JPS6338687B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal detection device that detects changes in the amount of light from an optical path set in space as a signal.

Generally, automated devices detect various physical quantities using predetermined detection devices and automatically control the entire device. One of these signal detection devices is a photointerrupter that can detect changes in the amount of light as a signal. This device has the feature of being able to detect various physical quantities without contact, and is used by being connected to the input circuits of various control devices. As shown in FIG. 1, a conventional photointerrupter 1 connects a light emitting element 2 and a light receiving element 3 via an optical path 1 disposed in a setting space 4. The presence or absence of a detected member (not shown) that interrupts the optical path 1 is converted into a change in the amount of light, and the light receiving element outputs this optical signal as an electric signal to the input circuit of the control device. The light receiving element 3 of this photo interrupter 1 faces the setting space 4 and is fixed to a support member 6 protruding from the base 5, and receives light incident from the setting space 4 side at all angles. . Therefore, the light receiving element 3 has an optical path l.
In addition to the light that passes through the setting space 4, disturbance light that passes through the setting space 4 from the outside is also likely to be received, which has the disadvantage of increasing the noise level (hereinafter simply referred to as S/N) with respect to the output signal of the light receiving element 2. It showed characteristics.

Furthermore, this photo interrupter 1 has a light emitting element 2.
and the light receiving element 3 must be arranged opposite to each other via the optical path l through which the detected member passes, and are mounted apart from the input circuit side connected to these elements.

An object of the present invention is to provide a signal detection device that can eliminate noise caused by ambient light.

This invention supports each end of a light transmitting fiber and a light receiving fiber on a common set optical axis using a base that integrally projects a pair of light-shielding support members arranged in parallel with each other with a space in between. A cone-shaped aperture with the light-receiving end face of the light-receiving fiber at the apex is formed in the support member that supports the light-receiving fiber, and the inclination angle of the aperture with respect to the center line is such that the light received by the light-receiving fiber is transmitted by total reflection. The light-receiving angle is set to be smaller than the light-receiving angle that indicates the range in which the light-receiving fiber is received.

According to this invention, the light-receiving fiber transmits the received optical signal to the light-receiving element, and the light-receiving element can generate an output signal. Furthermore, among the light that enters the light-receiving end face of the light-receiving fiber, the light that is repeatedly totally reflected within the light-receiving fiber and transmitted to the light-receiving element is only the light that has entered at an angle of incidence within the acceptance angle corresponding to the critical angle of the light-receiving fiber. I get robbed. In particular, the function of the aperture reliably removes disturbance light that attempts to enter at an angle greater than the acceptance angle, and the surface facing the light-receiving fiber can encompass the surface facing the aperture, allowing the light that can directly enter the light-receiving end surface to be transmitted. Light can be reliably restricted to only light from the fiber side.

The present invention will be described below with reference to the accompanying drawings.

FIG. 2 shows a signal detection device 7 as an embodiment of the present invention, which is connected to an input circuit 8 of a control device (not shown). The signal detection device 7 includes a light-shielding rigid material facing the passage R of the detected member 9;
Here, it has a base 10 made of plastic. The base is formed integrally with this, and the space 1
A pair of support members 12, 1 facing each other through 1
3 stands out. A light-receiving end 141 of an optical fiber 14 for light-receiving is provided at the center of one support member 12.
However, the light transmitting end portions 151 of the optical fibers 15 for transmitting light are respectively fixed to the center portion of the other supporting member 13. Moreover, the light receiving end 141 of the light receiving fiber 14 and the light transmitting end 151 of the light transmitting fiber 15 are connected to the space 11.
They are disposed on a common optical axis (hereinafter simply referred to as a set optical axis) l1 set through the optical axis. The set optical axis l1 in the space 11 intersects with the path R of the detected member 9, and this detected member 9 moves along the set optical axis l1 during operation.
Block 1.

The pair of support members 12 and 13 respectively form a light transmitting fiber facing surface 16 and a light receiving fiber facing surface 17 perpendicular to the set optical axis l1 on the side facing the space 11. Light-receiving fiber facing surface 1 of support member 13
The light transmitting end face 152 at the tip of the light transmitting end portion 151 is supported in the middle of the light transmitting end portion 7 so as to overlap with the light transmitting end face 152 at the tip of the light transmitting end portion 151 . on the other hand,
In the middle of the light transmitting fiber facing surface 16 of the support member 12, there is provided a light transmitting fiber facing surface 16 with the light transmitting fiber facing surface 16 as the bottom surface side, a light receiving end surface 142 at the tip of the light receiving end portion 141 as the apex side, and a set optical axis l1 as the center. A linear conical opening 18 is recessed. In this manner, the pair of support members 12 and 13 have the light transmitting fiber facing surface 16 and the light receiving fiber facing surface 17 facing each other through the space 11 having the length L. Therefore, the light transmitting end face 15
2 and the light-receiving end surface 142 have a length L and the depth of the aperture 18, that is, the light-receiving end surface 1
They face each other apart from each other by the length L1 up to 42.

The light-receiving fiber 14 has its light-receiving end 141 supported by the support member 12 , and its other end is connected to the light-receiving surface of the light-receiving element 19 that is directly connected to the input circuit 8 , and its light-sending end 151 is supported by the support member 13 . The other end of the light transmitting fiber 15 is connected to a light emitting element 20 which is directly connected to the input circuit 8. Therefore, the light from the light emitting element 20 driven by a well-known constant current circuit is transmitted to the light transmitting end 151 by the light transmitting fiber 15, and this light is irradiated from the light transmitting end face 152 along the set optical axis l1. When passing through the space 11, the light is interrupted by the detected member 9 and enters the light receiving end face 142 of the light receiving fiber. The incident light is transmitted through the receiving fiber 14
is transmitted to the other end side, and the light receiving element 19
The light is received by the The light received by the light-receiving fiber 14 is a signal whose light amount changes, and this light amount change signal is detected by the light-receiving element 19. That is, the light receiving element 19 that has received the light amount change signal will issue an output signal I corresponding to the light amount change signal to the input circuit 8.

Here, of the light incident on the light receiving end face 142 of the light receiving fiber 14, the incident angle of the incident light transmitted by total reflection will be explained using FIG.

The light-receiving fiber 14 has a core portion 143 with a refractive index n _c in the center, and a core portion 143 with a refractive index n _d smaller than the central portion on the outside thereof.
It has a clad part 144, and the whole is bendable. The core portion 143 forms an optical waveguide, and light is transmitted through repeated total reflections even in the bent core portion. Light receiving end surface 142 with respect to core portion 134
Among the more incident lights, the A ray has a relatively small incident angle θ, is totally reflected at the interface 145 between the core portion 143 and the cladding portion 144, and is transmitted to the other end side. On the other hand, the B ray enters the core portion 143 at a relatively large incident angle θ1 and then exits to the cladding portion 144 through the interface 145. Therefore, the light receiving end surface 1
Among the lights that are incident on 42 and repeatedly transmitted through total reflection to the other end, the C ray enters at the maximum angle of incidence, that is, the acceptance angle θ _nax , and is refracted at the refraction angle θ2, and then enters the interface 145 with an incident angle of is incident at a critical angle θ _c and proceeds along the interface 145. By the way, the relationship between the numerical aperture NA of the light-receiving fiber 14 and the refractive indices n _c and n _d of the core and cladding parts, and the relationship between the numerical aperture NA and the light-receiving angle θ _nax are expressed by equations (1) and (2). It will be done.

NA＝√ ² _c − ² _d ……(1) θ _nax = sin ^-1 NA ……(2) Therefore, the acceptance angle θ _nax is determined by the numerical aperture NA, and the incident angle within this acceptance angle θ _nax is Light receiving end face 1
Only the light incident on the receiving fiber 14 will be transmitted by the receiving fiber 14.

The opening 18 formed in the support member 12 supporting the light receiving fiber 14 has a conical wall surface 181 whose inclination angle α is set to a smaller value than the light receiving angle θ _nax . That is, as shown in FIG.
1 is drawn into and arranged inside the support member 12. Then, an opening 18 is formed having a conical wall surface 181 that gradually expands at an inclination angle α with the light receiving end surface 142 on the apex side. An extension line of this opening 18 (indicated by a two-dot chain line in FIG. 4) reaches the light-receiving fiber facing surface 17 of the support member 13. The light receiving fiber facing surface 17 has a rectangular shape, has a sufficient area to encompass the circular aperture facing surface S defined by the extension line of the aperture, and is formed in the same shape as the light transmitting fiber facing surface 16. Ru. Note that the light receiving fiber facing surface 17 and the light transmitting fiber facing surface 16 are in the space 11.
It is desirable to be made of a light-absorbing material so that it can prevent reflection even if it receives disturbance light that enters from the outside.

Light-receiving end surface 14 of the signal detection device 7 shown in FIG.
Light with an incident angle of zero as a light change signal is incident on the light receiving element 19 from the light transmitting end face 152 side.
and is converted into an output signal I. In this case, the light-receiving fiber 14 has a characteristic of transmitting all the light incident on the light-receiving end face 142 to the light _{-receiving element 19 within the light-receiving angle θ nax .} Only the light beam at the incident angle passes through the aperture 18 and enters the light receiving end surface 142.
In this case, the support member 13 blocks disturbance light that attempts to directly enter the light-receiving end surface 142 within the inclination angle α, so that only light emitted from within the circular aperture facing surface S defined by the extension line of the aperture 18 is allowed to enter. be. However, since the receiving fiber facing surface 17 of the support member 13 does not reflect the light rays from the space 11, only the light rays from the light transmitting end surface 152 enter the light receiving end surface 142. Moreover, as shown in FIG.
2 and the light transmitting fiber facing surface 16 are aligned, the light that crosses the upper edge of both supporting members 12 and 13 and directly enters the light receiving end surface 142 at a large angle of incidence of θ3 or more is transmitted through the aperture. 18 was formed, it was eliminated. That is, disturbance light having a relatively large incident angle is prevented from directly entering the light receiving end surface 142 because the light receiving end surface 142 is disposed deep within the aperture 18 . As in the conventional case (see Fig. 5), the disturbance light having an incident angle of θ3 or more is directly transmitted to the light receiving end face 14.
2, some diffuse reflection may occur around this light-receiving end surface, and in particular, in the case of disturbance light having a large amount of light, a relatively large amount of this diffuse reflection light occurs. Therefore, the receiving fiber 14 may receive and transmit the diffusely reflected light at an angle within the receiving angle θ _nax , which is included as noise in the light amount change signal and deteriorates the S/N characteristic of the output signal I. Sometimes I let it happen. Such inconveniences can be eliminated by arranging the light-receiving end surface 142 on the back side of the support member 12, which is the apex side of the conical opening 18.

In the signal detection device 7 shown in FIG. 2, an aperture 18 having an inclination angle α smaller than the light-receiving angle θ _nax is formed, and a light-receiving end face 142 is disposed at the back of the aperture 18. With this opening, the light that is directly incident on the light receiving end surface 142 can be restricted to only the light that is incident from the light transmitting end surface 152. Therefore, all of the disturbance light passing through the supporting members 12 and 13 is irradiated onto the light receiving fiber facing surface 17 or the light transmitting fiber facing surface 16. Most of this irradiated light is absorbed by both opposing surfaces 16 and 17,
Even if there is reflected light that reaches the light-receiving end face 142 after repeated reflections, the light will be attenuated to a negligible extent. Therefore, the receiving fiber 14
The light amount change signal received by the light receiving element 19 has almost no adverse effect due to ambient light, and the light receiving element 19 receiving this light amount change signal is correct, that is, there is no fluctuation due to noise.
An output signal I with good S/N characteristics can be sent to the input circuit 8.

Furthermore, in order to detect the light amount change signal, the signal detection device 7 shown in FIG. 142 can be arranged separately. Therefore, the connection portions of the electrical wiring that are susceptible to vibration are supported on the input circuit 8 side at desired positions, and it is possible to prevent the generation of noise from these connection portions.

The inclination angle α of the aperture of the signal detection device 7 shown in _FIG . In other words, it is desirable that the light-receiving fiber facing surface 17 be large enough to encompass the opening facing surface S formed by the opening extension line facing the opening 18 having the inclination angle α. On the other hand, if it is necessary to make the light-receiving fiber facing surface 17 smaller, by setting the inclination angle α of the aperture 18 to be relatively small, the aperture facing surface S becomes smaller, thereby preventing disturbance light from entering the light-receiving end surface 142. be able to. This inclination angle α is determined by the receiving fiber facing surface 1 relative to the length L of the space.
7 may be larger than the light receiving angle θ _nax if it is sufficiently large. Furthermore, in some cases, the inclination angle α may be formed at a negative angle, ie, in a conical shape opposite to the conical opening shown in FIG. Further, the opening 18 is not limited to a conical shape, but may be formed in an elliptical cone shape.

[Brief explanation of the drawing]

Figure 1 is a perspective view of a conventional photo interrupter.
Fig. 2 is a perspective view of a signal detection device as an embodiment of the present invention, Fig. 3 is an explanatory diagram of the acceptance angle of the light receiving fiber used in the above signal detection device, and Fig. 4 is formed in the above signal detection device. FIG. 5 is a schematic diagram of a conventional signal detection device. 7...Signal detection device, 10...Base, 11...
Space, 12, 13... Support member, 14... Light receiving fiber, 141... Light receiving end, 142... Light receiving end face, 15... Light transmitting fiber, 151... Light transmitting end, 152... Light transmitting end face , 17...Light transmitting fiber opposing surface, 18...Aperture, 19...Light receiving element, 20
...Light emitting element, l1 ... Setting optical axis, θ _nax ... Light reception angle, α ... Inclination angle, I ... Output signal.

Claims (1)

[Scope of Claims] 1. A base integrally protruding from a pair of supporting members arranged in parallel with each other with a space in between, and a sending end portion that receives light from a light source and sends out the light, which supports one of the supporting members. A light transmitting fiber is fixed to a member, and a light receiving end is fixed to the other support member so as to face the light transmitting fiber on a common set optical axis, and the light received by the light receiving end is transmitted to a light receiving element. a light-receiving fiber that leads to the light-receiving fiber, and a cone-shaped opening with the light-receiving end face at the tip of the light-receiving end portion facing the apex side is recessed in the surface of the other support member facing the light-transmitting fiber; The inclination angle of the aperture with respect to the center line is set to a smaller angle than the acceptance angle indicating the range of total internal reflection transmission of the light received by the light receiving fiber, and the circular aperture facing surface defined by the extension line of the aperture is set to one side of the aperture. 1. A signal detection device characterized in that the signal detection device is surrounded by a surface of a support member facing a light receiving fiber. 2. The signal detection device according to claim 1, wherein the surface of the one support member facing the light-receiving fiber is made of a light-absorbing material.