JPH01283725A - Optical fiber type photoelectric switch - Google Patents

Abstract

PURPOSE:To make it possible to keep a light reception amount unchanged instead of the changes of luminous efficacy, temperature characteristic and transmission factor by controlling the driving level of a light projection element based on the output of a light reception element. CONSTITUTION:The light of a light projection element 3 is led to a measuring range by an optical fiber 4 for light projection and an optical fiber 11 for measurement and is radiated to the measuring range from the end of the optical fiber 4 for light projection. Also the optical fiber 11 for measurement is provided in parallel to an optical fiber 6 for light reception and is led to a second light reception element 12 inside the main body of a photoelectric switch. And the light projection level of the light projection element 3 is controlled so that the light reception amount of the second light reception element 12 may be constant. Accordingly, it is possible to change the driving level of the light projection element 3 to keep the light reception amount always constant even when the luminous efficacy of the light projection element 3 is deteriorated or the temperature characteristics of light projection and reception elements are deteriorated or when the light reception amount is changed because of the curved state of the optical fiber for light projection and reception or the deterioration of the transmission factor.

Description

[Detailed Description of the Invention] [Field of the Invention] The present invention relates to a photoelectric switch using an optical fiber, and more particularly to an optical fiber type photoelectric switch that can always receive light from a light projecting element at a constant level. It is.

[Prior art]

In the conventional optical fiber type photoelectric switch, for example, as shown in FIG. 5, when the switch is operated, a control signal is given from the photoelectric switch main circuit 1 to the drive circuit 2 to pulse-light the light emitting element 3. A light projecting optical fiber 4 is provided at the tip of the light emitting device 3 and guided to an object detection area. If there is a detection object 5, a part of the reflected light from the object enters the light-receiving optical fiber 6, and the reflected light is guided to the light-receiving element 7 in the photoelectric switch via the optical fiber 6. Then, a current signal corresponding to the light receiving level of the light receiving element 7 is sent to the I/
The voltage signal is converted into a voltage signal by the V conversion circuit 8 and is applied to the photoelectric switch main circuit 1. The photoelectric switch main circuit 1 outputs an object detection signal by amplifying this level and making a discrimination based on a predetermined darkness value.

[Problem to be solved by the invention]

However, according to such a conventional optical fiber type photoelectric switch, the luminous efficiency of the light emitting element 3 may deteriorate or the light emitting element 3 may
．． The amount of light received varies depending on the temperature characteristics of the light receiving element 7. In addition, the transmittance changes depending on the usage conditions of the light emitting and light receiving optical fibers 4.6, especially the degree of curvature thereof, and changes due to aging of the optical fibers, so the amount of received light changes. Furthermore, if the optical fiber itself is damaged and the optical path is cut off, the light receiving element 7 will no longer be able to receive the reflected light. Conventional optical fiber type photoelectric switches have the disadvantage of not being able to confirm such abnormal conditions.

The present invention was made in view of the problems of conventional optical fiber type photoelectric switches, and is a technology that prevents the amount of received light from changing regardless of changes in luminous efficiency and temperature characteristics 5 transmittance. This will be a major issue.

[Structure and effects of the invention]

(Means for Solving the Problems) The present invention includes a light projecting unit that drives a light projecting element, a light projecting optical fiber that guides the light of the light projecting element to a detection area, and a light receiving element that detects reflected light obtained by the light receiving element. An optical fiber type photoelectric switch has a light-receiving part that identifies the presence or absence of an object by detecting the presence or absence of an object, and a light-receiving optical fiber that guides reflected light obtained from the detection area to a light-receiving element of the light-receiving part. A measuring optical fiber that is installed in parallel with the light receiving optical fiber and guides a part of the light from the light emitting element directly to the photoelectric switch body, and a second light receiving element that receives the light obtained at the end of the measuring optical fiber. , and a power control circuit that controls the drive level of the light emitting element based on the output of the second light receiving element.

(Function) According to the present invention having such characteristics, the light from the light emitting element is guided to the measurement area by the light emitting optical fiber and the measuring optical fiber, and is directed from the end of the light emitting optical fiber to the measurement area. irradiated. Furthermore, since the measuring optical fiber is also arranged in parallel with the light receiving optical fiber, it is guided as it is to the second light receiving element within the photoelectric switch body. Then, the light projection level of the light projecting element is controlled so that the amount of light received by the second light receiving element is constant.

(Effects of the Invention) Therefore, according to the present invention, when the light emitting efficiency of the light emitting element deteriorates, the temperature characteristics of the light emitting/receiving element deteriorates, or the light emitting/receiving optical fiber is bent, the transmittance deteriorates, etc. Since the driving level of the light emitting element is changed so that the amount of received light is always constant even when the amount of light changes, these fluctuations can be eliminated and the detection distance will not change. Effects can be obtained.

[Explanation of Examples]

FIG. 1 is a diagram showing an optical fiber type photoelectric switch according to an embodiment of the present invention. In this figure, the same parts as in the conventional example are given the same reference numerals. In this embodiment, the light projecting element 3 is lit in pulses by the drive circuit 2, and the light projecting optical fiber 4 and the measuring optical fiber 11 are provided at the tip of the light projecting element 3. The measuring optical fiber 11 is provided in parallel with the light emitting optical fiber 4, is bent at the tip of the light emitting optical fiber 4, and is guided to the photoelectric switch body together with the light receiving optical fiber 6. A light receiving element 7 is arranged at the tip of the light receiving optical fiber 6 as in the conventional example, and an I/V conversion circuit 8 for converting the current output into a voltage signal is connected. A second light-receiving element 12 having the same characteristics as the light-receiving element 7 is also provided on the measurement optical fiber 11, and a current signal corresponding to the light-receiving level is given to an I/V conversion circuit 13 and converted into a voltage signal. Ru. The voltage output of the I/V conversion circuit 13 is given to a power control circuit 14 and a comparison circuit 15. The power control circuit 14 controls the drive circuit 2 based on the I/V conversion output.
The light projection level for driving the light projection element 3 is controlled by applying a control signal to the light projection element 3. In addition, a certain low level darkness value is set in the comparison circuit 15, and the optical fiber 1
1, and its output is given directly to the outside or to a disconnection alarm display (not shown). The photoelectric switch main circuit 1 provides an operation signal to the power control circuit 14 when the photoelectric switch is operated, and detects the presence or absence of an object by discriminating the output of the I/V conversion circuit 8 at a predetermined darkness value level, thereby detecting the object. Give the output to the outside. Further, the output of the comparison circuit 15 is directly outputted to the outside as a disconnection detection signal. Here, the drive circuit 2 and the light projecting element 3 constitute a light projecting section that intermittently lights up the light projecting element 3 in response to a signal from the photoelectric switch main circuit l.
Light receiving element 7. The I/V conversion circuit 8 and the photoelectric switch main circuit 1 constitute a light receiving section that identifies the presence or absence of an object based on the reflected light obtained by the light receiving element 7.

Next, the I/V conversion circuit 13 and power control circuit 14 according to this embodiment will be explained with reference to FIG. 2. The signal obtained by the light receiving element 12 is given to the operational amplifier 21 of the I/V conversion circuit 13 and converted into a voltage signal. Since the light projecting element 3 is lit in pulses, the signal obtained by the operational amplifier 21 is a pulsed signal. Therefore, this signal is applied to an integrating circuit consisting of a resistor R1 and a capacitor C1, and the integrated output is sent to an operational amplifier 22 connected as a voltage follower.
The voltage signal is applied to the power control circuit 14 as a voltage signal corresponding to the received light level.

The power control circuit 14 has an operational amplifier 23 that amplifies the deviation between this voltage signal and a reference level, and its operational amplified output is given to the base of the transistor Trl. The collector of the transistor Tri is connected to the power supply terminal, and the emitter thereof is connected to the light projecting element 3 and the transistor Tr2 between the ground terminals. The drive circuit 2 described above is connected to the base of the transistor Tr2 to turn on the transistor Tr2 in pulses. Further, the output of the operational amplifier 22 is given to the operational amplifier 24 constituting the comparator circuit 15, and if the signal is below a certain darkness value, it outputs a fiber breakage detection signal and lights up a light emitting diode 25 as an indicator. ing.

Next, the operation of this embodiment will be explained with reference to time charts. FIG. 3(a) shows the pulse lighting output of the drive circuit 2, and after time t1, the light emitting element 3 is activated by this signal.
is pulsed. The light projection signal is then given to the light projection optical fiber 4 and the measuring optical fiber 11, and is irradiated onto the detection area from the light projection optical fiber 3. In addition, since the measurement optical fiber 11 is bent near the measurement area, it is guided to the photoelectric switch body together with the light receiving optical fiber 6.
The light receiving element 12 converts it into a current signal. Figure 3 (
bl indicates this light reception signal, and its output is I
The signal is applied to the /V conversion circuit 13, converted into a voltage signal, and further integrated. Therefore, as shown in FIG. 3(C), a substantially direct current signal having a level corresponding to the amount of received light is obtained from the operational amplifier 22. And this signal is the power control circuit 1
4, and the difference from the reference voltage is amplified and applied to the transistor Tri. Therefore, the output of the voltage control circuit 14 becomes a DC signal corresponding to the received light level as shown in FIG. 3(d), and the driving current of the light projecting element 3 is defined. Now, when the amount of light received by the light receiving element 12 decreases after time t2, the output of the operational amplifier 22 also decreases as shown in FIG. 3(C). Therefore, as shown in Figure 3 (dl), the power control signal increases and the voltage applied to the light emitter 3 increases.The light intensity of the light emitter 3 therefore increases.Therefore, for the same object, the same The reflected light is obtained by the light receiving element 7, and the detection distance of the object does not change.

As described above, in the present invention, the light from the light emitting element is guided directly to the light receiving element via the optical fiber, the amount of light is monitored, and the amount of light emitted is controlled thereby. Also, optical fibers 4 and 6
If 11 and 11 are disconnected, the light from the light projecting element 3 cannot be received by the light receiving element 12, so that a disconnection detection output is obtained from the comparing circuit 15. In the circuit example shown in FIG. 2, the disconnection detection output causes the light emitting diode 25 for disconnection notification to light up.

In this embodiment, an optical fiber for measurement is installed in parallel with the optical fibers for light emission and light reception, and its central part is curved to guide the light from the light emission element directly to the light reception element. As shown in FIG. 4 (al), the measurement optical fiber 11 is an optical fiber lla whose one end is connected to the light emitting element 3, and an optical fiber llb whose one end is connected to the light receiving element 12, and a prism 25 is provided at the end thereof. Also, Figure 4(b)
As shown in the figure, a 7-shaped reflecting mirror 26 may be provided in place of the prism to guide the light from the optical fiber lla to the optical fiber llb. Further, as shown in FIG. 4(C), a white plate-shaped diffuse reflection plate 27 may be provided in place of the prism or the reflecting mirror to guide the light emitted from the optical fiber 11 to the optical fiber llb. Further, only the light emitting optical fiber 4 is connected to the light emitting element 3, and a half mirror 28a is provided at the tip of the optical fiber 4 as shown in FIG. may be reflected by the mirror 28b and guided to the light receiving element 12 via the optical fiber 11 for measurement. In either case, the drive level of the light emitting element is controlled by guiding the light obtained from the light emitting element to the light receiving element via the measurement optical fiber installed in parallel with the light emitting/receiving optical fiber. ing.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the overall configuration of an optical fiber photoelectric switch according to an embodiment of the present invention, Fig. 2 is a circuit diagram showing its main parts, Fig. 3 is a time chart showing its operation, and Fig. 4 5 is a diagram showing another example of light emitting and receiving optical fibers and measuring optical fibers, and FIG. 5 is a diagram showing the overall configuration of a conventional optical fiber type photoelectric switch. 1. --- Photoelectric switch main circuit 2 --- Drive circuit 3 --- Light emitting element 4 --- Optical fiber for series light installation 6 --- Optical fiber for light reception 7. 12・
...--Photo-receiving element 8.13--I/V conversion circuit 14--Power control circuit 15--Comparison circuit 21-24--Operation amplifier patent applicant Tateishi Electric Co., Ltd. Agent Patent Attorney Yoshiki Okamoto (and other names) Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] (1) A light projecting unit that drives a light projecting element, a light projecting optical fiber that guides the light of the light projecting element to a detection area, and identifying the presence or absence of an object by detecting the reflected light obtained from the light receiving element. An optical fiber type photoelectric switch having a light receiving section and a light receiving optical fiber that guides reflected light obtained from a detection area to a light receiving element of the light receiving section, wherein the light emitting optical fiber and the light receiving optical fiber are arranged in parallel with each other. , a measuring optical fiber that directly guides a portion of the light from the light emitting element to the photoelectric switch body; a second light receiving element that receives the light obtained at the end of the measuring optical fiber; and the second light receiving element. An optical fiber photoelectric switch comprising: a power control circuit that controls the drive level of the light emitting element based on the output of the element.