Patent Publication Number: US-6339306-B1

Title: Control device for stepper motor, control method for the same, and timing device

Description:
This application is a continuation of application Ser. No. 09/020,223, filed Feb. 6, 1998, U.S. Pat. No. 6,194,862. 
    
    
     BACKGROUND OF INVENTION 
     The present invention relates to a control device for an electronic timepiece, and in particular to a control device for controlling a stepping motor used in an electronic timepiece which uses kinetic energy to drive a electricity generating device to provide electronic power for driving the stepping motor. 
     In recent years, timing devices, such as wrist-watches, have been sold with built-in electricity generators in which the energy generated by the movement of the user&#39;s arm is converted into electricity which is used to drive the stepping motor which moves the hands of the device. These timing devices operate without batteries and can continuously run off the energy generated by the user&#39;s movement. Also, these timing devices eliminate the often cumbersome process of changing batteries as well as help reduce the environmental hazard associated with battery disposal. As a result, built-in electricity generators are being closely evaluated for future widespread use in wristwatches and similar devices. 
     Generally, electronic timepieces that incorporate electricity generators include a stepping motor for driving the hands of the timepiece. These stepping motors, also referred to as a pulse motors or digital motors, are driven by pulse signals and are also extensively used as actuators for digital control devices. In recent years, compact electronic devices and information equipment have been developed in which portability is desirable, and compact and lightweight stepping motors are in widespread use as actuators for this equipment. Representative of such electronic devices are timing devices including electronic timepieces, time switches and chronographs. 
     Referring now to FIG. 12, there is shown a prior art timing device  9 , for example a wristwatch, which includes a stepping motor  10 , a driving circuit  30  for driving stepping motor  10 , a gear train  50  for transferring the force of stepping motor  10 , a second hand  61 , a minute hand  62 , and an hour hand  63  which are moved by gear train  50 . Stepping motor  10  generates magnetic force in response to driving pulses supplied from a control device  20 . Stepping motor  10  includes a driving coil  11 , a stator  12  which is excited by driving coil  11 , and a rotor  13  which rotates within stator  12  as a result of the excited magnetic field. By selecting a disk-shaped bipolar permanent magnet for rotor  13 , a PM-type (Permanent Magnet rotational) stepping motor is formed. Stator  12  is provided with a magnetism saturating unit  17  so that the different magnetic poles that result from the magnetic force generated by driving coil  11  are generated at the phases (poles)  15  and  16 , respectively surrounding rotor  13 . Also, an internal notching  18  is provided at the appropriate location on the inner periphery of stator  12  so that cogging torque is generated and rotor  13  is stopped at the appropriate position. 
     The rotation of rotor  13  of stepping motor  10  is transferred to each of the timepiece hands by gear train  50  which includes a fifth gear  51  meshing with a fourth gear  52 , which also meshes with a third gear  53 , which meshes with a center wheel  54 . Center wheel  54  meshes with a minute wheel  55 , which meshes with an hour wheel  56 . Second hand  61  is connected to the axis of fourth gear  52 , minute hand  62  is connected to the axis of center wheel  54 , and hour hand  63  is connected to the axis of hour wheel  56 . Time is displayed by each of the timepiece hands operating synchronously with the rotation of rotor  13 . Of course, a transfer system for displaying the year, month, and day (not shown) may also be connected to gear train  50 . In order for timing device  9  to display the time as a result of the rotation of stepping motor  10 , stepping motor  10  is supplied with driving pulses which are based on counting (timing) of signals generated by a reference frequency. 
     Control device  20 , which controls stepping motor  10 , includes a pulse synthesizing circuit  22  for generating reference pulses of a standard frequency using a reference oscillator  21  such as a crystal oscillator, or pulse signals of a different pulse width or timing. The reference pulses are input to a control circuit  23  for controlling stepping motor  10  based on the various pulse signals supplied from pulse synthesizing circuit  22 . Control circuit  23  has a driving control circuit  24  which receives the reference pulses for controlling driving circuit  30 , and a detecting circuit  25  for detecting whether driving rotor  13  rotated. Driving control circuit  24  includes: a driving pulse supplying unit  24   a  for supplying driving pulses to driving circuit  30  which in turn drives driving rotor  13  of stepping motor  10 ; a rotation detection pulse supplying unit  24   b  for outputting rotation detecting pulses to detection circuit  25  for inducing induction voltage to determine whether driving rotor  13  rotated in response to the driving pulse; a magnetic detection pulse supplying unit  24   c  for outputting magnetic field detecting pulses to detection circuit  25  prior to the output of the driving pulse, for inducing induction voltage to detect the presence of a magnetic field external to stepping motor  10 ; an auxiliary pulse supplying unit  24   d  for generating an auxiliary pulse that has an effective electric power that is greater than that of the driving pulse, the auxiliary pulse being output if the driving pulse does not cause driving rotor  13  to rotate or if an external magnetic field has been detected; and a demagnetizing pulse supplying unit  24   e  for producing a demagnetizing pulse having a polarity that is opposite that of the auxiliary pulse and which is used to demagnetize driving coil  11  after the auxiliary pulse is output. 
     Detecting circuit  25  includes a rotating detecting unit  26  for comparing the rotation detecting induction voltage, obtained by outputting the rotation detecting pulse, with a set value, and detecting whether driving rotor  13  rotated. Detecting circuit  25  also includes a magnetic field detecting unit  27  for comparing the magnetic field detecting induction voltage, obtained by outputting the magnetic field detecting pulse, with a set value for detecting the presence of a magnetic field. 
     Referring now to FIG. 13, there is shown rotation detecting unit  26  which employs a pair of comparators,  29   a  and  29   b , to compare the value of the bi-directional excitation voltage generated in driving coil  11  with a set value SV 1 , to determine whether driving rotor  13  has rotated. Comparator  29   a  receives one input from the standard signal SV 1  and a second input φ 1  from one side of driving coil  11  and produces a first comparison signal. Similarly, comparator  29   b  receives a first input SV 1  and a second input φ 2  from the other side of driving coil  11  and produces a second comparison signal. An OR gate  29   c  receives the first and second comparison signals and produces an output to driving control circuit  24 . Similarly, magnetic field detecting unit  27  uses a pair of inverters,  28   a  and  28   b , each having a threshold value of SV 2 , which receive the inputs of φ 1  and φ 2 , respectively. These inverted signals are input to an OR gate  28   c  for detecting the presence of a magnetic field. The results of each comparison are fed back to driving control circuit  24 , and are used for controlling stepping motor  10 . 
     Driving circuit  30 , which supplies various driving pulses to stepping motor  10  under the control of driving control circuit  24 , coupled between driving control circuit  24  and a battery  41 , has a bridge circuit which includes a serially connected p-channel MOSFET  33   a  and n-channel MOSFET  32   b , and serially connected p-channel MOSFET  33   b  and n-channel MOSFET  32   a , configured for controlling the voltage supplied to stepping motor  10  from battery  41 . Also included are a pair of rotation detecting resistors  35   a  and  35   b  connected in parallel to the p-channel MOSFET  33   a  and  33   b , respectively, and a pair of sampling p-channel MOSFET,  34   a  and  34   b , coupled between ground, driving circuit  24  and resistors  35   a ,  35   b  respectively for supplying chopper pulses to resistors  34   a  and  35   b . Control pulses having different polarities and pulse widths are output from supplying unit  24   a  through  24   e  of driving control circuit  24  to the gate electrodes of each of MOSFET  32   a ,  32   b ,  33   a ,  33   b ,  34   a  and  34   b  according to the respective timings. Thus, driving pulses having different polarities drive driving coil  11  and pulses for inducing induction voltage for rotation detection of rotor  13  and magnetic field detection are supplied. 
     Referring now to FIG. 14, there is shown a timing chart illustrating the control signals supplied to gates GP 1 , GN 1 , and GS 1  of the p-channel MOSFET  33   a , n-channel MOSFET  32   a , and sampling p-channel MOSFET  34   a , respectively, for excitation of a magnetic field of one polarity across driving coil  11 , and to gates GP 2 , GN 2  and GS 2  of the p-channel MOSFET  33   b , n-channel MOSFET  32   b , and sampling p-channel MOSFET  34   b , respectively, for excitation of a magnetic field of a reverse polarity across driving coil  11 . Control device  20  controls the movement of the timepiece hands each second, by supplying a series of control pulses to driving circuit  30  which in turn controls stepping motor  10 . At the beginning of a timing cycle, pulses SP 0  and SP 1  are output from driving control circuit  24  for detecting whether a magnetic field is present which causes rotation detection to be unreliable. Pulse SP 0 , which is output at the time t 1 , is used for detecting the presence of a magnetic field due to high-frequency noise. The control signals for outputting magnetic field detecting pulse SP 0  are supplied by magnetic field detecting pulse supplying unit  24   c  to gate GP 1  of the p-channel MOSFET  33   a  on the driving side (driving pole side) i.e. the side of driving circuit  30  from which driving pulse P 1  is output. Magnetic field detecting pulse SP 0  is a continuous control pulse having a pulse width of approximately 20 ms and is used to detect magnetic noise caused by, for example, the switching of household electrical appliances such as electric blankets or infrared foot-warmer tables. After pulse SP 0  is output, a control signal for outputting a magnetic field detecting pulse SP 1  for detecting alternating current magnetic fields of 50 to 60 Hz is output at time t 2  by magnetic detecting pulse supplying unit  24   c  to gate GP 2  of p-channel MOSFET  33   b  on the side that is opposite to the driving pole side (i.e. reverse pole). Magnetic field detecting pulse SP 1  is an intermittent chopper pulse having a duty ratio of approximately ⅛, and samples the electric current induced in driving coil  11  by the alternating current magnetic field thus enabling magnetic field detection unit  27  of detecting circuit  25  to detect the presence of a magnetic field. Also, because the magnetic field detecting capabilities of the driving side, i.e., the p-channel MOSFET  33   a  and the n-channel MOSFET  32   a , deteriorates after an auxiliary pulse is applied, control pulse SP 1  is output to gate GP 2  of p-channel MOSFET  33   b  which is at the opposite pole of the driving side (reverse pole). Such magnetic field detection is disclosed in detail in Japanese Examined Patent Publication No. 3-45798. 
     After magnetic field detecting pulses SP 0  and SP 1  are output, control pulses for outputting driving pulse P 1  at time t 3  is supplied by driving pulse supplying unit  24   a  to gate GN 1  of the n-channel MOSFET  32   a  and gate GP 1  of the p-channel MOSFET  33   a  of the driving pole side. The effective electric power of the driving pulse P 1  is reduced to approximately the limit of rotation of driving rotor  13 , and is selected such that driving pulse P 1  has pulse width of, e.g. W 10 . The control signal for outputting driving pulse P 1  can vary the pulse width of driving pulse P 1  thereby controlling the effective electric power of driving pulse P 1 . If driving rotor  13  does not rotate in response to driving pulse P 1  and it is therefore necessary to output auxiliary pulse P 2  to rotate driving rotor  13 , the pulse width of driving pulse P 1  is widened thereby increasing its effective electric power. On the other hand, if rotor  13  is continuously driven for a predetermined number of times by driving pulses P 1  having the same pulse width, the effective electric power of driving pulse P 1  can be reduced by narrowing its pulse width. 
     After driving pulse P 1  is output, rotation detection pulse supplying unit  24   b  outputs a rotation detection pulse SP 2  to gate GP 1  of the p-channel MOSFET  33   a  on the driving side and to sampling p-channel MOSFET  34   a  at time t 4  for detecting whether rotor  13  rotated. Rotation detecting pulse SP 2  is a chopper pulse with a duty ration having approximately ½, and causes the induction electric current induced in driving coil when rotor  13  rotates to be output to rotation detecting resister  35   a . The voltage across rotation detecting resister  35   a  is compared by rotation detecting unit  26  of detecting circuit  25  with a set value SV 1  for determining whether driving rotor  13  has rotated. 
     If the induction voltage induced by rotation detecting pulse SP 2  is not at least set value SV 1 , it is determined that rotor  13  did not rotate, and a control signal for outputting auxiliary pulse P 2  at time t 5  is output from auxiliary pulse supplying unit  24   d  to gate GP 1  of n-channel MOSFET  32   a  on the driving side and also to gate GP 1  of p-channel MOSFET  33   a . Auxiliary pulse P 2  has a width of W 20  and has a greater effective electric power than driving pulse P 1 . Thus, auxiliary pulse P 2  has sufficient energy to ensure that rotor  13  rotates. Auxiliary pulse P 2  is output instead of driving pulse P 1  when the rotation of rotor  13  is not detected and when a magnetic field is detected by either of magnetic field detecting pulses SP 0  and SP 1 . If a magnetic noise is present in the area of stepping motor  10 , it is possible that rotation detecting pulse SP 2  falsely detects the rotation of rotor  13  thereby causing errors in the movement of the timepiece hands. Accordingly, if a magnetic field is detected, an unnecessary auxiliary pulse P 2  is output for detecting rotation, which while increasing power consumption, will prevent errors in the movement of the timepiece hands. 
     If auxiliary pulse P 2  is output, a control pulse for outputting a demagnetizing pulse PE at time t 6  is supplied by the demagnetizing pulse supplying unit  24   e  to gate GN 2  of n-channel MOSFET  32   b , which is at the reverse pole, and to gate GP 2  of the p-channel MOSFET  33   b . Demagnetizing pulse PE, a pulse which is of reverse polarity to auxiliary pulse P 2 , reduces the residual magnetic flux of driving coil  11  which is generated by the high effective electric power of auxiliary pulse P 2 . After demagnetizing pulse PE is output, one cycle of the rotational driving of stepping motor  10  by one step angle is completed. 
     One second after time t 1 , the next cycle of rotational driving of stepping motor  10  by one step angle starts at t 11 . In this cycle, MOSFET  32   b ,  33   b , and  34   b  which were on the reverse side in the previous cycle now become the driving pole side. As with the previous cycle, pulse SP 0  is first output at time t 11  for detecting magnetic flux noise due to high-frequency noise, and then pulse SP 1  is output at time t 12  for detecting noise due to a low-frequency alternating current magnetic field. If magnetic noise is not detected, driving pulse P 1  is output at time t 13 . Because auxiliary pulse P 2  has been output in the previous cycle, the effective electric power of driving pulse P 1  is increased, and a driving pulse P 1  a width W 11  (where W 11 &gt;W 10 ) is output at time t 13 . Next, rotation detecting pulse SP 2  is output at time t 14 , and if rotation of rotor  13  is detected, the cycle ends. 
     Referring now to FIG. 15, there is shown a flow chart of the above-described operation of control device  20 . First, in step ST 1 , a timing reference pulse is counted and a one second time duration is measured. If it is determined that one second elapses, then in step ST 2 , a high-frequency magnetic field is detected using magnetic field detecting pulse SP 0 . If a high-frequency magnetic field is detected, then, in step ST 7 , auxiliary pulse P 2  having a greater effective electric power than driving pulse P 1  is output instead of the driving pulse P 1 , thus preventing errors in the movement of the timepiece hands from occurring due to unreliable rotation detection. If a high-frequency magnetic field is not detected, in step ST 3 , the presence of an alternating current magnetic field of a low-frequency is detected in steps using magnetic field detecting pulse SP 1 . If an alternating current magnetic field is present, then in step ST 7 , auxiliary pulse P 2  is output thus preventing errors in the movement of the timepiece hands from occurring. 
     If no magnetic field is detected in any steps ST 2 , ST 3 , then in step ST 4 , driving pulse P 1  is output and, in step ST 5  it is determined whether rotor  13  has rotated by output of rotation detecting pulse SP 2 . If the rotation of rotor  13  is not confirmed, then in step ST 7 , auxiliary pulse P 2  having a greater effective electric power than driving pulse P 1  is output thereby ensuring that rotor  13  is rotated. After auxiliary pulse P 2  is output, in step ST 8 , demagnetizing pulse PE is output, and in step ST 10 , the level of driving pulse P 1  is adjusted higher (first level adjustment). If rotation was not confirmed in step ST 5 , using driving pulse P 1  with the same effective electric power will result in the defective rotation being repeated. Accordingly, in step ST 11 , the cause for the defective rotation which made the output of auxiliary pulse P 2  necessary is determined and, in step ST 12 , the output of driving pulse P 1  is set to a higher voltage level to avoid repeated defective rotation in the next cycles. The system then returns to step ST 1 . 
     If, in step ST 5 , the rotation of rotor  13  as a result of driving pulse P 1  was detected, the effective electric power of driving pulse P 1  is adjusted lower in step ST 6  (second level adjustment). In many cases, the effective electric power of driving pulse P 1  is reduced after it is confirmed several times that rotor  13  has rotated in response to driving pulse P 1 . By performing such control, the power consumption of pulse P 1  is reduced, and error in the movement of the timepiece hands is prevented from occurring in areas where there are magnetic fields from electric and electronic appliances. Accordingly, a timing device with high reliability and low power consumption is realized. 
     When an electricity generating device, which converts energy from the movement of the user into electricity, is added to the timepiece, another generator that has a similar configuration as that of stepping motor  10  is introduced. The electricity generating device includes a generating rotor that rotates within a stator, the generating rotor rotates by way of an energy transferring device, such as a rotating weight, thereby changing kinetic energy into rotational energy. 
     However, the magnetic flux generated by the generator also generates noise that may interfere with the rotation detection of driving rotor  13  thereby lowering the reliability and accuracy of timing device  9 . The noise from the generator has a frequency approximately in the range of 200 to 300 Hz and is not easily detected by magnetic field detecting pulse SP 0 , which is normally designed to detect high frequency noise, or magnetic field detecting pulse SP 1 , which is used to detect alternating magnetic flux in the 50 to 60 Hz. Furthermore, the generator only generates electricity when the rotating weight rotates due to the user&#39;s arm movement. Accordingly, the magnetic field generated by the generator is irregular, and often only e.g., 100 ms. Therefore, it is likely that this noise may be generated at the same time that rotation detecting pulse SP 2  is being output even if pulse SP 0  or pulse SP 1  did not previously detect the presence of magnetic flux. Also, because half-wave rectification, which requires minimal space and is inexpensive to implement, is generally used in electronic timepieces, the magnetic noise is directional. Thus, there is no guarantee that when using the conventional detection system, the presence of magnetic noise will not cause the rotation of rotor  13  to be falsely detected. Furthermore, even if magnetic noise is detected and auxiliary pulse P 2 , having a greater effective electric power, is output, the magnetic detection capabilities in the same direction will deteriorate due to effects of residual magnetism. 
     Thus, in order to achieve a highly reliable timing device, it is necessary that control devices for stepping motors built in to timing devices along with alternating current electricity generating devices be provided so that the magnetic field generated by the generating device can be eliminated. 
     SUMMARY OF THE INVENTION 
     A control device that compensates for external magnetic fields, including magnetic fields generated by an on board electricity generating device, is provided. In order to inhibit effects of the magnetic field generated by the electricity generating device as much as possible, the detection of the alternating current magnetic field is performed not only at the reverse pole side to the driving pole side, but is also performed at the driving pole side, in order to increase the likelihood of detection of the magnetic field. 
     The present invention includes a control device for a stepping motor. The stepping motor includes a driving rotor that is rotatably driveable within a driving stator that includes a driving coil. The driving rotor is subjected to multipolar magnetization by electric power which is supplied via a condenser. The electric power is generated by an electricity generating device which includes an electricity generating rotor rotating within an electricity generating stator. The electricity generating device is driven by a kinetic energy transferring apparatus. 
     The control device includes a driving circuit for supplying driving pulses to the driving coil for driving the driving rotor. A rotation detecting pulse supplying unit supplies rotation detection pulses following the driving pulse for inducing induction voltage to detect the rotation of the driving rotor. A magnetic detection pulse supplying unit supplies magnetic field detection pulses prior to the driving pulse for inducing a magnetic field detecting induction voltage to detect the presence of a magnetic field external to the stepping motor. A detection circuit compares the rotation detecting induction voltage and magnetic field detecting induction voltage obtained by the rotation detecting pulse and magnetic field detecting pulse, respectively, with respective set values, thus detecting whether rotation of the driving rotor occurred and the presence of a magnetic field. An auxiliary pulse supplying unit supplies an auxiliary pulse of effective electric power that is greater than the driving pulse if either the driving rotor does not rotate in response to the driving pulse or when the external magnetic field has been detected. The magnetic detection pulse supplying unit supplies to the driving coil, prior to the driving pulse, a first magnetic field detection pulse and a second magnetic field detecting pulse each of different polarity for detecting magnetic fields of approximately the same frequency band. 
     The present invention also includes a method for controlling a stepping motor in which a driving rotor is rotatably driveable within a driving stator having a driving coil, the driving rotor having been subjected to multipolar magnetization by electric power which is stored in a condenser, the electric power being generated by an electricity generating device which includes an electricity generating rotor that rotates within an electricity generating stator, the electricity generating device being driven by a kinetic energy transferring apparatus. The control method includes a driving step in which driving pulses are supplied to the driving coil for driving the driving rotor. In a rotation detecting step, driving coil rotation detection pulses are output following the driving pulse and the induced induction voltage is compared with a first set value for detecting whether rotation occurred. In a magnetic field detecting step, magnetic field detection pulses are output to the driving coil prior to the driving pulse and the induced induction voltage is compared with a second set value for detecting the presence of a magnetic field external to the stepping motor. Magnetic field detecting pulses of different polarities are output to the driving coil in order to detect magnetic fields of approximately the same frequency band. In an auxiliary pulse supplying step, an auxiliary pulse of effective electric power greater than that of the driving pulse is supplied in the event that the driving rotor does not rotate in response to the driving pulse or when an external magnetic field has been detected. 
     By detecting alternating current magnetic flux on the pole opposite to the driving pole side (reverse pole) in addition to the driving pole side, there is a greater possibility that the presence of a magnetic field will be detected, even in cases where the magnetic field is being generated by the electricity generator which primarily effects the driving side of the driving coil. In conventional systems, detection of the alternating current magnetic fields on the driving side is not performed. This gives rise to the danger that a magnetic field may be present on the driving side which would result in false positive rotation detection and lead to error in the movement of the timepiece hands. However, in the present invention, the probability of detecting magnetic fields is improved by performing the detection of alternating current magnetic fields on the driving side as well as on the reverse pole side because magnetic fields may then be detected at both poles and also, the detection time is doubled. This greatly improves the reliability of timing devices especially for those that include an electricity generating device because magnetic fields can be detected with a high degree of sensitivity. 
     Also, considering the fact that the magnetic field generated by the electricity generating device is irregular and often as short as 100 ms in duration, it is impossible to determine at what point during the driving cycle of the stepper motor the magnetic fields will be introduced. Accordingly, it is also advantageous to supply magnetic field detecting pulses immediately following the rotation detecting pulse to determine the accuracy of the rotation detection and whether the rotation detection may have been influenced by magnetic noise. Therefore, under the present invention, a control device for a stepping motor is provided which supplies a magnetic field detecting pulse to the driving coil before the driving pulse is output and also immediately following the output of the rotation detecting pulse thereby increasing the reliability of magnetic field detection. In this way, a method of controlling the stepping motor is provided which includes a first magnetic field detecting step in which magnetic field detection pulses are output to the driving coil before the driving pulse and the induced induction voltage is compared with a second set value for detecting the presence of magnetic fields external to the stepping motor. The control method of the present invention also adds a second magnetic field detecting step in which the magnetic field detection pulse is output to the driving coil following the rotation detecting pulse and the induced voltage is compared with a second set value thereby detecting the presence of a magnetic field external to the stepping motor. 
     Generally, electric power from the electricity generating device is supplied to the control device of the stepping motor via a capacitor or condensor. As a result, the voltage of the driving pulses and other control signals supplied to the stepping motor changes in proportion to the charging voltage stored in the condensor. As the charging voltage increases, the signal-to-noise (S/N) ratio of the driving pulse also increases which tends to reduce magnetic field detection capabilities. Thus, according to the control device and method of the present invention, the set value for detecting the presence of a magnetic field described above is made to vary with the charging voltage. In this way, the probability of detecting a magnetic field is increased by lowering the set value when the charging voltage increases so that magnetic field detection sensitivity does not deteriorate. 
     In a preferred embodiment, instead of trying to detect the presence of a magnetic field generated by the electricity generating device, it is determined whether electricity is being generated by the electricity generating device and, if electricity is being generated, it is assumed that a magnetic field which would effect rotation detection is present. Accordingly, in the control device of the stepping motor of this embodiment, an auxiliary pulse is supplied by the auxiliary pulse supplying unit if it is determined that the electricity generating device is generating electricity without even detecting whether a magnetic field is present. Also, although magnetic field detection capabilities are reduced when an auxiliary pulse having a greater effective electric power than the driving pulse is supplied, this is of no consequence because the determination of whether to supply an auxiliary pulse is based on whether electricity is being generated and not on the presence of a magnetic field. Accordingly, the reliability of control device of the stepping motor is further improved. 
     If the device has a short-pulse supplying unit for supplying short-pulses to the driving coil which have a shorter cycle than the drive pulses, for example, fast-forward pulses or reverse pulses, it is preferable that the short-pulse supplying unit stop supplying the short-pulse when electricity is being generated in order to prevent error in the movement of the timepiece hands. In particular, the voltage of the reverse pulses (which drive the rotor in the reverse direction) may fluctuate when electricity is being generated because these pulses are combinations of a plurality of short pulses which are particularly vulnerable to noise. The voltage of the fast-forward pulses may also fluctuate because these pulses also have short cycles. Accordingly, it is preferable that reverse driving as well as fast-forward pulses be forcibly terminated during electricity generation. 
     If a magnetic field is detected, or if the generating device is generating electricity and auxiliary pulses have been output, there is a high possibility that a residual magnetic field may remain in the driving coil which will adversely impact rotation detection. Accordingly, in a preferred embodiment, a driving pulse having a greater effective electric power than the immediately preceding diving pulse is supplied after the auxiliary pulse is output. These higher power driving pulses which will ensure rotor rotation are supplied a certain number of times following the output of the auxiliary pulse. In this way, the need to detect whether or not rotation occurred is eliminated in this situation and error in the movement of the timepiece hands can be prevented. The effective electric power of these driving pulses can be adjusted by either varying the pulse width or voltage. In addition, by supplying a demagnetizing pulse having a different polarity than that of the auxiliary pulse for demagnetizing the driving coil following the output of the auxiliary pulse and immediately before the next driving pulse, a substantial increase in the effective voltage of the driving pulse is achieved. 
     As described above, a control device and a method for controlling a stepping motor is provided in which the effects of the magnetic field generated by the electricity generating device stored within the device is minimized. This result is accomplished in several ways including, but not limited to: improving the probability of detection of the magnetic field; assuming the presence of a magnetic field if the electricity generating device is generating electricity instead of trying to detect the presence of magnetic fields; and supplying a driving pulse having greater effective electric power than the previous driving pulse following the auxiliary pulse. Thus, by using a control device according to the present invention, a stepping motor that can perform movement of the timepiece hands in a stable manner and with high reliability is provided. Also, by constructing a timepiece which includes a stepping motor control device according to the present invention, a stepping motor which moves the hands on the face of the timepiece using driving pulses, a pulse synthesizing unit which outputs pulse signals of a plurality of frequencies, and an electricity generating device capable of supplying the necessary electrical power, a highly precise timepiece can be provided which may be used anytime and anywhere without the use of batteries. 
     Furthermore, the method of controlling a stepping motor according to the present invention can be implemented in a computer-readable medium such as in the control program of a logic circuit or a microprocessor, and is therefore not restricted to timing devices and can also be applied to various motor devices which require intermittent and highly precise hand movements. 
     Accordingly, it is an object of the present invention to provide a control device for controlling a stepping motor for use in a timepiece together with an alternating current electricity generating device in which the effects of external magnetic fields and, in particular, the magnetic field generated by the generating device are eliminated thereby providing a highly reliable timepiece. 
     It is another object of the present invention to provide a highly precise timing device with a built in electricity generating device so that the need to replace and discard batteries is eliminated. 
     Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification. 
     The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the constructions hereinafter set forth, and the scope of the invention will be indicated in the claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a fuller understanding of the invention, reference is had to the following description taken in connection with the accompanying drawings, in which: 
     FIG. 1 is a schematic representation of a timing device including a stepping motor and electricity generating device constructed in accordance with the present invention; 
     FIG. 2 is a schematic representation of the detecting circuit used in the timing device shown in FIG. 1; 
     FIG. 3 is a graph of the condenser charging voltage over time; 
     FIG. 4 is a flowchart illustrating the control method of the control device according to a first embodiment of the present invention; 
     FIG. 5 is a timing chart illustrating the operation of the control device in accordance with the method of FIG. 4; 
     FIG. 6 is a flowchart illustrating the control method of the control device according to a second embodiment of the present invention; 
     FIG. 7 is a timing chart illustrating the operation of the control device in accordance with the method of the second embodiment of the invention; 
     FIG. 8 is a flowchart illustrating the control method of the control device according to a third embodiment of the present invention; 
     FIG. 9 is a timing chart illustrating the operation of the control device in accordance with the third embodiment of the invention; 
     FIG. 10 is a flowchart illustrating the control method of the control device according to a fourth embodiment of the present invention; 
     FIG. 11 is a timing chart illustrating the operation of the control device in accordance with the fourth embodiment of the invention; 
     FIG. 12 is a schematic representation of a prior art timing device; 
     FIG. 13 is a schematic representation of the detecting circuit employed in the timing device shown in FIG. 12; 
     FIG. 14 is a timing chart illustrating the operation of the control device in accordance with the prior art; and 
     FIG. 15 is a flowchart illustrating the control method of the control device in accordance with the prior art. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to FIG. 1, there is shown a schematic diagram of a timing device  1  of the first embodiment. In timing device  1 , stepping motor  10  is driven by control device  20 , and the movement of stepping motor  10  is transferred via gear train  50  to second hand  61 , minute hand  62 , and hour hand  63 . Because the basic construction of stepping motor  10 , gear train  50 , and control device  20  is the same as described above with respect to FIG. 12, common elements will be denoted with like reference numerals and the detailed description thereof will be omitted. 
     Timing device  1  is provided with an electricity generating device  40  which acts as an electric power source. Electricity generating device  40  is an alternating current electricity generating device of the electromagnetic induction type and includes a generating rotor  43  that rotates within a generating stator  42  and is capable of outputting electricity induced in a generating coil  44 . Further, timing device  1  uses a rotating weight  45  for transferring kinetic energy to generating rotor  43  via a speed-increasing gear  46 . In timing device  1 , which may be in the form of a wristwatch, for example, rotating weight  45  captures the natural movements of the arm of the user which causes rotating weight  45  to rotate within timing device  1 , thereby generating electricity capable of driving timing device  1 . 
     The power output from electricity generating device  40  is half-wave rectified by a diode  47 , and is then temporarily stored in a large capacity condenser  48 . The driving voltage for driving stepping motor  10  is supplied by condenser  48  is coupled between ground, coil  44  and driving circuit  30  supplies condenser  48  power to driving circuit  30  of control device  20  via a booster/reducer circuit  49 . Booster/reducer circuit  49  is connected in parallel with condenser  48  and includes a plurality of condensers  49   a ,  49   b , and  49   c , so that multi-step boosting and reduction can be performed. In this way, the voltage supplied to driving circuit  30  from driving control circuit  24  of control device  20  may be adjusted by way of a control signals φ 11  transmitted between driving control circuit  24  and booster/reducer circuit  49 . The output voltage of booster/reducer circuit  49  is also supplied to driving control circuit  24  via a monitoring circuit φ 12  so that, by monitoring the minute increases or decreases in output voltage, driving control circuit  24  may determine whether electricity generating device  40  is generating electricity. 
     Control circuit  23 ′, included in control device  20 , includes driving control circuit  24  and detecting circuit  25 ′. Driving control circuit  24  includes: driving pulse supplying unit  24   a , which supplies driving pulses P 1  to driving coil  11  via driving circuit  30 ; rotation detecting pulse supplying unit  24   b , which supplies rotation detecting pulse SP 2  following driving pulses P 1 ; magnetic field detecting pulse supplying unit  24   c , which supplies magnetic field detecting pulse SP 0  and SP 1  for detecting a magnetic field before driving pulse P 1  is output; auxiliary pulse supplying unit  24   d , which supplies auxiliary pulses P 2  having a greater effective electric power than that of driving pulses P 1 ; and demagnetizing pulse supplying unit  24   e  for supplying demagnetizing pulses PE following auxiliary pulses P 2 . 
     By controlling booster/reducer circuit  49 , the effective electric power of driving pulse P 1  supplied by driving pulse supplying unit  24   a  can be adjusted. The effective electric power of driving pulse P 1  can be varied by adjusting the pulse width and/or the voltage so that fine control of the driving voltage becomes possible. Thus driving pulse P 1  having an optimal voltage for rotating driving rotor  13  can be supplied thereby conserving electricity. 
     Furthermore, driving pulse supplying unit  24   a  acts as a short-pulse supplying unit for supplying short pulses including fast-forward pulses, reverse pulses and short-cycle driving pulses. However, because the voltage supplied to driving circuit  30  during electricity generating is difficult to stabilize and may cause the voltage level of driving pulses to fluctuate, driving timing device  1  during electricity generation may lead to errors in the movement of the hands. This is especially the case with fast-forward pulses which, have a short pulse width that is necessary so that they can be output in short intervals before driving rotor  13  comes to a halt. Because these short pulses are likely to be adversely affected by the presence of an external magnetic field, the generation of fast-forward pulses are forcibly terminated when there is a high possibility that there is electricity being generated, for example, when an external magnetic field is detected, and the movement of the hands resumes at normal speed. Thus, a signal φ 12  is used to monitor the output of electricity generating device  40  and terminate the fast-forward pulses if it is determined that electricity is being generated. This also applies to the driving pulses generated by driving pulses supplying unit  24   a  used to drive rotor  13  in a reverse direction (reverse pulses). Reverse driving pulses are also short pulses because two or three of the reverse pulses need be output in order to drive one step angle. Therefore, because the reverse driving pulses may also be adversely affected by the presence of an external magnetic field, it is preferable that these pulses are terminated during electricity generation as well. 
     Magnetic field detecting pulse supplying unit  24   c  is configured to output pulses SP 1  for detecting low-frequency alternating current magnetic fields from the reverse pole side, as is done in the conventional devices, as well as for detecting the same frequency band magnetic fields from the driving side thereby greatly increasing the probability of detecting magnetic fields. Because electricity generating device  40  generates electricity based on the movement of rotating weight  45  that rotates generating rotor  43 , electricity generation is intermittent and often occurs for short intervals of time, for example 100 ms. Therefore, if magnetic field detecting pulse SP 1  is output on the reverse side alone, as in the conventional devices it is possible that electricity is being generated during the outputting of rotation detecting pulse SP 2 , and rotation detection errors would occur due to the magnetic field generated by electricity generating device  40 . Furthermore, because the electric power from electricity generating device  40  is half-wave rectified by diode  47 , there is the possibility that, depending on the direction of rectification, the alternating current magnetic field may not be present on the reverse pole side. Therefore, by outputting alternating current magnetic field detecting pulses SP 1  from both the driving pole and the reverse pole side, the detection interval is extended and the presence of the magnetic field on the driving side may also be detected. Accordingly, the probability of detecting the magnetic field is greatly increased, and the error in movement of the hands due to erroneous rotation detection is prevented. 
     In prior art systems, detection of an alternating current magnetic field is generally not done on the driving side because the presence of a residual magnetic field resulting from auxiliary pulse P 2  makes detection almost impossible. However, in the present invention, detection of magnetic fields which affect rotation detection is improved by detecting the presence of a magnetic field on both the driving and reverse pole sides, which also extends the time spent on detecting magnetic fields. Accordingly, there is an increased likelihood of detecting magnetic field generated by the electricity generating device  40  which, because of their frequency, that is greater than the conventional 50 to 60 Hz alternating current magnetic field and bursty properties, are otherwise difficult to detect. Thus, erroneous detection of rotation of rotor  13  is prevented. 
     Referring now to FIGS. 2-3, there is shown a detecting circuit  25 ′ including a rotation detecting unit  26 , and a magnetic field detecting unit  27 ′ which includes a detecting unit  27   a  and a setting unit  27   b . Setting unit  27   b  controls the production of set value SV 2  used by magnetic field detecting unit  27 ′ for detecting the voltage inducted by driving coil  11  in response to magnetic field detecting pulses SP 0  and SP 1 . Set value SV 2  is controlled by a controlling circuit  28   f  which, for example, may use a variable resistor, which varies in response to φ 13  from drive control circuit  24  to adjust set value SV 2 . By lowering the value of set value SV 2 , the sensitivity detection of magnetic fields is further increased. 
     Detection unit  27   a  of magnetic field detection unit  27 ′ uses a pair of comparators,  28   d  and  28   e , for comparing the voltage generated in driving coil  11  in each direction, respectively, with set value SV 2 . Comparator  28   d  receives one input from set value SV 2  and a second input φ 1  from one side of driving coil  11  and produces a first comparison signal. Similarly, comparator  28   e  receives one input from set value SV 2  and a second input φ 2  from the other side of driving coil  11  and produces a second comparison signal. An OR gate  28   c  receives the first and second comparison signals and produces an output to driving control circuit  24 . 
     As shown in FIG. 3, when electricity generating device  40  generates electricity and electric power is stored in condenser  48 , the charging voltage, Vc, increases with the passage of time. Thus, the S/N ratio between the control signal φ 13  and noise, Ln, due to magnetic fields increases, i.e., noise level Ln decreases relative to control signal φ 13 . As a result, the ability to detect magnetic fields generated by electricity generating device  40  decreases as charging voltage Vc increases even though the intensity of the magnetic field itself does not decrease. To prevent this from occurring, φ 13 , which is proportional to charging voltage Vc, is supplied from driving control circuit  24  to setting unit  27   b . So that set value SV 2  may be adjusted to increase detection sensitivity. 
     Like the conventional device previously described, in timing device  1 , auxiliary pulse supplying unit  24   d  of driving control circuit  24  supplies auxiliary pulse P 2  having greater effective electric power than driving pulse P 1 . If it is determined by rotation detecting unit  26  of detection circuit  25  that driving rotor  13  did not rotate or if a magnetic field is detected by magnetic field detecting unit  27 , auxiliary pulse P 2  is output ensuring that driving rotor  13  rotates. However, because the detection capabilities of magnetic field detecting unit  27  is increased in the present invention, auxiliary pulses P 2  may be output without having to actually determine whether rotor  13  is rotated. Therefore, the effects of the magnetic field generated by electricity generating device  40  or externally are minimized, thereby enabling movement of the hands with very high reliability. 
     Auxiliary pulse supplying unit  24   d , according to the present embodiment, may be configured to supply different auxiliary pulses suitable in a variety of situations. These include supplying auxiliary pulses for when driving rotor  13  does not rotate in response driving pulse P 1 , when a high-frequency magnetic field has been detected using magnetic field detecting pulse SP 0 , and when low-frequency magnetic field has been detected using magnetic field detecting pulse SP 1 . Although it is possible to keep the effective power of these different auxiliary pulses the same, it is possible to supply auxiliary pulses having different effective electric powers for each of these situations. 
     Also, according to the present embodiment, demagnetizing pulse supplying unit  24   e , which outputs demagnetizing pulses PE, is constructed so that the output of demagnetizing pulse PE is delayed from being output immediately after auxiliary pulse P 2 , as in conventional systems, and instead output immediately before the next driving pulse P 1  is output. As a result, the effective electric power of the next driving pulse P 1  is increased so that sufficient energy for rotating rotor  13  is provided without the need to increase the actual energy level of driving pulse P 1 . In this way, errors in the movement of hands can be prevented while also reducing the need to use auxiliary pulses having greater power to rotate rotor  13  when magnetic fields from the electricity generating device or external magnetic fields are present. Also, by supplying driving pulse P 1  having a substantially high effective electric power, the rotation of rotor  13  is thereby eliminating the need to perform rotation detection and magnetic field detection which is usually ineffective following the output of auxiliary pulse P 2 . 
     Referring now to FIG. 4, there is shown a flowchart of the method of controlling stepping motor  10  employed in timing device  1  according to the present embodiment. Flowchart steps that correspond to steps previously described in connection with the control method described in FIG. 15 are denoted by the same reference numerals, and detailed a description thereof will be omitted. 
     First, in step ST 1 , a one second duration of time is measured for movement of the hands. After one second has elapsed, in step ST 21  a determination is made whether auxiliary pulse P 2  was output in the previous cycle. If auxiliary pulse P 2  was output in the previous cycle, in step ST 25 , demagnetizing pulse PE having a reverse polarity than that of auxiliary pulse P 2  is output immediately before driving pulse P 1  is output in step ST 26 . Accordingly, in the cycle following output of auxiliary pulse P 2 , the electric power of demagnetizing pulse PE is used to substantially increase the effective electric power of driving pulse P 1 . 
     If auxiliary pulse P 2  has not been output in the previous cycle, in step ST 2 , it is determined whether high-frequency magnetic fields are present using magnetic field detecting pulse SP 0 , as in the conventional systems. However, in the present embodiment, magnetic field detecting unit  27  adjusts set value SV 2  according to charging voltage VC, so that a high level of detection sensitivity of magnetic fields is maintained even as charging voltage VC rises. If a high-frequency magnetic field was detected in step ST 4 , it is possible that it is because electricity generating device  40  is generating electricity. Therefore, if short pulses, such as fast-forward pulses or reverse pulses, are being output, the output of those short pulses are forcibly terminated in step ST 15 . Further, in step ST 7 , auxiliary pulse P 2 , having a greater effective electric power than driving pulse P 1 , is output instead of driving pulse P 1  thus ensuring that rotor  13  rotates and preventing errors in the movement of the hands due to unreliable rotation detection. 
     If no high-frequency magnetic field is detected in step ST 2 , in steps ST 23  and ST 24 , magnetic field detecting pulses SP 1  are output to the driving pole side and the reverse pole side, respectively, to determine whether a low-frequency alternating current magnetic field exists. Because set value SV 2 , used in steps ST 23  and ST 24  to evaluate the induction voltage caused by the magnetic field, varies with charging voltage Vc, high detection capabilities are maintained even as charging voltage Vc changes as the output of electricity generating device  40  changes. If an alternating current magnetic field is detected, it is possible that it is because of electricity generating device  40  generating electricity which may cause the voltage levels of short pulse to become unstable. Therefore, if a low frequency field is detected in step ST 23  or step ST 24 , in step ST 15 , the output of short pulses is forcibly terminated as described above. Also, auxiliary pulse P 2  is output in step ST 7  instead of driving pulse P 1 , thus preventing an error in the movement of the hands. 
     If there is no detection of magnetic field in steps ST 2 , ST 23  or ST 24 , driving pulse P 1  is output in step ST 4 , and then, in step ST 5 , rotation detecting pulse SP 2  is output to determine whether rotor  13  rotated. If the rotation cannot be confirmed, auxiliary pulse P 2 , having a greater effective electric power than driving pulse P 1 , is output in step ST 7 , thereby ensuring that rotor  13  rotates. In conventional control methods, once auxiliary pulse P 2  is output, demagnetizing pulse PE is also output immediately thereafter. However, in the present invention, demagnetizing pulse PE is not output at this time but instead is output in step ST 25  immediately before driving pulse P 1  of the next cycle is output, as described above. 
     If auxiliary pulse P 1  was output in step ST 7 , level adjustment of driving pulse P 1  (first level adjustment) is performed in step ST 10 . In this way, a driving pulse P 1 , having a greater effective electric power than driving pulse P 1 , is supplied for the next cycle. On the other hand, if rotation of rotor  13  was confirmed in step ST 5 , level adjustment for lowering the effective electric power of driving pulse P 1  (second level adjustment) is performed in step ST 6 . In many cases, the effective electric power of driving pulse P 1  is lowered at certain cycles. By performing level adjustment of driving pulse P 1 , the power consumption of driving pulse P 1  is reduced and errors in the movement of the hands due to magnetic fields from electric household appliances are eliminated so that timing device  1  with high reliability and low power consumption is provided. 
     Referring now to FIG. 5, there is shown a timing chart illustrating the operation of control device  20  according to the present embodiment. As with the conventional device depicted in FIG. 14, FIG. 5 illustrates the control signals that are supplied to gates GP 1 , GN 1 , and GS 1  of the p-channel MOSFET  33   a , n-channel MOSFET  32   a , and sampling p-channel MOSFET  34   a , respectively, for excitation of driving coil  11  of a magnetic field of one polarity, and to gates GP 2 , GN 2 , and GS 2  of the p-channel MOSFET  33   b , n-channel MOSFET  32   b , and sampling p-channel MOSFET  34   b , respectively, for excitation of a magnetic field of the reverse polarity. Like elements to those described in FIG. 14 are denoted by the same reference numerals and a description thereof is omitted. 
     Initially, when one second of time elapses in step ST 1 , and no output of auxiliary pulse P 2  has occurred in the previous cycle, operation moves from step ST 21  to ST 2 . In step ST 2 , the first cycle begins when magnetic field detecting pulse SP 0  is output at time t 21  for detecting a high-frequency magnetic field. Next, in steps ST 23  and ST 24 , control signals are supplied so that magnetic field detecting pulses SP 1  are output at time t 22  and t 23 , respectively, for detecting alternating current magnetic fields at both pole gates GP 1  and GP 2 . If no magnetic field is detected in steps ST 23  and ST 24 , driving pulse P 1  having a pulse width of, for example W 10 , is supplied at time t 24  in step ST 4 . Next, rotation detecting pulse SP 2  is output at time t 25  in step ST 5 . If the rotation of driving rotor  13  is detected, this cycle is completed, and the system returns to step ST 1  and conducts timing. 
     When the next cycle is started at time t 31 , a control signal for outputting magnetic field detecting pulse SP 0  for detecting a high-frequency noise magnetic field is supplied to the driving pole side gate GP 2  which is on the opposite side as compared to the previous cycle. Subsequently, control signals are supplied to output magnetic field detecting pulses SP 1  to each pole gate GP 2  and GP 1  at time t 32  and t 33 , respectively. If electricity generating device  40  has started generating electricity, the induction voltage generated by the magnetic field reaches set value SV 2 , and a magnetic field is detected in steps ST 23  or ST 24 . Once the magnetic field has been detected, the rotation of rotor  13  is ensured by outputting auxiliary pulse P 2  in step ST 7 , having a greater effective electric power than driving pulse P 1 , instead of driving pulse P 1 , at time t 34 . 
     When the next cycle is started at time t 41 , a determination is made in step ST 21  as to whether auxiliary pulse P 2  was output in the previous cycle. If auxiliary pulse P 2  was output, demagnetizing pulse PE is immediately output in step ST 25 , with driving pulse P 1  being output immediately thereafter at time t 42  in step ST 26 . Because demagnetizing pulse PE has a reverse polarity than that of auxiliary pulse P 2 , and driving pulse P 1  of the next cycle is output immediately after the output of demagnetizing pulse PE, the effective electric power output of driving pulse P 1  is substantially increased. By increasing the effective electric power output of driving pulse P 1 , rotation of rotor  13  is ensured even in the presence of a magnetic field attributable to electric power generation or a residual magnetic field and, because rotation detection can be omitted, the danger of an erroneous rotation detection is eliminated. Also, because magnetic field detection capabilities deteriorate as a result of auxiliary pulse P 2  being output, the fact that magnetic field detection can be omitted is immensely advantageous. Thus, by timing demagnetizing pulse PE in such a manner, movement of the hands can be conducted reliably. Further, the energy of demagnetizing pulse PE can also be used to rotate rotor  13 , so that overall electricity consumption can also be reduced. 
     After driving pulse P 1  is output in the step ST 26 , the system returns to step ST 1  and conducts timing. Then, when the next cycles begins, magnetic field detecting pulse SP 0 , used for detecting high-frequency magnetic field noise, is output at time t 51  in the same manner as described above. Also, pulses SP 1  for detecting alternating current magnetic fields, are sequentially output to both pole sides at time t 52  and t 53 , respectively. When electricity generating device  40  has stopped generating electricity and a magnetic field is not detected, driving pulse P 1  is output at time t 54 , and thereafter, rotation detecting pulse SP 2  is output. If rotation of rotor  13  is not detected in step ST 5 , auxiliary pulse P 2  is output in step ST 7 . At this point demagnetizing pulse PE is not output and the cycle is completed. Once the next cycle begins at time t 61 , demagnetizing pulse PE is then output at time t 61 . 
     At time t 62 , a driving pulse P 1 ′ having a substantially increased effective power as compared to driving pulse P 1 , is output so that the rotation of rotor  13  is ensured. The effective electric power of driving pulse P 1 ′ was increased in step ST 10  because, for example, rotation could not be detected in the previous cycle. In the present embodiment, driving pulse P 1 ′ has a pulse width W 11  that is wider than the width of driving pulse P 1  output in the previous cycle. However, by using booster/reducer circuit  49 , the effective electricity of driving pulse P 1 ′ may be controlled by increasing the voltage level instead of or in addition to increasing the pulse width. 
     Referring now to FIGS. 6,  7 , operation of timing device  1  in accordance with a second embodiment will be described. Because timing device  1  of the second embodiment uses the same structure as the previous embodiment, a detailed description of the drawings will be omitted. 
     In control device  20  of timing device  1 , according to the second embodiment, output voltage φ 12  of booster/reducer circuit  49  is monitored to determine whether electricity generating device  40  is generating electricity. If it is found that electricity generating device  40  is generating electricity, fast-forward pulses output by driving pulse supplying section  24   a  is forcibly terminated. Also, because reliable rotation detection is difficult to accomplish in the presence of electricity generation, magnetic field detecting pulses SP 0  and SP 1  are not output, and auxiliary pulse P 2 , which has a greater effective electric power, than driving pulse P 1 , is output. The effective energy of auxiliary pulse P 2  is selected so that rotation of rotor  13  is ensured thereby eliminating the need to perform rotation detection. Accordingly, errors in the movement of the hands resulting from noise generated by rotation detection and from unreliable rotation detection can be prevented. Also, because auxiliary pulse P 2  decreases magnetic field detection capabilities, detecting whether electricity is being generated instead further improves reliability. 
     The flowchart of FIG. 6 depicts the control method of stepping motor  10  employed in the second embodiment. Flowchart steps that correspond to steps in the previous embodiment are denoted by the same reference numerals, and a detailed description thereof will be omitted. 
     First, in step ST 1 , one second of time is measured for movement of the hands. Next, in step ST 31 , it is determined whether electricity generating device  40  is generating electricity. If electricity generating device  40  is generating electricity, voltages will fluctuate causing errors in the movement of the hands. Accordingly, any fast-forward control or reverse control pulses being output from driving pulse supplying section  24   a  are forcibly terminated. Furthermore, considering that rotation detection is unreliable when electricity is being generated by electricity generating device  40 , magnetic field detecting pulses SP 0  and SP 1  are not output, and auxiliary pulse P 2  is output instead of pulse P 1  in step ST 7  thereby ensuring that rotor  13  is rotated. Therefore, because in the this embodiment, magnetic field detecting pulses SP 0  and SP 1  and rotation detecting pulse SP 2  are omitted when electricity is being generated and auxiliary pulse P 2  is supplied overall, power consumption related to driving rotor  13  is optimally reduced. 
     If electricity is not being generated by electricity generating device  40 , magnetic field detecting pulse SP 0  is used for determining whether an external high-frequency magnetic field is present in step ST 2 , and magnetic field detecting pulse SP 1  is used for determining whether an external alternating current magnetic field (low-frequency noise) is present in step ST 3 , as described above. Then, if there is no detection of magnetic fields which would interfere with rotation detection in either step ST 2  or ST 3 , driving pulse P 1  is output in step ST 4 , and subsequently, a rotation detecting pulse SP 2  is output in step ST 5 , for detecting whether rotation of rotor  13  occurred. If rotation cannot be detected, auxiliary pulse P 2  is output in step ST 7 , thereby ensuring that rotor  13  is rotated. Next, in step ST 8 , demagnetizing pulse PE is output, followed by the level adjustment of driving pulse P 1  in ST 10 , if necessary. If, in step ST 5 , rotation of rotor  13  is detected, level adjustment is performed in step ST 6  if rotation occurred, thereby lowering the effective electric power of driving pulse P 1 , if the conditions are favorable. 
     Referring now to FIG. 7, there is shown a timing chart illustrating the operation of control device  20  according to the second embodiment. As with the previous embodiment described in FIG. 5, FIG. 7 illustrates the control signals that are supplied to gates GP 1 , GN 1 , and GS 1  of the p-channel MOSFET  33   a , n-channel MOSFET  32   a , and sampling p-channel MOSFET  34   a , respectively, and to the gates GP 2 , GN 2 , and GS 2  of the p-channel MOSFET  33   b , n-channel MOSFET  32   b , and sampling p-channel MOSFET  34   b , respectively, of driving circuit  30 . Like elements to those described in FIG. 5 are denoted by the same reference numerals and a detailed description thereof is omitted. 
     Initially, after a certain amount of time (one second) elapses in step ST 1 , and no electricity generation is detected in step ST 31 , the operation moves to ST 2  where magnetic field detecting pulse SP 0  is output at time t 71  for detecting high-frequency magnetic fields. Next, in step ST 3 , magnetic field detecting pulse SP 1 , which detects alternating current magnetic fields, is output at time t 72  to gate GP 2  of the reverse pole side. Because in the second embodiment the operation of control device  20  depends on the detection of electricity generation and not on whether a magnetic field is present, there is no need to determine whether a magnetic field is present as a result of electricity generation. Accordingly, magnetic field detecting pulse SP 1 , which detects the alternating current magnetic field, is only output to the side opposite of the driving side (reverse side). 
     If a magnetic field is not detected in steps ST 2  and ST 3 , driving pulse P 1  is output at time t 73  in step ST 4 , and subsequently, rotation detecting pulse SP 2  is output at time t 74  in step ST 5 . Then, if the rotation of driving rotor  13  is detected, this cycle is completed, and the system returns to step ST 1  and conducts timing. 
     When the next cycle is started at time t 81 , it is first determined whether electricity generation is present and, in the event that it is, the system proceeds to step ST 7  in which control signals for outputting auxiliary pulse P 2  to gates GP 2  and GN 2  of the driving pole side, which is the reverse from the previous cycle, are supplied. Driving rotor  13  completely rotates by means of auxiliary pulse P 2  rendering rotation detection unnecessary, and thereafter, demagnetizing pulse PE is output from the reverse pole side at time t 82  in step ST 8 , thereby completing the cycle. 
     When the next cycle is started at time t 83 , if electricity generation is detected in step ST 31 , the system proceeds to step ST 7 , in which control signals for outputting auxiliary pulse P 2  to gates GP 1  and GN 1  of the driving pole side, which is the reverse from the previous cycle, are supplied. Driving rotor  13  completely rotates by means of the auxiliary pulse P 2  rendering rotation detection unnecessary, and thereafter, demagnetizing pulse PE is output from the reverse pole side at time t 84  in step ST 8 , thereby completing the cycle. 
     When the next cycle is started at time t 91 , if electricity generation is detected in step ST 31 , the system performs magnetic field detecting in steps ST 2  and ST 3 , and outputs both high-frequency detecting pulse SP 0  and low-frequency detecting pulse SP 1 . If a magnetic field is not detected, driving pulse P 1  is output at time t 93  and the rotation of rotor  13  is confirmed at time t 94 . If a magnetic field is detected by either of the detecting pulses SP 0  or SP 1 , auxiliary pulse P 2  is output instead of the driving pulse P 1 , ensuring that rotor  13  rotates and rendering rotation detection unnecessary. 
     Thus, in timing device  1  constructed according to the second embodiment, a control method is employed in which it is assumed that a magnetic field, which would affect rotation detection, is present if electricity generating device  40  is generating electricity. Accordingly, the difficult and unreliable step of detecting the presence of a magnetic field generated by electricity generating device  40  is omitted thereby simplifying device control and eliminating error in movement of the hands. Also the consumption of electricity tends to decrease during electricity generation because movement of the hands is conducted using auxiliary pulse P 2  which has great effective power. However, because the steps of detecting magnetic fields and detecting rotation of the rotor are also omitted, when auxiliary pulse P 2  is used, the increase in overall electricity consumption as a result auxiliary pulse P 2  is minimized. Furthermore, because it is possible that driving voltage will fluctuate during electricity generation, fast-forward and reverse are forcibly terminated. Thus, by monitoring whether electricity is being generated, timing device  1  according to the second embodiment achieves extremely high reliability and eliminates error in the movement of the hands. 
     Referring now to FIGS. 8,  9 , timing device  1  operating in accordance with a third embodiment will be described. Because timing device  1  of the third embodiment uses the same structure as the embodiment described in FIG. 1, a detailed description of the drawings will be omitted. 
     Control device  20  of timing device  1  according to the third embodiment takes advantage of the fact that once a magnetic field is detected and auxiliary pulse P 2  is supplied, electricity generating device  40  continues to operate for a certain period of time. Thus, it is assumed that a magnetic field is present for a certain number of cycles after auxiliary pulse P 2  is output and, as a result, highly reliable processing is achieved. Driving pulse supplying unit  24   a  of the present embodiment is configured so that if auxiliary pulse P 2  is output, a driving pulse P 1 ″ is supplied which has an effective electric power that is several levels greater than the driving pulse P 1  previously supplied. Also, in this embodiment, it is assumed that electricity generation occurs whenever a magnetic field is detected, so fast-forward and reverse operations are forcibly terminated to prevent error in movement of the hands resulting from voltage fluctuation. Also, because auxiliary pulse P 2  causes magnetic field detecting capabilities to deteriorate, detection of the magnetic field is not performed for the predetermined number of cycles in which driving pulses P 1 : having a greater effective electrical power are output. 
     The flowchart of FIG. 8 depicts the method of controlling stepping motor  10  employed in the third embodiment. Flowchart steps that correspond to steps in the previous embodiment are denoted by the same reference numerals, and a detailed description thereof will be omitted. 
     First, in step ST 1 , one second of time is measured for movement of the hands. Next, in step ST 41 , it is determined whether the preceding cycle is within a predetermined number of cycles C (certain time span) from the output of auxiliary pulse P 2 . If the number of cycles from the most recent cycle in which auxiliary pulse P 2  output is within C cycles, it is assumed that a magnetic field or the effects of a residual magnetic field are present, and that magnetic field detection is still unreliable. Accordingly, detection of the magnetic field is not performed within C cycles from most recent auxiliary pulse P 2 , and short pulses, such as fast-forward and reverse pulses, are forcibly terminated in step ST 42 , and a driving pulse P 1 ″ is supplied in step ST 43 , which has a level that is several degrees greater in effective electric power than that of driving pulse P 1  previously supplied, thereby ensuring the rotation of rotor  13 . As a result, the rotation detection step may be omitted and errors in the movement of the hands are eliminated. Then, the system returns to step ST 1  and conducts timing. 
     If the number of cycles from the output of the most recent auxiliary pulse P 2  exceeds C cycles, magnetic field detecting pulse SP 0  is used for detecting external high-frequency magnetic field in step ST 2 , and the detection of alternating current magnetic field is conducted for both pole sides in step ST 23  and step ST 24 , respectively. Thus, the magnetic field generated by electricity generating device  40  can be easily detected. If a magnetic field is detected in steps, ST 2 , ST 23  and ST 24 , rotation detection is unreliable so the system proceeds to step ST 15  in which short pulse driving is stopped and then to ST 7  in which auxiliary pulse P 2 , having a greater effective electrical power than driving pulse P 1 , is supplied. 
     If there is no detection of magnetic fields which might interfere with rotation detection, driving pulse P 1  is output in step ST 4  and, thereafter, rotation detecting pulse SP 2  is output in step ST 5  to determine whether rotor  13  rotated. If rotation of rotor  13  cannot be confirmed, auxiliary pulse P 2 , having a greater effective electrical power than driving pulse P 1 , is supplied in step ST 7 , thereby ensuring that rotor  13  rotates. Next, in step ST 8 , demagnetizing pulse PE is output and, thereafter, the level of driving pulse P 1  is adjusted in step ST 10 , if necessary. If in step ST 5 , the rotation of rotor  13  by driving pulse P 1  is confirmed, level adjustment is performed in step ST 6  to lower the effective electric power of driving pulse P 1 , if the conditions are favorable. 
     Referring now to FIG. 9, there is shown a timing chart illustrating the operation of control device  20  according to the third embodiment. As with the second embodiment described in FIG. 7, FIG. 9 illustrates the control signals that are supplied to gates GP 1 , GN 1 , and GS 1  of the p-channel MOSFET  33   a , n-channel MOSFET  32   a , and sampling p-channel MOSFET  34   a , respectively, and to gates GP 2 , GN 2 , and GS 2  of the p-channel MOSFET  33   b , n-channel MOSFET  32   b , and sampling p-channel MOSFET  34   b , respectively, of driving circuit  30 . Like elements to those described in FIG. 7 are denoted by the same reference numerals and a detailed description thereof is omitted. 
     After a certain amount of time (one second) elapses in step ST 1 , if, in step ST 41 , it is determined that C cycles have already elapsed from the last auxiliary pulse P 2  supplied, operation proceeds to step ST  2  in which magnetic field detecting pulse SP 0  is output at time t 101  for detecting high-frequency noise magnetic field. Next, in steps ST 23  and ST 24 , control signals for outputting magnetic field detecting pulses SP 1  are supplied to the reverse pole side gate GP 2  and driving pole side gate GP 1  at time t 102  and t 103 , respectively. If there is no detection of magnetic fields in these steps, driving pulse P 1  of voltage V 10  is supplied at time t 104  in step ST 4  and, then, in step ST 5 , rotation of rotor  13  is detected at time t 105 . If the driving rotor  13  was rotated, the system returns to step ST 1  and conducts timing. 
     When the next cycle is started at time t 111 , high-frequency magnetic field detecting pulse SP 0  is output as described above, and thereafter, alternating current magnetic field detecting pulse SP 1  is output at time t 112  on the reverse pole side and, at time t 113 , on the driving pole side. If a magnetic field is detected by magnetic field detecting pulse SP 1 , the system proceeds to step ST 7 , and auxiliary pulse P 2 , having a greater effective electrical power than driving pulse P 1 , is output at time t 114 . Thereafter, a demagnetizing pulse PE is output at time t 115 , thus completing the cycle. 
     When the next cycle starts at time t 121 , in step ST 41 , if, for example, C is set to 2, the present cycle is within C cycles from a cycle in which auxiliary pulse P 2  was output. Accordingly, the system proceeds to step ST 42 , and the various magnetic field detecting steps are not performed. If fast-forward driving is being performed, this is forcibly terminated in step ST 42 . In the case of normal driving, driving pulse P 1 ″ is selected and output in step ST 43 , driving pulse P 1 ″ being of a level several degrees greater in effective electric power than that of driving pulse P 1  which was supplied at time t 104 . In timing device  1  of the present embodiment, booster/reducer circuit  49  can be used to change the voltage of driving pulse P 1 . Accordingly, at time t 121 , driving pulse P 1 ″ having a voltage of V 11  or greater (where V 11 &gt;V 10 ) is output if a magnetic field was detected. Thus, a highly reliable and accurate timing device  1  is provided without having to detect the presence of magnet noise or whether rotor  13  rotated. 
     The next cycle, which starts at time t 131 , is also within C cycles of the last auxiliary pulse P 2  (for C=2). Accordingly, driving pulse P 1 ″ is output in step ST 43  at time t 131 . 
     The next cycle, which starts at time t 141 , is beyond C cycles from the last auxiliary pulse P 2 . In this case, magnetic field detecting pulses SP 0  and SP 1  are output at times t 141 , t 142 , and t 143 , respectively, so as to detect whether a magnetic field is present. If a magnetic field is not detected, driving pulse P 1 , having an effective electrical power of voltage of V 10  that is approximately equal to the effective electrical power of driving pulse P 1  output at time t 104 , is output at time t 144 , and rotation detecting pulse SP 2  is output at time t 145 . On the other hand, if a magnetic field is detected, auxiliary pulse P 2  is output again, and driving pulse P 1 ″ of increased effective electrical power is output for the next two cycles. 
     Although FIG. 9 illustrates increasing the effective electrical power of driving pulse P 1 ″ by increasing its voltage, the effective electrical power may also be increased by increasing the pulse width of driving pulse P 1 ″. Alternatively, both voltage and pulse width characteristics may be used for controlling the effective electrical power of driving pulse P 1 ″, or driving pulse P 1 , P 1 ″, or auxiliary pulse P 2  may be comprised of a plurality of sub-pulses with the effective electrical power controlled according to the duty ratio thereof. Further, the detection of magnetic fields may also be conducted at each cycle even following the output of auxiliary pulse P 2  so that magnetic field detecting capabilities during electricity generation is increased. 
     Referring now to FIGS. 10-11, timing device  1  operating in accordance with a fourth embodiment will be described. Because timing device  1  of the fourth embodiment uses the same structure as the embodiment described in FIG. 1, a detailed description of the drawings will be omitted. 
     Control device  20  according to the fourth embodiment is constructed so as to further improve the reliability of detecting the magnetic fields generated by electricity generating device  40  which may be as little as 100 ms in duration. To accomplish this, magnetic field detecting pulse supplying unit  24   c  supplies magnetic field detecting pulses SP 1  before driving pulse P 1 , and also supplies magnetic field detecting pulses SP 1  again following rotation detecting pulse SP 2 . Furthermore, the polarity of the two magnetic field detecting pulses SP 1  are changed in order to further improve the probability of detecting the presence of magnetic fields. 
     The flowchart of FIG. 10 depicts the method of controlling stepping motor  10  employed in the fourth embodiment. Flowchart steps that correspond to steps in previous embodiment are denoted by the same reference numerals, and detailed a description thereof will be omitted. 
     First, in step ST 1 , one second of time is measured for movement of the hands. Next, if one second has elapsed, magnetic field detecting pulse SP 0  is used for determining whether external high-frequency magnetic fields are present in step ST 2 . If no field is present, a magnetic field detecting pulse SP 1  is used for detecting external alternating current magnetic field (low-frequency noise) at one pole side in steps ST 23 , as described above. If a magnetic field is detected in steps ST 2  or ST 23 , rotation detection of rotor  13  becomes unreliable, so the system proceeds to step ST 15 , in which short pulses such, as fast forward and reverse pulses, are forcibly terminated, and to step ST 7 , in which auxiliary pulse P 2 , having a greater effective electrical power than driving pulse P 1 , is supplied. 
     If no magnetic fields, which might interfere with rotation detection, are detected in these steps, driving pulse P 1  is supplied in step ST 4 , and then, in step ST 5 , rotation detecting pulse SP 2  is outputted to determine whether rotor  13  has rotated. If the rotation of rotor  13  cannot be confirmed, auxiliary pulse P 2 , having a greater effective electrical power than driving pulse P 1 , is supplied in step ST 7 , so that the rotation of rotor  13  is ensured. Thereafter, in step ST 8 , demagnetizing pulse PE is output, and in step ST 10 , the level of driving pulse P 1  is adjusted, if necessary. 
     If the rotation of rotor  13 , in response to driving pulse P 1  is detected in step ST 5 , then in step ST 24 , magnetic field detecting pulse SP 1  is output for detecting the presence of external alternating current magnetic fields (low-frequency magnetic fields) at the pole side that is opposite to the pole tested in step ST 23 . If an alternating current magnetic field is detected in step ST 24 , there is a high possibility that rotation detection was erroneous, so auxiliary pulse P 2  is supplied in step ST 7 , as described in the previous embodiment. Thus, the probability of detecting the presence of a magnetic field is greatly improved by supplying magnetic field detecting pulses SP 1  at two steps: before driving pulse P 1  is output, and following rotation detecting pulse SP 2 . 
     Because electricity generating device  40  generates electricity in short, irregular bursts, even if no magnetic noise was detected before driving pulse P 1  was supplied, magnetic noise may be present at the time when rotation detecting pulse SP 2  is output. Accordingly, in the fourth embodiment magnetic noise is detected immediately after rotation detecting pulse SP 2  is output as well, so that there is a high probability that magnetic fields will be detected thus making rotation detection highly reliable. 
     Referring now to FIG. 11, there is shown a timing chart illustrating the operation control device  20  according to the fourth embodiment. As with the previous embodiments described in FIGS. 7 and 9, FIG. 11 illustrates the control signals that are supplied to gates GP 1 , GN 1 , and GS 1  of the p-channel MOSFET  33   a , n-channel MOSFET  32   a , and sampling p-channel MOSFET  34   a , respectively, and to the gates GP 2 , GN 2 , and GS 2  of the p-channel MOSFET  33   b , n-channel MOSFET  32   b , and sampling p-channel MOSFET  34   b , respectively, of driving circuit  30 . Like elements to those described in FIGS. 7 and 9 are denoted by the same reference numerals and a detailed description thereof is omitted. 
     After a certain amount of time (one second) elapses in step ST 1 , magnetic field detecting pulse SP 0  used for detecting high-frequency noise magnetic fields is output at time t 151 . Next, in step ST 23 , a control signal, to output magnetic field detecting pulse SP 1  for detecting alternating current magnetic fields is supplied to gate GP 2  which is on the reverse pole side, and a magnetic field detecting pulse SP 1  is output at time t 152 . If magnetic fields are not detected, driving pulse P 1  having a pulse width W 10  is supplied in step ST 4  at time t 153 , and then, in step ST 5 , rotation detection of driving rotor  13  is performed at time t 154 . In this embodiment, following rotation detection, at time t 155 , a control signal to output a magnetic field detecting pulse SP 1  for detecting alternating current magnetic fields is supplied in step ST 24  to gate GP 21  which is on the driving side, and the second detection of low-frequency magnetic field is performed. If a magnetic field is detected by the second magnetic field detecting pulse SP 1 , the system proceeds to step ST 7 , and auxiliary pulse P 2 , having a greater effective electric power than driving pulse P 1 , and having a pulse width of W 20  (where W 20 &gt;W 10 ), is output at time t 156 , and thereafter at time t 157 , demagnetizing pulse PE is output. 
     When the next cycle is started at time t 161 , high-frequency magnetic field detecting pulse SP 0  is output, as above, and thereafter, pulse SP 1 , for detecting alternating current magnetic fields, is output at time  162 . If a magnetic field is not detected at this time, driving pulse P 1  is supplied at time t 163 , and rotation detecting pulse SP 2  is supplied at time t 164 . Afterwards, magnetic field detecting pulse SP 1  is output for a second time at time t 165  and, if a magnetic field is not detected at this time, the indication that rotation occurred in step ST 5  is deemed reliable. 
     Also, in this embodiment, magnetic field detecting pulse SP 1  for the reverse pole side is output before driving pulse P 1 , while magnetic field detecting pulse SP 1  for the driving pole side is output following the rotation detecting pulse SP 2 , so as to facilitate magnetic noise detection on the side at which error easily occurs during rotation detection. Alternatively, magnetic field detecting pulse SP 1  may be output to the driving pole side before driving pulse P 1 , and magnetic field detecting pulse SP 1  maybe output to the reverse pole side following rotation detecting pulse P 2 . In yet another embodiment, magnetic field detecting pulses SP 1  of different polarities may each be output before driving pulse P 1 , and then, following rotation detecting pulse SP 2 , magnetic field detecting pulses SP 1  of either one polarity or two polarities may be output, thereby further increasing the probability of detecting a magnetic field. 
     As described above, timing device  1 , constructed in accordance with the present invention, increases the probability of detecting the presence of a magnetic field so that magnetic fields generated by built-in electricity generating device  40  can be detected. This prevents the adverse effects of a magnetic field generated by electricity generating device  40 , in addition to the effects of external magnetic fields from causing errors in the movement of the hands of timing device  1 . Because it is assumed that a magnetic field is present during the generation of electricity, hand movements can be performed with high precision even though built-in electricity generating device  40  generates electricity, and thus magnetic noise, in short, irregular bursts. In this way, the precision of timing device  1  is vastly improved and can also be used without a battery. 
     The benefits of the present invention are not limited to timing devices, such as wristwatches or the like, but can also be provided for multiple-function timepieces such as chronographs or other generating devices, and also for devices and apparatuses having built-in stepping motors. 
     Also, the waveform of the pulses described above, i.e., driving pulse P 1 , auxiliary pulse P 2 , magnetic field detecting pulses SP 0  and SP 1 , and rotation detecting pulse SP 2 , etc. are illustrated only as examples, and it goes without saying that the waveforms can be set according to the properties of stepping motor  10  employed in timing device  1 . Also, in the above example, the present invention was described as having a two-phase stepping motor which is favored for use in timing devices  1 , but it is needless to say that the present invention can be also applied to stepping motors having three-phases and higher, in the same manner. Also, instead of performing common control of each phase, the driving pulses may be provided at pulse widths and timing appropriate for each phase. Also, it is needless to say that the driving method of stepping motor  10  is by no means restricted to single-phase excitation, and may employ two-phase excitation or 1-2 phase excitation. 
     As described above, the control method and control device  20  according to the present invention increases the probability of magnetic field detection so that magnetic fields generated by electricity generating device  40  can be detected. Also, because it is assumed that a magnetic field is present during the generation of electricity, a driving pulse having a greater effective electric power than driving pulse P 1 , such as auxiliary pulse P 2  is output. Accordingly, by using control device  20  and method of the present invention, the effects of a magnetic field from electricity generating device  40  stored in timing device  1 , or a device having a stepping motor, can be greatly minimized thereby providing a highly accurate timing device  1  which can be used anytime and anywhere without batteries. 
     The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and the apparatus embodying features of construction, combinations of elements and arrangement of parts which are adapted to effect such steps, all as exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the aims.