JPH0152707B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal detection device that detects a member to be detected that interrupts an optical axis set in a space.

Generally, automated equipment detects various physical quantities and automatically controls the entire equipment. The photointerrupter used in this automatic control device has the feature of being able to detect various physical quantities without contact, and plays an important role as an input circuit for 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 l arranged in a setting space 4, and connects a detected member (not shown) to interrupt this optical path l. The presence or absence is converted into a change in the amount of light, which is received as a signal and output to the input circuit of the control device. The light emitting element 3 of this photo interrupter 1 is fixed to a support member 6 facing the setting space 4 and protruding from the base 5.
It receives light incident from the setting space 4 side at all angles. Therefore, in addition to the light from the light receiving element 2 passing through the optical path l, the light receiving element 3 is likely to receive disturbance light passing through the setting space 4 from the outside, and the noise level with respect to the output signal of the light receiving element 2 is likely to be received. (hereinafter simply referred to as S/N) exhibited poor characteristics such as a high ratio.

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. If this photo interrupter 1 is installed in a device that generates a lot of vibration, electrical noise may be generated at the connection portion of the connection wiring to the input circuit side, deteriorating the S/N characteristic. Moreover, since the light-emitting element 2 and light-receiving element 3 that make up this photo interrupter 1 are separate and independent from the control device main body side, the input circuits of each of these photo interrupters 1 are consolidated and configured to enable centralized signal processing. It is also difficult.

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

This invention supports each end of a light transmitting fiber and a light receiving fiber through a space on a common set optical axis using a base, and the light passing through the set optical axis in the space changes depending on the detected member. The device detects the change in the amount of light from the light-receiving fiber due to the change in the amount of light from the light-receiving fiber as a signal, and the support member on the base side that supports the light-sending fiber is formed with a surface facing the light-receiving fiber perpendicular to the set optical axis;
Further, the angle formed by the straight line connecting the outer peripheral edge of the facing surface of the light receiving fiber and the light receiving end surface of the light receiving fiber with the set optical axis is set to be larger than the light receiving angle of the light receiving fiber.

According to this invention, the light transmitted by the light receiving fiber can be detected as a signal, and the light receiving element that receives this can generate an output signal. Therefore, of the light that enters the light-receiving end face of the light-receiving fiber, the light that repeats total reflection within the light-receiving fiber and is 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. Therefore, light incident at an angle greater than or equal to the acceptance angle, that is, disturbance light, is removed. Furthermore, if the angle between the set optical axis and the straight line connecting the outer periphery of the facing face of the receiving fiber and the receiving end face is greater than or equal to the receiving angle, all of the light directly incident on the receiving end face and transmitted will be transmitted from the facing face of the receiving fiber. The disturbance light that directly enters the light-receiving end face is not transmitted to a predetermined position by the light-receiving fiber.

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). This signal detection device 7 has a base 10 made of a light-shielding rigid material, here plastic, and facing the path R of the detected member 9. The base 10 is integrally formed therewith, and has a pair of supporting members 12 and 13 protruding from the base 10, which are opposed to each other with a space 11 in between. One support member 12
A light receiving end 141 of a light receiving optical fiber 14 is fixed to the center of the support member 13, and a light transmitting end 151 of a light transmitting optical fiber 15 is fixed to the center 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 arranged on one common optical axis (hereinafter simply referred to as a set optical axis) l1 set through the space 11. The set optical axis l1 in the space 11 intersects with the path R of the detected member 9, and the detected member 9 blocks the set optical axis l1 during operation. A pair of support members 1
2 and 13 form a light transmitting fiber facing surface 16 and a light receiving fiber facing surface 17, which are perpendicular to the set optical axis l1, on the side facing the space 11, respectively. A light-receiving end surface 142 at the tip of the light-receiving end portion 141 is arranged in the middle of the light-transmitting fiber facing surface 16 so that it overlaps with the light-receiving end surface 142 at the tip of the light-receiving fiber-opposing surface 16. Light transmitting end surface 152 at the tip of
are arranged so that they overlap. In this way, 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 receiving end surface 142 on one support member 12 side and the support member 13 on the other side
It faces the light transmitting end surface 152 on the side via a set optical axis l1 having a length L. The light receiving end 14 is attached to the support member 12.
The other end of the light-receiving fiber 14 supported by the light-receiving fiber 14 is connected to the light-receiving surface of the light-receiving element 18 that is directly connected to the input circuit 8. The end thereof is connected to a light emitting element 19 which is directly connected to the input circuit 8 .

Therefore, light from the light emitting element 19 driven by a well-known constant current circuit is transmitted to the light transmitting end portion 151 by the light transmitting fiber 15, and is irradiated from the light transmitting surface 152 along the set optical axis l1. This light is space 11
When passing through, it is interrupted by the member to be detected 9 and enters the light receiving end face 142 of the light receiving fiber. The incident light is transmitted to the other end side by the light-receiving fiber 14 and is received by the light-receiving element 18 . The amount of light guided by this light receiving fiber 14 changes. This is a light amount change signal indicating the presence or absence of the detected member 9 in the space, and is detected by the light receiving element 18. The light receiving element 18 receiving the light amount change signal issues an output signal I corresponding to the light amount change signal to the input circuit 8.

Next, the relative relationship between the light-receiving fiber 14 and the light-receiving fiber facing surface 17 of the support member 13 will be explained with reference to FIGS. 3 and 4.

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 of this light-receiving fiber forms an optical waveguide, and light is repeatedly transmitted through total reflection even in the bent core portion. Of the light incident on the core section 143 from the light-receiving end surface 142, ray A enters the core section 143 at a relatively small incident angle θ, is totally reflected at the interface 145 between the core section and the cladding section, and is reflected to the other end side. transmitted. On the other hand, after the B ray enters the core portion 143 at a relatively large incident angle θ1, it escapes from the interface 145 into the cladding portion 144. Therefore, among the light that enters the light-receiving end face 142 and is repeatedly transmitted through total reflection to the other end, the C ray that enters at the maximum angle of incidence, that is, the light-receiving angle θ _nax , and is refracted at the refraction angle θ2, is 145
The light is incident at a critical angle θ _c as an incident angle and proceeds along the interface 145 . By the way, the numerical aperture of the receiving fiber 14
NA is expressed as the product of the refractive index of air (n≈1) and the sine of the acceptance angle θ _nax as shown in equation (1). That is, NA=n ₀ sinθ _nax ...(1) Here, the law of refraction is expressed by the light receiving end surface 142 and the interface 1.
45, equations (2) and (3) are obtained.

n _c /n ₀ = sinθ _nax /sinθ2 ...(2) n _d /n _c = sinθ _c /sin90゜=cosθ2 ...(3) Substituting equations (2) and (3) into equation (1) Obtain equation (4).

NA=n ₀ sinθ _nax = n _c sinθ2 = n _c (√1−2 ² )=√ _c ² − _d ² ...(4) Equation (5) is obtained from equations (1) and (4).

θ _nax = sin ^-1 NA = sin ^-1 √ _c ² − _d ² ...(5) In other words, the numerical aperture NA is calculated from the refractive index n _c and n _d of the core and cladding parts of the receiving fiber, and the numerical aperture NA From this, the acceptance angle θ _nax can be determined.

Furthermore, if the diameter of the core portion of the light-receiving fiber 14 is d, the boundary coordinates (x _c , y _c , o) of the core end, that is, the light-receiving end surface 142, are the set optical axis l1 and the light-receiving end surface 1.
With the intersection O with 42 as the base point, the direction of the constant optical axis l1 as the Z axis, and the X and Y axes taken at right angles to this, (6)
It is expressed by the formula.

x _c ² + y _c ² = d ² /4 ...(6) On the other hand, the receiving fiber facing surface 17 has the constant optical axis l1
and is located at a position L from the base point O. An arbitrary point P on the outer peripheral edge 171 of the light-receiving fiber facing surface 17 is (X ₀ , y ₀ , L), and a point Q (x _c , y _c , O)
The angle Q _o formed by the straight line l2 connecting these and the set optical axis l1
is expressed by equation (7).

Incidentally, the critical incident angle of light that enters the light-receiving end face 142 and is transmitted to the other end side by total internal reflection within the light-receiving fiber 14, that is, the light-receiving angle θ _nax , has the relationship shown in equation (5). Therefore, if the angle θ _o between the straight line l2 and the constant optical axis l1 is set to be greater than the light-receiving angle θ _nax , the disturbance light that directly enters the light-receiving end face 142 is regulated by the light-receiving fiber opposing surface 16.

That is, the disturbance light cannot be incident at a small incident angle within the acceptance angle θ _nax , and the directly incident disturbance light also escapes from the interface 145 of the light receiving fiber because the incident angle is greater than the acceptance angle θ _nax . , the light is totally reflected within the core portion and is not transmitted to the other end of the light-receiving fiber. The setting condition for the outer peripheral edge 171 of the surface facing the light-receiving fiber is θ _o >θ _nax . to this
By substituting equations (5) and (7), equation (8) is obtained.

In equation (8), the numerical aperture NA is a constant determined by the manufacturing conditions of the light-receiving fiber, and L is a constant determined by the usage conditions. Here, any point P (x ₀ , y ₀ , L) on the outer peripheral edge 161 that satisfies equation (8) and gives the minimum value of the angle θ _o that the straight line l2 makes with the set optical axis l1
seek. In equation (8), (x ₀ −X _c ) ² + (y ₀ −y _c ) ²
The condition for the minimum is when either x ₀ −x _c or y ₀ −y _c is zero and x _c or y _c is maximum. For example, (i) when x ₀ = l _w , x _c = d/2, y ₀ −y _c = 0, equation (8) is sin ^-1 NA＜tan ^-1 lw−d/2/L ……(9 ) (ii) When y ₀ = lh, yc = d/2, x ₀ −x _c = 0, equation (8) is sin ^-1 NA＜tan ^-1 lh−d/2/L ……(10) That is , the shape of the receiving fiber facing surface 17 of the signal detection device 7 shown in FIG.
If it is determined to satisfy equations (9) and (10), disturbance light to the light receiving fiber 14 can be removed. In addition,
The light transmitting fiber 15 may be the same as the light receiving fiber 14, and in some cases, fibers with different characteristics may be used instead.

The signal detection device 7 shown in FIG.
2 and a light transmitting end face 152 disposed opposite to this in the direction of the set optical axis l1.
The light receiving fiber 14 receives a signal indicating a change in the amount of light at the time when the light amount is cut off, and the light receiving element 18 optically connected to the receiving fiber 14 generates an output signal I corresponding to the light amount change signal. The light received by the light-receiving element 18 is only that which is received by the light-receiving fiber 14 at its light-receiving end face 142 and transmitted through repeated total reflection within the core portion 143. The light transmitted through the core portion 143 is only incident on the light receiving end face 142 at an incident angle smaller than the light receiving angle θ _nax . Therefore, the light-receiving fiber 14 removes the disturbance light incident at an angle larger than the light-receiving angle θ _nax , and the noise of the signal detection device 7 can be reduced, that is, the S/N characteristic is improved. Moreover, the light receiving end surface 142
The light-receiving fiber facing surface 16 covering the front side thereof is formed in such a shape that the entire outer peripheral edge 161 blocks at least light incident on the light-receiving end surface 142 at an incident angle within the light-receiving angle θ _nax . Therefore, the light that directly enters the light-receiving end face 142 is the light from the light-transmitting end face 152 of the light-transmitting fiber, and the light that enters at an angle within the light-receiving angle θ _nax is necessarily from the light-receiving fiber opposing face 17. Only reflected light will be reflected. When this reflected light is reflected by the light-receiving fiber facing surface 17, it is greatly attenuated and therefore does not act as harmful noise. That is, if the receiving fiber facing surface 17 is formed in a shape that satisfies equation (8), in addition to regulating the incident light by the receiving fiber 14, it will also block external light directly directed toward the receiving end surface 142 within the receiving angle θ _nax . Therefore, the noise of the signal detection device 7 can be largely removed, and the S/N characteristics can be improved. In addition, it is possible to secure a passage for the detected member between the light receiving end face 142 and the light receiving fiber facing surface 17, and the thickness of the detected member can be adjusted with a degree of freedom, so that it can be used in a wide range of fields. Further, the signal detection device 7 to which the present invention is applied detects the light amount change signal by moving the light transmitting end face 152 and the light receiving end face 142 to a desired location away from the light receiving element 19 and the light receiving element 18 which are directly connected to the input circuit 8. Can be freely placed in any position. Therefore, the connection portions of the electrical wiring that are susceptible to vibration can be supported on the input circuit 8 side, and generation of noise from these connection portions can be prevented. Moreover, when there are a plurality of input circuits in the control device, it is easy to consolidate these and it is also easy to centrally process signals.

In the above, the light receiving element 18 may be a photodiode, a phototransistor, a photoconductive element,
Alternatively, a solar cell can be used, and as the light emitting element 19, various light emitting diodes adapted to the wavelength sensitivity characteristics of the light receiving element can be used.

The signal detection device 7 shown in FIG.
was a light blocking type that completely interrupted the light and repeatedly turned on and off, but by further adjusting the combination of the light receiving element and the light emitting element, a light intensity change signal was generated based on the variable amount of transmitted light of the translucent detected member 9. It can also be configured to detect.

[Brief explanation of drawings]

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 a diagram illustrating the acceptance angle of a light receiving fiber used in the above signal detection device, and FIG. 4 is a perspective view of a light receiving fiber of the above signal detection device. It is a shape explanatory view of an opposing surface. 7...Signal detection device, 9...Member to be detected, 10...Base, 11...Space, 12, 13...Support member, 14...
Light receiving fiber, 141... Light receiving end, 142... Light receiving end surface, 15... Light transmitting fiber, 151... Light transmitting end,
152...Light transmitting end surface, 17...Light receiving fiber opposing surface,
171... Outer periphery, 18... Light receiving element, 19... Light emitting element, l1... Set optical axis, l2... Straight line connecting outer periphery and light receiving end surface, L... Length of space, θ _nax ... Light receiving angle, I
...output signal.

Claims (1)

[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 transmitter whose sending end that receives the light source light and sends out the light is fixed to one of the supporting members. an optical fiber; and a light-receiving fiber whose light-receiving end is fixed to the other supporting member so as to face the light-receiving fiber on a common set optical axis, and which guides light received at the light-receiving end to a light-receiving element. and is configured to detect as a signal a change in the amount of light from the light-receiving fiber due to a change in the light passing through the set optical axis in the space due to the detected member, wherein the light-transmitting fiber is The supporting member has a surface facing the light receiving fiber that is spaced apart from the light receiving end face facing the space of the light receiving fiber by a set length and is perpendicular to the set optical axis, and has an outer peripheral edge of the surface facing the light receiving fiber and the above light receiving fiber. A signal detection device characterized in that the angle between a straight line connecting an end face and a set optical axis is set to be larger than a light receiving angle indicating a range in which light received by a light receiving fiber can be transmitted by total reflection.