Abstract:
A rotation detecting device includes a rotation detecting unit for providing first and second rotation signals in response to rotation of a rotating object and a signal processing circuit for processing the signals to provide rotation data such as the rotation direction, rotation speed and rotation position. The signal processing circuit includes a reversal signal forming circuit for providing a reversal signal changing in response to a change of the rotation direction, a level-change-prohibiting section for forming a level-change prohibiting signal to mask the first rotation signal during one pulse width from the first rising edge to the first falling edge after the change of the rotation direction of the rotor is detected, and a rotation data processing circuit for forming from the reversal signal and the level-change prohibiting signal a signal having triple-level pulses that synchronize with the pulses of the first rotation signal except for first one of the pulses being masked after each change of the rotation direction and change voltage level when the rotation direction changes.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     The present application is based on and claims priority from Japanese Patent Application 2005-366973, filed Dec. 20, 2005, the contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a signal processing circuit of a rotation detecting device that obtains data about rotation of a rotating object, such as the rotation position, the rotation speed and/or the rotation direction of the rotating object.  
         [0004]     2. Description of the Related Art  
         [0005]     As shown in  FIG. 6 , a common rotation detection device includes a pair of magnetic sensors  1 ,  2 , a magnetic rotor  80  that rotates with a rotating object and a signal processing circuit  100 . The magnetic rotor  80  has a plurality of teeth having mountains  80   a  and valleys  80   b . The processing circuit  100  is constituted of a rotation data forming section  101 , a rotation direction detecting section  102  and a masking section  103 . When the magnetic rotor  80  rotates, the magnetic sensors  1 ,  2  provide rotation signals Sa and Sb, which are inputted to the processing circuit  100 . Thus, the data about the rotation of the rotating object are obtained.  
         [0006]     As shown in  FIG. 7 , the rotation data forming section  101  provides a rectangular signal whose level changes in synchronism with the rising edge of the rotation signal Sa or Sb when the magnetic rotor  80  rotates in a normal direction. When the rotation direction of the rotating object changes from one direction to the other direction, the rotation direction detecting section  102  detects the change of the direction by change in the phase-relationship between the rotation signals Sa and Sb. Then, the masking section  103  masks the first edge after the change of the rotation direction to obtain an output signal OUT 1  that has the same pulse width or duty ratio as the rotation signal Sa, as long as the duty ratio is about 50% or higher.  
         [0007]     However, if the duty ratio of the rotation signals Sa, Sb is as low as about 25% as shown in portion (a) of  FIG. 8 , the output signal OUT 1  after the masking may be reversed as shown in portion (b) of  FIG. 9 , resulting in that the output signal OUT 1  has an entirely different duty ratio. If, for example, the rotation detecting device is set to an engine, the position of the crankshaft of an engine can not be accurately detected.  
       SUMMARY OF THE INVENTION  
       [0008]     Therefore, an object of the invention is to provide an improved signal processing circuit with a rotation detecting device.  
         [0009]     Another object of the invention is to provide a rotation detecting device that can detect accurate rotation data that include the duty ratio of a rotation signal.  
         [0010]     According to a feature of the invention, a signal processing circuit a rotation detecting device includes a reversal signal forming means for providing a bi-level reversal signal (Rev) changing from one level to the other in response to a change of rotation direction of a rotor, a level-change-prohibiting section for forming a level-change prohibiting signal (Ce) to mask a first rotation signal (Sa) during one pulse width from the first rising edge to the first falling edge after the change of the rotation direction of the rotor is detected and a rotation data processing means for forming a triple level output signal (OUT 2 ) having triple-level pulses that synchronize with the pulses of the first rotation signal (Sa) except for first one of the pulses being masked after each change of the rotation direction and change voltage level from one level to another when the rotation direction changes one direction to the other direction.  
         [0011]     In the above signal processing circuit, the rotation sensing unit preferably includes a first rotation sensors for providing the first rotation signal (Sa) and a second rotation sensor for providing a bi-level second rotation signal (Sb) in response to rotation of the rotor at a phase different from the first rotation signal. In this case, the reversal signal forming means includes a reversal signal detecting section for detecting a change of rotation direction by a change in phase of the first rotation signal (Sa) relative to the second rotation signal (Sb). The reversal signal forming means further includes a reversal signal forming section for providing a bi-level reversal signal (Rev) according to direction of rotation of the rotor.  
         [0012]     In addition, the rotation data processing means may include an edge detecting section for detecting edges of the first rotation signal (Sa), a first output signal forming section for forming a bi-level first output signal (OUT 1 ) having pulses that synchronize with the pulses of the first rotation signal (Sa) except for one pulse being masked right after each change of the rotation direction and a rotation data processing section for forming the triple level second output signal (OUT 2 ) based on the first bi-level output signal (OUT 1 ) and the reversal signal (Rev).  
         [0013]     A rotation detecting device having the above signal processing circuit may include as the rotor a magnetic disk having teeth on the periphery thereof and as the first and/or second rotation sensors a magnetic sensor disposed opposite the magnetic disk. Such a rotation detecting device may include a rotary disk having a plurality of slits on the periphery thereof as the rotor; and a light emitting diode and a photo transistor disposed opposite said rotary disk. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     Other objects, features and characteristics of the present invention as well as the functions of related parts of the present invention will become clear from a study of the following detailed description, the appended claims and the drawings. In the drawings:  
         [0015]      FIG. 1  is a circuit diagram of a signal processing circuit of a rotation detecting device according to a preferred embodiment of the invention;  
         [0016]      FIG. 2  is a time chart showing signals at various portions of the signal processing circuit of the rotation detecting device according to the preferred embodiment;  
         [0017]      FIG. 3  is a table showing operating conditions of main portions of the signal processing circuit of the rotation detecting device according to the preferred embodiment;  
         [0018]      FIG. 4  is a time chart showing at main portions of the signal processing circuit;  
         [0019]      FIG. 5  is a schematic diagram showing a main portion of the rotation detecting device of the rotation detecting device according to the preferred embodiment;  
         [0020]      FIG. 6  is a block diagram showing a prior art signal processing circuit;  
         [0021]      FIG. 7  is a time chart showing a relationship between a rotation signal having a higher duty ratio and the output signal of the prior art signal processing circuit; and  
         [0022]      FIG. 8  is a time chart showing a relationship between a rotation signal having a lower duty ratio and the output signal of the prior art signal processing circuit. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]     A signal processing circuit of a rotation detecting device according to a preferred embodiment of the present invention will be described with reference to the appended drawings.  
         [0024]     As shown in  FIG. 1 , the signal processing circuit  100  is constituted of a reversal detecting section  10  connected to a first magnetic sensor  1  and a second magnetic sensor  2 , an edge detecting section  20 , a level-change-prohibiting section  30 , an output signal forming section  40 , a reversal signal forming section  50  and a rotation data processing section  60 .  
         [0025]     The reversal detecting circuit  10  includes a pair of D-flip-flop circuits  11  and  13 , an inverter  14  connected to a Q-terminal of the second D-flip-flop circuit  13 , a NOR circuit  15 , a NAND circuit  16 , an exclusive (Ex) OR circuit  17 , a NAND circuit  18 , etc.  
         [0026]     The reversal detecting section  10  detects a reversal of the rotor  80  by a change in the phase of the first rotation signal Sa relative to the second rotation signal Sb. The edge detecting section  20  detects all the edges of the first rotation signal Sa. The level-change-prohibiting section  30  provides a level-change prohibiting signal Ce to prohibit the level change of the signal inputted thereto in synchronism with the first rising edge and the first falling edge of the first rotation signal Sa after detection of the reversal by the reversal detecting section  10 . The output signal forming section  40  masks the first pulse of the signal inputted thereto after detection of the reversal according to the level-change-prohibiting signal Ce to provide a signal OUT 1  that includes information of the reversal of the rotor  80 .  
         [0027]     The above operation of the signal processing circuit will be described in more detail with reference to  FIGS. 1 and 2 .  
         [0028]     The first rotation signal Sa is inputted from the first magnetic sensor  1  to a clock terminal of the first D-flip-flop circuit  11  of the reversal detecting section  10  and to a clock terminal of the second D-flip-flop circuit  13  thereof via an inverter  12 , and the second rotation signal Sb is also inputted from the second magnetic sensor  2  to D-terminals of the first and second D-flip-flop circuits  11 ,  13 , as shown in (a) and (b) of the time chart shown in  FIG. 2 .  
         [0029]     The first D-flip-flop circuit  13  provides output signal Q 1 , as shown in (c), in which the preceding rising edge of the first rotation signal latches the logical level of the second rotation signal Sb in the normal rotation. That is, level “0” is maintained at the normal rotation, and level “1” is maintained at the reversed rotation.  
         [0030]     The second D-flip-flop circuit  13  provides via the inverter  14  a second output signal Q 2 B, as shown in (d), in which the preceding falling edge of the first rotation signal Sa latches the logical level of the second rotation signal Sb in the normal rotation. That is, level “ 0 ” is maintained at the normal rotation, and level “ 1 ” is maintained at the reversed rotation. However, the level change of the second output signal Q 2 B is retarded by one pulse of the first rotation signal Sa from the level change of the first output signal Q.  
         [0031]     Signals Qm 1 , Qm 2  shown in (f) and (g) are respectively the output signals of the NOR circuit  15  and the NAND circuit  16 . The Ex OR circuit  17  has input terminals respectively connected to the output terminals of the NOR circuit  15  and the NAND circuit  16  and provides a reversal detection dignal Ra as shown in (h) of  FIG. 2 . The reversal detection dignal Ra rises up when the first rotation signal Sa rises up right after the reversal of the rotor  80  shown in  FIG. 8  and falls down just when the first rotation signal Sa first falls down.  
         [0032]     The signals Qm 1 , Qm 2  are sent to the NAND circuit  18  to form an output signal Rb, as shown in (o) of  FIG. 2 . The signal Rb rises up just when the first rotation signal Sa rises up after the rotation direction of the rotor  80  changes from a normal direction to the reversed direction and falls down after the rotation direction of the rotor  80  changes from the reversed direction to the normal direction.  
         [0033]     The edge detecting section  20  includes a delay circuit  21  connected with the first magnetic sensor  1  and an exclusive (Ex) OR circuit  22  has input terminals respectively connected with the first magnetic sensor  1  and the delay circuit  21 .  
         [0034]     The delay circuit  21  delays the first rotation signal Sa by about  10  microseconds, and the Ex OR circuit  22  provides a clock signal CLKa having the pulse width of 10 microseconds, as shown in (e) of  FIG. 2 . This clock signal CLKa synchronizes with all the rising and falling edges of the first rotation signal Sa.  
         [0035]     The level-change-prohibiting section  30  includes a delay circuit  31 , a D-flip-flop circuit  32  and a NOR circuit  33  that has a pair of input terminals respectively connected with the delay circuit  31  and the Q terminal of the D-flip-flop circuit  32 .  
         [0036]     The delay circuit  31  delays the reversal detection dignal Ra by about 5 microseconds to provide a delay signal RaD as shown in (i). The D-flip-flop circuit  32  has a D-terminal connected with the delay circuit  31  and a clock terminal connected to the Ex OR circuit  22  to latch the delay signal RaD in synchronism with the rising edge of the clock singal CLKa, thereby providing a latch signal RaS that delays from the reversal detection signal Ra by one pulse thereof, as shown in (j) of  FIG. 2 . The NOR circuit  33  provides “0” level of the level-change prohibiting signal Ce while the level of the delay signal RaD or the latch signal RaS is “1”, as shown in (k) of  FIG. 2 .  
         [0037]     The output signal forming section  40  includes delay circuits  41 ,  42 , a NAND circuit  43 , an inverter  44  and a D-flip flop circuit  45 . The output signal forming section  40  provides an output signal OUT 1  whose pulses synchronize with the pulses of the first rotation signal Sa except for one pulse being masked right after each change of the rotation direction is detected.  
         [0038]     The delay circuit  41  is constituted of about ten (10) series-connected inverters to delay the signal Ce by about 2 microseconds and filter the signal Ce to remove a steepled wave voltage of it. The delay circuit  42  is constituted of about twenty (20) series-connected inverters to delay the clock signal CLKa by about 10 microseconds to form a clock signal CLKb, as shown in (1) of  FIG. 2 . A series circuit of the NAND circuit  43  and the inverter  44  forms a clock signal CLKc, as shown in (m) of  FIG. 2 , which is inputted to a clock terminal of the D-flip-flop circuit  45  to provide the signal OUT 1 , as shown in (n) of  FIG. 2 . The signal OUT 1  has “1” level signals that synchronize with the pulses of the first rotation signal Sa except for one pulse being masked right after the change of the rotation direction is detected.  
         [0039]     Incidentally, the clock signal CLKc does not appear as long as the level of the level-change prohibiting signal Ce is “0”. The level-change prohibiting signal Ce also prohibits the clock signal CLKc while the rotation direction of the rotor  80  frequently changes in a chattering operation, as indicated by CT in  FIG. 2 . Accordingly, generation of abnormal pulses can be prevented.  
         [0040]     The reversal signal forming section  50  includes an inverter  51 , a NOR circuit  52  and an inverter  53 . The reversal signal forming section  50  provides a reversal signal Rev.  
         [0041]     The inverter  51  provides the inverted signal CeDB of the output signal of the Delay circuit  41 , as shown in (p) of  FIG. 2 . The NOR circuit  52  has input terminals respectively connected to the inverter  51  and the NAND circuit  18 . The series circuit of the NOR circuit  52  and the inverter  53  forms the reversal signal Rev, which is shown in (q) of  FIG. 2 . When the rotor  80  rotates in the normal direction, the level of the reversal signal is “0”, while the level of the reversal signal is “1” when it rotates in the other direction.  
         [0042]     The rotation data processing section  60  includes inverters  61 ,  63 ,  65 , NAND circuits  62 ,  64 , resistors R 1 , R 2 , transistors Tr 1 , Tr 2  and a DC power source connected to an end of the resistor R 1 . The rotation data processing section  60  provides a triple level signal OUT 2  whose level changes as the rotation direction of the rotor  80  changes.  
         [0043]     The NAND circuit  62  has input terminals respectively connected to the D-flip-flop circuit  45  and the inverter  53  via the inverter  61 , and the NAND circuit  64  has input terminals respectively connected to the D-flip-flop circuit  45  and the inverter  53 . The NAND circuit  62  controls the transistor Tr 1  via the inverter  63 , and the NAND circuit  64  controls the transistor Tr 2  via the inverter  65 . Therefore, the transistors Tr 1 , Tr 2  turn on or off to provide the signal OUT 2 , which is shown in  FIGS. 3 and 4 . The signal OUT 2  has three levels, that is, H (high level), L (low level) and M (middle level).  
         [0044]     When the rotor  80  rotates in the normal direction, the level of the reversal signal Rev is “0”, as shown in (q) of  FIG. 2  or  4 . In the meantime, the level of the output signal OUT 2  of the rotation data processing section  60  becomes “H” as long as the level of the signal OUT 1  is “0”, and the level of the output signal OUT 2  becomes “L” as long as the level of the signal OUT 1  is “1”, as shown in (n), (q), (r) of  FIG. 4 . When, on the other hand, the rotor  80  rotates in the reversed direction, the level of the reversal signal Rev is “1”. In the meantime, the level of the output signal OUT 2  of the rotation data processing section  60  becomes “H” as long as the level of the signal OUT 1  is “0”, and the level of the output signal OUT 2  becomes “M” as long as the level of the signal OUT 1  is “1”. Thus, the output signal OUT 2  changes its level when the rotation of the rotor  80  changes from one direction to the other.  
         [0045]     Even if the duty ratio of the rotation signal Sa becomes as low as 25%, the output signals OUT 1 , OUT 2  provide the same duty ratio or logical level transition as the rotation signal Sa.  
         [0046]     The arrangement of magnetic rotor  80  and the magnetic sensors  1 ,  2  shown in  FIG. 6  may be replaced by an optical rotary encoder. The rotary encoder includes a rotary disk  90  having a plurality of slits  90   a , a shaft  91 , a pair of photo-transistors  92   a ,  92   b  disposed at one side of the rotary disk  90 , a light emitting diode  93  with a magnifying glass  94  and amplifiers  95   a ,  95   b.    
         [0047]     When a light is emitted from the light emitting diode  93 , the light is magnified by the magnifying glass  94 . The magnified light passes through the slits  90   a  and received by the phototransistors  92   a ,  92   b , which convert the light into electric signals. The amplifiers  95   a ,  95   b  amplify the electric signals to form the rotation signals Sa and Sb, which are different in phase from each other. These signals are inputted to the reversal detecting section  10  to obtain the output signal OUT 1  and/or the output signal OUT 2  in the same manner as described above.  
         [0048]     In the foregoing description of the present invention, the invention has been disclosed with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made to the specific embodiments of the present invention without departing from the scope of the invention as set forth in the appended claims. Accordingly, the description of the present invention is to be regarded in an illustrative, rather than a restrictive, sense.