JP2004215315A - Photo-electric sensor and sensitivity setting method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photo-electric sensor in which a judgement threshold can easily be set based upon only one of two states to be judged. <P>SOLUTION: The photo-electric sensor includes: a lighting unit for irradiating a detection region with light; a light receiving unit for directly or indirectly receiving the light from the lighting unit and outputting a detecting signal corresponding to a quantity of received light; a setting unit for setting the judgement threshold; and a judgement unit for judging whether the detection region is in a first optical state or in a second optical state on the basis of the detecting signal from the light receiving unit and the preset judging threshold. The setting unit has: a means for setting a real received light quantity in the first optical state or the second optical state of the detection region as a reference value; and a means for setting a received light quantity designated by the ratio to the reference value as the judging threshold. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

An object of the present invention is to provide a method for setting the sensitivity of a photoelectric sensor in which sensitivity adjustment is easy.

  Photoelectric sensors having a light emitter and a light receiver include a transmission type and a reflection type. In a transmission type photoelectric sensor, basically, a light emitter and a light receiver are opposed to each other at a predetermined distance, and an object enters into an optical path (detection area) formed between the light emitter and the light receiver. At this time, object detection is performed by utilizing the fact that the amount of light directly emitted by the light receiver of the light emitted from the light emitter changes. The reflection type photoelectric sensor is provided with the light emitting direction of the light emitter and the light incident direction of the light receiver aligned side by side, and the light emitted from the light emitter is reflected indirectly by the light receiver to receive the light. The object is detected from the change in the amount. That is, this reflection type photoelectric sensor eliminates the reflected light by the object when the object is not present in the detection area on the optical axis of the light projector, and according to the distance to the object when the object is present in the detection area. It is configured to perform object detection by utilizing the fact that reflected light of an intensity (amount of received light) is received.

  Such photoelectric sensors that detect the optical state in the optical path formed between the light emitter and the light receiver as a change in the amount of light received by the light receiver are used for various purposes such as object detection and object determination. You. Note that the optical state in the optical path refers to a light transmission amount (propagation rate) and the like depending on the reflectance and transmittance of light on the detection target, its shape, the distance to the detection target, and the like.

By the way, in this type of photoelectric sensor, conventionally, as disclosed in Patent Document 1, setting and calibrating the light receiving sensitivity of the photoelectric sensor under predetermined conditions has been performed. Specifically, the calibration of the light receiving sensitivity is performed by adjusting a light receiving level determination threshold (threshold) that changes depending on whether an object is present or not according to the light receiving level at that time. The light receiving sensitivity may be adjusted by adjusting the gain of the sensing amplifier or adjusting the amount of light emitted from the light projector. As a conventional example, FIG. 3 shows a procedure for setting a determination threshold in sensitivity setting.
(1)
The amount of received light is obtained without an object (work).
(2)
The amount of received light is obtained in a state where there is an object (work).
(3)
A determination threshold is determined from (1) and (2).
Therefore, two measurements are required, one with an object and one without.

However, when one of the two states to be determined is unstable, for example, when the brightness of the background changes when there is no target object, it is not possible to set the determination threshold using the method described above. Have difficulty. An object of the present invention is to provide a photoelectric sensor capable of easily setting a determination threshold based on only one of two states to be determined in order to solve such a problem.

  The present invention sets a light emitting device that projects light to a detection area, a light receiving device that directly or indirectly receives light from the light emitting device and outputs a detection signal according to the amount of received light, and a determination threshold value for determination. Determining means for determining whether the detection area is in the first optical state or the second optical state based on a detection signal from the light receiver and a predetermined determination threshold value In the photoelectric sensor having: a setting means for setting, as a reference value, one of the actual light receiving amounts in the first optical state and the second optical state of the detection area, and a ratio to the reference value. Means for setting the amount of light received specified by the above as a determination threshold value.

Also, a light emitter for projecting light to the detection area, a light receiver for directly or indirectly receiving light from the light emitter and outputting a detection signal according to the amount of received light, and a setting for setting a judgment threshold value for judgment Means, and determination means for determining which of the first optical state and the second optical state the detection area is in based on the detection signal from the light receiver and a preset determination threshold. In the sensitivity setting method of the photoelectric sensor having, in the first optical state of the detection area and one of the actual light reception amount in the second optical state as a reference value and the received light amount specified by the ratio to this reference value, It is characterized in that it is set in the setting means as a judgment threshold.

  According to the present invention, the determination is made even when one of the two states to be determined is unstable, for example, when the brightness of the background changes when there is no detection target in the detection area. It is possible to easily set the determination threshold based on only one of the two power states.

1 to 4, the same components are denoted by the same reference numerals and described.
FIG. 4 is a block diagram of the photoelectric sensor (photoelectric switch) of the present invention. The control unit 1 causes the light projector 3 (for example, a light emitting diode) facing the detection area 2 to emit light. The light from the light projector 3 changes according to the optical state of the detection area 2, and the light is received by the light receiver 4 (for example, a photodiode) and converted into an electric signal corresponding to the amount of received light. The electric signal is sent to the determination means 5 as received light amount data. The determination means 5 compares the received light amount data with a determination threshold value to determine the presence or absence of the target. The determination threshold for determining the presence or absence of the target is set in the setting unit 7 by teaching.

FIG. 1 shows an actual teaching state of a transmission type photoelectric switch in which light from the light projector 3 is directly received by the light receiver 4 through the detection area 2. First, a predetermined operation (for example, pressing and holding for 10 seconds or more) is applied to the operation means 6 (for example, a push button switch) of the setting means 7 to switch the operation state of the photoelectric switch from the detection mode to the setting mode. In the setting mode, various setting operations can be performed. Next, the state where there is no detection target 11 (work) in the detection area 2 is maintained. The optical state (first optical state) of the detection area 2 at this time is a state in which the light emitted from the light projector 3 is completely transmitted and received by the light receiver 4. 100% is set based on this state. That is, a predetermined operation is performed on the operation unit 6 to store the actual amount of received light from the light receiver 4 in the reference value storage unit 8 (for example, a memory). Then, “100” is displayed as a percentage on the display means 10 (for example, a 7-segment display).

Next, a value obtained by multiplying this reference value by a value slightly higher than the transmittance of the target object is to be used as a determination threshold. As an example, if the transmittance of the work is known to be 80%, a ratio of 90% to the amount of received light (reference value) without the target work is set as the determination threshold. That is, when a predetermined operation is applied to the operation unit 6 to change the display of the display unit 10 to “90” and the finalizing operation is performed, a light receiving amount of 90% of the reference value is determined as the determination threshold and the determination threshold storage unit 9 ( (For example, a memory). Finally, a predetermined operation is applied to the operation means 6 to switch the operation state of the photoelectric switch from the setting mode to the detection mode. With this setting, when the work 11 does not exist in the detection area 2 in the detection mode, the light reception amount of the light receiver 4 becomes 100%, and the light reception amount is larger than the determination threshold (90%). It is determined that 11 does not exist. When the work 11 exists in the detection area 2, the light having the transmittance of 80% is received by the light receiver 4 and the amount of received light is lower than the determination threshold (90%) as shown in the lower diagram of FIG. You.

  Next, FIG. 2 shows an actual teaching state of the reflection type photoelectric switch in which the light from the light projector 3 is reflected by the detection area 2 and received by the light receiver 4, that is, indirectly received. First, the photoelectric switch is switched to the setting mode. In a state where there is no work 11 in the detection area 2, the amount of light received by reflection from the background 12 is set to 100% as a reference value. Next, when the ratio between the reflectance of the background 12 and the reflectance of the workpiece 11 is known, a value obtained by multiplying the reference value by a value slightly lower than the reflectance of the workpiece 11 in consideration of the ratio is set as a determination threshold. I do. As an example, when it is known that the reflectance of the work 11 is 1.2 times the reflectance of the background, a ratio of 1.1 times the reference value, that is, a light receiving amount of 110% is set as the determination threshold. . Then, the operation state of the photoelectric switch is switched from the setting mode to the detection mode. With this setting, when the workpiece 11 does not exist in the detection area 2 in the detection mode, the received light amount (100%) is smaller than the determination threshold value (110%), so that it is determined that the workpiece 11 does not exist. When the work 11 is present in the detection area 2, the reflected light (120%) from the work is received by the light receiver 4 and the amount of received light is larger than the determination threshold (110%) as shown in the lower diagram of FIG. Is determined. Upon receiving the output signal of the judging means 5, the judgment result is displayed on the display means.

In the above description, as the first and second optical states of the detection area 2, a change in the state of transmission or reflection depending on the presence or absence of the work 11 in the detection area 2 is exemplified, but the present invention is not limited thereto. The subject of the present invention includes a change in the optical state due to a change in the size, surface roughness, color, refractive index, and the like of the work 11 in the detection region 2.
Further, in order to realize the above setting means and determination means, the configuration may be made using so-called hardware resources such as a variable resistor and a comparator, or may be made using so-called software resources for operating a microcomputer by a program. You may. Each configuration is a well-known and conventional technique in a photoelectric switch, and which configuration is adopted is not directly related to the gist of the present invention, and thus the detailed description is omitted.

Furthermore, the application of the present invention is not limited to photoelectric sensors. The present invention is also applicable to proximity sensors of various detection methods such as an induction type (magnetic field), a capacitance type (electric field), and an ultrasonic type (sound). For example, in the case of an induction type proximity switch, one coil also serves as an excitation coil (corresponding to a light emitter) and a detection coil (corresponding to a light receiver), and a first magnetic state and a second magnetic state of a detection area are provided. It may be considered that the state is determined.

Judgment value setting for transmission type photoelectric switch Judgment value setting of reflective photoelectric switch Flow chart of conventional example of sensitivity setting of photoelectric switch Block diagram of photoelectric switch

Explanation of reference numerals

REFERENCE SIGNS LIST 1 control means 2 detection area 3 light emitter 4 light receiver 5 determination means 6 operation means 7 setting means 8 reference value storage means 9 threshold value storage means 10 display means 11 work 12 background

Claims (2)

A light emitter for projecting light to the detection area, a light receiver for directly or indirectly receiving light from the light emitter and outputting a detection signal according to the amount of received light, and setting means for setting a judgment threshold for judgment A determination unit that determines whether the detection area is in the first optical state or the second optical state based on a detection signal from the light receiver and a preset determination threshold. In the sensor,
The setting means is means for setting one of the actual light reception amounts in the first optical state and the second optical state of the detection area as a reference value, and the light reception amount designated by a ratio to the reference value. Means for setting as a determination threshold value. A light emitter for projecting light to the detection area, a light receiver for directly or indirectly receiving light from the light emitter and outputting a detection signal according to the amount of received light, and setting means for setting a judgment threshold for judgment A determination unit that determines whether the detection area is in the first optical state or the second optical state based on a detection signal from the light receiver and a preset determination threshold. In the sensitivity setting method of the sensor,
Setting an actual light receiving amount of one of the first optical state and the second optical state of the detection area as a reference value and a light receiving amount designated by a ratio with respect to this reference value as a determination threshold in the setting means; A sensitivity setting method for a photoelectric sensor.

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