Abstract:
This optical encoder includes a light emitting section and a plurality of light receiving elements placed so as to be aligned in one direction in an area where a light beam from the light emitting section may reach. The moving object includes a light-ON section and a light-OFF section. The light receiving element detects movement of the moving object when the light-ON section and the light-OFF section of the moving object pass through a predetermined position corresponding to the light receiving element A light receiving signal processing section receives inputs of a plurality of light receiving signals with different phases from a plurality of the light receiving elements, performs signal processing including at least one signal processing among a logical operation processing, an addition processing, and a subtraction processing on a plurality of the light receiving signals, and outputs an output signal containing a plurality of signal components which are different in phase and different in signal level with respect to a predetermined threshold level.

Description:
This Nonprovisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2007-177199 filed in Japan on Jul. 5, 2007 and Patent Application No. 2008-129779 filed in Japan on May 16, 2008, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to an optical encoder for detecting the position, the movement speed, the moving direction and the like of a moving object with use of a light receiving element, and more specifically relates to an optical encoder which is preferably used for, for example, printing presses such as copying machines and printers, as well as FA (Factory Automation) equipment. 
     Conventionally, an optical encoder has been proposed in which a plurality of light receiving elements are placed in an array direction of the slits of a rotor at intervals of ¼ of the array pitch of the slits and in which output signals of these light receiving elements are compared so as to obtain rotation information with high reliability (JP S59-40258 A). 
     In an optical encoder disclosed in JP 2005-61896 A, a method for enhancing the precision of detecting the movement amount of a moving object by generating and outputting triangular waves is employed. 
     It has been disclosed in JP 2000-121390 A that pulse conversion is applied to an A-phase signal and a B-phase signal, which have phase difference of 90 degrees, so that these signals are outputted as one A/B-phase pulse signal which is PWM-modulated corresponding to the moving direction of the scale, as a result of which the A-phase and B-phase measurement pulse signals can be outputted with one transmission line. 
     It has been disclosed in JP S60-88316 A that two phase outputs from a rotary encoder are converted to get counter pulses corresponding to two phases, and one counter pulse is phase-inverted and is added to the other counter pulse, so that signals can be transmitted with a single output signal line. 
     In the optical encoder disclosed in JP S59-40258 A, the relative position change and the moving direction of a moving object (rotor) are detected with use of two output signals of A-phase and B-phase which are different in phase from each other by 90 degrees. 
     However, in the optical encoder of JP S59-40258 A, two outputs are provided and therefore interconnections for two outputs are required, which makes the optical encoder lack in simplicity of the signal output interconnections and thereby makes the optical encoder unsuitable for pursuit of miniaturization of a mounting area. Moreover, since the timing of two output signals which should have phase shift of 90 degrees may be changed due to the difference in length of two output interconnections and to the influence of noise applied to each interconnection and the like, an output method with higher reliability is necessary. 
     In JP 2000-121390 A, pulse conversion is applied to an A-phase signal and a B-phase signal which have phase difference of 90 degrees, so that these signals are outputted as one A/B-phase pulse signal which is PWM-modulated corresponding to the moving direction of the scale. 
     However, while in the case of a moving object which constantly moves at a fixed cycle, it is possible to detect the moving direction with a PWM (Pulse Width Modulation) signal, in the case of a moving object which does not move at a fixed cycle, it becomes difficult to detect the moving direction of the moving object with high precision due to the pulse width of an output pulse and to the influence of jitter on output components. Moreover, in a signal composed of signal components of two phases, the number of counts of the moved positions in one cycle is only for one phase, and therefore the resolution is also reduced by half compared to the resolution in the optical encoder of JP S59-40258 A. 
     Moreover in JP S60-88316 A, one of the counter-pulse signals of two phases acquired from the rotary encoder is phase-inverted before these two signals are added together so as to achieve transmission of two signals with a single output signal line. However, as with the case of JP 2000-121390 A, the resolution is reduced by half, which makes it impossible to acquire relative position information with high precision. 
     Further, it is aimed in both JP 2000-121390 A and JP S60-88316 to reduce the total number of interconnections by signal processing, though devices such as counters, pulse modulators and oscillators are needed. This not only limits the available frequencies but also requires synchronization with an output section and complicates the configuration, which makes it difficult to miniaturize the portion where an encoder module is mounted. 
     Further in JP 2000-121390 A, PWM modulation is performed under microcomputer control corresponding to the movement information on the moving object. In short, since the PWM modulation is applied depending on the processing speed of the microcomputer or the frequency of an internal oscillator, it is difficult to determine the moving direction at the moment the moving direction of the moving object changes. 
     Similarly in JP S60-88316 A, the allowable cycle of the moving object depends on the frequency of oscillators. Therefore, although increasing the frequency of the oscillator makes it possible to cover a wide frequency ranges, consumed electric current is increased and therefore this solution is not suitable for practical use. 
     Moreover, although it is aimed in both JP 2000-121390 A and JP S60-88316 to reduce the total number of interconnections by signal processing, devices such as counters, pulse modulators and oscillators are needed, and this requires synchronization with an output section and thereby complicates the configuration. Consequently, it becomes difficult to miniaturize the portion where an encoder module is mounted. 
     Also in the optical encoder disclosed in JP 2005-61896 A, as with the optical encoder disclosed in JP S59-40258 A, it is necessary to use two phase outputs for detecting the moving direction. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the present invention is to provide an optical encoder which is capable of detecting movement information including relative position information and moving direction with high precision, usable in a large frequency range, and which allows reduction in total number of output interconnections so as to be optimal for miniaturization. 
     In order to accomplish the object, an optical encoder of the present invention comprises: 
     a light emitting section; and 
     a light receiving section having a plurality of light receiving elements placed so as to be aligned in one direction in an area where a light beam from the light emitting section may reach, for detecting movement of a moving object which is composed of a light-ON section for enabling the light beam to come incident into the light receiving element when the moving object passes through a predetermined position corresponding to the light receiving element, and a light-OFF section for disabling the light beam from coming incident into the light receiving element when the moving object passes through a predetermined position corresponding to the light receiving element, the light-ON section and the light-OFF section alternately passing through the predetermined position when the moving object moves in the one direction, 
     the optical encoder further comprising a light receiving signal processing section for receiving inputs of a plurality of light receiving signals with different phases from a plurality of the light receiving elements, performing signal processing including at least one signal processing among a logical operation processing, an addition processing, and a subtraction processing on a plurality of the light receiving signals, and outputting an output signal containing a plurality of signal components which are different in phase and different in signal level with respect to a predetermined threshold level. 
     According to the optical encoder of the invention, the light receiving signal processing section converts a plurality of light receiving signals different in phase into an output signal containing a plurality of signal components different in phase and different in signal level with respect to a predetermined threshold level. With this output signal, it becomes possible to transmit a plurality of movement information sets with use of a single transmission path. The output signal has a plurality of output components with different phases in one cycle, so that position information with high precision can be obtained, and miniaturization of encoder modules as well as simplification of electric interconnections can be achieved without lowering the resolution. 
     In the configuration of the invention, since it is not necessary to configure a synchronous circuit with an internal oscillator, the movement speed of a moving object from is not limited on the circuit. Therefore, according to the invention, it becomes possible to obtain stable outputs in a large frequency range. 
     The optical encoder of one embodiment, further comprises a plurality of detection sections composed of the light receiving section and the light receiving signal processing section so that a plurality of the detection sections detect movement of a plurality of moving objects which move in directions different from each other. 
     In the optical encoder of the present embodiment, even in the case where there are two or more moving objects, it becomes possible to obtain highly precise movement information on two or more moving objects and to reduce the number of the transmission paths of output signals by half, so that miniaturization of encoder modules as well as simplification of electric interconnections can be achieved. For example, in the case of detecting moving directions such as two dimensional and three dimensional moving directions with two or more moving objects, the number of the transmission paths of output signals can be reduced by half from conventional number of 4 and 6 to 2 and 3. 
     In the optical encoder of one embodiment, the light receiving signal processing section comprises a subtraction circuit for subtracting a plurality of light receiving signals and generating an output signal containing a plurality of signal components which are different in phase and different in signal level with respect to a predetermined threshold level. 
     In the present embodiment, the light receiving signal processing section subtracts a plurality of light receiving signals with the subtraction circuit so as to generate an output signal containing a plurality of signal components different in phase and different in signal level with respect to a predetermined threshold level. Therefore, unlike the conventional example in which a single pulse is created and outputted with use of a pulse modulator or an oscillator, signal processing sections can sufficiently be integrated and reduction in mounting area can be achieved. 
     In the optical encoder of one embodiment, the light receiving signal processing section comprises: 
     an exclusive OR circuit for calculating exclusive OR of first and second signals, which are obtained from a plurality of the light receiving signals and which are different in phase from each other by 90 degrees, and outputting a third signal; 
     an AND circuit for calculating a logical AND of the third signal outputted from the exclusive OR circuit and one signal out of the first and second signals, and outputting a fourth signal; and 
     a subtraction circuit for subtracting the fourth signal outputted from the AND circuit from the other signal out of the first and second signals, and outputting a fifth signal. 
     In the present embodiment, with the exclusive OR circuit, the AND circuit and the subtraction circuit, the light receiving signal processing section generates a fifth signal containing a plurality of signal components different in phase and different in signal level with respect to a predetermined threshold level, and changes the pulse width of a plurality of signal components of the fifth signal different in signal level. Therefore, in the present embodiment, the pulse width of one phase with respect to the threshold level can be changed with the fifth signal obtained by performing simple logical operation and subtraction on first and second signals which are obtained from a plurality of light receiving signals and which are different in phase from each other by 90 degrees. Therefore, the fifth signal can change a logical value by the forward or backward moving direction of the moving object, and can avoid the detection error regarding whether the moving direction is forward or backward. 
     In the optical encoder of one embodiment, the light receiving signal processing section comprises a comparison section for comparing a signal outputted from the subtraction circuit with a predetermined reference voltage, and outputting a comparison result. 
     In the present embodiment, the comparison section included in the light receiving signal processing section outputs the result of comparison between an output signal of the subtraction circuit which may be changed by various optical conditions and a predetermined reference voltage, so that it becomes possible to stabilize the threshold level, avoid downstream signal processing from being complicated due to change in output signals from the subtraction circuit, and to thereby avoid potential malfunction. 
     The threshold level of the outputs from the comparison section can arbitrarily be changed with the reference voltage. Consequently, it becomes possible to take out only an arbitrary output component in the output of the comparison section, and when high precession is not required, it also becomes possible to obtain only the information on one phase in the information on a plurality of phases contained in the output signal from the subtraction circuit. 
     In the optical encoder of one embodiment, the light receiving signal processing section comprises a negative feedback circuit including an operational amplifier with an inverting input terminal for receiving an input of the fifth signal outputted from the subtraction circuit and with a non-inverting input terminal for receiving an input of a predetermined reference voltage. 
     In the present embodiment, the threshold level of the fifth signal from the subtraction circuit can be stabilized by the negative feedback circuit, and by adjusting the gain in the negative feedback circuit, it becomes possible to easily adjust amplitude values of the output signals from the negative feedback circuit with respect to the threshold level. 
     In the optical encoder of one embodiment, the light receiving signal processing section comprises a reference voltage section which can change a value of the predetermined reference voltage. 
     In the optical encoder of the present embodiment, by changing the value of the predetermined reference voltage by the reference voltage section included in the light receiving signal processing section, it becomes possible to take out only an arbitrary output component in the output of the comparison section without increasing the number of the output interconnections from the light receiving signal processing section. 
     In the optical encoder of one embodiment, the light receiving signal processing section comprises an analog signal generation circuit for generating an analog signal, and outputting an output signal containing an analog signal component of the analog signal generated by the analog signal generation circuit. 
     In the optical encoder of the present embodiment, precession in detecting the movement amount of the moving object can be enhanced corresponding to the resolution of analog signal components included in an output signal outputted by the light receiving signal processing section. Moreover, it becomes possible to detect the moving direction of the moving object on the basis of waveform fluctuation of the analog signal components. 
     It is to be noted that as the analog signal generation circuit, the circuits formed by adding capacity to an amplifier section for amplifying light receiving signals, a logic output circuit section and the like may be employed so as to provide time width to the rising edge and the falling edge of signals. As the analog signal generation circuit, the circuit may also be employed which, for example, reduces the gain of the amplifier section which amplifies light receiving signals so as to provide time width to the rising edge and the falling edge of signals. These circuits can all be configured very easily. The analog signals are not limited to those obtained from the light receiving signals but may be, for example, clock signals which form triangular waves. 
     In the optical encoder of one embodiment, the light receiving signal processing section comprises: 
     a digital signal generation circuit for generating a digital signal from the light receiving signal, the digital signal being different in phase from the analog signal generated by the analog signal generation circuit; and 
     a subtraction circuit for subtracting the analog signal and the digital signal and for generating an output signal containing a plurality of signal components which are different in phase and different in signal level with respect to a predetermined threshold level. 
     In the optical encoder of this embodiment, the output signal is generated by the subtraction circuit included in the light receiving signal processing section, so that change in time constant due to change in gain of the aforementioned amplifier section and to addition of capacity are avoidable. Further, since any additional circuit such as oscillators is not necessity, it becomes possible to detect the movement amount and the moving direction of the moving object with high precision without provision of frequency dependence. 
     An electronic equipment of one embodiment includes the optical encoder according to the present invention and further has a comparison section for comparing an output signal, which is outputted from the light receiving signal processing section and which contains a plurality of signal components different in phase and different in signal level with respect to a predetermined threshold level, with a reference voltage corresponding to the threshold level, and for outputting a comparison result. 
     In the electronic equipment of the present embodiment, the comparison section can output a signal converted into a digital signal by comparing the output signal from the optical encoder with the reference voltage corresponding to the threshold level. More specifically, even when an output signal from the optical encoder is an analog output signal and therefore direct signal processing by microcomputers and the like cannot be performed, the output signal can be converted into a digital signal by the comparison section. Therefore, the movement information on the moving object can be obtained by inputting the digitized output signal from the comparison section into the microcomputer included in the electronic equipment. For example, employing the electronic equipment of the present embodiment in ink head sections in ink-jet printers makes it possible to easily obtain the movement information on the ink head sections as moving objects while the number of interconnections outputted from the optical encoder is still reduced. 
     An electronic equipment of one embodiment includes the optical encoder of the one embodiment and further has a comparison section for comparing an output signal, which is outputted by the light receiving signal processing section and which contains an analog signal component, with a plurality of different reference voltages and for outputting a plurality of digital signals based on a comparison result. 
     In the optical encoder in the present embodiment, with a plurality of digital signals outputted by the comparison section, highly precise movement information on the moving object can be obtained. Moreover, since the comparison section outputs digital signals, direct signal processing by microcomputers and the like can be performed. 
     Moreover, the electronic equipment in one embodiment includes the optical encoder according to the present invention. According to the electronic equipment, it becomes possible to achieve miniaturization by reducing the number of interconnections for optical encoders and to detect movement information with high precision. 
     According to the optical encoder of the present invention, the light receiving signal processing section converts a plurality of light receiving signals different in phase into an output signal containing a plurality of signal components different in phase and different in signal level with respect to a predetermined threshold level. With this output signal, it becomes possible to transmit a plurality of movement information sets with use of a single transmission path. Moreover, since the output signal has a plurality of output components with different phases per one cycle, position information can be obtained with high precision, and miniaturization of encoder modules as well as simplification of electric interconnections can be achieved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: 
         FIG. 1  is a schematic view showing an optical encoder in a first embodiment of the invention; 
         FIG. 2  is a waveform chart showing each signal waveform in a light receiving signal processing section of the first embodiment; 
         FIG. 3A  is a schematic view showing an optical encoder in a second embodiment of the invention; 
         FIG. 3B  is a schematic view showing a modified example of the second embodiment; 
         FIG. 4  is a waveform chart showing each signal waveform in a light receiving signal processing section of the second embodiment; 
         FIG. 5  is a schematic view showing an optical encoder in a third embodiment of the invention; 
         FIG. 6A  is a waveform chart showing each signal waveform in a light receiving signal processing section of the third embodiment; 
         FIG. 6B  is a waveform chart showing each signal waveform in a light receiving signal processing section of the third embodiment; 
         FIG. 7  is a circuit diagram showing a modified example of the reference voltage section of the third embodiment; 
         FIG. 8  is a circuit diagram showing a principle part of an optical encoder in a fourth embodiment of the invention; 
         FIG. 9A  is a schematic view showing a part of an optical encoder in a fifth embodiment of the invention; 
         FIG. 9B  is a circuit diagram showing a part of a light receiving signal processing section in the optical encoder of the fifth embodiment; 
         FIG. 10  is a waveform chart showing each signal waveform in a light receiving signal processing section of the fifth embodiment; 
         FIG. 11  is a view showing a part of a light receiving signal processing section in electronic equipment of a sixth embodiment of the invention; 
         FIG. 12A  is a waveform chart showing each signal waveform in a light receiving signal processing section of the sixth embodiment; and 
         FIG. 12B  is a waveform chart showing each signal waveform in a light receiving signal processing section of the sixth embodiment; 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinbelow, the present invention will be described in details in conjunction with the embodiments with reference to the drawings. 
     First Embodiment 
       FIG. 1  shows an optical encoder in a first embodiment of the invention. The first embodiment is composed of a moving object  1 , a light receiving section  2 , and a light emitting section  3 . The light emitting section  3  is constituted of light emitting elements such as LEDs (Light Emitting Diodes). The light receiving section  2  has three light receiving elements  11  to  13 . The moving object  1  is movable in the direction shown by arrow X 1  or X 2 , with a light-ON section  6  and a light-OFF section  7  being alternately arranged in the moving direction. With the array pitch of the light-ON section  6  being P, the moving direction size (width size) of the light-ON section  6  and the light-OFF section  7  is (½)P. The light-ON section  6  passes a light beam from the light emitting section  3  to the light receiving section  2  side, while the light-OFF section  7  does not pass the light beam from the light emitting section  3  to the light receiving section  2  side. Although the light receiving elements  11  to  13  are constituted from photo diodes in the present embodiment, they may be constituted from phototransistors. In the present embodiment, the width size of each light receiving element  11  to  13  is set to ( 1/12)P. Each light receiving element  11  to  13  is adjacent to each other without intervals in the moving direction. 
     Therefore, with 1 pitch P being set to 360 degrees, light receiving signals A, B and C respectively outputted by light receiving elements  11 ,  12 ,  13  each have a phase shifted from each other by 30 degrees as shown in  FIG. 2 . The light receiving signals A, B, C outputted by the light receiving elements  11 ,  12 ,  13  are inputted into an AND circuit  17  via current distributors  14 ,  15 ,  16  and an AD converter (not shown) and are subjected to AND operation. The AND circuit  17  outputs a wave-like AND signal A·B·C shown in  FIG. 2  to three exclusive OR circuits  18  to  20 . 
     The AND signal A·B·C and a light receiving signal A traveling via the current distributor  14  and the AD converter are inputted into the exclusive OR circuit  18 , which calculates exclusive OR of both the signals and outputs a calculated signal A′ to an addition circuit  22 . The AND signal A·B·C and a light receiving signal B traveling via the current distributor  15  and the AD converter are inputted into the exclusive OR circuit  19 , which calculates exclusive OR of both the signals and outputs a calculated signal B′ to the addition circuit  22 . The AND signal A·B·C and a light receiving signal C traveling via the current distributor  16  and the AD converter are inputted into the exclusive OR circuit  20 , which calculates exclusive OR of both the signals and outputs a calculated signal C′ to an amplification circuit  21 . Then, the addition circuit  22  adds the calculated signals A′, B′ and a signal  2 C′ amplified twofold by the amplification circuit  21  together and outputs a wave-like output signal as shown in  FIG. 2 . 
     The current distributors  14  to  16 , the AD converter, the AND circuit  17 , the exclusive OR circuits  18 ,  19 ,  20 , the amplification circuit  21 , and the addition circuit  22  constitute a light receiving signal processing section. 
     In the output signal, as shown in  FIG. 2 , a pulse S 1  which rises between a threshold level 0 and a threshold level 1 serves as an A-phase signal component, a pulse S 2  which rises between the threshold level 1 and a threshold level 2 serves as a B-phase signal component, and a pulse S 3  which rises exceeding the threshold level 2 serves as a C-phase signal component. Therefore, in the downstream signal processing section, the relative movement information on the moving object  1  can be obtained by, for example, counting rising edge components with respect to the threshold levels  0  to  2 . Moreover, the forward and the backward (X 1 , X 2 ) of the moving direction of the moving object  1  may be distinguished based on the precedent or following relation of the pulse rising edges of the A-phase signal component and the C-phase signal component. Therefore, according to the present embodiment, the addition circuit  22  can incorporate A to C three phase signal components, which are different in signal level and phase, in an output signal outputted to a single transmission path without losing movement information components. Therefore, in the present embodiment, it becomes possible to obtain highly precise movement information while achieving miniaturization and simplification of electric interconnections. 
     Although one detection section composed of the light receiving section  2  and the light receiving signal processing section is provided in this embodiment, a plurality of detection sections may be provided so that the movement of a plurality of moving objects which move in the directions different from each other may be detected by a plurality of the detection sections. Accordingly, it becomes possible to obtain highly precise movement information on two or more moving objects, to reduce the number of transmission paths of output signals by half, and to achieve miniaturization of encoder modules and simplification of electric interconnections. For example, in the case of detecting moving directions such as two dimensional and three dimensional moving directions with two or more moving objects, the number of the transmission paths of output signals can be reduced by half from conventional number of 4 and 6 to 2 and 3. Although the two-dimensional moving directions may be, by way of example, a direction X and a direction Y which inclines 90 degrees with respect to the direction X, it should naturally be understood that the angle of inclination is not limited to 90 degrees but may be any angle as long as different moving directions can be formed. Moreover, it also should be understood that a direction X, a direction Y and a direction Z as the three-dimensional directions are not limited to those forming right angles with each other like rectangular-coordinates. 
     Second Embodiment 
       FIG. 3A  shows an optical encoder in a second embodiment of the invention. The second embodiment is composed of a moving object  31 , a light receiving section  32 , and a light emitting section  33 . The light emitting section  33  is constituted from light emitting elements such as LEDs (Light Emitting Diodes). 
     The light receiving section  32  has four light receiving elements  41  to  44 . The moving object  31  is movable in the direction shown by arrow X 1  or X 2 , with a light-ON section  36  and a light-OFF section  37  being alternately arranged in the moving direction. With the array pitch of the light-ON section  36  being P, the moving direction size (width size) of the light-ON section  36  and the light-OFF section  37  is (½)P. The light-ON section  36  passes a light beam from the light emitting section  33  to the light receiving section  32  side, while the light-OFF section  37  does not pass the light beam from the light emitting section  33  to the light receiving section  32  side. It is to be noted that the light receiving elements  41  to  44  are made of photodiodes. In the present embodiment, the width size of each light receiving element  41  to  44  is set to (¼)P. Each light receiving element  41  to  44  is adjacent to each other without intervals in the moving direction. 
     A light receiving signal A+ outputted by the light receiving element  41  is inputted into a non-inverting input terminal of a differential amplifier  51  via a current voltage conversion section  45 , while a light receiving signal A− outputted by the light receiving element  43  is inputted into an inverting input terminal of the differential amplifier  51  via a current voltage conversion section  46 . A light receiving signal B− outputted by the light receiving element  42  is inputted into an inverting input terminal of a differential amplifier  52  via a current voltage conversion section  48 , while a light receiving signal B+ outputted by the light receiving element  44  is inputted into a non-inverting input terminal of the differential amplifier  52  via a current voltage conversion section  47 . 
     The differential amplifier  51  amplifies a difference between the light receiving signal A+ converted into voltage and the light receiving signal A− converted into voltage, and outputs this amplified signal to an AD converter  53 . The differential amplifier  52  amplifies a difference between the light receiving signal B+ converted into voltage and the light receiving signal B− converted into voltage, and outputs this amplified signal to an AD converter  54 . 
     Then, the AD converter  53  converts the amplified signal inputted from the differential amplifier  51  into a digital signal A and outputs it to a subtraction circuit  55 , while the AD converter  54  converts the amplified signal inputted from the differential amplifier  52  into a digital signal B and outputs it to a subtraction circuit  55 . Then, the subtraction circuit  55  subtracts the digital signal B from the digital signal A, and outputs a subtracted signal (A−B). 
     In the second embodiment, the current voltage conversion sections  45  to  48 , the differential amplifiers  51 ,  52 , the AD converters  53 ,  54 , and the subtraction circuit  55  constitute a light receiving signal processing section. 
     The column “A-PHASE PRECEDENCE” of  FIG. 4  shows the signal waveforms of the digital signals A, B outputted from the AD converters  53 ,  54  and the subtracted signal (A−B) outputted by the subtraction circuit  55  when the moving object  31  moves in the direction of arrow X 1 . The column “B-PHASE PRECEDENCE” of  FIG. 4  shows the signal waveforms of the digital signals A, B outputted from the AD converters  53 ,  54  and the subtracted signal (A−B) outputted by the subtraction circuit  55  when the moving object  31  moves in the direction of arrow X 2 . 
     According to the present embodiment as shown in  FIG. 4 , the digital signal B is subtracted from the digital signal A in the subtraction circuit  55  so that a subtracted signal (A−B) containing an A-phase component As and a B-phase component Bs which are different in phase and different in signal level with respect to a predetermined threshold level SL is generated as an output signal. 
     In the present embodiment, as shown in the “A-PHASE PRECEDENCE” column in  FIG. 4 , it can be determined that the moving object  31  moves in the direction of arrow X 1  when the A-phase component As on the upper side of the threshold level SL precedes the B-phase component Bs on the lower side of the threshold level SL. As shown in the column “B-PHASE PRECEDENCE” in  FIG. 4 , it can be determined that the moving object  31  moves in the direction of arrow X 2  when the B-phase component Bs precedes the A-phase component As. 
     Moreover in the present embodiment, unlike the conventional example in which a single pulse is created and outputted with use of a pulse modulator or an oscillator, it becomes possible to obtain the subtracted signal (A−B) having a plurality of output components As and Bs which are different in phase in one cycle, to acquire highly precise position information, and to achieve simplification of electric interconnections and reduction of a mounting area only by adding the subtraction circuit  55  which can sufficiently be integrated in the signal processing section. 
       FIG. 3B  shows a modified example of the second embodiment. In this modified example, a comparison section  66  is connected to the output side of the subtraction circuit  55 . This comparison section  66  is composed of an operational amplifier  64 , a feedback resister  63  connected to between the output side of the operational amplifier  64  and an inverting input terminal of the operational amplifier  64 , and a reference voltage section  65  connected to a non-inverting input terminal of the operational amplifier  64 . In this modified example, as shown in  FIG. 3B , a subtracted signal (A−B) outputted by the subtraction circuit  55  is inputted into the comparison section  66 . The subtracted signal (A−B) is inputted into the inverting input terminal of the operational amplifier  64  included in the comparison section  66 , while a reference voltage from the reference voltage section  65  is inputted into the non-inverting input terminal of the operational amplifier  64 . According to output signals of the operational amplifier  64 , stable threshold levels can be obtained. Moreover, by changing the value of the reference voltage generated by the reference voltage section  65 , it becomes possible to take out and output a desired signal component from the subtracted signal (A−B). For example, in the case where information about the moving direction is not required, or in the case where high precision is not required of the movement information, the reference voltage is set to be a supply voltage or a ground (GND) so that movement information only on one phase out of the A-phase and B-phase can be acquired. 
     In the modified example, the output of the operational amplifier  64  is returned to the inverting input terminal by a negative feedback circuit formed by the feedback resister  63 , and therefore desired output amplitude can be obtained by changing the resistance of the feedback resister  63 . Moreover, it is also possible to curtail the amplitude fluctuation of output signals by connecting a diode, instead of the feedback resister  63 , to between the output of the operational amplifier  64  and the inverting input terminal thereof. 
     In the present embodiment, as shown in  FIG. 7 , a collector of an npn transistor  71  may be connected to the reference voltage section  65 , while a base thereof may be connected to a junction point between a resistance  72  and a resistance  73 , and a voltage Vcc of a power supply connected to the resistance  72  may be set at a fixed value or more, so that the reference voltage inputted into the non-inverting input terminal of the operational amplifier  64  can be changed. Thereby, it becomes possible to change the reference voltage inside the light receiving signal processing section only by adjusting supply voltage and to take out and output a desired signal component from the subtracted signal (A−B) without increasing the number of output interconnections from the light receiving signal processing section. Consequently, external signal processing can be simplified when a plurality of output components are outputted with one transmission path. 
     Third Embodiment 
       FIG. 5  shows an optical encoder in a third embodiment of the present invention. The third embodiment is different from the aforementioned second embodiment in the point that an exclusive OR circuit  61  and an AND circuit  62  are connected to between the AD converters  53 ,  54  and the subtraction circuit  55  of the second embodiment, and in the point that a comparison section  66  is connected to the output side of the subtraction circuit  55 . Therefore, the third embodiment is similar to the second embodiment in the point that the moving object  31 , the light receiving section  32 , the light emitting section  33  and the current voltage conversion sections  45  to  48  shown in  FIG. 3A  are provided. Therefore, in this third embodiment, component members identical to those in the second embodiment are designated by identical reference numerals, and description will be mainly given of the portions different from the second embodiment. 
     As shown in  FIG. 5 , in the third embodiment, an output line  67  of the AD converter  53  and an output line  68  of the AD converter  54  are connected to the input side of the exclusive OR circuit  61 . The output line  68  of the AD converter  54  and an output line  69  of the exclusive OR circuit  61  are connected to the input side of the AND circuit  62 . Also, an output line  70  of the AND circuit  62  and the output line  67  of the AD converter  53  are connected to the input side of the subtraction circuit  55 . 
     The output of the subtraction circuit  55  is connected to the comparison section  66 . The comparison section  66  is composed of a operational amplifier  64 , a feedback resister  63  connected to between the output side of the operational amplifier  64  and an inverting input terminal of the operational amplifier  64 , and a reference voltage section  65  connected to a non-inverting input terminal of the operational amplifier  64 . 
     In the third embodiment, digital signals A, B as first, second signals which are outputted from the AD converters  53 ,  54  and which are different in phase from each other by 90 degrees are inputted into the exclusive OR circuit  61 , which outputs a third signal I generated by calculating exclusive OR of the digital signals A and B into the output line  69 . 
     The AND circuit  62  calculates logical AND of the digital signal B inputted from AD converter  54  and the third signal I inputted from the exclusive OR circuit  61 , and outputs a fourth signal J to the output line  70 . Then, the subtraction circuit  55  subtracts the fourth signal J from the digital signal A inputted from the AD converter  53 , and outputs a fifth signal K. 
       FIG. 6A  shows signal waveforms of digital signals A, B as the first and second signals, the third signal I, the fourth signal J, and the fifth signal K when the moving object  31  shown in  FIG. 3  moves in the direction of arrow X 1 .  FIG. 6B  shows signal waveforms of digital signals A, B as the first and second signals, the third signal I, the fourth signal J, and the fifth signal K when the moving object  31  shown in  FIG. 3  moves in the direction of arrow X 2 . 
     In the signal waveform of the fifth signal K shown in  FIG. 6A  and  FIG. 6B , a signal component As on the upper side of a threshold level SL corresponds to the digital signal A, while a signal component Bs on the lower side of the threshold level SL corresponds to the digital signal B. Therefore, in the present embodiment, the rising edge of the pulse of the signal component As and the rising edge of the pulse of the signal component Bs are independently counted so that information on relative position change can be obtained, and the fifth signal K can be transmitted with use of a single transmission path without lowering the resolution. 
     Moreover, the moving direction of the moving object  31  can be detected by detecting the temporal relationship of the pulse waveforms of the signal component As and the signal component Bs in the fifth signal K. For example, when the moving object  31  moves in the direction of arrow X 1 , the pulse waveform of the signal component Bs is generated immediately after the pulse waveform of the signal component As falls as shown in  FIG. 6A . On the contrary, when the moving object  31  moves in the direction of arrow X 2 , the pulse waveform of the signal component Bs is generated after the lapse of ¼ cycle of the fifth signal K after the pulse waveform of the signal component As falls as shown in  FIG. 6B . 
     Therefore, the moving direction of the moving object  31  can easily be detected by detecting the time difference between the signal component As and the signal component Bs in the fifth signal K outputted by the subtraction circuit  55 . In  FIG. 6A  and  FIG. 6B , the “As LOGICAL VALUE” under the waveform of the fifth signal K shows logic results “1” and “0” indicating whether or not the signal component As, which is sampled every ¼ cycle (25% of a duty cycle) of the signal K, is H (H level) with respect to the threshold level SL. In  FIG. 6A  and  FIG. 6B , the “Bs LOGICAL VALUE” under the waveform of the fifth signal K shows logic results “1” and “0” indicating whether or not the signal component Bs, which is sampled every ¼ cycle (25% of a duty cycle) of the signal K, is L (L level) with respect to the threshold level SL. 
     Since the logic result of a section surrounded with a dashed dotted line BR in  FIG. 6A  and the logic result of a section surrounded with a dashed dotted line BR in  FIG. 6B  are different, it becomes possible to determine whether the moving object  31  moves in the direction of arrow X 1  or in the direction of arrow X 2  by comparing the logic results of both the sections. For example, displaying the signal waveform of the fifth signal K on waveform displays such as oscilloscopes makes it possible to detect the moving direction based on the difference in signal waveform, and this allows detection of the moving direction of the moving object at any moment. In the present embodiment, with the fifth signal K outputted by the subtraction circuit  55 , a logical value can be changed by the forward or backward moving direction of the moving object  31 , and it can correctly be detected whether the moving direction is forward or backward. 
     In the present embodiment, as shown in  FIG. 5 , the fifth signal K of the subtraction circuit  55  is inputted into the comparison section  66 . The fifth signal K is inputted into the inverting input terminal of the operational amplifier  64  included in the comparison section  66 , while a reference voltage from the reference voltage section  65  is inputted into the non-inverting input terminal of the operational amplifier  64 . According to output signals of the operational amplifier  64 , stable threshold levels can be obtained. Moreover, by changing the value of the reference voltage generated by the reference voltage section  65 , it becomes possible to take out and output a desired signal component from the fifth signal K. For example, in the case where information about the moving direction is not required, or in the case where high precision is not required of the movement information, the reference voltage is set to be a supply voltage or a ground (GND) so that movement information only on one phase out of the A-phase and B-phase can be acquired. 
     In this embodiment, the output of the operational amplifier  64  is returned to the inverting input terminal by a negative feedback circuit formed by the feedback resister  63 , and therefore desired output amplitude can be obtained by changing the resistance of the feedback resister  63 . Moreover, it is also possible to curtail the amplitude fluctuation of output signals by connecting a diode, instead of the feedback resister  63 , to between the output of the operational amplifier  64  and the inverting input terminal thereof. 
     In the present embodiment, as shown in  FIG. 7 , a collector of an npn transistor  71  may be connected to the reference voltage section  65 , while a base thereof may be connected to a junction point between a resistance  72  and a resistance  73 , and a voltage Vcc of a power supply connected to the resistance  72  may be set at a fixed value or more, so that the reference voltage inputted into the non-inverting input terminal of the operational amplifier  64  can be changed. Thereby, it becomes possible to change the reference voltage inside the light receiving signal processing section only by adjusting supply voltage and to take out and output a desired signal component from the fifth signal K without increasing the number of output interconnections from the light receiving signal processing section. Consequently, external signal processing can be simplified when a plurality of output components are outputted with one transmission path. 
     Fourth Embodiment 
       FIG. 8  shows a principle part of an optical encoder in a fourth embodiment of the invention. The fourth embodiment is different from the aforementioned second embodiment in the point that a low pass filter  81  composed of a resistance  82  and a capacitor  83  is connected between the AD converter  53  and the subtraction circuit  55  of the second embodiment shown in  FIG. 3A . 
     In the fourth embodiment, with the low pass filter  81  as an analog signal generation circuit, the rising edge and the falling edge of a square wave of the digital signal A outputted by the AD converter  53  shown in the  FIG. 4  can be temporally dulled to make an analog waveform. Consequently, in the column “A-PHASE PRECEDENCE” in  FIG. 4  showing the case where the moving object  31  of  FIG. 3A  moves in the direction of arrow X 1 , the rising edge of the A-phase component and the rising edge of the B-phase component of a subtracted signal (A−B) are smoothed corresponding to the time constant decided by the resistance  82  and the capacitor  83  of the low pass filter  81 . 
     On the contrary, in the column “B-PHASE PRECEDENCE” in  FIG. 4  showing the case where the moving object  31  of  FIG. 3A  moves in the direction of arrow X 2 , the falling edge of the A-phase component and the falling edge of the B-phase component of a subtracted signal (A−B) are smoothed corresponding to the time constant decided by the resistance  82  and the capacitor  83  of the low pass filter  81 . 
     Therefore, according to the present embodiment, as shown in the column “A-PHASE PRECEDENCE” in  FIG. 4 , it can be determined that the moving object  31  moves in the direction of arrow X 1  when the rising waveform of the A-phase component As of the subtracted signal (A−B) is smooth. As shown in the column “B-PHASE PRECEDENCE” in  FIG. 4 , it can be determined that the moving object  31  moves in the direction of arrow X 1  when the falling-edge waveform of the A-phase component As of the subtracted signal (A−B) is smooth. 
     Therefore, according to the fourth embodiment, the moving direction of the moving object  31  can easy be determined by very simple circuit alteration, that is to connect the low pass filter  81  to between the AD converter  53  and the subtraction circuit  55  of the second embodiment. 
     Instead of connecting the low pass filter  81  to between the AD converter  53  and the subtraction circuit  55 , a low pass filter may be connected to between the AD converter  54  and the subtraction circuit  55  so as to convert the digital signal B into a signal with analog waveform. What is necessary is to select signals to be converted into analog signals so that A-phase precedence and B-phase precedence can be distinguish. In short, the analog signals for conversion to analog signals are not limited to those obtained from the light receiving signals but may be, for example, clock signals which form a triangular wave. 
     Fifth Embodiment 
       FIGS. 9A and 9B  show an optical encoder in a fifth embodiment of the invention. The fifth embodiment is different from the third embodiment in (1), (2) and (3) points shown below. 
     (1) As shown in  FIG. 9B , the subtraction circuit  55  and the comparison section  66  of  FIG. 5  are replaced with a subtraction circuit  90 . 
     (2) As shown in  FIG. 9A , four light receiving elements  41 ,  42 ,  43 ,  44  are respectively connected to current distributors  91 ,  92 ,  93 ,  94 , which input light receiving signal A+, A−, B+, B− into current voltage conversion sections  45 ,  46 ,  47 ,  48  of  FIG. 9B . 
     (3) As shown in  FIG. 9A , a current voltage conversion section  95  connected to the current distributors  91 ,  92 , a current voltage conversion section  96  connected to the current distributors  93 ,  94 , a subtraction circuit  97  with an input side connected to the current voltage conversion sections  95 ,  96 , and a comparator  98  for receiving an output signal of the subtraction circuit  97  are provided, and the output side of the comparator  98  is connected to the input side of the subtraction circuit  90  of  FIG. 9B . 
     In the fifth embodiment, the current voltage conversion section  95  of  FIG. 9A  converts a signal ((A+)+(B−)) formed by adding light receiving signals A+ and B− into a voltage signal, and inputs it into the subtraction circuit  97 . The movement of 1 pitch P of the moving object  31  corresponds to one cycle of the added signal ((A+)+(B−)). The current voltage conversion section  96  converts a signal ((A−)+(B+)) formed by adding light receiving signals A− and B+ into a voltage signal, and inputs it into the subtraction circuit  97 . The movement of 1 pitch P of the moving object  31  corresponds to one cycle of the added signal ((A−)+(B+)). The added signal ((A−)+(B+)) and the added signal ((A−)+(B+)) are different in phase by 180 degrees. 
     Then, the subtraction circuit  97  subtracts the signal ((A−)+(B+)) from the signal ((A+)+(B−)), and inputs this subtracted signal into the comparator  98 . The comparator  98  compares the subtracted signal with a fixed voltage VA from a direct current power supply  99  and outputs an analog output signal A 1 out. The analog output signal A 1 out is an analog waveform with a half-cycle triangular waveform as shown in  FIG. 10  regardless of the moving direction of the moving object  31 . One cycle of the triangle-wave analog output signal A 1 out corresponds to 1 pitch movement of the moving object  31 . 
     As in the third embodiment, the AND circuit  62  of  FIG. 9B  calculates logical AND of a digital signal B inputted from the AD converter  54  and a third signal I inputted from the exclusive OR circuit  61 , and outputs a fourth signal J to the output line  70 . One cycle of the fourth signal J corresponds to 1 pitch movement of the moving object  31  as shown in  FIG. 10 . 
     Then, the fourth signal J and the analog output signal A 1 out outputted from the subtraction circuit  97  are inputted into the subtraction circuit  90 , which subtracts the fourth signal J from the analog output signal A 1 out, and outputs an analog output signal A 2 out. 
     The column “A-PHASE PRECEDENCE” in  FIG. 10  shows signal waveforms of the analog output signal A 1 out, the fourth signal J, and the analog output signal A 2 out when the moving object  31  moves in the direction of arrow X 1 . In this case, the analog output signal A 2 out has such a signal waveform that a square wave of ¼ cycle is outputted on the lower side the moment the analog output signal A 1 out falls. When the moving object  31  moves in the direction of arrow X 2 , as shown in the column “B-PHASE PRECEDENCE” in  FIG. 10 , the analog output signal A 2 out has such a signal waveform that a square wave is outputted on the lower side with a delay of ¼ cycle after the analog output signal A 1 out falls. 
     Therefore, according to the fifth embodiment, in the case of A-PHASE PRECEDENCE, the rectangular wave component of the analog output signal A 2 out outputted by the comparator  98  appears immediately after the triangular wave component of the analog output signal A 1 out. In the case of B-PHASE PRECEDENCE, the rectangular wave component of the analog output signal A 2 out outputted by the comparator  98  appears with a delay of ¼ cycle from the triangular wave component of the analog output signal A 1 out. With such a difference in waveform, the moving direction of the moving object  31  can easily be detected. According to the fifth embodiment, the movement amount is detectable with high precision because of the portion of the triangular wave of the analog output signal A 2 out. Moreover, in the fifth embodiment, change in gain of the amplifier and change in time constant are unnecessary, so that stable operation can be implemented in a wide frequency range. 
     Although the output signal J which is a logical AND between the exclusive OR of the digital signals A and B and the digital signal B is used as a digital signal in the embodiment, an AND signal between the exclusive OR of the digital signals A and B and the digital signal A may be used as a digital signal. What is necessary is to use digital signals which allow distinction between A-phase precedence and B-phase precedence. 
     Sixth Embodiment 
       FIG. 11  shows a sixth embodiment which is electronic equipment having the optical encoder of the first embodiment of the invention. The sixth embodiment is different from the aforementioned first embodiment in the point that first, second and third comparators  101 ,  102 ,  103  connected to the output side of the addition circuit  22  of the first embodiment in  FIG. 1  are provided. Therefore, in the sixth embodiment, description is mainly given of the difference from the first embodiment. 
     In the sixth embodiment as shown in  FIG. 11 , three comparators, first to third comparators  101  to  103  are provided as comparison sections, and non-inverting input terminals of these three comparators  101  to  103  are connected to the output side of the addition circuit  22 . 
     An inverting input terminal of the first comparator  101  is connected to a direct current power supply  105  which generates a first reference voltage V 0 . An inverting input terminal of the second comparator  102  is connected to a direct current power supply  106  which generates a second reference voltage V 1 . Also, an inverting input terminal of the third comparator  107  is connected to a direct current power supply  107  which generates a third reference voltage V 2 . The first, second and third reference voltages V 0 , V 1 , V 2  respectively correspond to threshold levels  0 ,  1 ,  2  shown in  FIG. 2 ,  FIG. 12A  and  FIG. 12B . 
       FIG. 12A  is a wave form chart showing the waveforms of light receiving signals A, B, C, the waveform of an output signal Y of the addition circuit  22 , and the waveforms of output signals XA, XB, XC of the first, second, third comparators  101 ,  102 ,  103  when the moving object  1  of  FIG. 1  moves in the direction of arrow X 1 .  FIG. 12B  is a wave form chart showing the waveforms of light receiving signals A, B, C, the waveform of an output signal Y of the addition circuit  22 , and the waveforms of output signals XA, XB, XC of the first, second, and third comparators  101 ,  102 ,  103  when the moving object  1  of  FIG. 1  moves in the direction of arrow X 2 . 
     As shown in  FIG. 12A  and  FIG. 12B , the waveform of the output signal XA from the first comparator  101  is a waveform in which the logic is switched by rising and falling of the light receiving signals A and C. Since the movement amount of the moving object  1  can be detected with only the output signal XA, it is possible to provide only the first comparator  101  out of the first to third comparators  101  to  103 . It is also possible to provide only any one of the first to third comparators  101  to  103 . 
     The moving direction of the moving object  1  is undetectable with only the output signal XA. Then, the moving direction of the moving object  1  is detectable by detecting the difference in logic switching between the output signal XA and the output signal XC. For example, an exclusive OR of the output signal XA and the output signal XC is obtained in an exclusive OR circuit, and a signal Z of this exclusive OR is inputted as a counter clock signal. On the basis of the precedent or following relation of the signal Z of the exclusive OR, signals different in pulse width can be outputted, and the forward or backward (X 1 , X 2 ) of the moving direction of the moving object  1  can be determined based on the length of the pulse width of the signals. 
     Moreover, instead of obtaining an exclusive OR of the output signal XA and the output signal XC, an exclusive OR of the output signal XA and the output signal XB may be obtained in an exclusive OR circuit, and a signal Z 2  of the exclusive OR may be inputted as a counter clock signal. Signals different in pulse width may be outputted based on the precedent or following relation of the signal Z 2  of the exclusive OR. In short, as shown in  FIG. 12A  and  FIG. 12B , the moving direction of the moving object  1  can be detected by using the fact that the waveforms of the output signal XB and the output signal XC are different by the forward or backward moving direction of the moving object  1 , and therefore it becomes possible to appropriately select any method, other than the method disclosed, for signal processing for these output signals. As for the signal processing, any easy method with use of microcomputers should be selected. 
     Therefore, according to the electronic equipment of the sixth embodiment, the first, second and third comparators  101 ,  102 ,  103  which compare the first, second and third reference voltages V 0 , V 1 , V 2  with the output signal of the addition circuit  22  are connected to the AND circuit or an exclusive OR circuit, and an external signal processing section having a counter, so that movement information including the movement amount and the moving direction of the moving object  1  can easily be obtained while the number of output interconnections is still reduced. 
     According to the electronic equipment having the optical encoder of the first to fifth embodiments, it becomes possible to reduce the number of interconnections for the optical encoder so as to achieve miniaturization and to detect movement information with high precision. For example, by employing the electronic equipment of the sixth embodiment in ink head sections in ink-jet printers, it becomes possible to easily obtain the movement information on the ink head sections as moving objects while the number of interconnections outputted from the optical encoder is still reduced. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.