Patent Publication Number: US-8540417-B2

Title: Chronograph timepiece

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a chronograph timepiece having a time indicating function and a time measuring function. 
     2. Description of the Related Art 
     Conventionally, there has been developed a chronograph timepiece in which a plurality of motors are mounted to respectively drive a plurality of hands and which is equipped with a chronograph function that is, a time measuring function, in addition to a function to indicate time information as a basic function wherein the driving of the hands is effected electrically by the motors, with the zero-restoring of chronograph hands being effected by a mechanical structure such as a heart cam (See, for example, JP-A-61-73085 and JP-A-2006-90769). 
     In the related-art chronograph timepiece, stepping motors are used as the motors. As shown in  FIG. 7 , drive pulses of different polarities are alternately supplied to a section between a first terminal OUT 1  and a second terminal OUT 2  of a drive coil, whereby the motors are continuously rotated in a fixed direction. When a reset operation is performed on an operation unit, the driving by the drive pulses is stopped at that point in time, and the driving of the motors is stopped. 
     In this way, in the related-art chronograph timepiece, the driving of the motors is immediately stopped through the reset operation, so that, due to the cam zero-restoring at the time of reset operation, backlash is generated in a train wheel for transmitting the rotation of the motors to the chronograph hands. Thus, even when the cam zero-restoring is unlocked and drive pulses are output to thereby drive the motors at the time of the subsequent start operation, hand movement is not effected by an amount corresponding to the backlash, with the result that the hand movement operation of the chronograph hands is delayed. 
     SUMMARY OF THE INVENTION 
     It is an aspect of the present invention to provide a chronograph timepiece whose chronograph hands are electrically drive-controlled and mechanically zero-restoring-controlled, wherein even if backlash is generated due to the zero-restoring, the chronograph hands can be moved normally at the time of the next time measurement start. 
     According to the present invention, there is provided a chronograph timepiece including: a drive control unit starting a time measurement operation in response to a start operation of an operation unit, electrically hand-movement-driving a chronograph hand by driving a chronograph hand movement motor according to the time measured, and resetting the time measurement operation in response to a reset operation of the operation unit; and a mechanical structure mechanically zero-restoring and setting the chronograph hand in response to the reset operation, wherein, even after the reset operation is performed, the drive control unit drives the chronograph hand movement motor by a predetermined amount. 
     In the chronograph timepiece of the present invention which is of a construction in which the chronograph hand is electrically drive-controlled and mechanically zero-restoring-controlled, even if backlash is generated due to zero-restoring, it is possible to move the chronograph hand normally at the time of the next time measurement start. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating the configuration of a chronograph timepiece according to a first embodiment of the present invention; 
         FIGS. 2A and 2B  are schematic plan views illustrating the mechanical construction of a chronograph timepiece according to an embodiment of the present invention; 
         FIG. 3  is an external plan view of a chronograph timepiece according to an embodiment of the present invention; 
         FIG. 4  is a schematic diagram illustrating the construction of a stepping motor used in a chronograph timepiece according to an embodiment of the present invention; 
         FIG. 5  is a timing chart for a chronograph timepiece according to the first embodiment of the present invention; 
         FIG. 6  is a timing chart for a chronograph timepiece according to a second embodiment of the present invention; and 
         FIG. 7  is a timing chart for a conventional chronograph timepiece. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following, a chronograph timepiece according to an embodiment of the present invention will be described with reference to the drawings.  FIGS. 1 and 5  are diagrams illustrating the first embodiment of the present invention,  FIG. 6  is a diagram illustrating the second embodiment of the present invention, and  FIGS. 2 through 4  are diagrams common to the two embodiments. In the drawings, the same portions are indicated by the same reference numerals. 
     A chronograph timepiece  1  is a chronograph timepiece of a construction in which chronograph hands are electrically drive-controlled and mechanically zero-restoring-controlled. As shown in  FIG. 3 , the chronograph timepiece  1  is in the form of a wristwatch, and is equipped with time hands (an hour hand  11 , a minute hand  12 , and a second hand  13 ) rotated around a center axis C 1  and indicating the current time, and is equipped with chronograph hands (a chronograph second hand  14  rotated around a center axis C 2  and a chronograph minute hand  15  rotated around a center axis C 3 ). 
     For example, by turning a winding stem  16  in a state in which it has been drawn out by two steps in a direction D 1 , it is possible to rotate the time hands  11  through  13 , and by turning the winding stem  16  in a state in which it has been drawn out by one step in the direction D 1 , it is possible to change a date  17  of a date indicator displayed through a window. The operation of the chronograph timepiece  1  related to usual time indication is the same as that of an ordinary electronic timepiece and is well known by those skilled in the art, so that, in the following, a description of the structures, functions and operations related to the usual hand movement will be omitted. 
     In the chronograph timepiece  1 , the chronograph hands  14  and  15  are electrically drive-controlled by a stepping motor, and are zero-restoring-controlled by a mechanical mechanism. 
     In the chronograph timepiece  1 , by depressing a start/stop button  18  in a direction A 1 , an instruction is given to start or stop a chronograph operation (time measurement operation) by the chronograph timepiece  1 . More specifically, the start/stop of the chronograph operation means the start/stop of the hand movement of the chronograph hands  14  and  15 . As described below, in relation to this, there are effected the operation of an electrical drive system and the retention of electrical positional information on the chronograph hands. In some cases, however, there is no need to retain the electrical positional information on the chronograph hands. 
     Further, in the chronograph timepiece  1 , by depressing a reset button  19  in a direction B 1 , an instruction is given to reset the chronograph operation by the chronograph timepiece  1 , that is, to restore (zero-restore) it to an initial state. More specifically, the reset of the chronograph operation means a forcible restoring (zero-restoring) of the chronograph hands  14  and  15  to the initial positions (time indicating positions), the setting of the hand movement of the chronograph hands  14  and  15 , and the reset of the electrical positional information on the chronograph hands. 
     The start/stop button  18  and the reset button  19  constitute operation units. 
     First, a mechanical structure  5  and an operation related to the start, hand movement and zero-restoring of the chronograph timepiece  1  will be described mainly with reference to  FIGS. 2A and 2B . 
     Apart from a time hand movement motor (time indicating motor)  105 , the chronograph timepiece  1  is equipped with a chronograph hand movement motor (chronograph motor)  35 ; when it is rotated, the chronograph hand movement motor  35  moves the chronograph hands  14  and  15  via a chronograph hand movement train wheel  36 . 
     The time hand movement motor  105  and the chronograph hand movement motor  35 , whose constructions will be described below, are stepping motors generally used for timepieces. Each of the stepping motors has a stator having a rotor accommodation hole and a positioning portion determining a rotor stop position, a rotor arranged inside the rotor accommodation hole, and a drive coil; it rotates the rotor by generating a magnetic flux in the stator through supply of alternating signals (drive pulses) whose polarities are alternately different to the drive coil, and stops the rotor at a position corresponding to the positioning portion. Each time it is alternately driven drive pulses of different polarities, the rotor is rotated by a predetermined angle (e.g., 180 degrees) at one time; even if the driving is continuously effected with a plurality of in-phase drive pulses, when the rotation has been effected by the first drive pulse, no rotation is caused by the second in-phase drive pulse onward. 
     The chronograph timepiece  1  is equipped with a chronograph second cam  22  mounted to a chronograph second arbor  21  with the chronograph second hand  14  and a chronograph minute cam  24  mounted to a chronograph minute arbor  23  with the chronograph minute hand  15 . 
     Further, the chronograph timepiece  1  is equipped with a hammer operating first lever (hereinafter also referred to as the “hammer operating lever B”)  25 , a hammer operating second lever (hereinafter also referred to as the “hammer operating lever A”)  26 , and a hammer  27 . 
     The chronograph second cam  22 , the chronograph minute cam  24 , and the hammer  27  constitute a setting mechanism, and the hammer operating second lever  26  and the hammer  27  constitute a releasing unit. Further, the hammer operating second lever  26  and the hammer  27  also constitute a lever unit. 
     The hammer operating first lever  25  is rotatable between a reference position J 1  (indicated by a solid line in  FIG. 2B ) and a zero-restoring position J 2  (indicated by a solid line in  FIG. 2A  and by a dotted line in  FIG. 2B ), and a positioning pin  25   a  thereof is engaged with a spring-like positioning member  29  provided with an engagement groove, whereby positioning is effected at the reference position J 1  or the zero-restoring position J 2 . An elongated hole  26   a  of the hammer operating second lever  26  is engaged with a pin  25   b  of the hammer operating first lever  25 . When the hammer operating first lever  25  is moved from the reference position J 1  to the zero-restoring position J 2  and set in position, the hammer operating second lever  26  is moved from a reference position K 1  (indicated by a solid line in  FIG. 2B ) to a zero-restoring position K 2  (indicated by a solid line in  FIG. 2A  and by a dotted line in  FIG. 2B ). 
     On the other hand, when the hammer operating second lever  26  is moved from the zero-restoring position K 2  to the reference position K 1  and set in position, the hammer operating first lever  25  is moved from the zero-restoring position J 2  to the reference position J 1  and set in position. 
     An elongated hole  27   a  of the hammer  27  is engaged with a pin  26   b  of the hammer operating second lever  26 , and, according to the position setting of the hammer operating second lever  26  to the reference position K 1  or the zero-restoring position K 2 , positioning is effected at a reference position M 1  (indicated by a solid line in  FIG. 2B ) or at a zero-restoring position M 2  (indicated by a solid line in  FIG. 2A  and by a dotted line in  FIG. 2B ). 
     When the hammer  27  is set at the zero-restoring position M 2 , a second hammer portion  27   b  of the hammer  27  strikes the chronograph second cam  22  to zero-restore the chronograph second hand  14  to the initial position, and a minute hammer portion  27   c  thereof strikes the chronograph minute cam  24  to zero-restore the chronograph minute hand  15  to the initial position. 
     When the chronograph timepiece  1  is in a zero-restoring (reset) state S 2  shown in  FIG. 2A , if the start/stop button  18  is depressed in the direction A 1 , a protrusion  26   c  of the hammer operating second lever  26  is pressed in the direction A 1 , and the lever  26  is displaced from the position K 2  to the position K 1  and, at the same time, the hammer operating first lever  25  is displaced from the position J 2  to the position J 1 , and the hammer  27  is displaced from the position M 2  to the position M 1 . As a result, the rotation setting (zero-restoring) of the heart cams  22  and  24  and the chronograph hands  14  and  15  by the hammer portions  27   b  and  27   c  is released. As a result, the mechanical structure  5  is restored to the state S 1 , and the chronograph hands  14  and  15  become rotatable. 
     On the other hand, when the chronograph timepiece  1  is in the start state or hand movement state S 1  shown in  FIG. 2B , if the reset button  19  is depressed in a direction B 1 , the protrusion  25   c  of the hammer operating first lever  25  is pressed in the direction B 1 , and the hammer operating first lever  25  is displaced from the position J 1  to the position J 2 . When the hammer operating first lever  25  is displaced from the position J 1  to the position J 2 , the hammer operating second lever  26  engaged with the lever  25  is moved from the position K 1  to the position K 2  on the one hand, and the hammer  27  engaged with the lever  26  is moved from the position M 1  to the position M 2 , with the second hammer  27   b  and the minute hammer  27   c  striking the second heart  22  and the minute heart  24  to zero-restore the chronograph second hand  14  and the chronograph minute hand  15 . 
     The electrical aspect of the chronograph timepiece  1  as far as it is related to the mechanical structure  5  shown in  FIGS. 2A and 2B  is as follows. 
     When the chronograph timepiece  1  is in the reset state S 2  shown in  FIG. 2A , if the start/stop button  18  is depressed in the direction A 1 , the start/stop button  18  presses a start/stop switch spring  33  exerting a biasing force in a direction A 2  in the vicinity of the depth end thereof and closes a contact portion  34 , generating a start signal Pa via the contact portion  34 . When the chronograph timepiece  1  is in the start state S 1  shown in  FIG. 2B , if the start/stop button  18  is depressed in the direction A 1 , the start/stop button  18  presses the start/stop switch spring  33  and closes the contact portion  34 , generating a stop signal Pb via the contact portion  34 . 
     On the other hand, when the chronograph timepiece  1  is in the start state (or stop state) S 1  shown in  FIG. 2B , if the reset button  19  is depressed in the direction B 1 , the reset button  19  presses a reset switch spring  31  exerting a biasing force in a direction B 2  in the vicinity of the depth end thereof and closes a contact portion  32 , generating a reset signal Qa via the contact portion  32 . 
     Of the above operations, the following more detailed description will center on the start and progress of the start operation when the start/stop button  18  is depressed in the direction A 1  in the zero-restoring state S 2  of  FIG. 2A . 
     That is, as the start/stop button  18  is depressed in the direction A 1 , the electric start signal Pa is issued via the switch contact  34  on the one hand, whereby the chronograph hand movement motor  35  is rotated; on the other hand, through the rotation of the hammer  27  as a result of the rotation of the hammer operating second lever  26 , the mechanical zero-restoring control state is released, and the hand movement is mechanically permitted (i.e., the mechanical setting is released). 
     As will be described in detail below, for the chronograph timepiece  1  to operate properly and for the time indication to be executed accurately, it is necessary for the rotor position of the chronograph hand movement motor  35  and the polarity of a drive pulse supplied from a motor drive circuit  53  to be matched with each other. In the chronograph timepiece  1 , control is effected such that re-start is caused in a state in which the rotor position of the motor  35  and the polarity of the drive pulse supplied from the motor drive circuit  53  are matched with each other, whereby the chronograph hand movement motor  35  can be rotated reliably, thereby preventing generation of a state in which hand movement is impossible at the time of re-start of the chronograph operation. 
     Next, an electrical drive mechanism  6  of the chronograph timepiece  1  will be described mainly with reference to the block diagram of  FIG. 1  while referring to the mechanical structure  5  of  FIG. 2 . 
     In  FIG. 1 , the chronograph timepiece  1  is equipped with an oscillation circuit  101  generating a signal of a predetermined frequency, a frequency divider circuit  102  effecting frequency division on the signal from the oscillation circuit  101  and outputting a timepiece signal serving as a reference for time indication and time measurement, a control circuit  103  performing a time indicating operation and a time measurement operation based on the timepiece signal and performing various control operations, a time motor drive circuit  104  rotating a time hand movement motor  105  in response to a time control signal from the control circuit  103 , and a time hand movement motor  105  rotating the time hands  11  through  13  of an analog display unit  109 . 
     Further, the chronograph timepiece  1  is equipped with a chronograph motor drive circuit  106  driving the chronograph hand movement motor  35  in response to a chronograph control signal from the control circuit  103 , and the chronograph hand movement motor  35  rotating the chronograph hands  14  and  15  of the analog display unit  109 . 
     Further, the chronograph timepiece  1  is equipped with the analog display unit  109  having the time hands  11  through  13  and the chronograph hands  14  and  15  and displaying time, measured time, etc., the start/stop button  18  giving an instruction to start and stop the time measurement operation, and the reset button  19  resetting the time measurement operation. 
     Here, the oscillation circuit  101 , the frequency divider circuit  102 , the control circuit  103 , the time motor drive circuit  104 , the chronograph drive circuit  106 , and the rotation detection circuit  108  constitute a drive control unit. Further, the rotation detection circuit  108  constitutes a rotation detection unit. 
     The rotation of the chronograph hand movement motor  35  of the chronograph timepiece  1  is controlled by the control circuit  103  based on a time signal output through frequency division of an output signal from the oscillation circuit  101  by the frequency divider circuit  102 . 
     The control circuit  103  performs time indicating operation based on a timepiece signal from the frequency divider circuit  102 , and outputs a time control signal to the time motor drive circuit  104  at a predetermined time hand drive frequency, effecting control so as to drive the time hand movement motor  105 . The time motor drive circuit  104  drives the time hand movement motor  105  in response to the time control signal. The time hands  13  through  15  of the analog display unit  109  are rotated by the time hand movement motor  105  to display the current time. 
     The start/stop button  18  and the reset button  19  are connected to the control circuit  103 . 
     When time measurement (chronograph) operation is to be performed, the control circuit  103  performs time measurement based on the timepiece signal in response to the start operation of the start/stop button  18 , and outputs a chronograph control signal to the chronograph motor drive circuit  106  at a predetermined chronograph hand drive cycle, effecting control so as to drive the chronograph hand movement motor  35 . The chronograph drive circuit  106  drives the chronograph hand movement motor  35  in response to the chronograph control signal. The chronograph hands  14  and  15  of the analog display unit  109  are rotated by the chronograph hand movement motor  35  to display measured time whenever necessary. 
     The rotation detection circuit  108  detects an induction signal VRs generated by the chronograph hand movement motor  35  and detects the rotating condition of the chronograph hand movement motor  35 . As will be described in detail below, the control circuit  103  effects the rotation control of the chronograph hand movement motor  35  based on the rotation detection result of the rotation detection circuit  108 . 
     The control circuit  103  receives the start signal Pa imparted via the contact portion  34  in response to the depression of the start/stop button  18  (start operation) when the chronograph timepiece  1  is in the zero-restoring (reset) state S 2 . In response to the start signal Pa, the control circuit  103  starts time measurement operation based on the timepiece signal from the frequency divider circuit  102 , and outputs a time control signal to the chronograph motor drive circuit  106  so as to rotate the chronograph hands  14  and  15  at a predetermined chronograph hand drive cycle. 
     In response to the time control signal, the time motor drive circuit  104  rotates the chronograph hand movement motor  35  alternately by drive signals of different polarities. The chronograph hand movement motor  35  is alternately driven by the drive pulses of different polarities to rotate in one direction by a predetermined angle at one time. As a result, the rotation of the chronograph hand movement motor  35  is transmitted to the chronograph hands  14  and  15  via the chronograph hand movement train wheel  36 , and the chronograph hands  14  and  15  are moved. 
     Upon receiving the stop signal Pb imparted via the contact portion  34  in response to the depression of the start/stop button  18  (stop operation) when the chronograph timepiece  1  is in the start state S 1 , the control circuit  103  causes the chronograph motor drive circuit  106  to effect drive stop in response to the stop signal Pb, thereby stopping the time measurement operation. As a result, the rotation of the chronograph hand movement motor  35  is stopped, and the hand movement of the chronograph hands  14  and  15  via the chronograph hand movement train wheel  36  is stopped. 
     Upon receiving the reset signal Qa imparted via the contact portion  32  in response to the operation of the reset button  19  (reset operation) when the chronograph timepiece  1  is in the start state S 1 , the control circuit  103  resets the time measurement counter (not shown) inside the control circuit  103  to zero in response to the reset signal Qa, and causes the chronograph motor drive circuit  106  to effect drive stop, thereby resetting the time measurement operation. As a result, the rotation of the chronograph hand movement motor  35  is stopped, and the hand movement of the chronograph hands  14  and  15  via the chronograph hand movement train wheel  36  is stopped. Further, the chronograph hands  14  and  15  are zero-restored and set to predetermined positions by the mechanical structure  5 . 
       FIG. 4  is a schematic view of the chronograph hand movement motor  35  used in an embodiment of the present invention; the drawing shows an example of a timepiece stepping motor generally used in analog electronic timepieces. 
     In  FIG. 4 , the stepping motor  35  is equipped with a stator  201  having a rotor accommodating through-hole  203 , a rotor  202  rotatably arranged in the rotor accommodating through-hole  203 , a magnetic core  208  joined to the stator  201 , and a drive coil  209  wound around the magnetic core  208 . When the stepping motor  105  is used in an analog electronic timepiece like the chronograph timepiece  1 , the stator  201  and the magnetic core  208  are fixed to a main plate (not shown) by screws or swaging (not shown) to be joined to each other. The drive coil  209  has a first terminal OUT 1  and a second terminal OUT 2 . 
     The rotor  202  is magnetized in two poles (S-pole and N-pole). At an outer end portion of the stator  201  formed of a magnetic material, there are provided a plurality of (two in this embodiment) cutouts (outer notches)  206  and  207  at positions opposed to each other, with the rotor accommodating through-hole  203  therebetween. Saturable portions  210  and  211  are provided between the outer notches  206  and  207  and the rotor accommodating through-hole  203 . The saturable portions  210  and  211  are not magnetically saturated by the magnetic flux of the rotor  202 ; when the coil  209  is magnetized, they are magnetically saturated and are increased in magnetic resistance. The rotor accommodating through-hole  203  is formed as a circular hole in which a plurality of (two in this embodiment) semicircular cutouts (inner notches)  204  and  205  are integrally formed at opposing portions of the through-hole of a circular contour. 
     The cutouts  204  and  205  constitute positioning portions for determining the stop position of the rotor  202 . As shown in  FIG. 4 , in a state in which the drive coil  209  is not magnetized, the rotor  202  is at rest in a stable fashion at a position corresponding to the positioning portions, in other words, at a position where the magnetic pole axis A of the rotor  202  is orthogonal to a segment connecting the cutouts  204  and  205  (i.e., a position where it makes an angle θ 0  with respect to the direction X of the magnetic flux flowing through the stator  201 ). 
     When, in this state, a rectangular-wave drive pulse of one polarity (Here, it is assumed, for example, that the first terminal OUT 1  side is a positive pole and that the second terminal OUT 2  side is a negative pole) is supplied from the motor drive circuit  53  to a section between the terminal OUT 1  and OUT 2  of the drive coil  209 , and an electric current (i) is passed in the direction of the arrow in  FIG. 4 , a magnetic flux is generated in the stator  201  in the direction of the dashed arrow line. As a result, the saturable portions  210  and  211  are staturated and the magnetic resistance is increased; after this, due to the mutual action between the magnetic poles generated in the stator  201  and the magnetic poles of the rotor  202 , the rotor  202  rotates 180 degrees in the direction of the solid arrow line in  FIG. 4 , and stops in a stable manner at the position of an angle θ 1 . 
     Next, a rectangular-wave drive pulse of reversed polarity (This time, in order that the driving may be of reverse polarity, the first terminal OUT 1  side is the negative pole, and the second terminal OUT 2  side is the positive pole) is supplied from the motor drive circuit  53  to the terminals OUT 1  and OUT 2  of the drive coil  209 , and an electric current is passed in the direction opposite to the arrow as shown in  FIG. 4 , then, a magnetic flux is generated in the stator  201  in the direction opposite to that of the dashed arrow line. As a result, the saturable portions  210  and  211  are first saturated, and then, due to the mutual action of the magnetic poles generated in the stator  201  and the magnetic poles of the rotor  202 , the rotor  202  rotates 180 degrees in the same direction as in the above case, and stops in a stable manner at the position of the angle θ 0 . 
     From this onward, drive pulses of different polarities (alternating signals) are supplied to the drive coil  209 , whereby the above operations are repeatedly performed, making it possible to continuously rotate the rotor  202  in the direction of the solid arrow line by 180 degrees at one time. Ina case where the driving is successively effected with drive pulses of the same polarity, the rotor  202  is not rotated by the second drive pulse of the same polarity onward; as described above, continuous rotation is possible through alternate driving with drive pulses of different polarities. 
       FIG. 5  is a timing chart related to the chronograph timepiece  1  of the first embodiment of the present invention. 
     Regarding the chronograph timepiece  1  of the first embodiment, constructed as described above, mainly the operation when the reset operation is performed by the reset button  19  will be described with reference to  FIGS. 1 through 5 . 
     When the chronograph timepiece  1  is in the reset state S 2  shown in  FIG. 2A , if the start/stop button  18  is depressed in the direction A 1  to perform start operation, the control circuit  103  starts time measurement based on a timepiece signal from the frequency divider circuit  102 , and a chronograph control signal is output to the chronograph motor drive circuit  106  at the chronograph hand drive frequency, effecting control so as to drive the chronograph hand movement motor  35 . 
     As shown in  FIG. 5 , in response to the chronograph control signal, the chronograph drive circuit  106  supplies drive pulses of alternately different polarities to the section between the first terminal OUT 1  and the second terminal OUT 2  of the chronograph hand movement motor  35  to drive the motor. The chronograph hands  14  and  15  of the analog display unit  109  are rotated by the chronograph hand movement motor  35 , and the measured time is displayed whenever necessary. 
     On the other hand, when the chronograph timepiece  1  is in the start state or hand movement state S 1  shown in  FIG. 2B , if, at the point in time T 1  of  FIG. 5 , the reset button  19  is depressed in the direction B 1  to perform reset operation, the protrusion  25   c  of the hammer operating first lever  25  is pressed in the direction B 1 , and the hammer operating first lever  25  is displaced from the position J 1  to the position J 2 . When the hammer operating first lever  25  is displaced from the position J 1  to the position J 2 , the hammer operating second lever  26  engaged with the lever  25  is moved, on the one hand, from the position K 1  to the position K 2 , and the hammer  27  engaged with the lever  26  is moved from the position M 1  to the position M 2 , with the second hammer  27   b  and the minute hammer  27   c  striking the second heart cam  22  and the minute heart cam  24  to zero-restore and set the chronograph second hand  14  and the chronograph minute hand  15 . As a result, the chronograph timepiece  1  is restored to the reset state S 2  of  FIG. 2A . 
     Further, in response to the reset operation, the control circuit  103  controls the chronograph drive circuit  106  such that the chronograph hand movement motor  35  is driven by a previously determined amount and then stopped. That is, in response to the reset operation, the control circuit  103  supplies the chronograph control signal to the chronograph motor drive circuit  106  so as to rotate the chronograph hand movement motor  35  a predetermined number of times until the point in time T 2 , when rotation of the chronograph hand movement motor  35  through the mechanical zero-restoring operation is impossible. In this case, it ought to be impossible for the chronograph hand movement motor  35  to be rotated through the above-described mechanical zero-restoring operation; however, due to the presence of backlash in the chronograph hand movement train wheel  36 , the chronograph hand movement motor  35  is rotated a predetermined number of times until the backlash is run out (i.e., until the point in time T 2 ). 
     In the first embodiment, in order to drive the motor by the predetermined amount, in response to the reset operation, the control circuit  103  determines whether the chronograph hand movement motor  35  has rotated or not based on the rotation detection result of the rotation detection circuit  108  each time the chronograph hand movement motor  35  is driven, controlling the chronograph motor drive circuit  106  so as to effect the rotation drive until the chronograph hand movement motor  35  ceases to rotate (i.e., until the point in time T 2 ). 
     In the example of  FIG. 5 , the control circuit  103  judges the motor to be in a rotation state when, after the time measurement operation is reset, the rotation detection circuit  108  detects that the induction signal VRs generated immediately after the driving by each drive pulse has exceeded a predetermined reference threshold voltage Vcomp, and judges the motor to be in a non-rotation state when the rotation detection circuit  108  detects that the induction signal VRs has not exceeded the predetermined reference threshold voltage Vcomp. 
     The control circuit  103  stops the driving at the point in time T 2  when the chronograph hand movement motor  35  is judged to be in the non-rotation state. Thus, the chronograph control circuit  106  performs rotation drive until the backlash is run out and the chronograph hand movement motor  35  ceases to rotate. When the chronograph hand movement motor  35  has been driven until it ceases to rotate, the control circuit  103  stores, in a storage unit (not shown) inside it, the polarity of the drive pulse with which the driving has been effected the last time as information (drive pulse polarity information) for determining the polarity of the drive pulse with which the driving is to be effected at the time of the next time measurement start. The drive pulse polarity information is information for determining the polarity of the drive pulse with which the driving is to be started at the time of the next time measurement start based on the polarity of the drive pulse with which the driving has been effected the last time. 
     Next, when the chronograph timepiece is in the reset state S 2  of  FIG. 2A , if start operation is performed again on the start/stop button  18 , in response to the start operation the control circuit  103  controls the chronograph motor drive circuit  106  so as to start driving with a drive pulse of a polarity reverse to the polarity stored referring to the drive pulse polarity information stored in the storage unit. The chronograph drive circuit  106  drives the chronograph hand movement motor  35  with the drive pulse of a polarity reverse to the polarity stored in the storage unit. 
     The chronograph hand movement motor  35  is a stepping motor rotated by being alternately driven with drive pulses of different polarities; since it is driven with a drive pulse of a polarity different from that of the previous drive, it can be rotated in a normal fashion. Further, even if backlash is generated due to the zero-restoring, the driving is stopped in a state in which the backlash has been run out, and the chronograph hand movement motor  35  can be reliably rotated at the time of the next time measurement start, so that the chronograph hands can be moved in the normal fashion. 
     While in the above-described example, the polarity of the drive pulse with which the driving has been effected the last time is stored as the drive pulse polarity information in the storage unit, it is also possible to store the polarity of the drive pulse with which the driving is to be effected next. In this case, in response to the next start operation, the chronograph motor drive circuit  106  is controlled so as to start driving with a drive pulse of the polarity stored in the storage unit; also in this case, the chronograph motor drive circuit  106  controls the chronograph hand movement motor  35  with a drive pulse of a polarity reverse to that of the drive pulse with which the driving has been effected the last time, so that the motor can be normally rotated to effect hand movement. 
       FIG. 6  is a timing chart for a chronograph timepiece  1  according to a second embodiment of the present invention. The second embodiment differs from the first embodiment in that the drive timing is as shown in  FIG. 6  instead of being as shown in  FIG. 5 , and that there is no need to provide the rotation detection circuit  108  shown in  FIG. 1 ; otherwise, it is of the same construction and operation as the first embodiment. In the following, the difference of the second embodiment from the first embodiment will be described mainly with reference to  FIG. 6 . 
     When reset operation is performed by the reset button  19  at the point in time T 1  during time measurement operation, the control circuit  103  controls the chronograph drive circuit  106 , in response to the reset operation, so as to stop the driving at the point in time T 2  after the chronograph hand movement motor  35  has been rotated by a predetermined amount. 
     The above-mentioned predetermined amount is set to a rotation amount allowing the backlash to be run out. Further, the predetermined amount can be the number of times that the driving is effected which makes it possible to run out the backlash. 
     As in the first embodiment, in the second embodiment also, drive pulse polarity information is stored in the storage unit. 
     Next, when the chronograph timepiece is in the reset state S 2  of  FIG. 2A , if start operation is performed again on the start/stop button  18 , the control circuit  103  controls, in response to the start operation, the chronograph motor drive circuit  106 , with reference to the drive pulse polarity information stored in the storage unit, so as to start driving with a drive pulse of a polarity reverse to that of the drive pulse with which driving has been effected the last time. The chronograph motor drive circuit  106  starts the rotation-drive of the chronograph hand movement motor  35  with a drive pulse of a polarity reverse to that of the drive pulse with which the driving has been effected the last time. 
     As a result, it is possible to rotate the chronograph hand movement motor  35  in the normal fashion. Further, it is possible to stop the driving with backlash run out, and to reliably rotate the chronograph hand movement motor  35  at the time of the next time measurement start, so that it is possible to move the chronograph hands in the normal fashion. 
     As described above, according to the above embodiments of the present invention, there is provided a chronograph timepiece  1  including a drive control unit starting a time measurement operation in response to a start operation of an operation unit, electrically hand-movement-driving chronograph hands  14  and  15  by driving a chronograph hand movement motor  35  according to the time measured, and resetting the time measurement operation in response to a reset operation of the operation unit; and a mechanical structure  5  mechanically zero-restoring the chronograph hands  14  and  15  in response to the reset operation, wherein the drive control unit drives the chronograph hand movement motor  35  by a predetermined amount even after the reset operation has been performed. 
     If the above-mentioned predetermined amount is set to a number of times of driving that allows backlash of the train wheel  36  to be completely run out, it is possible to completely eliminate abnormality in hand movement due to the backlash; however, in a case where it suffices to suppress abnormality in hand movement to some degree, the predetermined amount may be set to a number of times of driving less than the above-mentioned number of times of driving. 
     When the predetermined amount is a driving amount allowing the backlash to be completely run out, it is possible, as in the first embodiment, to adopt the above-mentioned predetermined amount and to effect rotation drive until the rotation detection circuit  108  detects that the chronograph hand movement motor  35  has ceased to rotate. 
     Further, as in the above-described embodiments, there is stored drive pulse polarity information for determining the polarity of the drive pulse with which driving is to be effected at the time of the next time measurement start based on the polarity of the drive pulse with which the driving has been effected the last time, and, referring to the drive pulse polarity information in response to the next start operation, the chronograph hand movement motor  35  is started to be driven with a drive pulse of a polarity reverse to that of the drive pulse with which the driving has been effected the last time by the predetermined amount, whereby it is possible to reliably start hand movement at the time of time measurement start. 
     Regarding the drive pulses for the chronograph hand movement motor  35 , the drive pulses at the time of usual chronograph hand movement drive and the drive pulses with which driving is effected after the reset operation may be drive pulses of the same energy or drive pulses of differing energy. 
     The present invention is applicable to various types of chronograph timepieces in which driving of the time hands and the chronograph hands is effected electrically by motors, and in which, in the reset state, setting is effected by a mechanical mechanism such that the chronograph hands do not move, with the driving of the chronograph hands being effected after the releasing of the setting by the mechanical mechanism.