Electronic Timepiece

1. Field of the Invention

This invention relates to an electronic timepiece which can effect the compensation operation with respect to external shock so as to prevent its erroneous operation.

2. Description of the Prior Art

Many attempts have been made to drive a step motor by a small power output under no load or light load and by a large power output under a heavy load. In this case, the load mainly consists of a solid resistance load such as a wheel train, week date feeding mechanism or the like and of a fluid resistance load such as oil or the like. The above mentioned attempts can compensate for these loads, but are insufficient in compensation action with respect to the external shock load and hence have the drawback that, when a step motor is reversely rotated by 1 step due, for example, to the reversely rotating shock, the timepiece is delayed by 2 seconds. As a result, in order to prevent the step motor from rotating in a reverse direction, the drag torque between the permanent magnet rotor and the stator can not be made too large. As a result, the power input required to rotate the rotor by 1 step for the purpose of making the potential energy large becomes large. Thus, it is impossible to reduce the electric power required for the electronic timepiece to a value smaller than a certain limit.

An object of the invention, therefore, is to provide an electronic timepiece which can eliminate the above mentioned drawbacks which have been encountered with the prior art techniques, which can effect the compensation action with respect to the shock load so as to stabilize the step operation of the motor, and which can further reduce the electric power to be consumed by the motor.

A feature of the invention is the provision in an electronic timepiece comprising a step motor composed of an electromagnetic coil excited by two phase alternating driving signals, a permanent magnet rotor and a stator, of the improvement comprising means for changing over said electromagnetic coil from a closed circuit condition to an open circuit condition and vice versa, means for detecting shocks and operative to detect an induced voltage to be generated in the electromagnetic coil when said rotor under its standstill condition is subjected to external shock, means for discriminating the shock direction by the difference between the output delivered from said shock detection means and the driving signal, and means for controlling the driving signal on the basis of the output delivered from said shock direction discriminating means.

Further objects and features of the invention will be fully understood from the following detailed description with reference to the accompanying drawings.

FIG. 1 is a block diagram of one embodiment of an electronic timepiece as a whole according to the invention;

FIG. 2 is a block diagram of another embodiment of an electronic timepiece as a whole combined with load detection and compensation circuits according to the invention;

FIG. 3 is a block diagram of essential parts of the electronic timepiece shown in FIG. 2;

FIG. 4 is a time chart illustrating outputs signals delivered from respective parts shown in FIG. 3 under the condition in which the step motor is subjected to the reversely rotating shock;

FIG. 5 is a time chart illustrating output signals delivered from respective parts shown in FIG. 3 under the condition in which the step motor is subjected to the forwardly rotating shock;

FIG. 6 is a time chart illustrating output signals delivered from respective parts shown in FIG. 3 under the condition in which the step motor is subjected to the reversely rotating shock immediately before generation of the normal driving signal;

FIG. 7 is a time chart illustrating output signals delivered from respective parts shown in FIG. 3 under the condition in which the step motor is subjected to the forwardly rotating shock immediately before generation of the normal driving signal;

FIGS. 8(1) and 8(2) are plan views of two examples of a step motor for electronic timepieces;

FIGS. 9(5) and 9(6) are plan views illustrating the conditions when the step motor is subjected to the shock;

FIGS. 9(1), 9(2), 9(3) and 9(4) are wave form diagrams showing induced voltage wave forms to be generated at one end of an electromagnetic coil;

FIGS. 10(5), 10(6), 10(1), 10(2), 10(3) and 10(4) are diagrams for illustrating the operation of a driving circuit when it is supplied with an electromagnetic coil switching signal; and

FIG. 11 is a wave form diagram illustrating induced voltage wave forms to be generated at the electromagnetic coil by means of the electromagnetic coil switching signal when the step motor is subjected to the shock.

FIG. 1 shows one embodiment of an electronic timepiece as a whole according to the invention. In FIG. 1, reference numeral 1 designates a crystal oscillation circuit operative to generate a signal to be used as a reference signal to the timepiece; 2 a frequency divider circuit composed of a multistage flipflop and operative to divide the frequency of the signal delivered from the crystal oscillation circuit 1 into 1 second signal required for the timepiece; 3 a signal conversion circuit operative to combine the outputs delivered from proper output stages of the frequency divider circuit 2 so as to generate a normal driving signal required under normal condition, a compensation driving signal for compensating an erroneous operation of a step motor when it is subjected to a reversely rotating shock, a delay driving signal operative, when the step motor is subjected to the shock immediately before generation of the normal driving signal, to delay the normal driving signal until the shock has ceased, a 2 phase high frequency signal operative to open or close an electromagnetic coil at a high speed, a signal showing difference in phase of the normal driving signal and any other signals required for detecting the shock, and 4 a driving circuit operative to be driven by the signal conversion circuit 3 and drive a step motor 5. The step motor 5 is connected through a transmission mechanism such as a wheel train or the like to a display means such as an hour hand, minute hand, second hand or the like, not shown in FIG. 1. Reference numeral 6 designates a shock detection circuit operative to detect the induced voltage generated in an electromagnetic coil 5a when the step motor is subjected to an external shock load during the period when the driving signal is supplied from the driving circuit 4 to the step motor 5 and throughout total duration except several milliseconds after the supply of the driving signal has been stopped and supply its output to a control circuit 7. The control circuit 7 functions to discriminate the direction of the shock on the basis of the signal delivered from the shock detection circuit 6 and the phase signal of the driving signal delivered from the signal conversion circuit 3 so as to generate a control signal which is supplied to the signal conversion circuit 3 and delay the driving signal and functions to generate a compensation driving signal if the step motor is subjected to the reversely rotating shock.

The invention will now be described in detail with reference to FIG. 3 which concretely shows essential parts of an electronic timepiece according to the invention.

In FIG. 3, reference numeral 21 designates a crystal oscillation circuit; 22 a frequency divider circuit which functions in the same manner as that shown in FIG. 1; 23 a signal conversion circuit composed of a normal driving signal generation circuit 23a, compensation driving signal generation circuit 23b, delay driving signal generation circuit 23c, electromagnetic coil switching signal generation circuit 23d, phase discrimination circuit 23e for the normal driving signal, selection gates 23f, 23g, NOR gates 23h, 23i, AND gates 23j, 23k, 23l, 23m, OR gates 23n, 23p, and inverters 23q, 23r. Each of these circuits function to generate a signal required for its role by means of a combination of the outputs delivered from the proper output stages of the frequency divider circuit 22. These signals can easily be generated, so that means for generating these signals are not shown in FIG. 3.

The normal driving signal generation circuit 23a generates alternately at every 1 second alternate pulse signals .phi..sub.1, .phi..sub.2, the output terminals for delivering these signals .phi..sub.1, .phi..sub.2 being properly connected to input terminals of the selection gates 23f, 23g.

The compensation driving signal generation circuit 23b generates a signal .phi..sub.3 required for the compensation driving operation when the step motor is subjected to the reversely rotating shock, the output terminal for delivering this signal .phi..sub.3 being connected to input terminals of the AND gates 23i, 23k whose respective output terminals are connected to respective input terminals of the selection gates 23f, 23g. This compensation driving signal .phi..sub.3 is set to be generated after the shock has ceased, so that its pulse width may be made equal to the pulse width of the normal driving signals .phi..sub.1, .phi..sub.2.

In the present embodiment, the pulse width of the normal driving signals .phi..sub.1, .phi..sub.2 and compensation driving signal .phi..sub.3 is set to a pulse width which is shorter than 5.9 m sec. In addition, each of these signals may be of a split pulse instead of a continuous pulse.

The output terminals of the selection gates 23f, 23g are connected to input terminals of the NOR gates 23h, 23i whose output terminals are connected to the input terminals of the AND gates 23s, 23t and to a driving circuit 24.

The delay driving signal generation circuit 23c generates a delayed driving signal .phi..sub.4 when the step motor is subjected to the shock immediately before the normal driving signal and after the shock has ceased. The output terminal of the delay driving signal generation circuit 23c is connected to input terminals of the AND gates 23l, 23m whose output terminals are the input terminals of the NOR gates 23h, 23i.

The electromagnetic coil switching signal generation circuit 23d generates a relatively high frequency continuous signal having a pulse width .omega..sub.1 such as signals .phi..sub.5, .phi..sub.6 shown in FIG. 4 and .phi..sub.10, .phi..sub.11 shown in FIGS. 10(6) and 11. The output terminals for delivering these signals .phi..sub.5, .phi..sub.6 are connected through the OR gates 23n, 23p to the AND gates 23s, 23t respectively.

The phase discrimination circuit 23e generates an output signal .phi..sub.7 corresponding to the normal driving signals .phi..sub.1, .phi..sub.2. The output terminal of the phase discrimination circuit 23e is connected to the input terminals of the AND gates 23k, 23l and a selection gate 27e of a control circuit 27 to be described later. In addition, the output terminal of the phase discrimination circuit 23e is connected through the inverter 23q to the other input terminals of the AND gates 23j, 23m and selection gate 27e whose output terminal is connected to the selection gates 23f, 23g and compensation driving signal generation circuit 23b.

The output terminal of an OR gate 27f of the control circuit 27 is connected to the input terminals of the OR gates 23n, 23p and delay driving signal generation circuit 23c.

In FIG. 3, reference numeral 24 designates a driving circuit including two P channel MOS transistors 24a, 24b and two N channel MOS transistors 24c, 24d. Drains of the MOS transistors 24a, 24c are connected with each other, while drains of the MOS transistors 24b, 24d are connected with each other. Sources of the MOS transistors 24a, 24b are connected in common to the plus terminal V.sub.DD of an electrical supply source and sources of the MOS transistors 24c, 24d are connected in common to the minus terminal V.sub.SS of the electrical supply source. The gates of the four MOS transistors 24a, 24b, 24c, 24d are separated one from the other and the gate of the MOS transistor 24a is connected to the output terminal of the NOR gate 23h provided in the signal conversion circuit 23. The gate of the MOS transistor 24b is connected to the output terminal of the NOR gate 23i provided in the signal conversion circuit 23, the gate of the MOS transistor 24c is connected to the output terminal of the AND gate 23s provided in signal conversion circuit 23 and the gate of the MOS transistor 24d is connected to the output terminal of the AND gate 23t.

In FIG. 3, reference numeral 25 designates an electromagnetic coil of the step motor having ends connected between common drains a.sub.o, b.sub.o of the driving circuit 24.

Reference numeral 26 shows a shock detection circuit composed of an inverter 26a having an input terminal connected to the common drain a.sub.o of the driving circuit 24, an inverter 26b having an input terminal connected to the output terminal of the inverter 26a, an AND gate 26e having an input terminal connected to the output terminal of the inverter 26b, an inverter 26c having an input terminal connected to the common drain b.sub.o of the driving circuit 24, an inverter 26d having an input terminal connected to the output terminal of the inverter 26c and an AND gate 26f having an input terminal connected to the output terminal of the inverter 26d. The output terminals of the AND gates 26e, 26f are connected to the input terminals of AND gates 27a, 27b.

The control circuit 27 is composed of the AND gates 27a, 27b, R-S flipflops 27c, 27d, the selection gate 27e and the OR gate 27f. The output terminal of the AND gate 27a is connected to the set terminal of the R-S flipflop 27c, the output terminal of the AND gate 27b is connected to the set terminal of the R-S flipflop 27d, the output terminal of the R-S flipflop 27c is connected to the selection gate 27e and to the input terminal of the OR gate 27f and the negation output terminal of the R-S flipflop 27c is connected to the input terminal of the AND gate 27b. The output terminal of the R-S flipflop 27d is connected to the selection gate 27e and to the other input terminal of the OR gate 27f and the not output terminal of the R-S flipflop 27d is connected to the input terminal of the AND gate 27a.

FIG. 4 shows a time chart at respective parts shown in FIG. 3 when the step motor is subjected to a reversely rotating shock at a time between the normal driving signals. Section I is a condition under which the shock load is absent and the outputs .phi..sub.14, .phi..sub.15 delivered from the shock detection circuit 26 are LOW (hereinafter will be called as L signals), so that the outputs .phi..sub.18, .phi..sub.19 delivered from the control circuit 27 are also the L signal. The NOR gate 23h of the signal conversion circuit 23 generates a reverse signal .phi..sub.8 of the normal driving signal .phi..sub.1, the reverse signal .phi..sub.8 being supplied to the gate of the MOS transistor 24a and to one of the input terminals of the AND gate 23s. To the other input terminal of the AND gate 23s is supplied the electromagnetic coil switching signal .phi..sub.5 so that the AND gate 23s generates a signal such as .phi..sub.10. Meanwhile, the output signal .phi..sub.9 delivered from the NOR gate 23i is a HIGH signal (hereinafter will be called as H signal) so that the electromagnetic switching signal .phi..sub.6 becomes the output signal .phi..sub.11 delivered from the AND gate 23t. If the signal .phi..sub.8 is changed over from the H signal to the L signal, the MOS transistors 24a, 24d shown in FIG. 3 become ON to cause current to flow through the electromagnetic coil 25 in a.sub.o .fwdarw.b.sub.o direction, thereby rotating the rotor in a given direction.

FIGS. 8(1) and 8(2) show a step motor for electronic timepieces used in general and composed of a stator 101, 102 and 201, 202; a rotor 103 and 203; and an electromagnetic coil 104 and 204. The pulse width of the driving signal .phi..sub.8 is set to t.sub.1 msec and the electromagnetic coil switching signal .phi..sub.10 is not generated during t.sub.2 msec after the driving pulse .phi..sub.8 has been supplied to the AND gate 23s. This is because of the fact that the shock detection circuit 26 does not detect the induced voltage due to the free oscillation of the rotor after it has been normally driven. If use is made of the duration t.sub.2 msec for the purpose of detecting the conventional wheel train load, a signal which becomes L signal during t.sub.1 +t.sub.2 msec is supplied to the AND gates 26e, 26f instead of their input signals .phi..sub.8, .phi..sub.9 so as not to generate during this time the shock detection outputs .phi..sub.14, .phi..sub.15.

FIG. 2 shows another embodiment of an electronic timepiece as a whole according to the present invention. The electronic timepiece shown in FIG. 2 is the same in connection and arrangement as that shown in FIG. 1, but further comprises a load detection circuit 15 connected in parallel with the shock detection circuit 13 in order to prevent the generation of the shock detection outputs .phi..sub.14, .phi..sub.15 during the time t.sub.1 +t.sub.2 msec. After the lapse of t.sub.2 msec, the electromagnetic coil switching signals .phi..sub.5, .phi..sub.6 are generated and supplied to respective input terminals of the AND gates 23s, 23t whose outputs .phi..sub.10, .phi..sub.11 are supplied to the gates of the MOS transistors 24c, 24d. The operation of the driving circuit 24 by means of the electromagnetic coil switching signals .phi..sub.5, .phi..sub.6 will be described later in detail.

In section II shown in FIG. 4, NOR gate 23i of the signal conversion circuit 23 generates a reverse signal .phi..sub.9 of the normal driving signal .phi..sub.2 which is supplied to the gate of the MOS transistor 24b and to one of the input terminals of the AND gate 23t. If the signal .phi..sub.9 is changed over from an H signal to an L signal, the MOS transistors 24b, 24c only shown in FIG. 3 become ON to cause current to flow the electromagnetic coil 25 in b.sub.o .fwdarw.a.sub.o direction, thereby rotating the rotor in a given direction. From t.sub.2 msec after the driving signal has been supplied, the electromagnetic coil switching signals .phi..sub.5, .phi..sub.6 are generated from the electromagnetic coil switching signal generation circuit 23d and supplied as respective outputs .phi..sub.10, .phi..sub.11 delivered from the AND gates 23s, 23t to the driving circuit 24.

FIG. 10 illustrates the operation of the driving circuit 24 by means of the electromagnetic coil switching signals .phi..sub.10, .phi..sub.11. The driving signals .phi..sub.8, .phi..sub.9 are H signals and the P channel MOS transistors 24a, 24b are OFF, so that it is sufficient to consider the operation of the N channel MOS transistors 24c, 24d.

Under the condition shown in FIG. 10(1), both the electromagnetic coil switching signals .phi..sub.10, .phi..sub.11 are H signals so that the transistors 24c, 24d become ON. The resistances under conduction conditions of the transistors 24c, 24d and the electromagnetic coil 25 form a closed circuit. Under such condition, if the step motor is subjected to shock, the movement of the rotor causes the induced voltage to be generated in the coil 25 to make current flow therethrough.

Under the condition shown in FIG. 10(2), the transistor 24d becomes OFF. Immediately before this condition, if current i flows through the electromagnetic coil 25, it generates the induced voltage L(di/dt) since the input impedance of the shock detection inverter 26c is considerably large, and as a result, it is possible to know that the step motor is under shock load.

Under the condition shown in FIG. 10(3), the electromagnetic coil 25 is connected in the closed circuit.

Under the condition shown in FIG. 10(4), the transistor 24c becomes OFF and the shock detection inverter 26a is set to be supplied with the induced voltage. The shock detection inverters 26c, 26a are alternately operated. This is because of the fact that the MOS transistors 24a, 24b, 24c, 24d have parasitic diodes 24e, 24f, 24g, 24h, respectively, (see FIG. 10(5)) and that lower than -0.3 V of the negatively induced voltage becomes clamped so that it is necessary to utilize the positively induced voltage only.

FIG. 11 shows the induced voltage in the electromagnetic coil 25. As shown in FIG. 11, the electromagnetic coil 25 generates at its terminal a.sub.o a signal .phi..sub.12 and at its terminal b.sub.o a signal .phi..sub.13 which is reverse with respect to the signal .phi..sub.12.

FIGS. 9(1), 9(2), 9(3) and 9(4) show envelopes of the waves of the induced voltage signal .phi..sub.12 viewed at the terminal a.sub.o of the electromagnetic coil 25. FIG. 9(1) shows the signal .phi..sub.12 generated when the step motor is subjected to a shock after the driving pulse .phi..sub.8 has been supplied to the driving circuit 24 and the step motor has rotated by 1 step and then come to a standstill. FIG. 9(2) shows the signal .phi..sub.12 generated when the step motor is subjected to a shock after the driving pulse .phi..sub.9 has been supplied to the driving circuit 24 and the step motor has rotated by 1 step and then came to a standstill. FIGS. 9(1) and 9(3) show forwardly rotating shock waves and FIGS. 9(2) and 9(4) show reversely rotating shock waves. The wave shown in FIG. 9(4) can be detected by the shock detection inverter 26a. The wave shown in FIG. 9(2) must be detected by the shock detection inverter 26c.

In the section II shown in FIG. 4, if the step motor is subjected to a reversely rotating shock, in the first place the output .phi..sub.14 is delivered from the shock detection circuit 26 and supplied to the input terminal of the AND gate 27a of the control circuit 27. In this case, the R-S flipflops 27c, 27d together with the outputs .phi..sub.16, .phi..sub.17 thereof are set to 0 and the not output .phi..sub.17 is the H signal. The signal .phi..sub.14 functions to set through the AND gate 27a the R-S flipflop 27c l. As a result, the not output .phi..sub.16 becomes the L signal so that the signal .phi..sub.15 can not pass through the AND gate 27b. As a result, the output .phi..sub.17 remains as the L signal.

That is, if the first positive direction voltage of the induced voltage due to a shock is detected by the inverter 26a, an not output .phi..sub.16 becomes the H signal. If the first positive direction voltage of the induced voltage due to the shock is detected by the inverter 26c, the signal .phi..sub.17 becomes the H signal.

The phase discrimination circuit 23e of the signal conversion circuit 23 is set so as to deliver an L signal output by means of the ordinary driving signal .phi..sub.8 and deliver an H signal output by means of the reversing signal .phi..sub.9. In this case, the reversing signal .phi..sub.9 causes the phase discrimination circuit 23e to deliver an H signal, so that the control circuit output .phi..sub.19 is generated, thereby showing that the step motor is subjected to an reversely rotating shock. The control circuit output .phi..sub.18 becomes an H signal during t.sub.5 m sec to cause the compensation driving signal generation circuit 23b to generate its output .phi..sub.3 which becomes the compensation driving signal which is in phase with the reversing signal .phi..sub.9. This compensation driving signal functions to correct the erroneous operation when the step motor becomes reversely rotated by the shock.

When the step motor is not reversely rotated, this compensation driving signal does not operate the rotor, so that there is no inconvenience.

After a shock has been detected, the electromagnetic switch signal can be stopped. In the present embodiment, in order to improve the stability of the electronic timepiece circuit, the OR gate output .phi..sub.19 of the control circuit 27 is set such that it becomes an H signal irrespective of the direction of shock after the shock has been detected and that the electromagnetic switching signal is prohibited during a given time.

FIG. 5 shows a time chart at respective parts shown in FIG. 3 when the step motor is subjected to a forwardly rotating shock at a time between the normal driving signals in a similar manner as that shown in FIG. 4. Contrary to the case shown in FIG. 4, the signal .phi..sub.15 becomes the first detection output and the signal .phi..sub.17 becomes an H signal. The output signal .phi..sub.18 delivered from the control circuit 27 remains as an L signal, and as a result, the compensation driving signal .phi..sub.3 is not generated. The output signal .phi..sub.19 becomes an H signal and the electromagnetic coil switching signal is prohibited for a given time.

If the step motor is subjected to a forwardly rotating shock, even when the rotor is forwardly rotated by 1 step, the rotor is not operated by the normal driving signal and the erroneous operation is compensated. As a result, it is not necessary to generate the compensation driving signal.

FIG. 6 shows a time chart at respective parts shown in FIG. 3 when the step motor is subjected to the reversely rotating shock immediately before the step motor is subjected to the normal driving signal .phi..sub.9. As shown in FIG. 6, in the first place, the output signal .phi..sub.15 is generated to make the output signal .phi..sub.17 of the R-S flipflop 27d an H signal. Since the not signal .phi..sub.7 of the output signal .phi..sub.7 delivered from the phase discrimination circuit 23e is also an H signal, the output signal .phi..sub.18 delivered from the control circuit 27 becomes an H signal. As a result, a compensation pulse is generated after the shock has ceased and the normal driving pulse .phi..sub.9 is delayed and then supplied to the driving circuit 24. As a result, it is possible to correct the erroneous operation of the step motor even when it is rotated in the reverse direction by the shock.

FIG. 7 shows a time chart at respective parts shown in FIG. 3 when the step motor is subjected to the forwardly rotating direction immediately before the step motor is subjected to the normal driving pulse .phi..sub.9. As shown in FIG. 7, the normal driving pulse .phi..sub.9 is delayed and supplied to the driving circuit after the shock has ceased.

As stated hereinbefore, the electronic timepiece according to the invention is capable of correcting the erroneous operation of the step motor by means of a compensation signal if the step motor is subjected to an external shock load in such direction that the shock tends to reversely rotate the step motor, of delaying the normal driving signal if the step motor is subjected to an external shock load immediately before the normal driving signal and hence preventing the erroneous operation of the step motor, thereby significantly improving the stability of the electronic timepiece, and decreasing the drag torque produced between the rotor and the stator of the step motor and hence decreasing the power input required for rotating the rotor by 1 step, thereby considerably reducing the consumed electric power.