JP2015115182A - Photoelectric switch and object detection system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photoelectric switch and an object detection system which can detect both an opaque body and a mirror surface reflector and in which deterioration in detection accuracy due to installation inclination of a polarization filter is improved.SOLUTION: A reflector 4 has characteristics for reflecting light including circular polarization rotating in the same direction as incident light. A light projection side-polarization filer 3 and a light receiving side-polarization 5 have characteristics passing only a polarization component in a specific rotation direction out of the incident light therethrough. The rotation directions of circular polarization through which the light projection side-polarization filer 3 and the light receiving side-polarization 5 pass are made to have the same direction.

Description

  The present invention relates to a polarized reflector type photoelectric switch using a circular polarization filter, and an object detection system using the photoelectric switch.

  Conventionally, a polarized reflector type photoelectric switch has been used to detect a product flowing on a production line of a factory. Hereinafter, when simply described as “photoelectric switch” in the present specification, it refers to a polarized reflector type photoelectric switch.

The configuration of a binocular photoelectric switch using a conventional linear polarization filter will be described with reference to FIG.
The conventional photoelectric switch is opposed to the light projecting element 21 and the light projecting lens 22, the reflector 24 facing the light projecting lens 22 through the light projecting side polarizing filter 23, and the reflector 24 through the light receiving side polarizing filter 25. A light receiving lens 26 and a light receiving element 27 are provided.

  The light projecting element 21 is an element such as an LED. The light projecting lens 22 is a lens that projects light emitted from the light projecting element 21 onto the reflector 24 via the light projecting side polarizing filter 23. The light projecting side polarization filter 23 is a linear polarization filter that allows only linearly polarized light in the vertical direction to pass therethrough. The reflector 24 has a characteristic of retroreflecting incident light and distorting polarized light. The light-receiving side polarizing filter 25 is a linear polarizing filter that passes only the light of the linearly polarized light in the horizontal direction out of the light reflected by the reflector 24. The light receiving lens 26 is a lens that focuses the light that has passed through the light receiving side polarizing filter 25 onto the light receiving element 27. The light receiving element 27 is an element that converts the light intensity of the received light into an electric signal and outputs it.

Next, the operation of the conventional photoelectric switch when there is no sensing object will be described with reference to FIG.
First, the light projecting element 21 emits light A including light having a plurality of random polarization directions. Next, the light projecting side polarization filter 23 allows only the linearly polarized light B included in the light A to pass therethrough. Next, the reflector 24 distorts the polarized light while retroreflecting the light B, and reflects the light C that has become elliptically polarized light in either the left or right direction. Next, the light-receiving side polarizing filter 25 allows only the linearly polarized light D included in the light C to pass therethrough.
Finally, the light receiving element 27 receives the light D and transmits a signal corresponding to the light intensity of the light D to a detection unit (not shown). The detection unit receives the signal and determines that the photoelectric switch is ON and “the detection object does not exist”.

Next, the operation of the conventional photoelectric switch when the detection object is an opaque body such as paper will be described with reference to FIG. Hereinafter, when simply described as “opaque body” in the present specification, it means an ideal opaque body that does not reflect light at all or diffuses and reflects only a very small amount of light that does not affect detection.
First, the light projecting element 21 emits light A including light having a plurality of random polarization directions. Next, the light projecting side polarization filter 23 allows only the linearly polarized light B included in the light A to pass therethrough. Next, the opaque body blocks the light B without reflecting it.
Therefore, the light receiving element 27 does not receive light and does not transmit a signal to a detection unit (not shown). The detection unit determines that the photoelectric switch is OFF and “the detection object is present”.

Next, the operation of a conventional photoelectric switch when the detection object is a specular reflector such as a metal will be described with reference to FIG.
First, the light projecting element 21 emits light A including light having a plurality of random polarization directions. Next, the light projecting side polarization filter 23 passes only the linearly polarized light B in the vertical direction included in the light A. Next, the specular reflector specularly reflects the light B on the surface, and reflects the linearly polarized light C ′ in the vertical direction in the same manner as the light B. Next, the light-receiving side polarization filter 25 blocks the linearly polarized light C ′ in the vertical direction without passing it.
Therefore, the light receiving element 27 does not receive light and does not transmit a signal to a detection unit (not shown). The detection unit determines that the photoelectric switch is OFF and “the detection object is present”.

  As described above, an opaque body such as paper and a specular reflector such as metal can be detected using a conventional photoelectric switch. In particular, in the configuration in which the presence / absence of the detection object is determined based on the presence / absence of light reception by the light receiving element 27, the light receiving element 27 becomes It prevents receiving the specular reflection light from the specular reflector so that the specular reflector can be detected.

However, in the conventional photoelectric switch, if there is a deviation in the orthogonal relationship between the polarization direction of the light projecting side polarizing filter 23 and the polarization direction of the light receiving side polarizing filter 25, a mirror surface malfunction is likely to occur when detecting a specular reflector. There was a problem that the detection accuracy deteriorated.
That is, when installing the light projecting side polarizing filter 23 and the light receiving side polarizing filter 25, one of them is inclined in the in-plane direction perpendicular to the optical axis, and the polarization direction of the light projecting side polarizing filter 23 and the light receiving side polarizing filter 25 are set. 9, the light B that has passed through the light-projecting side polarizing filter 23 and the light C ′ that is specularly reflected by the specular reflector are slightly received-side polarized light, as shown in FIG. The light in the polarization direction of the filter 25 is included.
Therefore, the light receiving element 27 receives the light D ′ that has passed through the light receiving side polarizing filter 25 and transmits a signal corresponding to the light intensity of the light D ′ to a detection unit (not shown). The detection unit receives the signal and determines that the photoelectric switch is ON and “the detection object does not exist” despite the presence of the specular reflector.

On the other hand, Patent Document 1 discloses a coaxial photoelectric switch using a circular polarizing filter.
The configuration of a coaxial photoelectric switch using the circularly polarizing filter according to Patent Document 1 will be described with reference to FIG.
The photoelectric switch according to Patent Document 1 includes a light projecting element 31 oriented in a direction orthogonal to the light receiving axis direction, a light receiving element 32 oriented in the light receiving axis direction, and 45 ° with respect to the light projecting element 31 and the light receiving element 32, respectively. Opposite the lens 34 through the half mirror 33 inclined and opposed, the lens 34 facing the light receiving axis direction and inclined by 45 ° with respect to the half mirror 33, and the light transmitting / receiving side polarizing filter 35 and the reflector side polarizing filter 36. The reflector 37 is provided. The half mirror 33 is configured to reflect the light emitted from the light projecting element 31 toward the lens 34 and pass the light received through the lens 34.

The light transmitting / receiving side polarizing filter 35 includes a linear polarizing filter 351 that allows only linearly polarized light in the vertical direction to pass through, and a quarter wavelength plate 352 that is bonded to the linear polarizing filter 351 with a delay axis inclined by 45 °. A circularly polarizing plate.
When light is incident from the linear polarizing filter 351 side, first, the linear polarizing filter 351 passes only linearly polarized light in the vertical direction. Next, the quarter wavelength plate 352 converts the linearly polarized light in the vertical direction into circularly polarized light. On the other hand, when light is incident from the ¼ wavelength plate 352 side, the linear polarization filter 351 allows only linearly polarized light in the vertical direction to pass therethrough.

The reflector-side polarizing filter 36 includes a linear polarizing filter 361 that passes only linearly polarized light in the horizontal direction and a quarter-wave plate 362 that is bonded to the linear polarizing filter 361 with a delay axis inclined by 45 °. It is a circularly polarizing plate.
When light enters from the linear polarizing filter 361 side, first, the linear polarizing filter 361 passes only the linearly polarized light in the horizontal direction. Next, the quarter wavelength plate 362 converts the linearly polarized light in the horizontal direction into circularly polarized light. On the other hand, when light is incident from the ¼ wavelength plate 362 side, the linear polarization filter 361 allows only linearly polarized light in the horizontal direction to pass therethrough.

  The light projecting / receiving side polarizing filter 35 and the reflector side polarizing filter 36 are disposed facing each other such that the quarter wavelength plate 352 side and the quarter wavelength plate 362 side face each other. That is, when the light receiving axis direction is viewed from the lens 34 side, the rotational direction of the circularly polarized light after passing through the light projecting / receiving side polarizing filter 35 is opposite to the rotational direction of the circularly polarized light after passing through the reflector side polarizing filter 36. Configured to be oriented.

  The reflector 37 is a corner cube reflector having a characteristic of recursively reflecting incident light and distorting polarized light.

Next, the operation of the photoelectric switch according to Patent Document 1 when no sensing object is present will be described with reference to FIG.
First, the light projecting element 31 emits light A including light having a plurality of random polarization directions. Next, the light projecting / receiving side polarizing filter 35 converts only the linearly polarized light in the vertical direction included in the light A into circularly polarized light B in the predetermined direction. Next, the reflector-side polarizing filter 36 allows only horizontal linearly polarized light included in the light B to pass therethrough. Next, the reflector 37 recursively reflects the linearly polarized light, distorts the polarized light, and reflects the light that has become elliptically polarized light that rotates in either the left or right direction. Next, the reflector-side polarizing filter 36 converts only the light in the horizontal direction included in the elliptically polarized light into circularly polarized light C that rotates in the direction opposite to the predetermined direction. Next, the light projecting / receiving side polarizing filter 35 allows only the linearly polarized light D included in the light C to pass therethrough.
Finally, the light receiving element 32 receives the light D, and the photoelectric switch is turned on. In this case, it is determined that “the detected object does not exist”.

Next, the operation of the photoelectric switch according to Patent Document 1 when the detected object is an opaque body such as paper will be described with reference to FIG.
First, the light projecting element 31 emits light A including light having a plurality of random polarization directions. Next, the light projecting / receiving side polarization filter 35 converts only the linearly polarized light in the vertical direction included in the light A into the circularly polarized light B rotating in a predetermined direction. Next, the opaque body blocks the light B without reflecting it.
Therefore, the light receiving element 27 does not receive light and the photoelectric switch is turned off. In this case, it is determined that “the detected object exists”.

  As described above, an opaque body such as paper can be detected using the photoelectric switch according to Patent Document 1. In particular, since both the light projecting / receiving side polarizing filter 35 and the reflector side polarizing filter 36 are circularly polarizing plates, even if the polarizing filter is installed, even if it is inclined in the in-plane direction perpendicular to the optical axis, the detection accuracy is increased. Will not deteriorate.

However, the photoelectric switch of Patent Document 1 has a problem that a specular reflector cannot be detected.
That is, when the sensing object is a specular reflector, as shown in FIG. 12, the specular reflector specularly reflects light B, and reflects circularly polarized light C ′ whose rotation direction is opposite to that of light B. Next, the light projecting / receiving side polarizing filter 35 passes the linearly polarized light D ′ included in the light C ′.
Therefore, the light receiving element 32 receives the light D ′ and the photoelectric switch is turned on. In this case, it is determined that “the detected object does not exist” despite the presence of the specular reflector.

JP 2008-112629 A (see paragraphs [0057] to [0073], FIGS. 1 to 4 etc.)

  As described above, the conventional photoelectric switch can detect the specular reflector, but has a problem that the detection accuracy deteriorates due to the installation inclination of the polarizing filter. On the other hand, the photoelectric switch according to Patent Document 1 has a problem that the specular reflector cannot be detected while the detection accuracy is not deteriorated due to the installation inclination of the polarizing filter.

  The present invention has been made to solve the above-described problems, and is a photoelectric switch and object detection that can detect both an opaque body and a specular reflector, and that has improved the deterioration of detection accuracy due to the inclination of a polarizing filter The purpose is to provide a system.

  The photoelectric switch according to the present invention includes a light projecting unit, a reflector facing the light projecting unit through the light projecting side polarizing filter, and a light receiving unit facing the reflector through the light receiving side polarizing filter. Reflects light that contains circularly polarized light that rotates in the same direction as the incident light, and the light-projecting side and light-receiving side polarizing filters transmit only the circularly polarized light component in the specific rotation direction of the incident light. The rotation direction of the circularly polarized light passing through the light projecting side polarizing filter and the light receiving side polarizing filter is the same direction.

  According to this invention, since it comprised as mentioned above, both an opaque body and a specular reflector can be detected, and degradation of the detection accuracy by the installation inclination of a polarizing filter can be improved.

It is explanatory drawing which shows the structure and operation | movement of a photoelectric switch which concern on Embodiment 1 of this invention (when a detection object does not exist). It is explanatory drawing which shows the structure and operation | movement of a photoelectric switch which concern on Embodiment 1 of this invention (when a detection object is an opaque body). It is explanatory drawing which shows the structure and operation | movement of a photoelectric switch which concern on Embodiment 1 of this invention (when a detection object is a specular reflector). It is explanatory drawing which shows the structure and operation | movement of a photoelectric switch which concern on the modification of Embodiment 1 of this invention. It is explanatory drawing which shows the structure and operation | movement of a photoelectric switch which concern on the modification of Embodiment 1 of this invention. It is explanatory drawing which shows the structure and operation | movement of the conventional photoelectric switch (when a detection object does not exist). It is explanatory drawing which shows the structure and operation | movement of the conventional photoelectric switch (when a detection object is an opaque body). It is explanatory drawing which shows the structure and operation | movement of the conventional photoelectric switch (when a detection object is a specular reflector). It is explanatory drawing which shows the structure and operation | movement of the conventional photoelectric switch (when a mirror surface malfunction occurs). It is explanatory drawing which shows the structure and operation | movement of a photoelectric switch which concern on patent document 1 (when a detection object does not exist). It is explanatory drawing which shows the structure and operation | movement of a photoelectric switch which concern on patent document 1 (when a detection object is an opaque body). It is explanatory drawing which shows the structure and operation | movement of a photoelectric switch which concern on patent document 1 (when a detection object is a specular reflector).

Hereinafter, in order to explain the present invention in more detail, modes for carrying out the present invention will be described with reference to the accompanying drawings.
Embodiment 1 FIG.
First, the configuration of the photoelectric switch according to the first embodiment of the present invention will be described with reference to FIG. The photoelectric switch according to Embodiment 1 includes a light projecting element 1 and a light projecting lens 2, a reflector 4 that faces the light projecting lens 2 through a light projecting side polarizing filter 3, and a reflector through a light receiving side polarizing filter 5. 4 includes a light receiving lens 6 and a light receiving element 7 facing each other.

  The light projecting element 1 is an element such as an LED. The light projecting lens 2 is a lens that projects the light emitted from the light projecting element 1 onto the reflector 4 via the light projecting side polarizing filter 3. The light projecting element 1 and the light projecting lens 2 constitute a light projecting unit.

The light-projecting side polarization filter 3 passes only circularly polarized light that rotates in a single direction out of light incident from the front surface, and circularly polarized light that rotates in the same direction as the single direction among light incident from the back surface. It is a circularly polarizing filter having the characteristic of passing only light.
Further, the light projecting side polarizing filter 3 is configured as a separate member from the light projecting unit. As an example, it is configured as a film member attached to the surface of the light projecting lens 2 or an attachment member externally attached to the light projecting portion.

  The reflector 4 has a characteristic of reflecting the light including the circularly polarized light rotating in the same direction as the incident light while retroreflecting the incident light. As an example, it is composed of a corner cube reflector in which a corner cube is formed on an acrylic resin plate.

  The light receiving side polarizing filter 5, like the light projecting side polarizing filter 3, passes only circularly polarized light rotating in a single direction out of the light incident from the front surface and is unidirectional among the light incident from the back surface. Is a circularly polarizing filter having a characteristic of passing only circularly polarized light that rotates in the same direction.

  The light receiving lens 6 is a lens that condenses the light that has passed through the light receiving side polarizing filter 5 onto the light receiving element 7. The light receiving element 7 is an element that receives the light collected by the light receiving lens 6, converts the light intensity into an electric signal, and outputs the electric signal to a detection unit (not shown). The light receiving element 7 and the light receiving lens 6 constitute a light receiving unit.

  Further, the light receiving side polarizing filter 5 is configured as a separate member from the light receiving unit. As an example, it is configured as a film member attached to the surface of the light receiving lens 6 or an attachment member attached to the light receiving portion.

  In addition, the rotation direction of the circularly polarized light passing through the light projecting side polarizing filter 3 and the light receiving side polarizing filter 5 is assumed to be the same direction.

Next, the operation of the photoelectric switch according to Embodiment 1 when there is no sensing object will be described with reference to FIG.
First, the light projecting element 1 emits light A including light in a plurality of random polarization directions. Next, the light projecting side polarizing filter 3 allows only circularly polarized light B included in the light A that rotates in a predetermined direction to pass therethrough. Next, the reflector 4 reflects the light C that has been elliptically polarized light that recursively reflects the light B and distorts the polarized light and rotates in the same direction as the circularly polarized light of the light B. Next, the light-receiving side polarizing filter 5 allows only circularly polarized light D included in the light C to rotate in the same direction.
Finally, the light receiving element 7 receives the light D and transmits a signal according to the light intensity of the light D to a detection unit (not shown). The detection unit receives the signal and determines that the photoelectric switch is ON and “the detection object does not exist”.

Next, the operation of the photoelectric switch according to Embodiment 1 when the detected object is an opaque body such as paper will be described with reference to FIG.
First, the light projecting element 1 emits light A including light in a plurality of random polarization directions. Next, the light projecting side polarization filter 3 allows only circularly polarized light included in the light A rotating in a predetermined direction to pass therethrough. Next, the opaque body blocks the light B without reflecting it.
For this reason, the light receiving element 7 does not receive light and does not transmit a signal to a detection unit (not shown). The detection unit determines that the photoelectric switch is OFF and “the detection object is present”.

Next, the operation of the photoelectric switch according to Embodiment 1 when the detection object is a specular reflector such as a metal will be described with reference to FIG.
First, the light projecting element 1 emits light A including light in a plurality of random polarization directions. Next, the light projecting side polarization filter 3 passes only circularly polarized light B included in the light A that rotates in a predetermined direction. Next, the specular reflector reflects the light B on the surface in a specular manner and reflects the circularly polarized light C ′ rotating in the opposite direction to the light B. Next, the light-receiving side polarizing filter 5 blocks the circularly polarized light C ′ in the reverse direction without passing it.
For this reason, the light receiving element 7 does not receive light and does not transmit a signal to a detection unit (not shown). The detection unit determines that the photoelectric switch is OFF and “the detection object is present”.

As described above, the photoelectric switch according to Embodiment 1 includes the light projecting element 1 and the light projecting lens 2, the reflector 4 that faces the light projecting lens 2 via the light projecting side polarizing filter 3, and the light receiving side polarizing filter. 5 includes a light-receiving lens 6 and a light-receiving element 7 that face the reflector 4 via 5, and the reflector 4 has a characteristic of reflecting light including circularly polarized light that rotates in the same direction as the incident light, and is a light-projecting side polarization filter 3 and the light-receiving side polarizing filter 5 pass only circularly polarized light rotating in a single direction among the light incident from the front surface, and only light rotating in the same direction as the single direction among the light incident from the back surface. The circularly polarized light passing through the light-projecting side polarizing filter 3 and the light-receiving side polarizing filter 5 has the same rotational direction.
Therefore, the light C ′ specularly reflected by the surface of the specular reflector does not pass through the light receiving side polarizing filter 5, and both an opaque body such as paper and a specular reflector such as metal can be detected. Further, since the linear polarizing filter is not used, the mirror surface malfunction due to the installation inclination of the light projecting side polarizing filter 3 and the light receiving side polarizing filter 5 is eliminated, and the deterioration of detection accuracy can be improved.

In addition, the light projecting side polarizing filter 3 is a separate member from the light projecting unit (the light projecting element 1 and the light projecting lens 2), and the light receiving side polarizing filter 5 is separate from the light receiving unit (the light receiving lens 6 and the light receiving element 7). It comprised so that it might become a member.
Therefore, a photoelectric switch can be simply realized using the existing light projecting unit and light receiving unit.

In the first embodiment, the light-projecting side polarizing filter 3 and the light-receiving side polarizing filter 5 are configured as separate members, but instead of the light-projecting side polarizing filter 3 and the light-receiving side polarizing filter 5, as shown in FIG. It is good also as a structure provided with the light projection / reception side polarizing filter 8 which consists of one continuous circularly polarizing film.
In this case, the number of members can be further reduced and the cost can be reduced.

Further, as shown in FIG. 5, instead of the light projecting lens 2 and the light receiving lens 6, a configuration of a coaxial photoelectric switch including a half mirror 9 and a lens 10 may be employed.
In this case, the light projecting element 1 faces the light projecting axis direction, the light receiving element 7 faces the direction orthogonal to the light projecting axis direction, and the half mirror 9 is inclined by 45 ° with respect to the light projecting element 1 and the light receiving element 7 respectively. The lens 10 is configured to face the projection axis direction and to be inclined by 45 ° with respect to the half mirror 9. The half mirror 9 is configured to pass the light emitted from the light projecting element 1 and reflect the light received through the lens 10 toward the light receiving element 7.
The light projecting element 1, the half mirror 9 and the lens 10 constitute a light projecting part, and the light receiving element 7, the half mirror 9 and the lens 10 constitute a light receiving part. In the case of the configuration of a coaxial photoelectric switch, a smaller and lighter photoelectric switch can be obtained by integrating the light projecting unit and the light receiving unit.

  Moreover, in Embodiment 1, although the reflector 4 was comprised with the corner cube reflector made from an acrylic resin, it is not restricted to this. Any material and shape may be used as long as they have the property of reflecting light including circularly polarized light that rotates in the same direction as the incident light.

  The light-projecting side polarizing filter 3 and the light-receiving side polarizing filter 5 pass only circularly polarized light that rotates in a single direction out of the light incident from the front surface, and the single direction of the light incident from the back surface. Any material and structure may be used as long as they have a property of passing only light rotating in the same direction. Moreover, you may comprise using not only a flexible film raw material but the plate-shaped member with thickness, for example, the plate-shaped member formed with the plastics.

  In the first embodiment, an object detection system that detects a detection object consisting only of an opaque body or a specular reflector using a photoelectric switch has been described. However, both are combined, and a part of the system has a specular reflector. An opaque body may be detected.

  In addition, within the scope of the invention, the invention of the present application can be modified with any component of the embodiment or omitted with any component of the embodiment.

1, 21, 31 Emitting element 2, 22 Emitting lens 3, 23 Emitting side polarizing filter 4, 24, 37 Reflector 5, 25 Receiving side polarizing filter 6, 26 Receiving lens 7, 27, 32 Receiving element 8, 35 Projection / Reception Side Polarizing Filter 9, 33 Half Mirror 10, 34 Lens 36 Reflector Side Polarizing Filter 351, 361 Linear Polarization Filter 352, 362 1/4 Wave Plate

Claims (7)

In a photoelectric switch including a light projecting unit, a reflector facing the light projecting unit through a light projecting side polarizing filter, and a light receiving unit facing the reflector through a light receiving side polarizing filter,
The reflector has a property of reflecting light including circularly polarized light that rotates in the same direction as the incident light,
The light projecting side polarizing filter and the light receiving side polarizing filter have a characteristic of transmitting only a circularly polarized light component in a specific rotation direction of incident light,
The photoelectric switch, wherein the circularly polarized light passing through the light projecting side polarizing filter and the light receiving side polarizing filter has the same rotation direction.   The photoelectric switch according to claim 1, wherein the light projecting side polarizing filter is a separate member from the light projecting unit, and the light receiving side polarizing filter is a separate member from the light receiving unit. The light emitting side polarizing filter and the light receiving side polarizing filter are configured in a film shape,
The photoelectric switch according to claim 2, wherein the light projecting side polarizing filter is attached to a light projecting lens of the light projecting unit, and the light receiving side polarizing filter is attached to a light receiving lens of the light receiving unit.   3. The photoelectric switch according to claim 2, wherein the light projecting side polarizing filter is an attachment member externally attached to the light projecting unit, and the light receiving side polarizing filter is an attachment member externally attached to the light receiving unit. .   2. The photoelectric switch according to claim 1, wherein the light projecting side polarizing filter and the light receiving side polarizing filter are configured as a continuous integral plate member.   The photoelectric switch according to claim 1, wherein the reflector is a corner cube reflector.   An object detection system for detecting an opaque body and a specular reflector using the photoelectric switch according to claim 1.

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