supplies a current to the coil130of the motor13, and also determines whether or not a value of the current flowing through the coil130exceeds the upper limit current value Imax. The details of the driver and detection circuit50C will be described later with reference toFIG. 17.

The number-of-steps control circuit36C includes a presettable down-counter, and outputs a drive period signal TD. The number-of-steps control circuit36C sets the drive period signal TD in an H level until a preset value of the presettable down-counter set by a setting signal is counted down and becomes 0 by using a clock signal CL, and turns the drive period signal TD to an L level when the presettable down-counter becomes 0. The setting signal which is input to the number-of-steps control circuit36C is input from, for example, the CPU23via the bus27.

The decoder38C which is a drive control unit outputs the gate signals P1, P2, N1, N2, N3, and N4for the driver and detection circuit50C as illustrated in timing charts inFIGS. 19 to 21according to states of the ON/OFF switching signal TON for a current output, the drive polarity signal PL, and the drive signal DON.

The differentiation circuit371C outputs a differentiation pulse (clock signal CL) whenever the drive polarity signal PL rises and falls.

The AND circuit41C receives an output DT2from the driver and detection circuit50C, an inverted signal of the output TM2from the second timer32C, and the output TM0from the zeroth timer35C. An output from the AND circuit41C is input to the AND circuit81along the output TM3from the third timer33C. An output from the AND circuit81is input to a clock input of the flip-flop40.

The AND circuit42C receives an inverted signal of an output DOFF from the SR latch circuit80and the drive period signal TD. An output DON from the AND circuit42C is input to the decoder38C and the OR circuit44C.

The OR circuit44C receives an inverted signal of the output DON and the output TM1from the first timer31C, and outputs a signal to the SR latch circuit39.

The OR circuit45C receives an output TON from the SR latch circuit39and an inverted signal of the output DON, and an output signal from the OR circuit45C is input to the reset terminal R of the first timer31C.

The AND circuit46C receives the output TON and the output DON, and an output signal from the AND circuit46C is inverted to be input to the reset terminal of the second timer32C.

The OR circuit47C receives the clock signal CL output from the differentiation circuit371C and an inverted signal of the output DON, and an output from the OR circuit47C is input to the reset terminal R of the third timer33C.

The AND circuit82receives an output signal from the AND circuit41C and an inverted signal of the output TM3, and an output signal from the AND circuit82is input to a set terminal S of the SR latch circuit80.

The output TM4is input to a reset terminal R of the SR latch circuit80, and an output signal DOFF from the SR latch circuit80is inverted to be input to the reset terminal of the fourth timer34C and the AND circuit42C.

Configurations of Driver and Detection Circuit

The driver and detection circuit50C includes a driver51and a current detection circuit61C as illustrated inFIG. 17. The driver51is the same as that in the first embodiment and is thus given the same reference numeral, and a description thereof will be omitted.

The current detection circuit61C includes a second reference voltage generation circuit63, comparators651and652, and a complex gate69. The complex gate69is a single element having a function equivalent to a combination of AND circuits671and672and an OR circuit690. In other words, the first reference voltage generation circuit62of the current detection circuit61is changed to the second reference voltage generation circuit63.

The second reference voltage generation circuit generates a voltage corresponding to the upper limit current value Imax. Therefore, the output DT2from the current detection circuit61C is turned to an H level in a case where the current I flowing through the coil130exceeds the upper limit current value Imax, and is turned to an L level in a case where the current I is equal to or less than the upper limit current value Imax. Thus, the current detection circuit61C is an upper limit detection unit detecting that the current I flowing through the coil130exceeds the upper limit current value Imax.

Control Process of Motor Control Circuit

Next, control performed by the motor control circuit30C of the present embodiment will be described with reference to a flowchart inFIG. 18, and timing charts inFIGS. 19 to 21.FIG. 19is a timing chart illustrating an operation of the motor control circuit30C during normal times,FIG. 20is a timing chart in a comparative example in which a defect occurs due to a disturbance such as an external magnetic field, andFIG. 21is a timing chart illustrating an operation of the motor control circuit30C in a case where a disturbance such as an external magnetic field occurs.

Operation of Motor Control Circuit

As illustrated inFIG. 18, the CPU23of the IC20outputs a setting signal for setting a movement amount of a pointer to the number-of-steps control circuit36C of the motor control circuit30C (SC1). In the present embodiment, a setting signal for setting the number of steps to “4” is output.

In a case where the setting value n=4 is set in the number-of-steps control circuit36C according to the setting signal, the drive period signal TD is turned to an H level, the output DON from the AND circuit42is turned to an H level, the decoder38C turns on the driver51of the motor13by using the gate signals P1, P2, N1, N2, N3, and N4(SC2), and thus a forward current flows through the coil130, in the same manner as in the first embodiment.

Next, the current detection circuit61C determines whether or not the current I flowing through the coil130exceeds the upper limit current value Imax (SC3). As described above, the current detection circuit61C continuously performs the determination process in SC3until voltages generated in the detection resistors58and59exceed a reference voltage generated from the second reference voltage generation circuit63(NO in SC3).

On the other hand, in a case where a determination result in SC3is YES, the current detection circuit61C turns the detection signal DT2to an H level, a reset signal is input to the SR latch circuit39, and the signal TON is turned to an L level. In a case where the signal TON is turned to an L level, the decoder38C controls the gate signals so as to turn off the driver51(SC4).

Next, it is determined whether or not a time from drive starting or drive resuming is within the mask time t30(SC5). The zeroth timer35C measuring the mask time t30cancels a reset state thereof when the output DON is turned to an H level, and starts to measure a time. Therefore, in a case where the output TM0from the zeroth timer35C has an L level, the time from drive starting or drive resuming is within the time t30, and thus a determination result in SC5is YES. On the other hand, in a case where the output TM0from the zeroth timer35C has an H level, the time from drive starting or drive resuming exceeds the time t30, and thus a determination result in SC5is NO.

In a case where a determination result in SC5is NO, it is determined whether or not the ON time Ton of the driver51measured by the second timer32C is shorter than the time t32(SC6). In a case where the signal TON is turned to an H level, the second timer32C cancels a reset state thereof, and starts to measure a time. The output TM2has an L level in a case where a measured time is shorter than the time t32, and the output TM2has an H level in a case where the measured time is equal to or longer than the time t32. Therefore, in SC6, a determination result is YES in a case where the output TM2has an L level, and a determination result is NO in a case where the output TM2has an H level.

In a case where a determination result in SC5is YES, or a determination result in SC6is NO, it is determined whether or not the time t31has elapsed from turning-off of the driver51(SC7). In a case where a determination result in SC7is NO, the determination in SC7continuously waits until the time t31elapses, that is, the output TM1from the first timer31C is turned to an H level.

In a case where a determination result in SC7is YES, that is, the output TM1is turned to an H level, output from the OR circuit44C is turned to an H level, the output TON from the SR latch circuit39is turned to an H level, and thus the decoder38C turns on the driver51(SC2). Hereinafter, the motor control circuit30C repeatedly performs SC2to SC7until a determination result in SC6is YES.

In a case where a determination result in SC6is YES, an elapsed time from starting of a step measured by the third timer33C is within the first setting time t33(SC8). In a case where a determination result in SC8is NO, the mask time t30elapses such that the output TM0has an H level, the current I exceeds the upper limit current value Imax such that the detection signal DT2has an H level, and the ON time is shorter than the time t32such that the output TM2has an L level. Therefore, an output from the AND circuit41C has an H level. In a case where a determination result in the process in SC8is NO, an elapsed time from starting of the step exceeds the time t33such that the output TM3has an H level, and thus an output from the AND circuit81also has an H level. Thus, a clock signal is input to the flip-flop40, the drive polarity signal PL is inverted, and thus a polarity is switched (SC9). Therefore, in the third embodiment, the second timer32C, the third timer33C, the zeroth timer35C, the current detection circuit61C, the flip-flop40, and the decoder38C configure a polarity switching unit which determines whether or not a polarity switching condition is satisfied, and switches a polarity of a drive signal.

Since the drive polarity signal PL is inverted, the clock signal CL is output from the differentiation circuit371C, the number-of-steps control circuit36C reduces the remaining number of steps by one (SC10), repeatedly performs SC2to SC11until the remaining number of steps becomes 0 (until a determination result in SC11is YES), and thus the motor13can be normally driven as illustrated inFIG. 19.

As described above, since an ON time of the driver51, that is, the motor13and a rotation angle of the rotor133are correlated with each other, the time t32is set to a value generated when the rotor133is rotated by a predetermined angle (for example, 180° in a bipolar rotor) corresponding to rotation in one step. Therefore, in a case where an ON time is shorter than the time t32, it can be detected that the rotor133is rotated by a predetermined angle. However, as illustrated inFIG. 19, an ON time may be temporarily shorter than the time t32even if the rotor133is not rotated by a predetermined angle right after driving is started (first step). In order to prevent a wrong determination in this case, the mask time t30is set in the first step, and control is performed such that an ON time is compared with the time t32after the mask time t30elapses.

Operation (Comparative Example) During Occurrence of Defect

Here, for comparison with the present embodiment, a description will be made of an example in which a defect occurs due to the influence of an external magnetic field or impact in a case where the third timer33C and the fourth timer34C are not provided, with reference to a timing chart inFIG. 20.

An ON time and an OFF time of the driver51depend on an inverse induced voltage generated in the coil130, but the inverse induced voltage changes due to the influence of an external magnetic field or impact, and thus a relationship between an ON time or an OFF time and a rotational position of the rotor133may not be established. For example, as illustrated inFIG. 20, there is a case where an ON time is shorter than the time t32due to the influence of an external magnetic field or impact before a timing at which the rotor133is regarded to be rotated by 180°, thus polarity switching is performed although the rotor133is not rotated, so that driving is finished despite a predetermined number of steps not being finished.

The example illustrated inFIG. 20is an example of defect occurrence patterns, and defects of other various patterns occur due to a disturbance.

Operation in Third Embodiment

A description will be made of an operation for preventing the defect in the present embodiment with reference toFIGS. 18 and 21.

InFIG. 18, in a case where a determination result in SC6is YES, and polarity switching in SC7is immediately performed, there is a probability that the defect as illustrated inFIG. 20may occur due to the influence of an external magnetic field or the like.

Therefore, in the present embodiment, in a case where a determination result in SC6is YES, as described above, it is determined whether or not a time from drive starting in each step (drive starting in each phase) is within the first setting time t33(SC8).

The third timer33C cancels a reset state thereof and starts to measure a time in a state in which the clock signal CL has an L level at a timing at which the output DON is turned to an H level, that is, at the time of drive starting and drive resuming, that is, in the first step, in a state in which the output DON has an H level and the clock signal CL is turned to an H level, that is, a polarity is switched. In a case where the time t33has elapsed from drive starting in each step, the third timer33C turns the output TM3to an H level. Therefore, in a case where the output TM3has an L level, a determination result in SC8is YES. In a case where the output TM3has an H level, a determination result in SC8is NO.

In a case where a determination result in SC8is NO, as described above, the process in SC9of switching a polarity and the process in SC10of reducing the number of steps by one, and, in a case where the remaining number of steps becomes 0 in SC11, a pointer drive process inFIG. 18is finished.

On the other hand, in a case where a determination result in SC8is YES, since an output from the AND circuit41C has an H level, and the output TM3has an L level, an output from the AND circuit82to which the output TM3is inverted to be input has an H level, and the output DOFF from the SR latch circuit80has an H level. Thus, the output DON of the AND circuit42C has an L level, and thus driving of the driver51is stopped (SC12). Therefore, in the third embodiment, the second timer32C, the third timer33C, the SR latch circuit80, and the decoder38C are provided to configure a drive stopping unit.

In a case where driving of the driver51is stopped, it is determined whether or not the standby setting time t34has elapsed from starting of the stop (SC13). In other words, the fourth timer34C measuring the time t34starts measurement when the output DOFF is turned to an H level, and, in a case where the time t34elapses and an output from the fourth timer34C is turned to an H level, the SR latch circuit80is reset, and the output DOFF is turned to an L level. In a case where the output DOFF is turned to an L level, the output DON is turned to an H level, and thus driving of the driver51is resumed (SC2). Thereafter, SC2to SC13are repeatedly performed as appropriate, the driving is continuously performed until n becomes 0. In a case where n becomes 0, a determination result in SC11is YES, and driving is finished.

The time t30to the time t34respectively measured by the timers31C to35C may be set according to characteristics or drive voltages of the motor13, and, for example, the time t30is set to 1500 μsec, the time t31is set to 25 μsec, the time t32is set to 20 μsec, the time t33is set to 1000 μsec, and the time t34is set to 1 sec.

Effects of Third Embodiment

According to the third embodiment, the same effects as those in the first and second embodiments can be achieved.

In other words, in the motor control circuit30C, in a case where an ON time of the driver51is shorter than the time t32within the time t33from starting of a step, driving of the driver51is stopped, and thus it is possible to prevent the motor13from being driven in a state of being influenced by a disturbance such as an external magnetic field.

Therefore, it is possible to prevent the occurrence of a problem that the motor13is not accurately controlled due to a disturbance, and thus a hand position is inaccurate.

In a case where the current I exceeds the upper limit current value Imax, the motor control circuit30C turns off the driver51, and can thus prevent the current I from exceeding the upper limit current value Imax and can easily reduce power consumption.

In a case where rotation of the rotor133is detected during an ON time of the driver51, wrong detection may tend to be performed in a first step right after driving is started, but the mask time t30is set, and thus wrong detection can be prevented.

The motor control circuit30C is provided with the timers31to35in addition to the current detection circuit61C which is an upper limit detection unit comparing the current I with the upper limit current value Imax, and can perform control by only measuring an ON time of a drive unit or an OFF time of the drive unit. Thus, a configuration of the motor control circuit30C can be simplified.

Fourth Embodiment

Next, a fourth embodiment of the present disclosure will be described with reference toFIGS. 22 to 31.

An electronic timepiece1D of the fourth embodiment is an analog electronic timepiece having a universal time function as illustrated inFIG. 22. The electronic timepiece1D includes a minute hand6D and an hour hand7D which are center hands, a second hand5D disposed on the six o'clock side, a city hand4D indicating a time zone, a crown8D, and buttons9A and9B.

As illustrated inFIG. 23, in the same manner as the electronic timepiece1of the first embodiment, the electronic timepiece1D includes a quartz crystal resonator11which is a signal source, a battery12which is a power source, push switches S1and S2which are turned on and off in conjunction with an operation on the buttons9A and9B, switches S3and S4which are turned on and off in conjunction with an extraction operation on the crown8D, and a first motor14, a second motor15, a third motor16, and an IC20D for the timepiece.

The first motor14, the second motor15, and the third motor16are the same stepping motors as the motor13of the first embodiment, and thus a description thereof will be omitted.

The second hand5D is moved by the first motor14, and indicates a second of a time point. The city hand4D is moved by the second motor15, and indicates a representative city of a set time zone.

The minute hand6D and the hour hand7D are moved by the third motor16in conjunction with each other. Thus, the minute hand6D displays a minute in 180 divisions per turn, and the hour hand7D displays an hour in 2160 divisions per turn.

As illustrated inFIG. 23, the IC20D has connection terminals OSC1and OSC2connected to the quartz crystal resonator11, input/output terminals K1to K4connected to the switches S1to S4, power source terminals VDD and VSS connected to the battery12, and the output terminals O1to O6connected to the coils130of the motors14to16.

Circuit Configuration of IC

As illustrated inFIG. 24, the IC20D includes an oscillation circuit21, a frequency division circuit22, a CPU23for control of the electronic timepiece1D, a ROM24, an input/output circuit26, and a bus27. The IC20D includes a first motor control circuit30D driving the first motor14, a second motor control circuit30E driving the second motor15, a third motor control circuit30F driving the third motor16, a magnetic field detection circuit17D which is a magnetic field detector, and a current detection circuit18D.

The oscillation circuit21, the frequency division circuit22, the CPU23, the ROM24, the input/output circuit26, and the bus27have the same configurations as those in the first embodiment.

The first motor control circuit30D drives the first motor14every second, and is thus configured with a control circuit capable of achieving low power consumption, employed in a wristwatch or the like. In other words, the first motor control circuit30D performs control in which a main drive pulse having a small pulse width is output, then an induced voltage of the coil130of the first motor14is measured, so that it is detected whether or not the rotor133is being rotated, and, in a case where the rotor133is not rotated, a correction drive pulse (fixed pulse) fixed to a pulse width larger than that of the main drive pulse is output such that the rotor133is reliably rotated. The magnetic field detection circuit17D is provided along with the first motor control circuit30D, a magnetic field detection pulse is output to the coil130of the first motor before a main drive pulse is output, and an induced voltage generated in the coil130is detected by the magnetic field detection circuit17D, so that the presence or absence of an external magnetic field is detected.

Here, in a case where an external magnetic field is not detected, the first motor control circuit30D performs low power consumption drive control of outputting the main drive pulse so as to detect rotation, and outputting the correction drive pulse in a case where rotation is not detected. In a case where an external magnetic field is detected, the first motor control circuit30D reliably rotates the rotor133by outputting the correction drive pulse (fixed pulse) instead of the main drive pulse. In this case, it is not necessary to detect rotation of the rotor133.

The second motor control circuit30E drives the second motor15with a fixed pulse to be normally rotated and reversely rotated.

In the electronic timepiece1D, in a case where the button9A is pushed, the second motor control circuit30E causes the city hand4D to be moved in a normal rotation direction (clockwise direction), and to indicate a city name of the next time zone. In a case where the button9B is pushed, the second motor control circuit30E causes the city hand4D to be moved in a reverse rotation direction (counterclockwise direction), and to indicate a city name of the next time zone.

A time zone is typically set every hour, and, thus, whenever the buttons9A and9B are pushed, the time zone is changed every hour. A time zone which is not set every hour may be present, such as India which is set in a time zone of +5.5 hours with respect to UTC. In this case, when the buttons9A and9B are pushed, the next time zone of a set time zone may be selected.

The third motor control circuit30F includes the same driver51as in each of the embodiments as illustrated inFIG. 25. However, the motor control circuits30,30B, and30C of the embodiments include the logic circuits driving the transistors52to57of the driver51, but, in the present embodiment, the logic circuits driving the transistors52to57of the driver51are not provided. In the present embodiment, the CPU23directly controls the transistors52to57via the bus27, so as to control driving of the third motor16. Thus, in the fourth embodiment, the CPU23configures a drive control unit, a polarity switching unit, and a drive stopping unit.

The current detection circuit18D is provided along with the third motor control circuit30F. As illustrated inFIG. 25, the current detection circuit18D includes a first reference voltage generation circuit62, a second reference voltage generation circuit63, comparators641,642,651, and652, and complex gates68and69. The complex gate68is a single element having a function equivalent to a combination of AND circuits661and662and an OR circuit680. The complex gate69is a single element having a function equivalent to a combination of AND circuits671and672and an OR circuit690. In other words, the current detection circuit18D has a combined configuration of the current detection circuits61and61C.

The outputs DT1and DT2as detection results in the current detection circuit18D are detected by the CPU23via the bus27, and the CPU23controls the driver51of the third motor control circuit30F according to the outputs DT1and DT2.

The third motor control circuit30F drives the third motor16to move the hands every 20 seconds during normal hand movement. In this case, the minute hand6D is moved by 2 degrees (=360/180), and the hour hand7D is moved by ⅙ degrees (=360/2160).

During a time zone changing operation using the buttons9A and9B, the third motor control circuit30F moves the minute hand6D and the hour hand7D according to a changed time zone. For example, in a case where a time zone advances by an hour by using the button9A, the minute hand6D and the hour hand7D are moved by +60 minutes in conjunction therewith.

Next, a description will be made of an operation of the electronic timepiece1D of the fourth embodiment with reference to flowcharts inFIGS. 26 and 27.

In a case where an input from the switch S1connected to the input/output terminal K1of the IC20D is detected according to a push operation on the button9A, the CPU23outputs a drive pulse from the second motor control circuit30E, so as to subject the city hand4D to one-step normal rotation (rightward rotation corresponding to a clockwise direction) (SD1). In this case, in conjunction with the movement of the city hand4D, the CPU23sets a completion number of steps which is a total number of steps until driving of the minute hand6D and the hour hand7D is completed, and initializes a variable n for counting the number of steps to 0.

For example, in a case where the city hand4D indicates a time zone as a result of advancing by one hour, the CPU23sets the completion number of steps to 180 which is the number of steps for moving the minute hand6D and the hour hand7D by +60 minutes. In a case where the city hand4D indicates a time zone as a result of advancing by thirty minutes, the CPU23sets the completion number of steps to 90.

In a case where the city hand4D indicates a time zone as a result of returning by one hour, the CPU23sets the completion number of steps to 1980 (=180×11). In the present embodiment, since the minute hand6D and the hour hand7D driven by the third motor control circuit30F are set to be movable only in the normal rotation direction, in a case where the city hand4D is returned by one hour, the minute hand6D and the hour hand7D are moved in the normal rotation direction by eleven hours due to the twelve-hour clock.

Next, the CPU23starts fast-forward control of the minute hand6D and the hour hand7D (SD2), and turns on the driver51of the third motor control circuit30F for the minute and hour hands (SD3).

After the driver51is turned on, the CPU23detects the current I flowing through the coil130by using the current detection circuit18D, and determines whether or not the current I is equal to or more than the upper limit current value Imax (SD4). In a case where a determination result in SD4is NO, the CPU23continuously performs the determination process in SD4.

In a case where a determination result in SD4is YES, the CPU23turns off the driver51(SD5). Thereafter, the CPU23determines whether or not the current I flowing through the coil130is equal to or less than the lower limit current value Imin (SD6). In a case where a determination result in SD6is NO, the CPU23continuously performs the determination process in SD6.

In a case where a determination result in SD6is YES, the CPU23determines whether a step is the first step after drive starting or the first step after drive resuming (SD7).

In a case where a determination result in SD7is NO, the CPU23determines whether or not a proportion of the period Ton in which the driver51is in an ON state is higher than that in the previous time (SD8). The proportion of the period Ton is obtained by Ton/(Ton+Toff).

Here, the period Ton, the period Toff, the induced voltage V, the drive voltage E, the drive current i, and the coil resistance R have a relationship of the following Equation (6), and a timing which is the optimum for switching a drive polarity may be estimated on the basis of the induced voltage V.
V=E*Ton/(Ton+Toff)−R*i(6)

FIG. 28is a waveform diagram illustrating drive signals during normal control in the output terminals O5and O6connected to the coil130of the third motor16, andFIG. 29is a graph illustrating Ton/(Ton+Toff) in the first and second steps. In other words, as illustrated inFIG. 28, the first step is a period A in which a drive signal is output from the output terminal O5, and the second step is a period B in which a drive signal is output from the output terminal O6.

As illustrated inFIGS. 28 and 29, a proportion of Ton in each pulse in the first step, that is, Ton/(Ton+Toff) is 0.8 in a first pulse, decreases to about 0.4 in a second pulse, then gradually increases up to tenth to twelfth pulses, and then decreases.

Ton/(Ton+Toff) in the second step is about 1.0 in a first pulse, and has a tendency to decrease according to an increase in the number of pulses.

On the other hand, in a case where a hand is moved under an external magnetic field, the above-described relationship may not be established due to the influence of the magnetic field, and thus Ton/(Ton+Toff) changes unlike during normal times.FIGS. 30 and 31illustrate an example thereof. Ton/(Ton+Toff) is the same as during normal times in the first step, but, in the second step and subsequent steps, Ton/(Ton+Toff) greatly decreases in a second pulse, then increases up to an eighth pulse, and then rapidly decreases. In such an environment, for example, Ton/(Ton+Toff) in the second pulse may possibly decrease to a switching setting value (0.3 in the present embodiment) or less, and thus it may be wrongly determined that the rotor133is rotated before the rotor133is rotated by 180 degrees. The switching setting value is not limited to 0.3, and may be set according to a specification or the like of the motor16.

The CPU23determines whether or not Ton/(Ton+Toff) is higher than that in the previous time (SD8) in a case of the second step and subsequent steps (NO in SD7). A case where Ton/(Ton+Toff) is higher than that in the previous pulse in the second step and subsequent steps is a case where a hand is moved under an external magnetic field as described above.

In a case where a determination result in SD8is NO, and a determination result in SD7is YES, the CPU23determines whether or not Ton/(Ton+Toff) is equal to or lower than 0.3 (SD9). As illustrated inFIGS. 29 and 31, in control in the first step, Ton/(Ton+Toff) decreases to about 0.4 in a second pulse, but, then, gently increases, and then decreases. A case where Ton/(Ton+Toff) is equal to or lower than 0.3 is a case where the rotor133is regarded to be rotated by 180°. Also in control in the second step, Ton/(Ton+Toff) is equal to or lower than 0.3 in a case where the rotor133is regarded to be rotated by 180°.

Thus, in the present embodiment, in SD9, it is determined whether or not Ton/(Ton+Toff) is equal to or lower than 0.3, and thus it is determined whether or not the rotor133is rotated.

In the present embodiment, the rotation determination condition for the rotor133in SD9is used in both of the first step and the second step, but a rotation determination condition in the first step may be separately set by taking into consideration the tendency illustrated inFIGS. 29 and 31.

On the other hand, inFIG. 26, in a case where a determination result in SD7is NO, and a determination result in SD8is YES, there is a high probability that the influence of an external magnetic field may be received. Therefore, in a case where a determination result in SD8is YES, the CPU23stops driving of the driver51, also stops the fast-forwarding process for the minute and hour hands (SD10), and finishes the process. In this case, the minute hand6D and the hour hand7D are not corrected by a change amount of a time zone, but fast-forwarding is resumed in a case where the influence of an external magnetic field disappears through an interruption process per second which will be described later.

In a case where a determination result in SD9is NO, the CPU23repeatedly performs the processes in SD3to SD9.

In a case where a determination result in SD9is YES, the CPU23switches a polarity (SD11), and adds 1 to the number of steps n (SD12). The CPU23determines whether or not the number of steps n is the completion number of steps (for example, 180) (SD13), returns to SD3in a case where a determination result in SD13is NO, and continuously performs fast-forwarding of the minute hand6D and the hour hand7D. In a case where a determination result in SD13is YES, the CPU23determines that fast-forwarding of the minute hand6D and the hour hand7D, corresponding to the change amount (for example, one hour) of the time zone, is finished, and finishes the driving.

Next, a description will be made of an interruption process of 1 Hz performed by the CPU23in order to move the second hand5D with reference toFIG. 27.

The CPU23detects an external magnetic field every second in order to move the second hand5D (SD21). Specifically, an external magnetic field detection pulse is output from the first motor control circuit30D to the coil130of the first motor14, and an induced voltage generated in the coil130is detected by the magnetic field detection circuit17D such that an external magnetic field is detected.

The CPU23determines the presence or absence of an external magnetic field on the basis of a detection result in the magnetic field detection circuit17D (SD22). In a case where it is determined that an external magnetic field is present (YES in SD22), the CPU23causes the first motor control circuit30D to move the second hand5D with a fixed pulse (SD23). In a case where it is determined that an external magnetic field is absent (NO in SD22), the CPU23causes the first motor control circuit30D to move the second hand5D according to the above-described low power consumption drive control (SD24).

In a case where the second hand5D is moved in SD24, the CPU23determines whether or not fast-forwarding of the minute and hour hands is stopped (SD25). In a case where a determination result in SD25is YES, the CPU23returns to SD23inFIG. 26, and resumes the fast-forwarding process of the minute and hour hands. In other words, stopping of fast-forwarding of the minute and hour hands (SD10) is performed in a case where a determination result in SD8inFIG. 26is YES, that is, there is the influence of an external magnetic field, and thus fast-forwarding may be resumed in a case where it is determined that an external magnetic field disappears.

In a case where a determination result in SD25is NO, and the second hand is moved in SD23, the CPU23determines that fast-forwarding of the minute and hour hands is being performed (SD26). An interruption process of one second occurs not only during changing of a time zone but also during normal time display. Therefore, a case where a determination result in SD25is NO includes a case where fast-forwarding of the minute and hour hands is performed, and the minute and hour hands are moved for normal time display without performing fast-forwarding.

Similarly, a case where an external magnetic field is detected and the second hand is moved with a fixed pulse includes a case where fast-forwarding of the minute and hour hands is performed, and the minute and hour hands are moved for normal time display without performing fast-forwarding. For example, as illustrated inFIG. 26, fast-forwarding of the minute and hour hands is not stopped in the first step (YES in SD7) after drive starting, and thus fast-forwarding of the minute and hour hands may be performed even in a case where an external magnetic field is detected through an interruption process of 1 Hz.

Therefore, the CPU23determines whether or not fast-forwarding of the minute and hour hands is performed in SD26, and causes the third motor control circuit30F to perform a normal display process using the minute and hour hands (SD27) in a case where the fast-forwarding is not performed (No in SD26). In the present embodiment, the CPU23drives the third motor control circuit30F by one step every twenty seconds, and moves the minute hand6D twice, that is, by ⅓ of the scale (6 degrees) of one minute.

On the other hand, in a case where a determination result in SD26is YES, since fast-forwarding of the minute and hour hands is performed in the flowchart inFIG. 26, the third motor control circuit30F is not required to be controlled in the flowchart inFIG. 27, and thus the process is finished.

Effects of Fourth Embodiment

According to the fourth embodiment, the same effects as those in the first to third embodiments can be achieved.

In other words, in the motor control circuit30D, in control after the second step and subsequent steps, in a case where a proportion of an ON time in each pulse is higher than in the previous pulse, that is, Ton/(Ton+Toff) is higher than in the previous time (YES in SD8), it is determined that there is the influence of a disturbance such as an external magnetic field, driving of the driver51is stopped, and a fast-forwarding process for the minute and hour hands is stopped. Therefore, it is possible to prevent the motor13from being driven in a state of being influenced by the disturbance such as an external magnetic field, and therefore to prevent the occurrence of a problem that the motor13is not accurately controlled due to the disturbance, and thus a hand position is inaccurate.

In the first step in which an operation which is different from that in the second step and subsequent steps is performed, the determination in SD8is not performed, and thus it is possible to prevent a wrong determination of the presence or absence of a disturbance in the first step.

In SD9, since it is detected that Ton/(Ton+Toff) is reduced to 0.3 or less, and it is determined that the rotor133is rotated up to a predetermined angle, driving of the rotor133in each step can be performed with high accuracy.

The motor control circuit30D is provided with the current detection circuit18D which compares the current I flowing through the coil130with the upper limit current value Imax and the lower limit current value Imin, turns off the driver51in a case where the current I exceeds the upper limit current value Imax, and turns on the driver51in a case where the current I is less than the lower limit current value Imin. Therefore, it is possible to simplify drive control for the driver51.

The motor control circuit30D can be easily configured since the CPU23controls the driver51without using a dedicated logic circuit performing drive control for the driver51.

In the fourth embodiment, in a case where Ton/(Ton+Toff) is higher than in the previous time after the second step and subsequent steps (YES in SD8), it is determined that there is the influence of an external magnetic field, and fast-forwarding of the minute and hour hands is stopped, but a result of detecting a magnetic field every second in SD21may be held, and fast-forwarding of the minute and hour hands may be temporarily prohibited according to the result.

Detection of an external magnetic field is not limited to a case of being performed by using the first motor14, and may be performed by using the second motor15driving the city hand4D. In other words, a magnetic field detection pulse has a small pulse width, and does not rotate the rotor133, and thus an external magnetic field may be detected by using any motor.

Fifth Embodiment

Next, a fifth embodiment of the present disclosure will be described with reference toFIGS. 32 and 33.

In the fifth embodiment, a control flow in the electronic timepiece1D of the fourth embodiment is changed. Therefore, a configuration or the like of the electronic timepiece1D is the same as that in the fourth embodiment, and thus a description thereof will be omitted.

In the fifth embodiment, as illustrated inFIGS. 32 and 33, in a case where fast-forwarding of the minute and hour hands is stopped due to an external magnetic field, two-step driving is performed, it is determined whether or not the influence of the external magnetic field disappears on the basis of a relationship between the ON period Ton and the OFF period Toff of the driver51at that time, and it is controlled whether or not fast-forwarding of the minute and hour hands is resumed on the basis of a result thereof.

Thus, fast-forwarding control for the minute and hour hands inFIG. 32(SD1to SD13) is the same as the control in the fourth embodiment inFIG. 26, and is thus given the same reference sign, and a description thereof will be omitted.

In the fifth embodiment, in a case where a determination result in SD8is YES, that is, it is determined that there is the influence of an external magnetic field, the CPU23performs a process inFIG. 33. In other words, the CPU23stops fast-forwarding of the minute and hour hands (SD31), and waits for a standby setting time t6to elapse (SD32). The time t6is, for example, one second, and may be set to a time for which it can be expected that the influence of an external magnetic field disappears in a case where the CPU23waits for the time t6.

After the time t6elapses, the CPU23performs two-step driving, that is, performs the same processes in SD3to SD12inFIG. 32twice, determines the presence or absence of an external magnetic field again, and determines whether or not fast-forwarding of the minute and hour hands is resumed according to a determination result.

Thus, after a determination result in SD32is YES, the CPU23turns on the driver51of the third motor control circuit30F for the minute and hour hands (SD33), and determines whether or not the current I exceeds the upper limit current value Imax (SD34).

The CPU23repeatedly performs the determination process in SD34until a determination result in SD34is YES, and turns off the driver51in a case where a determination result is YES (SD35).

After the process in SD35is performed, the CPU23determines whether or not the current I is less than the lower limit current value Imin (SD36), and repeatedly performs the determination process in SD36until a determination result in SD36is YES.

In a case where a determination result in SD36is YES, the CPU23determines whether or not Ton/(Ton+Toff) is equal to or lower than 0.3, that is, the rotor133is rotated by a predetermined angle (SD37).

In a case where a determination result in SD37is NO, the CPU23returns to SD33and continuously performs the process, and, in a case where a determination result is YES, the CPU23switches a polarity (SD38) and adds 1 to the number of steps n (SD39) in the same manner as in SD11and SD12. Consequently, one-step driving is finished.

Next, the CPU23starts driving in the second step, turns on the driver51of the third motor control circuit30F (SD40), determines whether or not the current I exceeds the upper limit current value Imax (SD41), and turns off the driver51(SD42) in a case where a determination result in SD41is YES.

After the process in SD42is performed, the CPU23determines whether or not the current I is equal to or less than the lower limit current value Imin (SD43), determines whether or not Ton/(Ton+Toff) is higher than in the previous time, that is, there is the influence of an external magnetic field (SD44) in a case where a determination result in SD43is YES, and returns to SD31and performs two-step driving again in a case where a determination result in SD44is YES.

On the other hand, in a case where a determination result in SD44is NO, the CPU23determines whether or not the Ton/(Ton+Toff) is equal to or lower than 0.3, that is, the rotor133is rotated by a predetermined angle (SD45), returns to SD40and continuously performs the process in a case where a determination result in SD45is NO, returns to SD11and continuously performs the process since it is not necessary to detect the presence or absence of an external magnetic field through two-step driving in a case where a determination result is YES, and performs fast-forwarding of the minute and hour hands to a position corresponding to a changed time zone.

Effects of Fifth Embodiment

According to the fifth embodiment, the same effects as those in the fourth embodiment can be achieved.

In the fourth embodiment, in a case where fast-forwarding of the minute and hour hands is stopped due to the influence of an external magnetic field, the presence or absence of an external magnetic field is detected during an interruption process of 1 Hz for second driving, and fast-forwarding is resumed, but, in the fifth embodiment, the presence or absence of an external magnetic field is determined during driving every two steps of the third motor16driving the minute and hour hands, and fast-forwarding is resumed. In other words, since a process is completed in the third motor control circuit30F, the fifth embodiment is applicable to a timepiece in which a second hand is normally driven with a fixed pulse, and which does not have an external magnetic field detection function.

In the fifth embodiment, in a case where a determination result in SD8is YES, two-step driving is performed, but the influence of an external magnetic field may be determined in one step, and may be determined through plural-step driving of three or more steps.

Other Embodiments

The present disclosure is not limited to the above embodiments, and modifications, alterations, and the like within the scope of the present disclosure capable of realizing some aspects of the embodiments are included in the present disclosure.

For example, in the motor control circuit30C of the third embodiment, an ON time of the driver51, polarity switching based on an elapsed time from starting of a step, and stopping of driving of the driver are selected, but only an ON time of the driver51may be selected. In the same manner as in the first modification example, polarity switching may be controlled for an ON time of the driver51, and stopping of driving of the driver51may be controlled for an elapsed time from the time of starting driving or the time of switching a polarity. Such controls may be combined with each other.

In the third embodiment, the flow returns to SC2after the standby setting time t4elapses in SC13, but, in the same manner as in the second embodiment, control may be performed such that an external magnetic field is detected instead of SC13, and the flow returns to SC2in a case where it is determined that there is no external magnetic field.

A magnetic field detector is not limited to detecting an external magnetic field through chopper amplification, such as the magnetic field detection circuit71, and may include a control unit that brings at least one end of the coil130into any one of a high impedance state, a pull-down state, and a pull-up state, and a voltage detection unit that detects a voltage generated in one end of the coil130. A dedicated magnetic sensor may be used.

In the above-described respective embodiments, the electronic timepiece1is of a wristwatch type but may be, for example, a table clock. The motor control circuit of the embodiments of the present disclosure is not limited to controlling a motor driving a pointer of a timepiece, and may be applied to a control circuit or the like for a motor for a pointer indicating a measured value in each of various meters. Particularly, since a difference in a drive amount of a motor is small even in a case where the influence of a disturbance is received, the motor control circuit is not limited to an electronic timepiece, and may be used for various electronic apparatuses.