JPH0681028B2 - Photoelectric detector - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a reflective photoelectric detector, and more particularly to a reflective photoelectric detector that detects a mark such as a sheet conveyed by a roller.

[Outline of Invention]

The photoelectric detector according to the present invention receives a reflected wave signal by using a light receiving section having a light receiving area in which the light receiving areas of two surfaces which are divided into four and are diagonally divided are substantially equal to each other. The light receiving levels of the pair of light receiving regions formed are added, and the mark of the reflected wave object is detected based on the difference. By doing so, even if there is a change in the projection direction of the sheet to be detected, the output levels of the respective addition means change at the same time, so that it is possible to detect a sheet from any direction without malfunctioning.

[Prior art and its problems]

In a conventional reflective photoelectric switch that detects a mark on a sheet, a focusing lens is used to focus the light of a light-emitting element at a predetermined position on the sheet, and the mark on the sheet is detected by a change in the reflected light level. I have to. Such a reflection type photoelectric switch has a problem that the reflected light level may change due to a minute fluctuation of the sheet in the direction of the projection axis, and the mark may be detected at an incorrect position. Therefore, there is also known a means for separating the projected light into two and irradiating them to different positions on the sheet, and detecting the mark on the sheet based on the difference in the reflected light level of each light. Then, there was a problem that the configuration of the optical system becomes complicated. There is also known a photoelectric switch in which the light receiving area is divided into two and the mark is detected based on the temporal change of the level. In such a case, the mark should be detected according to the division state of the light receiving area. However, there is a problem in that the sheet conveyance direction that can be performed is regulated and the degree of freedom in the attachment direction is lost.

[Object of the Invention]

The present invention has been made in view of the above problems of the conventional photoelectric detector, and even if the sheet to be detected changes a minute distance in the direction of the light projection axis, it does not cause a malfunction and is surely on the sheet. It is an object of the present invention to provide a photoelectric detector that can detect a mark and can attach the light receiving portion in any direction.

[Constitution and effect of the invention]

The present invention is a reflection-type photoelectric detector that irradiates a detection target with light and detects an object based on reflected light. The light-receiving area is divided into four, and the sum of the light-receiving areas of two diagonal light-receiving areas is obtained. Light-receiving parts that are substantially equal to each other and have different light-receiving areas, and first and second adding means that respectively add outputs of light-receiving regions that form diagonal angles of the light-receiving parts, and first and second And signal processing means for outputting an object detection output by both outputs of the adding means.

As described above, in the photoelectric detector according to the present invention, the outputs of the light-receiving regions that are diagonally divided by the four-divided light-receiving portions are added, and the mark on the sheet is detected based on the added light-receiving level difference. There is. Therefore, when the detected object fluctuates in the direction of the projection axis and the detected distance changes, the added light-receiving level also fluctuates at the same time. Therefore, by canceling the change, malfunction can be prevented. Further, since the light receiving area of the light receiving section is divided into four, the mark can be detected when the projection of the mark passes through the light receiving section from any direction, and the light receiving element can be mounted in any direction. is there.

[Explanation of Examples]

(Structure of Embodiment) FIG. 2 is a schematic view showing an optical system of a photoelectric switch according to an embodiment of the present invention. In the figure, a light projecting unit 1 including a light source such as a lamp is arranged at a focus position of a focusing lens 3 via a half mirror 2. The focusing lens 3 focuses the light from the light projecting unit 1 and irradiates it onto the sheet 4 which is conveyed perpendicularly to the optical axis as shown in the drawing. Marks 5 are provided on the sheet 4 at predetermined intervals, and an optical system is arranged so that the marks are located at the focal position of the focusing lens 3. Then, the reflected light from the sheet 4 is given to the half mirror 2 through the focusing lens 3, and a part of the reflected light passes through the half mirror 2 as it is and is applied to the composite photodiode 6. Here, the photodiode 6 has photodiodes PD-a, PD-b, PD-c as shown in the front view and the side view in FIGS. 3 (a) and 3 (b) and the connection diagram in FIG. 3 (c). , P
It is assumed that four photodiodes made of Dd are combined. Here, the light receiving areas of the composite photodiodes 6 are different from each other, and the light receiving areas of two diagonal photodiodes, that is, the sum of the light receiving areas of the photodiodes PD-a and PD-c, and PD -b and PD-d
Are configured so that the sums of the light receiving areas of are equal to each other.

Next, FIG. 1 is a block diagram showing the structure of a photoelectric switch according to an embodiment of the present invention. In this figure, a pair of photodiodes located diagonally of the composite photodiode 6
The outputs of PD-a and PD-c are given to the summing amplifier 11, and the outputs of the other photodiodes PD-b and PD-d are given to the summing amplifier 12. The adder amplifiers 11 and 12 add these output levels to each other and amplify them with a predetermined amplification factor, and give their respective outputs to the subtraction circuit 13. The subtraction circuit 13 detects the level difference by subtracting the outputs of the two addition amplifiers 11 and 12, and supplies the output to the comparison circuit 14.
A predetermined threshold level Vth is given to the comparison circuit 14, and when the output exceeds that output, the object detection output is output by the output circuit 15
Is output to the outside via. The constant voltage circuit 16 is a power supply circuit that supplies a constant voltage to each unit.

(Operation of this Embodiment) Next, the operation of the photoelectric switch of this embodiment will be described with reference to the waveform diagrams. As shown in FIG. 2, assuming that the light focused by the light source is applied to the sheet 4 and the mark 5 is applied as the sheet 4 is conveyed, the projected image 5 s is projected on the focusing lens 3 and the half mirror 2. It passes through the composite-type photodiode 6 via. 4 (a)-(d) are the projected images.
It is a figure which shows the time change of a relative position when 5s passes the photodiode 6, and FIG. 5 (a)-(c) is a waveform diagram of each part corresponding to it. As shown in FIG. 4 (a), when the projection 5s of the mark 5 first reaches the photodiodes PD-a and PD-d after the time t1, the photodiode PD-d
Since the light receiving area of is larger than the light receiving area of PD-a, the output of the summing amplifier 11 does not decrease so much as shown by the solid line A in FIG. Fall to. Then, as shown in FIG. 4B, after the time t2 when the projected image 5s reaches the dividing line dividing the photodiode 6, the light receiving area of the photodiode PD-c is larger than the light receiving area of the photodiode PD-b. Therefore, the decrease in the output level of the adding amplifier 11 is larger than the decrease in the output of the adding amplifier 12. Then, as shown in FIG. 4 (c), the time
When the projection image 5s reaches t3 and covers the composite photodiode 6, the outputs of the respective summing amplifiers 11 and 12 coincide with each other. Furthermore, after t4, the rear end of the projected image 5s of the mark 5 is the photodiode PD-a, P.
The output of the summing amplifier 12 has a higher rate of rise than the output of the summing amplifier 11 as shown by the solid lines A and B in FIG. 5 (a) until time t5 when it starts passing through Dd and reaches the dividing line of the photodiode 6. Further, after time t5, the increase rate of the output level of the summing amplifier 11 becomes higher than that of the summing amplifier 12 until time t6 when the rear end of the projection image 5s finishes passing through the photodiodes PD-b and PD-c. Therefore, by subtracting these outputs from the subtraction circuit 13, a waveform as shown in FIG. 5 (b) is obtained.
By comparing this output difference with the predetermined threshold value Vth by the comparison circuit 14, the object detection output can be obtained as shown in FIG. 5 (c).

Here, even if the sheet 4 is moved back and forth by a small distance in the direction of the projection axis, the light receiving outputs of all the diodes of the composite type photodiode 6 divided into four regions are changed at the same time. It is possible to prevent malfunction due to fluctuations.

In this embodiment, the optical system is arranged so that the projection image 5s of the mark 5 passes through the composite photodiode 6 in the direction of arrow I in FIG. 6, but the projection image 5s passes through in the direction of arrow II. It is possible to arrange a photodiode so as to configure an optical system. Furthermore, even if the optical system is arranged in all other directions, for example, in the direction shown by the arrow III, the mark can be surely detected in the same manner, and the photodiode installation direction can be arbitrarily determined. is there.

(Explanation of Other Embodiments) In this embodiment, as shown in FIG. 3, a composite photodiode 6 composed of four photodiodes each having a different light receiving region is used, but as shown in FIG. A light receiving element 20 such as a composite type photodiode having a light receiving region divided into four is used, and a slit 21 is provided on the front surface thereof so that the light receiving area of each photodiode is the same as that of the photodiode shown in FIG. It is also possible to configure the light receiving unit by dividing the sum of the areas of PD and PD-c so as to be equal to the sum of the photodiodes PD-b and PD-d.

Although FIG. 1 has been described using the light projecting unit 1 that is continuously turned on as a light source, a light emitting diode can be pulse-driven as a light source as shown in FIG. In this case, the clock signal of the oscillator circuit 30 is applied to the light emitting diode 31 and the gate circuits 32 and 33. Then light emitting diode 3
1 is pulse-driven to irradiate one point on the sheet 4 via the focusing lens 3, and the reflected light is given to the composite photodiode 6 composed of PD-a to PD-d as described above. The two sets of outputs are added to the summing amplifier as in the embodiment of FIG.
It is amplified by 11, 12 and its output is given to the gate circuits 32, 33. The gate circuits 32 and 33 are opened / closed by the drive clock signal of the oscillation circuit 30 to give only the reflected wave to the detection circuits 34 and 35 of the next stage. The detection circuits 34 and 35 output a signal corresponding to the received light level by rectifying and smoothing the reflected light output passing through the gate circuit, and give it to the subtraction circuit 13. The subsequent operation is the same as that of the above-described embodiment, and when the output of the subtraction circuit 13 is equal to or more than the predetermined value, the object detection output is generated via the comparison circuit 14. In this case, it is possible to remove the noise due to the disturbance light applied between the intermittent pulses, and it is possible to greatly reduce the possibility of malfunction.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of a photoelectric switch according to the present invention, FIG. 2 is a schematic diagram showing a configuration of an optical system thereof, and FIG. 3 is an example of a composite photodiode having different light receiving areas. Yes, FIG. 3 (a) is the front view, FIG.
FIG. 3B is a side view and FIG. 3C is a connection diagram thereof.
Further, FIG. 4 is a diagram showing a temporal change of the projected image 5s passing through the light receiving element as the sheet is conveyed, and FIG. 5 is a time showing a level change of each portion of the photoelectric switch which changes as the projected image passes. FIG. 6 is a chart showing the direction of a projected image passing through a photodiode, FIG. 7 is a schematic view of a light receiving element showing another embodiment of the present invention, and FIG. 8 is another embodiment of the present invention. It is a block diagram of the photoelectric switch shown. 1 ... Projector, 2 ... Half mirror, 3 ... Focusing lens, 4 ... Sheet, 5 ... Mark, 5s ... Projection image, 6,20
...... Composite photodiodes, PD-a to PD-d …… Photodiodes, 11,12 …… Adding amplifier, 13 …… Subtracting circuit, 14
…… Comparison circuit, 15 …… Output circuit, 16 …… Constant voltage circuit, 21
...... Slit, 30 ...... oscillation circuit, 31 …… light emitting diode, 32,33 …… gate circuit, 34,35 …… detection circuit

Claims (3)

[Claims] 1. A reflection type photoelectric detector for irradiating a detection object with light and detecting an object based on reflected light, wherein a light receiving area is divided into four, and a sum of light receiving areas of two diagonal light receiving areas is obtained. Light-receiving parts that are substantially equal to each other and have different light-receiving areas, and first and second adding means that respectively add the outputs of the light-receiving regions that form diagonal angles of the light-receiving parts; And a signal processing unit which outputs an object detection output by both outputs of the second adding unit. 2. The photoelectric detector according to claim 1, wherein the light receiving section has a composite type light receiving element having a light receiving region divided into four. 3. The light receiving section has a composite light receiving element having a light receiving area divided into four equal parts, and the sum of the light receiving areas of two light receiving areas diagonally forming the respective light receiving areas is provided on the front surface thereof. The photoelectric detector according to claim 1, characterized in that slits are provided which are substantially equal to each other and have different light receiving areas of respective light receiving regions.