JP2015115186A - Photoelectric switch - Google Patents

Abstract

In detection of a transparent body using a photoelectric switch, high detection performance is required in order to detect a slight attenuation of light amount due to transmission through the transparent body. Transparent body detection is stably performed without providing particularly high detection performance. A light projecting unit that projects light onto a detection region, a light receiving unit that receives light from the detection region, and is disposed opposite to the light projecting unit across the detection region. In the photoelectric switch including the detection unit 5 that detects the presence or absence of the transparent body 50 in the detection region based on the amount of received light, the photoelectric switch is provided on the light projecting surface of the light projecting unit 1, and includes the first of the incident light in the specific rotation direction. The first circularly polarizing filter 3 that transmits only the circularly polarized component, and the second circle that is provided on the light receiving surface of the light receiving unit 2 and that is opposite to the rotation direction of the first circularly polarized component of the incident light. And a second circular polarization filter 4 that transmits only the polarization component. [Selection] Figure 1

Description

  The present invention relates to a photoelectric switch that detects the presence or absence of a transparent body in a detection region.

  For example, the photoelectric switch sets a detection area for a conveyance path on which an object to be detected is conveyed, and detects the presence or absence of the object in the detection area. The photoelectric switch includes a light projecting unit that projects light onto the detection region, a light receiving unit that receives the light through the detection region, and a detection unit that detects the presence or absence of an object in the detection region based on the amount of light received by the light receiving unit. It consists of and. When the object passes through the detection region, the light from the light projecting unit is blocked or reflected and the amount of light received by the light receiving unit changes, so the presence or absence of the object in the detection region is detected from this change. (For example, refer to Patent Document 1). The photoelectric switch includes a transmission type, a reflection type, and a reflector type.

  The transmissive photoelectric switch is configured such that a light projecting unit and a light receiving unit are arranged to face each other with a detection region interposed therebetween. In addition, the reflection type photoelectric switch has a light projecting unit and a light receiving unit arranged side by side toward the detection region. In addition, the reflector type photoelectric switch has a light projecting unit and a light receiving unit arranged side by side, and a reflector plate that reflects the light projected by the light projecting unit to the light receiving unit side is arranged opposite to each other with the detection region interposed therebetween. is there. Patent Document 1 discloses a reflector type photoelectric switch.

  Here, when the object to be detected is a transparent body (an object with high transmittance), the change in the amount of light received by the light receiving unit due to the transparent body passing through the detection region is small. Therefore, there is a problem that it is easily affected by environmental changes (temperature change, lens dirt, cloudiness, etc.), and the stability of transparent body detection is low.

On the other hand, a photoelectric switch that can stably detect a transparent body by using circularly polarized light is known (see, for example, Patent Document 2). The photoelectric switch disclosed in Patent Document 2 includes a light projecting system for projecting first circularly polarized light and a light receiving system for receiving second circularly polarized light that is opposite to the rotation direction of the first circularly polarized light. And a reflecting plate that reflects the incident light by converting the rotation direction of the circularly polarized light to the opposite direction.
Thereby, when there is no transparent body in the detection region, the second circularly polarized light projected from the light projecting system is in a direction opposite to the rotation direction of the first circularly polarized light by the reflecting plate. It is converted into circularly polarized light and received by the light receiving system. On the other hand, when there is a transparent body in the detection region, the transparent body disturbs the polarization state of the first circularly polarized light from the light projecting system. Therefore, the component of the second circularly polarized light that is converted and reflected by the reflecting plate is reduced, and the amount of light received by the light receiving system is reduced. Therefore, the amount of change in the amount of light received by the transparent body can be increased, and the stability of transparent body detection can be improved.

JP 2009-37784 A JP 2008-112629 A

  However, the photoelectric switch disclosed in Patent Document 2 uses a change in the amount of received light as a reference for detecting a transparent body. However, in the photoelectric switch disclosed in Patent Document 2, the amount of decrease in the amount of light due to the transmission through the transparent body is very small. Therefore, the detection unit of the photoelectric switch has a high detection level that can capture the slight amount of decrease. There was a problem that performance was required.

  The present invention has been made in order to solve the above-described problems, and is a photoelectric switch that can stably detect a transparent body without having a particularly high detection performance as compared with a general product. The purpose is to provide.

  The photoelectric switch according to the present invention includes a light projecting unit that projects light to a detection region, a light receiving unit that is disposed opposite to the light projecting unit across the detection region, and that receives light from the detection region, and a light receiving unit. In a photoelectric switch including a detection unit that detects the presence or absence of a transparent body in the detection region based on the amount of received light, a first circularly polarized component in a specific rotation direction is provided on a light projecting surface of the light projecting unit. The first circularly polarizing filter that transmits only the first circularly polarizing filter and the light receiving surface of the light receiving unit, and transmits only the second circularly polarized light component that is opposite to the rotation direction of the first circularly polarized light component in the incident light. And a second circularly polarizing filter.

  According to this invention, since it comprised as mentioned above, a transparent body detection can be performed stably, without providing especially high detection performance compared with a general product.

It is a figure which shows the structure of the photoelectric switch which concerns on Embodiment 1 of this invention. It is a figure explaining the detection operation by the photoelectric switch which concerns on Embodiment 1 of this invention, (a) It is a figure which shows the flow of light of a photoelectric switch, (b) At each location by the presence or absence of the object of a detection target It is a table | surface which shows the state of light.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings described below, main optical paths that contribute to the detection operation are illustrated as necessary. In this case, effects of weak reflection, transmission, absorption, diffusion, and the like are omitted for convenience.
Embodiment 1 FIG.
FIG. 1 is a diagram showing a configuration of a photoelectric switch according to Embodiment 1 of the present invention.
For example, the photoelectric switch sets a detection region for a transport path in which a transparent body 50 (transparent body 50 that disturbs polarization) to be detected is transported, and detects the presence or absence of the transparent body 50 in the detection region. . As shown in FIG. 1, the photoelectric sensor includes a light projecting unit 1, a light receiving unit 2, first and second circular polarization filters 3 and 4, and a detection unit 5.

The light projecting unit 1 projects light onto the detection area. As shown in FIG. 1, the light projecting unit 1 includes a light projecting element (for example, LED) 11 and a light projecting lens 12.
The light projecting element 11 emits light (natural light, that is, light whose polarization state is disturbed) and outputs the light to the detection region side.
The light projecting lens 12 condenses the light emitted by the light projecting element 11.

The light receiving unit 2 is disposed so as to face the light projecting unit 1 with the detection region interposed therebetween, and receives light from the detection region. As shown in FIG. 1, the light receiving unit 2 includes a light receiving lens 21 and a light receiving element 22.
The light receiving lens 21 collects light from the detection region.
The light receiving element 22 receives light collected by the light receiving lens 21.

  The first circularly polarizing filter 3 is provided on the light projecting surface of the light projecting unit 1 (front surface of the light projecting lens 12), and only the circularly polarized light component (first circularly polarized light component) in a specific rotation direction is included in the incident light. It is transparent. Here, the first circular polarization filter 3 may transmit only the left-handed circularly polarized light component, or may transmit only the right-handed circularly polarized light component. Note that “only” described in the present invention means that the ratio of the circularly polarized component in the specific rotation direction to the transmitted light is 100%, in other words, the light component other than the circularly polarized component in the specific rotation direction. Is not allowed to mix with transmitted light at all, and even if those light components are mixed to such an extent that they can be ignored in practice, the gist of the present invention is not impaired. In addition, the first circularly polarizing filter 3 may be fixed by, for example, forming a sheet-like member and directly sticking it to the front surface of the light projecting lens 12, or by an attachment part (first mounting part). The projection lens 12 may be detachable from the front surface. At this time, since the filter 3 is not a linear polarization filter but a circular polarization filter, there is no influence on the sensor accuracy even if a precise mounting angle accuracy is not required.

The second circularly polarizing filter 4 is provided on the light receiving surface of the light receiving unit 2 (the front surface of the light receiving lens 21), and of the incident light, a circularly polarized component (in a direction opposite to the rotation direction of the first circularly polarized component) ( Only the second circularly polarized light component) is transmitted. The second circularly polarizing filter 4 may be fixed by, for example, forming a sheet-like member and directly attaching it to the front surface of the light receiving lens 21, or receiving light by an attachment portion (second mounting portion). The lens 21 may be detachable from the front surface. At this time, since the filter 4 is not a linear polarization filter but a circular polarization filter, there is no influence on the sensor accuracy even if a precise mounting angle accuracy is not required.
The light projecting unit 1 and the light receiving unit 2 to which the first and second circularly polarizing filters 3 and 4 are attached may be existing ones.

  The detection unit 5 detects the presence or absence of the transparent body 50 in the detection region based on the amount of light received by the light receiving unit 2 (light receiving element 22). Here, the detection unit 5 determines that there is no transparent body 50 in the detection region when there is no light reception by the light reception unit 2, and determines that there is a transparent body 50 in the detection region when there is light reception by the light reception unit 2. To do.

  Next, the operation of the photoelectric switch configured as described above will be described with reference to FIG. 2A and 2B are diagrams for explaining the detection operation by the photoelectric switch according to Embodiment 1 of the present invention. FIG. 2A is a diagram showing the light flow of the photoelectric switch. FIG. 2B is an object to be detected (polarized light). It is a table | surface which shows the state of the light in each location by the presence or absence of the transparent body 50) which disturbs. In FIG. 2A, for simplification, only the internal configuration of the light projecting unit 1 and the light receiving unit 2 is illustrated, and the detection unit 5 is not illustrated.

First, the case where the transparent body 50 does not exist in the detection region will be described.
When performing the transparent body detection with the photoelectric switch, first, the light projecting element 11 of the light projecting unit 1 emits light and outputs it to the detection region side, and the light projecting lens 12 condenses this light. The light at this time (light A shown in FIG. 2) is natural light, and the polarization state is disturbed.

  Next, the first circularly polarizing filter 3 transmits only the right (left) rotating circularly polarized component of the light collected by the light projecting lens 12. Thereby, the light (light B shown in FIG. 2) projected on the detection region becomes right (left) circularly polarized light. Thereafter, since the transparent body 50 does not exist on the detection region, this light is incident on the second circular polarization filter 4 as it is (light C shown in FIG. 2).

  Next, the second circular polarization filter 4 transmits only the circularly polarized component rotated left (right) out of the light from the detection region. However, since the incident light (light C shown in FIG. 2) is right (left) circularly polarized light, this light is shielded by the second circular polarization filter 4 and does not reach the light receiving unit 2 side (FIG. 2). There is no light D shown in FIG. As a result, the light receiving unit 2 (light receiving element 22) does not receive light, and the detection unit 5 determines that the transparent body 50 is not present in the detection region.

Next, the case where the transparent body 50 that disturbs the polarization exists in the detection region will be described.
In this case, similarly to the above, the light projecting element 11 of the light projecting unit 1 emits light and outputs it to the detection region side, and the light projecting lens 12 condenses this light. The light at this time (light A shown in FIG. 2) is natural light, and the polarization state is disturbed.

  Next, the first circularly polarizing filter 3 transmits only the right (left) rotating circularly polarized component of the light collected by the light projecting lens 12. Thereby, the light (light B shown in FIG. 2) projected on the detection region becomes right (left) circularly polarized light. Thereafter, the light enters the transparent body 50 existing on the detection region, and the polarization state is disturbed by the transparent body 50 (light C shown in FIG. 2). Thereafter, this light enters the second circularly polarizing filter 4.

  Next, the second circular polarization filter 4 transmits only the circularly polarized component rotated left (right) out of the light from the detection region. Here, the incident light (light C shown in FIG. 2) is in a state in which the polarization state is disturbed, and since it contains a circularly polarized component rotated left (right), the light receiving unit 2 Left (right) circularly polarized light is output to the side (light D shown in FIG. 2). Thereafter, this light is received by the light receiving unit 2 (light receiving element 22), and the detection unit 5 determines that the transparent body 50 exists in the detection region.

  As described above, according to the first embodiment, by using the first and second circular polarization filters 3 and 4, the amount of received light becomes almost zero when there is no transparent body 50 in the detection region, and the detection region has Since the amount of received light is relatively increased when the transparent body 50 is present, and the presence of the transparent body 50 in the detection region is detected by detecting an increase in the amount of light with a zero reference, the rate of change of the signal is growing. As a result, it is possible to detect transparent objects that are resistant to the effects of environmental changes, and easily and stably detect transparent objects without using a photoelectric switch with low hysteresis (high resolution) and high detection performance. Can be performed. In addition, since the change rate of the signal is large due to the configuration that detects the increase in the amount of light with zero reference, delicate sensitivity adjustment of the photoelectric switch becomes unnecessary.

  In the present invention, any constituent element of the embodiment can be modified or any constituent element of the embodiment can be omitted within the scope of the invention.

DESCRIPTION OF SYMBOLS 1 Light projection part 2 Light reception part 3 1st circular polarization filter 4 2nd circular polarization filter 5 Detection part 11 Light projection element 12 Light projection lens 21 Light reception lens 22 Light reception element 50 Transparent body

Claims (2)

Based on a light projecting unit that projects light to a detection region, a light receiving unit that is disposed opposite to the light projecting unit across the detection region, and that receives light from the detection region, and the amount of light received by the light receiving unit In a photoelectric switch including a detection unit that detects the presence or absence of a transparent body in the detection region
A first circular polarization filter that is provided on the light projecting surface of the light projecting unit and transmits only the first circular polarized light component in the specific rotation direction of the incident light;
A second circular polarization filter that is provided on the light receiving surface of the light receiving unit and transmits only the second circularly polarized light component that is opposite to the rotation direction of the first circularly polarized light component in the incident light. A photoelectric switch characterized by that. A first mounting portion that allows the first circular polarizing filter to be attached to and detached from the light projecting surface of the light projecting portion and / or a second that allows the second circular polarizing filter to be attached to and detached from the light receiving surface of the light receiving portion. The photoelectric switch according to claim 1, further comprising: a mounting portion.

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