JPH0640889U - Photoelectric object detector - Google Patents

Abstract

(57) [Summary] [Purpose] It is possible to stably detect an object located in a short range as well as a long range. [Structure] The photoelectric object detection device includes a first light emitting unit 1 and a second light emitting unit 2. The first light emitting unit 1 projects focused light toward an object located at a relatively long distance. The second light emitting unit 2 emits divergent light toward an object located at a relatively short distance. The pair of light emitting units 1 and 2 are selectively driven by the driving unit 10. The first and second light emitting units 1 and 2 are provided with a common light receiving unit 3, which receives reflected light from an object and outputs an electric signal according to the light intensity. The detection unit 11 processes the electric signal to generate a detection signal indicating the presence or absence of an object.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a photoelectric object detection device. More specifically, the present invention relates to a photoelectric sensor that uses a light emitting element to project light toward an object and uses a light receiving element to receive reflected light to detect the object.

[0002]

[Prior art]

 FIG. 5 schematically shows the structure of a conventional photoelectric sensor. The photoelectric sensor includes a light emitting element 101 and a light receiving element 102. The light emitted from the light emitting element 101 becomes focused light 104 or spot light via the condensing lens 103, and is projected toward the object 105 in front. The reflected light 106 from the object 105 is imaged on the light receiving surface of the light receiving element 102 via the condenser lens 107. When the object 105 does not exist, no image appears on the light receiving surface of the light receiving element 102. Therefore, the presence or absence of the object 105 can be detected according to the change in the amount of received light. Since the conventional photoelectric sensor uses focused light in the form of a beam, the light can effectively reach an object located at a relatively long distance, and a sufficient amount of reflected light necessary for detection can be obtained. .

[0003]

[Problems to be solved by the device]

 The problem to be solved by the present invention will be briefly described with reference to FIG. FIG. 6 shows a state in which the object 105 is located at a relatively short distance in the conventional photoelectric sensor. As the object 105 approaches, the angle formed by the optical path of the focused light 104 and the optical path of the reflected light 106 increases, and the imaging position on the light receiving element 102 moves outward. When the object 105 approaches, the image formation by the condenser lens 107 deviates from the light receiving surface of the light receiving element 102, which makes it impossible to detect the object. That is, in the conventional photoelectric sensor, it is possible to detect an object located at a long distance by using focused light, but on the contrary, there is a problem that a dead point occurs in a short distance range.

[0004]

[Means for Solving the Problems]

 In view of the above-mentioned problems of the conventional technology, an object of the present invention is to provide a photoelectric sensor capable of effectively detecting not only long-distance objects but also short-distance objects. The following measures have been taken to achieve this goal. That is, the photoelectric object detection device according to the present invention diverges toward the object located at a comparatively short distance and the first light emitting part which projects the focused light toward the object located at a relatively long distance. And a second light emitting unit that emits light. The first and second light emitting units selectively emit light by the driving unit. Further, a common light receiving portion is provided for the first and second light emitting portions, receives the reflected light from the object, and outputs an electric signal according to the light intensity. This electric signal is processed by the detection unit to obtain a detection signal representing the presence or absence of an object.

The drive unit includes a selection circuit that alternately drives the first and second light emitting units. Alternatively, the drive unit may include a selection circuit that continuously selects one of the first and second light emitting units and deselects the other. The detection unit may output a detection signal indicating distance information of the object in addition to the presence / absence information of the object.

[0006]

[Action]

 According to the present invention, there is provided a first light emitting unit for emitting focused light and a second light emitting unit for emitting divergent light. Focused light has a long reach and can obtain a sufficient amount of reflected light even for an object at a long distance. On the other hand, the divergent light cannot illuminate a distant place, but can sufficiently illuminate an object located in the vicinity, and can secure the amount of reflected light necessary for detection. Focused light and divergent light are switched alternately, and the common light receiving unit receives the reflected light from the object. Therefore, the photoelectric object detection device according to the present invention can effectively detect a distant object as in the conventional case, and can also effectively detect a nearby object which has been a dead point in the past.

In addition, when the long distance and the short distance are constantly monitored at the same time, the first and second light emitting units are alternately driven as described above, but depending on the installation location of the photoelectric object detection device, the long distance and the short distance may be changed. Alternatively, it may be sufficient to monitor either one of the short range and the short range. At this time, it is possible to continuously select and drive the required light emitting unit and deactivate the other unnecessary light emitting unit. Furthermore, when monitoring both the perspective range, it is possible to output not only the presence information of the object but also the detection signal including the distance information.

[0008]

【Example】

 Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic block diagram showing the overall configuration of a photoelectric object detection device according to the present invention. As shown in the figure, the present device includes a first light emitting section 1, a second light emitting section 2, and a common light receiving section 3 which is shared by both. These light emitting portion and light receiving portion are incorporated in the frame 4. The first light emitting unit 1 projects focused light toward an object located at a relatively long distance. Therefore, the first light emitting unit 1 is composed of a combination of the light emitting element 5 and the condenser lens 6. The second light emitting unit 2 also emits divergent light toward an object located at a relatively short distance. Therefore, the second light emitting section 2 is composed only of the light emitting element 7 which serves as a diffused light source. Further, the common light receiving unit 3 receives the reflected light from the object and outputs an electric signal according to the light intensity. Therefore, the common light receiving unit 3 is composed of a condenser lens 8 for collecting reflected light to form an image and a light receiving element 9 arranged on the image forming surface.

The pair of light emitting elements 5 and 7 are selectively driven by the driving unit 10. For example, the driving unit 10 alternately drives the light emitting elements 5 and 7. Alternatively, instead of this, one of the light emitting elements 5 and 7 may be continuously selectively driven and the other may be in a non-selected state. A detection unit 11 is connected to the light receiving element 9 and processes an electric signal to generate a detection signal indicating the presence or absence of an object. In some cases, the detection unit 11 can output a detection signal representing distance information of the object in addition to the presence / absence information of the object.

Next, the operation of the photoelectric object detection device shown in FIG. 1 will be described in detail with reference to the geometrical optical diagram of FIG. First, when the first light emitting section is selectively driven, the light emitted from the light emitting element 5 becomes focused light through the condenser lens 6 and is projected onto the object 12 located at a far distance in the front direction of the optical axis. Be illuminated. The focused light can reach a relatively far distance, and the far detection range reaches, for example, about 3 m. The reflected light from the object 12 is condensed by the condenser lens 8 and a spot is imaged on the light receiving surface of the light receiving element 9. Therefore, the amount of received light changes depending on the presence or absence of the object 12, and the detection operation can be performed. However, when the object 12 approaches within a range of 1 m, for example, the spot deviates from the light receiving surface and it becomes impossible to perform effective object detection.

Next, when the second light emitting section is selectively driven, the light emitting element 7 emits light. Since the condenser lens is not arranged on the front surface of the light emitting element 7, the light becomes a divergent light or a diffused light as it is, and illuminates a wide front area. When the object 12 enters this irradiation range, the reflected light is collected by the focusing lens 8 and an image of the object 12 is formed on the light receiving element 9. Therefore, the amount of received light changes depending on the presence or absence of the object 12, and an effective detection operation is performed. However, unlike focused light, the effective reach of divergent light is short. Therefore, only an object located within a relatively short range (for example, within 1 m) can be detected. Even if the object 12 is off the focusing axis or the spot axis with respect to the light receiving surface of the focusing lens 8, the reflected light of the object 12 is diffusely reflected at a short distance, so that it is relatively strong reflected light. Therefore, it is possible to obtain a sufficient change in the amount of received light. As described above, according to the present invention, the complementary use of the first light emitting portion and the second light emitting portion can effectively cover both the near and far ranges. At this time, the common light-receiving portion can be used also for the first and second light-emitting portions, and the number of components can be increased by one light-emitting element as compared with the conventional one.

FIG. 3 is a block diagram showing an electrical configuration example of the photoelectric object detection device shown in FIG. As shown in the figure, this device uses infrared light emitting diodes IR DS and IRDL as a pair of light emitting elements. On the other hand, the infrared light emitting diode IRDS projects divergent light and is used for detecting the short-distance object S. The other infrared light emitting diode IRDL projects focused light to the front via a condenser lens and is used for detecting a long-distance object L. The light emitting diode may be visible light or infrared light. As described above, the drive unit 10 is connected to the pair of infrared light emitting diodes IRDS and IRDL. The driving unit 10 includes a pair of drivers DRS and DRL, and drives the corresponding infrared light emitting diodes IRDS and IRDL, respectively. A modulation circuit MDL is connected to the pair of drivers DRS and DRL and supplies a high frequency modulation signal. Further, a selection circuit SEL is connected to the drivers DRS and DRL so that the pair of infrared light emitting diodes IRDS and IRDL are alternately selected and driven in a predetermined cycle. Alternatively, instead of this, the selection circuit SEL can perform control to continuously selectively drive one of the pair of light emitting diodes IRDS and IRDL and set the other to a non-selected state.

A light receiving element is incorporated for receiving the reflected light from the object S or L and outputting an electric signal corresponding to the light intensity. This light receiving element is composed of, for example, a photodiode P D. The detector 11 is connected to the photodiode PD as described above. The detection unit 11 includes a preamplifier AMP that amplifies only the AC component of the electric signal output from the photodiode PD, a high-pass filter HPF that passes only the high frequency modulation signal component contained in the amplified AC component, It is composed of an AC / DC converter AC / DC that converts this high-frequency modulated signal component into a corresponding DC signal, and an analog / digital converter A / D that converts this direct current signal into a corresponding digital signal or sample data. Has been done. Further, a pair of memories MS and ML are connected to the analog / digital converter A / D, and the short range sample data and the long range sample data are stored in synchronization with the switching signal from the selection circuit SEL. To do. A processing circuit PRS is connected to the pair of memories MS and ML, and the stored sample data is sequentially accessed by accessing the memory and compared with a predetermined reference value to generate a detection signal indicating the presence or absence of an object. To do. In some cases, in addition to the presence / absence information of the object, a detection signal representing the distance information of the object may be output.

The operation will be described with reference to FIG. The selection circuit SEL sequentially generates switching signals at a predetermined cycle. In response to the switching signal, the pair of drivers DRS and DRL alternately drive the corresponding infrared light emitting diodes IRDS and IRDL to project the focused light and the divergent light toward the monitoring area. The focused light and the divergent light are intermittently modulated according to the high frequency modulation signal supplied from the modulation circuit MDL. This is to distinguish from noise light added from the outside world. The light reflected from the short-distance object S or the long-distance object L is received by the photodiode PD, and an electric signal is obtained according to the received light amount. When this electric signal is AC-amplified and only the high frequency modulation component is filtered, a high frequency modulation signal component in which the noise component is substantially removed can be obtained. The amplitude value changes according to the fluctuation of the reflected light amount. That is, when the focused light or divergent light illuminates the object, its amplitude value increases. By performing AC / DC conversion of this high-frequency modulation signal component and then analog / digital conversion, short-distance sample data and long-distance sample data corresponding to a pair of infrared light emitting diodes IRDS and IRDL can be alternately obtained. . A detection signal indicating the presence or absence of an object can be obtained by comparing these sample data with a predetermined reference value. The reference value is set separately for long distance and short distance. The sample data itself can be used to set the reference value.

Finally, a specific configuration example of the processing circuit PRS shown in FIG. 3 will be described with reference to FIG. This processing circuit includes a switching unit 111 as an input stage. The switching unit 111 temporarily switches the sample data read from the memories MS and ML (not shown) in response to a control signal input from the outside when no object exists in the monitoring area, for example. belongs to. The switching unit 111 includes, for example, a pair of transmission gates 112 and 113 connected in parallel with each other, and an inverter 114 for selectively conducting the pair of transmission gates in response to a control signal.

A reference value setting unit 115 is connected to the output terminal of one transmission gate 113. The reference value setting unit 115 receives the sample data switched via the transmission gate 113, sets and holds the digital value as it is as a reference value. The reference value setting unit 115 is composed of, for example, a sample and hold circuit. The comparison unit 116 is connected to the reference value setting unit 115, and is also connected to the memories MS and ML via the switching unit 111. The comparing unit 116 alternately receives the short range sample data and the long range sample data via the other transmission gate 112 of the switching unit 111 during the object detection operation, and their digital values and the short range reference values corresponding to the digital values. , And outputs a detection signal indicating the presence or absence of an object in the surveillance area by comparing it with the long-distance reference value. The comparison unit 116 includes, for example, a window comparator and the like, and compares the sample data with reference values set corresponding to the short distance and the long distance, and when the sample data deviates from a predetermined allowable range, the window comparator is provided. The output level of is inverted. A gate unit 117 is connected to the output terminal of the comparison unit 116, forcibly prohibiting the output of the detection signal while the control signal is being input, and prevents the malfunction of the object detection device.

[0017]

[Effect of device]

 As described above, according to the present invention, the first light emitting unit that projects the focused light toward an object located at a relatively long distance and the divergent light toward an object located at a relatively short distance. A second light emitting unit for projecting light is provided, and a common light receiving unit for receiving reflected light from an object and outputting an electric signal according to the light intensity is provided. With this structure, the photoelectric object detection device according to the present invention has an effect that it can perform stable object detection from a short distance to a long distance. Also, by selectively driving only one of the first and second light emitting parts, there is an effect that the photoelectric object detection device can be used as a limited type only for long distance or only for short distance. .

[Brief description of drawings]

FIG. 1 is a schematic view showing the overall structure of a photoelectric object detection device according to the present invention.

FIG. 2 is a geometrical optical diagram for explaining the operation of the photoelectric object detection device according to the present invention.

FIG. 3 is a block diagram showing an electrical configuration of a photoelectric object detection device according to the present invention.

FIG. 4 is a block diagram showing a specific configuration example of a processing circuit included in the circuit shown in FIG.

FIG. 5 is a schematic diagram showing a conventional photoelectric object detection device.

FIG. 6 is a schematic diagram for explaining a problem of a conventional photoelectric object detection device.

[Explanation of symbols]

 1 1st light emission part 2 2nd light emission part 3 Common light receiving part 4 Frame 5 Light emitting element 6 Condensing lens 7 Light emitting element 8 Condensing lens 9 Light receiving element 10 Driving part 11 Detection part

Claims (4)

[Scope of utility model registration request] 1. A first light emitting unit that projects focused light toward an object located at a relatively long distance, and a second light emitting unit that projects divergent light toward an object located at a relatively short distance. , A driving unit that selectively drives the first and second light emitting units, a common light receiving unit that receives reflected light from an object and outputs an electric signal according to the light intensity, and processes the electric signal And a detection unit that generates a detection signal indicating the presence or absence of an object. 2. The photoelectric object detection device according to claim 1, wherein the drive unit includes a selection circuit that alternately drives the first and second light emitting units. 3. The photoelectric object detection device according to claim 1, wherein the drive unit includes a selection circuit that continuously selects one of the first and second light emitting units and deselects the other. 4. The photoelectric object detection device according to claim 1, wherein the detection unit outputs a detection signal representing distance information of the object in addition to the object presence / absence information.