ELECTRONIC TIMEPIECE

Abstract: An electronic timepiece comprises an oscillator circuit (1) for generating an oscillating signal having a predetermined frequency, and a frequency divider circuit (2) responsive to the oscillating signal for supplying an output for intermittently driving a movable actuator (6). Storage means (7) are provided for storing kinetic energy of the actuator, together with means (10) for controlling release of the stored energy for smoothly driving a time keeping hand (9). Setting means (11) stop the time keeping hand during correction of the time displayed by the timepiece. The frequency divider circuit is arranged such that at least a portion thereof is held during time correction in the state prevailing immediately prior to time correction. This may be achieved by employing state holding means (3; 77; 75) for holding the at least a portion of the frequency divider circuit in said state during time correction. Alternatively, the frequency divider circuit may be arranged such that the at least a portion thereof is set in said state during time correction.

Description: The present invention relates to an electronic timepiece. When correcting a known step driven watch, the second hand is first brought to a halt by pulling out the winder stem whereby driving pulses for a stepping motor for advancing the hand are discontinued. After correction, movement of the hand is recommenced by pushing the winder stem back in, which results one second later in the driving pulses being generated again. If the second hand is stopped at the zero second position and the winder stem is pushed in synchronously with a time signal from a TV or the like, then the second hand will reflect the time accurately. As in the case of the known step driven watch, the correction of a known sweep driven watch involves stopping the second hand by pulling out the winder stem whereby motor driving pulses are discontinued, and subsequently re-starting the second hand by pushing in the winder stem to recommence generation of the motor driving pulses. An arrangement for setting a driving shaft and a driven shaft of a sweep driven watch, employing a magnetic mechanism and a viscous fluid device, is disclosed in Japanese published Patent No. JP-A-50 087 066. A further arrangement for setting a wheel train coupled to the driven shaft only is disclosed in Japanese Published Patent No. JP-A-62 161 581. In each case, motor driving pulses are generated one second after the time correction is complete if a motor driving frequency of 1 Hz is employed, and 1/N seconds after the correction is complete is the frequency is N Hz. A sweep driven watch operates on the following principle: First, an energy storage member, such as a hair spring or the like, is wound up by a stepping motor, and then the spring is allowed to uncoil whilst the torque generated by the spring is balanced with a load torque applied by a viscous fluid device or the like. In one known design, a rotor immersed in viscous oil generates a load torque which is proportional to the angular velocity of the rotor, and the load torque is arranged to increase according as the hair spring increases, and to decrease according as the torque of the spring decreases, thus keeping the uncoiling speed of the hair spring constant. The hair spring, in this instance, is connected to the second hand through a gear wheel train so that the second hand sweeps its path smoothly. Accordingly, in normal operation, the speed of the hair spring as it uncoils is held to a constant value whenever the stepping motor is driven at a predetermined period, and the torque of the uncoiling hair spring and the load torque of the rotor in the viscous oil are balanced at all times. However, in the prior art sweep driven watch, the balance between the torque of the uncoiling spring and the load torque of the rotor fluctuates temporarily if the periodicity of the energy supplied to the hair spring is disturbed, and so the angular velocity of the second hand changes. Then, when the periodicity of the energy supply is normalised by the stepping motor, the torque balance point is also returned to normal. However, the angular velocity variation of the second hand will now be expressed as a time deviation. This phenomenon is particularly conspicuous after time correction, as will be apparent from the following illustrative example. In a case where the driving frequency of the stepping motor is 1 Hz, let it be assumed that the winder stem is pulled out 0.8 seconds following generation of a respective motor driving pulse. The gear wheel train connected to the driven shaft of the hair spring halts, and the torque of the hair spring is held steady so long as the winder stem remains pulled out. If the winder stem is pushed in synchronously with a time signal or the like, the gear wheel train is released at the same time, and the hair spring uncoils gradually to start the second hand sweeping its path once more. The next motor driving pulse is generated one second after the time when the winder stem is pushed in. Therefore, the condition of the hair spring from the time of the motor driving pulse immediately before the winder stem was pulled out to the time of the motor driving pulse immediately after the winder stem was pushed in is such that the energy is not supplied thereto effectively for 1.8 seconds, when the duration of the time correction period is deducted. A normal energy supply period is one second and therefore in this case energy is not supplied for a further 0.8 seconds, which is why the torque balance fluctuates and the second hand goes temporarily slow. Eventually, the torque balance returns to normal but after a delay, which in this case is 0.8 seconds. Thus, accurate correction of the time is not achieved. As will be apparent from the above example, if the motor driving frequency is 1 Hz, then the delay produced by time correction will be a maximum of one second. However, in such a sweep driven watch, the motor driving frequency does not particularly need to be 1 Hz, and an arbitarary frequency may be selected according to circumstances in connection with a reduction ratio of the gear wheel train. Generally, if the motor driving frequency is N Hz, then the delay will be 1/N seconds at the longest, and the lower the frequency is, the more conspicuous the delay becomes. The present invention seeks to reduce such a problem, and to provide a sweep driven timepiece in which more accurate time correction is possible by keeping a more constant torque balance at the time of correction. According to the present invention, there is provided an electronic timepiece comprising an oscillator circuit for generating an oscillating signal having a predetermined frequency, a frequency divider circuit responsive to the oscillating signal for generating an output for intermittently driving a movable actuator, storage means for storing kinetic energy of the actuator, means for controlling release of the stored energy for smoothly driving a time keeping hand, and setting means for stopping the time keeping hand during correction of the time displayed by the timepiece, characterised in that the frequency divider circuit is arranged such that at least a portion thereof is held during time correction in the state prevailing immediately prior to the time correction. Preferably, state holding means are provided for holding the at least a portion of the frequency divider circuit in said state during time correction. For example, the state holding means may be in the form of a gate circuit for inhibiting the supply of the oscillating signal to the frequency divider circuit or for inhibiting the supply of a signal within the frequency divider circuit to the at least a portion which is held in said state during time correction. Alternatively, the state holding means may comprise a control circuit for stopping the oscillator circuit from generating the oscillating signal. Another aspect of the invention features an electronic timepiece comprising an oscillator circuit for generating an oscillating signal having a predetermined frequency, a frequency divider circuit responsive to the oscillating signal for generating driving pulses having a frequency of N Hz for intermittently driving a movable actuator, storage means for storing kinetic energy of the actuator, means for controlling the release of the stored energy for smoothly rotating a time keeping hand, and setting means for stopping the time keeping hand during correction of the time displayed by the timepiece, characterised in that the frequency divider circuit is arranged to be set to a predetermined state when the setting means are operated such that the driving pulse immediately following time correction is generated less than 1/N seconds after release of the setting means. A further aspect of the invention features an electronic timepiece provided with an oscillator circuit for generating an oscillating signal having a predetermined frequency, a frequency divider circuit responsive to the oscillating signal for generating driving pulses having a frequency of N Hz for intermittently driving a movable actuator, storage means for storing kinetic energy of the actuator, means for controlling release of the stored energy for smoothly driving a time keeping hand, and setting means for stopping the time keeping hand during correction of the time displayed by the timepiece, characterised by re-set means arranged to co-operate with the setting means for re-setting a part of the frequency divider circuit such that a driving signal having a frequency of N Hz is generated at a predetermined time after release of the re-set means, the setting means being arranged to be operated during time correction for longer than the re-set means. The invention will be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is block diagram of a sweep driven watch embodying the present invention; Figure 2 and Figure 3 are sectional views through a drive mechanism of the watch; Figure 4 is a plan view showing parts of the drive mechanism and a second hand setting lever; Figure 5 is a timing chart for the signals generated in the circuitry in Figure 1; Figure 6 (a) is a block diagram of a prior art circuit; Figure 6 (b) is a timing chart for the signals generated in the circuit of Figure 6 (a); Figure 7 (a) is a circuit diagram illustrating a modification of the circuitry shown in Figure 1; Figure 7 (b) is a timing chart for the signals generated in the circuitry of Figure 7 (a); Figure 8 is a circuit diagram illustrating another modification of the circuitry shown in Figure 1; Figure 9 is a circuit diagram illustrating another modification of the circuitry shown in Figure 1; Figure 10 is a circuit diagram illustrating a further modification of the circuitry shown in Figure 1; and Figure 11 is a plan view of a modified arrangement for the drive mechanism shown in Figure 4. Figure 1 is a block diagram of one embodiment of a sweep driven watch according to the invention having an oscillator circuit 1, which normally generates a standard signal ⊘ 32768 having a frequency of 32768 Hz and which has a miniature crystal oscillator as an oscillation source. A frequency divider circuit 2 generates a signal of a frequency appropriate for operating the hands of the watch by sequentially dividing the standard signal ⊘ 32768 received through an AND gate 3. A motor driving circuit 4 generates motor driving pulses according to a timing signal supplied by the frequency divider circuit 2 in order to drive a coil 5 for a stepping motor. In this embodiment, the motor driving pulses have a frequency set at 1 Hz. When a motor driving pulse is applied to the motor coil 5, a rotor 6 of the stepping motor rotates to wind up a hair spring 7. The hair spring 7 is connected to a second hand 9 through a gear wheel train 8 such that the second hand 9 moves on the uncoiling of the hair spring 7. At the same time, a load torque of a rotor 10 of a viscous oil device is transferred to the hair spring 7 through the wheel train 8. The torque of the uncoiling hair spring 7 and a load torque proportional to the velocity of the rotor 10 are balanced to allow the second hand 9 to sweep smoothly. Referring now to Figures 2 and 3, and Figure 4, a second hand drive mechanism of the watch includes a second hand setting lever 11 mounted on a base plate 201. The stepping motor comprises a stator 202, the coil 5 and the rotor 6, and the rotor 6 rotates through 180° once per second. The rotation of the rotor 6 is transferred to a hair spring wheel 206 through a fifth wheel 205. A driving wheel 206a and a driven wheel 206b of the hair spring wheel 206 are coupled together through the hair spring 7, the construction being such that a force operates so as to reduce their mutual turning angle. In this embodiment, a torque of 30 mg mm per rad of the mutual turning angle is generated. The rotational frequency of the hair spring wheel 206 is 2.8 rpm. An intermediate wheel 207 meshes with the driven wheel 206b, a rotor pinion 208a of the viscous oil device and a fourth wheel 209. The second hand 9 is fixed to the fourth wheel 209, and a minute hand 212 is fixed to a centre wheel 211. The centre wheel 211 comprises a centre pinion 211a and a centre gear 211b, which will slip mutually when a torque equal to or greater than a predetermined value is applied thereto. The fourth wheel 209 rotates at 1 rpm and, since a reduction ratio of 2.1 is set between the oil device rotor pinion 208a and the fourth wheel 209, the rotational frequency of the oil device rotor 10 is 2.1 rpm. The rotational frequency of the stepping motor rotor 6 is 30 rpm, and hence the reduction ratio between the rotor 6 and the rotor 10 is about 14. The oil device rotor 10 comprises the rotor pinion 208a, a rotor shaft 208b and a rotor plate 208c, the rotor plate 208c rotating within a cavity 213 closed by a cap 214. The cavity 213 is charged with silicone oil 215 and, when the rotor 10 rotates, a load proportional to the angular velocity thereof is applied to the rotor plate 208c by means of viscous friction. The clearance between the rotor plate 208c, the walls of the cavity 213 and the cap 214, and the viscosity of the silicone oil 215 are set so that the load will be about 40 mg mm when the rotor 10 rotates at 2.1 rpm. The cap 214 and a yoke 216 are made from materials of high magnetic permeability, whereas the rotor shaft 208b is made from carbon steel, and therefore a magnetic flux produced by a magnet 217 forms a magnetic circuit passing through the yoke 216, the rotor shaft 208b and the cap 214. A magnetic fluid 218 is drawn toward a space defined between the rotor core 208b and the cap 214, thus preventing the silicone oil 215 from leaking out of the cavity 213. By forming the cavity 213 within an engineering plastics housing, and by creating an interference fit between the cap 214 and the housing to prevent leakage of the silicone oil 215 between an outer periphery of the cap 214 and the housing, and further by using a material having a relatively small coefficient of thermal expansion, leakages due to a malfunction in the interference fit or a difference in expansion of the housing and the cap 214 as the result of the generation of high temperatures is prevented. Further, a centre hole in the cap 214 has a burred finish, thus functioning as a reservoir for the magnetic fluid 218. Stepwise rotation of the stepping motor rotor 6 is transferred to the driving wheel 206a through the fifth wheel 205. Since the torque of the hair spring and the load torque of the oil rotor device 10 are balanced, the driven wheel 206b is caused to rotate slowly at first. The torque stored in the hair spring 206c increases according to the difference in rotational frequency between the driving wheel 206a and the driven wheel 206b, and the rotational frequency of the driven wheel 206b increases until a constant speed of rotation as high as that of the driving wheel 206a is reached at about 2.8 rpm. In this case, the driven wheel 206b is wound up at about 1 rad relative to the driving wheel 206a, and the uncoiling force of the spring operates at 30 mg mm. The torque of the hair spring 7 changes before and after a winding action in accordance with step driving of the driving wheel 206a. However, since the load torque applied by the oil device rotor 10 changes in proportion to angular velocity, if the torque of the hair spring 7 increases tending to make the oil device rotor 10 turn faster, the viscous load increases to inhibit an increase of the angular velocity. Conversely, if the torque of the hair spring 7 decreases then the decrease in the angular velocity is also inhibited, whereby the oil device rotor 10 is capable of running at an almost constant speed. When the time displayed by the watch is to be corrected, the second hand setting lever 11 engages the intermediate wheel 207 and at the same time comes into contact with the re-set part of a circuit block whereby to stop the motor driving pulses from being supplied from an IC providing the motor driving circuit 4, and thus to stop rotation of the rotor 6. The torque applied by the rotor 6 and the stator 202 of a general stepping motor is about 30 mg mm, the torque of the hair spring 7 is 30 mg mm when the oil device rotor 10 rotates at 2.1 rpm, and the reduction ratio between the rotor 6 and the hair spring wheel 206 is about 11, and therefore the hair spring 7 maintains the wound condition reached before time correction. When time correction is completed, the driven wheel 206b is thus ready for rotation. A setting lever 220 engages within a groove in a winder stem 12, and a projection 220a of the lever is held in a slot 222a of a setting lever spring 222. A clutch wheel 223 having a square centre hole is mounted on the winder stem 12, which has a square shaft, and thus the clutch wheel 223 is movable longitudinally of but rotates integrally with the winder stem 12. A yoke 224 is subjected to a clockwise turning force by a spring 224a, and a wall 201a of the base plate 201 functions as a stop limiting movement of the yoke 224. The yoke 224 engages within a groove in the clutch wheel 223 to hold the clutch wheel 223 in position. The second hand setting lever 11 is held in position by the projection 220a of the setting lever 220. When the winder stem 12 is pulled out, the setting lever 220 is rotated clockwise, and the projection 220a is moved across a crest to a new locating position within the slot 222a of the setting lever spring 222. The yoke 224 is rotated counter-clockwise by a tail portion 220b of the setting lever 220, and the clutch wheel 223 advances concurrently to engage teeth of a setting wheel 225. The second hand setting lever 11 is rotated clockwise by the projection 220a of the setting lever 220, and comes into contact with the intermediate wheel 207 to stop rotation of the intermediate wheel 207. At the same time, a re-set spring 219a of the second hand setting lever 11 comes into contact with a re-set switch 246 of the circuit block (the state of contact not being indicated), and stops rotation of the stepping motor rotor 6. As described above, the hair spring 7 holds its angle in such a state, and thus the second hand can be rotated immediately time correction is completed. By rotating the winder stem 12 when it is pulled out, the clutch wheel 223 is made to rotate the setting wheel 225, and the minute hand 212 fixed on the centre pinion 211a can be corrected through a minute wheel 226. The centre wheel 211b is coupled to the intermediate wheel 207 through a third wheel 227 and a fourth wheel 209, and slips relative to the centre pinion 211a if the intermediate wheel 207 is not rotated so that the second hand 9 does not move during such correction. In this embodiment, the intermediate wheel 207 is held set. However, a similar effect is obtainable by setting any of the driven wheel 206b, the fourth wheel 209, the rotor 10, the third wheel 227 and the centre wheel 211b. An example for obtaining a normal rotational speed for the second hand after time correction will now be described. Referring to Figure 1, when the winder stem 12 is pulled out, the wheel train 8 is set by the second hand setting lever 11 as described hereinbefore, the torque of the hair spring 7 is held constant, and the re-set switch 246 is closed and a re-set terminal of a circuit board 228 receives a high level signal. In this case, an output Rs of a chattering prevention circuit 14 becomes high, and information that the watch is in a state ready for time correction is provided. This state is called the "re-set state" hereinafter. When Rs is low, an output of a NAND gate 15 becomes high and the output CL of the AND gate 3 is the signal ⊘ 32768 for input to the frequency divider circuit 2. However, when Rs becomes high, the output of the NAND gate 15 becomes low, CL also becomes low, and the count information at the point in time when RS became high is retained in the frequency divider circuit 2. A resistance 13 serves to hold Rs low when the re-set switch 246 is open. Figure 5 is a timing chart showing signals generated in the circuitry of Figure 1. Motor driving pulses are generated with a period of one second in the drive state when RS is low. The motor driving pulses are generated synchronously with the fall in the signal ⊘1 having a frequency of 1 Hz, generated by the frequency divider circuit 2. In the re-set state where Rs is high, CL becomes low, the frequency divider circuit 2 is locked, and the motor driving pulses are not generated. When the re-set state is released again, Rs is re-set to low, CL becomes the signal ⊘ 32768, the frequency divider circuit 2 starts counting. Since the count content of the frequency divider circuit 2 was retained at the time the re-set state commenced, counting continues from the count value present at the time the re-set state started. That is, in Figure 5, the sum of a time t₁ from the motor driving pulse immediately before the re-set state was actuated to the moment when Rs becomes high and a time t₂ from the release of the re-set state when Rs becomes low to the motor driving pulse immediately thereafter is kept at one second at all times. Thus, the period for collecting stored energy in the hair spring 7 remains accurately the same even during time correction, and time deviation after the correction may be kept to 0 seconds. The signal Ren in Figure 5 is a signal for preventing actuation of the re-set state when the motor driving pulses are generated, which signal is synchronised with the motor driving pulses generated from the motor driving circuit 4 of Figure 1. That is, when each motor driving pulse is generated, the signal Ren becomes low and the re-set state cannot be initiated by the NAND gate 15. If such a function is not provided, then the re-set state may commence during the generation of a motor driving pulse and the motor coil 5 may remain conductive throughout the re-set state, which is undesirable from the point of view of power consumption. If the re-set state is actuated when the signal Ren is low, the signal ⊘ 32768 is supplied to the frequency divider circuit 2 until generation of the motor driving pulse is over, and the frequency divider circuit 2 proceeds with counting until such time, and so no problems arise. In Figure 1, the AND gate 3 is provided after the oscillator circuit 1 for the input of the clock signal to the frequency divider circuit 2, and the clock input is inhibited during the re-set state. The circuit shown in Figure 8 features an alternative possibility. The parts shown in Figure 8 which are similar to those shown in Figure 1 are identified by the same reference numerals and will not be described. As shown in Figure 8, the oscillator circuit 1 is replaced by an oscillator circuit 71 having a crystal resonator 72 as an oscillation source, and an amplifying inverter 73 for generating an oscillating signal having a frequency of 32768 Hz. An inverter 74 serves for waveform shaping and generates an output ⊘ 32768 in the form of a square wave for input to the frequency divider circuit 2. A transistor 75 limits the power supply to the amplifying inverter 73 during the re-set state and, when the output of an AND gate 76 becomes high, the transistor 75 is turned off to stop the supply of the oscillating signal ⊘ 32768 to the frequency divider circuit 2. An internal count value within the frequency divider circuit 2 may thus be retained as in the embodiment of Figure 1. Figure 6 (a) is a block diagram of a prior art arrangement, wherein the same reference numerals are employed for parts which have already been described, and Figure 6 (b) is a timing chart for the signals generated therein. In this configuration, when a re-set state is actuated and Rs becomes high, the output of an AND gate 16 becomes high to re-set the frequency divider circuit 2, and thus the count values therein are all returned to their initial low value. The time from release of the re-set state to generation of the first motor driving pulse is one second as shown in Figure 6 (b). As a result, if the time from the motor driving pulse immediately before actuation of the re-set state to the re-set signal Rs becoming high is t₁, an effective interval between the two motor driving pulses before and after time correction, namely the overall interval less the time during which the hair spring 7 is set, will be 1 + t₁ seconds. Thus, the next period for collecting energy in the hair spring 7 is delayed by t₁ seconds, and while the second hand 9 begins to move immediately after release of the re-set state, its angular velocity drops transitorily as a result of the decrease in the energy stored in the hair spring 7, thus resulting in time deviation. The time lag t₁ will be one second at the longest and 0.5 seconds on average. An application of the present invention to the circuit shown in Figure 6 (a) will now be described with reference to Figure 9, wherein the same reference numerals are employed for parts which have already been described. The frequency divider circuit 2 comprises a plurality of 1/2 frequency dividers to a total of 15 stages. In the circuitry of Figure 9, the output of the AND gate 16 is applied to re-set inputs of the first 9 stages of the 1/2 frequency dividers, which generate a signal ⊘ 64 (64 Hz), and is supplied to an AND gate 77 by way of an inverter 78 for inhibiting supply of the signal ⊘ 64 to the next 6 stages of the 1/2 frequency dividers, which generate the signal ⊘1. In such a construction, each 1/2 frequency divider in the first 9 stages of the frequency divider circuit 2 is re-set to its initial low value at the time the re-set state is commenced, and each 1/2 frequency divider in the second 6 stages retains its count value at the time the re-set state is actuated. In this case, since the later stages of the frequency divider circuit 2, weighted by a predetermined amount, retain data, virtually no time lag will arise at the time of correction. That is, the portion which retains no data is the portion for generating frequencies higher than 64 Hz, and therefore any delay is kept from exceeding 1/64 seconds (15.6 msec), which is beyond human detection ability and hence is insignificant. Thus, a construction wherein data is retained only in the later stages of the frequency divider circuit is within the scope of the invention. In Figure 9, the construction is such that the data within the 1/2 frequency dividers for receiving the signal ⊘ 64 (64 Hz) is retained. However, a set of the 1/2 frequency dividers other than that shown may also be arranged to retain data within the scope of the invention. Further, the front stages of the frequency divider circuit 2 may alternatively be set to retain data, the AND gate 77 may be omitted and only some of the 1/2 frequency dividers in the front stages may be set to retain data. Such constructions are also effective, with the signal to the later stages being inhibited, to obtain an equivalent effect. For ease of inspection during the manufacturing process, shipping or the like, it is convenient for the frequency dividing circuit to be set to a predetermined value when the re-set state is actuated. The reason for this is that circuit inspection at the time of actuating the re-set state and checking of the motor driving pulses at the time of releasing the re-set state is facilitated thereby. Figure 10 shows an embodiment of the invention featuring a test circuit for carrying out such a requirement. Parts illustrated in Figure 10 which are similar to those shown in the other Figures are identified by the same reference numerals and will not be described further. In the state where nothing is connected to a test terminal 79, a "test" signal is pulled low by a resistance 80, and the output of an AND gate 81 is also low. That is, the output of the AND gate 81 remains low even during the re-set state and so the frequency divider circuit 2 is not re-set and the circuit operates in the same way as the circuit of Figure 1 during ordinary time correction. However, when the test terminal 71 is high and the re-set switch 246 is closed, since the "test" signal is high, the output of the AND gate 81 also becomes high and the frequency divider circuit is re-set. Thus, by applying a "test" signal to the test terminal only at the time of inspection, better inspection efficiency may be realised in the sweep driven watch of the invention. Figure 7 (a) is a circuit diagram of another modification of the circuitry shown in Figure 1, like parts being identified by the same reference numerals, and Figure 7 (b) is a timing chart for the signals generated therein. This embodiment combines re-setting of the frequency divider circuit during testing when the re-set state is initiated, which enhances inspection efficiency, and a decrease in time deviation during ordinary time correction. In Figure 7 (a) the output of the AND gate 16 becomes high in the re-set state, and the count content within a portion of the frequency divider circuit 2 is re-set. The frequency divider circuit 2 has a plurality of 1/2 frequency dividers connected in series and arranged such that only the 1/2 frequency divider for generating the signal ⊘1 is set to retain its count value while the other 1/2 frequency dividers are re-set. Thus, as shown in Figure 7 (b), the signal ⊘1 falls 0.5 seconds after release of the re-set state, and a motor driving pulse is consequently generated 0.5 seconds later. Accordingly, an effective interval between the two motor driving pulses before and after time correction is t₁ + 0.5 seconds, and since t₁ can be from 0 to 1 second in duration, variation of the period of one second for collecting energy in the hair spring 7 is ± 0.5 seconds, or 0 seconds on average. That is, time deviation following correction is 0 seconds on average, and 0.5 seconds at worst. This provides a substantial improvement as compared with a conventional case wherein the deviation is 0.5 seconds on average or one second at worst. Thus, a definite benefit is obtainable simply through modifying an initial value to which the frequency divider circuit 2 is re-set. However, the set/re-set combination of the 1/2 frequency dividers within the frequency divider circuit 2 need not necessarily be the same as shown in Figure 7. Instead of retaining the count value within just one of the frequency dividers during the re-set state, the count value may be retained in more than one of the dividers whereby the time from release of the re-set state to the generation of the next motor driving pulse will be still be shorter than one second. Accordingly, deviation occurring at the time of correction will be kept shorter than one second at the longest. Turning now to Figure 11, a modified arrangement for the second hand drive mechanism will be described. As shown in Figure 1, a hair spring 510 is arranged so as to be expanded in response to rotation of the hair spring wheel 509, and a nose formed by a bend 510a in the spring 510 is engaged within a groove 509c in the wheel 509 so that its diametrical position is regulated by a wall 509d. A viscous oil device rotor 514 subjected to a frictional load created by a viscous fluid 517 is used as a control means. The parts are mounted on a base plate 521, and further include a wheel train bearing 522, and a coil 501 for generating a magnetic field for driving a rotor 505 through a stator 504 and a magnetic core 502, which is fixed to the base plate 521 by a screw 503. A reduction ratio is obtained through a sixth pinion 506, a fifth gear 507 and a fifth pinion 508, which isolates the rotor 505 from the hair spring 510 to avoid any influence from the magnetic force and which drives the hair spring wheel 509, and thence a hair spring pinion 511 through the hair spring 510. A fourth wheel 515, to which the hands are coupled, is driven through a fourth idler 512, and an intermediate wheel 518 is connected to the viscous fluid device rotor 514 for braking the fourth wheel 515, thereby improving the adaptability of the layout. In this case, the hair spring pinion 511, the fourth idler 512 and the fourth wheel 515 are disposed linearly so as to prevent inclination of the axis of the fourth idler at the time of assembly. The fourth wheel 515, the intermediate wheel 518 and a rotor pinion 513 are also disposed linearly, likewise so as to prevent inclination of the axis of the intermediate wheel 518. A braking force from the rotor 514 and a driving force from the re-coiling hair spring 510 are both applied to the fourth wheel 515, and therefore it is preferable for the rotor connection and the hair spring connection to overlap each other in order to reduce variations in the torque as a result of changes in side pressure. On the other hand, it is preferable for both to be positioned opposite each other in order to minimise deflection of the hands. Accordingly, in the present embodiment, the construction is arranged such that both connections are almost orthogonal to each other, and the driving and braking forces operate in the same direction as a force applied to the fourth wheel 515 by a second hand setting lever 520 at the time of correction, thereby ensuring that a tenon is pushed in one direction only to suppress deflection of the hands. The hair spring gear 509 and the stator 504 are kept from overlapping each other by the fifth gear 507 and the fifth pinion 508, and the hair spring pinion 511, the fourth idler 512, the fourth wheel 515, the intermediate wheel 518 and the rotor pinion 513 are engaged in a row so as to avoid overlap and thereby realise a thin construction. By installing a hand on the hair spring pinion 511, the fourth idler 512, the intermediate wheel 518 or the rotor pinion 513, a small watch with a second hand can easily be constructed. A stud wheel 523 is provided for driving the hour hand, and a pinion 524 is engageable by a clutch wheel 537 in response to the action of a setting lever 531 and a yoke 530 under the control of a winder stem 532, for correcting the hour hand and the minute hand. A third wheel 525 is provided for decelerating the fourth wheel 515, with which the second hand engages, and for driving the minute hand. An integrated circuit 533 has an oscillator circuit incorporating a crystal resonator 535 as described above, and the integrated circuit 533 and the crystal resonator 535 supply motor driving pulses to the rotor 505 of the stepping motor through the coil 501 by way of circuitry on a board 534. The circuitry is powered by a battery 536. The reference numeral 541 denotes an axis of rotation of the second hand setting lever 520. A re-set terminal 540 for re-setting the integrated circuit 533 is connected to the positive terminal of the battery 536 and controls the supply of current to the coil 501 for stopping rotation of the rotor 505. A projection 539a connected to the positive terminal of the battery 536 and a circuit retainer 539, connect the second hand setting lever 520 to the positive side of the battery through a setting lever pivot 531a, the setting lever 531 and a guide dowel 531b. A contact 520a comes into contact with the re-set terminal 540, and a setting part 520b stops rotation of the fourth wheel 515 by engagement therewith. The setting lever 520 turns on the axis 541 under the influence of the guide boss 531b of the setting lever 531 when the winder stem 532 is pulled out in the direction indicated by an arrow, and thus the setting part 520b and the contact 520a are moved. Mechanical setting by the setting part 520b and electrical re-setting by the contact 520a are initiated concurrently so as to prevent the angle that the hair spring is wound from varying as a result of time correction. However, since it is very difficult to initiate both concurrently, the circuit may be designed to drive the stepping motor rotor soon after the release of the re-set state to allow the mechanical setting to be released without the hair spring re-coiling excessively and causing time deviation before the rotor is driven. On the other hand, in the case of a circuit in which the rotor is driven instantly at the time of release of the re-set state, the circuit timing must also be set so as to prevent time deviation due to excessive expansion of the hair spring at the time of correction. In order to correct any deviation between the re-set of the circuit and the mechanical timing, therefore, the rotor is preferably actuated at a time corresponding to one half a step after release, and the re-set timing is shifted in the circuitry so that any deviation in timing between re-setting and rotor driving is corrected at the time of start up. Another possibility if desired, is for the shape of the second hand setting lever to be altered to allow a difference in the stroke of the lever for bringing it into engagement with the wheel train and in the stroke of the lever for bringing it into contact with the re-set contact of the re-set switch. In this case, the wheel train is engaged first at the time of correction and the circuit is re-set with some delay, then the wheel train may be released with some delay after correction is completed. That is, the time during which the wheel train is engaged is longer than the time in which the circuit is in the re-set state, and so the effective interval between the two motor driving pulses generated before and after the time correction is reduced and any time lag is minimised. In the embodiments described, the second hand setting lever operates to set the fourth wheel. However, if time correction is carried out with energy stored in the hair spring, then the second hand is ready to move continuously at the time the setting is released and so any construction may be employed. Further, the hair spring wheel is turned intermittently, and so a frictional force is applied at the time of start up, thus starting the second hand in good condition. Additionally, in the described embodiments, the motor driving pulses are all supplied at a frequency of 1 Hz. However, an arbitrary motor driving pulse output frequency may be set to suit the reduction ratio of the wheel train leading to the second hand. The invention is not limited to such frequencies of 1 Hz only, since an equivalent effect may be obtained with arbitrary other frequencies. As described above, the periodicity of the energy supply to a hair spring is not disturbed, and a balance between the torque of the hair spring and a load torque of a viscous oil device rotor is maintained substantially constant at the time of correction through a simple construction comprising a gate for inhibiting a clock input to the frequency divider circuit at the time when correcting the sweep driven watch, or a switch element for cutting a power supply to the oscillator circuit so as to stop the oscillations of the oscillator circuit. Thus, the second hand is ready for continued sweeping at a normal rate immediately on pushing in the winder stem after the time correction is over. That is, a transient fluctuation in its angular velocity is prevented when the winder stem is pushed in, and an accurate time correction will be ensured. The effect is particularly conspicuous in a watch whose main function is time keeping, and the circuit load required therefor is minimised, which is advantageous. Further, as shown in Figure 10, the state of a frequency divider circuit can be set to a specific value at the time of correction simply by adding a test circuit, so that test conditions during inspection and shipping may be standardised and production efficiency will be enhanced.

Claims: An electronic timepiece comprising an oscillator circuit (1) for generating an oscillating signal having a predetermined frequency, a frequency divider circuit (2) responsive to the oscillating signal for generating an output for intermittently driving a movable actuator (6), storage means (7) for storing kinetic energy of the actuator, means (10) for controlling release of the stored energy for smoothly driving a time keeping hand, and setting means (11) for stopping the time keeping hand during correction of the time displayed by the timepiece, characterised in that the frequency divider circuit is arranged such that at least a portion thereof is held during time correction in the state prevailing immediately prior to the time correction. A timepiece according to claim 1, characterised by state holding means (3; 77; 75) for holding the at least a portion of the frequency divider circuit in said state during time correction. A timepiece according to claim 2, characterised in that the at least a portion of the frequency divider circuit includes a plurality of frequency dividers. A timepiece according to claim 2 or 3 characterised in that the state holding means comprise a gate circuit (3) for inhibiting the supply of the oscillating signal to the frequency divider circuit. A timepiece according to claim 2 or 3 characterised in that the state holding means comprise a gate circuit (77) for inhibiting the supply of a signal generated within a first portion of the frequency divider circuit to a second portion of the frequency divider circuit. A timepiece according to claim 2 or 3 characterised in that the state holding means comprise a control circuit (75) for stopping the oscillator circuit from generating the oscillating signal. A timepiece according to any of claims 2 to 6 characterised by means (246, 14, 15; 246, 14, 76; 246, 14, 16, 78) for operating the state holding means. A timepiece according to any of claims 2 to 7 characterised by means (79, 80, 81) for over-riding the state holding means to re-set the at least a portion of the frequency divider circuit. A timepiece according to claim 1 characterised in that the at least a portion of the frequency divider circuit is arranged to be set into said state during time correction. A timepiece according to any preceding claim characterised in that the storage means comprises a hair spring. A timepiece according to any preceding claim characterised in that the release controlling means comprises a rotor immersed in a viscous fluid. A timepiece according to any preceding claim which is a watch. An electronic timepiece comprising an oscillator circuit (1) for generating an oscillating signal having a predetermined frequency, a frequency divider circuit (2) responsive to the oscillating signal for generating driving pulses having a frequency of N Hz for intermittently driving a movable actuator (6), storage means (7) for storing kinetic energy of the actuator, means (10) for controlling the release of the stored energy for smoothly rotating a time keeping hand (9), and setting means (11) for stopping the time keeping hand during correction of the time displayed by the timepiece, characterised in that the frequency divider circuit is arranged to be set to a predetermined state when the setting means are operated such that the driving pulse immediately following time correction is generated less than 1/N seconds after release of the setting means. An electronic timepiece provided with an oscillator circuit (1) for generating an oscillating signal having a predetermined frequency, a frequency divider circuit (2) responsive to the oscillating signal for generating driving pulses having a frequency of N Hz for intermittently driving a movable actuator (6), storage means (7) for storing kinetic energy of the actuator, means (10) for controlling release of the stored energy for smoothly driving a time keeping hand (9), and setting means (11) for stopping the time keeping hand during correction of the time displayed by the timepiece, characterised by re-set means (246) arranged to co-operate with the setting means for re-setting a part of the frequency divider circuit such that a driving signal having a frequency of N Hz is generated at a predetermined time after release of the re-set means, the setting means being arranged to be operated during time correction for longer than the re-set means.

Inventors: HAYAKAWA, MOTOMU, MIYAZAWA, OSAMU, TAKAHASHI, OSAMU
Applicants: SEIKO EPSON CORPORATION
Application year: 1989
Main classification: G04C9
IPC codes: G04C9