Electricity: motive power systems – Open-loop stepping motor control systems
Reexamination Certificate
2000-06-20
2002-11-05
Fletcher, Marlon T. (Department: 2837)
Electricity: motive power systems
Open-loop stepping motor control systems
C318S599000, C318S603000
Reexamination Certificate
active
06476579
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a pulse motor driving device, a pulse motor driving method, a timepiece device, and a timepiece device control method, and a-more particularly, to a device for driving a pulse motor used in, for example, an analog timepiece having a magnetic generator, and to a method for driving such a pulse motor, and to a timepiece device, such as an analog timepiece, and to a method for controlling such a timepiece device.
2. Background Art
Recent years have seen remarkable technological innovations in timepiece devices (that is, electronic timepieces), such as a wristwatch. The power consumption of the presently used timepiece devices has come to be suppressed to about 0.5 &mgr;W. Incidentally, the breakdown of power consumption of such a timepiece device is considered as follows. The power consumption of an electric circuit system of the timepiece device is 20 percent of that of the entire device. The power consumption of a pulse motor for moving hands of the device accounts for the remaining 80 percent of that of the entire device. Reduction of the power consumption of this pulse motor is, therefore, considered as the key to a further reduction of the power consumption of the device.
Thus, the conventional timepiece device (or electric timepiece) has a part configured in such a manner as to operate as follows. That is, after supplying a driving current to the pulse motor, the part detects whether or not the pulse motor is actually rotated by the driving current. If not, the timepiece device forces the pulse motor to rotate, and increases a driving current to be supplied thereto the next time. However, after the lapse of a predetermined time, the timepiece device decreases a driving current. Consequently, the effective value of the magnitude of the driving current to be supplied to the pulse motor is a value, at which the frequency of increasing the power consumption of the pulse motor and that of decreasing the power consumption thereof are in balance, that is, a value close to the lowest value of the driving current, at which the pulse motor can rotate, from a macroscopic viewpoint. This enables suppression of excessive power consumption of the pulse motor. Thus, the power consumption of the pulse motor is reduced.
However, recently, it has been pointed out that a magnetic field generated outside the timepiece adversely affects the rotation of the pulse motor. That is, as above described, the effective value of the magnitude of the driving current to be supplied to the pulse motor is obtained as a value, at which the frequency of increasing the power consumption of the pulse motor and that of decreasing the power consumption thereof are in balance, close to the lowest value thereof. When an external magnetic field is applied to the pulse motor, to which the driving current, whose magnitude is the effective value, is supplied, the magnitude of a magnetic field generated by the driving current is reduced, with the result that the pulse motor does not rotate.
Further, recently, electronic timepieces each having a built-in generator for generating electric power are coming on the market. In brief, such a generator converts a reciprocating motion, such as a swinging motion of a hand, to a rotary motion, and then transmits this rotary motion to a magnetized rotor to thereby cause an electromotive force in a coil. Thus, a magnetic field generated in a timepiece body adversely affects the rotation of the pulse motor.
Moreover, the serious influence of the magnetic field is not limited to the fact that the pulse motor does not rotate. As described above, the electronic timepiece has a part adapted to detect whether or not the pulse motor actually rotates, after supplying a driving current to the pulse motor. Although such a detecting part may be constituted by a mechanical device, an electrical device, which detects the rotation of the pulse motor according to whether or not an electric current is induced in the coil thereof as damped oscillations are caused after the rotation thereof, is suitable for such a detecting part, in view of the spatial constraints on the timepiece body.
However, even when the rotation of the pulse motor is electrically detected, if a magnetic field is generated, an induced current caused by the magnetic field is superposed on the coil in addition to the induced current caused due to the damped oscillations. Thus, although the pulse motor does not rotate actually, the detecting part may erroneously detect that the pulse motor rotates.
As described above, to reduce the power consumption of the electronic timepiece, the effective value of the magnitude of the driving current is lowered after the lapse of the predetermined time. When the effective value of the magnitude of the driving current is lowered, naturally, the pulse motor is liable to enter a non-rotation state. Incidentally, the probability of an occurrence of the erroneous detection is represented by a ratio of the frequency of an occurrence of the case, in which the pulse motor is detected as not rotating actually, to the frequency of an occurrence of the case, in which the pulse motor is detected as rotating. Therefore, when the pulse motor is apt to enter the non-rotation state, the numerator of this ratio increases, so that the probability of an occurrence of the erroneous detection rises. Further, when an erroneous detection actually occurs, the forced rotation of the pulse motor is not caused. This has an important influence on the time indication accuracy of the timepiece. That is, the conventional electronic timepiece enabled to reduce the power consumption has a drawback in that such accuracy is extremely deteriorated.
To eliminate this drawback, a first example of the conventional timepiece device, namely, an analog electronic timepiece, which has a generator and is described in the PCT international publication No. WO98/41906 Official Gazette, is adapted to output a correction driving pulse signal, whose effective power level is high, for the purpose of moving hands with reliability, during an operating time for moving hands, in the case that the power generation of the generator is detected. Furthermore, in the case that the correction driving pulse is outputted, a demagnetizing pulse signal is outputted so as to reduce a magnetic field generated in response to the correction driving pulse whose effective power level is high.
Moreover, a second example of the conventional timepiece device, namely, another analog electronic timepiece having a generator, which has a generator and is described in the European Patent Application Publication No. EP-0704774-A1 Official Gazette, is adapted to output a normal driving pulse signal, whose effective power level is lower, by periodically lowering the duty ratio of the normal driving pulse signal so as to reduce the power consumption thereof.
Furthermore, to reduce the power consumption and the electric power of the pulse motor, a normal driving pulse signal, whose number of constituent pulses (hereunder referred to as the “number of teeth”) included during a time period for outputting the normal driving pulse signal are reduced and whose effective power level is low, is outputted when it is decided that the voltage of a capacitor is higher than a predetermined voltage. Conversely, when it is decided that the voltage of the capacitor is lower than the predetermined voltage, a normal driving pulse signal, whose “number of teeth” is increased and whose effective power level is high, is outputted. Further, when the “number of teeth” of the normal driving pulse signal should be changed, the “number of teeth” is changed without altering the duty ratio used at the last hand movement.
In the case of the first example of the conventional timepiece device, the effective power level of the correction driving pulse signal is high, so that the power consumption of the pulse motor is large. Especially, the conventional analog electronic timepiece having the generator has a drawback in that a ti
Akahane Hidehiro
Furukawa Tsuneaki
Iida Kenji
Iijima Yoshitaka
Nakamiya Shinji
Fletcher Marlon T.
Seiko Epson Corporation
Watson Mark P.
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