JPH02141021A - Regressive reflection type photoelectric switch - Google Patents

Abstract

PURPOSE:To stably detect an object having a birefringent mirror surface by separating light reflected by a regressive reflecting plate into a specific polarized component and another component polarized in the direction normal to the polarized direction of the specific component and comparing light quantities of the two polarized components. CONSTITUTION:While the light l1 projected on a regressive reflecting plate 4 is randomly polarized light, the reflected light l2 from the plate 4 becomes a specific polarized component irrespective whether or not the plate 4 has a birefringent property, since the reflected light l2 is passed through a polarizing filter 5. When an object has a birefringent mirror surface, on the other hand, the reflected light becomes randomly polarized light as it is, since the incident light is the randomly polarized light. Therefore, a specific polarized component and another polarized component polarized in the direction normal to the polarized direction of the specific component are separated from the reflected light l2 and light quantities of the two components are compared with each other. As a result, detection of an object having a birefringent mirror surface becomes possible.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial Application Field The present invention relates to a retroreflective photoelectric switch that can accurately detect even objects having birefringent surfaces.

(B) Conventional technology A retroreflective photoelectric switch is composed of a switch body in which, for example, a light emitting element and a light receiving element are housed in one case, and a regressive reflector. The switch body and the retroreflector are provided facing each other with an appropriate distance between them, and light from the light projecting element is reflected by the recursion reflector and enters the light receiving element.

When an object passes between the switch body and the retroreflector,
This light is blocked by an object, and the presence of the object is detected.

However, when the surface of the object is a mirror surface, the light from the light projecting element is reflected by the mirror surface and enters the light receiving element, so that the presence of the object may not be detected. Therefore, as a retroreflective photoelectric switch that can detect the presence of an object even in such cases, Fig. 6 (a) and Fig. 6 0))
The following are known.

In the retroreflective photoelectric switch shown in FIG. 6(a), a polarizing filter 3 is placed in front of the light emitting lens 33 and the light receiving lens
5a and 35b are provided, and the polarizing filter 35a transmits the vertically polarized light component, and the polarizing filter 35b transmits the horizontally polarized light component, respectively. The light II from the light projecting element 32 is transmitted through the light projecting lens 33 and then through the polarizing filter 35a, and only the vertically polarized component is directed toward the retroreflector 34.

When this vertically polarized light component 7!1 is reflected by the retroreflector 34, it becomes elliptically polarized light. Only the horizontally polarized component of this reflected light 12 is separated by a polarizing filter 35b, which is focused by a light receiving lens 36 and converted into an electrical signal by a light receiving element 38a. On the other hand, light! .

When reflected by a mirror surface, the vertically polarized component is reflected as is, so the reflected light 12 becomes only the vertically polarized component and cannot pass through the polarizing filter 35b.

Therefore, since no light is incident on the light receiving element 38a, the presence of an object can be detected.

In the retroreflective photoelectric switch shown in FIG. 6(b), a polarizing filter 35a that transmits vertically polarized light components is placed in front of the light emitting lens 33, and a polarizing beam splitter 37 is placed behind the light receiving lens 36. The reflected light 2□ is separated into a horizontally polarized component and a vertically polarized component, and each is detected by separate light receiving elements 38a and 38b.

This retroreflective photoelectric switch includes light receiving elements 38a, 38
The presence or absence of a specular object can be detected based on the ratio of the amounts of light detected in b. In other words, the reflected light 12 from the retroreflector 34 is elliptically polarized light, so it has a certain ratio of horizontally polarized light components and vertically polarized light components, but the light reflected from the mirror surface is mostly composed of only vertically polarized light components. Therefore, the presence or absence of a specular object can be detected from the ratio of the light amounts of both components. Compared to the one shown in Fig. 6(a), this retroreflective photoelectric switch does not require high structural precision, has less parallax, and has the features of being able to distinguish between the light reflected by the retroreflector and the specularly reflected light. are doing.

(C) Problems to be Solved by the Invention The conventional retroreflective photoelectric switch described above is capable of detecting a mirror surface, for example, a polished metal object. However, an object such as a film attached to an aluminum surface has birefringence, just like a retroreflector. That is, since linearly polarized light has the property of being reflected as elliptically polarized light, the conventional retroreflective photoelectric switch described above has a problem in that it cannot detect such objects.

The present invention has been made in view of the above, and an object of the present invention is to provide a retroreflective photoelectric switch capable of detecting an object whose surface has birefringence.

(d) Means for Solving the Problems In order to solve the above problems, the retroreflective photoelectric switch of the present invention includes a light projecting means for projecting randomly polarized light, and a retroreflective photoelectric switch for reflecting the light from the light projecting means. a reflecting plate; a polarizing filter disposed on the optical path near the reflective surface of the recurrent reflecting plate; and separating the light reflected by the recurrent reflecting plate into the specific polarization component and a polarization component perpendicular to the specific polarization component. A polarized light component separation means, and two polarized light components separated by this polarized light component separation means,
It is comprised of a light receiving means that receives each light and converts it into an electrical signal, and a determining means that compares the light amounts of the two polarized light components and determines the presence or absence of an object based on the electrical signals from the light receiving means.

(E) Function In the recursive reflective photoelectric switch of the present invention, the light projected onto the recurrent reflector is randomly polarized light, but since the reflected light passes through a polarizing filter, the regressive reflector has birefringence. Regardless of whether or not there is a specific polarization component, the reflected light will be only a specific polarized component. On the other hand, if the object has a birefringent mirror surface, the incident light is randomly polarized, so the reflected light remains randomly polarized (note that even in the case of a non-birefringent mirror surface, the incident light is randomly polarized). similar). Therefore, it is possible to detect an object having a birefringent mirror surface by separating a specific polarization component and a polarization component orthogonal thereto from the reflected light and comparing the amounts of these lights.

(F) Embodiment An embodiment of the present invention will be described below with reference to FIGS. 1 to 5.

FIG. 1 shows the optical system of this embodiment of a retroreflective photoelectric switch (hereinafter simply referred to as a photoelectric switch). 2 is
A light emitting element such as a light emitting diode (LED) that emits randomly polarized light. Light from light projecting element 2 2. The light beams pass through the projection lens 3 to become substantially parallel light beams, and are projected onto the retroreflector plate 4 .

In this embodiment, the retroreflector 4 is of a total reflection corner cube type. A polarizing filter 5 is attached to the reflective surface of the retroreflector 4.

This polarizing filter 5 transmits only horizontally polarized light components.

Note that the polarizing filter 5 only needs to be on the optical path near the retroreflector 4, and may be placed apart from the retroreflector 4.

The reflected light 12 from the retroreflector 4 is focused by the light receiving lens 6. The light transmitted through the light-receiving lens 6 is separated into vertically polarized light components and horizontally polarized light components by a polarizing beam splitter (polarized light component separation means) 7, and each is received by light receiving elements (for example, photodiodes) 8a and 8b.

FIG. 3 is a diagram illustrating the circuit of the photoelectric switch according to the embodiment. The light projecting element 2 is driven to emit light by a drive circuit 11. On the other hand, the light receiving signals of the light receiving elements 8a and 8b are respectively I! , OG amplifiers 12a and 12b, and both are input to a differential amplifier 13 and a summing amplifier 14. here,
The reason why the Ilog amplifiers 12a and 12b are used is to prevent the amplifiers from becoming saturated and being unable to perform differential calculations when the amount of light received by the light receiving elements 8a and 8b is large.

The outputs of the differential amplifier 13 and the summing amplifier 14 are input to waveform shapers (comparators) 15a and 15b, respectively. A reference voltage V is applied to these waveform shapers 15a and 15b, respectively. The outputs of the waveform shapers 15a and 15b are:
The signal is input to an AND circuit 16, and the output of this AND circuit 16 becomes the output signal of the photoelectric switch.

Next, the operation of the photoelectric switch according to the embodiment will be explained with reference to FIG.

First, consider the case where no object exists, that is, the case where reflected light returns from the retroreflector 4 and the polarizing filter 5 [column (1) in FIG. 5]. Projection light! 1 is randomly polarized light, but it passes through the polarizing filter 5 and becomes only a horizontally polarized light component. This light is reflected by the retroreflector 4 and becomes elliptically polarized light, but it passes through the polarizing filter 5 again, so that the reflected light 12 has only a horizontally polarized component.

Therefore, the light receiving element 8a receives almost no amount of light, and the outputs of the log amplifiers 12a and 12b are, for example, 1 mV, respectively.
It becomes 10mV. Accordingly, if the amplification degree is 10 times, the outputs of the differential amplifier 13 and the summing amplifier 14 are each 9
0mV, 110mV. Then, the reference voltage V is 2
If it is 0 mV, the outputs of the waveform shapers 15a and 15b will both be High, and the output of the AND circuit 16 will also be High.
h.

Next, in the case of a general light-shielding object [see (2) a in Figure 5]
think of. In this case, since the amounts of light received by the light receiving elements 8a and 8b are both zero, the log amplifiers 12a, 12b,
The outputs of the differential amplifier 13 and the summing amplifier 14 are both OmV.
Therefore, the outputs of the waveform shapers 15a and 15b are both Low.
becomes. Therefore, the output of the AND circuit 16 becomes Low, and the presence of an object can be detected.

In the case of an object with a mirror surface [see column (3) in Figure 5], the projected light I2I is randomly polarized light, so regardless of whether this mirror surface has birefringence, the reflected light 2 is Randomly polarized and reflected light! ! , 2, the horizontally polarized light component and the vertically polarized light component have approximately the same ratio. Therefore, the amounts of light received by the light receiving elements 8a and 8b are approximately equal, and the outputs of the log amplifiers 12a and 12b are both 50 mV, for example. The outputs of the differential amplifier 13 and the summing amplifier 14 are
OmV and 10100O, respectively, and the waveform shaper 15
The outputs of a and 15b each become LowSHigh. Therefore, the output of the AND circuit 16 is still Low, and the presence of an object can be detected.

When the object has a diffuse reflection surface, for example, when it is a blank sheet of paper (see (4) 4rlI in FIG. 5), the reflected light 12 becomes randomly polarized light, and the amounts of light received by the light receiving elements 8a and 8b are approximately equal. At this time, the outputs of the log amplifiers 12a and 12b are both 5 mV, for example, and the outputs of the differential amplifier 13 and the summing amplifier 14 are Om V and 100 mV, respectively.
becomes. Therefore, the outputs of the waveform shapers 15a and 15b become Low and High, respectively, and the output of the AND circuit 16 becomes Low, and the presence of the object is detected.

FIG. 2 shows a modification of the optical system of the photoelectric switch of the embodiment. In this modification, a cat's eye shape is used as the retroreflector 4°. The total reflection corner cube-shaped regressive reflector 4 has birefringence and converts linearly polarized light into elliptically polarized light. Therefore, when the projected light ll passes through the polarizing filter 5, it is attenuated by 50%, and the retroreflector 4
When the light is reflected and transmitted through the polarizing filter 5 again, it is further attenuated by 50%. Even if a polarizing filter is ideal and has no attenuation and only separates polarized light, it is reflected light! 2 is the projection light 2. It is attenuated to 25% (=50% x 50%) of .

On the other hand, with the cat's eye-shaped retroreflector 4,
Since light is reflected while maintaining its polarization plane, it is reflected light! 2
is only attenuated by 50% with respect to the projected light r,
The amount of reflected light is 2 compared to the total reflection corner cube type.
It has the advantage of being doubled. Note that whether a total reflection corner chive type or a cat's eye type is used, the polarization direction of the polarization filter 5 and the polarization direction of the polarization beam splitter 7 (or the polarization filter 9b described below) are as follows. They need to roughly match. In other words, the mounting angle of the photoelectric switch and the mounting angle of the retroreflector are limited to a certain angular relationship.

In the modification shown in FIG. 2, the polarizing beam brick 7 is replaced by a half mirror 9a and polarizing filters 9b, 9c.
is used. The polarizing filter 9b is arranged to transmit the horizontally polarized component of the reflected light P2, and the polarizing filter 9c is arranged to transmit the vertically polarized component of the reflected light 2□. In this configuration, the light receiving element 8
Although the amount of light received by a and 8b is reduced to about 1/4, stable operation can be expected because polarized light separation is reliably performed.

FIG. 4 shows a modification of the circuit of the photoelectric switch according to the embodiment. This modification employs a well-known light modulation method in the circuit configuration shown in FIG. 3, making it less susceptible to disturbance light and electrical noise, and adding a stable operation display function. In FIG. 4, the same reference numerals as in FIG. 2 indicate the same components.

In this variant, the light projection element 2 is driven by a square wave oscillator 20. On the other hand, the output of the AND circuit 16 is input to the gate 17. This gate 17 is connected to the square wave oscillator 2
0, and the signal passing through the gate 17 is integrated by an integrator 18, then shaped by a waveform shaper (comparator) 19, and is used as an output signal of the photoelectric switch.

On the other hand, the output of the differential amplifier 13 is input to the gate 21. This gate 21 also operates in conjunction with the square wave oscillator 20 , and the signal passing through the gate 21 is integrated by an integrator 22 and input to a waveform shaper 23 . This waveform shaper 23
If the reference voltage V' of the waveform shapers 15a and 15b is 20 mV, it is set to about 40 mV.

If the output of the differential amplifier 13 is stable,
The output of the waveform shaper 23 becomes T4 i g h, and LE
D24 lights up. Check whether the photoelectric switch is operating stably using this L P, D 24.

This makes it easier to mount the photoelectric switch and retroreflector at the optimal angle.

In addition, in the above modification, it is also possible to use only one of the light modulation method and the stable operation indicator light, and the design can be changed as appropriate.

(G) As described in detail of the invention, the retroreflective photoelectric switch of the present invention includes a light projecting means for projecting randomly polarized light, a retroreflective plate for reflecting the light from the light projecting means, and a retroreflective plate for reflecting the light from the light projecting means. a polarizing filter disposed on the optical path near the reflective surface of the retroreflector, and a polarization component separation means for separating the light reflected by the retroreflector into the specific polarization component and a polarization component perpendicular to the specific polarization component. , a light receiving means that receives the two polarized light components separated by the polarized light component separation means and converts them into electrical signals; and a light receiving means that compares the amounts of light of the two polarized light components based on the electrical signals from the light receiving means. Since it is composed of a determining means for determining the presence or absence of an object, it has the advantage that objects having birefringent mirror surfaces can be stably detected.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating an optical system of a retroreflective photoelectric switch according to an embodiment of the present invention, FIG. 2 is a diagram illustrating a modification of the same optical system, and FIG. 4 is a block diagram illustrating a circuit configuration of the photoelectric switch, FIG. 5 is a block diagram illustrating a modification of the same circuit configuration, FIG. 5 is a diagram illustrating the operation of the retroreflective photoelectric switch, and FIG. (a) and FIG. 6(b) are diagrams respectively showing optical systems of a conventional retroreflective optical misinch. 2: Light projecting element, 4: Regression reflector, 5: Polarizing filter, 7: Polarizing beam splitter, 8a.
8b: Light receiving element, 13: Differential amplifier, 14: Summing amplifier, 5a/15b: Waveform shaper, 6: AND circuit.

Claims (1)

[Claims] (1) A light projection means for projecting randomly polarized light, a retroreflection plate for reflecting the light from the light projection means, a polarizing filter disposed on the optical path near the reflection surface of the retroreflection plate; polarization component separation means for separating the light reflected by the retroreflection plate into the specific polarization component and a polarization component orthogonal thereto; and two polarization components separated by the polarization component separation means,
It is characterized by comprising a light receiving means for receiving each light and converting it into an electric signal, and a determining means for comparing the light amounts of the two polarized light components and determining the presence or absence of an object based on the electric signals from the light receiving means. A retroreflective photoelectric switch.