Abstract:
A step motor control device detects a rotational driving state of a step motor. In a first detection period immediately after termination of the rotational driving state of the step motor, selected switch elements are controlled so that a first detection signal is obtained. If the step motor is not in a rotational driving state, the first detection signal is suppressed to a low voltage that is equal to or lower than a threshold value. In a second detection period immediately after lapse of the first detection period, selected switch elements are controlled so that a second detection signal of high and stable voltage is obtained in accordance with the rotational driving state of the step motor.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a step motor control device that rotationally drives a step motor and detects the presence/absence of the rotation of the step motor, and to an electronic timepiece utilizing the step motor control device. 
   2. Description of the Prior Art 
   In an electronic timepiece, a step motor is used as a motor that rotationally drives time hands such as an hour hand or a minute hand. 
     FIG. 5  is a front view showing a step motor used in such electronic timepiece having an hour hand or a minute hand and described in JP57-18440 B (pgs. 1-2. FIG. 1) (hereinafter “Patent Document 1”). 
   In  FIG. 5 , the step motor includes a stator  501  made of a magnetic material, a coil  207  wound around on the stator  501 , and a bipolar rotor  502  disposed within the stator  501 . In the stator  501 , there are saturable portions  503 ,  504  and inner notches  505  and  506  for determining a stop position of the rotor  502 . 
   When a drive pulse of a rectangular wave is supplied to the coil  207  to allow a current i to flow in a direction indicated by an arrow in  FIG. 5 , a magnetic flux develops in the stator  501  in the direction indicated by the arrow. As a result, the saturable portions  503  and  504  are first saturated, and thereafter the rotor  502  rotates in the direction indicated by the arrow (counterclockwise) in  FIG. 5  by 180 degrees due to the interactions between a magnetic pole developed in the stator  501  and a magnetic pole developed in the rotor  502 . Subsequently, a pulse current different in the polarity is alternately allowed to flow in the coil  207 , to thereby conduct the same operation as the above and rotate the rotor  502  counterclockwise in increments of 180 degrees. 
     FIG. 6  is a circuit diagram showing a conventional step motor control device for conducting the rotation control of the step motor. The circuit is structured such that a rotation drive circuit and a rotation detecting circuit are integrated together (for example, refer to Patent Document 1). 
   In  FIG. 6 , p-channel MOS transistors Q 1 , Q 2  and n-channel MOS transistors Q 3 , Q 4  are structural elements of the motor drive circuit, and the coil  207  of the step motor is connected between a source connection point of the transistor Q 1  and the transistor Q 3  and a source connection point of the transistor Q 2  and the transistor Q 4 . 
   On the other hand, a detection resistor  208  connected in series with the n-channel MOS transistors Q 3  to Q 6  and the transistor Q 5 , a detection resistor connected in series with the transistor Q 6 , and a comparator  210  are structural elements of the rotation detecting circuit. 
   The gates of the respective transistors Q 1  to Q 6  are connected to a control circuit  103 . A connection point OUT 2  of the detection resistor  208  and the coil  207  and a connection point OUT 1  of the detection resistor  209  and the coil  207  are connected to an input section of the comparator  210 . Also, the input section of the comparator  210  is inputted with a predetermined threshold voltage Vss. 
     FIG. 7  is a timing chart for the case of conducting rotation control and detection control in the step motor control device shown in FIG.  6 . 
   The operation of the conventional step motor control device structured as described above will be described with reference to  FIGS. 5  to  7 . First, when a drive pulse P 1  is supplied to an input section Vi of the control circuit  103 , the transistors Q 2  and Q 3  become an on-state under the control by the control circuit  103 . As a result, a current flows in the coil  207  in a direction indicated by an arrow, and the rotor  502  rotates counterclockwise as shown in FIG.  5 . 
   On the other hand, a non-detection period IT, which is a period during which the rotation of the step motor is not detected, is provided for a given period T 7  immediately after the motor drive period, and a rotation detection period DT for detecting whether or not the step motor rotates is provided for a given period T 8  immediately after the non-detection period IT. 
   In the rotation detection period DT, a rotation detection control pulse SP 1  is supplied to the input section Vi of the control circuit  103 . The control circuit  103  controls the on/off operation of the transistor Q 4  at a given frequency in a state where the transistors Q 3  and Q 4  turn on in response to the rotation detection control-pulse SP 1 . 
   In this situation, a detection signal V 8  is taken out from the connection point OUT 1  of the rotation detection resistor  209  and the coil  207 . The detection signal having a waveform shown in  FIG. 7  is obtained as the detection signal V 8 . In  FIG. 7 , the detection voltage V 8  lower than VDD is generated when the rotor  502  vibrates counterclockwise in  FIG. 5 , and the detection voltage V 8  higher than VDD is generated when the rotor  502  vibrates clockwise in FIG.  5 . 
   In the case where the rotor  502  rotates, the detection signal V 8  that exceeds a given threshold voltage (Vss in this conventional example) is obtained, and a rotation detection signal of a high level is outputted from the comparator  210 . In the case where the rotor  502  does not rotate, because the detection signal V 8  does not reach the threshold voltage, the rotation detection signal Vs of a low level is outputted from the comparator  210 . It is possible to detect whether or not the step motor rotates on the basis of the rotation detection signal Vs. After the rotation detection has been completed, the transistors Q 3  and Q 4  are maintained in the on-state to brake the step motor. 
   In a subsequent motor drive period, a subsequent normal drive pulse P 1  is supplied to the input section Vi of the control circuit  103 . The control circuit  103  controls the transistors Q 1  and Q 4  to be on, and a drive current flows in the coil  207  in an opposite direction of the above drive current (counterclockwise in  FIG. 5 ) to thereby rotate the rotor  502  counterclockwise. 
   In the rotation detection period at this time, when the rotation detection control pulse SP 1  is supplied to the input section Vi of the control circuit  103 , the control circuit  103  controls the transistors Q 4  and Q 5  to be on, and controls the on/off operation of the transistor Q 3  at a given frequency. In this situation, a detection voltage V is taken out from the connection point OUT 2  of the resistor  208  and the coil  207 , and a level of the detection voltage V is judged by the comparator  210 . In the same manner as the above, in the case where the rotor  502  rotates, the rotation detection signal Vs of the high level is outputted from the comparator  210 , and in the case where the rotor  502  does not rotate, the rotation detection signal Vs of the low level is outputted from the comparator  210 . It is impossible to detect whether or not the step motor rotates in accordance with the rotation detection signal Vs. After the rotation detection has been completed, the transistors Q 3  and Q 4  are maintained in the on-state to brake the step motor. 
   In the step motor control device structured as described above, after the step motor has been driven by the drive pulse P 1 , the rotor  502  freely vibrates at a position where the rotor  502  should stop as a center. The free vibration of the rotor  502  is large immediately after the supply of the drive pulse P 1  is finished, and the rotor  502  vibrates in the same direction as a normal rotation direction (counterclockwise in the above-mentioned conventional example) due to the inertia. In the case where the rotor  502  vibrates counterclockwise, the current flows in a direction indicated by an arrow in FIG.  6 . 
   On the other hand, an equivalent circuit of the respective transistors Q 3  to Q 6  is made up of a series circuit comprising a switch  804  and a resistor  803 , and a diode  801  and a capacitor  802  which are connected in parallel with the series circuit, respectively, as shown in FIG.  8 . The respective transistors Q 3  to Q 6  are considered as an element equivalently having diodes in one way. 
   Accordingly, even though the step motor does not rotate, because the counterclockwise vibration of the rotor  502  is large within a given period immediately after the supply of the drive pulse P 1  is finished, the detection voltage V 7  that exceeds the threshold voltage Vss may be obtained as shown in FIG.  7 . That is, in the detection signal V 7  that is obtained in a given period T 7  immediately after the supply of the drive pulse P 1  is finished, a detection voltage having a large peak value is generated in the detection resistor  209  due to the large free vibration of the rotor  502  and misdetection is caused that the step motor is rotating. 
   Up to now, in order to prevent such misdetection, the control circuit has been structured such that a non-detection period IT having a given time width T 7  is set immediately after the supply of the drive pulse is stopped, thereby preventing detection of the rotation of the step motor in the non-detection period IT. Accordingly, there arises such a problem that the structure of the control circuit is complicated because of the provision of the non-detection period IT. 
   An object of the present invention is to provide a step motor control device in which it is possible to more surely detect the rotation of the step motor with a simple structure without any provision of the non-detection period IT. 
   Another object of the present invention is to provide an electronic timepiece in which it is possible to more surely detect the rotation of the step motor for driving the hour hand with a simple structure. 
   SUMMARY OF THE INVENTION 
   According to the present invention, there is provided a step motor control device including: first and second switch elements which are connected to each other in series; third and fourth switch elements which are connected to each other in series; a coil of a step motor which is connected between a node of the first and second switch elements and a node of the third and fourth switch elements; a first series circuit including a fifth switch element connected in parallel with the first switch element and a first detection element; a second series circuit including a sixth switch element connected in parallel with the third switch element and a second detection element; a control means for controlling an on/off operation of the first to fourth switch elements in response to a drive pulse to allow a current to flow in the coil to rotationally drive the step motor, and controlling an on/off operation of the fourth, third, fifth, and sixth switch elements in response to a rotation detection control pulse that is supplied immediately after the supply of the drive pulse is finished in a rotation detection period immediately after the rotation drive of the step motor in accordance with the drive pulse; and a detecting means for detecting the presence/absence of the rotation of the step motor on the basis of a comparison result of a voltage generated between the first and second detection elements and the coil with a given threshold voltage. 
   According to one aspect of the present invention, in the case where the step motor is rotationally driven by turning on the first and fourth switch elements in accordance with the drive pulse, the control means renders the fourth and fifth switch elements on and controls the on/off operation of the third switch element at a given frequency in a first given period immediately after the supply of the drive pulse is finished, and renders the third switch element and the sixth switch element on and control the on/off operation of the fourth switch element at a given frequency in a second given period after laps of the first given period. 
   According to another aspect of the present invention, in the case where the step motor is rotationally driven by turning the second and third switch elements on in accordance with the drive pulse, the control means renders the third and sixth switch elements on and controls the on/off operation of the fourth switch element at a given period immediately after the supply of the drive pulse is finished, and renders the fourth switch element and the fifth switch element on in the second given period and controls the on/off operation of the third switch element at a given frequency. 
   According to another aspect of the present invention, the detection means detects the presence/absence of the rotation of the step motor on the basis of the comparison result of the voltage generated between the first detection element and the coil with the threshold voltage when the fifth switch element is turned on, and detects the presence/absence of the rotation of the step motor on the basis of the comparison result of the voltage generated between the second detection element and the coil with the threshold voltage when the sixth switch element is turned on. 
   In the case where the step motor is rotationally driven by turning on the first and fourth switch elements in accordance with the drive pulse, the control means renders the fourth and fifth switch elements on and controls the on/off operation of the third switch element at a given frequency in a first given period immediately after the supply of the drive pulse is finished, and renders the third switch element and the sixth switch element on and controls the on/off operation of the fourth switch element at a given frequency in a second given period after lapse of the first given period. In the case where the step motor is rotationally driven by turning the second and third switch elements on in accordance with the drive pulse, the control means renders the third and sixth switch elements on and controls the on/off operation of the fourth switch element at a given frequency in the first given period immediately after the supply of the drive pulse is finished, and renders the fourth switch element and the fifth switch element on and controls the on/off operation of the third switch element at the given frequency in the second given period. The detection means detects the presence/absence of the rotation of the step motor on the basis of the comparison result of the voltage generated between the first detection element and the coil with the threshold voltage when the fifth switch element is in an on state, and the detection means detects the presence/absence of the rotation of the step motor on the basis of the comparison result of the voltage generated between the second detection element and the coil with the threshold voltage when the sixth switch element is in an on state. 
   Here, the first, third, fifth, and sixth switch elements may be made up of n-channel MOS transistors, and the second and fourth switch elements may be made up of p-channel MOS transistors. 
   Further, the first and second detection elements may be made up of resistors. 
   Further, according to the present invention, there is provided an electronic timepiece including a step motor that rotates time hands and a step motor control device that rotationally controls the step motor, the timepiece being characterized in that any of the step motor control devices described above is used as the step motor control device. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A preferred form of the-present invention is illustrated in the accompanying drawings in which: 
       FIG. 1  is a block diagram showing an electronic timepiece in accordance with an embodiment of the present invention; 
       FIG. 2  is a circuit diagram for explaining the operation of the step motor control device in accordance with the embodiment of the present invention; 
       FIG. 3  is a circuit diagram for explaining the operation of the step motor control device in accordance with the embodiment of the present invention; 
       FIG. 4  is a timing chart showing the step motor control device; 
       FIG. 5  is a front view showing a general step motor; 
       FIG. 6  is a circuit diagram for explaining the operation of a conventional step motor control device; 
       FIG. 7  is a timing chart of a conventional step motor control device; and 
       FIG. 8  is an equivalent circuit diagram of a general n-channel MOS transistor. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings. 
     FIG. 1  is a block diagram showing an electronic timepiece using a step motor control device in accordance with an embodiment of the present invention, and shows an example of an analog electronic wristwatch. 
   Referring to  FIG. 1 , an oscillating circuit  101  is connected to an input section of a control circuit  103  through a frequency dividing circuit  102 . A first output section of the control circuit  103  is connected to a step motor  105  for driving a time hand through a motor drive circuit  104 . A second output section of the control circuit  103  is connected to a control input section of a rotation detecting circuit  106 . The rotation detecting circuit  106  that detects whether or not the motor  105  rotates is connected between the motor  105  and the control circuit  103 . The rotation detecting circuit  106  structures a rotation detecting means. 
   The step motor  105  is identical in structure with the step motor shown in FIG.  5 . Also, the structure per se of the motor drive circuit  104  and the rotation detecting circuit  106  are identical with that shown in  FIG. 6 , but a method of controlling the on/off operation of the respective transistors Q 1  to Q 6  is different from the conventional example shown in  FIG. 6  as will be described later. 
   The frequency dividing circuit  102  divides a reference clock signal from the oscillating circuit  101  and outputs the divided reference clock signal to the control circuit  103 . The control circuit  103  receives a signal from the frequency dividing circuit  102  and outputs a drive pulse to the motor drive circuit  104 . In the drive pulse, there are prepared a normal drive pulse P 1  which is a drive pulse of a given pulse width smaller in an effective energy and a correction drive pulse that is a drive pulse of a wide width larger in the effective energy than the normal drive pulse, and the control circuit  103  selectively outputs the normal drive pulse and the correction drive pulse to the motor drive circuit  104  in accordance with a detection signal from the rotation detecting circuit  106 . In this example, the control circuit  103  structures a drive pulse generating means that generates a drive pulse. 
   The control circuit  103  supplies to the rotation detection circuit  106  a rotation detection control pulse necessary for executing the rotation detection of the motor  105 . In this example, the control circuit  103  structures a rotation detection control pulse generating means that generates means that generates the rotation detection control pulse. 
   The control circuit  103 , the motor drive circuit  104 , and the rotation detecting circuit  106  structure a control means. 
     FIGS. 2 and 3  are explanatory diagrams showing the operation of the motor drive circuit  104  and the rotation detecting circuit  106  in the step motor control device in accordance with an embodiment of the present invention, respectively, in which  FIG. 2  is an explanatory diagram showing the operation in a given period T 1  immediately after a drive pulse is blocked in a rotation detection period, and  FIG. 3  is an explanatory diagram showing the operation in a given period T 2  immediately after lapse of the given period T 1  in the rotation detection period. 
   In  FIGS. 2 and 3 , p-channel MOS transistors Q 1 , Q 2  and n-channel MOS transistors Q 3 , Q 4  are transistors contained in the motor drive circuit  104 , and a coil  207  of the motor  105  is connected between a source connection point of the transistor Q 1  and the transistor Q 3  and a source connection point of the transistor Q 2  and the transistor Q 4 . 
   N-transistor MOS transistors Q 5 , Q 6 , a rotation detection resistor  208  that is connected in series with the transistor Q 5 , a rotation detection resistor  209  connected in series with the transistor Q 6 , and a comparator  210  are included in the rotation detecting circuit  106 . 
     FIG. 4  is a timing chart for the step motor control device in accordance with this embodiment, which is a timing chart for the case of executing the rotation detection of the motor  105  by the rotation detecting circuit  106  in response to a rotation detection control pulse SP 1  after rotating the motor  105  in accordance with the normal drive pulse P 1 . 
   Hereinafter, the operation of the step motor control device and the electronic timepiece in accordance with the embodiment of the present invention will be described with reference to  FIGS. 1  to  4  and  FIGS. 5 and 8 . 
   First, in a motor drive period, the normal drive pulse P 1  is supplied to the motor drive circuit  104  from the control circuit  103 , whereby the motor drive circuit  104  rotationally controls the motor  105 . In this case, the transistors Q 2  and Q 3  of the motor drive circuit  104  are controlled to be on, as a result of which a drive current flows in the coil  207 , and the motor  105  rotates counterclockwise (in a direction indicated by an arrow) in a front view of  FIG. 5  by 180 degrees. 
   In a subsequent motor drive period, when a subsequent normal drive pulse P 1  is supplied to the motor drive circuit  104  from the control circuit  103 , the transistors Q 1  and Q 4  are controlled to be on, a drive current flows in the coil  207  in an opposite direction of the drive current, and the motor  105  rotates counterclockwise of the same direction by 180 degrees. 
   Thereafter, the above operation is repeated to continuously rotate the motor  105  counterclockwise. 
   On the other hand, a rotation detection period DT for detecting whether or not the motor  105  rotates (first rotation detection period T 1 +second rotation detection period T 2 ) is provided immediately after the respective motor drive periods. It is possible to appropriately select the first and second rotation periods T 1  and T 2  in accordance with the structure of the motor at the time of designing the motor. In the rotation detection period DT, the rotation detection control pulse SP 1  is supplied to the rotation detecting circuit  106  from the control circuit  103 . 
   In the first detection period T 1  immediately after the supply of the respective drive pulses P 1  has been completed (immediately after the motor drive stops), the motor drive circuit  104  and the rotation detecting circuit  106  controls the transistors Q 4  and Q 5  to be on in response to the rotation detection control pulse SP 1  from the control circuit  103  as shown in  FIG. 2 , and controls the on/off operation of the transistor Q 3  at a given frequency in accordance with the respective fine pulses that structures the rotation detection control pulse SP 1  in a state where the transistors Q 4  and Q 5  are turned on. In this state, the detection signal V 1  generated in the rotation detection resistor  208  is taken out from the terminal OUT 2 . 
   In the first detection period T 1 , a loop in a direction of a current Ik is structured by the transistor Q 5 , the detection resistor  208 , the coil  207 , and the transistor Q 4 . In this case, because the current Ik flows in an opposite direction of an equivalent diode  801  (refer to  FIG. 8 ) which structures the transistor Q 5 , the detection signal V 1  is suppressed to a low voltage within a given range, and therefore the detection signal V 1  of a high voltage which exceeds a given threshold value (Vss in this embodiment) is not obtained in the case where the motor does not rotate. As a result, it is possible to suppress the misdetection in the case where the motor does not rotate with a simple structure without setting the non-detection period IT even immediately after the supply of the drive pulse P 1  is stopped. 
   In the case where the voltage of the detection signal V 1  changes beyond the threshold voltage, that is, in the case where the motor  105  rotates, the rotation detection signal Vs of the high level which represents that the motor  105  rotates is outputted from the comparator  210 , and after the transistors Q 3  and Q 4  turn on and the motor rests, the period is shifted to a subsequent motor drive period. 
   On the other hand, in the second detection period T 2  provided immediately after lapse of the first detection period T 1 , the motor drive circuit  104  and the rotation detecting circuit  106  control the transistors Q 3  and Q 6  to be on in accordance with the rotation detection control pulse SP 1  from the control circuit  103  as shown in  FIG. 3 , and control the on/off operation of the transistor Q 4  at a given frequency in accordance with the respective fine pulses that structure the rotation detection control pulse SP 1  in a state where the transistors Q 3  and Q 6  are turned on. In this state, the detection signal V 2  generated in the rotation detection resistor  209  is taken out from the terminal OUT 1 . 
   In the second detection period T 2 , because a current Ik flows in a forward direction of the equivalent diode  801  that structures the transistor Q 6  (refer to FIG.  8 ), the detection signal V 2  is not limited, and therefore there is obtained the detection signal V 2  of a stable voltage responsive to the rotation of the motor. 
   In the case where the voltage of the detection signal V 2  changes beyond the threshold value, that is, in the case where the motor  105  rotates, the rotation detection signal Vs of the high level which represents that the motor  105  rotates is outputted from the comparator  210 , and after the transistors Q 3  and Q 4  turn on and the motor rests, the period is shifted to a subsequent motor drive period. 
   In the case where the motor  105  does not rotate, the detection signal V 2  does not exceed the threshold value over the entire detection period DT, and the rotation detection signal Vs of the low level which represents that the motor  105  is in a non-rotation state is outputted to the entire detection period DT from the comparator  210 . The control circuit  103  outputs the correction drive pulse wider in width than the normal drive pulse P 1  to the motor drive circuit  104  in response to the rotation detection signal Vs that is representative of non-rotation. The motor drive circuit  104  rotationally drives the motor  105  in response to the correction drive pulse. 
   In this manner, according to the step motor control device of this embodiment, it is possible to suppress a possibility of misjudging that the motor is rotated, in the case where the motor is not rotated, with a simple structure without providing the non-detection period IT, and it is possible to more surely detect the rotation of the step motor. 
   Also, according to the electronic timepiece of this embodiment, it is possible to more surely detect the rotation of the step motor for driving the hour hand with a simple structure. 
   In this embodiment, an example in which the step motor control device is used in the electronic timepiece was described, but it is possible to use the step motor control device in another electronic device. 
   According to the present invention, it is possible to more surely detect the rotation of the step motor with a simple structure without any provision of the non-detection period in the step motor control device. 
   Also, according to the present invention, in the electronic timepiece, it is possible to more surely detect the rotation of the step motor for driving the hour hand with a simple structure.