JP2003289244A - Multiple optical axis photoelectric sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multiple optical axis photoelectric sensor which can avoid the influence of coherent light without fail, even if it is in an environment where it receives coherent light from other devices. <P>SOLUTION: When scan action incapable of detecting coherent light in nonprojection periods have continued a specified number of times, this photoelectric sensor varies the scan cycle at random. Hereby, it becomes possible to detect the coherent light, and interference can be avoided by ordinary interference-avoiding action. In this case, the possibility of executing the same interference-avoiding action as in other multiple optical axis photoelectric sensors is very low, because this varies the scan cycle at random. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-optical axis photoelectric sensor for detecting an object located in a detection area by receiving light emitted from a plurality of light emitting elements by a plurality of light receiving elements corresponding to the light emitting elements. Regarding sensors.

[0002]

In this type of photoelectric sensor, a plurality of multi-optical axis photoelectric sensors are arranged side by side in order to detect the entry of an object into a wider area. In the case where a plurality of multi-optical axis photoelectric sensors are arranged side by side in this way, even if the projection timing and the light receiving timing are synchronized with each other due to the fact that the scan cycles of the multi-optical axis photoelectric sensors match. In some cases, mutual interference may occur that coincides with the light projection timing of the multi-optical axis photoelectric sensor, causing a problem of erroneous detection.

As a method of preventing such mutual interference, the light receiving state of the light receiving element is detected immediately before the light projecting timing of the own device, and when light is being received, light from other than the own device is received. That is, it has been used a method of preventing interference by shifting the light projecting timing of the device itself, assuming that they interfere.

However, for example, when the light emitting timing of the own device and the timing of the interfering light completely match immediately after the power is turned on, the interfering light is generated even if the light receiving state of the non-light emitting timing of the own device is detected. Since the interference light is not detected, the interference light is not detected although it is actually affected by the interference light, and it is not determined that the interference light is present. For this reason, even if the device itself is in the light-shielded state, the interference light is incident, so that it is erroneously determined to be the incident state.

The present invention has been made in view of the above circumstances, and an object thereof is a multi-optical axis photoelectric sensor capable of reliably avoiding the influence of interference light even in an environment in which interference light is received from another device. To provide.

[0006]

According to the present invention, a plurality of light projecting elements arranged in a line to irradiate light toward a detection area and a plurality of light projecting elements provided corresponding to the light projecting elements are provided. A plurality of light receiving elements that receive light from the area, a light projecting period in which the light projecting elements project light so as to sequentially scan at a predetermined light projecting timing, and a non-light projecting period in which none of the light projecting elements projects light. And a light emitting drive unit that repeats the scan operation, and activates a light receiving signal from the light receiving element in synchronization with the timing of the corresponding light emitting element in the light emitting period, and based on the light receiving signal from the light receiving element. And the interference light detecting means for detecting the interference light based on the light receiving signal from the light receiving element in the non-light projecting period, and the interference light detecting means interferes with each other. light When detected, a multi-optical axis photoelectric sensor including a scan cycle changing means for changing the scan cycle of the light projecting drive means so that the light projection timing does not overlap with the interference light, a random number generating means is provided, and the scan is performed. The cycle changing means randomly changes the scan cycle of the light projecting drive means by a numerical value determined according to the random number generating means when the scanning operation in which the interference light detecting means does not detect the interference light continues for a predetermined number of times. (Claim 1). According to such a configuration, when the interference light is detected in the non-light-projecting period, the scan cycle changing means changes the scan cycle of the light projecting drive means so that the light projection timing does not overlap with the interference light. The influence of interference light can be prevented.

By the way, when the projection timing and the coherent light completely overlap each other, the coherent light cannot be detected as described above. Therefore, even if an object exists in the detection area, the coherent light is detected. There is a risk that the light may enter and the object cannot be detected. Here, when the scanning operation in which the interference light detecting means does not detect the interference light continues for a predetermined number of times, the scanning cycle changing means randomly changes the scanning cycle of the light projecting drive means by a numerical value determined according to the random number generating means. Therefore, even if the projection timing and the interference light completely overlap with each other, the presence of the interference light is detected, and thereafter,
The influence of the interference light can be prevented in advance by changing the scan cycle of the light projection drive unit so that the interference light does not overlap the light projection timing. In this case, even if the interference light is from another multi-optical axis photoelectric sensor, it is possible to perform the same interference light avoiding operation as that of the other multi-optical axis photoelectric sensor as a result of adopting the random number generating means. It can be prevented as much as possible.

Further, according to the present invention, a plurality of light projecting elements arranged in a line to irradiate light toward the detection area and a plurality of light projecting elements provided corresponding to the light projecting elements are provided. A scanning operation including a plurality of light receiving elements for receiving light, a light projecting period in which the light projecting elements are projected to sequentially scan at a predetermined light projecting timing, and a non-light projecting period in which none of the light projecting elements is projected. And a light-emission driving unit that repeats the operation, and validates the light-receiving signal from the light-receiving element in synchronization with the timing of the corresponding light-emitting element during the light-projecting period, and detects the detection area based on the light-receiving signal from the light-receiving element In the non-light projecting period, the interference light detecting means for detecting the interference light based on the light receiving signal from the light receiving element, and the interference light detecting means detects the interference light. In this case, in the multi-optical axis photoelectric sensor including a scan cycle changing means for changing the scan cycle of the light projecting drive means so that the light projection timing does not overlap the interference light, a random number generating means is provided, and the scan cycle variable The means changes the scan cycle in the light projecting drive means when the scanning operation in which the interference light detecting means does not detect the interference light continues a random number of times determined according to the random number generating means. Item 2).

According to this structure, the scanning period changing means is arranged so that when the scanning operation in which the interference light detecting means does not detect the interference light continues for a random number of times determined by the random number generating means, the light projecting drive means is provided. Even if the light projection timing and the interference light completely overlap, the existence of the interference light is detected, and after that, the interference light does not overlap the light projection timing. The scan cycle of the light driving means can be changed, and the influence of interference light can be prevented in advance.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION (First Embodiment) A first embodiment in which the present invention is applied to a multi-optical axis photoelectric sensor having four optical axes will be described below with reference to FIGS. 1 to 4. FIG. 1 schematically shows the electrical configuration of a multi-optical axis photoelectric sensor. In FIG. 1, a multi-optical axis photoelectric sensor 1 is composed of a light projector 2 and a light receiver 3 which are installed with a detection area sandwiched therebetween.

The projector 2 is a projecting side CP that controls the entire system.
It is mainly composed of U4, and this projecting side CPU4
And a plurality of drive circuits 6 connected to the selection circuit 5, and a plurality of light projecting elements 7 connected to each of the drive circuits 6.

The light-projecting side CPU 4 is connected so as to input a synchronizing signal from the light receiver 3 as will be described later, and for sequentially selecting the drive circuit 6 with respect to the selecting circuit 5 based on this synchronizing signal. It is designed to output a selection signal. The selection circuit 5 sequentially selects and drives the light projecting elements 7 through the drive circuit 6 based on the selection signal given from the light projecting CPU 4.

The light projecting element 7 emits a light projecting signal toward the detection area when driven by the drive circuit 6.
The projector 2 as a whole is configured such that the pulsed light of ch1 to ch4 is sequentially emitted from the light projecting element 7 toward the detection area at a predetermined projecting timing.

The light receiver 3 is a light receiving side CP for controlling the entire device.
A plurality of light receiving elements 9 which are configured mainly by U8 and which output a light receiving signal when receiving the light emitted from the light projector 2 toward the detection area, and a plurality of light receiving amplifiers respectively connected to these light receiving elements 9. 10, a plurality of light receiving comparators 11 connected to respective output terminals of these light receiving amplifiers 10, and these light receiving comparators 1
1 is connected to each output terminal of an analog switch 12, an analog switch 12 is turned on / off in accordance with a selection signal from the light-receiving side CPU 8, and a selection circuit 13 is connected to each output terminal of the light-receiving amplifier 10. A plurality of interference detection comparators 14 connected
And a logical sum circuit (hereinafter referred to as an OR circuit) 15 which takes the logical sum of the outputs of the interference detection comparators 14 and outputs the logical sum to the CPU 8 on the light receiving side.

The light-receiving amplifier 10 receives light from the detection area in the light-receiving element 9 and amplifies the light-receiving signal output, and outputs it to the light-receiving comparator 11 and the interference detection comparator 14, respectively. The light receiving comparators 11 each have a preset first threshold value (set to substantially the same value), and the light receiving signal amplified by the light receiving amplifier 10 is the first threshold value. When the threshold value is exceeded, the power supply voltage V
High level signal of about cc (hereinafter referred to as "H" signal)
Is output, and when the value does not exceed the first threshold value, approximately GN
It is configured to output a low level signal (hereinafter, referred to as an “L” signal) that matches the D level.

The analog switch 12 is on / off controlled by the selection circuit 13, and when it is turned on, the output of the light receiving comparator 11 is passed to input the analog switch 12 to the light receiving side CPU 8. When the analog switch 12 is off, the output of the light receiving comparator 11 is not input to the light receiving side CPU 8, and the input voltage to the light receiving side CPU 8 is maintained at, for example, "L" level. .

The selection circuit 13 inputs a selection signal from the CPU 8 on the light receiving side and sequentially turns on / off the selected analog switch 12. Light receiving side CPU8
Outputs a synchronization signal in accordance with a period (synchronization timing) in which the light reception signal preset in the light-emission-side CPU 4 is valid as described above, and outputs a selection signal of the analog switch 12 to the selection circuit 13. The presence of an object in the detection area is determined by inputting each output from the enabled analog switch 12 at the synchronization timing. As described above, the multi-optical axis photoelectric sensor 1 has not only the basic function of detecting an object located in the detection area but also the interference avoidance function for avoiding the influence of the interference light. Hereinafter, the interference avoidance function is realized. The configuration for this will be briefly described.

The interference detecting comparators 14 each have a second threshold value set in advance (set to substantially the same value), and the light receiving amplifier 10
When the light reception signal amplified in (1) is equal to or higher than the second threshold value, an "H" signal is output, and when the amplified light reception signal is not equal to or higher than the second threshold value, an "L" signal is output to the OR circuit 15. ing.

Note that the first threshold value set in the light receiving comparator 11 and the second threshold value set in the interference detecting comparator 14 are set to different values, with respect to the first threshold value. And the second threshold value is set small.
This is because the signal level of the interference light is usually smaller than that of the received light signal, so that the interference light is reliably detected.

The OR circuit 15 is composed of, for example, a wired OR circuit, and functions as a negative logic OR circuit. The light-receiving side CPU 8 has an OR circuit 15
The signal of the logical sum obtained in (1) is detected during a preset valid period (non-light-projecting period).

The light projecting drive means in the present invention is composed of the light projecting side CPU 4 and the selection circuit, the judging means is composed of the light receiving side CPU 8 and the light receiving comparator 11, and the interference light judging means is the light receiving side. The CPU 8, the interference detection comparator 14, and the OR circuit 15 are included, and the scan cycle changing unit and the random number generating unit are included in the light-receiving side CPU 8.

Next, the operation of the above configuration will be described. [Light-shielding detection (light emitting period)] The light receiving side CPU 8 is
A synchronizing signal for synchronizing with the PU 4 is generated based on the internal clock and output to the projecting CPU 4. Emitter side C
The PU 4 outputs a selection signal to the selection circuit 5 based on this synchronization signal. At this time, the selection circuit 5 selects the drive circuit 6 by the selection signal.
Gives light emission commands P1 to P4 to the drive circuit 6, whereby the light emitting element 7 sequentially emits the pulsed lights of ch1 to ch4 at a predetermined light emitting timing.

On the other hand, the light receiving side CPU 8 is the light emitting side CPU 4
When the synchronizing signal is output to, the selection signal is output to the selection circuit 13. At this time, the selection circuit 13 causes the selection signal c
The analog switch 12 of h1 is controlled to be turned on, and the light receiving signal from the light receiving element 9 for ch1 is validated for a predetermined period including a predetermined light emitting timing.

The received light signal received by the light receiving element 9 is
After being amplified by the light receiving amplifier 10, it is compared with the first threshold value by the light receiving comparator 11. At this time, if the pulsed light from the light projecting element 7 is not shielded in the detection area, the light receiving comparator 11 outputs a comparison output between the light receiving signal amplified by the light receiving amplifier 10 and the first threshold value to the light receiving side. The "H" signal is input to the CPU 8 and the "L" signal is input if the light is shielded.

The light-receiving side CPU 8 determines whether or not the signal input at a predetermined timing is the "H" signal based on the synchronization signal output to the light-emitting side CPU 4, and from this result, the light is shielded in the detection area. It is determined whether or not it has been done. After that, the CPU 4 on the light projecting side outputs a selection signal to the selection circuit 5 to select the drive circuit 6 for ch2.
Pulsed light is projected from the light projecting element 7 of ch2 at a predetermined projecting timing.

On the other hand, the light-receiving side CPU 8 outputs a selection signal to the selection circuit 13 after a lapse of a predetermined period enabled in ch1, and the selection circuit 13 turns off the analog switch 12 of ch1 based on this selection signal. And c
By similarly turning on the analog switch 12 of h2 and validating it for a predetermined period, the light projection signal is received during this valid period and the result of comparison with the first threshold value of the amplified light reception signal is shown. It is input to the light receiving side CPU 8.

By the above-described operation, the pulsed light is repeatedly projected from the light projecting element 7 of the light projecting device 2 toward the detection area in the order of ch1 to ch4, and the light receiving device 3 facing the light projecting device 2 operates. The light receiving element 9 receives these pulsed lights during an effective period including the period of the light emission timing, and the result of comparison between the light receiving signal amplified within this enabled period and the first threshold value is the received light. The data is intermittently input to the side CPU 8 (see FIG. 2), and it is possible to determine whether or not the object is located in the detection area based on the result.

[Interference light detection (non-light emission period)] Light emission side CPU
As shown in FIG. 2, 4 stops the light projection for a predetermined period (which changes depending on the state of the interference light), and the light-receiving side CPU 8 starts the detection of the interference light during this non-light projection period.

Here, the light-receiving side CPU 8 starts the detection of the input voltage from the OR circuit 15 in the non-light projecting period (start of the interference light determining period). Interference detection comparator 1
Reference numeral 4 is a second light receiving signal amplified by the light receiving amplifier 10.
Compare with threshold. In this case, when the received light signal is equal to or higher than the second threshold, the interference detection comparator 14
The "H" signal is output, and the "H" signal is input to the light-receiving side CPU 8. When the light receiving signal does not exceed the second threshold value, the “L” signal is output and the “L” signal is input to the light receiving side CPU 8.

When the interference light enters the light receiving element 9 of the light receiver 3, the light receiving element 9 detects the interference light as a light receiving signal, and the light receiving amplifier 10 amplifies the light receiving signal. As a result, since the "H" signal is input from the OR circuit 15 during the non-light-emission period, the light-receiving side CPU 8 can determine that the interference light has entered, and the light-emission timing does not overlap with the interference light. The well-known interference avoidance operation is performed. As described above, the scanning operation including the light projecting period in which the light projecting element 7 is sequentially projected at a predetermined light projecting timing and the non-light projecting period in which none of the light projecting elements 7 is projected is repeated. Done.

[Interference Avoidance Operation] FIG. 3 shows an interference avoidance operation of the light receiving side CPU 8 according to the present invention. In FIG. 3, when the interference light is not detected for the first time (S
= 0) (S101: YES), a random number is generated (S10
2) Based on this, the number X of monitoring scans is set (S
103). For example, if the random number is "3", the number X of monitoring scans is set to 3 scans (X = 3).

Next, the number S of scans in which no interference light is detected and the number X of monitoring scans are compared (S104).
In this case, since the number of monitoring scans is 3, the normal cycle is maintained until the scanning operation in which the interference light is not detected continues three times (S105). As a result, the detection operation is performed in the normal scan cycle described above, and the scan number S is incremented when the detection operation ends (S106).

When the scanning operation in which the interference light is not detected is repeated three times (S = 3) (S104: NO),
The scan cycle is changed (S107). There are various methods for changing the scan cycle, but in the present embodiment, the scan cycle is shortened by a predetermined time. As a result, as shown in FIG. 4, it is possible to detect the light projected from the other multi-optical axis photoelectric sensor 1, and it is possible to reliably execute the interference light avoiding operation. When the scan cycle is shortened by a predetermined time, S = 0 is set to restore the initial state (S108).

According to such an embodiment, when the number of scan operations in which the interference light cannot be detected during the non-light-projecting period continues for the number of monitoring scans determined by the random number, the scan cycle is changed. Even if interference light having the same cycle as the scan cycle enters from the multi-optical axis photoelectric sensor 1, it is possible to reliably detect the interference light and reliably execute the interference avoiding operation. In this case, since the number of monitoring scans is determined by a random number, the other multi-optical axis photoelectric sensor 1
It is extremely unlikely to perform the same interference avoidance action as
Interference light can be detected reliably.

(Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIG. The second embodiment is characterized in that the scan cycle is randomly changed by a random number.

In FIG. 5 showing the operation of the CPU 8 on the light receiving side, the number of monitoring scans is fixed (for example, X = 3) (S
201), when the scanning operation in which the interference light cannot be detected is repeated three times (S202: NO), a random number is generated (S2).
05), the scan cycle is shortened by a random number (S20).
6). In this case, although the number of monitoring scans is fixed to three, the scanning cycle is randomly changed as a means for varying the scanning cycle, so that the interference light from other multi-optical axis photoelectric sensors 1 is surely obtained. Can be detected.

According to such an embodiment, when the number of scan operations in which the interference light cannot be detected continues for the number of monitoring scans, the scan cycle is randomly changed. Therefore, similar to the first embodiment. Therefore, the interference avoidance operation can be executed by surely detecting the interference light from the other multi-optical axis photoelectric sensor 1.

The present invention is not limited to the above embodiments, but the number of monitoring scans and the scan cycle may be changed at the same time randomly.

[0039]

As is apparent from the above description, according to the multi-optical axis photoelectric sensor of the present invention, when the scanning operation in which the interference light is not detected continues for a predetermined number of times, the scanning cycle is randomly changed, When the scanning operation that does not detect the interference light is repeated a random number of times, the scan cycle is made variable, so that the influence of the interference light can be reliably avoided even in an environment where the interference light is received from another device. It has an excellent effect that it can be done.

[Brief description of drawings]

FIG. 1 is a block diagram schematically showing an electrical configuration according to a first embodiment of the present invention.

FIG. 2 is a timing diagram showing a detection operation and an interference light detection operation.

FIG. 3 is a flowchart showing an operation of a light-receiving side CPU of a light receiver.

FIG. 4 is a timing diagram showing an interference avoidance operation.

FIG. 5 is a diagram corresponding to FIG. 3 in the second embodiment of the present invention.

[Explanation of symbols]

Reference numeral 1 is a multi-optical axis photoelectric sensor, 2 is a light emitter, 3 is a light receiver, 4 is a light emitting side CPU (light emitting drive means), 5 is a selection circuit (light emitting drive means), 7 is a light emitting element, and 8 is light receiving. Side CPU (determination means, interference light determination means, scan cycle variable means, random number generation means), 9 is a light receiving element, 11 is a light receiving comparator (determination means), 14 is an interference detection comparator (interference light determination means), 15 Is an OR circuit (interference light determination means).

Claims (2)

[Claims] 1. A plurality of light projecting elements arranged in a line so as to irradiate light toward a detection area, and a plurality of light emitting elements provided corresponding to these light projecting elements and receiving light from the detection area. A light receiving element, a light projecting period in which the light projecting element projects light so as to sequentially scan at a predetermined light projecting timing, and a non-light projecting period in which none of the light projecting elements projects light. The driving means and the light receiving period from the light receiving element in the light projecting period are activated in synchronization with the timing of the corresponding light projecting element, and the light blocking state in the detection area is set based on the light receiving signal from the light receiving element. Judgment means for judging, interference light detection means for detecting interference light based on a light reception signal from the light receiving element in the non-light projection period, and if the interference light detection means detects interference light, A multi-optical axis photoelectric sensor having a scan cycle varying means for varying the scan cycle of the light projecting drive means so that the timing does not overlap with the interference light, wherein a random number generating means is provided, and the scan cycle varying means comprises the interference When the scanning operation in which the light detecting means does not detect the interference light continues for a predetermined number of times, the scanning cycle of the light projecting driving means is randomly varied by a numerical value determined according to the random number generating means. Axis photoelectric sensor. 2. A plurality of light projecting elements arranged in a line so as to irradiate light toward the detection area, and a plurality of light emitting elements provided corresponding to these light projecting elements and receiving light from the detection area. A light receiving element, a light projecting period in which the light projecting element projects light so as to sequentially scan at a predetermined light projecting timing, and a non-light projecting period in which none of the light projecting elements projects light. The driving means and the light receiving period from the light receiving element in the light projecting period are activated in synchronization with the timing of the corresponding light projecting element, and the light blocking state in the detection area is set based on the light receiving signal from the light receiving element. Judgment means for judging, interference light detection means for detecting interference light based on a light reception signal from the light receiving element in the non-light projection period, and if the interference light detection means detects interference light, A multi-optical axis photoelectric sensor having a scan cycle varying means for varying the scan cycle of the light projecting drive means so that the timing does not overlap with the interference light, wherein a random number generating means is provided, and the scan cycle varying means comprises the interference When the scanning operation in which the light detecting means does not detect the interference light is repeated a random number of times determined according to the random number generating means, the scanning cycle in the light projecting drive means is varied. .