Stepping motor control device and method thereof and timepiece

Abstract: This invention provides a control device and control method for achieving a small-sized long-life timepiece by further reducing power consumption of a stepping motor for driving the watch hands. If no rotor rotation is identified by rotation detection pulse SP2 following the first drive pulse P1, an auxiliary pulse P2 is applied. Then, in a following predetermined number of cycles (for example 3), a second drive pulse P11 is applied having an effective power several increment levels higher than the first drive pulse P1. This second drive pulse P11 drives the timepiece during temporarily increased load due to meshing tolerance etc. After completion of the three cycles, driving returns to the first drive pulse P1 having low-energy effective power. Accordingly, the level of the effective power of the first drive pulse can be maintained in a state reduced to the minimum level to achieve further reduction of power consumption.

Description: A stepping motor, which is sometimes also referred to as a pulse motor, an incremental movement motor or a digital motor, is a type of motor driven by pulse signals and often utilised as an actuator for digitally controlled devices. Recently, compact-sized electronic devices or information equipment have been developed which are suitable for portable use and small-sized light weight stepping motors have often been employed as actuators for those devices or equipment. Representative of such electronic devices are timepieces such as electronic watches, time switches and chronographs. FIG.7 illustrates an example of a timepiece such as a wristwatch including a stepping motor. The timepiece 9 is provided with a stepping motor 10, a control device 20 for driving the stepping motor 10, a gear train 50 for transmitting movement of the stepping motor, a second hand 61, a minute hand 62 and an hour hand 63 which are moved by the gear train 50. The stepping motor 10 is comprised of: a drive coil 11 for producing magnetic force by drive pulses applied from the control device 20; a stator 12 excited by the drive coil 11; and a rotor 13 rotated by magnetic field excited within the stator 12. The rotor 13 is constructed with a disc shaped two-poled permanent magnet to form a PM (Permanent Magnet) rotation type stepping motor 10. The stator 12 is provided with magnetic saturation parts 17 so as to generate opposite poles by the magnetic force produced by the drive coil 11 in each of phases (poles) 15 and 16, respectively, around the rotor 13. Also, in order to define the direction of rotation of the rotor 13, inside notches 18 are provided at appropriate positions on the inner periphery of the stator 12 for producing cogging torque so as to stop the rotor 13 at appropriate positions. The rotation of the rotor 13 is transmitted to each of the hands by the gear train 50 which is composed of: a fifth wheel 51 meshed with the rotor 13 via a spindle; a fourth wheel 52; a third wheel 53; a centre wheel 54; a minute wheel 55; and an hour wheel 56. A second hand 61 is mounted on a shaft of the fourth wheel 52. A minute hand 62 is mounted on the centre wheel 54 and an hour hand 63 is mounted on the hour wheel 56. Thus, time is displayed by means of those hands moving in synchronisation with the rotation of the rotor 13. Of course, it is possible to connect further transmission systems (not shown) for displaying day, month and year. In timepiece 9 driving pulses are periodically applied to stepping motor 10 by counting signals having a standard frequency (measuring time) in order to display time by rotation of the stepping motor 10. The control device 20 of this example for controlling the stepping motor 10 includes a pulse synthesising circuit 22 for generating standard pulses having a standard frequency or pulse signals having various pulse widths or timing by means of a standard oscillation source 21 such as a quartz crystal vibrator. Control device 20 also includes a control circuit 23 for controlling the stepping motor 10 in accordance with various pulses applied from the pulse synthesising circuit 22. The control circuit 23 is composed of a drive control circuit 24 for controlling a drive circuit and a detector circuit 25 for detecting rotation. The drive control circuit 24 is composed of: a drive pulse supply part 24a for supplying drive pulses to the drive coil 11 through the drive circuit for driving the rotor 13 to drive the stepping motor 10; a rotation-detecting pulse supply part 24b for producing, after the driving pulses, rotation-detecting pulses to induce induction voltage for detecting rotation of the driving rotor 13; an auxiliary pulse supply part 24c for producing auxiliary pulses having effective power larger than the rotation pulses when the driving rotor 13 fails to rotate; a degaussing pulse supply part 24d for producing, after the auxiliary pulses, degaussing pulses having opposite polarity to the auxiliary pulses for degaussing; and a level adjustment part 24e for adjusting the effective power of the driving pulses. The detecting circuit 25 is adapted to detect the presence or absence of rotation by comparing the induced voltage for rotation-detection obtained by rotation-detecting pulses with a predetermined value in order to feed the result of the detection back to the drive control circuit 24. The drive circuit 30 for supplying various drive pulses to the stepping motor 10 in accordance with control of the drive control circuit 24 includes a bridge circuit composed of series-connected p-channel MOS 33a and n-channel MOS 32b and p-channel MOS 33b and n-channel MOS 32a. It is adapted to enable control of power applied to the stepping motor 10 from a battery 41 by the MOSes. The drive circuit 30 is provided with resistors 35a and 35b for detecting rotation, each parallel-connected to p-channel MOS 33a and 33b, respectively, and series connected to p-channel MOS 34a and 34b. MOS 34a and 34b are for sampling and the arrangement is such as to apply chopper pulses to the resistors 35a and 35b. Accordingly, it is possible to apply drive pulses having opposite polarities or pulses for detecting rotation of the rotor 13 to the drive coil 11. This is achieved by applying control pulses having various polarities and pulse widths at respective timings to each of gates of the MOSes 32a, 32b, 33a, 33b, 34a and 34b from each of the pulse supply parts 24a to 24e of the drive control circuit 24. FIG. 8 illustrates the whole operation of the control device 20 in flow chart form. First, in step ST1 standard pulses for measuring time is counted to measure out one second. After passage of one second a drive pulse is produced in step ST2 controlled by drive pulse supply part 24a. Next, in step ST3 the rotation detecting pulse SP2 is produced under the control of the rotation detecting pulse supply part 24b for identifying rotation of the rotor 13 by comparing the voltage obtained with a predetermined value in the detection circuit 25. If rotation is not identified, a sub-routine is executed for rotating the rotor 13 without fail by utilising the auxiliary pulse. In this sub-routine, first in step ST4 the rotor 13 is rotated without fail by applying the auxiliary pulse P2 having a large effective power under the control of the auxiliary pulse supply part 24c. When the auxiliary pulse P2 is produced, the degaussing pulse PE is produced in step ST5 under the control of the degaussing pulse supply part 24d. Next in the level adjustment part 24e, effective power of the drive pulse P1 which is to be produced next is increased by one increment. Then, after execution of those steps, the operation returns to the main routine for executing the following processes. If in step ST3 rotation of the rotor 13 is confirmed, addition in a counter n is performed in step ST7 without executing the above sub-routine. Then, in step ST8, if the value in the counter n is less than the first predetermined value NO, the operation returns to the step ST1 to repeat the aforementioned steps. If the value in the counter n is equal to the first predetermined value NO, representing that the rotor 13 has rotated consecutively in a number of turns equal to the first predetermined value NO; in step ST9 the effective power of the next drive pulse P1 will be reduced by one increment by utilising the level adjustment part 24. Then, in step ST10 the counter n is cleared to 0 to make it ready for the next cycle. FIG. 9 illustrates a timing chart of the control signals to be applied to each of gates GP1, GN1 and GS1 of p-channel MOS 33a, n-channel MOS 32a and p-channel MOS 34a; in order to induce a magnetic field having a polarity of one direction in the drive coil 11. Fig. 9 also illustrates the control signals to be applied to each of gates GP2, GN2 and GS2 of p-channel MOS 33b, n-channel MOS 32b and p-channel MOS 34b; in order to induce a magnetic field having an opposite polarity in the drive coil 11. The device 20 for controlling the stepping motor is adapted to advance the hands once every second, to control the stepping motor 10 of timepiece 9 and to provide a train of the control signals cyclically to drive circuit 30. First, at time t1, a control signal for producing a drive pulse P1 having a pulse width W10, for example, is applied from the drive pulse supply part 24a of the drive control circuit 24. The signal is applied to the gate GN1 of the n-channel MOS 32a and to the gate GP1 of the p-channel MOS 33a on the side of the driving pole. Following the drive pulse P1, at time t2, a control pulse for producing the rotation detecting pulse SP2 to detect rotation of the rotor 13 is applied from the rotation detecting pulse supplying part 24b of the drive control circuit 24. This is applied to the gate GPI of p-channel MOS 33a and to the gate GS 1 of the MOS 34a on the side of the driving pole. The rotation detecting pulse SP2 is a chopping pulse having a duty cycle of about 1/2. It is adapted to obtain an induced current induced in the drive coil 11 as an output voltage of the rotation detecting resistor 35a, when the rotor 13 rotated. Then, the output voltage of the rotation detecting resistor 35a is compared with the predetermined value in the detection circuit 25 to identify whether the rotor 13 has rotated or not. If the voltage induced by the rotation detecting pulse SP2 does not reach the predetermined value, it is identified that the rotor 13 did not rotate and in step ST4 at time t3 a control pulse for producing the auxiliary pulse P2 is applied. The pulse P2 is applied from the auxiliary pulse supply part 24c of the drive control circuit 24 to the gate GN1 of the n-channel MOS 32a and to the gate GP1 of the p-channel MOS 33a on the side of the driving pole. The auxiliary pulse P2 is a drive pulse having a pulse width W20 with effective power larger than the drive pulse P1 containing energy sufficient to cause the rotor 13 to turn without fail. When the auxiliary pulse P2 is produced, next in step ST5 at time t4, a control pulse for producing the degaussing pulse PE is applied. Pulse PE is applied from the degaussing pulse supply part 24d of the drive control circuit 24 to the gate GN2 of n-channel MOS 32b and to the gate GP2 of the p-channel MOS 33b on the side of the opposite pole. This degaussing pulse PE is for reducing the residual magnetic flux of the stator 12 and the drive coil 11. This flux is produced by the auxiliary pulse P2 having larger effective power, the reduction being attained by applying a pulse having an opposite polarity to the auxiliary pulse P2. Upon application of the degaussing pulse PE, one cycle is completed of the train of operations for driving the stepping motor 10 by one increment of rotation angle. At time t11 after a lapse of one second from time t1, the next cycle starts for rotating the stepping motor 10 by one more increment of rotation angle. In this cycle the MOSes 32b, 33b and 34b which were in the opposite side in the previous cycle turn to be in the driving pole side. Similar to the previous cycle, first, at time t1 1 the drive pulse P1 is produced. But, as an auxiliary pulse P2 was produced in the previous cycle, a drive pulse P1 having effective power raised in one increment by the level adjustment part 24e is selected. A drive pulse P1 is produced at time t11, for example, having a pulse width W11 which is wider than that of the drive pulse in the previous cycle. Further, at time t12 a pulse SP2 for detecting rotation is produced. If no rotation of the rotor 13 is detected by this, then, at time t13, the auxiliary pulse P2 is produced and next at time t14 the degaussing pulse PE is produced. In the next cycle started at time t21, a drive pulse P1 having a much wider pulse width W12 is produced at time t21. Upon detection by the rotation detecting pulse SP2 produced at time t22 of rotation of the rotor 13 due to the drive pulse P1 having higher effective power, this cycle comes to an end. After the rotor 13 rotated by the predetermined number NO consecutively by the drive pulse P1 having the pulse width W12, a drive pulse P1 having one increment lower effective power, for example, having a pulse width W11 is produced in the next cycle starting from time t13. As described above, the level adjustment part 24e is adapted to select a drive pulse P1 having low effective power sufficient for driving rotationally the rotor 13 consecutively. This enables the provision of a small and thin timepiece 9 with long life span capable to perform accurate hands movement with low power consumption. Recently, the miniaturisation of the timepiece such as the wrist watch is advancing with reduced space for the battery, while longevity of the timepiece is extended. To attain these objects it is required to further reduce the power consumption of the stepping motor. Also, such a timepiece is developed as a wristwatch which can be driven without a battery by incorporating a generator for generating electricity in response to movement of a user's arm, etc. Since such a self-generating timepiece is required to have the capability of working long hours continuously even while it is left motionless without any generation of electricity; it is an important requirement to reduce power consumption of the stepping motor. The electrical energy of the drive pulse for driving the stepping motor is reduced by employment of the aforementioned control device or control method. However, the further detailed study conducted by the inventors of this invention reveals that in the cases where the auxiliary pulse is produced due to detection of non-rotation of the rotor caused by some amount of torque shortage, while the stepping motor has been rotated by a driving pulse with almost minimum level of torque; there are many cases where torque shortage takes place even when a drive pulse having one increment larger effective power is applied in the next cycle. Accordingly, once an auxiliary pulse is applied, continuous torque shortage takes place and in many cases only a single increment larger increase is not sufficient, causing such a drive pulse to be produced consecutively having two or three larger increments. Such result is thought to be caused by a large increase of meshing load due to minute variation of the positional relationship between wheel shafts and bearings or variation of meshing position between wheels. The wheels in a gear train undergo large torque variations when the auxiliary pulse is applied, after a drive pulse due to an error in hand movement. After an auxiliary pulse is applied and once a drive pulse energy level is raised by two or three increment levels, then the effective power level of the drive pulse drops by one increment after several turns. For example, with NO turns of rotation the drive pulse returns at last to the initial effective power level after an additional consecutive NO turns. However, if the meshing load increases during the above sequence, the level of the effective power again rises by one or two increments or further. Accordingly, even after the rotor has rotated consecutively to return the condition of the gear train to that before the auxiliary pulse is applied, thus reducing the torque necessary for rotation to a low level; the effective power of the drive pulse still remains at somewhat larger level, for example, one or two increments or more above the minimum required power. Also, study of causes of output of the auxiliary pulse reveals that in many cases problems were caused due to an accidental increase of the meshing load. Namely, since a gear train 50 for transmission of kinetic energy of the stepping motor 10 to hands is composed of a plurality of gear wheels, there can be cases where the meshing load increases periodically due to tolerances in manufacturing or the assembling process of these gear wheels. In the aforedescribed control method, the effective power of the drive pulse increases by one increment level, when the meshing load increases in even one increment of rotational angle, as the auxiliary pulse is produced. The effective power of the drive pulse would thus increase by two increment levels in the case that the meshing load increases during two increments of rotational angle in a given cycle of operation of the gear train. Further, if the condition of the gear train varies due to torque of the auxiliary pulse, larger torque still remains for two or three increments of rotation angle continuously. Accordingly, in the previous control device or method, even though a control method is employed which can apply a drive pulse having such effective power as is capable to apply the minimum required torque for rotating the rotor, in many instances in practice, a drive pulse is always applied which has an energy level several increment levels larger than necessary. GB 2094517A relates to improvements in or relating to stepping motor driven analogue timepieces. GB 2030734A describes a load measuring arrangement for a stepping motor. GB 2050005A relates to electronic timepieces having an analogue display driven by a stepping electric motor. Accordingly, it is an object of this invention to provide a control device and control method which is capable of further reducing the driving power of the stepping motor by applying drive pulses having an effective power as low as possible. A further object of this invention is to provide a control device and control method which can realise a smaller-sized long-life timepiece or such a self-generation type timepiece as is capable to keep time continuously even after being left motionless for many hours. According to a first aspect of the present invention, there is provided a device for controlling a stepping motor which is capable of rotatably driving a multi-poled rotor in co-operation with a stator having a drive coil, comprising: first driving means for applying a first drive pulse to said drive coil to rotate said rotor; rotation detection means for detecting whether said rotor is rotated by said first drive pulse or not; auxiliary means for applying an auxiliary pulse having an effective power larger than that of said first drive pulse when a rotation of said rotor is not detected; and level adjustment means for reducing the effective power of said first drive pulse incrementally after said rotor has rotated a first predetermined number of times consecutively, characterised by further comprising; second driving means for applying a second drive pulse after said auxiliary pulse is applied, the second drive pulse having an effective power level only one or several increments higher than the effective power level of said first drive pulse and the level of the second drive pulse being adjusted by said level adjusting means for a second predetermined number of times. According to a second aspect of the present invention, there is provided a device for controlling a stepping motor which is capable of rotatably driving a multi-poled rotor in co-operation with a stator having a drive coil, comprising: driving means for applying a first drive pulse to said drive coil to rotate said rotor; rotation detection means for detecting whether said rotor is rotated by said drive pulse or not; level adjustment means for reducing the effective power of said first drive pulse incrementally after said rotor has rotated a first predetermined number of times consecutively; auxiliary means for applying an auxiliary pulse having an effective power larger than that of said first drive pulse when rotation of said rotor is not detected; and degaussing pulse applying means for applying a degaussing pulse having an opposite polarity to the auxiliary pulse after the application of said auxiliary pulse, characterised by further comprising: delay means for delaying the application of the degaussing pulse until just before the next application of a drive pulse. According to a third aspect of the present invention, there is provided a method for controlling a stepping motor which is capable of rotatably driving a multi-poled rotor in co-operation with a stator having a drive coil, comprising: a first driving step for applying a first drive pulse to said drive coil to rotate said rotor; a rotation detection step for detecting whether said rotor is rotated by said first drive pulse or not; an auxiliary step for applying an auxiliary pulse having an effective power larger than that of said first drive pulse when rotation of said rotor is not detected; and a level adjustment step for reducing the effective power of said first drive pulse incrementally after said rotor has rotated a first predetermined number of times consecutively, characterised by further comprising: a second driving step for applying a second drive pulse after said auxiliary pulse is applied, the second drive pulse having an effective power level only one or several increments higher than the effective power level of said first drive pulse and the level of the second drive pulse being adjusted for a second predetermined number of times. According to a fourth aspect of the present invention, there is provided a method for controlling a stepping motor which is capable of rotatably driving a multi-poled rotor in co-operation with a stator having a drive coil, comprising: a driving step for applying a drive pulse to said drive coil to rotate said rotor ; a rotation detection step for detecting whether said rotor is rotated by said drive pulse or not; a level adjustment step for reducing the effective power of said first drive pulse incrementally after said rotor has rotated a first predetermined number of times consecutively; and an auxiliary step for applying an auxiliary pulse having an effective power larger than that of said drive pulse when rotation of said rotor is not detected, characterised by further comprising: a degaussing pulse applying step for applying a degaussing pulse having an opposite polarity to the auxiliary pulse after the application of said auxiliary pulse and just before the next application of a drive pulse. Embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which:- FIG. 1 is a drawing illustrating the general construction of a timepiece incorporating a stepping motor and a generation device in accordance with a first embodiment of the invention. FIG. 2 is a flow chart illustrating the control method of the control device shown in FIG. 1. FIG. 3 is a timing chart illustrating the operation of the control device shown in FIG. 1. FIG. 4 is a drawing illustrating the general construction of a timepiece incorporating a stepping motor and a generation device in accordance with a second embodiment of the invention. FIG. 5 is a flow chart illustrating the control method of the control device shown in FIG. 4. FIG. 6 is a timing chart illustrating the operation of the control device shown in FIG. 4. FIG. 7 is a drawing illustrating the general construction of a conventional timepiece. FIG. 8 is a flow chart illustrating the control method of the control device shown in FIG. 7. FIG. 9 is a timing chart illustrating the operation of the control device employed in the timepiece shown in FIG. 7. To attain the objects of the invention, this invention is adapted to apply a drive pulse having a somewhat larger effective power only for predetermined periods after the auxiliary pulse is produced. Also, it is adapted to apply drive pulse having a predetermined lower effective power after that period instead of increasing the effective power of drive pulse in a constant manner when the auxiliary pulse is applied. In many instances the torque would become lower during several turns of rotor rotation as the meshing load returns to the initial state, even in the case of increased meshing load due to application of the auxiliary pulse following the drive pulse. Also, in many instances, increase of the meshing load due to wheel gear tolerance is limited to take place only during one or several increments of rotation angle. Namely, the device of this invention for controlling a stepping motor, which is capable of rotatably driving a multi-poled rotor within a stator having a drive coil, is adapted to provide a second driving means for applying a second drive pulse having an effective power level one or several increments higher than the effective power level of a first drive pulse. The level of the second drive pulse is adjusted by a level adjustment means by a second predetermined number of times after the auxiliary pulse is applied. This is in addition to: a first driving means for applying the first drive pulse to the drive coil to rotate the rotor; a rotation detection means for detecting whether the rotor is rotated by the first drive pulse or not; an auxiliary means for applying the auxiliary pulse having the effective power larger than that of the first drive pulse, when a rotor rotation is not detected; and a level adjustment means for reducing the effective power of the first drive pulse incrementally after the rotor has rotated a first predetermined number of times consecutively. The second drive means is adapted to control the effective power of the drive pulse by varying pulse width of the drive pulse or by varying the voltage of the drive pulse. Also, the method of this invention is adapted to provide a second driving step for applying a second drive pulse having an effective power level one or several increments higher than the effective power level of a first drive pulse. The level of the second drive pulse is adjusted in a level adjustment step by a second predetermined number of times after the auxiliary pulse is applied. This is in addition to: a first driving step for applying the first drive pulse to the drive coil to rotate the rotor; a rotation detection step for detecting whether the rotor is rotated by the first drive pulse or not; an auxiliary step for applying the auxiliary pulse having an effective power larger than that of the first drive pulse, when a rotor rotation is not detected; and a level adjustment step for reducing the effective power of the first drive pulse incrementally after the rotor has rotated a first predetermined number of times consecutively. By providing such a second drive means or a second drive step as stated above, it is possible to deal with situations which require a drive pulse having a larger effective power for only a short while due to increased meshing load of the gear train without increasing the effective power of the first drive pulse. The effective power of the first drive pulse is reduced based on the actual result of consecutive rotation of the rotor. Accordingly, it is possible to attain a further reduction in power consumption of the stepping motor. That is, it is sufficient to apply the first drive pulse having a predetermined minimum required energy level in the time period in which hands can be moved by a drive pulse having a smaller effective power. Nonetheless, a state of applying the auxiliary pulse consecutively, which tends to result in large increase of power consumption, can be prevented. That is, the second drive pulse having a larger effective power is applied following to the auxiliary pulse in an increment of rotor rotation angle in which the load is increased. Considering the fact that it is only in a very short period as one or several incremental periods of rotor rotation angle that require a drive pulse having a large effective power, as a result of increased meshing load due to aforementioned causes; it is possible to cope with a period of large meshing load by bringing the timing of application of a degaussing pulse to just before the next drive pulse, to thus increase substantially the effective power of the drive pulse. Namely, in the device of this invention for controlling the stepping motor, it is effective to provide a means for applying a degaussing pulse, having an opposite polarity to the auxiliary pulse after the application of the auxiliary pulse, just before the next drive pulse. This is in addition to: a driving means for applying the drive pulse to rotate said rotor against the drive coil; a rotation detection means for detecting whether the rotor is rotated by the drive pulse or not; a level adjustment means for reducing the effective power of the first drive pulse incrementally after the rotor has rotated a first predetermined number of times consecutively; and an auxiliary means for applying the auxiliary pulse having an effective power larger than that of the drive pulse when rotor rotation is not detected. Also, in the method of this invention for controlling the stepping motor, it is effective to provide a step for applying a degaussing pulse, having an opposite polarity to the auxiliary pulse, after the application of the auxiliary pulse and just before the next drive pulse. This is in addition to: a driving step for applying the drive pulse to rotate said rotor against the drive coil; a rotation detection step for detecting whether the rotor is rotated by the drive pulse or not; a level adjustment step for reducing the effective power of the first drive pulse incrementally after the rotor has rotated a first predetermined number of times consecutively; and an auxiliary step for applying the auxiliary pulse having an effective power larger than that of the drive pulse when rotor rotation is not detected. By providing such means for applying a degaussing pulse or such a step for applying a degaussing pulse, it is possible to apply a drive pulse having substantially larger effective power after the auxiliary pulse without unnecessary power consumption. Accordingly, in other timing periods than those having increased meshing load, it is possible to apply a drive pulse having the effective power reduced to the minimum required level. Thus, it is possible to provide a device and method for control which can drive the stepping motor without fail and further reduce power consumption. As stated above, it is possible to provide a small sized high precision long life timepiece with minimal power consumption by realising a timepiece which is provided with the control device of this invention. Also, it is possible to realise a timepiece which is capable of consecutively driving the watch hands for many hours even if it is left motionless, by employing the device and method for control of this invention in a timepiece incorporating a power generating device. Also, it is possible to provide the method of this invention for controlling a stepping motor in the form of a logic circuit or a recording on a medium readable by a computer such as a program for controlling a microprocessor. It is possible to apply it not only to a timepiece but also to any device which requires the driving of a motor with low power consumption with high precision. First Example Referring the drawings the invention will be further described in detail as follows: FIG.1 illustrates the general construction of a timepiece 1 in accordance with the first example of the invention. The timepiece 1 drives a stepping motor 10 by a control device 20. It is adapted to move watch hands by transmitting the movement of the stepping motor 10 to a second hand 61, a minute hand 62 and an hour hand 63 via a gear train 50. The general construction of the stepping motor 10, the gear train 50 and the control device 20 is the same as those described in FIG. 7. Thus, like reference characters are utilised to denote like elements and detailed description thereof is omitted hereafter. The control circuit 23 employed in the control device 20 of the timepiece 1 of this example is also provided with a drive control circuit 24 and a detector circuit 25. The drive control circuit 24 is composed of: a first drive pulse supply part 24a for supplying the drive pulse P1 to the drive coil 11 through the drive circuit 30; a rotation-detecting pulse supply part 24b for producing, after the driving pulses, the rotation-detecting pulse SP2; an auxiliary pulse supply part 24c for producing the auxiliary pulse having larger effective power than the drive pulse; a degaussing pulse supply part 24d for producing, after the auxiliary pulses, the degaussing pulse PE; a level adjustment part 24e with capability for controlling the effective power of the driving pulse P1; and a second drive pulse supply part 24f which is capable of supplying the second drive pulse P11 having an effective power larger than the drive pulse P1 supplied from the first drive pulse supply part 24a. The second drive pulse supply part 24f is adapted to apply a second drive pulse P11 having an effective power several levels larger than the first drive pulse P1 for a second predetermined number of times (a cycle of MO times in the example) consecutively after the auxiliary pulse. Also, the timepiece 1 of the invention is adapted to apply electrical power from a battery 41 to the drive circuit 30 of the control device 20 through a voltage step-up step-down circuit 49. The voltage step-up step-down circuit 49 is adapted to perform multi-stepped step-up and step-down utilising a plurality of capacitors 49a, 49b and 49c. This provides the control voltage applied to the drive circuit 30 by the control signal  11 from the drive control circuit 24 of the control device 20. Also, the output voltage of the voltage step-up step-down circuit 49 is adapted to be applied to the drive control circuit 24 through a monitor circuit connected at 12, so as to monitor the output voltage. Accordingly, the effective power of the first drive pulse P1 and the second drive pulse P11 is determined by controlling the voltage step-up step-down circuit 49 by the level adjustment part 24e. It is possible to control the effective power of the first drive pulse P1 and the second drive pulse P11 by means of pulse width and voltage. Thus, it is possible to perform fine control of the drive power to realise power conservation by applying drive pulses having suitable power for rotating the rotor 13. FIG. 2 illustrates generally, in a flow chart, the method for controlling a stepping motor employed in the timepiece of the example. In this flow chart, the same steps as those described in FIG. 8 are denoted by like reference characters and detailed description thereof is omitted hereafter. First, in step ST1 one second is measured to move the hands. In the control device 20, next executed in step ST2 is identification of whether the value of a counter m has reached the second predetermined number MO or not. If the value of the counter m has reached the second predetermined number MO, the process advances to step ST2 to apply the drive pulse P1 in accordance with the control of the first drive pulse supply part 24a. On the other hand, if the counter m has not reached the second predetermined number MO, the process advances to step ST12 to output the second drive pulse P11 having a larger effective power, in accordance with control of the second drive pulse supply part 24f, in place of the first drive pulse P1. Then, in step ST13 addition to the count of counter m is executed. An auxiliary pulse P2 is applied in many cases in such time period having low efficiency due to poor meshing condition of the gear train caused by assembly tolerances, etc. The number of increments of rotation angle of the rotor in which the meshing load is increased due to the aforementioned reason is in most cases limited to one increment or several increments at the longest. Even if the meshing load increases due to a change in condition of the gear train caused by application of the auxiliary pulse P2, the meshing load would, in many cases, return to the initial lower level after several rotations of the rotor. Thus, it is possible to cope with such periods having the increased meshing load by applying the second drive pulse P11 having somewhat larger effective power, following the auxiliary pulse P2. After that it is possible to perform normal hands movement by the first drive pulse P1 having the smaller effective power previously applied. After application of the first or second drive pulse P1 or P11, a detector pulse SP2 is applied in step ST3 by the rotation detecting pulse supply part 24b. This is to identify the presence or absence of the normal rotor rotation by the detection circuit 25. Then, if the rotor 13 is found not to have rotated, the auxiliary pulse P2 is applied in step ST4 by the auxiliary pulse supply part 24c. Next in step ST5 the degaussing pulse PE is applied by the degaussing pulse supply part 24d. Further, in step ST6 the effective power of drive pulse is raised by one increment level. Thereafter, counter m for outputting the second drive pulse P11 is initialised in step ST15 to output the second drive pulse P11 in the next cycle. On the other hand, if in step ST3 the rotation of the rotor 13 is identified, the counter n of the first drive pulse P1 is increased in step ST7. Then, in step ST8, comparison is made with the first predetermined number NO for reducing the effective power of the first drive pulse P1. If the value in the counter n is equal to the first predetermined number NO, in step ST9 the effective power of the first drive pulse P1 is reduced by one increment. Then, the counter n is initialised in step ST10. FIG. 3 is a timing chart for the drive pulses applied to the stepping motor 10 from the control device of this embodiment. In FIG. 3, similar to FIG.9 previously explained, illustrates the control signals to be applied to each of gates GP1, GN1 and GS1 of p-channel MOS 33a, n-channel MOS 32a and p-channel MOS 34a in order to excite a magnetic field having a polarity of a certain direction (drive pole side) in the drive coil 11. Also illustrated are the drive pulses to be applied to each of gates GP2, GN2 and GS2 of p-channel MOS 33b, n-channel MOS 32b and p-channel MOS 34b in order to excite a magnetic field having a polarity of reverse direction as opposed to that of the drive side pole in the drive coil 11. Similar reference characters are utilised to denote similar elements as those in FIG. 9 and detailed description thereof is omitted hereafter. First, when time has lapsed in step ST1 of the aforedescribed flow chart, the first drive pulse P1 having a voltage V10 is outputted at time t41 to start the first cycle; as the auxiliary pulse P2 has yet to be output and, also, the value of the counter m has reached the second predetermined number MO. Next, at time t42 in step ST3, the rotation detecting pulse SP2 is output and if, no rotation is detected, the auxiliary pulse P2 is output at time t43 in step ST4. Upon output of the auxiliary pulse P2 a degaussing pulse PE is output at time t44 in step ST5, to complete one cycle. After a one second lapse from time t41 the next cycle is started. Since the auxiliary pulse P2 is output in the previous cycle, the counter m is cleared to 0. Since, in this cycle the value of the counter m has yet to reach the second predetermined number MO, a second drive pulse P11 having effective power levelled-up or larger than the first drive pulse P1 is produced at time t51 in step ST 12. As the timepiece of this example is adapted to adjust the voltage in the voltage step-up step-down circuit 49, a drive pulse having a voltage V11 higher than V10 is produced as the second drive pulse P11 at time t51. The voltage of a pulse to be applied to the stepping motor 10 from the drive circuit 30 is determined by controlling the voltage applied from the voltage step-up step-down circuit 49. But, to make the description simple, the voltages of the drive pulses are indicated with those of pulses for control shown in the timing chart. Following the second drive pulse P11, the rotation detecting pulse SP2 is applied at time t52 in step ST3 to identify rotation of the rotor 13. Similarly in the next cycle, the second drive pulse P11 is applied at time t61 and the rotation detecting pulse SP2 is applied at time t62. Further, in the next cycle the second drive pulse P11 is applied at time t71 and the rotation detecting pulse SP2 is applied at time t72. In the timepiece 1 of this example the second predetermined number MO is set at 3 and in the next cycle starting from time t81 the counter m of the second drive pulse P11 becomes 3. Accordingly, in the next cycle starting from time t81 the process advances from step ST11 to step ST2 to apply, at time t81, a first drive pulse P1 having a voltage V10'. Voltage V10' has an effective power one level higher than that in the previous cycle in which the auxiliary pulse P2 (at time t43) was applied. As stated above, when the load for driving the rotor 13 becomes higher and the auxiliary pulse P2 is applied, the conventional control device 20 is adapted to deal with such a condition by raising the effective power of the drive pulse (in this example, the first drive pulse) P1 incrementally by one level each time. But, the control device 20 employed in the timepiece of this example is adapted to deal with the condition of higher loads by first increasing the effective power of the first drive pulse P1 by one level, then next applying the second drive pulse P11 having an effective power one or several increment higher than that of the first drive pulse P1. As described before, most of the primary cause of load increase of the rotor 13 is the increased meshing load of the gear train due to minute dimensional irregularities in production or assembly processes. Further, most of the cause of continued higher load condition of the rotor 13 is due to continued higher load condition of the meshing load caused by tolerance or due to somewhat varied meshing condition from the time of smaller torque drive pulse caused by application of the larger torque auxiliary pulse. As a result such conditions often takes place cyclically but it tends to return, after several consecutive rotor rotations, to the initial condition in which the rotor can be rotated by the initial torque. Thus, the number of incremental rotational angles is small which require pulses having larger effective power due to increased load. Accordingly, as is shown in this example, it is possible to drive trough the incremental rotational angles having larger load without rotation error by applying drive pulses P11 having somewhat higher effective power than that of the drive pulse P1 normally applied following the auxiliary pulse P2. Further, since there is no need to apply the auxiliary pulses having very large torque consecutively, it is possible to return the condition of the gear train earlier, while reducing power consumption at the same time. After passing the incremental rotation angles having increased meshing load, it is possible to drive the rotor 13 by applying the drive pulse P1 with minimum effective power. Accordingly, it is possible to avoid such a situation as occurs in the conventional case which continues always applying drive pulses having energy one or two or more increment levels higher than that actually required. This enables the power consumption in the stepping motor to be further reduced. FIG. 4 illustrates the general construction of a timepiece 1 in accordance with a second example of the invention. The timepiece 1 of this example has almost the same construction as the one described in FIG. 1, so that like reference characters are utilised to denote like elements and detailed description thereof is omitted hereafter. The control circuit 23 employed in the timepiece 1 of this example is provided with: a drive pulse supply part 24a for supplying the drive pulse P1; a rotation-detecting pulse supply part 24b for producing the rotation-detecting pulses SP2 to detect rotation of the rotor 13; and an auxiliary pulse supply part 24c for producing the auxiliary pulse P2. The auxiliary pulse supply part 24c is adapted to apply an auxiliary pulse P2 having larger effective power when the detection circuit 25 detects whether the rotor 13 is rotated or not, similarly as described in the conventional circuit. Also, the degaussing pulse supply part 24d for controlling a degaussing pulse PE to be applied following the auxiliary pulse P2 is adapted to apply a degaussing pulse PE in later timing than the conventional one, just before the next drive pulse P1. By doing so the effective power of the next drive pulse P1 is enhanced to give sufficient energy for rotating the rotor 13. Accordingly, it is possible to apply a drive pulse having a substantially larger effective power in a cycle following the auxiliary pulse P2 without increasing the energy of the drive pulse P1 for overcoming the increment of rotation angles with increased meshing load which causes rotation error. Also, since consecutive application of the auxiliary pulse P2 can be prevented, it is possible to cause the meshing condition to return to the initial state of low meshing load earlier. Accordingly, the control circuit 20 for the stepping motor 10 of this example is adapted to drive the stepping motor 10 utilising the drive pulse P1 having approximately minimum effective power corresponding with lower meshing load; once the increments of rotation angles with increased load due to meshing tolerance or shift in a shaft position are overcome. Therefore, this serves to greatly reduce occurrence of application of the drive pulse P1 having an effective power several levels larger than the minimum value as in the conventional cases. This enables the power consumption for driving the stepping motor to be further reduced. FIG. 5 illustrates in a flow chart a method for controlling a stepping motor 10 employed in the timepiece 1 of this example. In this flow chart, the same steps as those described before are denoted by like reference characters and detailed description thereof is omitted hereafter. First, in step ST1 one second is measured for moving the hands. After a lapse of one second, a drive pulse P1 is produced in step ST2. Next, in step ST3 the rotation detecting pulse SP2 is produced for identifying whether the rotor 13 is rotated or not. If rotation is not identified, the sub-routine is executed for applying the auxiliary pulse P2. In this sub-routine, in step ST4 the auxiliary pulse P2 having a large effective power is applied. Next, the degaussing pulse PE is produced, then the effective power of the drive pulse P1 is increased by one increment level. In this example the timing for outputting the degaussing pulse PE by the degaussing pulse supply part 24d is adapted to be delayed. Lapse of time is measured in step ST21 to output the degaussing pulse PE in step ST5 just before the start of the next cycle or just before the output of the next drive pulse P1. Upon output of the degaussing pulse PE after the auxiliary pulse P2 is applied, the process returns to the main routine to advance to step ST7. As stated above, the control method in this example is adapted to raise the effective power of the drive pulse P1 by one increment level after the auxiliary pulse P2 is applied. Driving is thus effected with large power utilising the power of the degaussing pulse PE to prevent the condition in which the effective power of the drive pulse P1 is increased two or more levels consecutively by applying the auxiliary pulse again. On the other hand, if the rotation of the rotor 13 is identified in step ST3, the sub-routine for outputting the auxiliary pulse P2 is not executed. In step ST7 the value in the counter n is increased and compared in step ST8 with the first predetermined number NO. If the value in the counter n is equal to the predetermined number NO, the effective power of drive pulse P1 is further reduced by one increment in step ST9, to achieve power savings, and the counter n is initialised in step ST10. FIG. 6 illustrates in a timing chart for the drive pulse applied to the stepping motor 10 from the control device of this embodiment. In FIG. 6, similar to FIG.3, there is illustrated the control signals to be applied to each of gates GP1, GN1 and GS1 of p-channel MOS 33a, n-channel MOS 32a and p-channel MOS 34a. Further, FIG. 6 also shows the control signals to be applied to each of gates GP2, GN2 and GS2 of p-channel MOS 33b, n-channel MOS 32b and p-channel MOS 34b. Similar reference characters are utilised to denote similar elements as those aforedescribed and detailed description thereof is omitted hereafter. The initial cycle starts at time t91 by first applying a drive pulse P1 with voltage V10 from the driving pole side. Then at time t92 a rotation detecting pulse SP2 is applied. If the rotor 13 does not rotate due to meshing tolerance of the gear train etc., an auxiliary pulse P2 with larger effective power is applied from the driving pole side at time t93. Next, in the control method of this example, at time t94, which is just before time t101, when the next cycle starts, a degaussing pulse PE is applied from the opposite pole side. Immediately after output of the degaussing pulse PE the next cycle starts to output the next drive pulse P1 in the driving pole side, which corresponds with the opposite pole side of the previous cycle. Accordingly, the degaussing pulse PE and the drive pulse P1 comprise a pulse for driving the rotor 13, increasing substantial effective power, so that it is possible to rotate the rotor 13 even in an increment of rotation angles having increased meshing load, due to output of the auxiliary pulse P2. If rotation is detected by applying the rotation detecting pulse SP2 at time t102, in the next cycle at time t111 a drive pulse P1 is applied having a voltage V10' or a drive pulse is applied having an energy one increment level higher than that applied before the auxiliary pulse P2 is applied at time t93. As described above, in the control device and method of this example, when it becomes impossible to rotate the rotor 13 due to temporarily increased meshing load unless the auxiliary pulse P2 is utilised, it is possible to conduct precise hand movement by overcoming a high meshing load condition without increasing the effective power of the next drive pulse P1 by a number of consecutive increment levels. As aforedescribed, the timepiece 1 is adapted to apply a drive pulse having substantially higher effective power by either applying the second drive pulse P11 having larger effective power or bringing the timing of the degaussing pulse PE nearer to the next drive pulse P1 after output of the auxiliary pulse P2. Accordingly, it deals with the increased load caused by meshing tolerance which affects the stepping motor 10 only for very short periods without requiring an increase in the effective power of the drive pulse P1 more than necessary. Accordingly, when the meshing tolerance returns to the initial conditions and reduces the load on the stepping motor 10, a low level drive pulse having energy of about one increment higher than the predetermined effective power is applied. In the conventional state of the art the effective power of drive pulse P1 is raised by several increment levels due to instantaneous load increases caused by meshing tolerance or shift of the shaft caused by applying the auxiliary pulse following such a load increase, resulting in driving the stepping motor 10 by drive pulses having energy larger than the minimum required level. In contrast, this invention provides a way to deal with instantaneous load increases, while providing drive pulses having an effective power of the required minimum level when the load returns to normal level. Accordingly, it is possible to further reduce power consumption of a stepping motor compared with the conventional art. This achieves smaller long-life timepiece and provides a self-generating type timepiece which is able to work continuously even after being left motionless for a long time. Also, application of this invention is of course not limited only to timepieces such as wristwatches. It can also be applied to such multi-purpose timepieces as chronograph or other power generating systems and to devices generally incorporating a stepping motor. Further, it is obvious that the wave forms of the drive pulse P1, the auxiliary pulse P2 and the rotation detecting pulse SP2, etc. as shown are just for example and they can be determined in accordance with the characteristics of the stepping motor 10. Also, it is obvious that the invention similarly can be applied to a stepping motor with three or more phases, even though in the above examples the description of the invention is given in terms of stepping motor 10 with two phases suitable to a timepiece. Also, it is possible to apply drive pulses in pulse widths and timing suitable for each phase instead of applying a common control. Further, the drive system of the stepping motor is not limited to one phase magnetisation but of course may also be of two phase magnetisation or of one-two phase magnetisation. As described above, the control device and control method of this invention are adapted to drive the stepping motor with low power consumption by gradually reducing the effective power of drive pulses, while the stepping motor is rotated successfully by the drive pulse having a predetermined effective power. Even if the load increases instantaneously, perhaps due to the influence of the meshing tolerance of the gear train for transmitting the driving power of the stepping motor or due to the consequentially applied auxiliary pulse with large torque; this invention makes it possible to deal with such conditions without increasing the effective power itself of the drive pulses normally applied. This enables the stepping motor to be driven by drive pulse having an effective power which is reduced to the minimum limit. Accordingly, this invention drives the stepping motor with a power consumption much lower than the conventional arrangement. The invention thus provides a control device and control method suitable for future timepieces aiming at small-size and long-life and timepieces incorporating a generator without a need to have batteries. The aforegoing description has been given by way of example only and it will be appreciated by a person skilled in the art that modifications can be made without departing from the scope of the present invention.

Claims: A device (20) for controlling a stepping motor (10) which is capable of rotatably driving a multi-poled rotor (13) in co-operation with a stator (12) having a drive coil (11), comprising: first driving means (24a) for applying a first drive pulse (P1) to said drive coil to rotate said rotor; rotation detection means (24b) for detecting whether said rotor is rotated by said first drive pulse or not; auxiliary means (24c) for applying an auxiliary pulse (P2) having an effective power larger than that of said first drive pulse when a rotation of said rotor is not detected; and level adjustment means (24e, 49) for reducing the effective power of said first drive pulse incrementally after said rotor has rotated a first predetermined number of times consecutively, characterised by further comprising: second driving means (24f) for applying a second drive pulse (P11) after said auxiliary pulse is applied, the second drive pulse having an effective power level only one or several increments higher than the effective power level of said first drive pulse and the level of the second drive pulse being adjusted by said level adjusting means for a second predetermined number of times. A device for controlling a stepping motor as claimed in Claim 1, wherein said second driving means is capable of adjusting the effective power of the second drive pulse by varying the pulse width thereof. A device for controlling a stepping motor as claimed in Claim 1, wherein said second driving means is capable of adjusting the effective power of the second drive pulse by varying the voltage thereof. A device (20) for controlling a stepping motor (10) which is capable of rotatably driving a multi-poled rotor (13) in co-operation with a stator (12) having a drive coil (11), comprising: driving means (24a) for applying a first drive pulse (P1) to said drive coil to rotate said rotor; rotation detection means (24b) for detecting whether said rotor is rotated by said drive pulse or not; level adjustment means (24e, 49) for reducing the effective power of said first drive pulse incrementally after said rotor has rotated a first predetermined number of times consecutively; auxiliary means (24c) for applying an auxiliary pulse (P2) having an effective power larger than that of said first drive pulse when rotation of said rotor is not detected; and degaussing pulse applying means (24d) for applying a degaussing pulse (PE) having an opposite polarity to the auxiliary pulse after the application of said auxiliary pulse, characterised by further comprising: delay means for delaying the application of the degaussing pulse until just before the next application of a drive pulse. A method for controlling a stepping motor which is capable of rotatably driving a multi-poled rotor in co-operation with a stator having a drive coil, comprising: a first driving step for applying a first drive pulse to said drive coil to rotate said rotor; a rotation detection step for detecting whether said rotor is rotated by said first drive pulse or not; an auxiliary step for applying an auxiliary pulse having an effective power larger than that of said first drive pulse when rotation of said rotor is not detected; and a level adjustment step for reducing the effective power of said first drive pulse incrementally after said rotor has rotated a first predetermined number of times consecutively, characterised by further comprising: a second driving step for applying a second drive pulse after said auxiliary pulse is applied, the second drive pulse having an effective power level only one or several increments higher than the effective power level of said first drive pulse and the level of the second drive pulse being adjusted for a second predetermined number of times. A method for controlling a stepping motor as claimed in Claim 5, wherein said second driving step adjusts the effective power of the second drive pulse by varying the pulse width thereof. A method for controlling a stepping motor as claimed in Claim 5, wherein said second driving step adjusts the effective power of the second drive pulse by varying the voltage thereof. A method for controlling a stepping motor which is capable of rotatably driving a multi-poled rotor in co-operation with a stator having a drive coil, comprising: a driving step for applying a drive pulse to said drive coil to rotate said rotor ; a rotation detection step for detecting whether said rotor is rotated by said drive pulse or not; a level adjustment step for reducing the effective power of said first drive pulse incrementally after said rotor has rotated a first predetermined number of times consecutively; and an auxiliary step for applying an auxiliary pulse having an effective power larger than that of said drive pulse when rotation of said rotor is not detected, characterised by further comprising: a degaussing pulse applying step for applying a degaussing pulse having an opposite polarity to the auxiliary pulse after the application of said auxiliary pulse and just before the next application of a drive pulse. A timepiece, comprising: a device for controlling a stepping motor, as claimed in any one of Claims 1 to 3; a stepping motor for driving watch hands by said drive pulse; and a pulse synthesising means for applying pulse signals having a plurality of frequencies.

Inventors: HARA TATSUO, HARA, TATSUO
Applicants: SEIKO EPSON CORP, SEIKO EPSON CORPORATION
Application year: 1998
Main classification: G04C3
IPC codes: H02P8, G04C3, H02K37