Abstract:
A drive device includes stepper motors, each having an excitation coil and a rotor rotating based on variation in the excitation state of the excitation coil; driven members, each moving in accordance with the rotation of the rotor of the corresponding stepper motor; stoppers, each stopping the driven member mechanically at a zero position; and a controller, controlling the respective stepper motors so as to selectively performs either a normal operation in which the stepper motor is driven so as to rotate, or a zero-position detection operation in which the stepper motor is driven so that the driven member is moved to the stopper. The controller starts to perform the zero-position detection operation simultaneously in all of the stepper motors and changes the stepper motor which has terminated the zero-position detection operation to the normal operation without waiting for the termination of the zero-position detection operation in other stepper motors.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a drive device for stepper motors applicable to an on-board combination meter and so on and to an indicating apparatus using the drive device.  
         [0002]     For example, JP-A-2001-327193 discloses a drive device for controlling the driving of a plurality of stepper motors for use in a tachometer, a fuel meter and so on in an on-board combination meter of the sort mentioned above. The drive device includes a plurality of stepping motors, a plurality of driven members, a plurality of stoppers, a plurality of first excitation members, a plurality of second excitation members, a plurality of detection coils, a position detection member, and control member. Each of the stepping motors has a plurality of excitation coils as well as a rotor magnetized to have N and S magnetic poles and is rotated by following variations in the excitation state of the excitation coils. The driven members moves in response to the rotating operation of the respective rotors. The stoppers mechanically stop the respective driven members in position. The first excitation members rotate the rotors forward and backward by controlling the plurality of excitation coils. The second excitation members control the excitation state of the plurality of excitation coils according to exciting patterns constituted of a plurality of exciting steps for defining the excitation state of the plurality of excitation coils and which reversely rotate the rotors in the direction in which the driven members move to the predetermined positions. The detection coils generate induction voltage in response to the rotation of the rotors. The position detection member sequentially detect the presence or absence of the induction voltage generated in the detection coils during the control operation performed by the second excitation members and detect whether the driven members stop at the predetermined positions where the contact of the driven members against the stoppers is established on the basis of the presence or absence of the detected induction voltage. The control member stops the control operation performed by the first excitation members, and causes the second excitation members to start controlling when the control member receives a command signal. The control member stops the control operation performed by the second excitation members and causes the plurality of first excitation members to start controlling when all the driven members stop at the predetermined positions by the position detection member.  
         [0003]     In the drive device described in for example, JP-A-2001-327193, the plurality of stepper motors are such that the reset operation of restoring the driven members (pointers) in position (the zero positions) by a command signal based on ignition is started by a sequential predetermined timing deviation (e.g., a deviation of two excitation steps) and then each stepper motor is shifted to the normal operation wherein the stepper motor is rotated forward or backward according to measured values of the vehicle speed, the number of revolutions and so on after the set operation of the whole stepper motor is terminated.  
         [0004]     On the other hand, a drive device of another type is such that the sequence of zero-position detection of a plurality of stepper motors used in an on-board combination meter is controlled so that starting the detection of the zero positions is simultaneously made in the whole built-in stepper motor. In the drive device of this type, in order to deal with the time difference required to detect the zero positions of the stepper motors, it is arranged that any stepper motor that has terminated the zero-position detection waits for the termination of the zero-position detection by any other stepper motor and that each of the stepper motors simultaneously starts giving an indication in unison at a point of time the whole stepper motor terminates the zero-position detection.  
         [0005]     In the above-described drive device, the source voltage supplied to a computer within the drive device, used to control the drive device drops because of cranking when a starter is turned to subject an engine to the cranking in order to start the engine in such a state that a fuel meter together with a tachometer and a speedometer contained in the on-board combination meter has started giving an indication according to the measured value. When the computer is reset for preventing malfunction due to the source voltage drop, the computer thus reset causes the stepper motors to start zero-position detection process operation at the time the, power is supplied again immediately after the resetting. With the pointer deflected to an indicating value immediately before the resetting in the fuel meter, it takes time to detect the zero position until the pointer returns to the zero position. Therefore, the tachometer that should start giving an indication corresponding to the measured value after the engine is started cannot start normal operation for giving any indication corresponding to the measured value when the power is supplied to the drive device again until the zero-position detection process operation is terminated in other stepper motors that take time to perform the operation.  
         [0006]      FIG. 6  is a time chart illustrating the driving of a plurality of stepper motors by a conventional drive device by way of example. With a stepper motor  111  acting as a tachometer, a stepper motor  112  acting as a fuel meter and a stepper motor  113  acting as a speedometer, a drive device starts performing a zero-position detection process at time t 1  but does not start performing normal operation for giving an indication corresponding to the values measured by the stepper motors  111  and  113  even though the stepper motors  111  and  113  terminate the zero-position detection process at time t 2 . The drive device just waits for the delayed termination (time t 4 ) of the zero-position detection process performed by the stepper motor  112  and then assumes control so that the stepper motors  111 ,  112  and  113  start the normal operation in unison at time t 5 .  
         [0007]     As the tachometer operates not to give any indication of the number of revolutions of the engine immediately after the engine is started in the case described above, this nonconformity may give the driver a sense of discomfort.  
       SUMMARY OF THE INVENTION  
       [0008]     It is therefore an object of the present invention to provide a drive device for stepper motors and an indicating apparatus using the drive device capable of efficiently switching between the zero-position detection process operation of a plurality of stepper motors and normal operation.  
         [0009]     In order to achieve the above object, according to the present invention, there is provided a drive device, comprising:  
         [0010]     a plurality of stepper motors, each of which has an excitation coil and a rotor rotating in accordance with variation in an excitation state of the excitation coil;  
         [0011]     a plurality of driven members, each of which moves in accordance with rotation of the rotor of the corresponding stepper motor;  
         [0012]     a plurality of stoppers, each of which stops the corresponding driven member mechanically at a zero position; and  
         [0013]     a controller, which controls the respective stepper motors so as to selectively performs either a normal operation in which the stepper motor is rotatably driven, or a zero-position detection operation in which the stepper motor is driven so that the driven member is moved to the stopper for detecting the zero position of the driven member,  
         [0014]     wherein the controller starts to perform the zero-position detection operation simultaneously in all of the stepper motors; and  
         [0015]     wherein the controller changes the stepper motor which has terminated the zero-position detection operation to the normal operation before other stepper motor terminates the zero-position detection operation.  
         [0016]     In the above configuration, the drive device is capable of efficiently switching between the zero-position detection operation and normal operation in the plurality of stepper motors.  
         [0017]     Preferably, The drive device further comprising:  
         [0018]     a plurality of detection coils, each of which generates induction voltage in response to the rotation of the corresponding rotor; and  
         [0019]     a plurality of zero-position detection members, each of which detects contact of the corresponding driven member against the corresponding stopper at the zero position on the basis of level of the induction voltage from the corresponding detection coil. The controller changes the stepper motor which has terminated the zero-position detection operation to the normal operation on the basis of a zero-position detection signal from the corresponding zero-position detection member.  
         [0020]     In the above configuration, the drive device is capable of efficiently switching between the zero-position detection operation and normal operation in the plurality of stepper motors.  
         [0021]     According to the present invention, there is also provided an indicating apparatus having the drive device, comprising:  
         [0022]     a plurality of indicators, each of which has: 
        a dial plate, which has graduations; and     a pointer, which is provided on the driven member, and which points the scale on the dial plate, the pointer mechanically stopped by the stopper at a zero position of the graduations on the dial plate,        
 
         [0025]     wherein the controller controls the stepper motor so as to move the pointer toward the stopper by a full scale of the indicator in the zero-position detection operation.  
         [0026]     In the above configuration, the zero-position detection operation can be restored quickly to the normal operation. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]     The above objects and advantages of the present invention will become more apparent by describing in detail preferred exemplary embodiments thereof with reference to the accompanying drawings, wherein:  
         [0028]      FIG. 1  is a diagram showing an indicating apparatus incorporating a drive device for driving stepper motors according to an embodiment of the invention;  
         [0029]      FIG. 2  is a diagram showing an arrangement of the drive device in FIG.  1 ;  
         [0030]      FIG. 3  is a time chart showing signal waveforms of the respective parts of the drive device in  FIG. 1 ;  
         [0031]      FIG. 4  is a time chart explanatory of an example of a plurality of stepper motors driven by the drive device in  FIG. 1 ;  
         [0032]      FIG. 5  is an elevational view of an on-board combination meter as an indicating apparatus using the driving device according to the invention; and  
         [0033]      FIG. 6  is a time chart illustrating the driving of a plurality of stepper motors by a related drive device by way of example. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0034]     An embodiment of the invention will now be described by reference to the drawings.  
         [0035]      FIG. 1  is a diagram showing an indicating apparatus incorporating a drive device for driving stepper motors according to the embodiment of the invention. The indicating apparatus serves as an on-board combination meter including a tachometer  1 , a fuel meter  2  and a speedometer  3 . For example, the meters  1 ,  2  and  3  have corresponding stepper motors  11 ,  12  and  13 . The stepper motors  11 ,  12  and  13  respectively have a pair of excitation coils  11   a   1  and  11   a   2 , a pair of excitation coils  12   a   1  and  12   a   2  and a pair of excitation coils  13   a   1  and  13   a   2 , and rotors  11   b ,  12   b  and  13   b , each having and being magnetized by five sets of N and S magnetic poles alternately arranged, which are rotated by following variations in the excitation state of the pairs of excitation coils  11   a   1  and  11   a   2 ,  12   a   1  and  12   a   2  and  13   a   1  and  13   a   2 .  
         [0036]     Further, the indicating apparatus includes a plurality of pointers  21 ,  22  and  23  as driven members operating in response to the rotational operation of the rotors  11   b ,  12   b  and  13   b ; a plurality of gears  31 ,  32  and  33  for transmitting the torque of the rotors  11   b ,  12   b  and  13   b  to the pointers  21 ,  22  and  23 ; driving circuits  4  for rotating the rotors  11   b ,  12   b  and  13   b  by controlling the excitation state of the pairs of excitation coils  11   a   1  and  11   a   2 ,  12   a   1  and  12   a   2  and  13   a   1  and  13   a   2 ; and a plurality of stoppers  51 ,  52  and  53  for mechanically stopping the pointers  21 ,  22  and  23  at positions indicating a zero value (hereinafter called the zero positions).  
         [0037]     The driving circuits  4  will be described next. As shown in  FIG. 2 , the driving circuits  4  have a microcomputer  41  including a central processing unit (CPU)  41   a  for performing various processes according to programs, ROM  41   b  as a read only memory for storing programs to be processed by the CPU  41   a , work areas utilized by the CPU  41   a  at the various processing stages, and RAM  41   c  as a read/write memory having a data storage area for storing various kinds of data and so on. These components are mutually connected via bus lines.  
         [0038]     The CPU  41   a  receives an angle data signal D 1  calculated according to information provided by a rotary sensor (not shown) on the number of revolutions of an engine, an angle data signal D 2  calculated according to information provided by a liquid level sensor (not shown) on the residual quantity of fuel, an angle data signal D 3  calculated according to information provided by a vehicle speed sensor (not shown) on vehicle speed, and a high-level initialization command signal S 1  resulting from the operation of an ignition switch (not shown). The CPU  41   a  also transmits excitation pulses P 111 - 114 ,  121 - 124 ,  131 - 134  to both ends a and b of the excitation coils  11   a   1  and  11   a   2 , both ends a and b of  12   a   1  and  12   a   2  and both ends a and b of  13   a   1  and  13   a   2 , respectively.  
         [0039]     The driving circuits  4  have switches  42 ,  43  and  44  subjected to opening control by detection timing signals S 2 -S 4  supplied from CPU  41   a  to each of control terminals thereof. The switches  42 ,  43  and  44  are respectively provided on the connecting lines between the CPU  41   a  and one ends b of the excitation coils  11   a   1 ,  12   a   1  and  13   a   1 .  
         [0040]     The driving circuits  4  also have low-pass filters  45 ,  46  and  47  connected to one ends b of the excitation coils  11   a   1 ,  12   a   1  and  13   a   1 . The low-pass filter  45  includes a resistor R 1  connected between one end b of the excitation coil  11   a   1  and the ground a resistor R 2  one end of which is connected to one end b of the excitation coil  11   a   1 , and a capacitor C 1  connected between the other end of the resistor R 2  and the ground. The low-pass filter  46  includes a resistor R 3  connected between one end b of the excitation coil  12   a   1  and the ground, a resistor R 4  connected to one end b of the excitation coil  12   a   1  and a capacitor C 2  connected between the other end of the resistor R 4  and the ground. Further, the low-pass filter  47  includes a resistor R 5  connected between one end b of the excitation coil  13   a   1  and the ground, a resistor R 6  one end of which is connected to one end b of the excitation coil  13   a   1 , and a capacitor C 3  connected between the other end of the resistor R 6  and the ground.  
         [0041]     The driving circuits  4  receive the outputs of the low-pass filters  45 ,  46  and  47 , and have zero-position detection circuits  48 ,  49  and  50  as position detection members for transmitting to the CPU  41   a  a zero-position decision signal for deciding that the contact of the pointers  21 ,  22  and  23  against the stoppers  51 ,  52  and  53  has been established to hold the zero position.  
         [0042]     The operation of the indicating apparatus thus arranged above will now be described by reference to a time chart of  FIG. 3 . During the normal operation, the CPU  41   a  controls the excitation state of the excitation coils  11   a   1  and  11   a   2  with the excitation pulses P 111 - 114  having a first excitation pattern on a half-step driving system in response to the input of the angle data signal D 1  as well as controlling the driving of the stepper motor  11  so that the rotor  11   b  is reversibly rotated forward (Y 1 ) or backward (Y 2 ) in a manner corresponding to the angle data signal D 1  to make the pointer  21  indicate the numerical value of revolutions of the engine. During the initialization process, the CPU  41   a  controls the excitation state of the excitation coils  11   a   1  and  11   a   2  by switching the excitation pattern of the excitation pulses P 111 - 114  from the first excitation pattern to a second excitation pattern in order of excitation steps  1 → 8 → 7 → 6 → 5 → 4 → 3 → 2  as shown in  FIG. 3  in response to the input of the initialization command signal S 1  as well as controlling the driving of the stepper motor  11  so that the rotor  11   b  is rotated backward to make the pointer  21  move in the direction of the stopper  51  (i.e., in the direction of Y 2 ).  
         [0043]     During the initialization process, the zero-position detection circuit  48  receives induction voltage V 1  generated across the excitation coil  11   a   1  acting as a non-excited detection coil with one end opened via the low-pass filter  45  when the switch  42  controlled by the detection timing signal S 2  supplied from the CPU  41   a  at the timing of the excitation step  5  is opened and sends to the CPU  41   a  a zero-position decision signal S 5  for deciding that the contact of the pointer  21  against the stopper  51  has been established to hold the zero position when the induction voltage V 1  thus supplied becomes equal to or smaller than a preset threshold.  
         [0044]     On receiving the zero-position decision signal S 5  from the zero-position detection circuit  48 , the CPU  41   a  switches the excitation pattern of the excitation pulses supplied to the excitation coils  11   a   1  and  11   a   2 , from the second excitation pattern to the first excitation pattern and causes the rotor  11   b  to be reversibly rotated in a manner corresponding to the angle data signal D 1  to move the pointer  21  so as to indicate the numerical value of revolutions of the engine according to the measured value.  
         [0045]     Similarly, during the normal operation, the CPU  41   a  controls the excitation state of the excitation coils  12   a   1  and  12   a   2  with the excitation pulses P 121 - 124  having a first excitation pattern on the half-step driving system in response to the input of the angle data signal D 2  as well as controlling the driving of the stepper motor  12  so that the rotor  12   b  is reversibly rotated forward (Y 1 ) or backward (Y 2 ) in a manner corresponding to the angle data signal D 2  to make the pointer  22  indicate the residual value of fuel of the vehicle. During the initialization process, the CPU  41   a  controls the excitation state of the excitation coils  12   a   1  and  12   a   2  by switching the excitation pattern of the excitation pulses P 121 - 124  from the first excitation pattern to a second excitation pattern (though not shown but in order similar to those shown in  FIG. 3 ) in response to the input of the initialization command signal S 1  as well as controlling the driving of the stepper motor  12  so that the rotor  12   b  is rotated backward to make the pointer  22  move in the direction of the stopper  52  (i.e., in the direction of Y 2 ).  
         [0046]     During the initialization process, the zero-position detection circuit  49  receives induction voltage V 2  generated across the excitation coil  12   a   1  acting as a non-excited detection coil with one end opened via the low-pass filter  46  when the switch  43  controlled by the detection timing signal S 3  supplied from the CPU  41   a  is opened and sends to the CPU  41   a  a zero-position decision signal S 6  for deciding that the contact of the pointer  22  against the stopper  52  has been established to hold the zero position when the induction voltage V 2  thus supplied becomes equal to or smaller than a preset threshold.  
         [0047]     On receiving the zero-position decision signal S 6  from the zero-position detection circuit  49 , the CPU  41   a  switches the excitation pattern of the excitation pulses supplied to the excitation coils  12   a   1  and  12   a   2 , from the second excitation pattern to the first excitation pattern and causes the rotor  12   b  to be reversibly rotated in a manner corresponding to the angle data signal D 2  to move the pointer  22  so as to indicate the residual value of the fuel of the engine according to the measured value.  
         [0048]     During the normal operation, further, the CPU  41   a  controls the excitation state of the excitation coils  13   a   1  and  13   a   2  with the excitation pulses P 131 - 134  having a first excitation pattern on the half-step driving system in response to the input of the angle data signal D 3  as well as controlling the driving of the stepper motor  13  so that the rotor  13   b  is reversibly rotated forward (Y 1 ) or backward (Y 2 ) in a manner corresponding to the angle data signal D 3  to make the pointer  23  indicate the traveling speed value of the vehicle. During the initialization process, the CPU  41   a  controls the excitation state of the excitation coils  13   a   1  and  13   a   2  by switching the excitation pattern of the excitation pulses P 131 - 134  from the first excitation pattern to a second excitation pattern (though not shown but, in the order similar to those shown in  FIG. 3 ) in response to the input of the initialization command signal S 1  as well as controlling the driving of the stepper motor  12  so that the rotor  13   b  is rotated backward to make the pointer  23  contact with the stopper  53  and move in the direction of the stopper  51  (i.e., in the direction of Y 2 ).  
         [0049]     During the initialization process, the zero-position detection circuit  50  receives induction voltage V 3  generated across the excitation coil  13   a   1  acting as a non-excited detection coil with one end opened via the low-pass filter  47  when the switch  44  controlled by the detection timing signal S 4  supplied from the CPU  41   a  is opened and sends to the CPU  41   a  a zero-position decision signal S 7  for deciding that the contact of the pointer  23  against the stopper  53  has been established to hold the zero position when the induction voltage V 3  thus supplied becomes equal to or smaller than a preset threshold.  
         [0050]     On receiving the zero-position decision signal S 7  from the zero-position detection circuit  50 , the CPU  41   a  switches the excitation pattern of the excitation pulses supplied to the excitation coils  13   a   1  and  13   a   2 , from the second excitation pattern to the first excitation pattern and causes the rotor  13   b  to be reversibly rotated in a manner corresponding to the angle data signal D 3  to move the pointer  23  so as to indicate the traveling speed value of the vehicle according to the measured value.  
         [0051]      FIG. 4  is a time chart explanatory of an example of a plurality of stepper motors driven by the drive device according to the invention described above. More specifically, in case there are a stepper motor  11  functioning as a tachometer, a stepper motor  12  as a fuel meter and a stepper motor  13  as a speedometer, the driving circuits  4  simultaneously start the zero-position detection process at time t 1  in response to the initialization command signal S 1  and when the stepper motors  11  and  13  terminate the zero-position detection process at time t 2 , also start the normal operation for giving indications corresponding to the values measured by the stepper motors  11  and  13  at time t 3 .  
         [0052]     On the other hand, the driving circuits  4  so control the stepper motor  12  as to start the normal operation corresponding to the measured value at time t 5  after the stepper motor  12  where zero-position detection process remains delayed terminates the zero-position detection process at time t 4  later than time t 3 .  
         [0053]     Consequently, the stepper motors  11  and  13  are seen to make the tachometer and the speedometer give indications sooner by (t 5 −t 3 ) than before on comparison between  FIG. 4  and  FIG. 6 , so that the driver is restrained from feeling uncomfortable.  
         [0054]      FIG. 5  is an elevational view of an on-board combination meter as an indicating apparatus using the drive device as illustrated from FIGS.  1  to  4  according to the invention.  
         [0055]     As shown in  FIG. 5 , the on-board combination meter has a dial plate  61  for the tachometer  1  using the stepper motor  11 , a dial plate  62  for the fuel meter  2  using the stepper motor  12  and a dial plate  63  for the speedometer  3  using the stepper motor  13 . Moreover, the on-board combination meter has a dial plate  64  for a water-temperature gauge, which also uses a stepper motor (not shown) that is driven under the control of the driving circuits  4 .  
         [0056]     The dial plates  61 ,  62 ,  63  and  64  have graduations for use in indicating the number of revolutions of the engine, the residual quantity of fuel, traveling speed and water temperature, and the maximum value on each dial plate is set at an angle different from the zero position. In other words, a full scale from the zero position up to the maximum value on each of the dial plates  62  and  64  for the fuel meter  2  and water temperature is narrow, whereas the full scale on each of the dial plates  61  and  63  for the tachometer  1  and the speedometer  3  is set wider than that of each of the fuel meter  2  and water temperature.  
         [0057]     In the on-board combination meter, the driving circuits  4  control the corresponding stepper motors so that the stepper motors are reversely rotated by the full scale of each of the dial plates  61 ,  62 ,  63  and  64  at the time of performing the zero-position detection process.  
         [0058]     The zero-position detection process in the meter having a narrow full scale can be terminated quickly by thus controlling the driving of the driving circuits  4 , so that switching between the operation of performing the zero-position detection process and the normal operation in the plurality of stepper motors can be carried out efficiently.  
         [0059]     Although the embodiment of the invention has thus been described, the invention is not limited to the embodiment thereof but may be modified and applied in various different manners.  
         [0060]     Although the drive device has been used to control the driving of the three stepper motors according to the embodiment of the invention, for example, the invention is not limited to the embodiment thereof but may be arranged so that such a drive device is employed for controlling the driving of two to four or more of stepper motors.