JPH0741074Y2 - Optical fiber type photoelectric switch - Google Patents

Description

[Detailed description of the device]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection type photoelectric switch in which one optical fiber is used for both light projection and light reception.

[0002]

2. Description of the Related Art A reflection type photoelectric switch projects light at a detection position and determines the presence or absence of an object by the reflected light. As shown in FIG. 6, optical fibers 1 and 2 are used to project and receive light. Things can also detect minute objects in narrow places,
This has the advantage that the amplifier main body can be placed far away from the detection position, and the degree of freedom in attachment is great.

The reflection type photoelectric switch 3 includes an amplifier section 4
A light projecting optical fiber 1 which is optically coupled to a light projecting element 5 inside
And a light-receiving optical fiber 2 optically coupled to the light-receiving element 6
The light emitting element 5 is pulsed by a synchronizing signal output from the control unit 7 in the amplifier unit, the object 8 is irradiated with this light through the optical fiber 1, and the reflected light is received by the light receiving optical fiber 2. The light is guided to the element 6, the output of the light receiving element 6 is detected by the control unit 7, the presence or absence of an object is determined based on the magnitude of the reflected light, and the electrical signal is output.

[0004]

As described above, since the conventional reflection type photoelectric switch 3 uses the two independent optical fibers 1 and 2, it is necessary to bundle the two optical fibers and the wiring. There is a problem that the wiring work is restricted due to the increase in thickness, and it is particularly difficult to position the light emitting end and the light receiving end of the two optical fibers so as to face each other at a minute detection position at a predetermined angle. .

In order to solve this problem, it is conceivable to use one optical fiber for both light projection and light reception. However, if shared, a part of the light entering the optical fiber from the light projecting element is reflected by the base end of the optical fiber and is directly received by the light receiving element. For this reason, it is difficult to distinguish from the light reflected at the detection position and returning through the optical fiber. The problem is that a plastic optical fiber is used for the photoelectric switch,
This optical fiber is particularly problematic in that it is cut to the required length with a blade at the installation site, so-called free-cutting, and when the surface is not polished, the reflectance of the cut surface increases. Therefore, the object of the present invention is to solve this problem by providing a structure capable of eliminating the influence of the reflection at the base end even if one optical fiber is used for both light projection and light reception. To do.

[0006]

The optical fiber type photoelectric switch provided by the present invention comprises a single optical fiber for both light projection and light reception, which is attached with its tip facing the detection position, and a half mirror for separating light projection and light reception. Through, a light projecting element and a light receiving element arranged to face the base end of the optical fiber, and a polarizing plate of the light projecting element arranged between the light projecting element and the half mirror,
The polarization direction of the light projecting element is different from that of the light polarizing element by 90 °, and the output of the light receiving element and the polarizing plate of the light receiving element arranged between the half mirror and the light receiving element are compared with a predetermined determination level to determine whether there is an object. A light that is provided with a control unit that outputs an electric signal, and the polarization direction of the light reflected at the proximal end of the optical fiber differs from the polarization direction of the polarizing plate of the light receiving element by 90 °, and is reflected at the detection position and returns to the light receiving element. However, it loses the directionality of polarization due to repeated total reflection when it travels back and forth in the optical fiber, and has a component that matches the polarization direction of the polarizing plate of the light receiving element, so that the light receiving element reflects at the base end of the optical fiber. It is characterized in that the reflected light does not enter and the light reflected at the detection position enters.

[0007]

In the above structure, by providing the polarizing plates whose polarization directions are different by 90 ° on the front surfaces of the light projecting element and the light receiving element, the crosstalk component due to the reflection of the proximal end surface of the shared optical fiber is incident on the light receiving element. To cut. Therefore, it is possible to realize a configuration in which the light projected by the half mirror is separated from the light received, and one optical fiber is shared for both light projection and light reception.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described with reference to FIG.
In the optical fiber type photoelectric switch 9 shown in FIG. 1, the light projecting element 5, the light receiving element 6, the control unit 7, and the detected object 8 are
Since it is the same as or equivalent to that of the photoelectric switch 3 described in FIG. 5, the same reference numerals are given and the description thereof is omitted.

The feature of this structure is that the optical fiber 10 is commonly used for both light projection and light reception, so that the half mirror 1 for separating light projection and light reception is used.
The polarizing plates 12 and 1 whose polarization directions are different by 90 ° so that the reflected light generated on the end face 10a of the optical fiber 10 by not using
3 is arranged in front of the light projecting element 5 and the light receiving element 6. Reference numeral 14 is a surface reflecting mirror for parallelizing the optical axes of the light projecting element and the light receiving element.

The mounting relationship between these will be described. The light projecting element 5 and the light receiving element 6 are arranged so that their optical axes are parallel to each other. The base end face 10a of the optical fiber 10 is arranged on an extension of the optical axis of the light projecting element 5 so that the light is vertically incident. The half mirror 11 is 45 ° on the optical axis of the light projecting element 5.
It is arranged with an inclination. The surface reflecting mirror 14 is arranged in parallel with the half mirror 11 on the optical axis of the light receiving element 6.

The operation of the optical fiber type photoelectric switch 9 will be described. The light projecting element 5 receives the synchronization signal output from the control unit 7, and emits pulsed light at a predetermined cycle. This light is polarized by one polarizing plate 12, passes through the half mirror 11, and is incident on the base end face 10 a of the optical fiber 10. Then, the light passes through the optical fiber 10 and is irradiated from the tip surface 10b toward the object 8 at the detection position. The light reflected from the object 8 at the detection position enters the front end surface of the optical fiber 10, passes through the inside of the optical fiber 10 in the opposite direction, and enters the half mirror 11 from the base end surface 10a thereof. The half mirror 11 reflects this reflected light in the 90 ° direction and directs it to the surface reflecting mirror 14. The surface reflecting mirror 14 further reflects this on the optical axis of the light receiving element 6. This light passes through the other polarizing plate 13 and enters the light receiving element 6. The output of the light receiving element 6 is compared with a predetermined determination level by the control unit 7, and if it is larger than this, an electric signal indicating that there is an object is output.

Next, the meaning of using the polarizing plates 12 and 14 will be described. Half mirror 1 used in this structure
1 has been put to practical use in a photographer or the like, but if it is used as it is in a photoelectric switch, the reflected light K generated when the light of the light projecting element 5 strikes the base end face 10a of the optical fiber 10 as shown in FIG. But the half mirror 11 and the surface reflecting mirror 14
Crosstalk that is reflected by the incident light and enters the light receiving element 6 occurs, and the S / N ratio deteriorates, making it impossible to put into practical use. In particular, if this structure is adopted for a photoelectric switch using a plastic optical fiber, the optical fiber 10 is appropriately cut at a wiring site and used in a free-cut method without polishing. The end face reflected light K of the optical fiber 10 becomes extremely large.

However, as described above, the polarization direction is 90
If different polarizing plates 12 and 13 are arranged in front of the light projecting element 5 and the light receiving element 6, the base end face 10a of the optical fiber 10
The light from the light projecting element 5 reflected by
Due to the difference, it is impossible to pass through the polarizing plate 13 arranged on the front surface of the light receiving element 6, so that the crosstalk can be prevented.
Then, the reflected light from the detection position to be incident on the light receiving element 6 has its polarization state canceled by the fact that the detected reflection of the object 8 is normally diffuse reflection and the total reflection is performed a plurality of times in the optical fiber. Therefore, the component of the light whose polarization direction and the vibration direction of the polarizing plate 13 arranged on the front surface of the light receiving element coincide with each other and enter the light receiving element 6, and the crosstalk is extremely reduced, so that the object 8 can be detected. Become.

The end surface reflection of the optical fiber 10 is shown in FIG.
As shown in FIG.
0b, the light incident on the front end face 10b is smaller than the light incident on the base end face 10a due to the attenuation in the optical fiber, so that the influence is small and the sensitivity of the control unit 7 is small. It can be used without problems by adjusting the above judgment level to an appropriate value with a controller.

The tip end surface 10b of the optical fiber may be formed by a normal cutting method in which it is cut in a direction orthogonal to the axis as shown in FIG. 2, but when it is cut in an inclined direction as shown in FIG.
Most of the reflected light is totally reflected in the optical fiber and reflected at an angle that cannot be returned, so that crosstalk due to the reflected light on the tip surface 10b can be cut and the accuracy can be further improved.

An attachment structure for applying the above-mentioned structure of the present invention to a conventional photoelectric switch 3 using two optical fibers shown in FIG. 6 is shown in FIGS. 4 and 5. This is the half mirror 11, the surface reflecting mirror 14, the polarizing plates 12, 1.
Insert the optical fibers 1 and 2 extended from the light projecting element 5 and the light receiving element 6 and the proximal end portion of the optical fiber 10 of the present invention extended to the detection position into the housing 15 in which 3 is incorporated in the above-described arrangement. It has a structure to fix with screws. In this embodiment, the condenser lenses 16 and 17 are provided in front of the polarizing plates 12 and 13 in order to increase the optical coupling, but this can be omitted. In this structure, if the light projecting element 5 and the light receiving element 6 are directly attached to the two optical fiber attaching portions 18 and 19, the photoelectric switch 9 having the structure shown in FIG. 1 is obtained.

[0017]

According to the present invention, there is provided a structure in which the reflected light of the end face of the optical fiber facing the light projecting element does not enter the light receiving element but the reflected light of the object to be detected enters the light receiving element. Thus, the number of optical fibers can be reduced to one, and the thickness of the wiring can be reduced. Therefore, it is easy to handle and attach the optical fiber to the narrow detection position, and the manufacturing cost can be reduced.

[Brief description of drawings]

FIG. 1 shows the structure of a reflective photoelectric switch of the present invention.

FIG. 2 is a diagram showing end face reflected light in the reflective photoelectric switch shown in FIG.

FIG. 3 is a view showing another embodiment of the tip surface of the optical fiber of the present invention.

FIG. 4 is a plan view showing a structure of an attachment for implementing the present invention with a conventional photoelectric switch.

5 is a front view of the attachment shown in FIG.

FIG. 6 shows a conventional photoelectric switch using two optical fibers.

[Explanation of symbols]

 5 Light emitting element 6 Light receiving element 7 Control section 8 Object at detection position 9 Photoelectric switch 10 Optical fiber 11 Half mirror 12, 13 Polarizing plate

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G02B 6/28 G02B 6/28 N

Claims (1)

[Scope of utility model registration request] 1. An optical fiber, which is mounted both with its tip facing the detection position and which is also used for light emission and reception, and a half mirror for separating light emission and light reception, and is disposed so as to face the base end of the optical fiber. The optical element and the light receiving element, the polarizing plate of the light projecting element arranged between the light projecting element and the half mirror, and the polarizing direction of the polarizing plate of the light projecting element are different by 90 °, and between the half mirror and the light receiving element. The polarization of the light reflected at the base end of the optical fiber is equipped with the polarizing plate of the light receiving element placed and the control unit that compares the output of the light receiving element with a predetermined judgment level and outputs the presence or absence of an object as an electrical signal. The direction of light is different from the polarization direction of the polarizing plate of the light receiving element by 90 °, and the light reflected at the detection position and returning to the light receiving element loses the directionality of polarization due to repeated total reflection when traveling back and forth in the optical fiber. It has a component that matches the polarization direction of the polarizing plate of the element. By doing so, the light reflected by the base end of the optical fiber does not enter the light receiving element, but the light reflected by the detection position enters.