JP2016177875A - Reflector-type photoelectronic sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflector-type photoelectronic sensor capable of stably detecting a birefringent detection object with the use of a structure that can be easily assembled at a reduced cost.SOLUTION: A depolarizing film 8 is provided between a reflector 4 and a region X through which a detection object passes. The depolarizing film 8 is made of a material having high birefringence. The depolarizing film 8 lets a birefringent detection object T2 pass therethrough so as to attenuate its birefringence. The depolarizing film 8 also turns light, which has become elliptically polarized light A5 from vertically polarized light A2, into unpolarized light A6.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a reflector type photoelectric sensor that detects a detection target object based on the amount of returning light.

  FIG. 8A shows a conventional reflector type photoelectric sensor. In the conventional reflector type photoelectric sensor, first, the non-polarized light B 1 emitted from the light projecting element 1 is collected by the light projecting lens 2. The collected non-polarized light B1 passes only the linearly polarized light component in the vertical direction by the projection-side polarization filter 3 whose vertical direction is the polarization direction, and travels toward the reflector 4 as the vertical polarization B2. The reflector 4 is, for example, a corner cube reflector, and the vertically polarized light B2 that is regressively reflected by the reflector 4 becomes an elliptically polarized light B3. In the elliptically polarized light B3, only the linearly polarized light component in the horizontal direction passes through the light receiving side polarization filter 5 whose horizontal direction is the polarization direction, and is collected by the light receiving lens 6, and received by the light receiving element 7 as the horizontal polarized light B4. Based on the amount of received light entering the light receiving element 7, the presence or absence of a detection target is determined. This is because when there is a detection target, the amount of light received is reduced compared to when there is no detection target because the projected light is blocked.

  Further, when the object to be detected is a metal or the like and the light projection from the light projecting element 1 is specularly reflected, the reflected strong light may be directed to the light receiving element 7. This case is shown in FIG. In the specular reflection, the linearly polarized light is kept as it is, so that the vertically polarized light B2 is reflected and becomes the vertically polarized light B5. The vertically polarized light B5 is blocked by the light receiving side polarizing filter 5 and does not enter the light receiving element 7. In this way, by providing the polarizing filters whose polarization directions are orthogonal to each other on the light projecting side and the light receiving side, even if the object to be detected T1 is specularly reflected, the reflected light is received. Prevent entry into element 7. On the other hand, when the light-projecting side polarizing filter 3 and the light-receiving side polarizing filter 5 are not provided, the specularly reflected light enters the light receiving element 7 and the reflector photoelectric sensor is used as a detection target despite the presence of the detection target T1. There is a possibility that it will be judged as none. That is, if a polarizing filter whose polarization directions are orthogonal to each other on the light projecting side and the light receiving side as shown in FIG. 8 can be prevented from malfunctioning due to specular reflection, the configuration of FIG. Yes.

  Next, consider the case where the detection target is a transparent body having birefringence as shown in FIG. In this case, by passing through the detection target T2 having birefringence, the vertically polarized light B2 attenuates and becomes elliptically polarized light B6 due to the birefringence of the detection target T2. The elliptically polarized light B6 is retroreflected by the reflector 4 to become elliptically polarized light B7 having a different degree of polarization. The elliptically polarized light B7 is attenuated by passing through the detection target T2, and becomes elliptically polarized light B8 having a different degree of polarization due to the birefringence of the detection target T2. Then, the light receiving side polarizing filter 5 receives only a part of the elliptically polarized light B8, that is, the horizontal linearly polarized light component B9 by the light receiving element 7.

  However, since the state of the elliptically polarized light B8 toward the light receiving side polarizing filter 5 changes depending on the amount of birefringence at the detection target T2, the size of the linearly polarized light component B9 incident on the light receiving element 7 varies. That is, the amount of received light does not decrease much compared to the amount of received light when there is no detection target T2, or the amount of received light is even greater than the amount of received light when there is no detection target T2. In this case, erroneous determination of the reflector photoelectric sensor is caused. In addition, since the influence of birefringence varies depending on the direction of the detection target T2, it is difficult to stably detect the detection target T2 having birefringence in the reflector photoelectric sensor configured as shown in FIG. It was.

  Therefore, in Patent Document 1, in order to stably detect a detection target object that is not easily affected by specular reflection light generated by the detection target object and has birefringence, a polarizing filter, a quarter-wave plate, The structure which provided the circularly polarizing filter which consists of this to a sensor main body and a retroreflection part is described.

Japanese Patent No. 4158828

  In the case of the above configuration of Patent Document 1, the direction of the two members of the polarizing filter and the quarter wave plate constituting the circular polarizing filter are accurately aligned, and this circular polarizing filter is attached to the sensor body with other parts. It was necessary to incorporate it precisely considering the positional relationship with In other words, it was complicated to assemble. Moreover, since it is necessary to provide a circularly polarizing filter in both the sensor main body and the retroreflective portion, the assembly is complicated also in this respect, which may increase the cost.

  The present invention has been made in order to solve the above-described problems, and is a reflector photoelectric detector capable of stably detecting a detection object having birefringence by a structure that is easy to assemble and suppresses costs. The purpose is to obtain a sensor.

  The reflector type photoelectric sensor according to the present invention includes a light projecting element that emits light, a light projecting side polarizing filter through which light emitted by the light projecting element passes, and a light receiving side polarized light whose polarization direction is orthogonal to the light projecting side polarizing filter. A filter, a light-receiving element that receives light that has passed through the light-receiving side polarizing filter, a light-reflecting element that faces the light-projecting element and the light-receiving element across a region through which the detection object passes, and a region that reflects incident light; A depolarization unit is provided between the reflection unit and the polarization unit to depolarize light passing therethrough.

  According to the present invention, it is possible to stably detect a detection object having birefringence by a configuration that is easy to assemble and can reduce costs.

It is a block diagram of the reflector type photoelectric sensor which concerns on Embodiment 1 of this invention, and shows the state without a detection target object. It is a block diagram of the reflector type photoelectric sensor which concerns on Embodiment 1 of this invention, and shows the state with the detection target object which has birefringence. It is a block diagram of the reflector type photoelectric sensor which concerns on Embodiment 2 of this invention, and shows the state without a detection target object. It is a block diagram of the reflector type photoelectric sensor which concerns on Embodiment 2 of this invention, and shows the state with the detection target object which has birefringence. It is a block diagram of the reflector type photoelectric sensor which concerns on Embodiment 3 of this invention, and shows the state without a detection target object. It is a block diagram of the reflector type photoelectric sensor which concerns on Embodiment 3 of this invention, and shows the state with the detection target object which has birefringence. It is a block diagram which shows the modification of the reflector type photoelectric sensor which concerns on Embodiment 3 of this invention. It is a block diagram of the conventional reflector type photoelectric sensor. It is a figure explaining the property of the cell which constitutes a corner cube reflector.

Embodiment 1 FIG.
FIG. 1 shows the configuration of a reflector type photoelectric sensor according to Embodiment 1 of the present invention. The reflector type photoelectric sensor includes a light projecting element 1, a light projecting lens 2, a light projecting side polarizing filter 3, a light reflecting side reflector 4, a light receiving side polarizing filter 5, and a light receiving lens. 6, a light receiving element 7, and a depolarizing film 8 that depolarizes the polarized light. That is, the depolarization film 8 is added to the conventional reflector type photoelectric sensor shown in FIG.

The light projecting element 1 emits light, and is, for example, a light emitting diode.
The light projecting lens 2 collects and projects the light from the light projecting element 1.
The light projecting side polarizing filter 3 is a polarizing filter whose vertical direction is the polarization direction.
The reflector 4 recursively reflects light facing the light projecting element 1 and the light receiving element 7 across the region X through which the detection object passes, and is a corner cube reflector here.

The light-receiving side polarizing filter 5 is a polarizing filter whose horizontal direction is the polarization direction. That is, the polarization direction of the light projecting side polarizing filter 3 and the polarization direction of the light receiving side polarizing filter 5 are orthogonal. Note that the polarization direction of the light projecting side polarizing filter 3 may be the horizontal direction, and the polarization direction of the light receiving side polarizing filter 5 may be the vertical direction.
The light receiving lens 6 condenses the light on the light receiving element 7.
The light receiving element 7 receives light and outputs an electrical signal, and is, for example, a photodiode.

The depolarization film 8 depolarizes the light passing therethrough and is made of a material having birefringence. For example, polycarbonate, polyarylate, polyethylene terephthalate and the like. A material having strong birefringence is more desirable.
The depolarizing film 8 may be provided by being incorporated in a cover (not shown) of the reflector 4 or may be directly attached to the reflector 4. In any case, it is only necessary to be provided between the region X through which the detection object passes and the reflector 4, and fine installation accuracy and the like are unnecessary.

  In the reflector type photoelectric sensor shown in FIG. 1, the configuration other than the depolarization film 8 and the reflector 4 is a sensor body. Further, members that reflect light from the light projecting element 1 and direct it toward the light receiving element 7 such as the reflector 4 and the reflector 41 described later constitute a reflecting portion. Moreover, the depolarization film 8 comprises a depolarization part.

Next, a detection operation by the reflector type photoelectric sensor configured as shown in FIG. 1 will be described.
The non-polarized light A 1 emitted from the light projecting element 1 is collected by the light projecting lens 2. The collected non-polarized light A1 passes only the linearly polarized light component in the vertical direction by the projection-side polarizing filter 3 whose vertical direction is the polarization direction, and travels to the depolarization film 8 as the vertical polarized light A2. When the vertically polarized light A <b> 2 passes through the depolarizing film 8, the polarized light is canceled and becomes non-polarized light A <b> 3 and travels toward the reflector 4.

  The unpolarized light A3 is retroreflected by the reflector 4. At this time, since the light A3 is in a non-polarized state, it remains in the non-polarized state even if it is reflected by the reflector 4 which is a corner cube reflector. After the reflection, the non-polarized light A3 passes through the depolarization film 8 and travels toward the light receiving side polarizing filter 5. The non-polarized light A3 passes through only the linearly polarized light component in the horizontal direction by the light receiving side polarizing filter 5 whose horizontal direction is the polarization direction, and is collected by the light receiving lens 6, and received by the light receiving element 7 as the horizontal polarized light A4. Is done.

  The case where there is no detection target has been described above with reference to FIG. FIG. 2 shows a state in which the detection target T2 that is a transparent body having birefringence is placed in the optical path when passing through the region X. The operations already described with reference to FIG. 1 are omitted as appropriate. At this time, the vertically polarized light A2 passes through the detection target T2, and is attenuated and becomes elliptically polarized light A5 due to the birefringence of the detection target T2. Subsequently, when the elliptically polarized light A5 passes through the depolarizing film 8, the polarized light is canceled, and the light becomes an unpolarized light A6 and travels toward the reflector 4.

  The non-polarized light A6 is retroreflected by the reflector 4, passes through the depolarization film 8, and further passes through the detection target T2. The non-polarized light A6 is attenuated by passing through the detection target T2. Although the detection target T2 has birefringence, the polarization state of the light A6 is not disturbed because the light A6 is unpolarized. That is, when the non-polarized light A6 passes through the detection target T2, it becomes attenuated non-polarized light A7. Then, the non-polarized light A7 passes through only the linearly polarized light component in the horizontal direction through the light receiving side polarization filter 5 whose horizontal direction is the polarization direction, and is collected by the light receiving lens 6, and received by the light receiving element 7 as the horizontal polarized light A8. Is done.

The horizontal polarized light A8 received by the light receiving element 7 in FIG. 2 is attenuated to the extent that it passes through the detection target T2, and the amount of light is smaller than the horizontal polarized light A4 received by the light receiving element 7 in FIG. Based on this light amount difference, the reflector photoelectric sensor can determine the presence or absence of an object to be detected.
By providing the depolarization film 8 between the detection target T2 and the reflector 4, even if it passes through the detection target T2 and becomes elliptically polarized light A5, it is polarized as non-polarized light after passing through the depolarization film 8. Since the light is incident on the light receiving side polarizing filter 5 without being disturbed, the light receiving element 7 receives the horizontally polarized light A8 in which the attenuation of light by the detection target T2 is stably reflected.
On the other hand, the conventional reflector type photoelectric sensor shown in FIG. 8 (c) does not reflect the reflection at the reflector 4 and the passage of the detection target T2 even after passing through the detection target T2 to become the elliptically polarized light B6. Since the polarization state changes every time, the influence of attenuation by the detection target T2 was not stably reflected in the horizontally polarized light B9. Therefore, stable detection could not be performed.

In addition, the corner cube reflector is formed by arranging a plurality of cells, each of which includes a cell formed by intersecting a plurality of plane plates. The degree of change in polarization varies depending on which part of the cell reflects the light. FIG. 9 shows, as an example, the polarization state of light that is reflected back when vertically polarized light is incident on one cell. As shown in the figure, in one cell, the light reflected and returned is a region C1 in which the light is vertically polarized, and the light reflected and returned light is a region C2 in which the light is polarized in a direction inclined from the vertical direction. A region C3 where the returning light is elliptically polarized is mixed.
For this reason, when an object smaller than one cell size is set as the detection target in the conventional reflector type photoelectric sensor shown in FIG. 8A, the degree of change in polarization after the vertical polarization B2 is reflected is uneven. As a result, stable detection could not be performed.
On the other hand, in the case of the reflector type photoelectric sensor according to the first embodiment, since the polarization is eliminated by the depolarization film 8, unevenness disappears, and even a small detection object can be stably detected.

Instead of incorporating the depolarizing film 8 into a cover (not shown) of the reflector 4 or attaching it directly to the reflector 4, the reflector 4 and the depolarizing film 8 may be formed integrally. That is, a corner cube reflector may be made using the material of the depolarizing film 8 described above, and the reflector may be used as the reflector 4. In this case, the flat plate which comprises the cell of a corner cube reflector is formed with the material of the depolarizing film 8 mentioned above. In addition, in order to give reflectivity, what is necessary is just to perform the process of vapor-depositing a metal on the back surface of the plane plate formed with the material of the depolarization film 8.
Similarly, in the case of the bead type reflector described later in the second embodiment, a bead type reflector in which a plurality of beads using the material of the depolarization film 8 described above is arranged on the surface of a metal plate or the like is used, and the reflector is used. do it.

As described above, according to the reflector type photoelectric sensor according to the first embodiment of the present invention, the configuration in which the depolarization film 8 is provided allows the transparent body having birefringence to be a detection target. In addition, the light receiving element 7 can receive light in which attenuation of light by the detection target is stably reflected.
The depolarization film 8 is installed in a cover (not shown) of the reflector 4 or directly attached to the reflector 4, but does not require particularly fine accuracy. Moreover, if the reflector 4 is produced using the material of the depolarization film 8 from the beginning, the number of assembly steps will not increase.
As the depolarizing film 8, an inexpensive material such as polyethylene terephthalate can be appropriately selected. The sensor body itself can be a conventional one as shown in FIG.

Embodiment 2. FIG.
FIG. 3 shows the configuration of a reflector type photoelectric sensor according to Embodiment 2 of the present invention. This reflector type photoelectric sensor uses a bead type reflector 41 in which a plurality of beads are arranged instead of the reflector 4 which is the corner cube reflector shown in the first embodiment. About another structure, it is the same as that of the reflector type photoelectric sensor shown in FIG. Therefore, in FIG. 3, the same or corresponding parts as those in FIGS. 1 and 2 are denoted by the same reference numerals and description thereof is omitted.

  As described with reference to FIG. 8, the corner cube reflector has the property of changing the polarization of light before and after reflection. On the other hand, in the bead-type reflector 41, the polarization of light hardly changes before and after reflection. For this reason, when the bead type reflector 41 is used in the conventional reflector type photoelectric sensor shown in FIG. 8A, the vertical polarization B2 remains vertical polarization even if it is reflected by the reflector 41, and then the light receiving side polarization. Cut by filter 5. That is, even when there is no detection target, the same amount of received light as in the case where there is a detection is detected, and the presence / absence of the detection target cannot be determined.

  In the reflector type photoelectric sensor according to the second embodiment shown in FIG. 3, the light A3 that has passed through the depolarization film 8 and has become non-polarized light is recursively reflected by the reflector 41 and remains unpolarized in the light-receiving side polarizing filter 5. Head. The non-polarized light A3 passes through only the linearly polarized light component in the horizontal direction by the light receiving side polarization filter 5 whose horizontal direction is the polarization direction, and is received by the light receiving element 7 as the horizontally polarized light A4. The polarization state of light at each position on the optical path is the same in FIGS.

FIG. 4 shows a state in which the detection target T2 that is a transparent body having birefringence is placed in the optical path when passing through the region X. In this case, the unpolarized light A6 travels toward the reflector 41 as described with reference to FIG. Then, the non-polarized light A6 is recursively reflected by the reflector 41 without being polarized, and finally the horizontally polarized light A8 is received by the light receiving element 7 as described with reference to FIG.
The horizontal polarized light A8 received by the light receiving element 7 in FIG. 4 is attenuated to the extent that it passes through the detection target T2, and the amount of light is smaller than the horizontal polarized light A4 received by the light receiving element 7 in FIG. Based on this light amount difference, the reflector type photoelectric sensor configured by the reflector 41 can determine the presence or absence of the detection target. Thus, the detection operation using the bead type reflector 41 can be performed.

  As described above, according to the reflector photoelectric sensor according to the second embodiment of the present invention, the same effect as in the first embodiment can be obtained. In addition, when the depolarizing film 8 is provided, it is possible to perform the detection operation using the bead type reflector 41 that cannot be used in the conventional reflector type photoelectric sensor shown in FIG. Shown in Form 2.

Embodiment 3 FIG.
FIG. 5 shows a configuration of a reflector type photoelectric sensor according to Embodiment 3 of the present invention. This reflector type photoelectric sensor is different from the first and second embodiments in that circularly polarized light is used by providing a circularly polarizing filter having the same polarization direction as the light emitting side circularly polarizing filter 31 and the light receiving side circularly polarizing filter 51. . About another structure, it is the same as that of the reflector type photoelectric sensor shown in FIGS. Therefore, in FIG. 5, the same or corresponding parts as those in FIGS. 1 to 4 are denoted by the same reference numerals and the description thereof is omitted.

The non-polarized light A1 collected by the light projecting lens 2 passes through the light projecting side circular polarization filter 31 that is a circular polarization filter, becomes circularly polarized light A9, and travels toward the depolarization film 8. When the circularly polarized light A <b> 9 passes through the depolarization film 8, the polarized light is removed, and the light becomes unpolarized light A <b> 10 and travels toward the reflector 4.
The non-polarized light A10 is recursively reflected by the reflector 4. The unpolarized light A <b> 10 passes through the depolarization film 8 and travels toward the light-receiving side circularly polarizing filter 51. The non-polarized light A3 passes through the light receiving side circular polarizing filter 51, which is a circular polarizing filter, and is collected by the light receiving lens 6, and is received by the light receiving element 7 as circularly polarized light A11.

  FIG. 6 shows a state in which the detection target T2 that is a transparent body having birefringence is placed in the optical path when passing through the region X. The operations already described with reference to FIG. 5 are omitted as appropriate. At this time, the circularly polarized light A9 is attenuated by passing through the detection target T2, and becomes the light A12 whose polarization degree is changed due to the birefringence of the detection target T2. The light A12 is, for example, elliptically polarized light as shown in the figure. When the light A12 passes through the depolarization film 8, the light is depolarized to become non-polarized light A13 and travels toward the reflector 4.

  The unpolarized light A13 is retroreflected by the reflector 4, passes through the depolarization film 8, and further passes through the detection target T2. The non-polarized light A13 is attenuated by passing through the detection target T2. Although the detection target T2 has birefringence, the polarization state of the light A13 is not disturbed because the light A13 is non-polarized light. That is, when the non-polarized light A13 passes through the detection target T2, it becomes attenuated non-polarized light A14. The non-polarized light A14 passes through the light receiving side circular polarizing filter 51, which is a circular polarizing filter, and is collected by the light receiving lens 6 and received by the light receiving element 7 as circularly polarized light A15.

  The circularly polarized light A15 received by the light receiving element 7 in FIG. 6 is attenuated to the extent that it passes through the detection target T2, and the amount of light is smaller than the circularly polarized light A11 received by the light receiving element 7 in FIG. Based on this light amount difference, the reflector photoelectric sensor can determine the presence or absence of an object to be detected. Thus, the detection operation using circularly polarized light can be performed.

  When circularly polarized light is used for light projection and light reception, a reflector type photoelectric sensor of a coaxial optical system may be used as shown in FIG. In this case, the light projecting lens 2 and the light receiving lens 6 are integrated into the light projecting / receiving lens 9, and the light projecting side circular polarizing filter 31 and the light receiving side circular polarizing filter 51 are integrated into the circular polarizing filter 10. As the circularly polarizing filter 10, for example, a filter configured using cholesteric liquid crystal is used. A half mirror 11 is provided at a position where the circularly polarizing filter 10 is sandwiched between the depolarizing film 8.

  The non-polarized light A1 emitted from the light projecting element 1 passes through the half mirror 11, enters the light projecting / receiving lens 9, passes through the circular polarizing filter 10, becomes circularly polarized light A9, and travels toward the depolarization film 8. Further, the non-polarized light A10 that has been retro-reflected by the reflector 4 and passed through the depolarization film 8 passes through the circular polarizing filter 10 and the light projecting / receiving lens 9 and returns as circularly polarized light A11, and is reflected by the half mirror 11 and received. Element 7 is entered. Thus, the light projecting axis and the light receiving axis can be made substantially coaxial. The non-polarized light A1 emitted from the light projecting element 1 is reflected by the half mirror 11 toward the light projecting / receiving lens 9, and the circularly polarized light A11 from the light projecting / receiving lens 9 toward the light receiving element 7 passes through the half mirror 11. The light projecting element 1, the light receiving element 7, and the half mirror 11 may be disposed.

  Also for the reflector photoelectric sensor according to the third embodiment, a bead type reflector 41 may be used instead of the reflector 4 which is a corner cube reflector.

  As described above, according to the reflector photoelectric sensor according to the third embodiment of the present invention, the same effect as in the first embodiment can be obtained. In addition, when the depolarizing film 8 is provided, the detection operation can be performed not only with the linearly polarized light shown in the first embodiment but also with circularly polarized light as in the third embodiment.

  In the present invention, within the scope of the invention, any combination of the embodiments, or any modification of any component in each embodiment, or omission of any component in each embodiment is possible. .

DESCRIPTION OF SYMBOLS 1 Light projecting element 2 Light projecting lens 3 Light projecting side polarizing filter 4 Reflector 5 Light receiving side polarizing filter 6 Light receiving lens 7 Light receiving element 8 Depolarization film 9 Light projecting / receiving lens 10 Circular polarizing filter 11 Half mirror 31 Light projecting side circular polarizing filter 41 Reflector 51 Light-receiving side circular polarization filter

Claims (5)

A light emitting element that emits light;
A light projecting side polarizing filter through which the light emitted by the light projecting element passes;
A light receiving side polarizing filter whose polarization direction is orthogonal to the light emitting side polarizing filter;
A light receiving element that receives light that has passed through the light receiving side polarizing filter;
A reflecting portion that faces the light projecting element and the light receiving element across a region through which a detection object passes, and reflects incident light;
A reflector-type photoelectric sensor comprising a depolarization unit that is provided between the region and the reflection unit and depolarizes light passing therethrough. A light emitting element that emits light;
A light-projecting side circularly polarizing filter through which light emitted by the light projecting element passes;
A light-receiving side circular polarization filter;
A light receiving element that receives light that has passed through the light receiving side circularly polarizing filter;
A reflecting portion that faces the light projecting element and the light receiving element across a region through which a detection object passes, and reflects incident light;
A reflector-type photoelectric sensor comprising a depolarization unit that is provided between the region and the reflection unit and depolarizes light passing therethrough.   The reflector type photoelectric sensor according to claim 1, wherein the reflection part is a corner cube reflector or a bead type reflector that recursively reflects incident light.   The reflector type photoelectric sensor according to any one of claims 1 to 3, wherein the reflection portion and the depolarization portion are integrally formed. A circular mirror is provided at a position sandwiched between the depolarization unit, and includes a half mirror that transmits one of the light emitted by the light projecting element and the light received by the light receiving element and reflects the other,
The reflector type photoelectric sensor according to claim 2, wherein the circularly polarizing filter functions as the light projecting side circularly polarizing filter and the light receiving side circularly polarizing filter.

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