JP2968423B2 - Photoelectric sensor and method for correcting received light signal level - Google Patents

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 reading the presence or absence of a detection object or a color change or shading of the detection object, and a method of correcting a light receiving signal level thereof.

[0002]

2. Description of the Related Art A photoelectric sensor including a light projecting element and a light receiving element is used to read the presence or absence of an object moving on a conveyor and the color change or shading of the object. In this photoelectric sensor, light is emitted from a light emitting element to an object to be detected, and reflected light from the object is received by a light receiving element. When the detection target does not exist at the light irradiation position of the light emitting sensor, the light receiving element does not receive the light. Therefore, the presence or absence of the detection target can be detected based on the light receiving signal level output from the light receiving element. Similarly, when the detection target has a color change or shading, the amount of light received by the light receiving element changes due to a change in the reflectance due to the shading of the detection target or the like. 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. The signal level is determined by the curve 91 or 9 in FIG. 10 even if the reflectance of the detection target is constant.
As shown in FIG. 2, it greatly changes depending on the distance between the detection target and the light receiving lens. For this reason, when detecting a detection target based on a difference in the amount of reflected light from an 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 light receiving signal level curve 91 and the light receiving signal level curve 92 of the reflected light from the background, the allowable variation range of the distance between the detection target and the front surface of the photoelectric sensor is as follows. Since it is narrow as Δx, the sensitivity adjustment of the received light signal must be strictly maintained, and the transport accuracy needs to be maintained high to make the transport position of the detection target appropriate. In particular, there is a problem in that a malfunction occurs when detecting light and shade or when the detection surface has irregularities.

An object of the present invention is to correct the light receiving signal level of a light receiving element constituting a photoelectric sensor using distance information between an object to be detected and a light receiving lens, thereby removing the distance dependency of the light receiving signal. 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 receiving signal level thereof.

[0005]

According to a first aspect of the present invention, there is provided a photoelectric sensor which irradiates light to a detection target, and light reflected from the detection target of light emitted from the light projection element. A light-receiving element that receives light through a light-receiving lens and outputs a signal corresponding 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 to be detected. The light receiving element is
A photoelectric element for outputting a light receiving signal corresponding to the incident angle of the reflected light from the detection target, wherein the distance signal converting means for converting the light receiving signal output from the light receiving element into a distance signal; and an output of the distance signal converting means. It is characterized by comprising a calculating means for squaring and a distance dependency removing means for removing the distance dependency of the received light signal based on the calculation result of the calculating means.

According to a second aspect of the present invention, in the photoelectric sensor, the distance dependence removing means multiplies a light receiving signal by an output of the arithmetic means and adds a constant multiple of the light receiving signal to a result of the multiplication. This is an addition means.

According to a third aspect of the present invention, in the photoelectric sensor, the distance-dependency removing means controls the output of the calculating means to be equal to a value obtained by subtracting a constant from a square value of a distance signal corresponding to a predetermined distance. And a projection light amount adjusting means for adjusting the projection light amount of the light projection element.

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

According to a fifth aspect of the present invention, in the photoelectric sensor, the light receiving element includes at least two photodiodes.

According to a sixth 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 emitting element. The distance from the light receiving lens to the detection target is measured, the result of this measurement is squared, the light receiving signal of the light receiving element is multiplied, and 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 emitting element. The distance from the light receiving lens to the detection target is measured, the result of the measurement is squared, and the result is compared with a fixed value. In this comparison, the amount of light emitted from the light emitting element is adjusted so that the two coincide.

[0012]

According to the first aspect of the present invention, a light receiving signal is output from the light receiving element according to the incident angle of the reflected light on the detection target, and the light receiving signal is converted into a distance signal by the distance signal converting means. Further, by multiplying the square value of the distance signal by the light receiving signal and adding a constant multiple of the light receiving signal, the distance dependency of the light receiving signal is removed. In this manner, a light receiving signal based on only the reflectance of the detection target is obtained.

According to the second and sixth aspects of the present invention, the square value of the distance signal is multiplied by the light receiving signal of the light receiving element, and a constant multiple of the light receiving signal is added thereto. This is a value from which a decrease in the amount of reflected light that is inversely proportional to the square of the distance between the detection target and the light receiving lens is removed.

According to the third and seventh aspects of the present invention, the light projecting amount of the light emitting element is adjusted so that the square value of the distance signal matches a constant value obtained by subtracting a certain constant from a 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 amount of light emitted from the light emitting element is increased or decreased according to the magnitude of the distance between the detection target and the light receiving lens, and the distance between the detection target and the light receiving lens changes. Unaffected reflected light is received by the light receiving element.

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

In the invention described in claim 5, the light receiving element is constituted by 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]

FIG. 1 is a diagram showing a configuration of a photoelectric sensor according to an embodiment of the present invention and a change in an optical path reflected from an object to be detected. The photoelectric sensor 1 includes a light projecting element 2 including a laser diode, 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 converged by the lens 3 and is applied to a detection target. Light reflected from the detection target passes through the light receiving lens 4 and is collected on the light receiving element 5. P constituting the light receiving element 5
SD receives the reflected light from the detection object in the length range of 2x, and outputs both ends currents i _1, i ₂ corresponding to the condensing position.

In the positional relationship shown in FIG. 1, the following formula (1) is obtained based on the relationship between the isotopic angles. 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 a distance from the detection target position P _O where the reflected light is converged to the reference position _Pr at a distance _r . This distance R is
Equation (1) is expressed by equation (2). Similarly, the reference position P
Distance R + ΔR from _r to a position P ₁ distant by distance ΔR
Can be expressed by the equation (3), and the distance ΔR can be expressed by the equations (2) and (3) to (4).

When the reflected light from the object to be detected at the position P ₁ is condensed on the light receiving position S ₁ of the light receiving element 5, the ratio between the currents i _{1 and} i ₂ at both ends of the light receiving element is expressed by the following 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) To (7). By substituting equation (7) into equation (4), equation (8) can be obtained. In this way,
The distance ΔR from the reference position _Pr to the detection target is determined by the light receiving element 5
From both ends currents i _{1 and} i ₂ . But,
What matters 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 T, the distance from P ₁ to the light receiving lens 4 T + [Delta] T
Then, equations (9) and (10) are obtained.

[0020] As described above, in the light receiving element 5 that can obtain a distance signal, the amount of light reflected from the detection target is inversely proportional to the square of the distance from the detection target to the lens 4.

[0021] Thus, the ratio of the amount of light received W ₁ in the light receiving amount W _r and the light receiving position S ₁ at the reference light receiving position S _r can be represented by the following equation (11), the (11) equation (12)
It can be expressed as an equation. Here, the amount of received light W ₁ at the light receiving position S ₁ can be expressed as in equation (13) using the currents i _{1 and} i ₂ across the light receiving element 5. 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) equal to the amount of light received W _r as shown in FIG. This equation (14) is substituted into equation (12) to obtain equation (15).
Equation (20) is obtained by substituting equation (13) into equation (5) and rearranging. The (20) As is apparent from the equation, it is possible to obtain a value of being dependent on the distance to the detection object as received light output CW ₁ after correction.

[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 at both ends of the light receiving element 5 are
The signal is input to adders 13, 15 and a subtractor 14 via 12. The output of the amplifier 11 is input to the adder 13 via a resistor r ₁ having a resistance ratio of 1, and the output of the amplifier 12 is input via a resistor r _A having a resistance ratio A. As a result, a 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 a resistor r _B having a resistance ratio B, and the output of the amplifier 12 is input via a resistor r _C having a resistance ratio C. Therefore, a signal of (Bi ₁ −Ci ₂ ) is output from the subtractor 14. Further, the outputs of the amplifiers 11 and 12 are input to the adder 15 via a resistor r ₁ having a resistance ratio of 1. Therefore, the adder 15 outputs a signal of (i ₁ + i ₂ ).

A divider 16 and a square operation circuit 17 are connected to the subsequent stage of the adder 13 and the subtractor 14. The output signals of the adder 13 and the subtractor 14 are input to a divider 16, which outputs (Bi ₁ −Ci ₂ ) / (i ₁ ).
+ Ai ₂ ) is output. The output signal of the divider 16 is input to the multiplier 18 via the square operation circuit 17. The output of the square operation circuit 17 matches 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. This allows the multiplier 18
Output signal coincides 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 a resistor r ₁ having a resistance ratio of 1, and the output signal of the adder 15 is also input to the adder 19 via a resistor r _M having a resistance ratio of M. You. The input from the adder 15 to the adder 19 matches the second term on the right side of the equation (20). Therefore, the output to the adder 19 matches the right side of the equation (20). On the right side of this equation (20), A to C and M are constants K, reference distances R and α, β
The values of α, β, and γ are, as shown in equation (8), the focal length f, the distance D between the lenses 4, and の of the length of the light receiving range of the light receiving element 5. The length x, the distance x ′ from the central light receiving position S _o of 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 These values are determined by x _o , and are all fixed values depending on the arrangement state of the photoelectric sensor 1.

In this way, the added value of the currents at both ends of 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 corrected value. By adding, the light receiving lens 4
A light receiving signal level that depends only on the reflectance of the detection target can be output regardless of the distance from the detection target to the detection target.
That is, as shown in FIG. 3, the light receiving signal level output from the photoelectric sensor 1 is different from the threshold level C in the relationship between the light receiving signal level 51 of the light reflected from the mark and the light receiving signal level 52 of the light reflected from the base. In this case, the allowable 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 is not affected by the distance to the detection target, and depends only on the reflectance of 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 third aspect of the present invention. FIG.
In the circuit shown in (1), the error of the output of the square operation circuit 17 is detected by an error detection circuit 21 from the constant voltage V _0, and this error signal is supplied to the drive circuit 22 of the light emitting element 2. The voltage V ₀ compared with the output of the square operation circuit 17 in the error detection circuit 21 is equal to the voltage of the square operation circuit 17 at the reference position.
When the output of the V _1, which corresponds to (20) below the right side the square portion of the paragraph at the reference position. Thus, from the voltage corresponding to the constant M in the same paragraph and V _r (21) formula
Equation (22) is obtained.

V _r = V ₁ + V _M (21) V ₀ = V ₁ = V _r −V _M (22) As described above, the voltage output from the square operation circuit 17 is
Since the value changes only depending on the distance to the detection target and is not affected by the reflectance of the detection target, the error detection circuit 21 calculates the distance error of the position of the detection target with respect to the reference position. Since the driving voltage of the light emitting element 2 in the driving circuit 22 is controlled so as to correct the distance error, when the distance to the detection target is longer than the distance to the reference position, the driving voltage of the light emitting element 2 is reduced. When the distance to the detection target is shorter than the distance to the reference position, the driving voltage of the light projecting element 2 is reduced and the projected light quantity is reduced. By increasing or decreasing the light projection amount of the light projecting element 2 in accordance with the distance to the detection target, the adder 15
The distance error from the light receiving signal of the photoelectric sensor 1 which is the output of the photoelectric sensor 1 to the detection target can be removed, and a value depending only on the reflectance of the detection target can be output.

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
The signals are binarized via an A / D converter 31 via the first and the second 12 and input to the CPU 32. The CPU 32 executes the processing shown in FIG. That is, the CPU 32 reads current data on both ends of the light receiving element 5 from the A / D converter 31 at a predetermined timing (n1), and calculates distance data D using 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 Is multiplied by M times (i ₁ + i ₂ ) (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 dependence 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. The drive circuit 35 of the laser diode LD constituting the light projecting element 2 is connected to the CPU 32 via an error amplifier circuit 34. In this configuration, as shown in FIG. 8, the CPU 32 reads the digital data of the current at both ends of the light receiving element 5 from the A / D converter 31 (n11), calculates the distance data D, and calculates the square value of the distance data (n12). , N13). CPU32 compares the squared value D ² of the distance data and the reference value V _0, and outputs the error to the error amplifier 34 (n15). After a certain period of time, the digital data of the signal at both ends is read out again from the A / D converter 31 (n16), and the added value (i ₁ +
i ₂ ) is calculated as output data CW corresponding to the amount of light received by the light receiving element 5 and 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 projecting amount from the light projecting element 2.

As described above, even if a digital circuit is used, the same effect as 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.
a, 51b. This is the same in FIGS. 4, 5, and 7, and the photoelectric sensor of the present invention can be configured at a lower cost as compared with the case where a PSD is used.

[0031]

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

According to the second aspect of the present invention, an arbitrary value is obtained by multiplying the square of the distance signal based on the light receiving signal output from the light receiving element by the light receiving signal and adding a constant multiple of the light receiving signal thereto. 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 fixed distance from the photoelectric sensor.

According to the third aspect of the present invention, it is possible to feedback-control the amount of light emitted from the light emitting element so that the distance signal based on the light receiving signal output from the light receiving element becomes constant, and the detection from the photoelectric sensor is performed. Even when the distance to the target has changed, a light receiving signal independent of the distance to the detection target can be obtained by irradiating the detection target with light having a projected light amount corresponding to the change.

According to the invention described in claim 4, the detection accuracy can be improved by using the semiconductor position detecting element as the light receiving element.

According to the fifth aspect of the present invention, a relatively inexpensive photodiode can be used as the light receiving element, and there is an advantage that the photoelectric sensor of the present invention can be configured at low cost.

According to the sixth and seventh aspects of the invention, the correction for removing the distance dependency of the received light signal can be executed by the digital circuit.

[Brief description of the drawings]

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

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

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

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 light receiving signal level according to an 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 of correcting a light receiving 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 receiving signal level and a distance to a detection target in a conventional photoelectric sensor.

[Explanation of symbols]

 1-photoelectric sensor 2-light emitting element 4-lens 5-light receiving element

Continuation of front page (58) Fields investigated (Int.Cl. ⁶ , DB name) G01C 3/00-3/32 G01B 11/00-11/30 102 G01V 8/10

Claims (7)

(57) [Claims] A light projecting element for irradiating light to the object to be detected, and a reflected light of the light emitted from the light projecting element on the object to be detected is received via a light receiving lens to output a signal corresponding to a light receiving level. A light receiving element, and signal conversion means for converting a light receiving signal output from the light receiving element into a detection signal to be detected,
Wherein the light receiving element is a photoelectric element that outputs a light receiving signal in accordance with an incident angle of reflected light from a detection target, and converts the light receiving signal output from the light receiving element into a distance signal. Signal converting means, calculating means for squaring the output of the distance signal converting means, and distance dependency removing means for removing the distance dependency of the received light signal based on the calculation result of the calculating means. Photoelectric sensor. 2. The photoelectric conversion device according to claim 1, wherein said distance dependency removing means is a multiplying means for multiplying a light receiving signal by an output of said calculating means, and an adding means for adding a constant multiple of the light receiving signal to a result of the multiplication. Sensor. 3. The distance dependency removing means adjusts the light projecting amount of the light emitting element such that the output of the calculating means coincides with a value obtained by subtracting a certain constant from a square value of a distance signal corresponding to a predetermined distance. The photoelectric sensor according to claim 1, wherein the photoelectric sensor is a projection light amount adjusting unit. 4. The photoelectric sensor according to claim 1, wherein said light receiving element is a semiconductor position detecting element. 5. The photoelectric sensor according to claim 1, wherein said light receiving element comprises at least two photodiodes. 6. A distance from a light receiving lens to a detection target is measured based on a light receiving signal output from the light receiving element in accordance with an incident angle of reflected light on a detection target of light emitted from the light projecting element. And multiplying the received light signal of the light receiving element by a square operation, and then adding a constant multiple of the received light signal to correct the light receiving signal level of the photoelectric sensor. 7. A distance from a light receiving lens to a detection target is measured based on a light receiving signal output from the light receiving element according to an incident angle of reflected light on a detection target of light emitted from the light projecting element, and the measurement result is obtained. , And comparing with a constant value, and adjusting the amount of light emitted from the light emitting element so that the two values match in this comparison.