JP2005315725A - Photoelectric sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photoelectric sensor capable of comparatively accurate color detection with a simple circuit constitution even if a floodlighting interval is shortened. <P>SOLUTION: When a sheet used as a reference is arranged in a detection domain prior to detection operation, the magnitude of a received light signal level is compared relative to tricolor light received by a light receiving element 21 among lights floodlighted from floodlighting elements 11A, 11B, 11C, and the order from a smaller received light signal level of the tricolor light is stored based on the comparison result. At the detection operation time of a mark on the sheet W, a CPU 30 drives floodlighting circuits 12A, 12B, 12C in the stored order, and floodlights the tricolor light from the floodlighting elements 11A, 11B, 11C. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a photoelectric sensor capable of detecting the color of an object to be detected.

  As shown in FIG. 8, this type is provided with light projecting elements 1, 2, and 3 that emit red, blue, and green, respectively, and output from a central processing unit (hereinafter referred to as CPU 30) 8. Based on the (high level) light projection signals f1, f2, and f3, the light projecting operation is sequentially performed on the detection target at every predetermined time T. In addition, a light receiving element 4 is provided to receive the reflected light from the object to be detected for each light projecting operation, and according to the light received from the light receiving circuit 5 in synchronization with each light projecting signal f1, f2, f3. The signal a is output (low level), and after a period of light projecting with the three colors of light is completed, a light projecting operation with a predetermined period after a time longer than a predetermined time T has elapsed. Is to repeat.

  Further, since the received light signal a is very small, as shown in FIG. 9, a plurality of non-inverting AC amplifier circuits 7 comprising operational amplifiers A for amplifying the signal a are connected. Amplifying means 6 is provided, and a differential circuit comprising a coupling capacitor C and a resistor R1 is formed on the positive phase input side of the operational amplifier A in order to remove a direct current component which is a disturbance light component. The signal a is amplified by the amplifying means 6 and the amplified light receiving signal is output to the CPU 8.

  In order to detect the color of the detected object, light of three colors (red, green, and blue) is sequentially projected onto the detected object of the reference color prior to the detection operation, and reflected by the detected object. The CPU 8 calculates the ratio of the light reception signal level of each color to the sum of the light reception signal levels of the three colors of light (each peak value (bottom value) of the amplified signal) and stores it in a memory (not shown). .

Next, at the time of detection, light of three colors (red, green, and blue) is sequentially projected onto the detected object to be detected, and each color with respect to the sum of the received light signal levels of the three colors reflected on the detected object. The CPU 8 obtains the ratio of the received light signal level for each light and compares this ratio with the ratio stored before detection. If both ratios are substantially the same, the object to be detected at the time of detection is the reference object. It is determined that the color is the same as the color of the detected object.
Japanese Patent No. 3157463

  By the way, for example, when the object to be detected is transported, the measurement point on the object to be detected is shifted for each color of light when the time interval of the light of each color sequentially projected is long. Since an accurate received light signal level for each color of light cannot be obtained, highly accurate color discrimination cannot be performed. Therefore, it is desirable that the time interval of light of each color projected sequentially is as short as possible.

  However, in the above configuration, the coupling capacitor C for removing the DC component is indispensable for the AC amplifier circuit, but the accumulated charge is discharged at the end of input of the signal a (high level). Therefore, ringing due to overshoot and undershoot is induced in the received light signal b (amplified signal) output from the operational amplifier A after the rise of the signal a (see FIG. 10). In particular, in the case where an AC amplifier circuit is connected in multiple stages as in the above configuration, this ringing becomes considerably large at the final output. This becomes even more pronounced because the amount of accumulated charge increases with light having a large amount of received light (the amount of light received by the light receiving element 4).

  Therefore, in order to perform the next light projecting operation, after the ringing attenuates, that is, in the above configuration, it is necessary to wait until the light reception signal b is stabilized at Vcc (reference voltage value). When the next light projecting / receiving operation is performed before the light receiving signal b is stabilized at Vcc, the ringing caused by the light of the previously projected color is reduced. The light reception signal level (each peak value (bottom value) of the amplified signal) is affected, and there is a possibility that accurate color detection of the object to be detected cannot be performed.

  In view of this, it is conceivable that a path connected to the ground is provided in the coupling capacitor C, and the accumulated charge is released by short-circuiting the path during discharging to prevent ringing (see Patent Document 1 above). It is not desirable to provide a new path in the circuit because the circuit configuration becomes complicated.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a photoelectric sensor capable of color detection with relatively high accuracy even when the projection interval is shortened with a simple circuit configuration. .

  As means for achieving the above object, the invention of claim 1 is characterized in that light projecting means for emitting light of a plurality of wavelengths different from each other, and light of the plurality of wavelengths are spaced from the light projecting means for a predetermined time. A light projecting drive unit that performs a light projecting drive operation for sequentially projecting the light and repeatedly performing the light projecting drive operation at intervals longer than the predetermined time; and the light projected from the light projecting unit One or more light receiving elements that receive reflected light or transmitted light from the object to be detected, one light receiving amplification means that outputs a light reception signal amplified according to the amount of light received by the light receiving elements, and the light receiving amplification means In a photoelectric sensor comprising detection means for detecting the detection object based on the received light signal level for each of the different wavelengths of light output, the detection object serving as a reference is detected prior to the detection operation by the detection means. Comparing means for comparing the magnitudes of received light signal levels of light of different wavelengths output from the light receiving amplification means among the light projected from the light projecting means when arranged in the region; and the comparing means And storing means for storing the order of light of different wavelengths from the light receiving signal level starting from the lowest, based on the comparison result of the above, and during the detection operation by the detecting means, the light projecting driving means is stored in the storing means It is characterized in that the light projecting means is configured to project the light of the different wavelengths in the order in which they are performed.

  According to a second aspect of the present invention, there is provided a light projecting unit that emits light having a plurality of different wavelengths, and a light projecting driving operation for causing the light projecting unit to simultaneously project the light having the plurality of wavelengths at a predetermined time interval. A light projecting drive means for repeatedly performing the light projecting driving operation at intervals longer than the predetermined time, and reflected light or transmitted light from an object to be detected among the light projected from the light projecting means. A plurality of light receiving elements that receive light at different wavelengths, and an enabling unit that sequentially enables signals based on the light of the plurality of wavelengths received by the plurality of light receiving elements in synchronization with the light projecting timing of the light projecting unit And a light receiving amplification means for amplifying and outputting the signal validated by the validation means, and the detected signal based on the light reception signal level for each light of the different wavelength amplified and outputted by the light reception amplification means Object detection In the photoelectric sensor comprising the detecting means to perform, the light receiving amplification of the light projected from the light projecting means when a reference object to be detected is arranged in the detection area prior to the detecting operation by the detecting means. The comparison means for comparing the magnitudes of the received light signal levels for the light of different wavelengths output from the means, and the order from the light receiving signal level for the light of the different wavelengths based on the comparison result by the comparing means is stored. And a storage means for performing the detection operation by the detection means, wherein the enabling means is configured to enable the received light signals for the lights of different wavelengths in the order stored in the storage means. Have.

<Invention of Claim 1>
According to this configuration, different wavelengths output from the light receiving and amplifying means out of the light projected from the light projecting means when the reference detection object is arranged in the detection area prior to the detection operation by the detecting means. The magnitudes of the received light signal levels of the light beams of the different wavelengths are compared by the comparing means, and the order from the light receiving signal level of the light having a different wavelength based on the comparison result is stored in the storage means.

  During the detection operation, the light projecting drive means projects light of different wavelengths onto the light projecting means in the order stored in the memory means. Even if the interval of the predetermined time for projecting the light of each wavelength is shortened, the influence on the light reception signal level of the light received later can be reduced. It is possible to detect the color of the detected object with high accuracy.

<Invention of Claim 2>
According to this configuration, prior to the detection operation by the detection unit, when a detection target object serving as a reference is arranged in the detection area, the light output from the light reception amplification unit among the light projected from the light projection unit is different. The magnitude of the received light signal level for the light of the wavelength is compared by the comparison means, and the order from the light reception signal level of the light of the different wavelength from the smallest is stored in the storage means based on the comparison result.

  And, during the detection operation, since the signal based on the light of a plurality of different wavelengths is validated by the validating means in the order stored in the memory means, the light that is easily affected by overshoot based on the received light signal level, In other words, a signal based on light having a low light reception signal level is first activated, and even if the interval of a predetermined time for projecting light of each wavelength is shortened, the effect on the light reception signal level of light received later is affected. Therefore, it is possible to detect the color of the detection object with relatively high accuracy.

<Embodiment 1>
Embodiment 1 of the present invention will be described with reference to FIGS.
The photoelectric sensor of the present embodiment is used for detecting a mark on a sheet W (detected object) conveyed by, for example, a roller (not shown), and as shown in FIG. , 11B, 11C (light projecting means) of the three colors of light (lights of different wavelengths) sequentially reflected by the light receiving element 21 (light receiving means) of the light reflected on the sheet W (surface) A signal based on the amount of received light is amplified, and a mark on the sheet W is detected based on the amplified received light signal level (each peak value (bottom value) of the amplified signal).

1. Electrical Configuration of the Photoelectric Sensor 30 in the figure is a central processing unit (hereinafter referred to as CPU 30), which controls the light projecting / receiving operation and performs color discrimination based on the light receiving signal level. The CPU 30 is connected to light projecting elements 11A, 11B, and 11C that emit light in red, green, and blue through light projecting circuits 12A, 12B, and 12C (corresponding to the “light projecting drive unit” of the present invention), respectively. Yes. A light projection operation is performed on the sheet W based on the light projection signals f1, f2, and f3 (high level) output from the CPU 30.

  In addition, one light receiving element 21 is provided to receive the reflected light of the light irradiated to the sheet W from each of the light projecting elements 11A, 11B, and 11C. It is connected. On the output side of the light receiving circuit 22, there is provided light receiving amplifying means 24 formed by connecting an AC amplifier circuit 23 described later in a plurality of stages, and after the signal a (low level) output from the light receiving circuit 22 is amplified. The light reception signal c is sent to the CPU 30.

  As shown in FIG. 2, each AC amplifier circuit 23 is a non-inverting amplifier circuit having one operational amplifier A, and a coupling capacitor C and a resistor R1 are connected to the positive phase input side. . The other side of the resistor R1 is connected to a power supply (Vcc). That is, the signal a output from the light receiving circuit 22 is differentiated and then input to the positive phase input side of the operational amplifier A. As a result, the DC component that is the disturbance light component is removed, and only the AC component is input to the operational amplifier A. The resistor R1 forms a differentiating circuit on the positive phase input side of the operational amplifier A and has a function of flowing a bias current to the operational amplifier A.

  On the negative phase input side of the operational amplifier A, a feedback resistor R2 is inserted between the operational amplifier A and the output side, and the voltages on the negative phase input side and the positive phase input side of the operational amplifier A by the feedback resistors R2 and R3. Are divided so as to be substantially equal in the non-input state.

  Then, when the projection signal f1 (f2, f3) is output (high level) from the CPU 30, red (green, blue) light is emitted from the projection element 11A (11B, 11C) to the sheet W. . Then, a signal a is output (low level) from the light receiving circuit 22 based on the reflected light from the sheet W among the projected color light. The signal a is sent to the positive phase input side of the operational amplifier A through the coupling capacitor C. At this time, the DC component which is a disturbance light component is removed by the coupling capacitor C, and only the AC component is sent to the operational amplifier A.

  Here, the coupling capacitor C is charged when the signal a is input (low level) from the light receiving circuit 22. When the signal a returns to the non-input state (high level), the voltage input to the positive phase input side rises above the reference potential due to the potential difference of the coupling capacitor C, and then the charge stored in the coupling capacitor C gradually increases. The voltage on the positive phase input side of the operational amplifier A converges to the reference potential.

  Next, when a signal is input to the positive phase input side of the operational amplifier A, it is output as a signal b amplified by the operational amplifier A, and this signal b is negatively fed back to the negative phase input side of the operational amplifier A. Is done.

  Accordingly, overshoot occurs in the output waveform of the signal b output from the operational amplifier A, and ringing that repeats this overshoot and undershoot occurs due to the negative feedback of the signal b, and this ringing is the magnitude of the received light signal level. The time required for convergence increases according to the time. The light receiving and amplifying means 24 is composed of a plurality of stages of AC amplifying circuits 23, so that the signal b is further amplified to the received light signal c and then output to the CPU 30.

  Further, the CPU 30 is connected with a storage unit 31 (corresponding to the “storage unit” of the present invention), and the storage unit 31 emits light of three colors to be obtained that is obtained during teaching described later. Among them, the order from the smallest received light signal level (amplified signal magnitude) of the reflected light is stored.

  Further, the storage unit 31 stores a predetermined time (a time required for the ringing to converge when the received light signal level is the highest) necessary for the completion of the ringing measured in advance.

2. CPU Processing Next, CPU processing will be described with reference to the flowcharts of FIGS.
(A) Teaching Mode In the teaching mode, as shown in FIG. 3, when the teaching start signal is input, the CPU 30 outputs the projecting signal f1 to the projecting circuit 12A. Then, the light projecting circuit 12A projects red light from the light projecting element 11A and the spot position is adjusted to the reference color mark on the sheet by the operator. The reflected light is reflected by the mark on the sheet, and the reflected light is received by the light receiving element 21.

  The received light is sampled by the CPU 30 as a received light signal corresponding to the received light amount level, and the CPU 30 stores the received light signal level Zr (the peak value (bottom value) of the received light signal) in a memory (not shown). Store (S11).

  Next, the CPU 30 reads a predetermined time required to complete the ringing stored in the storage unit 31, and when detecting that this time has passed (S12), outputs the light projection signal f2 to the light projection circuit 12B. To do. Then, the light projecting circuit 12B projects green light from the light projecting element 11B, and the projected light is reflected by a reference mark on the sheet, and the reflected light is reflected by the light receiving element 21. Received light.

  The received light is sampled by the CPU 30 as a received light signal corresponding to the received light amount level, and the CPU 30 stores the received light signal level Zg in the memory (S13).

  Next, the CPU 30 reads a predetermined time required to complete the ringing stored in the storage unit 31, and when detecting that this time has elapsed (S14), outputs the light projection signal f3 to the light projection circuit 12C. To do. Then, the light projecting circuit 12C projects blue light from the light projecting element 11C, and the projected light is reflected by a reference mark on the sheet, and the reflected light is reflected by the light receiving element 21. Received light.

  The received light is sampled by the CPU 30 as a received light signal corresponding to the received light amount level, and the CPU 30 stores the received light signal level Zb in the memory (S15).

  Next, the CPU 30 reads a predetermined time required for the ringing stored in the storage unit 31 to end, and when detecting that this time has passed (S16), the light reception signal level of each color light stored in the memory. Zr, Zg, and Zb are read out, and the read-out light reception signal levels Zr, Zg, and Zb of each color are compared (S17, corresponding to “comparison means” of the present invention).

  Then, based on the comparison result of the light reception signal levels Zr, Zg, and Zb of each color (S17), the CPU 30 sequentially projects the light projecting circuit 12A from the light of the light reception signal level having a small color level every predetermined time T ′ (eg, 10 μs). , 12B, and 12C are transmitted with the light projection signals f1, f2, and f3, so that the light projecting circuits 12A, 12B, and 12C cause the light projecting elements 11A, 11B, and 11C to sequentially project the light of the light receiving signal level from a small color. The light projection driving operation is performed, and the light of the three colors thus projected is reflected by the mark on the sheet W, and the reflected light is sequentially received by the light receiving element 21.

  The received light is sampled by the CPU 30 as a received light signal corresponding to the received light level of each of red, green, and blue, and the CPU 30 receives the received light signal levels Yr, Yg, Yb (the received light signal of each color). The peak value (bottom value)) is added, and the ratio Sr, Sb, Sg obtained by dividing the received light signal level Yr, Yg, Yb for each color light by the added received light signal level Yr + Yg + Yb for each light. The ratios Sr, Sg, and Sb are obtained and stored in the memory (S18 to S23).

  And CPU30 memorize | stores the order from the light of the light reception signal level small color obtained based on the comparison result of the light reception signal level Zr, Zg, Zb of each color in the memory | storage part 31 (S24-S29, this invention). The teaching mode ends.

(B) Mark detection When the CPU 30 receives a signal that the conveyed sheet W has entered the detection area as shown in FIG. 4 during the mark detection operation, the CPU 30 receives the received light signal level stored in the storage unit 31. (In the following description, the order from the light of the color with the small received light signal level is the order of green, blue, and red), and the predetermined time T ′ in the read order. The projection signals f2, f3, and f1 are sequentially output to the projection circuits 12B, 12C, and 12A every (for example, 10 μs). Then, each of the light projecting circuits 12B, 12C, and 12A sequentially performs a light projecting driving operation for projecting the light projecting elements 11B, 11C, and 11A, and the projected light is reflected by the mark on the sheet W. Then, the reflected light is sequentially received by the light receiving element 21. The received light is output to the CPU 30 as a received light signal corresponding to each received light level of red, green, and blue, and the CPU 30 stores the received light signal levels Xr, Xg, and Xb in the memory (S31 to S31). S33).

Next, the CPU 30 reads out the light reception signal levels Xr, Xg, and Xb of each color light, adds the read light reception signal levels Xr, Xg, and Xb of each color light, and adds the received light reception signal levels Xr + Xg + Xb and each color. Ratios Tr, Tg, and Tb with the received light signal levels Xr, Xg, and Xb for each light are obtained.
Then, the CPU 30 stores these ratios Tr, Tg, Tb in the memory (S34 to S36).

  Next, the ratios Sr, Sg, Sb between the added light reception signal level Yr + Yg + Yb stored in the memory at the time of teaching and the light reception signal levels Yr, Yg, Yb for each color light are read, and the ratios Sr, Sg, Sb are read out. It is determined for each color whether or not the ratios Tr, Tg, Tb of the added light reception signal level Xr + Xg + Xb stored in the memory during the detection operation and the light reception signal levels Xr, Xg, Xb for each color light are equal (S37 to S39). . At this time, when the light ratios of all the colors are equal, it is determined that the light is detected (S37 to S39 are all “Y”, S40), and when the light ratio of any one color is different, it is determined that the light is not detected. (S37 to S39 are “N”, S41). Note that whether or not the ratios are substantially equal (substantially the same) may be determined to be equal if the ratios are not completely the same but are different within a predetermined range. For “within a predetermined range”, a range of ± 5% with respect to a reference ratio may be set as a threshold value, and those within this range may be determined to be substantially the same.

  When it is determined that the detection is made, the CPU 30 outputs a detection signal to the output circuit 32 and turns on an operation indicator lamp of a digital display (not shown). On the other hand, when it is determined that the detection is not performed, the detection signal is not output.

Then, after projecting the last light projecting element 11A (projecting light having the largest received light amount (light reception signal level)), an interval T ″ (which is longer than the projecting interval T ′ of the light of each color for a predetermined time) After the elapse of the time until the longest ringing of the last projected light ends (for example, 20 μs), the CPU 30 sends the light projection signals f2, f2 to the light projecting circuits 12B, 12C, 12A in a predetermined cycle. The outputs of f3 and f1 are repeated, whereby each of the light projecting circuits 12B, 12C, and 12A repeats the light projecting driving operation for sequentially projecting the light projecting elements 11B, 11C, and 11A at a predetermined cycle.
The above operation is continued until the CPU 30 receives a detection end signal.

3. As described above, according to this embodiment, prior to the detection operation by the CPU 30, when the reference mark is arranged in the detection area, the light is projected from the light projecting elements 11A, 11B, and 11C. The light receiving signal level of each color light received by the light receiving element 21 among the light is compared by the CPU 30, and the order from the light receiving signal level (light receiving amount) of the light of a different color based on the comparison result is stored in the storage unit. 31.

  At the time of the detection operation, the light projecting elements 12A, 12B, and 12C emit light of different colors in the order from the light of the light receiving signal level (the amount of received light) stored in the storage unit 31. 11B and 11C are projected.

  Here, for example, when light is not projected in order from a light receiving amount (light receiving signal level), light of a color with a large light receiving signal level, that is, a large overshoot is generated as shown in FIG. The light having the light reception signal level next to the light is projected (the red (R) light and the green (G) light in FIG. 5A are projected).

  In the case of light with a large overshoot, ringing that repeats a downshoot and overshoot thereafter occurs over a long period of time, and the time taken for the ringing to converge increases in proportion to the size of the overshoot. Therefore, the light receiving amplification means 24 receives the light signal of the next color before the ringing converges, and the magnitude of the light receiving signal level changes according to the deviation from the reference voltage value Vcc due to this ringing ( FIG. 5A shows a light reception signal level of green (G) light.

  As a result, the ratio of the light reception signal level of the light of each color also changes, so that the color sensor that detects the color of the sheet W based on the ratio of the light reception signal level hinders accurate mark detection.

  This is particularly affected by ringing when the light to be projected next (later) is light with a small received light amount (light reception signal level). Specifically, for example, if the level of overshoot or the like is 5, if the next light is light with a light reception signal level of 70, the ratio of the influence of the light reception signal level is about 7%. On the other hand, if the next light is light having a light reception signal level of 10, the influence ratio is 50%, the deviation of the light reception signal level is large, and the influence on the detection of the mark color of the sheet W is large. Become.

  However, according to the present embodiment, as shown in FIG. 5B, light is projected in order from light of a small amount of received light (light reception signal level) among light of three colors, that is, light with a short time for ringing to converge. As a result, even if the interval of the predetermined time until the third light is projected is shortened, the convergence time due to the large overshoot caused by the light with the largest received light amount (light reception signal level) is finally projected. The long ringing has a relatively small time until the start of the light projection operation in the next cycle, and thus has little influence on the light reception signal level in the next cycle.

  Furthermore, light with a small received light amount (light reception signal level) that is easily affected by ringing is projected first, and light with a large light reception amount (light reception signal level) that is relatively less susceptible to ringing is projected later. Therefore, even if the next (subsequent) light is affected by ringing due to the shortening of the light projection interval, the ringing that the subsequent light receives due to the large amount of received light (received light signal level). The effect of is relatively small.

<Embodiment 2>
In the second embodiment, as shown in FIG. 6, while three light projecting elements 11A, 11B, and 11C that project light of each color (red, green, and blue) are provided, each color of red, green, and blue is provided in front. Three light receiving elements 51A, 51B, and 51C each provided with color filters 52A, 52B, and 52C that transmit only the light of each color are provided, and the light of the colors that are sequentially projected from the light projecting elements 11A, 11B, and 11C, respectively. The light receiving elements 51A, 51B, 51C corresponding to the light are received.
The light receiving circuits 53A, 53B, 53C are connected to the common (one) amplifying means 25 via the switching elements 54A, 54B, 54C, and are sequentially switched in synchronization with the light projection signal. By turning on 54B and 54C, signals output from the respective light receiving circuits 53A, 53B and 53C are validated in order and input to the amplifying means 25.

<Embodiment 3>
In the first embodiment, the light reflected by the sheet W among the light of different colors sequentially projected from the three light projecting elements 11A, 11B, and 11C is sequentially received by one light receiving element 21.

  On the other hand, in the third embodiment, as shown in FIG. 7, one light projecting element 41 for projecting white light (simultaneously projecting light of a plurality of wavelengths) is provided, while three light receiving elements 51A, 51B, 51C is provided, and color filters 52A, 52B, and 52C that transmit only light of each color of red, green, and blue are provided in front of each of the light receiving elements 51A, 51B, and 51C.

  As a result, the light projected from the light projecting element 41 is reflected on the sheet W and then received as light of different colors by the respective light receiving elements 51A, 51B, 51C, and the respective light receiving elements 51A, 51B. , 51C is connected to the light receiving circuits 53A, 53B, 53C to output signals corresponding to the light receiving amounts (light receiving amount levels) of the light receiving elements 51A, 51B, 51C.

  Each light receiving circuit 53A, 53B, 53C is connected to a common (one) amplifying means 25 via switching elements 54A, 54B, 54C each consisting of an analog switch, and is amplified by the amplifying means 25. A light reception signal is output to the CPU 30. The other points are the same as those of the first embodiment, and the same components as those of the first embodiment are denoted by the same reference numerals and redundant description is omitted.

  Specifically, when the CPU 30 outputs a light projection signal to the light projection circuit 42 at every predetermined time T ′, white light is projected from the light projecting element 41 each time and white light is projected three times. After the light is emitted, a light projection signal of the next period is output after the elapse of a predetermined time 2T ′, and the white light projection operation is repeated. On the other hand, the switching elements 54A, 54B, 54C connecting the light receiving circuits 53A, 53B, 53C and the amplifying means 25 are turned on in order in synchronization with the output of the light projection signal (the “enabling means of the present invention”). Thus, signals corresponding to the amounts of received light of the respective colors output from the light receiving circuits 53A, 53B, and 53C are sequentially input to the amplifying means 25.

  According to the present embodiment, prior to the detection operation by the CPU 30, when the reference sheet W is disposed in the detection region, different wavelengths output from the amplification unit 25 among the light projected from the light projecting element 41. The CPU 30 compares the magnitude of the received light signal level with respect to the light of, and the order from the light receiving signal level of the light of different wavelengths from the lowest is stored in the storage means based on the comparison result.

  During the detection operation, the CPU 30 turns on the switching elements 54A, 54B, and 54C in the order stored in the storage unit 31 to turn on the received light amount (amplified) among the signals based on the three colors of light. (Light reception signal level at the time of light reception) is activated in order from the light with the lowest light level, and the activated signal is amplified, so light that is easily affected by overshoot based on the light reception signal level, that is, light with a low light reception signal level Even if the interval of the predetermined time for projecting the light of each wavelength is shortened, the influence on the light reception signal level of the light received later can be reduced. The color of the sheet W can be detected with high accuracy.

<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention, and further, within the scope not departing from the gist of the invention other than the following. Various modifications can be made.

  (1) In the above embodiment, the reflected light from the mark on the sheet W is received. However, the mark on the sheet W may be detected by receiving the transmitted light.

  (2) In the above-described embodiment, the interval T ′ of the predetermined time at which light of different colors is projected is constant, but is not limited thereto. For example, the next light may be projected at intervals that are not affected by ringing in accordance with the magnitude of the light reception signal level of the previously projected light.

  (3) In the above embodiment, the mark color of the sheet (detected object) is detected. However, a color other than the mark may be detected. For example, the color of the background portion other than the mark on the sheet W may be detected.

  (4) In the third embodiment, the configuration is such that white light is projected from one light projecting element 41. However, as in the first embodiment, three light projects that project light of three primary colors (red, green, and blue). The optical elements 11A, 11B, and 11C are provided, and the three light projecting elements 11A, 11B, and 11C are simultaneously projected to project white light, and the same effects as those of the third embodiment are achieved. May be.

  (5) At the time of teaching, when determining that the ringing has converged, it is assumed that the ringing has converged by elapse of a predetermined time measured in advance, and the next color light is projected. When the CPU 30 detects that the ringing has converged, light of the next color may be projected.

1 is a circuit diagram showing the entirety of a color sensor according to a first embodiment. Circuit diagram showing AC amplifier circuit Flow chart for teaching Flow chart during detection operation Timing chart showing signal waveform Circuit diagram showing the entire second embodiment Circuit diagram showing entire third embodiment Circuit diagram showing the entire conventional color sensor Circuit diagram showing AC amplifier circuit Timing chart showing signal waveform

Explanation of symbols

11A, 11B, 11C, 41 ... Projection element (projection means)
12A, 12B, 12C, 42 ... Projection circuit (projection drive means)
21, 51A, 51B, 51C ... light receiving element 22, 53A, 53B, 53C ... light receiving circuit 23 ... AC amplifier circuit 24, 25 ... light receiving amplification means 30 ... CPU
31 ... Storage part (storage means)
52A, 52B, 52C ... Color filter 54A, 54B, 54C ... Switching element A ... Operational amplifier C ... Coupling capacitor W ... Sheet

Claims (2)

A light projecting means for emitting light of a plurality of different wavelengths;
The light projecting unit is caused to perform a light projecting drive operation for sequentially projecting the light of the plurality of wavelengths at intervals of a predetermined time, and the light projecting drive operation is repeatedly performed at intervals longer than the predetermined time. Light driving means;
One or more light receiving elements that receive reflected light or transmitted light from the detected object out of the light projected from the light projecting means, and a light reception signal amplified in accordance with the amount of light received by the light receiving element is output. One light receiving and amplifying means;
In a photoelectric sensor comprising detection means for detecting the object to be detected based on a light reception signal level for each light of the different wavelength output from the light reception amplification means,
Prior to the detection operation by the detection means,
When the object to be detected that is the reference is arranged in the detection region, the light reception signal levels of light of different wavelengths output from the light reception amplification unit among the light projected from the light projection unit are compared. Comparing means to
Storage means for storing the order from the light reception signal level of the light of the different wavelength based on the comparison result by the comparison means,
During the detection operation by the detection means,
The light projecting drive unit causes the light projecting unit to project light of the different wavelengths in the order stored in the storage unit. A light projecting means for emitting light of a plurality of different wavelengths;
The light projecting means is configured to perform a light projecting drive operation for simultaneously projecting the light of the plurality of wavelengths with a predetermined time interval, and to perform the light projecting drive operation repeatedly at intervals longer than the predetermined time. Light driving means;
A plurality of light receiving elements for receiving reflected light or transmitted light from the detected object among the light projected from the light projecting means for each different wavelength;
Enabling means for sequentially enabling signals based on the light of the plurality of wavelengths received by the plurality of light receiving elements in synchronization with the light projection timing of the light projecting means;
A light receiving amplification means for amplifying and outputting the signal validated by the validation means;
In a photoelectric sensor comprising detection means for detecting the object to be detected based on a light reception signal level for each light of the different wavelength that is amplified and output by the light reception amplification means,
Prior to the detection operation by the detection means,
When the object to be detected that is the reference is arranged in the detection region, the light reception signal levels of light of different wavelengths output from the light reception amplification unit among the light projected from the light projection unit are compared. Comparing means to
Storage means for storing the order from the light reception signal level of the light of the different wavelength based on the comparison result by the comparison means,
During the detection operation by the detection means,
The photoelectric sensor is characterized in that the light-receiving signal for each light of the different wavelengths is validated in the order stored in the storage means.

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