JP3445324B2 - Photoelectric sensor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photoelectric sensor suitable for detecting, for example, a mark printed on the surface of a label. 2. Description of the Related Art FIG. 9 shows an example of detection by a photoelectric sensor of this type.
This will be described with reference to FIG. FIG. 9 shows a detection state of a black mark printed on a white sheet by the photoelectric sensor. The photoelectric sensor 1 is arranged at a position separated from the sheet 2 by a predetermined distance. The photoelectric sensor 1 includes a light projecting unit and a light receiving unit arranged side by side, and emits spot light from the light projecting unit and receives light reflected from the sheet 2 by the light receiving unit. . In this case, since the reflection intensity of the base portion is high and the reflection intensity of the black mark 2a is low in the white sheet 2, the photoelectric sensor 1 is printed on the sheet 2 based on the difference in the amount of light received by the light receiving section 1b. The mark 2a can be detected. FIG. 10 shows an example of the configuration of the photoelectric sensor. In FIG. 10, the light projecting element 3 projects pulse light corresponding to the pulse signal from the light projecting circuit 4 onto the sheet 2 in a condensed state, and the light receiving element 5 receives the reflected light from the sheet 2 and receives it. Output a signal. The light receiving signal from the light receiving element 5 is amplified by the amplifier circuit 6, synchronously detected by the synchronizing circuit 6 at the output timing of the pulse signal of the light projecting circuit 4, and then integrated by the integrating circuit 8. Therefore, by comparing the integration output of the integration circuit 8 with a predetermined detection level in the comparison circuit 9, a detection signal indicating that the mark has been detected can be output from the output circuit 10 to the outside. As a specific example of the detection using the photoelectric sensor having the above-mentioned configuration, there is one applied to a cutting device for cutting a sheet such as wrapping paper into a predetermined length. That is, as shown in FIG. 11, the marks 2a are printed at regular intervals on the back side of the sheet 2 sent out by the rollers 11, so that the photoelectric sensors 1 correspond to the movement locus of the marks 2a printed on the sheet 2. The sheet 2 can be cut at predetermined lengths by operating the cutter 12 at the timing when the detection signal is output from the photoelectric sensor 1. Here, the cut sheet 2 has a mark 2a for detecting the cutting position. Such a mark 2a is a cut end of the sheet 2 from the viewpoint of the appearance of the sheet 2. Since it is desirable to move the photoelectric sensor 1 as close as possible to the portion, the photoelectric sensor 1 for detecting the mark 2 a is arranged adjacent to the cutter 12. [0006] In addition, as a detection target of the photoelectric sensor 1,
There is an apparatus applied to a sorting device for sorting boxes of a specific color from boxes of different colors conveyed by a conveyor. In other words, the amount of light reflected from the box depends on the color of the box,
By using a photoelectric sensor 1 having a configuration in which a light reception signal indicating a light reception amount is output in an analog manner, a box of an arbitrary color can be detected based on the signal level of the light reception signal. In the case where the photoelectric sensor 1 is applied to a sheet cutting apparatus, the photoelectric sensor 1 may be rotated due to uneven rotation of the feed roller 11 or slippage between the roller 11 and the sheet 2. The sheet 2 is likely to bend at the detection position. In particular, when the photoelectric sensor 1 is disposed adjacent to the cutter 12 as described above, a guide for supporting the sheet 2 cannot be provided at the cutting position of the sheet 2 by the cutter 12, so that the sheet 2 is It becomes unstable in the direction and bends greatly. Therefore, from the proper position shown in FIG.
Since the position of the sheet 2 greatly fluctuates as shown in (c), when the mark 2a of the sheet 2 is detected by the photoelectric sensor 1 in such a state, the mark 2a by the photoelectric sensor 1 is detected. Detection becomes difficult. That is, FIG.
When the sheet 2 is located at the proper position as shown by (b) in FIG. 12, the mark 2 as shown by (b) in FIG.
Since only the received light amount level at the time of detecting a is lower than the detection level, the mark 2a printed on the sheet 2 can be detected. However, when the sheet 2 is bent and approaches the photoelectric sensor 1 as shown by (a) in FIG. 10, the base portion of the sheet 2 and the mark 2a are shown by (a) in FIG. Since any of the light reception level at the time of detecting the portion exceeds the detection level, it is impossible to detect the mark 2a. When the sheet 2 is bent and moves away from the photoelectric sensor 1 as shown in FIG. 10C, the detection of the base portion and the mark 2a of the sheet 2 is performed as shown in FIG. Since any of the received light amount levels at the time is lower than the detection level, it is impossible to detect the mark 2a in this case as well. On the other hand, when the photoelectric sensor 1 is applied to a box sorting device, the size of the box may be different, or the position of the box on the conveyor may be shifted and the distance from the photoelectric sensor may fluctuate. In such a case, the light receiving signal indicating the amount of light received from the photoelectric sensor 1 fluctuates, so that a box of a specific color cannot be detected based on the light receiving signal. In this case, it is conceivable to provide a distance sensor for measuring the distance between the photoelectric sensor 1 and the sheet 2, and to correct the integral output of the integrating circuit 8 of the photoelectric sensor 1 based on the distance detected by the distance sensor. However, this has the disadvantage that the overall configuration is complicated and large, and the cost is greatly increased. SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a configuration in which the brightness of a detected object is detected based on the amount of light received from the detected object. It is an object of the present invention to provide a photoelectric sensor that does not increase in size while reliably detecting the brightness of a detected object regardless of the size of the object and does not significantly increase the cost. [0012] The photoelectric sensor of the present invention comprises:
A light emitting element for projecting light onto the detected object is provided, and light reflected from the detected object is received at a position corresponding to the distance to the detected object, and first and second light receiving positions and amounts of received light are indicated. a one-dimensional position detecting element for outputting an output signal of providing, obtains a distance to the target object based on a ratio of the first and second output signals from the one-dimensional position detecting element
And the one-dimensional position detecting element
After obtaining the amount of light received by the child, a light receiving signal corresponding to the amount of received light is used to nullify the effect of the distance to the detected object .
And a correction means for outputting the output in a corrected state. The one-dimensional position detecting element receives light from the light projecting element reflected by the detected object at a position corresponding to the distance to the detected object, and receives the light at a position corresponding to the distance to the detected object. And a second output signal. And the correction means is a one-dimensional position
The distance to the detected object is determined based on the ratio of the first and second output signals from the detection element ,
Based on the amount of light received by the one-dimensional position detection element
Then, the light receiving signal corresponding to the light receiving amount is output in a state where the light receiving signal is corrected so as to nullify the influence of the distance to the detected object.
Thus, even if the amount of light received by the one-dimensional position detecting element changes according to the distance to the detected object, the change is invalidated, so that the brightness of the detected object can be reliably detected. The first embodiment of the present invention will be described below with reference to FIGS. FIG. 1 schematically shows the electrical configuration. In FIG. 1, a light projecting unit 21 includes a light projecting drive circuit 22 and a light projecting element 23, and projects a spot light from the light projecting element 23 to the detected object 24 in accordance with driving by the light projecting drive circuit 22. The light receiving means 25 mainly includes the position detecting element 26, and receives the reflected light from the detected object 24 on the position detecting element 26 in a condensed state. The position detection element 26 outputs a first output signal Va indicating the light receiving position and the light receiving amount.
And the second output signal Vb through the amplifier 27. In this case, the sum of the first and second output signals Va and Vb indicates the amount of light received by the position detecting element 26, and the ratio of the first and second output signals Va and Vb indicates the light receiving position of the position detecting element 26. ing. The correcting means 28 comprises a distance calculating means 29 and a received light amount calculating means 30. The distance calculating means 29 detects the light receiving position of the position detecting element 26 on the basis of the ratio of the first and second output signals Va and Vb, and based on the light receiving position, detects the light receiving position of the position detecting element 26 up to the detected object 24 by the principle of triangulation. Calculate the distance. The received light amount calculating means 30 detects the received light amount by the light receiving means 25 based on the sum of the first and second output signals Va and Vb, and calculates the received light amount to the distance to the detected object 24 by the distance calculating means 29. Is output in a state corrected according to. That is, since the reflected light from the detected object 24 received by the position detecting element 26 of the light receiving means 25 varies according to the distance to the detected object 24, correction is made to nullify the influence of the fluctuation. . Accordingly, the output signal from the received light amount calculating means 30 has a size corresponding to the brightness of the detected object 24 regardless of the distance to the detected object 24. Brightness and darkness of the detection object 24 can be reliably detected. FIG. 2 shows a specific example of the above configuration. In FIG. 2, the light projecting means 21 includes a light projecting drive circuit 22 and an LED 23 serving as a light projecting element. The LED 23 receives pulsed light as parallel light through a light projecting lens 21a based on a pulse signal from the light projecting drive circuit 22. Light is projected on the detection object 24. The light receiving means 25 comprises a PSD (Position Sensitive Device) 26, which is a one-dimensional position detecting element, and a current-voltage conversion amplifier 27. The PSD 26 focuses the light reflected from the object 24 through the light receiving lens 25a. Receive light. FIG. 3 schematically shows the structure of the PSD 26. In FIG. 3, a PSD 26 is a spot light position detecting element to which a silicon photodiode is applied, and is formed by forming an I layer between a P layer on the front surface and an N layer on the back surface of silicon. Here, the PSD 26 photoelectrically converts the incident light according to the amount of incident light to generate a photocurrent I, and
The generated photocurrent I is applied to the electrodes 26a and 26 provided on the P layer.
Output divided from b. In this case, the P layer is formed so as to have a uniform resistance value over the entire surface so as to function as a resistance layer, so that the photocurrent from the electrodes 26a and 26b reflects the distance between the incident light and the electrodes 26a and 26b (resistance Value) is output in inverse proportion to That is, as shown in FIG. 3, Zs is between the electrodes 26a and 26b of the PSD 26, the incident distance of light from the electrodes 26a and 26b is Za and Zb (Zs = Za + Zb), and the current generated by the incident energy is I. Then, the electrode 26a
, 26b output as current signals Ia, Ib as I = Ia + Ib, Ia = (Zb /
Zs) .I, Ib = (Za / Zs) .I Therefore, the amount of light received by the PSD 6 and the position of the incident light can be obtained based on the above equations. In FIG. 2, an amplifier 27 for converting current and voltage of the light receiving means 25 converts the first and second current signals Ia and Ib from the PSD 26 into first and second voltage signals Va and V, respectively.
Convert current to voltage to b. Distance calculation means 29 constituting correction means 28
Comprises a subtraction circuit 31, an addition circuit 32, and a division circuit 33. The subtraction circuit 31 subtracts the first and second voltage signals Va and Vb from the light receiving means 25 to obtain Va-Vb. The adder circuit 32 is provided with the first and second
Are added to obtain Va + Vb.
The division circuit 33 includes the subtraction circuit 31 and the addition circuit 3
(Va−Vb) / (Va + Vb)
). The received-light-amount calculating means 30 which constitutes the correcting means 28 together with the distance calculating means 29 comprises an adding circuit 32 and a variable amplifying circuit 34. In this case, the adding circuit 32 shares with the distance calculating means 29. I have. Variable amplification circuit 3
Numeral 4 corrects the operation value of the addition circuit 32 based on the operation value of the division circuit 33 so as to invalidate the influence of the distance to the detected object 24 as described later, and outputs the result. The comparison circuit 35 compares the output from the variable amplifier circuit 34 with the detection level and outputs a detection signal. The output circuit 36 drives a load (not shown) according to the detection signal from the comparison circuit 35. Next, the operation of the above configuration will be described. The LED 2 is driven according to the driving of the light emitting drive circuit 22 of the light emitting means 21.
The pulse light is output from 3 and converted into substantially parallel light by the light projecting lens 21a, and is irradiated on the detection target 24. Then, the reflected light from the detected object 24 is received by the PSD 26 in a condensed state by the light receiving lens 25a. At this time, the light receiving position of the PSD 26 is a position corresponding to the PSD 26 and the distance to the detected object, and the first current signal Ia (=
(Zb / Zs) .I) and the second current signal Ib (= (Z
a / Zs) .I) is output (however, Zs = Za + Z)
b, I = Ia + Ib), and the first and second current signals Ia, Ib are current-voltage converted by the amplifier 27 into first and second voltage signals Va, Vb. The distance calculating means 29 is provided with the light receiving means 2
Based on the first and second voltage signals Va and Vb from (5), (Va-Vb) / (Va + Vb) is calculated and output as a distance signal. This calculated value substantially corresponds to the light receiving position of the spot light on the PSD 26, and thus the distance to the detected object 24. Accordingly, the distance signal from the received light amount calculating means 25 is in a proportional relationship with the distance to the detected object 24 as shown in FIG. 4, and the detected object 24 is shown in (a), (b), ( The distance signal from the distance calculating means 29 corresponding to the position indicated by c) is shown in FIG.
Outputs shown in (b) and (c) are obtained. In this case, since the distance signal from the distance output unit 29 does not include the current I generated by the PSD 26, even if the amount of light received by the PSD 26 fluctuates with the brightness of the detected object 24, FIG.
The relationship between the distance and the output signal shown in is not affected. Therefore, even if the surface of the detected object 24 has a different color such as white or black, the distance output means 2
9 does not change. On the other hand, the adding circuit 32 in the distance calculating means 29 is a component of the light receiving amount calculating means 30, and the calculated value Va + Vb by the adding circuit 32 is the light receiving amount by the PSD 26. In this case, the amount of light received by the PSD 26 changes according to the brightness (reflectance) of the surface of the detected object 24 as shown in FIG. Further, even if the brightness of the detected object 24 is constant, the larger the distance to the detected object 24 is, the smaller the amount of light entering the PSD 26 is.
As shown in the figure, the value changes depending on the distance. Now, the variable amplification circuit 34 of the received light amount calculation means 30 adjusts the amplification factor based on the distance signal from the distance calculation means 29 shown in FIG.
And outputs a light receiving signal corresponding to only the brightness of the detected object 24 irrespective of the distance as shown in FIG. That is, the value calculated by the addition circuit 32 is affected according to the distance to the detected object 24 even if the brightness of the detected object 24 is constant. Is output in a state corrected according to the distance. Then, the comparison circuit 35 outputs a detection signal based on whether or not the light reception signal from the light reception amount calculation means 30 has exceeded the detection level. The output circuit 36 drives a load (not shown) when the detection signal is output from the comparison circuit 35. Accordingly, when detecting a black mark printed on a white sheet, the comparison circuit 35 is set so as to output a detection signal when the output signal from the light reception amount calculation means 30 falls below the detection level. You. When cutting is performed at the mark position on the sheet as described in the conventional example, the output circuit 36 drives the cutter at the timing when the detection signal is output from the comparison circuit 35. According to the above configuration, in the received light amount calculating means 30, the addition circuit 3 indicating the brightness of the detected object 24 is provided.
2 is corrected by the calculated value of the distance calculating means 29 indicating the distance to the detected object 24,
Since the light receiving signal corresponding to the light receiving amount by the PSD 26 is output in a state where the influence of the distance to the detected object 24 is nullified, the signal is simply output according to the light receiving amount of the light receiving element. As compared with the above, a signal corresponding to only the brightness of the detected object 24 can be output irrespective of the distance variation to the detected object 24. Accordingly, since a detection signal corresponding to the difference in brightness of the detected object 24 can be reliably detected, even if the color of the detected object 24 is slightly different, the detection can be reliably performed. Since a distance signal can be obtained from one light receiving means 25 in addition to the light receiving signal, the light receiving means 25
Need not be provided, and the number of parts can be greatly reduced. Therefore, compared to a configuration in which a light reception signal corresponding to the amount of light received from the reflective photoelectric sensor is corrected based on the distance signal from the distance sensor, the overall size can be reduced and the cost can be reduced. be able to. Further, in the present embodiment, the addition circuit 32 is shared by the distance calculating means 29 and the received light amount calculating means 30, so that the distance calculating means 29 and the received light amount calculating means 30 are used.
The configuration can be simplified as compared with the configuration in which the adder circuit 32 is provided for each of them. FIG. 7 shows a second embodiment of the present invention.
The same parts as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted. Only different parts will be described. That is, in FIG. 7, the received light amount calculating means 30 is only the addition circuit 32, and the light emitting drive circuit 22 which constitutes the correcting means 28 together with the received light amount calculating means 29, The drive current is adjusted. In this case, the light emission drive circuit 22 decreases the light emission drive current when the detected object 24 is at a short distance, and increases the light emission drive current when the detected object 24 is at a long distance. Thus, the amount of light received by the PSD 26 does not change regardless of the distance to the detected object 24. Accordingly, since the output from the light receiving amount calculating means 30 has the characteristic shown in FIG. 6, it is possible to reliably detect the brightness of the detected object 24 regardless of the distance to the detected object 24 as in the first embodiment. Can be. FIG. 8 shows another example of the distance calculating means 29 in the third embodiment of the present invention. In FIG. 8,
First and second voltage signals V provided from the light receiving means 25
a and Vb are given to the two logarithmic amplifier circuits 37 and 38, and the outputs from the logarithmic amplifier circuits 37 and 38 are output after being subtracted by the subtraction circuit 39. here,
The logarithmic amplifiers 37 and 38 calculate and output log Va and log Vb, respectively, and the subtraction circuit 39 calculates log Va / Vb.
Is output. Therefore, since the output from the subtraction circuit 39 is a signal corresponding to the distance to the detected object 24, the amount of light received by the PSD 26 or the amount of light emitted from the LED 23 is corrected based on the output from the subtraction circuit 39. Accordingly, the brightness of the detected object 24 can be reliably detected regardless of the distance to the detected object 24. In the above embodiment, the comparison circuit 35 compares the received light signal from the received light amount calculating means 30 with a predetermined detection level and outputs a detection signal. The output may be directly output to the outside. According to such a configuration, the output from the photoelectric sensor is not affected by the distance to the detected object 24 and has a size corresponding to only the brightness or color of the detected object 24. Further, the distance calculating means 29, the received light amount calculating means 30, and the comparing circuit 35 may be constituted by a microcomputer. In this case, a table of correction data corresponding to the distance to the detected object 24 is stored in advance in the ROM of the microcomputer, and a correction value is read from the correction data table based on the calculated distance data, so that the PSD 26 receives light. The amount may be corrected. The addition circuit 32 shared by the distance calculation means 29 and the received light quantity calculation means 30 may be provided separately. Further, a semiconductor laser may be used instead of the LED 23, and a two-division photodiode may be used instead of the PSD 26. In addition, in each of the above embodiments, the output from the distance calculating means 29 has been described as being substantially proportional to the distance to the detected object 24. However, when the detection accuracy of the photoelectric sensor is required, the distance The output from the calculating means 29 may be corrected so as to be proportional to the distance. As is apparent from the above description, according to the photoelectric sensor of the present invention, the light projecting element for projecting light to the object to be detected is provided, and the reflection from the object to be detected is provided. outputs the first and second output signals indicative of the light receiving position and the light-receiving amount with receiving the light at a position corresponding to the distance to the target object 1
A one-dimensional position detecting element, and a distance to the object to be detected is determined based on a ratio of the first and second output signals from the one-dimensional position detecting element, and based on an addition thereof,
After obtaining the amount of light received by the light receiving means, the received light signal corresponding to the amount of received light is invalidated by the influence of the distance to the detected object.
Provided a correction means for outputting the correction state as of,
Since the light receiving signal corresponding to the amount of light received by the one-dimensional position detecting element is prevented from being affected by the distance to the object to be detected, the brightness of the object to be detected is determined based on the amount of light reflected from the object to be detected. In the detection configuration, there is an excellent effect that the size of the detected object is not increased while the brightness of the detected object is reliably detected regardless of the fluctuation of the distance to the detected object, and the cost is not significantly increased. .

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a conceptual diagram of a first embodiment of the present invention. FIG. 2 is a schematic diagram showing an electrical configuration. FIG. 3 is a schematic diagram showing a PSD structure. FIG. FIG. 5 is a characteristic diagram showing the relationship between the distance to the object and the distance output. FIG. 5 is a characteristic diagram showing the relationship between the distance to the detected object and the received light output. FIG. 6 is a diagram corresponding to FIG. 5 in a corrected state. FIG. 8 corresponding to FIG. 2 showing a second embodiment of the present invention. FIG. 8 is a schematic view of a main part showing a third embodiment of the present invention. FIG. 9 is a side view of a photoelectric sensor showing a detection state in a conventional example. 10 Equivalent to FIG. 1 FIG. 11 is a perspective view showing a detection state by a photoelectric sensor. FIG. 12 is a characteristic diagram showing a relationship between a distance to an object to be detected and a received light amount level. , 22 is a light emitting drive circuit, 23 is a light emitting element, 24 is an object to be detected, 25 is light receiving means, 26 is a position detecting element 28 correction means 29 the distance calculating means, 30 is a light amount calculating section.

Continuation of the front page (56) References JP-A-3-46820 (JP, A) JP-A-2-27214 (JP, A) JP-A 63-48178 (JP, U) JP-A 63-108289 (JP , U) Fully open sho 59-139520 (JP, U) Fully open sho 61-102817 (JP, U) Full open hei 3-36985 (JP, U) (58) Fields surveyed (Int. Cl. ⁷ , DB) Name) H03K 17/00 G01S 7/48 G01S 17/00

Claims (1)

(57) [Claim 1] A light projecting element for projecting light on a detected object, and a light reflected from the detected object is received at a position corresponding to a distance to the detected object. outputs the first and second output signals indicative of the light receiving position and the light receiving amount provided 1
A one-dimensional position detecting element, and first and second output signals from the one-dimensional position detecting element
When calculating the distance to the detected object based on the ratio of
Both are added to the one-dimensional position detecting element based on the addition thereof.
And a correction means for outputting a light reception signal corresponding to the light reception amount in a corrected state so as to nullify the influence of the distance to the detected object. A photoelectric sensor characterized by the above-mentioned.