Abstract:
A photoelectronic sensor collectively adjusts the light emission intensity of plural light emitting elements and the light reception sensitivity of plural light receiving elements automatically or manually. In order to collectively adjust the light emission intensity of plural light emitting elements and the light reception sensitivity of single light receiving elements automatically, a photoelectronic sensor is configured such that constant current light emission signals are applied to the light emitting elements. Additionally, a light amount of the environment is measured by the light receiving elements and stored, and a reflection light amount from a body to be measured is stored. Furthermore, signal intensities indicating the respective light amounts are calculated, and optimal thresholds of light emission intensity and light reception sensitivity are provided automatically or manually, so that setting of sensor sensitivity is performed.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a photoelectronic sensor system which is provided with a sensor section including a light emitting element emitting a light emission signal and a light receiving element receiving a reflection signal obtained by reflecting the light emission signal from the light emitting element by a body to be detected or a transmission signal obtained by transmitting the light emission signal through the body to be detected, where the reflection signal obtained by reflecting the light emission signal by the body to be detected or the transmission signal obtained by transmitting the light emission signal by the body to be detected is captured by the light receiving element so that presence/absence of the body to be detected is detected. 
     2. Description of the Related Art 
     Conventionally, in storage or management of articles, detecting presence/absence of the articles or a storage position thereof is important for managing the storage number of the articles or a storage place or a storage position thereof at the so-called cell production step such as a manufacturing step of the articles, a manufacturing step of products using these articles or an assembling step thereof, or an inspecting step or at a use time of these articles. Since management information about the storage number, the storage place, or the storage position is transmitted to a host system or an automated machine at the next step so that automation of a manufacturing line or an inspection line, or a step in storage and management can be realized, photoelectronic sensors or the like are used. For example, in production of glasses for liquid crystal, glass plates for a disk, printed boards, or semiconductor substrate wafers, photoelectronic sensors are used for detecting a residence site of a wafer cassette or articles on a storage shelf, or presence/absence of articles. 
     Alternatively, in storage and management of regular articles or regular apparatuses, photoelectronic sensors are used for detecting presence/absence of the articles or the apparatuses, or a storage position thereof. 
     For example, Patent Literature 1 describes a photoelectronic sensor where light emission signal is guided from a light emitting element to a light emitting window by an optical fiber for light emission, the light emission signal emitted from the light emitting window is guided to a light receiving element through an optical fiber for light reception as light reception signal, and presence of a wafer is detected based upon blocking of the light emission signal performed by a wafer which is a body to be detected. However in this case, using of the optical fiber intervening in the light emitting element or the light receiving element attenuates light emission signal or light reception signal due to taking-in or a transmission distance of the light from the light emitting element, which results in such a problem that light emission with high luminance or light reception with high luminance cannot be achieved efficiently. That is, such a problem is included that reflection at a light taking-in portion of an optical fiber or attenuation of light due to an optical fiber makes effective utilization of an optical signal difficult and blocks improvement of sensitivity of a photoelectronic sensor. There is a problem that it is necessary to perform luminance adjustment of each of a plurality of light emitting elements or perform light reception sensitivity adjustment of each of a plurality of light receiving elements, which requires time and labor for adjustment, and readjustment is required due to change of environment according to installation or disturbance, so that complicated adjusting work is required. When the photoelectronic sensors are generally used for detecting a plurality of bodied to be detected, a bundle of optical fibers from a plurality of detecting units or a bundle of signal wires delivering signals from the detecting units to a control system causes a problem about size reduction or handling of the bundles, the detecting units must be adjusted individually, and works such as a rising adjustment work or adjustment work at a changing time of an installation place of the detecting units are complicated.
     Patent Literature 1: Japanese Patent No. 2874020   

     SUMMARY OF THE INVENTION 
     In an art disclosed in Patent Literature 1, the abovementioned problem occurs when light with high luminance is directly emitted toward a body to be detected or light is directly received from the body to be detected with high sensitivity without including a distance therebetween to detect. Further, there is such a problem that luminance adjustment of the light emitting device and light reception sensitivity adjustment of the light receiving device must be performed for each set of light emission and light reception, but the present invention has solved such a complicated work. 
     Namely, an object of the present invention is, for the purpose of eliminating the complicated work for adjustments of respective circuits inherent to such a conventional configuration, to perform stable light emission and light reception, to simplify light receipt function adjustment, and to achieve automation of adjustment of a photoelectronic sensor unit. 
     Another object of the present invention is to allow luminance adjustment of a plurality of light emitting circuits or sensitive adjustment of a plurality of light receiving circuits and solve a problem about malfunction due to environmental change or light noises. 
     In order to achieve the above objects, the present invention is configured such that adjusting luminance or sensitivity of a system comprising single or plural photoelectronic sensors, and adjusting a threshold to realize determination about luminance adjustment or gain adjustment corresponding to surrounding circumstances of installation of a photoelectronic sensor can be set collectively. 
     A photoelectronic sensor according to the present invention is comprised a child station input/output section, a sensor control section, and a sensor section, and connected to a parent station which transmits and receives a monitoring signal and a control signal as parallel signals to a control section by a transmission line. 
     The child station input/output section acquires a control signal directed to a station including the child station input/output section and included in serial transmission signals transmitted through the transmission line to perform control output to the sensor section and feed a monitoring signal to the transmission line as a detection result of the sensor section. 
     The sensor section includes one pair or plural pairs of a light emitting device and a light receiving device. 
     The sensor control section is disposed between the child station input/output section and the sensor section and comprises an A/D converter (an analog to digital converter), a storage element, a microprocessor unit (an MPU), a luminance adjusting circuit, a detection driving circuit, and a detecting circuit. 
     The A/D converter converts analog signal detected by the sensor section to digital signal data. 
     The storage element stores and holds the digital signal data from the A/D converter. 
     The MPU performs arithmetic processing or determination of the detection state based upon storage data stored in the storage element. 
     The luminance adjusting circuit generates a driving clock pulse signal driving the light emitting device in a time divisional manner by the control signal or according to a determination result of the MPU. 
     The detection driving circuit detects light reception signal intensity level of the light receiving device. 
     The light reception level date at a non light emission time of the light emitting device is stored as low light amount level data, and presence/absence of a body to be detected is determined based upon a difference obtained by subtracting the low light amount level data from light reception level data at a light emission time from the light emitting device. 
     Drive of the light emitting device may be controlled by constant current pulse corresponding to the drive clock pulse signal. 
     The light reception level data may be compared with comparison setting value set for comparison in advance, whereby sensitivity shortage is specified. 
     The light reception level data may be compared with the light reception level data of another light reception circuit at own station, whereby sensitivity shortage is specified 
     When sensitivity shortage is specified, luminance adjustment may be performed, and when the luminance adjustment exceeds an adjustment range, a gain of light reception signal may be gain-adjusted. 
     When the sensitivity shortage is specified, a gain of a light reception signal may be gain-adjusted, and if the luminance adjustment exceeds an adjustment range in that case, luminance adjustment may be performed. 
     An intermediate value obtained by subtracting the low light amount level data from the light reception level data of receiving the light emission signal at a light emission time may be used as a threshold and determination about whether the value obtained by the subtraction is higher than the threshold or lower than the threshold may be made. 
     A value obtained by multiplying an intermediate value between the light reception level data when the light emission signal is received and the low light amount level data by a coefficient may be set as a threshold, and whether the difference is above or below the threshold may be determined. 
     An initial value of the threshold value may be read from ROM data or externally, and the threshold may be sequentially updated based upon the light reception level data obtained when presence/absence of the body to be detected has been detected. 
     When the threshold is lower than a level stored in advance gain-adjustment may be performed for performing adjustment to a proper threshold is provided. 
     When the light reception level when the light emission signal is received is lowered to a predetermined level based upon stored data at a time when the luminance adjustment or gain adjustment has been completed, degradation of the light emitting device, degradation of the light receiving device, or loss of transparency of the sensor section may be determined so that a failure detection signal may be generated. 
     When the low light amount level data is higher in level as compared with a disturbance light abnormality value stored when the luminance adjustment and/or gain adjustment has been completed, an error signal may be outputted as detection of disturbance light. 
     When the light reception level data at a light emission time of the light emitting device is higher in level as compared with a predetermined superposition detection value, it may be determined that a plurality of bodies to be detected superposes with one another. 
     The photoelectronic sensor system according to the present invention provided with a plurality of the photoelectronic sensor according to the present invention mentioned above. 
     According to the photoelectronic sensor of the present invention, since a plurality of photoelectronic sensors can be adjusted collectively, rising adjustment, inspection adjustment, adjustment after exchange for failure, or the like can be performed extremely easily. 
     Further, according to the present invention, adjustment works such as initial setting of a plurality of photoelectronic sensors, periodic inspection adjustment performed thereafter, or adjustment performed at an environmental change time can be simplified, the photoelectronic sensors are hardly influenced by environment, confirmation about a factor at failure can be easily made. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a configuration diagram showing an embodiment of a photoelectronic sensor system where photoelectronic sensors according to the present invention is used; 
         FIG. 2  is an illustrative diagram of a child station which is an interruption type sensor; 
         FIG. 3  is a function block diagram of a parent station  FIG. 4  is a side illustrative diagram of the interruption type sensor; 
         FIG. 5  is a plan view of a sensor comb; 
         FIG. 6  is an illustrative diagram showing a state where detecting end portions of bodied is detected; 
         FIG. 7  is a function block wiring diagram of a child station input/output section and a sensor control section; 
         FIG. 8  is a block wiring diagram of another embodiment of a child station input/output section and a sensor control section including a luminance automatic adjusting function of the sensor control section; 
         FIG. 9  is a block wiring diagram of other embodiment of a child station input/output section and a sensor control section including a GAIN adjusting function of the sensor control section; 
         FIG. 10  is a function block wiring diagram of a sensor section; 
         FIG. 11  is a wiring diagram of a light emitting device; 
         FIG. 12  is a wiring diagram of a light receiving device; 
         FIG. 13  is a time chart diagram of signals of a child station; 
         FIG. 14  is a block diagram showing a peripheral circuit configuration of an MPU; 
         FIG. 15  is a time chart diagram showing an offset adjusting function; 
         FIG. 16  is a time chart diagram showing an object detecting function; 
         FIG. 17  is a time chart diagram showing a luminance shortage detecting function; 
         FIG. 18  is a time chart diagram showing a light emitting device failure; 
         FIG. 19  is a time chart diagram showing a light receiving device failure; 
         FIG. 20  is time chart diagram showing disturbance light error; 
         FIG. 21  is a time chart diagram at a detecting time of stacking of bodies to be detected; 
         FIG. 22  is a storage memory map diagram of a storage element; 
         FIG. 23  is a flow chart diagram showing a DATA collecting function; 
         FIG. 24  is a flow chart diagram showing a RAM DATA arithmetic processing  1 ; 
         FIG. 25  is a flow chart diagram showing a RAM DATA arithmetic processing  2 ; 
         FIG. 26  is a flow chart diagram showing a RAM DATA arithmetic processing  3 ; 
         FIG. 27  is a flow chart diagram showing a part of RAM DATA arithmetic processing  3  continuing to  FIG. 25 ; 
         FIG. 28  is a flow chart diagram showing a RAM DATA arithmetic processing  4 ; 
         FIG. 29  is a flow chart diagram showing a RAM DATA arithmetic processing  5 ; 
         FIG. 30  is a flow chart diagram showing a RAM DATA arithmetic processing  6 ; 
         FIG. 31  is a flow chart diagram showing a RAM DATA arithmetic processing  7 ; and 
         FIG. 32  is an illustrative diagram of light emitting devices and light receiving devices. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A photoelectronic sensor according to the present invention will be explained below based upon an embodiment with reference to the drawings. 
     Regarding a photoelectronic sensor according to the present invention, the embodiment will be explained with reference to  FIG. 1  to  FIG. 31 . 
       FIG. 1  is a configuration diagram showing an embodiment of a photoelectronic sensor system where photoelectronic sensors according to the present invention is used. 
     In the photoelectronic sensor system showen in  FIG. 1 , a child station configuring a region sensor of an interruption type is connected to transmission lines (a DP signal line  5  and a DN signal line  6 ), whereby communication control of the child station is performed through a parent station  4 . 
     Two transmission lines (the DP signal line  5  and the DN signal line  6 ) are arranged between the parent station  4  and the child station  10  which is the photoelectronic sensor of the photoelectronic sensor system, where a plurality of child stations  10  can be connected in parallel easily. Presence/absence of a body to be detected  11  is detected by a sensor section  9 , a detection signal is transmitted to a sensor control section  8 , and a result of signal processing performed by the sensor control section  8  is transmitted from a child station input/output section  7  to the parent station  4  through the transmission lines (the DP signal line  5  and the DN signal line  6 ). The parent station  4  transmits information about presence/absence of a body to be detected  11  to an input unit  2  of a control section  1  based on the transmission signal, and the photoelectronic sensor system performs system control according to the information about presence/absence of the body to be detected  11 . An output unit  3  of the control section  1  can control behavior of the child station  10  via the parent station  4  properly. 
       FIG. 2  is an illustrative diagram of the child station  10  which is the interruption type sensor. 
     The control section  1  and the parent station  4  transmits and receives signals each other through parallel signals, while serial signals are transmitted and received between the parent station  4  and the child station  10  through the DP signal line  5  and the DN signal line  6 . The child station  10  transmits and receives information about presence/absence of a body to be detected based upon a detection signal from the sensor section  9  via the DP signal line  5 , the DN signal line  6 , and the child station input/output section  7  through the sensor control section  8 . 
     A configuration of the interruption type sensor shown in  FIG. 2  is efficient in application to a case that a distance between a light emitting section  39  provided with a plurality of light emitting devices  18  and a light receiving section  40  provided with a plurality of light receiving devices  19  is relatively short. 
     Here, the sensor control section  8  and the child station input/output section  7  are configured as shown in  FIG. 8 . That is, since the light emitting device  18  and the light receiving device  19  share the child station input/output section  7  and the sensor control section  8 , simplification and cost reduction of the child station  10  can be achieved. 
       FIG. 3  is a function block diagram of a parent station. 
     The parent station  4  comprises an input data section  120  which performs parallel to serial conversion of serial signals received from the child station  10  to transmit the same to the input unit  2  of the control section  1  as a control input signal  135 , an output data section  121  which performs parallel to serial conversion of parallel signals received as a control output signal  136  from the output unit  3  of the control section  1  to take the same therein, a timing generating means  124 , control data generating means  125 , and a parent station output section  126 . The timing generating means  124  receives a basic signal for a clock signal from a crystal oscillation circuit  122  to generate a clock signal and adds a start signal and an end signal to the clock signal to generate a basic signal for a control signal not shown in Figure. 
     Transmission and reception timings of data of a parent station  4  is transmitted from parent station address setting means  123  to the timing generating means  124 . The parent station output section  126  comprises control data generating means  125  and a line driver  128 , and it receives power supply from a DC 24V power source  9  and a 0 V power source  10  to supply power to a whole system through a DP signal line  5  and a DN signal line  6 . 
     A parent station input section  132  of the parent station  4  comprises monitoring signal detecting means  131  and monitoring data extracting means  130 , and it transmits input data signal to the input data section  120 . The monitoring signal detecting means  131  detects data signals which are monitoring signals obtained from the child station  10  via the DP data signal line  5  and the DN data signal line  6 . The parent station  4  includes a transmission bleeder current circuit  129  serving as a transmission interface circuit. 
     The transmission bleeder current circuit  129  which is the interface circuit is connected to a line driver  128  within the parent station output section  126  and the parent station  4  transmits control data received from the control data generating means  125  of the parent station  4  together with a clock signal transmitted from the timing generating means  124  to the DP signal line  5  via an external signal connection section (DP side)  133  and to the DN signal line  6  via an external signal connection section (DN side)  134 . 
     The line driver  128  delivers data signal to the monitoring signal detecting means  131  of the parent station input section  132  and the monitoring data extracting means  130  obtains monitoring data signal in synchronism with a clock signal received from the timing generating means  124 . The line driver  128  delivers the monitoring data signal to the input data section  120  to transmit the same to the input unit  2  of the control section  1  as a parent station transmission signal  135 . 
     Thus, the parent station  4  is positioned between the control section  1  and the child station  10 , and it functions to receive child station information and deliver the signal to the control section and receive control signal from the control section to deliver the same to the child station  10 . 
       FIG. 4  is a side face illustrative diagram of the interruption type sensor. 
     The reflection type sensor  41  which is an embodiment of a photoelectronic sensor of the present invention transmits and receives information between the same and the parent station  4  through the DP signal line  5  and the DN signal line  6  utilizing a serial signal. The child station input/output section  7  serves as an interface with the DP signal line  5  and the DN signal line  6  to receive information about presence/absence of the body to be detected  11  which is detected by the sensor section  9  via the sensor control section  8  and transmit the same to the parent station  4  via the DP signal line  5  and the DN signal line  6 . A plurality of sensor combs  13  attached to an attaching plate  16  emit light emission signals  15  toward the bodies to be detected  11  and receive reflection signals from the bodies to be detected  11  to detect presence/absence of bodies to be detected  11  as light reception signals  14 . 
     A dummy comb  12  is provided for setting a detection limit when no body to be detected  11  is present. 
       FIG. 5  is a plan view of a sensor comb. Such a structure is adopted that a light emitting element  18  and a light receiving element  19  are provided at a distal end of the sensor comb  13  and an upper face of an end portion of a body to be detected  11  whose both ends are supported like a shelf and held in a multi-stage manner is detected, and a light emission signal from the light emitting element  18  is reflected by the upper face of the end portion of the body to be detected  11  and the reflection light is received by the light receiving element  19  so that presence of the body to be detected  11  is detected. 
       FIG. 6  is an illustrative diagram showing a state wherein an end portion of a body to be detected is detected. 
     The body to be detected  11  is a plate-like body such as a semiconductor wafer, a liquid crystal glass, or a printed board, where a light emission signal from a light emitting element  18  is hit on an end portion of the body to be detected  11 , and the reflection light is received by the light receiving element  19  so that presence/absence of the body to be detected  11  is detected. A detection signal is transmitted from the sensor section  9  to the sensor control section  8 , and after it is subjected to signal analysis, it is transmitted from the child station input/output section  7  to the parent station  4  through the DP signal line  5  and the DN signal line  6  as a presence/absence signal of the body to be detected  11 . In  FIG. 6 , two bodies to be detected  11  which are circular wafers and positioned on a lowermost stage are stored in a stacked state to each other, and such an abnormal state is detected by a light reception signal shown in  FIG. 21 . 
       FIG. 7  is a function block wiring diagram of the child station input/output section  7  and the sensor control section  8 . The child station input/output section  7  transmits and receives signals transmitted on the DP signal line  5  and the DN signal line  6 . On the other hand, the child station input/output section  7  receive an OUT signal  25  from MPU  20 , so that a detection result of the body to be detected  11  which has been determined by the MPU  20  basing upon the detection signal from the sensor section  9  is transmitted to the parent station  4 . The child station input/output section  7  transmits a signal directed from the parent station  4  to the sensor control section  8  to the MPU  20  as PRM signal  24 . 
     Transmissions of signal from the sensor control section  8  to the light emitting section  39  of the sensor section  9  and power supply are performed through connection of five lines of CP signal  28 , END signal  27 , TD signal  29  which is timing data signal, a power supply line Vcc (5V)  35 , and DN (0V)  36  which are shown in  FIG. 7 . Transmission of signal from the light receiving section  40  of the sensor section  9  and power supply are performed through connection of five lines of the power supply line Vcc (5V)  35 , the DN (0V)  36 , the CP signal  28 , the TD signal  29  which is the timing data signal, and a PHD  37  which are shown in  FIG. 7 . 
     The sensor control section  8  is provided with the MPU  20  serving as a central function, ROM  44  storing and holding comparison data and determination program data, RAM  45  storing and holding sensor level data and arithmetic result, a luminance adjusting circuit  21  performing luminance adjustment for light emission signal, a constant-current circuit  22  for suppressing fluctuation of light emission signal to perform stable light emission, a detection and light emission driving circuit  23  superposing driving current of the light emitting device on CP signal  28  to transmit the same, an A/D converter  40 , and a gain adjusting circuit  34 . 
     Since light emission currents of the light emitting devices can be suppressed to a constant value by using the constant-current circuit  22 , lights can be evenly emitted from the respective light emitting devices, which can result in easiness of setting. 
     The sensor control section  8  receives the PHD signal  37  obtained by superposing light reception end signal on signal received from the light emitting device  48  of the light emitting section from the light receiving section  40  of the sensor section  9 , adjusts gain of the PHD signal  37  at the gain adjusting circuit  34 , converts AIN signal  33  which is analog signal to a digital level signal at the A/D converter  40 , and it takes the digital level signal into an ADATA port of the MPU  20  as DOUTA signal  26 . Data conversion timing at the A/D converter  40  is controlled by an ENB signal  30  which is enable signal enabling A/D conversion by the MPU  20 . 
     In the sensor control section  8 , CK signal  43  serving as a basic signal for light emission or light reception is transmitted from the MPU  20  toward the sensor section  9 . 
       FIG. 8  is a block wiring diagram of another embodiment of the child station input/output section  7  and the sensor control section  8  including a luminance automatic adjusting function of the sensor control section  8 . In  FIG. 8 , the sensor control section  8  has such a configuration that the luminance adjusting circuit  21  shown in  FIG. 7  is replaced by a luminance automatic adjusting circuit  38  and AUT signal  39  is added as luminance automatic adjusting signal. 
     When the MPU  20  detects lowering of a light reception signal due to luminance shortage, it transmits AUT signal  39  which is luminance automatic adjusting signal to the luminance automatic adjusting circuit  38  for adjustment of a light reception signal to perform luminance automatic adjusting behavior. The light emitting device is connected to a constant-current source to emit light, and sensitivity variations inherent to a light receiving elements, variations of directionalities of lights from the light emitting devices, or the like can be made even by the luminance automatic adjusting function. 
     Further, the sensor control section  8  is provided with an A/D converter  40 , so that luminance adjustment of the light emitting device, light reception sensitivity adjustment, and accurate adjustment based upon feedback of data at an offset signal adjustment time can be performed. 
       FIG. 9  is a block wiring diagram of other embodiment of the child station input/output section  7  and the sensor control section  8  including GAIN adjusting function of the sensor control section. In  FIG. 9 , the sensor control section  8  has such a configuration that the GAIN adjusting circuit  34  shown in  FIG. 7  is replaced by a GAIN automatic adjusting circuit  34  and AUT signal  39  is added as a GAIN automatic adjusting signal. 
     When the MPU  20  detects lowering of light reception signal due to gain shortage, it transmits AUT signal  39  which is GAIN automatic adjusting signal to the GAIN adjusting circuit  34  for adjustment of light reception signal to perform GAIN adjusting behavior automatically. The light reception signal which has been automatically GAIN-adjusted is converted from analog data signal to digital data signal by the A/D converter  40  to be transmitted to the MPU  20 . In  FIG. 9 , the child station input/output section transmits a signal to the control section via the parent station  4  through the DP signal line  5  and the DN signal line  6 , but a high-speed photoelectronic sensor system can be established by directly connecting parallel signal to a parallel port of the control section without using a serial signal line shown in  FIG. 9  and without passing through the parent station. 
       FIG. 10  is a function block wiring diagram of the sensor section. 
     A clock signal generated at the parent station  4  is transmitted to the sensor section via the sensor control section  8  as clock pulse (CP) signal  28 . At the clock pulse (CP) signal  28 , a pulse whose duty cycle is longer than that of an ordinary clock pulse is used for a start signal, so that it is discriminated from an ordinary clock. The clock pulse (CP) signal  28  is pulse signal positioned between 0V and 24V in voltage level. 0V  36  and Vcc  35  are connected as a power source for the sensor section. A plurality of light emitting elements in the sensor section are driven by shift registers and drive of the first shift register is actuated by TD signal  29 . 
     Shift signal for the final shift register is returned to the sensor control section  8  as END signal  27 , so that behaviors of light emission and light reception configuring a pair are completed and behaviors of light emission and light reception of light emitting device and light receiving device configuring the first pair are started. 
     In the sensor section, the light receiving device receives PHD signal  37  which is light reception signal to transmit it to the sensor control section  8  regardless of non light emission time and light emission time of the light emitting device. 
       FIG. 11  is a wiring diagram of the light emitting device. 
     A light emitting device  48  comprises single or plural light emitting elements  18  and the number of light emitting elements and arrangement thereof are devised so as to adjust illuminance and a light emission area properly according to a use condition. 
       FIG. 12  is a wiring diagram of the light receiving device. 
     A light receiving device  49  comprises single or plural light receiving elements  19  and the number of light receiving elements and arrangement thereof are devised so as to adjust luminance and a light reception area properly according to a use condition. 
       FIG. 13  is a time chart diagram of signals of the child station. 
     Clock pulse (CP) signal  28  shown in an uppermost stage has a crest value from a signal voltage 0V to 24V. Signal is started from a start bit having a pulse width of 5 times that of an ordinary clock pulse. The start bit is signal for a child station  4  to recognize start of monitoring cycle. After the start bit, pulses corresponding to a plurality of child stations  4  are continued. 
     The case in  FIG. 13  shows an example where one child station corresponds to pulse signal of one bit. According to pulse corresponding to one bit corresponding to one child station, correspondence of input and output of the one child station  4  is obtained. 
     Next, the TD signal  29  from the sensor control section  8  is transmitted to the sensor section, so that shift register behavior of the sensor section starts. 
     Output pulse of Shift Reg.Q 1  which is behavior pulse of the shift register actuates LED  1  at a timing of channel  1  (CH 1 ) of the clock pulse (CP) signal  28 , so that the LED  1  emits light emission signal. The next Shift Reg.Q 2  operates at falling of a light emission signal of the CH 1  so that output thereof actuates LED 2 . 
     Thus, light emission signals are generated according to sequential shift register behaviors. 
     Shift signal of a shift register at the final stage where a series of shift register behaviors have been completed is returned to the sensor control section  8  as END signal  27 , so that light emission and light reception behaviors start from the first stage. Vcc  35  and 0V  36  supply power from the sensor control section  8  as power source of the sensor section. 
     PHD signal  37  is light reception signal obtained by connecting output signals of a plurality of light receiving elements in parallel. The light reception signal is sent to the sensor control section  8  and the PHD signal  37  which is analog signal is converted to digital light reception level signal by the A/D converter  40  of the sensor control section  8 . ENB signal  30  which is conversion timing signal is transmitted from the MPU  20  to the A/D converter  40 . 
       FIG. 14  is a block diagram showing a peripheral circuit configuration of the MPU. 
     In  FIG. 14 , the MPU  20  is connected to the ROM  44  and the RAM  45  which are storage elements through a local bus. The END signal  27 , the ADAT signal  26 , and the PRM signal  24  are inputted to an I/O  46  which is an I/O bus as input signals. ENB signal  30 , the OUT signal  25 , an OST signal  31 , an ACT signal  32 , a CK signal  50 , the TD signal  29 , the AUT signal  39  are outputted from the I/O  46  which is the I/O bus as output signals. 
       FIG. 15  is a time chart diagram showing an offset adjusting function. 
     The PHD signal  37  which is light reception signal includes the minimum offset signal Min Vofn and the maximum offset signal Max Vofn to potential of 0V. Set offset signal level Vofg is set from the minimum offset signal Min Vofn and the maximum offset signal Max Vofn. The set offset signal level Vofg is set to be larger than the maximum offset signal Max Vofn to mask fluctuation of the offset signal. 
     The light reception signal which is the PHD signal  37  shown by a broken line is adjusted such that the maximum light reception signal Max Vnd falls within a set value Vbg. The light reception signal Vsn is more than the set offset signal level Vofg and fluctuates within the set offset set value Vbg. 
     For determining presence/absence of a body to be detected, noises of light around an outer periphery is removed by removing offset signal component, whereby detecting presence/absence of a body can be detected accurately. 
       FIG. 16  is a time chart diagram showing an object detecting function. 
     In the light reception signal PHD signal  37 , light reception signal Vnd obtained when a body to be detected  11  is absent is represented by logical value “0” state, while light reception signal Vnd exceeding a threshold Vth and obtained when a body to be detected  11  is present is represented by logical value “1” state. Here, regarding the threshold Vth, it is an important fact to subtract the set offset signal level Vofg from the light reception signal PHD signal  37  and set the threshold Vth as an intermediate value between the logical value “0” state of the light reception signal Vnd obtained when a body to be detected  11  is absent and the logical value “1” state of the light reception signal Vnd obtained when a body to be detected  11  is present. Then this sensor is characterized in that an offset signal component is calculated using the light reception signal level at a non light emission time and, when presence/absence of a body to be detected  11  is determined, the offset signal component is subtracted from a light reception signal level so that influence of noise, fluctuation or change of offset signal level is eliminated. 
       FIG. 17  is a time chart diagram showing a luminance shortage detecting function. 
     In the light reception signal PHD  37 , when the minimum light reception signal Min Vnd 1  of the light reception signal Vnd   1    obtained when a body to be detected  11  is present at the logical value “1” state is lower than the sensitivity set limit value Vb 1 , luminance shortage is detected and adjustment is performed such that GAIN is raised to reach level of Vnd 1  shown in  FIG. 17 . 
       FIG. 18  is a time chart diagram showing a light emitting device failure. 
     In the light reception signal PHD signal  37  in  FIG. 18 , a value obtained by subtracting offset signal Vof 1  from light reception signal level Vs 1 , namely, (Vs 1 −Vof 1 ) must generally exceed a light emitting device failure value Vbdf. The light emitting device failure value Vbdf is set to an intermediate value between the threshold Vth for determining presence/absence of a body to be detected and the offset signal level Vofn. When the Min Vnd 0  which is the minimum light reception signal level, namely, the difference signal (Vs 1 −Vof 1 ) is smaller than the light emitting device failure value Vbdf, it is found that the light emitting device is out of order. When the light emitting device is in a normal state, a light reception signal level when a body to be detected is absent in the light reception signal PHD signal, (Vs 2 −Vof 2 ) exceeds the light emitting device failure value Vbdf. The light emitting device failure value Vbdf is provided as a criterion for light emitting device failure and, when the light reception signal example level is equal to or less than the criterion for light emitting device failure, warning for light emitting device failure is issued. 
       FIG. 19  is a time chart diagram showing a light receiving device failure. 
     In  FIG. 19 , a light receiving device failure value Vpdf is a criterion for light receiving device failure. Offset signal level when the light receiving device is in a normal state is signal level exceeding the light receiving device failure value Vpdf like the offset signal level Vof 1  of the channel  1  (CH 1 ) or the offset signal level Vof 3  of the channel  3  (CH 3 ). On the other hand, an example of signal level of the light receiving device failure is shown by offset signal level Vof 2  of the channel  2  (CH 2 ) in  FIG. 19 . The offset signal level Vof 2  of the channel  2  (CH 2 ) is less than the light receiving device failure value Vpdf, which indicates failure of the light receiving device of the channel  2  (CH 2 ). Simultaneously, warning for light receiving device failure is issued. 
       FIG. 20  is a time chart diagram showing disturbance light error. 
     In the case showed in  FIG. 20 , disturbance light abnormality is detected by using a disturbance light abnormality value Vofd. Then in the PHD signal  37  which is the light reception signal it is showen that disturbance light has generated at a light reception time of the channel  3  (CH 3 ). Offset signal level in a normal state where no disturbance light has generated is shown in offset signal level Vof 1  of the channel  1  (CH 1 ), offset signal level Vof 2  of the channel  2  (CH 2 ), and offset signal level Vof 25  of the channel  25  (CH 25 ). 
     That is, the offset signal level Vof 1 , Vof 2 , and Vof 25  are less than the criterion level shown by the disturbance light abnormality value Vofd at a non light emission time. The offset signal level Vof 2  of the channel  2  (CH 2 ) is the minimum of the offset signal level and it is stored as the minimum offset signal value MinVof 2 . In  FIG. 20 , an offset signal level Vof 4  of the channel  3  (CH 3 ) exceeds the disturbance light abnormality value Vofd despite non light emission time, which shows such a fact that the sensor has been subjected to disturbance light in a behavior time of the channel  3 (CH 3 ). 
       FIG. 21  is a time chart diagram at a detecting time of stacking of bodies to be detected. 
     In  FIG. 21 , signal level V 1   d  of the channel  1  (CH 1 ), signal level V 3   d  of the channel  3  (CH 3 ), signal level V 5   d  of the channel  5  (CH 5 ), and signal level V 25   d  of a channel  25  (CH 25 ) in the PHD signal  37  which are light reception signals at light emission time are less than the threshold Vth for detecting a body to be detected, which indicates absence of a body to be detected (logical value “0”). 
     On the other hand, signal level V 2   d  of the channel  2  (CH 2 ) and signal level V 4   d  of the channel  4  (CH 4 ) exceed the threshold Vth for detecting a body to be detected, which indicates presence of a body to be detected (logical value “1”). However, when signal level V 2   d  of the channel  2  (CH 2 ) and signal level V 4   d  of the channel  4  (CH 4 ) are compared with each other, in the signal level V 4   d  of the channel  4  (CH 4 ) is larger and exceed a superposition detection value DW 1 , and it exceeds an ordinary a body to be detected presence (logical value “1”) state. Since a reflection signal in this state is larger than that from one body to be detected, it is found that bodies to be detected are stacked to one another in the former, so that warning for stack detection is issued. 
       FIG. 22  is a storage memory map diagram of a storage element. 
     In a region of ROM  44  which is a nonvolatile memory region, a gain adjusting value Vofg, a luminance adjusting value Vbg, a threshold initial value Vth, a luminance shortage value Vb 1 , a light emitting device failure value Vbdf, a light receiving device failure value Vpdf, and a disturbance light abnormality value Vofd, and a superposition detection value DW 1  are stored and held. A program performing control using these parameters is PRM 1 . 
     On the other hand, rewritable data is stored in the RAM  45  region, namely, a gain adjusting value Vofg, a luminance adjusting value Vbg, a threshold initial value Vth, a luminance shortage value Vb 1 , a light emitting device failure value Vbdf, a light receiving device failure value Vpdf, and a disturbance light abnormality value Vofd which are automatically set according to program control are stored and held therein. A program for controlling RAM  45  region using these data parameters is PRM 2 . 
     In a DATA region in the RAM  45 , Vof 1  to Vof 25  regarding offset Vofn, Vs 1  to Vs 25  regarding Vsn regarding light reception signal level Vs 1  at a light emission time, V 1   d  to V 25   d  regarding difference signal data (light reception signal level) Vnd which is (Vsn−Vofn) are stored and held to the respective channels of the channel  1  (CH 1 ) to the channel  25  (CH 25 ). 
     Further, V 1   th  to V 25   th  regarding threshold value Vnth, V 1   d   0  to V 25   d   0  regarding light reception signal Vnd 0  obtained when a body to be detected  11  is absent, V 1   d   1  to V 25   d   1  regarding light reception signal Vnd 1  obtained when a body to be detected  11  is present are stored and held to the respective channels of the channel  1  (CH 1 ) to the channel  25  (CH 25 ). 
     Furthermore, as Min (minimum) data, the minimum offset signal MinVofn, the light reception signal levels MinVnd 0  and MinVnd 1  at the minimum light emission time are stored and held, the light reception signal level MaxVnd 0  and the maximum offset signal MaxVofn at the maximum light emission time are stored and held as Max (maximum) data, and fluctuations of respective light reception signal levels are stored and held, so that state change of the photoelectronic sensor and abnormality thereof are detected. 
       FIG. 23  is a flowchart diagram representing a DATA collecting function. 
     A procedure for DATA collection starts from start (START), where StartBit generation which is a signal of DATA collection start is first performed (Step S 1 ). Next, TD signal actuating the sensor section is generated (Step S 2 ). Next, input check of offset signal level Vof 1  is performed as light reception signal level at non light emission time (Step S 3 ). 
     Clock pulse CP output of the channel  1  (CH 1 ) is turned ON. The offset signal level Vof 1  of the channel  1  previously taken in is stored in the DATA region of RAM (Step S 4 ). Next, input which is light reception signal level Vs 1  at a light emission time is checked. The clock pulse CP output of the channel  1  (CH 1 ) is turned OFF. The light reception signal level Vs 1  at a light emission time is stored in the DATA region of RAM (Step S 5 ). 
     Next, input of offset signal level Vof 2  is checked (Step S 6 ). 
     Clock pulse CP output of the channel  2  (CH 2 ) is turned ON. The offset signal level data Vof 2  is stored in the DATA region of RAM (Step S 7 ). Next, input which is light reception signal level Vs 2  at the light emission time is checked (Step S 8 ). 
     The clock pulse CP output of the channel  2  (CH 2 ) is turned OFF. Subsequently, Vs 2  is stored in the DATA region of RAM (Step S 9 ). Similarly, data are sequentially taken in so that input of offset signal level Vof 25  of the final channel  25  in this example is checked (Step S 10 ). 
     Subsequently, clock pulse CP output of the channel  25  (CH 25 ) is turned ON. 
     The offset signal level Vof 25  is stored in the DATA region of RAM (Step S 11 ). 
     Next, input of light reception signal level Vs 25  at a light emission time is checked (Step S 12 ). 
     Subsequently, the clock pulse CP output of the channel  25  (CH 25 ) is turned OFF. The light reception signal level Vs 25  at a light emission time is stored in the DATA region of RAM (Step S 13 ). 
     Next, respective arithmetic processings of 1 to 7 are performed as arithmetic processing of RAMDATA (Step S 14 ). Then the procedure is returned to the first step. 
       FIG. 24  is a flowchart of a RAM DATA arithmetic processing  1  for performing offset adjustment. First of all in this arithmetic processing, comparative judgment is made about whether or not the maximum signal level Max Vof of offset is smaller than the gain adjustment value Vofg (Step S 15 ). When Max Vof is smaller than the gain adjustment value Vofg, offset signal OST is turned OFF (Step S 16 ). When Max Vof is larger than the gain adjustment value Vofg, the offset signal OST is turned ON (step S 17 ), and GAIN adjustment is then performed (Step S 18 ). Then the procedure is returned back to the first step of the program. 
     Next, determination is made about whether or not the minimum light reception signal Min Vnd 0  is smaller than the luminance adjustment value Vbg (Step S 19 ). When the minimum light reception signal Min Vnd 0  is smaller than the luminance adjustment value Vbg, action signal ACT is turned OFF (Step S 20 ). When the minimum light reception signal Min Vnd 0  is larger than the luminance adjustment value Vbg, ACT is turned ON (Step S 21 ), and the procedure is returned back to the top of the step S 19  after luminance adjustment has been performed (Step S 22 ). 
       FIG. 25  is a flowchart of a RAM DATA arithmetic processing  2  for performing signal extraction. 
     First of all, signal extraction of the channel  1  (CH 1 ) is performed (Step S 23 ). 
     Next, offset signal level Vof 1  at non light emission time is subtracted from light reception signal level Vs 1  at a light emission time to calculate signal level V 1   d  of the channel  1  (CH 1 ), and the calculation result of the signal level V 1   d  is stored in the DATA region of RAM (Step S 24 ). 
     Similarly, signal extraction of the channel  2  (CH 2 ) is performed (step S 25 ), signal level V 2   d  is calculated (Step S 26 ), and V 2   d  is stored in the DATA region of RAM. Similarly, signal extractions from the channel  3  to the channel  24  are performed, and V 3   d  to V 24   d  are stored in the DATA region of RAM. Finally, CH  25  signal is extracted (Step S 27 )           , signal level V 2   d  is calculated, and V 25   d  is stored in the DATA region of RAM (Step S 28 ).
       FIG. 26  and  FIG. 27  are flowchart diagrams of a RAM DATA arithmetic processing  3  for performing initial setting of object detection. 
     First of all, determination about whether the processing is initial setting is made (Step S 29 ). When the processing is the initial setting, “1” is set in a counter n (Step S 30 ). 
     Determination is made about whether the detection result of the channel n (CHn) is present “1” or is absent “0” (step S 31 ). Next, determination is made about whether the light reception signal level Vnd of n channel exceeds the threshold Vth (Step S 32 ). If Vnd≧Vth is satisfied, “1” is set in OUTn (Step S 33 ). Subsequently, Vnd is stored in Vnd 1  (Step S 34 ). 
     Vnd 1  is stored in the DATA region of RAM (Step S 35 ). 
     Next, “0” is stored in Vnd 1  of the DATA region of RAM (Step S 36 ). 
     Unless Vnd≧Vth is satisfied, “0” is set in OUTn (Step S 37 ). 
     Next, Vnd data is transferred to Vnd 0  (Step S 38 ). Vnd 0  is stored in the DATA region of RAM (Step S 39 ). 
     Next, data of double of Vth is stored in the DATA region of RAM, and further, storing to Vnd 1  is performed (Step S 40 ). 
     Next, operation of (Vnd 0 +Vnd 1 )÷2 is performed, and Vnth is stored in the DATA region of RAM (Step S 41 ). 
     1 is added to the counter n (Step S 42 ). 
     Whether or not the counter n has reached  25  is confirmed (Step S 43 ). 
     In the flowchart diagram, (Vnd 0 +Vnd 1 )÷2 is used as the threshold Vnth, but the threshold Vnth can be set to be higher or lower than (Vnd 0 +Vnd 1 )÷2 by multiplying the intermediate data by a coefficient. In this case, when an amount of light configuring noise component received from an environment is large, the threshold Vnth is set to be higher but the threshold Vnth is set to be lower in a noiseless environment, so that detection sensitivity can be increased. One of using a fixed threshold Vnth stored in the ROM and providing for the next detection time while a threshold is calculated in each case can be freely selected. 
     Subsequently, being showed in  FIG. 27 , determination about presence/absence of logical value “1”/“0” of a body to be detected of the channel  25  (CH 25 ) is performed (Step S 44 ). 
     Determination is made about whether or not the light emission time light reception signal level V 25   d  at light reception time of the channel  25  (CH 25 ) exceeds the threshold Vth (Step S 45 ). If V 25   d ≧Vth is satisfied, OUT 25  is set to “1” (Step S 46 ). V 25   d  is transferred to V 25   d   1  (Step S 47 ). 
     V 25   d   1  data is stored in the DATA region of RAM (Step S 48 ). 
     “0” is stored in V 25   d   0  of the DATA region of RAM (Step S 49 ). 
     Unless  25   d ≧Vth is satisfied, “0” is set in OUT 25  (Step S 50 ). 
     Data of V 25   d  is transferred to V 25   d   0  (Step S 51 ). 
     Data of V 25   d   0  is transferred to the DATA region of RAM (Step S 52 ). 
     A value of double of Vth is stored in the DATA region of RAM (Step S 53 ). 
     The half value of (V 25   do +V 25   d   1 ) is stored in V 25   th  of the DATA region of RAM (Step S 54 ). 
     The minimum offset level Min V 0   fn  is extracted (Step S 55 ). 
     The maximum offset level Max V 0   fn  is extracted (Step S 56 ). 
     The minimum light reception signal level Min Vndo is extracted (Step S 57 ). 
     The maximum light reception signal level Max Vndo is extracted (Step S 58 ). 
     The minimum light reception signal level Min Vnd 1  is extracted (Step S 59 ). 
       FIG. 28  is a flowchart diagram of a RAM DATA arithmetic processing  4  for object detection and threshold automatic setting continued from E terminal on the flowchart shown in  FIG. 26 . 
     First of all in this arithmetic processing, 1 is set in the counter n (Step S 60 ). 
     Next, determination about logical value “1”/“0” representing presence/absence of a body to be detected of CHn is made (Step S 61 ). 
     Next, determination is made about whether the light reception signal level Vnd of n channel exceeds the threshold Vth (step S 62 ). 
     If Vnd≧Vth is satisfied, “1” is set to OUTn (Step S 63 ). 
     Data of Vnd is transferred to Vnd 1  (Step S 64 ). 
     Vnd 1  is stored in the DATA region of RAM (Step S 65 ). 
     Unless Vnd≧Vth is satisfied, “0” is set to OUTn (Step S 66 ). 
     Data of Vnd is transferred to Vnd 0  (Step S 67 ). 
     Vnd 0  is stored in the DATA region of RAM (Step S 68 ). 
     The haof value of (Vndo+Vnd 1 )÷2 is stored in the Vnth of the DATA region of RAM (Step S 69 ). 
     Subsequently, 1 is added to the counter n (Step S 70 ). 
     Determination about whether or not n=25 is satisfied is made (step S 71 ). 
     If n=25 is satisfied, determination about whether or not CH  25  is logical value “1”/“0” is made (Step S 72 ). 
     Unless n=25 is satisfied, the procedure is continued to L terminal. 
     Next, determination is made about whether the light reception signal level Vnd of n channel exceeds the threshold Vth (Step S 73 ). 
     If V 25   d ≧Vth is satisfied, “1” is set in OUT 25  (Step S 74 ). 
     Data of V 25   d  is transferred to V 25   d   1  (Step S 75 ). 
     V 25   d   1  is stored in the DATA region of RAM (Step S 76 ). 
     Unless V 25   d ≧Vth is satisfied, “0” is set to OUT 25  (Step S 77 ). 
     Data of V 25   d  is transferred to V 25   d   0  (Step S 78 ). 
     V 25   d   0  is stored in the DATA region of RAM (step S 79 ). 
     The haof value of (V 25   d   0 +V 25   d   1 ) is stored in V 25   th  of the DATA region of RAM (Step S 80 ). 
       FIG. 29  is a flowchart diagram of a RAM DATA arithmetic processing  5  for performing luminance shortage detection continued from D terminal on the flowchart diagram shown in  FIG. 27 . 
     First of all in this arithmetic processing, determination about whether or not Min Vnd 1 &lt;Vb 1  is satisfied is made (Step S 81 ). 
     If Min Vnd 1 &lt;Vb 1  is satisfied, “1” is set in OUTe 1  (Step S 82 ). 
     Unless Min Vnd 1 &lt;Vb 1  is satisfied, “0” is set to OUTe 1  (Step S 83 ). 
     Then, data is transferred to the child station output section (Step S 84 ). 
       FIG. 30  is a flowchart diagram of a RAM DATA arithmetic processing  6  for detecting light emitting device and light receiving device failure continued from G terminal on the flowchart diagram shown in  FIG. 29 . 
     First of all in this arithmetic processing, determination about whether or not Max Vofn≧Vpdf is satisfied is made (Step S 85 ). 
     If Max Vofn≧Vpdf is satisfied, “0” is set in OUTe 3  (Step S 86 ). 
     Subsequently, determination about whether or not Min Vnd 0 &lt;Vbdf is satisfied is made (Step S 87 ). 
     If Min Vnd 0 &lt;Vbdf is satisfied, light emitting device failure is detected, and “1” is set in OUTe 2  (Step S 88 ). 
     Unless Min Vnd 0 &lt;Vbdf is satisfied, “0” is set in OUte 2  (Step S 90 ). 
     On the other hand, unless Max Vofn≧Vpdf is satisfied, light receiving device failure is detected, and “1” is set in OUTe 3  (Step S 89 ). 
     Then, data is transferred to the child station output section (Step S 91 ). 
       FIG. 31  shows a flowchart diagram representing DATA arithmetic processing function  7  according to the embodiment of the present invention.  FIG. 31  is a flowchart diagram of a RAM DATA arithmetic processing  7  for detecting disturbance light error continued from H terminal on the flowchart shown in  FIG. 30 . 
     First of all in this arithmetic processing, determination about whether or not |Max Vofn−Min Vofn|&gt;Vofd is satisfied is made (Step S 92 ). 
     If |Max Vofn−Min Vofn|&gt;Vofd is satisfied, “1” is set in OUTe 4  (Step S 93 ). 
     Unless |Max Vofn−Min Vofn|&gt;Vofd is satisfied, “0” is set in OUTe 4  (Step S 94 ). 
     Then, Data is transferred to the child station output section (Step S 95 ). 
       FIG. 32  is an illustrative diagram of a light emitting device and a light receiving device. 
     In  FIG. 32 , light emitting elements  18  are attached on a surface of a printed board  51  and light receiving elements  19  are attached on a back surface thereof, and a plurality of light emitting devices and a plurality of light receiving devices can be arranged on a small area by light-shielding the light emitting elements  18  and the light receiving elements  19  using a light-shielding plate  52 , so that size reduction of a photoelectronic sensor can be realized. The light emitting elements  18  can be attached on the back surface and the light receiving elements  19  can be attached on the front surface, namely they can be attached on the surfaces in opposite manner described above. 
     INDUSTRIAL APPLICABILITY 
     When detection of presence/absence of bodies to be detected, such as semiconductor wafers, liquid crystal glasses, or glass epoxy substrates stored in a multistage manner is detected, setting of sensors arranged in a multistage manner can be collectively performed by utilizing the present invention, so that adjustment work is made easy. Further, the photoelectronic sensor of the present invention is higher in sensitivity and simpler than that of the conventional one, which results in handling easiness and, can be utilized as an inexpensive photoelectronic sensor, which is widely used for detection of presence/absence of articles on an article shelf.