JPH0358475B2 - - Google Patents

Abstract

PURPOSE:To prevent misdetection by providing a position detecting means that outputs two detection signals which are proportional to the quantity of a reflected converged spot from a moving body to be detected and increase or decrease according to the movement extent of the body, and comparing the level ratio of both signals with a preset detection range. CONSTITUTION:When the body to be detected which has a high light reflection coefficient is present in a detection area wherein a speed limit point A is at distance la between la1-la2 and intense reflected light is photodetected, signal currents IA and IB outputted from PSD4 increase to saturate photodetecting circuits 21a and 21b and logarithmic amplifier circuits 22a and 22b, the signal current ratio IA/IB becomes ''1'', and the output lnVA/VB of subtracting circuit 23 becomes ''0'' to enter a distance unmeasurable state. The operation level Vs of a comparing circuit 24, however, is set above 0 all the time by a setting limiting means 24b, so it is judged that the body to be detected is present, and an output circuit 6 is put in operation. Therefore, misdetection due to the saturation of the amplifying means is prevented and equipment controlled by the output circuit 6 never operates abnormally.

Description

[Detailed description of the invention]

(Technical Field) The present invention relates to a reflective photoelectric switch that controls an output circuit by determining whether or not a detected object exists within a preset detection area. (Background Art) Figures 1 to 3 show basic examples of this type of reflective photoelectric switch.
It is a light projecting means for projecting a light beam P made of pulse modulated light onto a target, and includes an oscillation circuit 10 that generates a synchronization signal for setting the light projection timing, a drive circuit 11, and a light emitting diode, laser diode, etc. It is formed by an optical element 12 and a light projecting optical system 13 consisting of a condenser lens that forms a light beam P. Reference numeral 2 denotes a light receiving means juxtaposed with a predetermined distance l ₀ from the light projecting means 1, and the projecting and light receiving means 1 and 2 are arranged in a triangular manner with respect to the object X to be detected. This light receiving means 2 includes a condensing means 3 made of a convex lens for condensing the light reflected by the object to be detected The position detecting means 4 is arranged within the condensing plane of the condensing means 3 made of a convex lens, and the position detecting means 4 is arranged in the condensing plane of the condensing means 3 made of a convex lens, and changes the amount of light when the condensing spot S moves in one direction. It outputs a first detection signal IA that increases in proportion to the amount of movement and outputs a second detection signal IB that increases in proportion to the amount of light and decreases in accordance with the amount of movement. Here, in the basic example, this position detection means 4 is a one-dimensional position detection element (hereinafter referred to as
As shown in FIG. 3a, this PSD 4 is formed by forming a P layer 31a on the front surface of a flat silicon 31, an N layer 31b on the back surface, and an I layer 31c in the middle. Signal currents IA and IB corresponding to the position of the condensing spot S are output. This signal current IA is a signal that increases in proportion to the amount of movement of the condensing spot S in one direction, and the signal current IB is a signal that decreases in proportion to the amount of movement. Of course, it goes without saying that the signal currents IA and IB are proportional to the amount of light. FIG. 3b shows an equivalent circuit of the position sensing element 4, where Pi is a current source, Do is an ideal diode, Co is a junction capacitance, Pt is a parallel resistance, and Ro is an interelectrode resistance. The position detecting means 4 may be any device as long as it can obtain contradictory signal currents IA and IB according to the movement of the condensing spot S when the distance l changes; It may be formed by two light receiving elements, and a phototransistor, a photodiode, a solar cell, CdS, etc. are used as the light receiving element. 5 is a discrimination control means, which detects the detected object X based on the output of the position detection means 4.
The output circuit 6 is controlled by determining whether or not the detection area DE exists within a predetermined detection area DE. The discrimination control means 5 includes light receiving circuits 21a and 21b that amplify and convert signal currents IA and IB from the position detection means 4 into signal voltages VA and VB, logarithmic amplification circuits 22a and 22b, and a logarithmic amplification circuit 22a. output
A subtraction circuit 23 that subtracts the logarithmic amplification circuit 22b output lnVB from lnVA, and a subtraction circuit 23 output lnVA/
The subtraction circuit 23 compares VB with the operation level Vs set by the detection area setting volume 24a.
A comparator circuit 24 that outputs an H level when the output lnVA/VB is lower than the operating level Vs, and the emission timing of the light beam P from the light emission element 12 (the oscillation circuit 10
The comparison circuit 2 is synchronized with the synchronization signal output from the
It is formed with a signal processing circuit 25 that reliably determines whether or not the detected object X exists within the detection area DE by sampling the four outputs. It is designed to control an output circuit 6 consisting of a relay, a semiconductor switch element for load control, etc.
Note that the light receiving circuits 21a and 21b include a bandpass filter circuit that passes only a pulsed optical signal and cuts out a DC optical signal, or that passes only a specific frequency. Now, when the detected object X exists at distances l ₁ , l ₂ , l ₃ from the reflective photoelectric switch Y as shown in FIG. The positions of the condensing spots S are as shown in Fig. 4b, and when the position of the detected object X changes in the projection direction of the light beam P, the condensed beam S moves in the direction of the arrow M and is output from the PSD 4. The signal currents IA and IB thus generated become position signals corresponding to the position of the condensing spot S. In the discrimination control means 5, the signal currents IA and IB are detected by the light receiving circuits 21a and 21b.
Signal voltages VA and VB are formed proportional to
By subtracting lnVA and lnVB in the subtraction circuit 23, the subtraction circuit 23 outputs a logarithmic value lnVA/VB of the level ratio of the signal voltages VA and VB. The output lnVA/VB of this subtraction circuit 23 is the distance l from the reflective photoelectric switch Y to the detected object X.
The output lnVA/VB of the subtraction circuit 23 with respect to the distance l becomes as shown in FIG. Therefore, by appropriately setting the operating level Vs with the detection area setting volume 24a of the comparison circuit 24, an accurate detection area DE can be easily set.
When the output lnVA/VB of the subtraction circuit 23 becomes lower than the operating level Vs, the output of the comparison circuit 24 becomes H level, and the output circuit 6 is activated via the signal processing circuit 25. Note that the logarithmic amplification circuit 2
In place of 2a and 22b, a linear amplification circuit may be used, and in place of the subtraction circuit 23, a division circuit may be used to form the amplification means and the calculation means. Here, in the above-mentioned basic example, the discrimination control means 5 uses the signal current IA output from the PSD 4,
The output circuit 6 calculates the logarithm of the level ratio of the signal with IB amplified and determines whether the detected object X is within the detection area DE based on whether the calculated value is within the predetermined detection range. is activated, the detection area DE can be set regardless of the light reflectance of the object to be detected X, and furthermore, it is not affected by dirt on the optical systems 13 and 3 for projecting and receiving light. By the way, in such a basic example, even if the light reflectance of the detected object X or the distance l to the detected object X changes widely, and the amount of received light fluctuates widely, no malfunction will occur. To do this,
Light receiving circuits 21a, 21b and logarithmic amplification circuit 22
It is necessary to widen the dynamic range of the amplification means for the signal currents IA and IB consisting of a and 22b, and in addition to the change in the light reflectance of the detected object X, the range in which the detection area DE can be set must be considered. For example, the dynamic range of the width increasing means needs to be 4 to 5 orders of magnitude or more. However, since it is very difficult to achieve such a wide dynamic range, amplifying means having a dynamic range of about three digits is usually used. Therefore, when the detected object X has a high reflectance and the detection area DE is set nearby, the signal currents IA and IB
There has been a problem in that the amplifying means of the sensor becomes saturated and a distance measurement error occurs, which may cause the output circuit 6 to malfunction.
FIG. 6 is a diagram illustrating the above-mentioned problem, and shows changes in the output lnVA/VB of the subtraction circuit 23 and the outputs lnVA and lnVB of the logarithmic amplification circuits 22a and 22b with respect to the distance l. Now, as shown in figure b, the signal current
IB amplification means 21b and 22b are saturated at distance lβ,
The amplifying means 21a and 22a of the signal current IA are at a distance lα
If it is assumed that the subtraction circuit 23 output lnVA/VB no longer corresponds to the distance l in the interval from distance lβ to lα, a distance measurement error will occur, and in the interval below the distance lβ, the subtraction circuit 23 output lnVA /VB becomes "0" (IA/IB=1) and distance measurement becomes impossible.
However, "0" of the output lnVA/VB of the subtraction circuit 23 corresponds to the distance lc at which the condensing spot S is imaged at the center of the PSD 4 and the signal current ratios IA and IB are "1".
The solid line in FIG. 1A shows the case where saturation occurs in the light receiving circuits 21a, 21b or the logarithmic amplification circuits 22a, 22b, and the dotted line shows the case where saturation does not occur.
Here, when the operating level Vs is set to "0" or less as shown by the imaginary line in FIG. X is the detection area
When the amplification means of the signal currents IA and IB are saturated at DE', the output lnVA/VB of the subtraction circuit 23 becomes "0" and the output circuit 6 does not operate. Therefore, there was an inconvenience that the object to be detected X was not detected even though the object to be detected X existed within the detection area DE'. In other words, due to the saturation of the amplification means, the detected object If such a detection error occurs, the equipment controlled by the output circuit 6 may operate abnormally, which is dangerous. (Object of the Invention) The present invention has been made in view of the above points, and its object is to provide a photoelectric switch that can prevent the saturation error of the detected object when the amplification means is saturated. Our goal is to provide the following. (Disclosure of the Invention) Embodiment 1 FIG. 7 shows an embodiment of the present invention. In a photoelectric switch similar to the basic example described above, the operation level Vs of the comparison circuit 24 is set to "0" by the detection area setting volume 24a. A setting control means 24b that can be set freely is provided, and the detection range of the comparison and discrimination means is limited to the light receiving circuits 21a and 2, which are amplifying means.
1b and "0", which is the arithmetic means output when the logarithmic amplification circuits 22a and 22b are saturated, that is, the subtraction circuit 23 output. In other words, as shown in FIG. 8, the distance la ₁ of the nearest point A ₁ of the settable range A ₁ to _{A 2} of the far limit point A of the detection area DE is determined by the center point C determined by the PSD 4 and the condensing means 3. distance greater than lc (la ₁ lc)
It was made so that it would become so. Therefore _{, a} detected object
exists and strong reflected light R is received, the PSD
The detection signal output from 4, that is, the signal current IA,
As IB increases, the light receiving circuits 21a and 21b and the logarithmic amplification circuits 22a and 22b become saturated, and the signal current ratio
IA/IB becomes “1” and subtraction circuit 24 outputs
lnVA/VB becomes "0" and distance measurement becomes impossible, but in the first embodiment, the operating level Vs of the comparator circuit 24 is always set to 0 or higher by the setting limiting means 24b. Detected object X
is determined to exist, and the output circuit 6 is activated. Therefore, detection errors of the detected object X due to saturation of the amplification means are prevented, and there is no risk that the equipment controlled by the output circuit 6 will malfunction. In other words, in the present invention, when the amplifying means is saturated, the detected object
Since the detection area DE is set so that it is determined that it exists within DE and the output circuit 6 is activated,
With the addition of a so-called fail-safe function, danger can now be avoided. By the way, the center position Z of the condensing spot S on the PSD 4 in such a triangulation type photoelectric switch is determined by the distance between the condensing means 3 of the convex lens and the PSD 4, as shown in FIG. F
Then, Z=l ₀ ×F/l, and as the distance l increases, the change in Z with respect to the distance change Δl decreases from ΔZ ₁ to ΔZ ₂ as shown in FIG.
On the other hand, the signal current ratio output from Z and PSD4
The relationship between IA/IB is, if the length of PSD4 is L,
lnlA/IB=ln(L/Z-1), and as the change in Z ΔZ ₁ to ΔZ ₂ becomes smaller, the change in IA/IB also becomes smaller and the ranging accuracy decreases. However, when light hits the edge of PSD4, the signal current ratio IA/IB is the first
As shown in Figure 0, the curve becomes steep, so if this part is used, the drop in accuracy will be reduced. In other words, the focus spot S _' of the reflected light R of the detected object All you have to do is design a suitable optical system.
Here, in Fig. 8, the farthest point A ₂ and the condensing means 3
One end of the PSD 4 is positioned on a straight line connecting the center of The center is located slightly inside the edge of PSD4. Therefore, based on the above conditions and conditions, PSD4
The center of is the nearest point of the settable range of the detection area DE
Located on the straight line connecting A ₁ and the center of the condensing means 3,
The optical system and PSD 4 are arranged so that one end 4a of the PSD 4 is located on a straight line connecting the farthest point A ₂ of the settable range of the detection area DE and the center of the condensing means 3.
All you have to do is design the length. Therefore, the length of the PSD 4 is determined, and the point where the straight line connecting the other end 4b of the PSD 4 and the center of the condensing means 3 intersects with the optical axis of the light projecting means 1 is theoretically close to the detection area DE. This is the limit point B. In other words, when the distance l to the detected object Sensitive parts are formed. The distance lb of this near limit point B is lb=la ₂ ×lc/2la ₂ −lc. However, since the photoelectric switch needs to include a portion closer than the near limit point B (up to the vicinity of the light projecting optical system 13) in the detection area DE, the existence of this insensitive portion poses a problem. However, in reality, the condensing spot S on the PSD 4 is not a point but has a certain size, and by blurring the condensed beam and making the condensing spot S at the end 4b of the PSD 4 appropriately large, it is possible to Even if the center of the light spot S deviates from the end 4b of the PSD 4, a certain amount of reflected light can be focused on the PSD 4, making it possible to eliminate the above-mentioned insensitive portion. However, when blurring the focused beam to enlarge the focused spot S, if it is made too large, the focused spot S
Since the influence of reflection unevenness within the lens becomes large and the accuracy is significantly reduced, it is necessary to set the near limit point B appropriately in order to avoid making the focal spot S so large. As a result of conducting experiments on various systems in consideration of the above points, it was found that the near limit point B should be set with a relationship of at least lb2/3lc. Here, since the near limit point B is la ₂ ×lc/2la ₂ −lc, it is sufficient to satisfy the relationship Ra ₂ 2Rc. On the other hand, the above consideration ignores the size of the photoelectric switch body (for example, the distance l ₀ between the emitter and light receiver means 1 and 2), but in reality, the distance A ₁ of the detection area DE,
A, A ₂ and the size of the photoelectric switch body are approximately determined empirically from the point of view of ease of use, and taking this into account, we experimentally determined the desirable relationship between l ₀ and lc. lc/lo20 was obtained. The table below shows a specific example in which the length L of the PSD 4 is 3 mm and the dimensions of each part are designed based on the above conditions. However, f is the focal length of the condensing means 3 made of a convex lens, and d is the lens diameter.

[Table] l according to the above specific examples (A-1) to (A-3)
-lnIA/IB characteristics are shown in FIGS. 11 to 13, respectively. (Effects of the Invention) As described above, the present invention includes a light projecting means for projecting a light beam onto a moving detected object, and a light projecting means disposed at a predetermined interval on the side of the light projecting means. a condensing means for condensing light reflected from the light beam by the object;
A first detection signal is provided on the light collecting surface of the light collecting means, and outputs a first detection signal that is proportional to the amount of light and increases in accordance with the amount of movement when the light focusing spot moves in one direction, and is proportional to the amount of light and increases in accordance with the amount of movement. The second decreases accordingly
position detecting means for outputting a detection signal of It is a photoelectric switch that includes a comparison and discrimination means that compares and discriminates whether or not it is within the detection range and activates the output circuit when it is within the detection range, so it is possible to set the detection area regardless of the light reflectance of the object to be detected, and also to It has the advantage of not being affected by dirt on the light receiving optical system, and also has a setting restriction means that allows the detection range to be freely set to include the output of the calculation means when both amplification means are saturated. When both amplifying means are saturated, the output circuit is always activated, preventing misdetection of the object to be detected due to saturation of the amplifying means, and there is no risk of abnormal operation of equipment controlled by the output circuit. There is an advantage.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of a basic example according to the present invention,
Fig. 2 is a block circuit diagram of the same as above, Fig. 3 is a diagram showing the configuration and equivalent circuit of the position detection element used in the above, Figs.
The figure is a block circuit diagram of one embodiment of the present invention, and FIGS. 8 to 13 are explanatory diagrams of the same operation. 1 is a light projection means, 3 is a condensing means, 4 is a position detection means, 6 is an output circuit, 22a, 22b are logarithmic amplification circuits, 23 is a subtraction circuit, 24 is a comparison circuit, and 24b is a setting restriction means.

Claims (1)

[Claims] 1. A light projecting means for projecting a light beam onto a moving object to be detected, and a condenser disposed at a predetermined interval on the side of the light projecting means to collect light reflected from the light beam by the object to be detected. A first detection signal is provided on the light collecting surface of the light means and the light collecting means, and outputs a first detection signal which is proportional to the amount of light and increases in accordance with the amount of movement when the light collecting spot moves in one direction, and which is proportional to the amount of light. and a position detection means that outputs a second detection signal that decreases in accordance with the amount of movement, an amplification means that amplifies both detection signals, and a calculation means that calculates a level ratio of the detection signals based on the output of the amplification means. and a comparison/discrimination means for comparing and discriminating whether the output of the arithmetic means is within a preset detection range and operating an output circuit when the output is within the detection range, the photoelectric switch comprising a means for amplifying the detection range. A photoelectric switch characterized in that it is provided with a setting control means that can freely set the output of the calculation means when the output of the calculation means is saturated.