JPH07103755A - Photoelectric sensor and method for correcting received signal level - Google Patents

Abstract

PURPOSE:To provide a photosensor for producing an output that depends only on the optical reflectivity of an object by eliminating the distance dependency if the distance between them varies. CONSTITUTION:An adder 13 and a subtractor 14 for adding and subtracting current i1 and i2 at both terminals of a photodetector element 5 are provided and both output are divided by a division circuit 16 to obtain the distance signal to a target to be detected. A squaring circuit 17 for obtaining the square of the distance signal is provided and then a multiplication circuit 18 for multiplying the added value of current at both terminals of the photodetector element 5 by the output of the squaring circuit and an addition circuit for adding a multiple of the received signal to the multiplication result are provided. The multiplication circuit 18 and the addition circuit compensate the reception light signal of the photodetector element 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photoelectric sensor for detecting the presence / absence of a detection target, a color change of the detection target, or a reading / shading of the detection target, and a method of correcting the light reception signal level thereof.

[0002]

2. Description of the Related Art A photoelectric sensor composed of a light projecting element and a light receiving element is used for reading the presence / absence of an object moving on a conveyer, the color change of the object, or the reading of the shade. This photoelectric sensor irradiates an object to be detected with light from a light projecting element, and receives light reflected by the object at a light receiving element. When the detection target does not exist at the light irradiation position of the light projecting sensor, the light receiving element does not receive the light. Therefore, the presence or absence of the detection target can be detected by the light reception signal level output from the light receiving element. Similarly, when there is a color change or shade in the detection target, the amount of light received by the light receiving element changes due to the change in reflectance due to the shade of the detection target, etc. Can be determined.

[0003]

However, the amount of light reflected by the light receiving element that constitutes the photoelectric sensor from the detection target is inversely proportional to the square of the distance between the detection target and the light receiving lens, and therefore the light receiving element receives light. Even if the reflectance of the detection target is constant, the signal level is the curve 91 or 9 in FIG.
As shown in FIG. 2, it greatly changes depending on the distance between the detection target and the light receiving lens. Therefore, when detecting a detection target based on a difference in the amount of reflected light from the object, such as when detecting the presence or absence of a mark written on the surface of the object, as shown in FIG. When the threshold level C is set in the relationship between the curve 91 of the received light signal level and the curve 92 of the received signal level of the light reflected from the base, the allowable variation range of the distance between the detection target and the front surface of the photoelectric sensor is It is as narrow as Δx, the sensitivity adjustment of the received light signal must be strictly maintained, and the transport accuracy must be maintained high in order to properly position the transport position of the detection target. In particular, there is a problem that a malfunction occurs when detecting light and shade, or when the detection surface has irregularities.

An object of the present invention is to eliminate the distance dependency of the light receiving signal by correcting the light receiving signal level of the light receiving element which constitutes the photoelectric sensor using the distance information between the detection object and the light receiving lens. SUMMARY OF THE INVENTION It is an object of the present invention to provide a photoelectric sensor capable of accurately detecting only a change in reflectance of a detection target and a method of correcting a light reception signal level thereof.

[0005]

According to a first aspect of the present invention, there is provided a photoelectric sensor including a light projecting element for irradiating a detection target with light, and light reflected from the detection target for light emitted from the light projecting element. In a photoelectric sensor including a light receiving element that receives light through a light receiving lens and outputs a signal according to a light receiving level, and a signal conversion unit that converts the light receiving signal output from the light receiving element into a detection signal of a detection target. , The light receiving element,
A photoelectric element that outputs a light receiving signal according to an incident angle of reflected light from a detection target, and a distance signal converting unit that converts the light receiving signal output from the light receiving element into a distance signal, and an output of the distance signal converting unit. It is characterized in that a calculating means for squaring and a distance dependence removing means for removing the distance dependence of the received light signal based on the calculation result of the calculating means are provided.

According to a second aspect of the photoelectric sensor of the present invention, the distance dependence removing means adds multiplication means for multiplying the light reception signal by the output of the computing means, and adds a constant multiple of the light reception signal to the multiplication result. This is an addition means.

In the photoelectric sensor according to the third aspect of the present invention, the distance dependence removing means sets the output of the computing means to match the value obtained by subtracting a constant from the square value of the distance signal corresponding to the predetermined distance. In addition, the light projection amount adjusting means for adjusting the light projection amount of the light projecting element is used.

According to a fourth aspect of the photoelectric sensor of the present invention, the light receiving element is composed of a semiconductor position detecting element.

In a photoelectric sensor according to a fifth aspect of the present invention, the light receiving element is composed of at least two photodiodes.

According to a sixth aspect of the present invention, there is provided a method for correcting a received light signal level based on a received light signal output from a light receiving element according to an incident angle of reflected light on a detection target of light emitted from the light projecting element. It is characterized in that the distance from the light receiving lens to the detection target is measured, the measurement result is squared, the light receiving signal of the light receiving element is multiplied, and then a constant multiple of the light receiving signal is added.

According to a seventh aspect of the present invention, there is provided a method for correcting a light receiving signal level based on a light receiving signal output from a light receiving element according to an incident angle of reflected light on a detection target of light emitted from the light projecting element. It is characterized in that the distance from the light receiving lens to the detection target is measured, the measurement result is squared and then compared with a constant value, and the light projecting amount of the light projecting element is adjusted so that the two match.

[0012]

In the invention described in claim 1, the light receiving element outputs a light receiving signal corresponding to the incident angle of the reflected light on the detection target, and the light receiving signal is converted into the distance signal by the distance signal converting means. Further, the squared value of the distance signal is multiplied by the received light signal, and a constant multiple of the received light signal is added to remove the distance dependency of the received light signal. In this way, the received light signal based only on the reflectance of the detection target is obtained.

In the inventions described in claims 2 and 6, the square value of the distance signal is multiplied by the light receiving signal of the light receiving element, and the constant multiple of the light receiving signal is added to this. This is a value obtained by eliminating the decrease in the reflected light amount that is inversely proportional to the square of the distance between the detection target and the light receiving lens.

According to the invention described in claims 3 and 7, the light projection amount of the light projecting element is adjusted so that the square value of the distance signal matches a constant value obtained by subtracting a constant from the value corresponding to the light receiving signal level at a predetermined distance. Is adjusted. Therefore, by the feedback control based on the square value of the distance signal, the light projection amount of the light projecting element is increased or decreased according to the size of the distance between the detection target and the light receiving lens, and the distance between the detection target and the light receiving lens is changed. The reflected light that is not affected is received by the light receiving element.

In the invention described in claim 4, the light receiving element is a semiconductor position detecting element, and highly accurate detection can be performed.

In a fifth aspect of the invention, the light receiving element is composed of at least two photodiodes. Therefore, it is not necessary to use a relatively expensive photoelectric element for position detection, and the cost is reduced.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing the structure of a photoelectric sensor according to an embodiment of the present invention and changes in the optical path reflected from a detection target. The photoelectric sensor 1 includes a light projecting element 2 configured by a laser diode or the like, a light projecting lens 3, a light receiving lens 4, and a light receiving element 5 which is a photoelectric element for distance measurement such as a PSD (semiconductor position detecting element). The light emitted from the light projecting element 2 is focused by the lens 3 and is emitted to the detection target. The reflected light from the detection target passes through the light receiving lens 4 and is condensed on the light receiving element 5. P constituting the light receiving element 5
The SD receives the reflected light from the detection target in the range of the length 2x and outputs the both-end currents i _{1 and} i ₂ according to the condensing position.

In the positional relationship shown in FIG. 1, the following equation (1) is obtained based on the relationship of isotopes. Where the distance R
Is the center S _{O of the} light receiving element 5 from the front surface of the main body of the photoelectric sensor 1.
Is the distance from the detection target position P _O where the reflected light is condensed to the reference position P _r which is a distance _r away. This distance R is
It is expressed by equation (2) from equation (1). Similarly, this reference position P
Distance R + ΔR from _r to a position P _{1 that} is a distance ΔR away
Can be expressed by equation (3), and the distance ΔR can be expressed by equations (2) and (3) to (4).

When the reflected light from the detection object at the position P ₁ is focused on the light receiving position S ₁ of the light receiving element 5, the ratio of the currents i _{1 and} i ₂ across the light receiving element is expressed by equation (5). . this
(5) (6) is obtained from the formula, the distance Δx in the light-receiving element 5 from the receiving position S _r of the reflected light from the detection object located at the reference position P _r to the light receiving position S ₁ is (6) Therefore, it can be expressed by equation (7). By substituting equation (7) into equation (4), equation (8) can be obtained. In this way
The distance ΔR from the reference position P _r to the detection target is determined by the light receiving element 5
Can be obtained from the currents i _{1 and} i ₂ at both ends. But,
The problem here is the distance from the detection target to the light receiving lens 4. Therefore, the distance from Pr to the light receiving lens 4 is T, and the distance from P ₁ to the light receiving lens 4 is T + ΔT.
Then, equations (9) and (10) are obtained.

[0020] In the light-receiving element 5 capable of obtaining the distance signal as described above, the amount of received reflected light from the detection target is inversely proportional to the square of the distance from the detection target to the lens 4.

Therefore, the ratio of the received light amount W _{r at the} reference light receiving position S _r and the received light amount W ₁ at the light receiving position S ₁ can be expressed by the following equation (11), and this equation (11) is (12)
It can be expressed as an expression. Here, the received light amount W ₁ in the light receiving position S ₁ can be expressed as by using both ends currents i _1, i ₂ of the light-receiving element 5 (13). Here, K ² is a constant. Since the received light amount W ₁ of the light receiving position S ₁ is at the corrected so as to match the received light amount W _r in the light receiving position S _r of the reference, the light receiving output CW ₁ of the light receiving position S ₁ of the corrected (14) It becomes equal to the received light amount W _r as shown in. Substituting equation (14) into equation (12) yields equation (15),
Equation (20) is obtained by substituting Equation (13) into Equation 5 and rearranging. As is clear from the equation (20), a value that does not depend on the distance to the detected object can be obtained as the corrected light reception output CW ₁ .

[0022] FIG. 2 is a diagram showing a configuration of a signal conversion circuit of the photoelectric sensor. The currents i _{1 and} i ₂ across the light receiving element 5 are
It is input to the adders 13 and 15 and the subtractor 14 via 12. The output of the amplifier 11 is input to the adder 13 via the resistor r ₁ having the resistance ratio of 1, and the output of the amplifier 12 is input to the adder 13 via the resistor r _A of the resistance ratio A. As a result, the signal of (i ₁ + Ai ₂ ) is output from the adder 13. The output of the amplifier 11 is input to the subtractor 14 via the resistance r _B of the resistance ratio B, and the output of the amplifier 12 is input to the subtractor 14 via the resistance r _C of the resistance ratio C. Therefore, the subtractor 14 outputs a (Bi ₁ -Ci ₂ ) signal. Further, the outputs of the amplifiers 11 and 12 are input to the adder 15 via the resistor r ₁ having a resistance ratio of 1, respectively. Therefore, the adder 15 outputs the signal of (i ₁ + i ₂ ).

After the adder 13 and the subtractor 14, a divider 16 and a square operation circuit 17 are connected. The output signals of the adder 13 and the subtractor 14 are input to the divider 16, and the divider 16 outputs (Bi ₁ −Ci ₂ ) / (i ₁
The signal + Ai ₂ ) is output. The output signal of the divider 16 is input to the multiplier 18 via the squaring circuit 17. The output of the square calculation circuit 17 coincides with the square part in the first term on the right side of the equation (20). The output signal of the adder 15 is also input to the multiplier 18. By this, the multiplier 18
The output signal of is in agreement with the first term on the right side of the above equation (20). Further, the output signal of the multiplier 18 is input to the adder 19 via the resistance r ₁ having a resistance ratio of 1, and the output signal of the adder 15 is also input to the adder 19 via the resistance r _M of the resistance ratio M. It The input from the adder 15 to the adder 19 matches the second term on the right side of the expression (20). Therefore, the output to the adder 19 matches the right side of the expression (20). On the right side of the equation (20), A to C and M are constant K, reference distances R and α, β
And γ, and the respective numerical values of α, β, and γ are, as shown in equation (8), the focal length f, the arrangement interval D of the lens 4, and 1/2 of the length of the light receiving range of the light receiving element 5. Length x, distance x ′ from the central light receiving position S _{o in} the light receiving element 5 to the reference light receiving position S _r , and the vertical distance from the center of the lens 4 to the central light receiving position S _o of the light receiving element 5. It is a value that is determined by x _{o and} is a fixed value that depends on the arrangement state of the photoelectric sensor 1.

In this way, the added value of the current across the light receiving element 5 output from the adder 15 is corrected by the distance information output from the squaring circuit 17, and a constant multiple of the added value is used as the correction value. By adding the light receiving lens 4
It is possible to output the received light signal level that depends only on the reflectance of the detection target regardless of the distance from the detection target to the detection target.
That is, as shown in FIG. 3, the received light signal level output from the photoelectric sensor 1 is the threshold level C in the relationship between the received light signal level 51 of the reflected light from the mark and the received light signal level 52 of the reflected light from the base. In this case, the permissible variation range of the distance between the detection target and the front surface of the photoelectric sensor is ΔX, which is constant over a wide range, and the value depends only on the reflectance of the detection target without being affected by the distance to the detection target. can do.

FIG. 4 is a diagram showing a signal conversion circuit of an embodiment of the photoelectric sensor according to the invention described in claim 3. In FIG. Figure 2
The error detection circuit 21 detects an error between the output of the square calculation circuit 17 and the constant voltage V _0, and supplies the error signal to the drive circuit 22 of the light projecting element 2. The voltage V ₀ compared with the output of the square calculation circuit 17 in the error detection circuit 21 is the square calculation circuit 17 at the reference position.
When the output of V is V ₁ , this corresponds to the squared portion of the first term on the right side of equation (20) at the reference position. Therefore, if the voltage corresponding to the constant M in the second term is V _r , then from equation (21)
It becomes like the formula (22).

V _r = V ₁ + V _M (21) V ₀ = V ₁ = V _r −V _M (22) As described above, the voltage output from the squaring circuit 17 is
Since the value changes only by the distance to the detection target and is not affected by the reflectance of the detection target, the error detection circuit 21 obtains a distance error of the position of the detection target with respect to the reference position. Since the drive voltage of the light projecting element 2 in the drive circuit 22 is controlled so as to correct this distance error, when the distance to the detection target is longer than the distance to the reference position, the drive voltage of the light projecting element 2 is When the distance to the detection target is shorter than the distance to the reference position, the drive voltage of the light projecting element 2 is reduced and the light projection amount is decreased. In this way, by increasing or decreasing the light projection amount of the light projecting element 2 according to the distance to the detection target, the adder 15
It is possible to remove a distance error from the received light signal of the photoelectric sensor 1 to the detection target, which is the output of, and output a value that depends only on the reflectance of the detection target.

FIG. 5 is a block diagram showing a case where the output signal of the light receiving element is corrected using a digital circuit.
Each of the outputs i ₁ and i ₂ at both ends of the light receiving element 5 is an amplifier 1
1 and 12 are binarized via the A / D converter 31 and input to the CPU 32. The CPU 32 executes the processing shown in FIG. That is, the CPU 32 reads the current data across the light receiving element 5 from the A / D converter 31 at a predetermined timing (n1), and calculates the distance data D using the constants A to C stored in advance (n2). Furthermore, calculates the square value of the distance data D (n3), the sum of both ends output of the light receiving element 5 to the square value D ² of the distance data (i ₁ + i ₂₎ multiplied by (n4), which across the output M times the addition value (i ₁ + i ₂ ) of ( ₁ ) is added (n5), and this value is output as an analog signal via the D / A converter 33 (n6).

FIG. 7 is a block diagram showing a configuration in which the distance dependency of the light receiving signal is removed by changing the light projecting amount of the light projecting element 2 based on the light receiving signal of the light receiving element 5. A drive circuit 35 for a laser diode LD that constitutes the light projecting element 2 is connected to the CPU 32 via an error amplification circuit 34. In this configuration, as shown in FIG. 8, the CPU 32 reads the digital data of the current across the light receiving element 5 from the A / D converter 31 (n11) and calculates the distance data D and the square value of the distance data (n12). , N13). The CPU 32 compares the squared value D ² of the distance data with the reference value V ₀ and outputs the error to the error amplification circuit 34 (n15). Then, after a fixed time, digital data of both end signals is read again from the A / D converter 31 (n16), and the added value (i ₁ +
i ₂ ) is calculated as output data CW according to the amount of light received by the light receiving element 5, and this is output (n17, n1).
8). As described above, the light receiving amount is determined based on the light receiving signal of the light receiving element 5 after adjusting the light emitting amount from the light emitting element 2.

As described above, even if a digital circuit is used, the same effect as that of the configuration shown in FIGS. 2 and 4 can be obtained.

As shown in FIG. 9, two photodiodes 51 are used instead of the light receiving element 5 shown in FIG.
It can also be configured by a and 51b. This also applies to FIGS. 4, 5 and 7, and the photoelectric sensor of the present invention can be constructed at a lower cost than in the case of using a PSD.

[0031]

According to the first aspect of the invention, the distance signal representing the distance to the detection object is obtained based on the light receiving signal of the light receiving element, and the distance dependency of the light receiving signal is removed by using the distance signal. Since it is possible to obtain a received light signal based only on the reflectance of the detection target, it is not necessary to strictly define the distance to the detection target, and malfunction may occur due to deformation of the reflection surface of the detection target. Absent.

According to the second aspect of the present invention, the light receiving signal is multiplied by the square value of the distance signal based on the light receiving signal output from the light receiving element, and a constant multiple of the light receiving signal is added to it to obtain an arbitrary value. The light reception signal from the detection target at the position can be corrected to the light reception signal level of the light reflected from the detection target located at a certain distance from the photoelectric sensor.

According to the third aspect of the invention, the light projection amount of the light projecting element can be feedback-controlled so that the distance signal based on the light receiving signal output from the light receiving element becomes constant, and it is detected from the photoelectric sensor. Even when the distance to the target changes, a light reception signal that does not depend on the distance to the detection target can be obtained by irradiating the detection target with light having a light projection amount corresponding to the change.

According to the fourth aspect of the invention, the detection accuracy can be increased by using the semiconductor position detecting element as the light receiving element.

According to the invention described in claim 5, a relatively inexpensive photodiode can be used as the light receiving element, and there is an advantage that the photoelectric sensor of the invention can be constructed at a low cost.

According to the invention described in claims 6 and 7, the correction for removing the distance dependency of the received light signal can be executed by the digital circuit.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of a photoelectric sensor that is an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a main part of a photoelectric sensor according to a second aspect of the invention.

FIG. 3 is a diagram showing a relationship between a received light signal level of a photoelectric sensor according to an embodiment of the present invention and a distance to a detection target.

FIG. 4 is a circuit diagram showing a configuration of a main part of a photoelectric sensor according to an embodiment of the invention described in claim 3.

FIG. 5 is a block diagram showing a configuration of a photoelectric sensor to which a method of correcting a received light signal level according to the embodiment of the invention described in claim 4 is applied.

FIG. 6 is a flowchart showing a processing procedure in a control unit of the photoelectric sensor.

FIG. 7 is a block diagram showing a configuration of a control unit of a photoelectric sensor to which a method for correcting a light reception signal level according to the invention described in claim 5 is applied.

FIG. 8 is a flowchart showing a processing procedure of the control unit.

FIG. 9 is a circuit diagram showing a configuration of a main part of a photoelectric sensor according to another embodiment of the present invention.

FIG. 10 is a diagram showing a relationship between a light reception signal level and a distance to a detection target in a conventional photoelectric sensor.

[Explanation of symbols]

 1-Photoelectric sensor 2-Emitting element 4-Lens 5-Light receiving element

Claims (7)

[Claims] 1. A light projecting element for irradiating a detection target with light, and light reflected by the detection target of light emitted from the light projecting element is received through a light receiving lens and a signal corresponding to a light receiving level is output. A light receiving element, and signal conversion means for converting a light receiving signal output from the light receiving element into a detection signal of a detection target,
In the photoelectric sensor provided with, the light receiving element is a photoelectric element that outputs a light receiving signal according to the incident angle of the reflected light from the detection target, the distance to convert the light receiving signal output from the light receiving element into a distance signal The present invention is characterized in that a signal conversion means, a calculation means for squaring the output of the distance signal conversion means, and a distance dependence removing means for removing the distance dependence of the received light signal based on the calculation result of the calculation means are provided. Photoelectric sensor. 2. The photoelectric conversion device according to claim 1, wherein the distance dependence removing means is a multiplying means for multiplying the light receiving signal by the output of the computing means and an adding means for adding a constant multiple of the light receiving signal to the multiplication result. Sensor. 3. The distance dependence removing means adjusts the light projecting amount of the light projecting element so that the output of the computing means coincides with a value obtained by subtracting a constant from the square value of the distance signal corresponding to the predetermined distance. The photoelectric sensor according to claim 1, which is a light emission amount adjusting means. 4. The photoelectric sensor according to claim 1, wherein the light receiving element is a semiconductor position detecting element. 5. The photoelectric sensor according to claim 1, wherein the light receiving element is composed of at least two photodiodes. 6. The distance from the light receiving lens to the detection target is measured based on a light receiving signal output from the light receiving device according to the incident angle of the reflected light on the detection target of the light emitted from the light projecting element, and this measurement result Is squared and multiplied by the received light signal of the light receiving element, and then a constant multiple of the received light signal is added, and the received light signal level of the photoelectric sensor is corrected. 7. The distance from the light receiving lens to the detection target is measured based on the light reception signal output from the light reception device according to the incident angle of the reflected light on the detection target of the light emitted from the light projecting element, and this measurement result Is squared and then compared with a constant value, and the light projection amount of the light projection element is adjusted so that the two match in this comparison.