JP2544733B2 - Photoelectric switch - Google Patents

Description

TECHNICAL FIELD The present invention relates to a photoelectric switch for FA.

[Background Art] Conventionally, as a photoelectric switch for FA, the presence or absence of an object is detected by the reflected light amount of the light emitted to the detected object, but malfunction may occur due to the reflectance of the detected object or the influence of background light. I had a problem getting up. Therefore, as a solution to such a problem, the distance to the detected object is measured by a triangulation method, and it is determined whether or not the distance is shorter than a preset detection distance to detect the presence or absence of the object. There was one (for example, Japanese Patent Application No. 58-14163). FIG. 7 is a schematic configuration diagram showing the principle of distance measurement by the triangulation method. A light projecting means 3 including a light projecting element 1 such as a light emitting diode and a semiconductor laser and a light projecting lens 2 forms a light beam on a detected object X. Is irradiating. On the other hand, the light projecting means 3
As shown in FIG. 8, the light receiving means 6 composed of the light receiving lens 5 arranged at a predetermined distance BL on the side of the An image is formed on a semiconductor position sensor (hereinafter referred to as PSD) 7 which is a position detecting element. Where PS
Reciprocal position detection signals I _A , I _B corresponding to the position of the focused spot S are obtained from the output terminals of both ends of D7, and the determination control unit receives the position detection signals I _A , I _B. Then, the ratio I _A / I _B or lnI _A / I _B of the position detection signals I _A and I _B is calculated to form a signal corresponding to the distance R to the detected object X, and this signal is set to a predetermined reference voltage. The output circuit is controlled by determining whether or not the detected object X exists in the detection area by comparing with. In addition, PSD7
Has a so-called pin photodiode structure having a photoelectric effect on the surface, and a uniform p-type resistance layer is provided on the surface of a high resistance silicon substrate (i layer) having an n-type layer formed on the back surface side. Position detection signals I _A , I composed of opposite currents corresponding to the position of the focused spot S between a pair of output terminals provided at both ends of the mold resistance layer and a common terminal provided in the n-type layer. _B is flowing.

However, in such a conventional example, since the PSD7 is used as the position detection element, the cost becomes high and the interelectrode resistance of the PSD7 is high (the resistance of the p-type resistance layer is several tens of KΩ to several hundreds). Therefore, there is a problem that it becomes a noise generation source and the S / N of the position detection signals I _A and I _B is lowered to make it difficult to extend the detection distance.

Further, as another conventional example, as shown in FIG. 9, a photodiode pair 8a, 8a,
In some cases, b is used to improve the S / N of the position detection signals I _A and I _B to increase the detection distance. FIG. 10 (a) shows a division line of the photodiodes 8a and 8b in a direction orthogonal to the moving direction M of the focused spot S when the detected object X moves in the light projecting direction (a plane including the light projecting / receiving axis). (Direction perpendicular to the direction), and FIG. 10 (b)
Is a division line formed in a direction oblique to the moving direction M. FIG. 11 is a diagram showing a configuration example of the determination control means 10, the position detection signals I _A , I _B output respectively from the divided photodiodes 8a, 8b are voltage signals V _A by the light receiving circuits 11a, 11b. , V _B, and then logarithmically amplified by logarithmic amplification circuits 12a and 12b, respectively, and the subtraction circuit 13 subtracts the logarithmically amplified signals lnV _A and lnV _B , as shown in FIG. , Distance signal ln (V _A / V corresponding to distance R
_B ) is obtained. In the comparison circuit 14, the first
As shown in FIG. 2, whether or not the detected object X enters the detection area DE by comparing the distance signal ln (V _A / V _B ) with the reference voltage Vs set in advance by the distance setting volume VR. And outputs the object detection signal Vx (for example, the distance signal ln (V _A
/ V _B ) becomes the reference voltage Vs or less, the object detection signal Vx
Is output). This object detection signal Vx
Is determined by the signal processing circuit 15 to be a normal signal, and is output via the output circuit 16. The light projecting element 1
Are driven by the drive circuit 17 and emit light in synchronization with the clock signal generated by the oscillator circuit 18. On the other hand, in the signal processing circuit 15, the object detection signal Vx is sampled based on the clock signal to determine whether or not it is a normal signal. In addition, the light receiving circuit 11
Each of a and 11b is provided with a bandpass filter circuit that passes only a pulse signal of a specific frequency and cuts a DC component. In the above example, ln (V _A / V _B ) is calculated as the distance signal, but V _A / V _B , (V _A −V _B ) / (V _A +
V _B ), ln ((V _A −V _B ) / (V _A + V _B )) is calculated as a distance signal, and the determination control means is used to determine whether or not the detected object X exists in the detection area. 10 may be formed.

By the way, as described above, the divided photodiodes 8a, 8b
In the case of using as a position detecting element, the focused spot S by the light receiving means 6 is always the photodiodes 8a, 8b.
It is necessary to position it on the dividing line of, but in the same figure (a)
In the case where the division lines are provided orthogonally to each other as shown in (1), the focused spot S is likely to be moved onto one of the divided photodiodes 8a or 8b due to the movement of the detected object X in the light projecting direction, There is a problem that the detection distance range cannot be made too wide.

On the other hand, as shown in FIG. 7B, the dividing lines of the divided photodiodes 8a and 8b are formed obliquely to form a focused spot S.
, The position detectable range of the focused spot S becomes wider and the detection distance range can be widened. However, in this method, when the system is used as a photoelectric switch, the detected target range is detected. When the object X moves across the optical axis, the focused spot S is shown in FIG.
The distance R to the detected object X changes as shown in (c).
However, there is a problem in that the distance signal (lnV _A / V _B ) changes drastically even though the values are the same, resulting in malfunction. That is, when the detected object X moves across the optical axis,
When a part of the light beam is reflected by the object X to be detected, the focused spot S is missing, and a distance signal that is significantly different from the actual distance R is output, resulting in malfunction. There was a problem of doing.

[Object of the Invention] The present invention has been made in view of the above points, and an object thereof is to be able to set a long detection distance and to widen the detection distance range. An object of the present invention is to provide a photoelectric switch capable of preventing malfunction when a detected object moves in a direction crossing the optical axis.

DISCLOSURE OF THE INVENTION (Structure) The present invention relates to a light projecting means for projecting a light beam onto an object to be detected, and a light beam reflected by the object to be detected, which is arranged at a side of the light projecting means with a predetermined distance. And a photodiode arranged on the image plane of the light receiving means and divided so that the movement direction of the focused spot when the detected object moves in the light projecting direction intersects the dividing line. In a photoelectric switch consisting of a position detection element and a judgment control means for controlling an output circuit by judging whether or not a detected object is present in a predetermined detection area based on each divided photodiode output of the position detection element, An anamorphic lens that can be set so that the focused spot is extended in a direction orthogonal to the moving direction of the focused spot and the length of the focused spot is set to be slightly longer than the width of the divided photodiode. Form the light receiving lens of the light receiving means, and form a position detection element with a large number of divided photodiodes.When the divided photodiode output at both ends is larger than the other divided photodiode outputs, the object detection signal is By forming the determination control means for preventing the output, the detection distance can be set long, the detection distance range can be widened, and in the case where the detected object moves in the direction crossing the optical axis. This makes it possible to prevent malfunction.

(Embodiment 1) FIGS. 1 to 5 show an embodiment of the present invention, in which a light projecting means 3 for projecting a light beam onto an object X to be detected and a predetermined distance beside the light projecting means 3 are shown. A light receiving unit 6 arranged with DL to collect the reflected light of the light beam from the object X to be detected, and a converging spot when the object X to be detected is placed on the image plane of the light receiving unit 6 and moves in the light projecting direction. The photodiodes 8a, 8 are divided so that the moving direction M of S crosses the dividing line obliquely.
Based on the position detection element composed of b and the outputs of the divided photodiodes 8a and 8b of the position detection element, it is determined whether or not the detected object X exists in a predetermined detection area, and the output circuit 16
In a photoelectric switch similar to the conventional example (FIGS. 9 and 10 (b)) including the determination control means 10 for controlling the light spot, the focused spot S is moved in a direction orthogonal to the moving direction M of the focused spot S (projection). The light receiving lens 5 of the light receiving means 6 is formed by an anamorphic lens that is stretched in a direction perpendicular to a plane including the light receiving axis). The anamorphic lens is
The lenses have different curvatures and focal lengths depending on the cross-sectional direction of the lens, and the length of the extended linear focused spot S is set to be slightly longer than the width of the divided photodiodes 8a and 8b. ing. In FIG. 2, the focused spots S ₁ , S ₂ , and S ₃ are the distances R ₁ and R of the detected object X.
₂ shows an image forming position when it exists at ₂ and R ₃ .

The operation of the embodiment will be described below. Now, in the present embodiment, since the anamorphic lens is used as the light-receiving lens 5 which constitutes the light-receiving means 6, the linear condensed spot S is always formed on the photodiodes 8a and 8b. The light spot S is (S ₁ , S ₂ , S ₃ ) M as shown in FIG. 2 corresponding to the movement of the detected object X in the projection direction.
It is designed to move in the 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. Further, when the detected object X moves in a direction crossing the optical axis, as shown in FIGS. 3A to 3C, although the entire illuminance level is changed, the line length of the focused spot S is changed. Since the illuminance distribution in the direction is substantially constant, the ratio (I _A / I _B ) of the position detection signals I _A and I _B output from both photodiodes 8a and 8b does not change, and the correct distance signal is always obtained. (For example, lnV _A / V _B ) is obtained, erroneous determination control is not performed in the determination control unit 10, and no malfunction occurs when the detected object X moves across the optical axis. . 3A and 3B show a state in which a part of the light beam is reflected by the detected object X,
FIG. 3C shows the focused spot S in a state where the entire light beam is reflected by the detected object X.

Further, as shown in FIG. 4, the position detecting element is formed by a large number of divided photodiodes 8a, 8b, 8c, and the output of the divided photodiodes 8a, 8c at both ends is the other divided photodiode 8b. The determination control means 10 is formed so that the object detection signal is not output when the output is larger than the output of (1) to prevent malfunction due to the illuminance distribution of the line-shaped focused spot S in the line length direction.

Now, when the focused spot S focused by the light receiving lens 5 made of an anamorphic lens is imaged as shown in FIG. 5A, the illuminance distribution of the focused spot S is line length. It is almost constant in the direction.
However, when the detected object X moves across the optical axis, the illuminance distribution of the focused spot S changes as shown in FIGS. In the state where a part of the light beam is reflected (immediately after entering the light projection beam), the illuminance at one end of the focused spot S becomes slightly higher as shown in FIG. 5 (b). ,
There is a problem that distance measurement error occurs. In order to prevent such a problem from occurring, it suffices that both ends of the focused spot S do not enter the photodiodes 8a to 8c and the central portion is used. The ratio of the width of the photodiodes 8a to 8c to the line length of the focused spot S is set to 1 in order to increase the efficiency (enhance the light utilization efficiency)
When approaching to, there is a problem that a distance measurement error occurs due to the illuminance distribution of the focused spot S, and the determination control means 10 malfunctions. That is, when the illuminance at one end of the focused spot S increases, the current output from the photodiode 8a increases correspondingly, and the position detection signal I _A increases.
Error occurs in I _A / I _B , which causes an error component due to the illuminance distribution, and the determination control means 10 exists the detection target object X in a predetermined detection area based on an erroneous distance signal. There is a problem that it is determined whether or not the object detection signal is output. In this embodiment, since the position detection signal I _A is the current output from the photodiodes 8a and 8c at both ends, the distance signal I _A / I _B is the detected object X.
Distance signal when the object moves across the optical axis
I _A / I _B becomes a value larger than the value corresponding to the actual distance R (the value in the case shown in FIG. 5D in which the projection beam is totally reflected by the detected object X). In this case, the distance measurement error when the detected object X moves across the optical axis always causes an error such that the detected object X is distant, and the predetermined distance or less is set as the detection area. In a state in which the object detection signal is not output from the determination control means 10 that outputs the object detection signal when the detection object X enters the detection area, the detected object X starts to cross the optical axis. Malfunction is prevented. It should be noted that, when the projected light beam is completely reflected by the object X to be detected, the distance measurement error as described above does not occur. Therefore, as in the first embodiment, the normal distance determination is performed. It is needless to say that the object detection signal is output if the operation is performed and the detected object X exists in the detection area.

(Embodiment 2) FIG. 6 shows another embodiment.
The detection area changing prism 9 is movably arranged in the vicinity of the light receiving surface of the position detecting element composed of 8a and 8b, and the distance adjusting volume VR for setting the detection area in the conventional example is unnecessary. It is a thing.

Now, by moving the prism 9 arranged close to the light receiving surfaces of the photodiodes 8a and 8b, which are position detecting elements, the image forming position of the focused spot S can be changed, and the detected object at the same position can be detected. Distance signal I _A / I for object X
_{Since B} can be changed, the detection area can be set only by fixing the reference voltage Vs of the comparison circuit 14 to a constant value and adjusting the position of the prism 9. Therefore, as in the conventional example, the light receiving means 6
The positioning area is set with high accuracy and the detection area is set by adjusting the reference voltage Vs, which simplifies the work of setting the detection area, facilitates assembly, and reduces costs. There is.

[Effects of the Invention] As described above, the present invention provides a light projecting means for projecting a light beam onto an object to be detected, and a light beam reflected by the object to be detected, which is arranged at a side of the light projecting means with a predetermined distance. And a photodiode arranged on the image plane of the light receiving means and divided so that the movement direction of the focused spot when the detected object moves in the light projecting direction intersects the dividing line. In a photoelectric switch consisting of a position detection element and a judgment control means for controlling an output circuit by judging whether or not a detected object is present in a predetermined detection area based on each divided photodiode output of the position detection element, Anamorphic that can be set so that the focused spot is extended in the direction orthogonal to the moving direction of the focused spot and the length of the focused spot is set to be slightly longer than the width of the divided photodiode. The lens forms the light-receiving lens of the light-receiving means, and the photodiodes divided into a large number form the position detection element.When the divided photodiode output at both ends is larger than the other divided photodiode outputs, the object detection signal is Since the position detection element is formed by using a photodiode with a low internal resistance, the S / N of the position detection signal is increased and the detection distance is set longer because the position detection element is formed by using a photodiode with low internal resistance. By using an anamorphic lens that can set the focused spot length to be slightly longer than the split photodiode width, the light density on the split photodiode increases, which The light-receiving current generated in the split photodiode increases, allowing a longer measurable distance. Since the direction of the line is oblique to the moving direction of the focused spot, the detection distance range can be widened, and the receiving lens of the light receiving means is formed by an anamorphic lens to extend the focused spot. Therefore, it is possible to prevent a malfunction when the detected object moves in a direction crossing the optical axis. That is, when an anamorphic lens is used as a light-receiving lens to expand the focused spot, and when the detected object moves in a direction crossing the optical axis, the illuminance distribution of the focused spot in the line length direction becomes substantially constant. Therefore, the ratio of the position detection signals output from both photodiodes does not change, a correct distance signal can always be obtained, and the judgment control means does not perform erroneous judgment control, and the object to be detected is illuminated. It is possible to prevent erroneous operation when moving across the axis. In addition, when the detected object moves in the direction that crosses the optical axis, the focused spot is generated when a part of the projected beam is reflected by the detected object (immediately after entering the projected beam). The illuminance at one end may become slightly higher, but even in such a case, the object detection signal is not output from the determination control means when the split photodiode output at both ends is larger than the other split photodiode outputs. Therefore, there is an effect that it is possible to prevent a malfunction in the state where the detected object starts to cross the optical axis.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of the present invention, FIGS. 2 and 3 are explanatory views showing the configuration and operation of the same, FIG. 4 is a front view of relevant parts of the same, and FIG. 5 is operation of the same. Explanatory drawing, FIG. 6 is a schematic configuration diagram of another embodiment, FIG. 7 is a schematic configuration diagram of a conventional example, FIG. 8 is a front view of a main part of the same, and FIG. 9 is a schematic configuration diagram of another conventional example. , Fig. 10 (a) and (b) are front views of the main part of the above.
FIG. 11 is a circuit diagram of the above, and FIGS. 12 and 13 are operation explanatory diagrams of the same. 3 is a light emitting means, 5 is a light receiving lens, 6 is a light receiving means, and 8a to 8c.
Is a photodiode, 10 is determination control means, 14 is a comparison circuit, 16 is an output circuit, and X is an object to be detected.

Claims (2)

(57) [Claims] 1. A light projecting means for projecting a light beam onto an object to be detected, and a light receiving means arranged at a side of the light projecting means with a predetermined distance to collect light reflected by the object to be detected. A position detecting element, which is arranged on the image plane of the light receiving means and is divided into photodiodes so that the moving direction of the focused spot when the detected object moves in the light projecting direction intersects the dividing line, and a position detecting element. In the photoelectric switch including a determination control unit that determines whether or not the detected object is present in a predetermined detection area based on the output of each divided photodiode of, and controls the output circuit, Receiving light from the light receiving means with an anamorphic lens that can be stretched in the direction orthogonal to the moving direction and the length of the focused spot can be set to be slightly longer than the width of the split photodiode. Judgment control that prevents the object detection signal from being output when the output of the divided photodiodes at both ends is larger than the output of the other divided photodiodes. A photoelectric switch characterized by forming means. 2. A photoelectric switch according to claim 1, wherein a prism for changing a detection area is movably arranged near the light receiving surface of the position detecting element.