ANALOG ELECTRONIC TIMEPIECE

Abstract

A sweep motion second function is added to an analog electronic timepiece. Angular velocity control of a stepping motor for a seconds hand in which a rotor is provided is executed. A stepping motor model calculates an equation of motion and a circuit equation regarding the stepping motor in real time. Sweep drive is executed with a sweep drive pulse width generated through performing a proportional integral of the difference between angular velocity set to π (radians/second) and angular velocity of the stepping motor model. Correction of the load torque is executed using the rotor angle at the zero crossing of a back electromotive voltage generated across a coil of the stepping motor and the calculated angular velocity. A DC current is applied to coils disposed at bridges of a yoke and the detent torque of the stepping motor is reduced. Time lag is corrected using a GPS time signal.

Description

TECHNICAL FIELD

The present invention relates to an analog electronic timepiece having a step motion second function and a sweep motion second function.

BACKGROUND ART

Description will be made about methods in which step drive and sweep drive of a stepping motor mounted in a conventional analog electronic timepiece are executed in the analog electronic timepiece.

A configuration diagram of the stepping motor of the conventional analog electronic timepiece, illustrated in FIG. 9, will be described. A conventional stepping motor 9 is configured from a stepping motor 91 that includes a stator 91a composed of a coil 91e and a yoke 91b given a pair of slits 91c and a pair of inner notches 91d and does not have the detent torque, and a stepping motor 92 that includes a stator 92a composed of a coil 92e and a yoke 92b given a pair of slits 92c and a pair of inner notches 92d and does not have the detent torque. The stepping motor 91 and the stepping motor 92 share a rotor 93.

First, the step drive of the stepping motor 9 will be described. The magnetic pole direction of the rotor 93 is a direction 93a. The coil 91e is energized and subsequently the coil 92e is energized. Thereafter, the energization of the coil 91e is stopped and subsequently the coil 91e is energized in the reverse direction. Thereafter, the energization of the coil 92e is stopped and subsequently the coil 92e is energized in the reverse direction. Thereafter, the energization of the coil 91e is stopped and subsequently the energization of the coil 92e is stopped. Thereafter, the coil 92e is energized in the reverse direction for a short time. Through the above operation, the rotor 93 makes step rotation by 360 degrees in one second and the step movement of the seconds hand by one second is caused on the basis of a reduction gear train ratio of 1/60.

Next, the sweep drive of the stepping motor 9 will be described. The magnetic pole direction of the rotor 93 is the direction 93a. The coil 91e is energized by a continuous pulse and subsequently the coil 92e is energized by a continuous pulse. Thereafter, the energization of the coil 91e is stopped and subsequently the coil 91e is energized by a continuous pulse in the reverse direction. Thereafter, the energization of the coil 92e is stopped and subsequently the coil 92e is energized by a continuous pulse in the reverse direction. Thereafter, the energization of the coil 91e is stopped and subsequently the coil 91e is energized by a continuous pulse. Through the above operation, the rotor 93 makes sweep rotation by 360 degrees in one second and the sweep movement of the seconds hand by one second is caused on the basis of a reduction gear train ratio of 1/60.

The structure of a conventional stepping motor will be described with a plan view (a) and a sectional view along line A-A regarding the conventional stepping motor, illustrated in FIG. 7. The conventional stepping motor 7 is configured from a rotor 70 formed of a permanent magnet 70a with two poles and a stator 71 composed of a yoke 72 magnetically coupled to the permanent magnet 70a and a coil 73. In the yoke 72, a pair of steps 75a and 75b are formed in a detent torque generating part 75 in such a manner as to face a rotor hole 74.

A conventional rotor illustrated in FIG. 8 will be described. The conventional rotor 8 is composed of a rotor shaft 8a, a pinion 8b, and a permanent magnet 8c disposed on the rotor shaft 8a.

PRIOR ART DOCUMENT

Patent Documents

• Patent Document 1: JP-2013-122390-A
• Patent Document 2: JP-2017-046393-A

Non-Patent Document

• Non-patent Document 1: Akira Nikaido et al., The Institute of Electrical Engineers of Japan, MAG-77-23, (1977)

SUMMARY OF THE INVENTION

Problem to be Solved by the Invention

However, the conventional analog electronic timepiece involves a problem in the absence of shock resistance and the manufacturing cost because the two stepping motors that do not have the detent torque need to be used. Moreover, the sweep drive is open-controlled by the continuous pulse, and therefore involves a drawback that stability does not exist in the angular velocity of 2π (radians/second) regarding the rotor.

Means for Solving the Problem

In an analog electronic timepiece that has a step motion second function and a sweep motion second function, and executes step drive and sweep drive of a stepping motor configured from a rotor formed of a permanent magnet with two poles and a stator including a monolithic plate-shaped yoke having a rotor hole that the rotor enters, the yoke being magnetically coupled to the rotor, and a coil fixed to the yoke, in which the sweep motion second function is achieved by executing the sweep drive of the stepping motor by angular velocity control based on a stepping motor model. Load torque of the stepping motor model is corrected at every 180 degrees using angular velocity, the angular velocity being calculated by the stepping motor model, and a rotor angle at zero crossing of a back electromotive voltage generated across the coil.

Detent torque reducing coils for reducing detent torque are disposed at bridges near the rotor hole of the stator of the stepping motor, and a DC current is applied to the detent torque reducing coils and the detent torque is reduced at the time of the sweep drive.

The rotor of the stepping motor has an inertia.

The stepping motor is a stepping motor in which the yoke of the stepping motor includes a detent torque part including a structure that generates detent torque and a yoke part excluding the detent torque part, and the detent torque part is thinner than the yoke part and is located at a center of the yoke part in the thickness direction of the yoke part.

Immediately after the sweep motion second, a GPS time signal or a long-wave time signal is received and deviation of a seconds hand is corrected.

Advantage of the Invention

Step motion second and stable sweep motion second of the seconds hand can be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drive circuit diagram of a stepping motor according to the present invention.

FIG. 2 is a plan view (a) and a sectional view (b) along line A-A regarding the stepping motor according to the present invention.

FIG. 3 is a sectional view of a rotor of the stepping motor according to the present invention.

FIG. 4 is a time change diagram of set angular velocity (a), a sweep drive pulse (b), angular velocity (c), and an angle (d) according to the present invention.

FIG. 5 is a driver diagram according to the present invention.

FIG. 6 is a driver diagram of detent torque reducing coils according to the present invention.

FIG. 7 is a plan view (a) and a sectional view (b) along line A-A regarding a conventional stepping motor.

FIG. 8 is a sectional view of a rotor of the conventional stepping motor.

FIG. 9 is a configuration diagram of a stepping motor of a conventional analog electronic timepiece.

MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will be described in detail below based on the drawings.

Embodiment

In FIG. 2, a plan view (a) and a sectional view (b) along line A-A regarding a stepping motor according to the present invention are illustrated. The stepping motor according to the present invention is configured from a rotor 25 formed of a permanent magnet with two poles and a stator 21 composed of a coil 24 and a yoke 22. A detent torque part 23 of the yoke 22 is formed (23a) to be thinner than a yoke part 22c at the center of the yoke part 22c. A pair of detent torque reducing coils 2a and 2b for reducing the detent torque are disposed at bridges 22a and 22b, respectively, of the yoke 22 of the stator 21. At the time of sweep drive, as illustrated in FIG. 6, a DC current is applied from a p-type MOS 61 with a gate 61a to the detent torque reducing coils 2a (60a) and 2b (60b) connected in series in order to reduce the detent torque, and a DC magnetic field due to the DC current is in a clockwise direction 20a or 20b. Alternatively, it is also possible that the DC magnetic field be in an anticlockwise direction. The rotation direction of the rotor 25 is an anticlockwise direction 25a. Static angles 25b and 25c of the rotor 25 due to the detent torque and zero crossing angles 25d and 25e of a back electromotive voltage generated in a coil 17a of a stepping motor 17 illustrated in FIG. 1 are indicated.

A rotor of the stepping motor according to the present invention, illustrated in FIG. 3, will be described. A rotor 3 according to the present invention has a rotor shaft 3a, and the rotor shaft 3a is provided with an inertia 3d with a circular disc shape in addition to a pinion 3b and a permanent magnet 3c.

The embodiment of the present invention will be described with use of a drive circuit diagram of the stepping motor according to the present invention illustrated in FIG. 1, time change diagrams of set angular velocity (a), a sweep drive pulse (b), angular velocity (c), and an angle (d) according to the present invention illustrated in FIG. 4, a driver diagram according to the present invention illustrated in FIG. 5, and a driver diagram of the detent torque reducing coils according to the present invention illustrated in FIG. 6.

A drive circuit 1 of the stepping motor according to the present invention is configured from step drive/sweep drive switching means 10, and a sweep drive circuit 11 and step drive pulse generating means 12 that are switched by the step drive/sweep drive switching means 10, a driver A 16, and a driver B 20. Further, in FIG. 1, the stepping motor 17 (STM), the coil 17a, and detent torque reducing coils 20b and 20c connected in series are illustrated.

First, step drive will be described. The step drive pulse generating means 12 outputs a drive pulse 12a to the driver A 16 by the step drive/sweep drive switching means 10. A drive current is applied to the coil 17a for the STM 17 and the stepping motor STM 17 makes step rotation.

In FIG. 5, the driver A 16 illustrated in FIG. 1 is push-pull connected to a coil 50 (17a) by a p-type MOS 51 having a gate 51a, an n-type MOS 52 having a gate 52a, a p-type MOS 53 having a gate 53a, and an n-type MOS 54 having a gate 54a. In the step drive, at the time of drive-off, with respect to a power supply 55 and a ground 56, the gate 51a is at the low level and the p-type MOS 51 is turned on. Further, the gate 52a is at the low level and the n-type MOS 52 is turned off, the gate 53a is at the low level and the p-type MOS 53a is turned on, and the gate 54a is at the low level and the n-type MOS 54 is turned off.

Next, sweep drive will be described. Due to output of the step drive/sweep drive switching means 10, a set angular velocity/initial angle/initial drive pulse width command 13 of the sweep drive circuit 11 outputs an initial drive pulse width 13a, set angular velocity 13b, and an initial angle 13c. The initial angle 13c is decided through input of the output 12a of the step drive pulse generating means and determination of whether the static position is the static position 25b or 25c of the rotor 25 of a stepping motor 2 illustrated in FIG. 2 from the immediately-previous output 12a. Angular velocity 19b, an angle 19c, a drive current 19e, and a drive pulse width 142a are input to an STM model 19. The STM model 19 executes simulation in real time and outputs angular velocity 19a, the angle 19c, and a drive current 19d at a timing 42b immediately before the end of a pause period 42a of a sweep drive pulse in the sweep drive pulse (b) illustrated in FIG. 4, which is after a predetermined time from the drive pulse width 142a. The angular velocity 19a and the drive current 19d become the angular velocity 19b and the drive current 19e through LPFs (low-pass filters) 191 and 192, respectively. Meanwhile, the angular velocity 19a is input to a subtractor 141 and becomes a signal 141a through subtraction of the set angular velocity 13b. The signal 141a is input to a proportional integrator 15. In the proportional integrator 15, an output 15b of a proportional unit 15a having a proportionality constant KP and an output 15d of an integrator 15c having an integration constant KI are input to an adder 15e. An adder 142 adds an output 15f of the adder 15e and the initial drive pulse width 13a, and the sweep drive pulse width 142a is generated. The sweep drive pulse width 142a is input to the STM model 19 and simultaneously is input to a sweep drive pulse generating circuit 190 to which the angle 19s is input. The sweep drive pulse generating circuit 190 inputs, to the driver A 16, a sweep drive pulse 190a based on the sign of the sweep drive pulse width 142a and whether the angle 19c is in a range from 0 to π radians or in a range from π to 2π radians, and a drive current is applied to the coil 17a and sweep drive of the stepping motor STM 17 is caused.

Functions of the stepping motor STM model 19 will be described. At the time of the sweep drive pulse, the STM model 19 calculates the following two equations in real time.

$J·d^2\theta /{\mathrm{dt}}^2+r·d\theta /\mathrm{dt}=K·i·\sin \theta -\mathrm{Ts}·\sin \left\{2·\left(\theta -{\theta }_0\right)\right\}-T_L$ $L·\mathrm{di}/\mathrm{dt}+K·\sin \theta ·d\theta /\mathrm{dt}+R·i=V-\mathrm{Vs}\left(i\right)$

Here, in the former equation, J is the inertia moment of the rotor, θ is the rotor angle, t is the time, r is a friction coefficient, K is a torque constant, i is the coil current, Ts is a detent torque constant, θ₀ is the detent torque equilibrium stability angle of the rotor, and T_L is the load torque. In the latter equation, L is the self-inductance of the drive coil, K is a back electromotive voltage constant (same as the torque constant), R is the drive coil resistance, V is a supply voltage, and Vs(i) is the drop voltage of the drive MOS. The sign of the supply voltage V is determined depending on which combination is obtained from four combinations of the sign of the sweep drive pulse width 142a and whether the rotor angle θ is in a range from 0 to π radians or in a range from π to 2π radians.

At the time of stop of the drive pulse, the STM model 19 calculates the following two equations in real time.

$J·d^2\theta /{\mathrm{dt}}^2+r·d\theta /\mathrm{dt}=K·i·\sin \theta -\mathrm{Ts}·\sin \left\{2·\left(\theta -{\theta }_0\right)\right\}-T_L$ $L·\mathrm{di}/\mathrm{dt}+K·\sin \theta ·d\theta /\mathrm{dt}+\mathrm{Roff}·i=0$

Here, corresponding to turning-off of the driver A illustrated in FIG. 1, R is changed to Roff, and Rff is set to 10³ times of R, for example.

In the stop time of the sweep drive pulse width 142a, the gate 51a of the p-type MOS is at the high level, the gate 52a of the n-type MOS is at the low level, the gate 53a of the p-type MOS is at the high level, and the gate 54a of the n-type MOS 54 is at the low level. Thus, all MOSs are turned off. In the stop time of the drive pulse width 142a, zero crossing angle detection 18 detects the zero crossing angle from a back electromotive voltage generated across the coil 17a based on voltages 18a and 18b of both ends of the coil 17a, and inputs, to the STM model 19, a zero crossing angle 18c (the zero crossing angle 18c becomes either the angle 25d or 25e of the rotor 25 of the stepping motor 2 illustrated in FIG. 2, and is discriminated depending on which of the rising and the falling of the back electromotive voltage the zero crossing is obtained at) and corrects the load torque IL at every 180 degrees using the following expression.

$T_L=-J·d^2\theta /{\mathrm{dt}}^2-r·d\theta /\mathrm{dt}-\mathrm{Ts}·\sin \left\{2·\left(\theta -{\theta }_0\right)\right\}$

Next, the time change diagrams of the set angular velocity command (a), the sweep drive pulse (b), the angular velocity (c), and the angle (d) according to the present invention, illustrated in FIG. 4, will be described. In the angular velocity command (a), the set angular velocity command Wo 13a output by the set angular velocity/initial angle/initial drive pulse width command 13 of the sweep drive circuit 11 illustrated in FIG. 1 becomes n [radians/second] 41 because the reduction gear train ratio is set to 1/30. In the sweep drive pulse (b), the STM model 19 outputs the angular velocity 19a, the angle 19c, and the current 19d at the timing 42b immediately before the end of the stop period 42a of a sweep drive pulse sdp 42. In the angular velocity (c), the angular velocity ω exhibits a time change 43. At the angle at which the detent torque is generated, the angular velocity ω deviates from π [radians/second] and exhibits a mountain-shaped time change 43a. In the angle (d), the angle θ exhibits a time change 44 and a mountain-shaped time change 44a is caused at the angle at which the detent torque is generated. The control performance of the angular velocity at the time of sweep is approximately 1% of the set angular velocity command ω₀. Against losing or gaining of the seconds hand, a GPS time signal or a long-wave time signal is received to execute time correction as needed.

The inertia moment J of the rotor 3 according to the present invention, illustrated in FIG. 3, is set to approximately 60 times the inertia moment J of the conventional rotor. Furthermore, the steps 24a and 24b for generating the detent torque of the stepping motor 2 according to the present invention illustrated in FIG. 2 are set to ½ of the steps 75a and 75b, respectively, of the conventional stepping motor illustrated in FIG. 7. Moreover, the thickness of the part that generates the detent torque is set to 1/2.5 and the detent torque is set to approximately ⅕ of the detent torque of the conventional stepping motor 7. Furthermore, at the time of sweep drive, the gate 61 illustrated in FIG. 6 is set to the low level and the p-type MOS 61 is turned on to apply a DC current to the detent torque reducing coils 2a (20b, 60a) and 2b (20c, 60b) that are disposed at the bridges 22a and 22b of the yoke 22 and are connected in series. Thereby, a magnetic field is applied in the circumferential direction of the rotor hole and the detent torque is set to further ½. Thus, the detent torque is set to 1/10 of the detent torque of the conventional stepping motor 7 in total.

INDUSTRIAL APPLICABILITY

As illustrated by the above detailed description, according to the electronic timepiece of the present invention, step motion second and sweep motion second are possible with only one stepping motor compared with the conventional electronic timepiece using two stepping motors. As an analog electronic timepiece, a wrist watch, table clock, wall clock, or the like is possible.

DESCRIPTION OF REFERENCE CHARACTERS

• • 1: Drive circuit
  • 11: Sweep drive circuit
  • 12: Step drive pulse generating means
  • 19: STM model
  • 190: Sweep drive pulse generating circuit
  • 2, 7, 9, 17: Stepping motor
  • 3, 8, 25, 70, 93: Rotor
  • 21, 71, 91a, 92a: Stator
  • 22, 72, 91b, 92b: Yoke
  • 24, 50, 73, 91e, 92e: Coil
  • 2 a, 2b, 20b, 20c, 60a, 60b: Detent torque reducing coil
  • 23: Detent torque part
  • 24 a, 24b, 75a, 75b: Step
  • 91 d, 92d: Inner notch

Claims

1. An analog electronic timepiece that has a step motion second function and a sweep motion second function, and executes step drive and sweep drive of a stepping motor configured from a rotor formed of a permanent magnet with two poles and a stator including a monolithic plate-shaped yoke having a rotor hole that the rotor enters, the yoke being magnetically coupled to the rotor, and a coil fixed to the yoke, wherein the sweep motion second function is achieved by executing the sweep drive of the stepping motor by angular velocity control based on a stepping motor model.

2. The analog electronic timepiece according to claim 1, wherein load torque of the stepping motor model is corrected at every 180 degrees using angular velocity, the angular velocity being calculated by the stepping motor model, and a rotor angle at zero crossing of a back electromotive voltage generated across the coil.

3. The analog electronic timepiece according to claim 1, wherein detent torque reducing coils for reducing detent torque are disposed at bridges near the rotor hole of the stator of the stepping motor, anda DC current is applied to the detent torque reducing coils and the detent torque is reduced at time of the sweep drive.

4. The analog electronic timepiece according to claim 1, wherein the rotor of the stepping motor has an inertia.

5. The analog electronic timepiece according to claim 1, wherein the stepping motor is a stepping motor in which the yoke of the stepping motor includes a detent torque part including a structure that generates detent torque and a yoke part excluding the detent torque part, and the detent torque part is thinner than the yoke part and is located at a center of the yoke part in thickness direction of the yoke part.

6. The analog electronic timepiece according to claim 1, wherein, immediately after the sweep motion second, a GPS time signal or a long-wave time signal is received, and deviation of a seconds hand is corrected.