JP3860013B2 - 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 detecting, for example, intrusion into a press device, and more particularly to a device that prevents malfunction due to interference light.
[0002]
[Prior art]
An example of this type of multi-optical axis photoelectric sensor is disclosed in Japanese Patent No. 2911369. In this device, a light projector having a plurality of light projecting elements and a light receiver having a plurality of light receiving elements corresponding to each light projecting element are arranged to face each other. Constitutes the optical axis. The light projecting element provided in the light projector repeatedly performs a light projecting scan operation in which light is sequentially projected at a predetermined light projecting timing, and shields the optical axis based on this and a light reception signal from a light receiving element constituting the optical axis. It detects and detects the object intrusion into the detection area.
[0003]
By the way, a plurality of multi-optical axis photoelectric sensors may be installed in order to detect intrusion of an object in a wider area, and the multi-optical axis photoelectric sensors may be arranged close to each other as shown in FIG. is there. In such a case, for example, when any one of the optical axes of the multi-optical axis photoelectric sensor 61 installed at the upper side is performing light-shielding detection, light is projected from the multi-optical axis photoelectric sensor 62 installed at the lower side. Light may enter the light receiving element of the upper multi-optical axis photoelectric sensor 61 as interference light. Then, although the optical axis of the upper multi-optical axis photoelectric sensor 61 is shielded from light, the light from the lower multi-optical axis photoelectric sensor 62 enters as interference light, so that the malfunction of the optical axis cannot be detected. Will be caused.
[0004]
In order to prevent such a malfunction, it is necessary to control the light projection scan operation so that the light projection timing does not overlap between adjacent multi-optical axis photoelectric sensors. For this purpose, one of the two multi-optical axis photoelectric sensors 61 and 62 is set as a master station and the other is set as a slave station, and a synchronization signal is transmitted from the master station to the slave station. It is common to employ a synchronization method that allows an optical scanning operation to be performed. In this way, when the light projecting element in one of the multi-optical axis photoelectric sensors 61 is turned on, the other multi-optical axis photoelectric sensor 62 does not detect the light reception signal, so that there is an advantage that malfunction can be prevented.
[0005]
[Problems to be solved by the invention]
However, when the synchronization method as described above is adopted, the wiring work is troublesome, and there is a problem that the number of work steps accompanying installation increases.
Also, in this type of multi-optical axis photoelectric sensor, in general, interference light that detects whether or not a light reception signal appears on the light receiving element at a timing when none of the light projecting elements is turned on, and determines the presence or absence of interference light. In many cases, the detection operation is performed. Then, if the synchronization method is out of sync and accidentally coincides with the interference light detection timing, the light projection scan operation is originally performed in the same cycle, so interference light is periodically detected. Therefore, it may be determined that the sensor is abnormal.
[0006]
The present invention has been completed based on the above circumstances, and can prevent mutual interference between multi-optical axis photoelectric sensors without wiring a synchronization line between the multi-optical axis photoelectric sensors. An object of the present invention is to provide a multi-optical axis photoelectric sensor that can be used.
[0007]
[Means for Solving the Problems]
As a means for achieving the above object, the invention of claim 1 includes a plurality of light projecting elements, and a plurality of light receiving elements provided so as to constitute a plurality of optical axes opposite to the light projecting elements. A light projecting control means for repeating a light projecting scan operation for sequentially lighting the light projecting element group at a predetermined timing at a predetermined period; and a light receiving signal from each of the light receiving elements is formed so as to face the light emitting signal. A light-blocking detecting means for detecting a light-blocking state on the optical axis by detecting the light-projecting element in accordance with a lighting timing of the light-projecting element , and each light for the plurality of optical axes at a time when none of the light-projecting elements is lit. for each axis and a interference light detecting means for detecting the presence of the interference light based on a photodetection signal from the photodetection element, before the light projecting control means when the interference light is detected by the interference light detecting means Without changing the lighting interval of the light emitting element in the light-projecting scanning operation, characterized in it was made different start timings of the light projecting scanning operation.
[0008]
According to a second aspect of the present invention, in the first aspect, when the interference light is detected by the interference light detecting means, the start timing of the light projection scan operation corresponds to half of the lighting interval of the light projecting element. It is characterized by the time shift.
[0009]
[Action and effect of the invention]
<Invention of Claim 1>
For example, when the multi-optical axis photoelectric sensors are installed close to each other and the period of the light projection timing is the same, the light projection timing of one multi-optical axis photoelectric sensor and the light projection timing of the other multi-optical axis photoelectric sensor are May overlap on the time axis and cause mutual interference. In the multi-optical axis photoelectric sensor of the present invention, when there is a light reception signal from a time light reception signal when none of the light projecting elements is lit, the interference light detection means detects the interference light based on this. When the interference light is detected, the start timing of the light projection scanning operation of the light projection control unit is varied. As a result, the light projection timings of both multi-optical axis photoelectric sensors do not overlap, and mutual interference can be prevented.
[0010]
<Invention of Claim 2>
If the start timing of the light projection scan operation is shifted by a time corresponding to half the lighting interval of the light projecting elements, the temporal positional relationship between the light projection timings is farthest away. Thereby, the possibility of mutual interference can be reliably avoided.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described with reference to FIGS.
As shown in FIG. 1, the multi-optical axis photoelectric sensor 1 of the present embodiment is configured with a projector 2 and a light receiver 3 facing each other, and has, for example, a four-channel optical axis L. On the surface of the light projector 2 facing the light receiver 3, one LED (a total of four) LEDs 21 a to 21 d are arranged in a line in the vertical direction for each channel, and on the surface of the light receiver 3 facing the light projector 2. The photodiodes 31a to 31d (referred to as PDs 31a to 31d) paired with the LEDs 21a to 21d are also arranged in the vertical direction. Accordingly, the LEDs 21a to 21d correspond to light projecting elements, and the PDs 31a to 31d correspond to light receiving elements that form a pair with the light projecting elements and constitute an optical axis. In addition, a multi-optical axis photoelectric sensor 10 is disposed close to the lower part in FIG.
[0012]
FIG. 2 shows an electrical configuration of the multi-optical axis photoelectric sensor 1 of the present embodiment. The projector 2 is provided with drive circuits 22a to 22d for lighting the LEDs 21a to 21d, and each drive circuit 22a to 22d supplies a drive current to the LEDs 21a to 21d when receiving signals from the AND circuits 23a to 23d. Output signals from the shift register 24 and the light-projecting CPU 25 are input to the AND circuits 23a to 23d. When signals from both are input, signals are sent to the drive circuits 23a to 23d. The light projection side CPU 25 receives a light projection timing signal St from a light reception side CPU 35 provided in the light receiver 3 described later, and outputs this light projection timing signal St to the shift register 24 and the AND circuits 23a to 23d.
[0013]
The light projection timing signal St is a pulse signal having a predetermined cycle, and is generated by the light receiving side CPU 35 in order to determine the lighting timing of the LEDs 21a to 21d. Within one cycle (length T) of the projection timing signal St, four pulses are generated at equal intervals with a time ta, and after the fourth pulse, a pause period tb of a predetermined length is provided. Yes. Thereby, the light projection scanning operation in which the four LEDs 21a to 21d are sequentially turned on from the top to the bottom is repeatedly performed every period T. Therefore, the AND circuits 23a to 23d, the shift register 24, the light emitting side CPU 25, and the light receiving side CPU 35 constitute a light projecting control means for sequentially lighting the light projecting element group at a predetermined timing.
[0014]
On the other hand, the light receiver 3 includes light receiving amplifiers 32a to 32d for amplifying light reception signals from the PDs 31a to 31d at a predetermined amplification rate, respectively. The light receiving signals output from the light receiving amplifiers 32a to 32d are collected into a common signal line and taken into the comparator 34 via the analog switches 33a to 33d. When this light reception signal exceeds the reference value set in the comparator 34, the light incident detection signal Sd is input to the light receiving side CPU 35, and it is detected that light has entered.
[0015]
The light-receiving side CPU 35 shifts the light-shielding detection timing signal Sr whose cycle and phase coincide with those of the light-projecting timing signal St and the interference light detection timing signal Si whose phase is slightly advanced from the light-shielding detection timing signal Sr. Is being sent to. The shift register 36 that has received the light shielding detection timing signal Sr and the interference light detection timing signal Si from the light receiving side CPU 35 receives a gate control signal from the analog switch 33a for turning on the analog switches 33a to 33d connected thereto. The signals are sequentially sent to the analog switch 33d, and the received light signals from the PDs 31a to 31d are input to the comparator 34. Then, when the light shielding detection timing signal Sr is sent, each of the LEDs 21a to 21d is in a lighting state. Since the LEDs 21a to 21d are not lit, the interference light is detected depending on the presence or absence of the light incident detection signal from the comparator 34.
[0016]
Hereinafter, the operation of the light receiving side CPU 35 will be described with reference to FIGS. First, when the power of the multi-optical axis photoelectric sensor 1 is turned on, the light receiving side CPU 35 sends a light projection timing signal St to the light projecting side CPU 25 as shown in FIG. . In addition, the light receiving side CPU 35 sends the light shielding detection timing signal Sr and the interference light detection timing signal Si to the shift register 36 to sequentially turn on the analog switches 33a to 33d, and receives the light receiving signals from the PDs 31a to 31d as comparators 34. To detect light and detect interference.
[0017]
<Shading detection>
In the time chart of FIG. 3, when the level of the light blocking detection timing signal Sr is high (H), the light blocking detection routine shown in FIG. 4 is executed. For example, when there is no object that blocks the optical axis, the light from the LEDs 21a to 21d enters each of the PDs 31a to 31d. Is output. Therefore, the light receiving side CPU 35 determines that all the PDs 31a to 31d are in the light incident state (No in step S41).
Here, when the optical axis composed of the PD 31a is obstructed by an object, even if the analog switch 33a to which the PD 31a is connected is turned on, the light incident detection signal is not output from the comparator 34 and the light is not incident. (Yes in step S41), the light shielding detection is counted (step S42). Since the light from the LEDs 21b to 21d is incident on the PDs 31b to 31d, No is obtained in step S41. In the next cycle, the light shielding detection of the PDs 31a to 31d is repeatedly performed. At the time of detecting the light shielding of the PD 31a, since the light incident detection signal is not output from the comparator 34, it is determined that the light is not incident (Yes in step S41). Then, a count for detecting light shielding is added (step S42), and it is determined that the light axis constituted by the PD 31a is in a light shielding state twice (Yes in step S43), and a signal is sent to the output circuit 37. (Step S44), the process of being in the light shielding state is performed. When the light shielding detection for the lowermost PD 31d is completed (Yes in step S45), the light shielding detection count is reset, and the above operation is repeated again. As a result, it becomes clear that the analog switches 33a to 33d, the comparator 34, the light receiving side CPU 35, and the shift register 36 function as a light blocking detection unit that detects a light blocking state on each optical axis.
[0018]
<Interference light detection>
On the other hand, when the level of the interference light detection timing signal Si is H, the interference light detection routine shown in FIG. Normally, the light-shielding detection timing signal Sr of the multi-optical axis photoelectric sensor 1 and the light-shielding detection timing signals of the other multi-optical axis photoelectric sensors 10 are asynchronously out of phase, so The light from the light projecting element of the multi-optical axis photoelectric sensor 10 does not enter (corresponding to the period A in FIG. 3). Therefore, at the interference light detection timing, even if the light reception signals from the PDs 31a to 31d are sequentially enabled by the analog switches 33a to 33d, no light incident detection signal is output from the comparator 34. It is determined that the light is incident (No in step S51), and it is not determined that interference light has been incident.
[0019]
On the other hand, since each multi-optical axis photoelectric sensor 1 and 10 operates independently, for example, the light-shielding detection timing of the multi-optical axis photoelectric sensor 1 is delayed by the delay of the light-shielding detection timing of the multi-optical axis photoelectric sensor 10. In time, the interference light detection timing of the multi-optical axis photoelectric sensor 1 may overlap with the time axis. Then, light from the light projecting element of the multi-optical axis photoelectric sensor 10 enters when the multi-optical axis photoelectric sensor 1 is at the interference light detection timing (corresponding to a period B in FIG. 3). First, it is determined that interference light has entered the PD 31a on the uppermost optical axis (Yes in step S51), and incident light detection is counted (step S52). Subsequently, similarly, it is determined that the light is incident on the PD 31b on the next optical axis (Yes in Step S51), and the incident light detection is counted (Step S52). Thereafter, it is determined that the light is incident on the PDs 31c and 31d as well (Yes in step S51, step S52). Then, interference light detection is performed again for the PDs 31a to 31d, and when interference light detection for the lowermost PD 31d is completed (Yes in step S53), the interference light incident count is determined based on the interference light detection count for each optical axis. Make a decision. Eventually, since any optical axis is counted twice, it is determined that the interference light is incident (Yes in step S54). Then, the pause period tb until the next pulse of the interference light detection timing signal Si is generated is shortened by half of the time ta between adjacent pulses of the light shielding detection timing signal Sr to become a pause period tc (step S55). As a result, the pulse train of the light shielding detection timing signal Sr is shifted to the left in FIG. 3 compared to the pulse train of the light shielding detection timing signal (the uppermost stage in the figure) when the pause period tb is not shortened. As is clear from the above operation, the analog switches 33a to 33d, the comparator 34, the light receiving side CPU 35, and the shift register 36 function as interference light detection means that varies the start timing of the light projection scan operation of the light projection control means.
[0020]
As described above, according to the multi-optical axis photoelectric sensor 1 of the present embodiment, in the interference light detection, when light is incident twice on the same optical axis, the pause period tb is adjacent to the light-shielding detection timing signal Sr. The time is shortened by a time corresponding to half the time ta between pulses. As a result, if the periodic interference light emitted from the other multi-optical axis photoelectric sensor 10, the subsequent light shielding detection timing and the interference light are in the most separated positional relationship on the time axis, and the interference light is not incident. By avoiding this, mutual interference can be surely prevented. In addition, since it operates independently of the other multi-optical axis photoelectric sensors 10, there is no need for a synchronization line for synchronizing with the other multi-optical axis photoelectric sensors 10, and the wiring arrangement is simplified. Is also possible.
[0021]
<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 pause period is changed to be short on the condition that the interference light is continuously detected twice for the same optical axis. For example, the interference light is once or continuously three times. The pause period T2 may be changed on condition that the above is detected.
[0022]
(2) The same effect can be obtained not only by changing the suspension period tb to be shorter but also by changing it longer .
[Brief description of the drawings]
FIG. 1 is a perspective view showing the configuration of a multi-optical axis photoelectric sensor. FIG. 2 is a circuit diagram showing the electrical configuration of the multi-optical axis photoelectric sensor. FIG. 3 is a time chart showing the operation of the multi-optical axis photoelectric sensor. Flowchart of detection routine [FIG. 5] Flowchart of interference light detection routine [FIG. 6] Configuration perspective view of a conventional multi-optical axis photoelectric sensor [Explanation of symbols]
21a-21d ... LED
25: CPU on the light emitting side
31a-31d ... PD
33a to 33d ... Analog switch 34 ... Comparator 35 ... Light receiving side CPU
36: Shift register

Claims (2)

A plurality of light projecting elements, a plurality of light receiving elements provided so as to constitute a plurality of optical axes facing each of the light projecting elements, and a light projecting scan operation for sequentially lighting the light projecting element group at a predetermined timing And a light-projecting control means for repeating the light-receiving signal from each of the light-receiving elements and detecting the light-receiving signal in correspondence with the lighting timing of the light-projecting element that forms the optical axis facing the light-receiving signal. A light-blocking detecting means for detecting a light-blocking state in the light source, and the presence of interference light based on a light-receiving signal from the light-receiving element for each of the plurality of optical axes at a time when none of the light projecting elements is lit. a interference light detecting means detect, without changing the lighting interval of the light emitting element in the light-projecting scanning operation in the light emitting control means when the interference light is detected by the interference light detecting means, Multi-optical axis photoelectric sensor being characterized in that so as to vary the start timing of the-projecting optical scanning operation.   2. The multi-optical axis photoelectric sensor according to claim 1, wherein when the interference light is detected by the interference light detection means, the start timing of the light projection scanning operation is shifted by a time corresponding to half of the lighting interval of the light projecting element. Sensor.

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