JPS63206682A - Photoelectric switch - Google Patents

Abstract

PURPOSE:To widen a detection distance range by setting a detection distance long and to prevent erroneous operation when an object moves in a direction traversing an optical axis, by forming the light receiving lens of a light receiving means from an anamorphic lens. CONSTITUTION:Since an anamorphic lens is used as the light receiving lens 5 constituting a light receiving means 6, line-shaped condensed spots S are always formed on photodiodes 8a, 8b. These spots S move in directions S1-S3 corresponding to the movement of an object to be detected in a light projecting direction. Therefore, a detection distance is set long and a detection distance range can be widened. When the object to be detected moves in a direction traversing an optical axis, a whole of a illuminance level changes as shown by (a)-(c), the illuminance distribution of each spot in a line length direction becomes almost constant and, therefore, the ratio of the position detection signals IA, IB outputted from the photodiodes 8a, 8b does not change and an accurate distance signal is always obtained and no erroneous operation is generated.

Description

[Detailed description of the invention] [Technical field J The present invention relates to a photoelectric switch for FA.

[Background technology 1 Conventionally, photoelectric switches for FA have detected the presence or absence of an object based on the amount of light reflected from the light irradiated on the detected object, but malfunctions may occur due to the reflectance of the detected object or the influence of background light. There was a problem with waking up. Therefore, as a solution to these problems, the presence or absence of an object is detected by measuring the distance to the detected object using a triangulation method and determining whether the distance is closer than a preset detection distance. (For example, Japanese Patent Application No. 14163/1983)
No.) was there. FIG. 7 is a schematic configuration diagram showing the principle of distance measurement using the triangulation method. A light projecting means 3 consisting of a light projecting element 1 such as a light emitting diode or a semiconductor laser and a light projecting lens 2 emits a light beam onto an object X to be detected. is irradiated. On the other hand, as shown in FIG. 8, a light receiving means 6 consisting of a light receiving lens 5 arranged at a predetermined distance BL on the side of the light projecting means 3 condenses the light reflected by the detected object X of the light beam. The focused light beam S is configured to form an image on a semiconductor device sensor (hereinafter referred to as PSD) 7, which is a position detection element.

Here, a contradictory position detection signal I^+I[+ corresponding to the position of the light focusing block) S is obtained from the output terminals at both ends of the PSD 7, and this position detection signal IA,
In the determination control section to which I n is input, the position detection signal I
A+ 1. The ratio I A/I n or 0. n I
A/I B is calculated to form a signal corresponding to the distance R to the detected object X, and by comparing this signal with a predetermined reference voltage, it can be determined whether the detected object It is designed to make a judgment and control the output circuit. Note that the PSD 7 has a so-called pin photodiode structure with a photoelectric effect on the front side, and an n photodiode on the back side.
A uniform p-type paper resistance layer is provided on the surface of a high-resistance silicon substrate (i-layer) on which a type layer is formed, and a pair of output terminals provided at both ends of the p-type paper resistance layer and a pair of output terminals provided on the n-type layer are provided. A position detection signal IAIIIl consisting of contradictory currents corresponding to the position of the focused spot S flows between the common terminal and the common terminal.

However, in such a conventional example, since the PSD7 is used as a position detection element, the cost increases and the resistance between the electrodes of the PSD7 is high (the resistance of the p-type paper layer is several tens of Ω to (approximately several hundred ohms), it becomes a source of noise and causes the S of the position detection signals IA and IB to
There was a problem that /N decreased and it became difficult to increase the detection distance.

In addition, as another conventional example, as shown in FIG.
There was one that was designed to increase the detection distance by improving the S/N of A and IB. FIG. 10(a) shows the division lines of the photodiodes 8 at 8 b in a direction perpendicular to the moving direction M of the focused spot S when the detected object X moves in the light emitting direction (including the emitting and receiving light axis). (perpendicular to the surface), and FIG. 10(b) shows
The dividing line is formed in a direction oblique to the moving direction M. FIG. 11 is a diagram showing an example of the configuration of the determination control means 10, in which the position detection signal ■^wlB output from the divided photodiodes 8a and 8b, respectively, is converted into a voltage signal V^ by the light receiving circuits 11a and llb. r V B
After being converted into logarithmic amplifier circuits 12a and 12b, respectively
This logarithmically amplified signal αnVAy
By subtracting QnV1 in the subtraction circuit 13, a distance signal αn(VA/VA/
Va) can be obtained. In the comparison circuit 14, as shown in FIG. 12, this distance signal 0. n(V^/
Vn) and the reference voltage Vs set in advance with the separation setting volume VR, the detected object
Determine whether it has entered E and output the object detection signal V (for example, if the distance signal 0.n (V^/Ve) is the reference voltage V
s or less, an object detection signal Vx is output. This object detection signal V is determined by the signal processing circuit 15 as to whether it is a normal signal or not, and is outputted via the output circuit 16. Note that the light projecting element 1 is driven by a drive circuit 17 and emits light in synchronization with a clock signal generated by an oscillation circuit 18. On the other hand, the signal processing circuit 15 samples the object detection signal V based on the clock signal and determines whether it is a normal signal or not.

Further, the light receiving circuits 11a and llb are provided with a bandpass filter circuit that passes only a pulse signal of a specific frequency and cuts a DC component. Also, in the above example, α
Calculate n (V^/Vn) and calculate the distance signal and the distance signal, V
A/V11, (V A V s) / (V A + VB
), 0. n((V A V n)/(V A+V
The determination control means 10 may be configured to calculate B)) and use it as a distance signal to determine whether or not the detected object X exists within the detection area.

By the way, as mentioned above, the divided photodiodes 8a,
For those using 8b as a position detection element,
The light collecting spora) S by the light receiving means 6 must always be positioned on the dividing line of the 7 otiodiodes 8a and 8b, but if the dividing lines are orthogonal as shown in FIG. However, there is a problem in that the condensing spora) S tends to move onto one of the split photodiodes 8a or 8b due to the movement of the detected object X in the light projection direction, making it impossible to widen the detection distance range. Ta.

On the other hand, as shown in the same figure (b), when the division lines of the divided photodiodes 8a and 8b are formed diagonally to intersect with the moving direction of the condensing spora), the condensing spora) The range in which the position of S can be detected is widened, and the detection distance range can be widened. However, in this method, when the detected object X moves across the optical axis when used as a photoelectric switch, Focusing spot S is 131f
Although the distance R to the detected object X is the same, the distance signal (QnV
There was a problem in that the voltage (A/Vn) changed significantly and malfunction occurred. In other words, when the detected object X moves across the optical axis, a part of the light beam is reflected by the detected object There is a problem in that a distance signal that is significantly different from the distance R is output, resulting in malfunction.

LObject of the Invention J The present invention has been made in view of the above points, and its purpose is to be able to set a long detection distance, widen the detection distance range, and An object of the present invention is to provide a photoelectric switch that can prevent malfunctions when a detected object moves in a direction transverse to the optical axis.

[Disclosure of the Invention 1 (Structure) The present invention comprises a light projection means for projecting a light beam onto an object to be detected, and a light projection means arranged at a predetermined distance to the side of the light projection means to reflect light of the light beam by the object to be detected. A position consisting of a light-receiving means for condensing light, and a photodiode arranged on the imaging plane of the light-receiving means and divided so that when the object to be detected moves in the light projection direction, the direction of movement of the condensed spot is oblique to the dividing line. A photoelectric switch comprising a detection element and a determination control means that determines whether a detected object exists within a predetermined detection area based on the output of each divided photodiode of the position detection element and controls an output circuit. By forming the light receiving lens of the light receiving means with an anamorphic lens that stretches the light spot in a direction perpendicular to the direction of movement of the focused spot, the detection distance can be set long and the detection distance range can be widened. Furthermore, it is possible to prevent malfunctions when the detected object moves in a direction transverse to the optical axis.

(Embodiment 1) Fig. 1 and Fig. 2 show one embodiment of the present invention, in which one stage 3 of a light projector 8 for projecting a light beam onto an object to be detected A light receiving means 6 arranged at a distance DL and condensing the reflected light of the light beam from the detected object A position detection element consisting of photodiodes 8a and 8b divided so that the moving direction M of S (spora) S obliquely intersects the dividing line, and each divided photodiode 8a and 8b of the position detection element.
A conventional example (FIGS. 9 and 10) includes a determination control means 10 that determines whether the detected object X exists within a predetermined detection area based on the output and controls the output circuit 16.
b)) In a photoelectric switch similar to
The light-receiving lens 5 of the light-receiving means 6 is formed of an anamorphic lens that extends in the direction perpendicular to the moving direction M of the light-condensing spora) S (direction perpendicular to the plane containing the light emitting and receiving axes). Note that the anamorphic lens is a lens whose curvature differs depending on the cross-sectional direction of the lens, and the focal point and α distance differ. It is set to be slightly longer than the width of b. In FIG. 2, the condensing spora) S, , S2. S3 indicates the imaging position when the detected object X exists at distance R,, R2, R,.

The operation of the embodiment will be described below. In the present embodiment, since an anamorphic lens is used as the light-receiving lens 5 constituting the light-receiving means 6, a line-shaped condensing spora S is always formed on the photodiodes 8a and 8b. , this condensing spora) S is the detected object X
As shown in FIG. 2, (Sl
, S2. S3) It is designed to move in the M direction. Therefore, similarly to the conventional example shown in FIG. 10(b), the detection distance can be set long and the detection distance range can be widened. Furthermore, when the detected object X moves in a direction that crosses the optical axis, FIGS.
), although the overall illuminance level changes,
Since the illuminance distribution in the line length direction of the condensing spora) S is approximately constant, the ratio (I^/IB) of the device detection signal ■^+ra composed of both photodiodes 8a and 8b does not change. , always the correct distance signal (e.g. 0.nV
A/Vn) is obtained, the determination control means 10 will not perform erroneous determination control, and no malfunction will occur when the detected object X moves across the optical axis. Note that FIGS. 3(a) and 3(b) show the detected object
Figure 3 (c) shows a state where a part of the light beam is reflected at
) indicates a condensing spora ) S in a state where the entire light beam is reflected by the detected object X.

(Embodiment 2) FIG. 4 shows another embodiment, in which photodiodes 8a, 8b, 8c... are divided into many parts.
・(The iron position detection element is formed, and the split photodiodes at both ends (for example, 8 in Fig.
a, 8 c, 8 a, 8 e in the same figure (b),
8a in the same figure (c).

The determination control means 10 is formed so that an object detection signal is not output when the 8h output is larger than the output of other divided photodiodes, and malfunctions due to the illuminance distribution in the line length direction of the linear condensed spot S are prevented. This is what I did.

Now, when the condensing spora) S condensed by the light-receiving lens 5 made of an anamorphic lens is imaged as shown in FIG. It is approximately constant in the length direction. However, when the detected object X moves across the optical axis, the illuminance distribution of the condensing spora) S is as shown in Fig.
In the state where the projected beam changes as shown in b) to (d) and a part of the projected beam is reflected by the detected object X (immediately after entering the projected beam), As shown, the illuminance at one end of the condensed spot S becomes slightly high, resulting in a problem of distance measurement error. In order to prevent such a problem from occurring, it is possible to prevent both ends of the condensing spora (S) from entering the photodiodes 8a to 8c and use the central part, but the effective luminous flux When the ratio of the width of the photodiodes 88 to 8c and the line length of the condensing spora (S) approaches 1 in order to increase the light utilization efficiency (improve the light utilization efficiency), This causes a problem in that the determination control means 10 malfunctions due to a distance measurement error. That is, when the illuminance at one end of the focused spot S increases, the current output from the photodiode 8a increases accordingly, causing an error in the position detection signal IA, and an error also occurs in IA/III due to the illuminance distribution. The problem is that the determination control means 10 determines whether the detected object X exists within a predetermined detection area based on an incorrect distance signal and outputs an object detection signal. occurs. In this embodiment, since the position detection signal A is the current output from the photodiodes 8a and 8e at both ends, the distance signal IA/In is determined when the detected object X is on the optical axis. When moving across the distance signal
In becomes a value larger than the value corresponding to the actual distance R (the value in the case shown in FIG. 5(d) when the projected beam is completely reflected by the object to be detected X). In this case, the measurement error when the detected object X moves across the optical axis will cause an error as if the detected object X is always far away, and the area below the predetermined distance is the detection area, The determination control means 10, which is configured to output an object detection signal when the detected object X enters the detection area, does not output an object detection signal, and the detected object X has begun to cross the optical axis. Malfunctions are prevented. Note that when the projected beam is completely reflected by the object to be detected Needless to say, if the distance determination operation is performed and the detected object X exists within the detection area, an object detection signal is output.

(Embodiment 3) FIG. 6 shows yet another embodiment, in which a prism 9 for changing the detection area is movably disposed close to the light receiving surface of the position detection element consisting of photodiodes 8a and 8b. This eliminates the need for the distance adjustment volume VR for setting the detection area in the conventional example.

Now, there is a 7 otogiode 8a which is a position detection element.

By moving the prism 9 disposed close to the light-receiving surface of 8b, the imaging position of the condensing lens block S can be changed, and the distance signal IA/I to the detected object X at the same position can be changed. Since B can be changed, the detection area can be set simply by fixing the reference voltage Vs of the comparison circuit 14 to a constant value and adjusting the position of the prism 9. Therefore, compared to the conventional example in which the detection area is set by positioning the light receiving means 6 with high precision and adjusting the reference voltage Vs, the work of setting the detection area is simplified and the assembly This has the effect of making it easier and reducing costs.

[Effect of the Invention 1] As described above, the present invention includes a light projecting means for projecting a light beam onto an object to be detected, and a light projecting means disposed at a predetermined distance to the side of the light projecting means to reflect light of the light beam by the object to be detected. and a light receiving means for condensing the light, and a light receiving means arranged on the M image plane of the light receiving means such that when the object to be detected moves in the light projection direction, the direction of movement of the focused spot is diagonal to the dividing line. Judgment control that controls the output circuit by determining whether a detected object exists within a predetermined detection area based on the position detection element consisting of a photodiode and the output of each divided photodiode of the position detection element. The light receiving lens of the light receiving means is formed of an anamorphic lens that stretches the focused spot in a direction perpendicular to the moving direction of the focused spot, and the position detecting element is a photoelectric switch with low internal resistance. Since it is formed using a diode, the S/N of the position detection signal is high and the detection distance can be set long. Because I let you
The detection distance range can be widened, and since the light-receiving lens of the light-receiving means is formed of an anamorphic lens to elongate the focused spot, it is possible to prevent malfunctions when the detected object moves in a direction crossing the optical axis. It has the effect of being able to prevent this.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of an embodiment of the present invention, FIGS. 2 and 3 are explanatory diagrams showing the same configuration and operation, and FIG. 4 (a
) to (c) are plane views of main parts showing other embodiments, FIG. 5 is an explanatory diagram of the same operation as above, FIG. 6 is a schematic configuration diagram of still another embodiment, and FIG. A schematic configuration diagram; FIG. 8 is a front view of the main parts of the same as above; FIG. 9 is a schematic configuration diagram of another conventional example;
FIGS. 11A and 11B are front views of essential parts of the same as above, FIG. 11 is a circuit diagram of the same as above, and FIGS. 12 and 113 are explanatory views of the same as above. 3 is a light projecting means, 5 is a light receiving lens, 6 is a light receiving means, 8a~
8h is a photodiode, 10 is a determination control means, 14 is a comparison circuit, 16 is an output circuit, and X is an object to be detected.

Claims (3)

[Claims] (1) A light projecting means for projecting a light beam onto an object to be detected; a light receiving means disposed at a predetermined distance to the side of the light projecting means to collect light reflected from the light beam by the object to be detected; and a light receiving means a position detection element consisting of a photodiode arranged on the image forming plane of the image plane and divided so that when the object to be detected moves in the light projection direction, the condensed spot movement direction is diagonal to the division line; and each of the position detection elements. In a photoelectric switch that serves as a determination control means that determines whether or not a detected object exists within a predetermined detection area based on the outputs of the divided photodiodes and controls an output circuit, the condensed spot is moved in the direction of movement of the condensed spot. A photoelectric switch characterized in that a light-receiving lens of a light-receiving means is formed of an anamorphic lens that is stretched in a direction perpendicular to the . (2) A position detection element is formed by a photodiode divided into many parts, and a determination control means is formed so that an object detection signal is not output when the output of the divided photodiodes at both ends is larger than the output of the other divided photodiodes. A photoelectric switch according to claim 1, characterized in that: (3) A photoelectric switch according to claim 1, characterized in that a prism for changing the detection area is movably disposed close to the light receiving surface of the position detection element.