JP3825671B2 - Multi-axis photoelectric sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a multi-optical axis photoelectric sensor used for preventing accidents in a press apparatus, for example.
[0002]
[Prior art]
An example of this type of multi-optical axis photoelectric sensor is disclosed in Japanese Patent No. 3046400. This irradiates light toward a detection area from a plurality of light projecting elements included in the light projector, and sequentially activates the light receiving elements of the light receiver corresponding to these light projecting elements. By receiving light, judging the light blocking state, and sequentially enabling the light receiving signals from the plurality of light receiving elements at the non-light emitting timing to determine the light blocking state, the incident state due to the light source other than the light projecting element, that is, the interference light is Detect if there is no. Accordingly, there is an advantage that it is possible to quickly eliminate the occurrence of erroneous detection or the like due to interference light in the detection operation of the light shielding state.
[0003]
[Problems to be solved by the invention]
By the way, there is a demand to install a plurality of this type of multi-optical axis photoelectric sensors asynchronously with, for example, the same timing of light projection timing from a plurality of light projecting elements. FIG. 5 shows, for example, a case where a light projector 3 and a light receiver 4 each having five LEDs (light projecting elements) 1 and photodiodes (light receiving elements) 2 are installed, respectively, and have the same configuration in parallel below them. 1 schematically shows a configuration in which a projector A and a light receiver B are installed close to each other. The light projector 3 and the light projector A, and the light receiver 4 and the light receiver B have the same configuration.
[0004]
In FIG. 5, a light receiver 4 having a plurality of photodiodes 2 is provided corresponding to the light projector 3 having a plurality of LEDs 1, and the light receiver 4 of the light receiver 4 is synchronized with the light projection timing of each of the plurality of LEDs 1 at this time. Each photodiode 2 is positioned so as to receive light. At this time, the light irradiated from the LED 1 included in the projector A is positioned so as to go to the light receiver B. At the same time, the light receiver 4 is also irradiated as interference light.
[0005]
Here, the above configuration has the following problems. That is, when the interference light is detected by the light receiver 4, only one light receiving element is activated during a certain period, so that interference light is incident on other non-activated light receiving elements. In spite of this, it is erroneously determined that the interference light is not incident even if the interference light enters. In the case of the misjudgment, for example, even when the light from the light projecting element is originally blocked by the detected object at the time of detecting the light shielding, the interference light from the light projecting element of the light projector A is incident on the light receiving element of the light receiver 4. If the light is received, it may be erroneously determined that the light is not blocked (arrow in the figure).
[0006]
Therefore, a method of extending the time for enabling the light receiving element of each light receiver 4 in the interference light detection period can be considered. However, if the time for enabling each light receiving element is lengthened, the time for detecting the interference light becomes longer.As a result, the time for detecting the interference light with respect to the time for detecting the light shielding is greatly increased. The performance as a switch is degraded, which is not a preferable method.
[0007]
The present invention has been completed based on the above situation, and a light source such as a multi-optical axis photoelectric sensor can be used without significantly prolonging the period for determining the incident light state of interference light to the light receiving element. An object of the present invention is to provide a multi-optical axis photoelectric sensor capable of improving the detection accuracy of interference light even if it exists in the vicinity separately.
[0008]
[Means for Solving the Problems]
As means for achieving the above object, the invention of claim 1 is directed to a plurality of light projecting elements that are sequentially projected at a predetermined light projecting timing so as to irradiate light toward the detection area, and these light projecting elements. A plurality of light receiving elements provided corresponding to the elements for receiving light from the detection area, and a plurality of light receiving elements provided corresponding to each of the light receiving elements and outputting signals based on the light receiving signals from the light receiving elements A circuit, channel selection means for performing a light-shielding detection operation for sequentially enabling signals from these light-receiving circuit groups in accordance with the light projection timing, and outputs of the light-receiving circuit groups to a common output line When a signal indicating that the light receiving element is in a non-light-receiving state is given from the output circuit when the channel selection means is performing the light shielding detection operation, a light shielding detection signal is output. Interference light that outputs an interference light detection signal when a signal indicating that one of the light receiving elements is in a light receiving state is given from the output circuit at a non-light projection timing of the light projecting element The output circuit includes two transistors connected in an complementary manner to the output stage, and performs complementary output when the channel selection means performs the light shielding detection operation. The multi-optical axis photoelectric sensor, wherein the interference light determination means performs an open collector output when determining the interference light.
[0009]
[Action and effect of the invention]
When a plurality of light projecting elements are sequentially projected at a predetermined light projecting timing, light is received by a light receiving element provided corresponding to these light projecting elements, and a light receiving circuit group is detected by a light shielding detection operation of the channel selecting means. Are sequentially activated in accordance with the light projection timing. When the light from the light projecting element is not received by the light receiving element, a signal indicating that the light receiving element from the output circuit is in the light shielding state is output to the common output line, and the light shielding detecting means receiving this signal outputs the light shielding detection signal. Output.
[0010]
In addition, if any light receiving element receives light at the non-light emitting timing, a signal is output from the light receiving circuit that receives the light receiving signal, and the output circuit that receives this signal receives the light receiving element on the common output line. Outputs a signal indicating that When the interference light detecting means receives a signal indicating that the light receiving element is in a light receiving state, it outputs an interference detection signal.
[0011]
According to this, at the non-light projection timing, the interference light determination means sends out the interference light detection signal when the light reception signal from any one of the light receiving elements is input, so the interference light detection accuracy is improved while improving the interference light detection accuracy. The time for light detection can be greatly shortened. In addition, since the signal output to the light shielding and interference light judgment means at the light projection timing and the non-light projection timing is sent by a common output line, multiple output lines are not required, wiring is simplified, and the risk of failure is greatly increased. It also has the effect of being reduced.
[0012]
Note that a wired OR circuit shown in FIG. 6 is generally considered as a circuit configuration for sharing the output line. This configuration has the advantage that the circuit configuration is simple and stable operation is possible, but on the other hand, the collector potential fluctuates due to charge / discharge of the capacitive component present in the transistor, so the time interval is extremely long. When a short signal is input to the base, the collector potential may not be able to follow the change in the base signal. Then, when the light projection timing is close, there is a concern of causing false detection.
In view of this point, according to the present invention, the output stage of the output circuit is configured by two complementary connected transistors, and when the channel selection means performs a light shielding detection operation, the output is prevented by delaying the signal output. ing.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
<First Embodiment>
A first embodiment of the present invention will be described with reference to FIGS.
The multi-optical axis photoelectric sensor of the present embodiment is used for detection of foreign matter intrusion into a press apparatus, and is configured with the projector 1 and the light receiver 2 facing each other as shown in FIG. It has 4 channel optical axes. On the surface of the light projector 1 facing the light receiver 2, one LED 11a to 11d is arranged in a line in the vertical direction for each channel (on the surface of the light receiver 2 facing the light projector 1). , Photodiodes 21a to 21d (hereinafter referred to as PDs 21a to 21d) corresponding to light receiving elements paired with the LEDs 11a to 11d are arranged in the vertical direction. The LEDs 11a to 11d correspond to light projecting elements that emit light toward the detection area, and the PDs 21a to 21d correspond to light receiving elements that receive light from the detection area. In FIG. 1, another multi-optical axis photoelectric sensor is disposed below, but the configuration is the same as that of the multi-optical axis photoelectric sensor above.
[0015]
<Electrical configuration>
FIG. 2 shows an electrical configuration of the multi-optical axis photoelectric sensor of the present embodiment. The projector 1 includes drive circuits 12a to 12d that emit the LEDs 11a to 11d, a selection circuit 13 to which the drive circuits 12a to 12d are connected, and a light projection microcomputer 14 that controls the operation of the selection circuit 13. ing. The projecting microcomputer 14 generates a pulse signal (hereinafter referred to as a “projection timing signal”) for generating the above-described projection timing, and when there is no pulse signal, it is a non-projection timing. In this embodiment, after four pulse signals continue, a non-light projection timing (referred to as “interference light detection period”) of a predetermined time is provided, and this is repeated. The selection circuit 13 is provided with a multiplexer (not shown), and receives a light projection timing signal given from the light projection microcomputer 14 to drive a lower LED 11d from a drive circuit 12a that drives the upper LED 11a. Selection is made sequentially toward the circuit 11d, and a drive signal is sent out. The drive circuits 12a to 12d that have received the drive signal supply drive current to the LEDs 11a to 11d connected thereto to cause the LEDs to emit light. The generated light projection timing signal is sent to a light receiving microcomputer 26 corresponding to a light shielding detecting means and an interference light detecting means described later.
[0016]
On the other hand, the light receiver 2 is provided with four light receiving circuits 20a to 20d. Each light receiving circuit includes amplifier circuits 22a to 22d for amplifying the light received signals from the PDs 21a to 21d and comparators 23a to 23d. The comparators 23a to 23d have the received light received signals at or above a reference level set inside. A signal of a predetermined level voltage is output. The signal lines from the comparators 23a to 23d are branched into two, one being input to the output circuits 25a to 25d via the analog switches 24a to 24d, and the other being the output circuit without passing through the analog switches 24a to 24d. 25a to 25d. Output lines from these four output circuits 25 a to 25 d are combined into one common output line L 1 and connected to an input terminal of the light receiving microcomputer 26.
[0017]
The light receiving microcomputer 26 sequentially takes in the light projection timing signals from the light projection microcomputer 14 and sends a pulse signal to the selection circuit 27 in synchronization with the light projection timing signals. The selection circuit 27 is provided with four output terminals corresponding to the number of channels (4), the signal line from this is branched into two, one of which is connected to the control input terminals of the analog switches 24a to 24d, The other is connected to the output circuits 25a to 25d. From these output terminals, signals for sequentially turning on the analog switches 24a to 24d are output, and the selection circuit 27 and the analog switches 24a to 24d match the signals from these light receiving circuit 20 groups with the light projection timing. Thus, it functions as channel selection means for performing a light-shielding detection operation that is sequentially and selectively enabled. The signal output line L2 of the light receiving microcomputer 26 is connected to the output circuits 25a to 25d, and this signal output is set to the “H” level in the “interference light detection period”.
[0018]
Next, the internal configuration of the output circuits 25a to 25d will be described with reference to FIG. The output circuits 25a to 25d all have the same configuration, and here, the output circuit 25a will be described.
The output circuit 25a is configured as shown in FIG. 3 so as to receive a signal from the light receiving circuit 20a and the selection circuit 27 and perform a predetermined operation. Here, the output stage of the output circuit is configured by complementary connection of a PNP transistor 257 and an NPN transistor 258. The output terminal of the OR circuit 252 is connected to the base of the transistor 257, and a voltage source of, for example, + 5V is connected to the collector thereof. On the other hand, the output terminal of the OR circuit 255 is connected to the base of the transistor 258, and the emitter is connected to the ground. The emitter of the transistor 257 and the collector of the transistor 258 are connected, and a signal line corresponding to the output of the output circuit is attached to these connection points.
[0019]
Next, the operation of the multi-optical axis photoelectric sensor according to this embodiment will be described with reference to FIG.
<Shading detection>
When the power source of the multi-optical axis photoelectric sensor is turned on, as shown in FIG. 2, a light emitting timing signal from the light projecting microcomputer 14 is sent from the LED 11a on the upper end side to the LED 11e on the lower end side by the selection circuit 13. Thus, light is sequentially emitted from the LED 11a on the upper end side. At the same time, the light receiving microcomputer 26 of the light receiver 2 takes in the light projecting timing signal from the light projecting microcomputer 14 and sends out a pulse signal in synchronization with the light projecting timing signal. Upon receiving the pulse signal, the selection circuit 27 starts a light shielding detection operation. As a result, the light projected from the LED 11a is received by the PD 21a, and the received light signal from the light is amplified by the light receiving circuit 20a. When the signal reaches a predetermined level, the signal is output and the analog is turned on. The signal passes through the switch 24a and is input to the output circuit 25a. Then, the output signal of the output circuit 25a is input to the light receiving microcomputer 26 via the common output line L1, and it is determined that the light shielding state is not established. Here, if it is determined that light is not incident on the PD 21a and is in a light-shielded state, a control signal (corresponding to a light-shielded detection signal) for displaying the light-shielded state is sent out. Thereafter, the light blocking detection operation is performed in synchronization with the light projection timing signal for the PDs 21b to 21d.
[0020]
<Interference light detection>
When the light shielding detection is completed for the lowermost PD 21d, it becomes an “interference light detection period” in which no light is emitted from any of the LEDs 11a to 11d, and the light receiving microcomputer 26 sets the signal output line L2 to the “H” level. Here, for example, when the PD 21a receives a certain amount or more of light, a signal is output from the light receiving circuit 20a, and then a signal is output from the output circuit 25a. Then, it is determined that the interference light is received by the light receiving microcomputer 26. If it is determined that the interference light is incident, the light receiving microcomputer 26 transmits a control signal (corresponding to the interference light detection signal) for displaying that the interference light is incident on a display device (not shown). Thereafter, the light shielding detection and the interference light detection are alternately repeated.
[0021]
Now, the operation of the output circuits 25a to 25d in the light shielding detection and the interference light detection will be described in detail with reference to FIG.
As shown in FIG. 3, when the signal from the selection circuit 27 is input to the analog switch 24a, the output signal from the comparator 23a is input to the output circuit 25a via the analog switch 24a. The output signal is input to the NOT circuit 251, and the output thereof is input to the OR circuit 252. Further, the output signal from the comparator 23a is input to a negative logic EXOR circuit 253. A signal from the selection circuit 27 is input to the EXOR circuit 253, and an output thereof is input to the NOR circuit 254. Then, the NOR circuit 254 obtains the negation of the logical sum and inputs it to the OR circuit 255. On the other hand, the light receiving circuit 20a signal inputted without going through the analog switch 24a is inputted to the AND circuit 256, and the "H" level signal from the light receiving microcomputer is inputted here, and this logical product is obtained. This is input to the OR circuit 255. The signal is input to the OR circuit 252 and the NOR circuit 254, and the output of the NOR circuit 254 is input to the OR circuit 255. A binary logic signal is input to all the inputs of the output circuit 25a.
[0022]
The table of FIG. 4 shows the relationship between the signal level at each measurement point {circle around (1)} to {circle around (5)}, the operating state of the transistors 257 and 258, and the signal level of the output {circle around (6)}. First, in the light shielding detection, a signal from the selection circuit 27 is input (point (1) becomes a high level (H)), and light is not incident on the PD 21a and a signal from the light receiving circuit is output. If not (low level (L) at point (3)), the output of the OR circuit 252 is H and the transistor 257 is turned off. Further, the output of the OR circuit 255 becomes H, and the transistor 258 is turned on. Therefore, the output is L. On the other hand, when the signal from the light receiving circuit is output (H at point (3)), the OR circuit 252 and the OR circuit 255 become L. Then, the transistor 257 is turned on, the transistor 258 is turned off, and the output becomes H.
In the interference light detection, a signal of “H” level is outputted to the signal output line L2 (H at the point {circle around (2)}, and if no signal is outputted from the light receiving circuit 20a here ({circle around (3)}). The output of the OR circuit 252 is L and the output of the OR circuit 255 is L. Therefore, both the transistor 257 and the transistor 258 are turned off, and the output becomes high impedance (Hi-Z), so that no signal appears. When the signal from the light receiving circuit 20a is output (H at point (3)), the outputs of the OR circuit 252 and the OR circuit 255 are both H, the transistor 257 is turned on, and the transistor 258 is turned off. The output is L. The output circuits 25b to 25d perform the same operation.
[0023]
As a result, the output state when the light-shielding detection is performed is H or L, and the light receiving microcomputer 26 outputs L (a signal indicating that it is in the non-light-incident state according to claim 1). If it is H, it is determined that it is not in the light shielding state. In the interference light detection, the output is high impedance or L. When the output is high impedance, the light receiving microcomputer 26 determines that the interference light is not detected, and the output is L (Claim 1). (Corresponding to a signal indicating that there is a light receiving state), it is determined that any of the PDs 21a to 21d is receiving interference light. At the time of detection of light shielding, the on / off states of the transistor 257 and the transistor 258 are inverted, which means that they are complementary outputs. On the other hand, when the interference light is detected, the transistor 257 is in the off state, and the transistor 258 repeats the on / off operation, which becomes an open collector output.
[0024]
Thus, according to the multi-optical axis photoelectric sensor of this embodiment, when performing interference light detection in the “interference light detection period”, it is possible to simultaneously detect the incidence of interference light on the PDs 21a to 21d of all channels. Even when light is incident on some of the PDs 21a to 21d, the interference light can be detected instantaneously.
[0025]
Further, the output lines of the output circuits 25a to 25d are commonly used in the light shielding detection operation and the interference light detection operation, and the signal output lines of the output circuits 25a to 25d are combined into one common output line L1 to receive light. 26 is connected. This makes it possible to simplify the wiring inside the sensor compared to the multi-optical axis photoelectric sensor in which signal lines are individually provided, and accordingly, the effect of reducing the risk of sensor failure can be obtained.
[0026]
Further, the output side of each of the output circuits 25a to 25d is composed of complementary transistors 257 and 258, which are complementary outputs in the light-shielding detection and open collector outputs in the interference light detection. In addition, if an open collector output is used at the time of light shielding detection, there is a problem that the collector output cannot follow when a signal with a short pulse width is input to the base, but in the case of light shielding detection as in this embodiment. If complementary output is used, high-speed response is possible.
[0027]
<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention, and further, within the scope not departing from the gist of the invention other than the following. Various modifications can be made.
(1) In the above embodiment, the interference light detection operation is performed after the light projection of the LEDs 11a to 11d is completed. For example, the LEDs 11a to 11d existing between the light projection timings of the LEDs 11a to 11d are light projected. The interference light detection operation may be performed during a period during which no interference occurs.
[0028]
(2) In the above-described embodiment, one LED and one PD are provided for each channel. However, the number of LEDs and PDs is not particularly limited to four. There may be four or more.
[Brief description of the drawings]
1 is a perspective view of a multi-optical axis photoelectric sensor. FIG. 2 is a circuit diagram showing an electrical configuration of the multi-optical axis photoelectric sensor. FIG. 3 is a circuit diagram showing an electrical configuration of an output circuit. Table showing relationship between input and output [FIG. 5] Perspective view of conventional multi-optical axis photoelectric sensor [FIG. 6] Circuit diagram showing electrical configuration of wired OR [Description of symbols]
11a-11d ... LED
20a to 20d ... Light receiving circuits 21a to 21d ... Photodiode (PD)
24a to 24d ... analog switches 25a to 25d ... output circuit 26 ... light receiving microcomputer 27 ... selection circuit

Claims (1)

A plurality of light projecting elements that are sequentially projected at a predetermined light projecting timing to irradiate light toward the detection area;
A plurality of light receiving elements provided corresponding to these light projecting elements and receiving light from the detection area;
A plurality of light receiving circuits provided corresponding to each of the light receiving elements and outputting signals based on light receiving signals from the light receiving elements;
Channel selection means for performing a light-shielding detection operation for sequentially and selectively enabling signals from these light receiving circuit groups according to the light projection timing;
A plurality of output circuits for outputting each output of the light receiving circuit group to a common output line;
A light-blocking determination unit that outputs a light-blocking detection signal when a signal indicating that the light-receiving element is in a non-light-receiving state is provided from the output circuit when the channel selection unit performs the light-blocking detection operation;
Interference light determining means for outputting an interference light detection signal when a signal indicating that any of the light receiving elements is in a light receiving state is given from the output circuit at a non-light projecting timing of the light projecting element;
The output circuit includes two transistors connected in an complementary manner to the output stage, and performs complementary output when the channel selection means performs the light shielding detection operation, and the interference light determination means includes the interference light determination means. A multi-optical axis photoelectric sensor that performs an open collector output when determining interference light.

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