JP2002333487A - Photoelectric sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the presence of interference light judged even under a light projection period or just after the finish of light projection. SOLUTION: Sampling data from an A/D converter 7 are stored in a storage means 9 as reference data in plural sampling timings within a prescribed period including the light projection period under a detection condition of a detected object 5 in an environment not affected by the interference light in a setting operation. The sampling data from the A/D converter 7 are stored temporarily in the same sampling timings in a detection operation, the sampling data is compared with the reference data when an ON signal is output from the converter 7, detection is determined when both of them are consistent, and non- detection is judged when both of them are not consistent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a light projecting means for projecting a pulse light, and a light receiving means for receiving the pulse light projected from the light projecting means and outputting a light receiving signal. The present invention relates to a photoelectric sensor that determines the presence or absence of an object to be detected based on a light receiving signal from a means.

[0002]

In this type of photoelectric sensor, the presence or absence of an object to be detected is determined by receiving the light emitted from the light emitting means by a light receiving signal. In an environment where (noise light) enters, even if the object to be detected is not detected, a light receiving signal is output from the light receiving means in accordance with the input of the interference light. It is in the detection state, and the detected object cannot be correctly detected.

[0003] In Japanese Patent Publication No. 62-7733, the light receiving level is detected at a timing immediately before light emission.
It is determined based on the light receiving level whether or not the light is on.
At this time, when it is determined that the light is in the incident state, it is determined that the interference light is incident and the light emission timing is shifted to prevent the interference.

However, this Japanese Patent Publication No. 62-7733.
In the device disclosed in Japanese Patent Application Laid-Open No. H11-157, the interference light is determined only at the timing immediately before the light is projected, so that the interference light that enters immediately after the light cannot be detected. In this case, since a normal light receiving signal is generated immediately after the light is projected, it is actually impossible to determine the presence or absence of the interference light based on the light receiving level immediately after the light is projected. In addition, since a normal light receiving signal is generated during light projection, it is needless to say that the presence or absence of interference light cannot be determined based on the signal level of the light receiving signal.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a photoelectric sensor capable of determining the presence or absence of interference light even during a light projection period or immediately after the light emission ends. is there.

[0006]

SUMMARY OF THE INVENTION The present invention comprises a light projecting means for projecting pulse light, and a light receiving means for receiving the pulse light projected from the light projecting means and outputting a light receiving signal. In a photoelectric sensor that determines the presence or absence of an object to be detected based on a light receiving signal from the light receiving unit, the photoelectric sensor outputs the light receiving signal output from the light receiving unit at a plurality of sampling timings in a predetermined period including a light emitting period of the light emitting unit. Sampling means for sampling a signal level is provided, and storage means for storing sampling data by the sampling means as reference data in a detection state of an object to be detected in an environment in which no interference light exists, and from the light receiving means at a predetermined determination timing. Comparing means for comparing the signal level of the received light signal with a predetermined reference level. When it is determined that the signal level of the light receiving signal exceeds a predetermined reference level, the sampling data by the sampling unit is compared with the reference data stored in the storage unit corresponding to the sampling timing of the sampling data, When at least one of the comparison differences between the two exceeds a set value, a determination means for determining that interference light has been received is provided.

According to such a configuration, the sampling means outputs the signal from the light receiving means at a plurality of sampling timings in a predetermined period including the light emitting period of the light emitting means in a detection state of the detected object in the environment where no interference light exists. The signal level of the received light signal is sampled. Then, the storage means stores the sampling data sampled by the sampling means in the storage means as reference data.
Thus, the storage unit sequentially stores the reference data corresponding to the sampling timing.

[0008] The comparing means compares at a predetermined judgment timing whether the signal level of the light receiving signal from the light receiving means exceeds a predetermined reference level. At this time, when the comparing means determines that the signal level of the light receiving signal from the light receiving means has exceeded a predetermined reference level, the case where the object to be detected is correctly detected and the case where the interference light is received are determined. Therefore, the judging unit compares the sampling data from the sampling unit with the reference data stored in the storage unit corresponding to the sampling timing of the sampling data. At this time, when at least one of the comparison differences between the sampling data and the reference data exceeds a set value, it is determined that the interference light has been received. This allows
It is possible to determine the presence or absence of interference light even during the light emitting period or immediately after the light emitting end.

In the above arrangement, the judging means receives the interference light when the comparing means judges that the signal level of the light receiving signal from the light receiving means has not exceeded a predetermined reference level and when it has judged that the signal level has exceeded the predetermined reference level. When it is determined that the interference light is not detected, when it is determined that the interference light is exceeded, when it is determined that the interference light is not received, it is preferable that the detection is determined (claim 2).

According to such a configuration, when the light receiving means does not receive light at the predetermined determination timing, it is in a non-detection state. Therefore, the determining means determines that the comparing means has a signal level of a light receiving signal from the light receiving means. If it is determined that the value does not exceed the predetermined reference level, it can be determined that no detection has occurred. Further, when the comparing means determines that the signal level of the light receiving signal from the light receiving means has exceeded a predetermined reference level, there are a case where the detected object is correctly detected and a case where the interference light is received. From the above, the determination means can determine that detection has not been performed when determining that interference light has been received as described above, and can determine that detection has been performed when determining that interference light has not been received as described above. . As a result, the detected object can be correctly detected without being affected by the interference light.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a reflection type photoelectric sensor will be described below with reference to the drawings.
FIG. 1 is a block diagram schematically showing a configuration of the photoelectric sensor. In FIG. 1, a photoelectric sensor 1 mainly includes a CPU (corresponding to a sampling unit and a judgment unit) 2.
The CPU 2 gives a drive command to the light projecting means 3 at a predetermined cycle. The light projecting means 3 includes an LED (not shown) and a drive circuit, and the drive circuit receives a drive command from the CPU 2 and energizes the LED to emit, for example, infrared pulse light from the LED. . Light receiving means 4
Is provided so as to receive the pulse light projected from the light projecting means 3 and reflected by the detected object 5, and to output the received pulse light as a light receiving signal. The light receiving means 4 includes a phototransistor and a light receiving circuit (not shown). The light receiving circuit outputs a light receiving signal by discriminating and amplifying an AC component from a light receiving signal from the phototransistor. An A / D converter 6 is connected to the light receiving means 4.
The signal level of the light receiving signal output from the light receiving means 4 is converted into digital data and output to the CPU 2.

On the other hand, the light receiving means 4 is connected to a comparator (corresponding to a comparing means) 7. This comparator 7
Compares the light receiving signal level from the light receiving means 4 with a predetermined reference level, and outputs an ON signal to the CPU 2 when the light receiving signal level exceeds the reference level. In this case, the reference level is set to a level sufficiently higher than the light receiving signal level when the detected object 5 is at the predetermined detection position.

The setting switch 8 is a slide switch, and is provided for switching between RUN (detection state) and SET (setting state). The switching position (RUN / SET) of the setting switch 8 switches between a setting state in which the CPU 2 is initialized and a detection state in which a normal detection operation is performed.

When the setting switch 8 is switched to the SET position, the CPU 2 determines that the operation is the setting operation, emits pulse light from the light projecting means 3 at a predetermined cycle, and sets a predetermined period including the light projecting period. , The digital data from the A / D converter 6 is sequentially stored in the storage means 9 as reference data at a predetermined sampling timing.

The CPU 2 sets the setting switch 8 to RU.
In the state where the position has been switched to the N position, it is determined that the detection operation is being performed, and pulse light is emitted from the light projecting means 3 at a predetermined cycle, and A / D is performed at a predetermined sampling time as described later.
Digital data input from converter 6 and storage means 9
The presence of the interference light is determined based on the result of comparison with the reference data stored in the storage device. It is a feature.

Next, the operation of the above configuration will be described. FIG. 2 is a timing chart showing each signal. This figure 2
, The CPU 2 gives a light emitting command to the light emitting means 3 based on the clock. As a result, as shown in the figure, the light projecting means 3 emits pulse light of a predetermined period.

The light receiving means 4 receives the pulse light emitted from the light emitting means 3 and reflected by the detected object 5, and outputs a light receiving signal corresponding to the light receiving level. In this case, since the light receiving means 4 is configured to discriminate and amplify only the AC component of the light receiving signal, the light receiving signal output from the light receiving means 4 has a waveform obtained by differentiating the light emitting signal and the light emitting signal. At the end of light, it undershoots below zero level. The initial setting operation and the normal detection operation are performed based on the operation of the photoelectric sensor 1 as described above.

In order to perform a normal detection operation of the detected object 5, it is necessary to first perform an initial setting before the operation. This initial setting is necessary for judging the presence of the interference light. In the environment not affected by the interference light, the detected object 5 is located at a predetermined detection position, and the setting switch 8 is set to the SET position. Photoelectric sensor 1 in the switched state
To work. Under such environmental conditions, the light received by the light receiving means 4 is only light reflected from the detected object 5 after being emitted from the light emitting means 3, and the light receiving means 4 may not receive the interference light. Absent.

FIG. 3 is a flowchart showing the initial setting operation of the CPU 2. In FIG. 3, the CPU 2 determines whether any of the timings T1 to T5 has come (S101), and when it comes to the timing T1 (S101: YES), the input from the A / D converter 6 is received. The data is sampled and stored in the storage means 9 as the reference data M1 (S102). This timing T1
Is set to a timing advanced by one clock from the light projection timing as shown in FIG. in this case,
At timing T1, neither the pulse light nor the interference light from the light projecting means 3 enters the light receiving means 4, so that the reference data M1 is at the zero level. Also, CPU2
Is the timing T2 (S103: YE
S), the transmission of the light emission pulse is started (S10).
4) The input data from the A / D converter 6 is sampled and stored in the storage means 9 as the reference data M2 (S105). That is, the timing T2 is set to the light emission start timing as shown in FIG.
In this case, at timing T2, it is general that neither the pulse light nor the interference light from the light projecting means 3 enters the light receiving means 4, so that the reference data M2 is at the zero level.

When the timing T3 has come (S106: YES), the CPU 2 terminates the transmission of the light projection pulse (S107), samples the input data from the A / D converter 6, and outputs the reference data M3. Is stored in the storage means 9 (S108). That is, the timing T3 is set to the light emission end timing as shown in FIG. In this case, although the timing at which the light emission from the light emitting means 3 ends at the timing T3, since the electrical configuration of the light receiving means 4, especially the operation of the differentiating circuit, has substantially reached the peak level of the light receiving signal, Data M3 is substantially the maximum signal level of the light receiving signal.

When the timing T4 has come (S109: YES), the CPU 2 samples the input data from the A / D converter 6 and stores it in the storage means 9 as reference data M4 (S110). This timing T4 is one time later than the light emission end timing as shown in FIG.
The timing is set to be delayed by the clock. In this case, the timing T4 is a timing when the light emission from the light emitting means 3 is finished,
The light receiving signal undershoots the zero level due to the electrical configuration of the light receiving means 4, particularly the operation of the differentiating circuit, and the reference data M4 is negative level data.

Then, when it is time T5 (S111: YES), the CPU 2 turns on the A / D converter 6.
Is sampled and stored in the storage means 9 as reference data M5. The timing T5 is set so as to be two clocks later than the light emission end timing as shown in FIG. In this case, at timing T5, the influence of the electrical characteristics of the light receiving means 4 has been eliminated, so that the reference data M5 is at the zero level. By performing the initial setting as described above, the reference data M1 to M5 at the timings T1 to T5 can be sequentially stored in the storage unit 9.

Now, in order to detect that the detected object 5 is at a predetermined detection position, the photoelectric sensor 1 is operated with the setting switch 8 switched to the RUN position. FIG. 4 shows a detection operation of the CPU 2. In FIG.
The photoelectric sensor 1 determines whether any of the timings T1 to T5 has been reached, and when the timing T1 has been reached (S201: YES), the A / D converter 6
, And temporarily stores the data as sampling data D1 in the storage unit 9 (S
202).

Similarly, every time the timing T2 to T5 is reached (S203: YES, S206: YES, S20
9: YES, S211: YES), A / D converter 6
Is sampled and temporarily stored in the storage means 9 as sampling data D2 to D5 (S205, S208, S210, S212). In this case, transmission of the light emission pulse is started at timing T2 (S204), and transmission of the light emission pulse is ended at timing T3 (S207).

On the other hand, the CPU 2 detects the state of the output from the comparator 7 and temporarily stores the state (S
213). In this case, when the detected object 5 is at the predetermined detection position, the output from the comparator 7 is in the ON state. Even when the detected object 5 does not exist, the output from the comparator 7 is in the ON state when the interference light enters at the timing T3.

As described above, during the detection operation, the CPU 2 samples the light receiving signal at the predetermined timings T1 to T5 to sample data D1 to D5.
And the output state from the comparator 7 is temporarily stored.

At timing T5, the CPU 2 determines whether the output from the comparator 7 has been turned on (S214), and if it is off (S21).
4: NO), it is determined that the detected object 5 does not exist and is not detected (S220). On the other hand, when the output state from the comparator 7 is the ON state (S214: YE
S), it is determined that either the detected object 5 exists or the detected object 5 does not exist and the interference light is incident, and a comparison process is performed (S215).

FIG. 5 is a flowchart showing the comparison processing of the CPU 2. In FIG. 5, the CPU 2 first
It is determined whether the sampling data D1 matches the reference data M1. That is, the sampling data D1 and the reference data M1 are called out from the storage means 9 and the difference data S1 is calculated by executing D1-M1 (S1).
301), the absolute value of the difference data S1 is compared with a predetermined error range SM (S302). At this time, if the absolute value of the difference data S1 is smaller than the predetermined error range SM, it is determined that the sampling data D1 matches the reference data M1.

When it is determined that the sampling data D1 matches the reference data M1, the sampling data D2 to D5 are similarly converted to the reference data M1.
It is determined whether or not each of them matches with M2 to M5 (S304).
To S315), when it is determined that they all match, the comparison result is OK (S316), and when it is determined that at least one does not match, the comparison result is NG (S317).

Then, when the CPU 2 determines that the comparison result is OK as a result of the execution of the above-described comparison processing (S216: YES in FIG. 4), the CPU 2 finally determines that the detection has been made (S219). On the other hand, when it is determined that the comparison result is NG (S216: NO), it is determined that the interference light is detected (S217), and it is finally determined that the interference light is not detected (S218).

As described above, when it is determined that the interference light is received at the light emission timing, the influence of the interference light is avoided by changing the period of the light emission pulse or shifting the light emission timing. can do. Further, by outputting the detection of the interference light to the outside, it can be notified that the interference light is received.

According to such an embodiment, the CPU 2
Means that the sampling data in a predetermined period including the light emitting period is stored in the storage means 9 as reference data, and if it is determined that the signal level of the received light signal exceeds the predetermined reference level during the detection operation, the sampling is performed. By comparing the data with the reference data, the influence of the interference light is determined, and when it is determined that the interference light is affected, it is finally determined that the light is not detected. Unlike the conventional configuration in which the interference light is determined, the presence of the interference light can be determined even during the light projection period or immediately after the light emission ends, and the influence of the interference light can be avoided.

The present invention is not limited to the above embodiment, but can be modified or expanded as follows. As a result of the comparison processing between the sampling data and the reference data, when it is finally determined that the detection is performed, the sampling data at that time may be updated and stored as the reference data. Switching between the setting operation and the detection operation may be automatically executed in response to an external command. The present invention may be applied to a transmission sensor.

[0034]

As is apparent from the above description, according to the photoelectric sensor of the present invention, in the state where the object to be detected is detected in the environment where no interference light exists, a plurality of light beams in a predetermined period including the light emitting period of the light emitting means are detected. At the sampling timing, the signal level of the light receiving signal from the light receiving means is sampled and stored as reference data. At a predetermined judgment timing, the signal level of the light receiving signal from the light receiving means is compared with a predetermined reference level. If the signal level exceeds a predetermined reference level, the sampling data is compared with reference data stored corresponding to the sampling timing of the sampling data, and at least one of the comparison differences between the two sets the set value. When it exceeds the threshold, it is determined that the interference light has been received. It can determine the presence or absence of the interference light, an excellent effect that reliably and it is possible to correspond to the influence of the interference light.

[Brief description of the drawings]

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

FIG. 2 is a timing chart showing output timing of each signal.

FIG. 3 is a flowchart showing a setting operation of a CPU.

FIG. 4 is a flowchart showing a detection operation of the CPU.

FIG. 5 is a flowchart showing a comparison processing operation of the CPU;

[Explanation of symbols]

1 is a photoelectric sensor, 2 is a CPU (sampling means, judgment means), 3 is a light emitting means, 4 is a light receiving means, 7 is a comparator (comparing means), and 9 is a storage means.

Claims (2)

[Claims] A light projecting means for projecting pulse light; and a light receiving means for receiving the pulse light projected from the light projecting means and outputting a light receiving signal. A photoelectric sensor that determines the presence or absence of an object to be detected based on a sampling unit that samples a signal level of a light receiving signal output from the light receiving unit at a plurality of sampling timings in a predetermined period including a light emitting period of the light emitting unit; A storage means for storing sampling data by the sampling means as reference data in a detection state of an object to be detected in an environment where no interference light exists; a signal level of a light reception signal from the light receiving means at a predetermined determination timing and a predetermined reference Comparing means for comparing the signal level of the light receiving signal from the light receiving means with a predetermined reference If it is determined that exceeds the level is compared with the reference data corresponding to the sampling timing of the sampling data and the sampling data stored in the storage means according to said sampling means,
A photoelectric conversion device comprising: a determination unit configured to determine that interference light has been received when at least one of the comparison differences between the two exceeds a set value. 2. The method according to claim 1, wherein the comparing unit determines that the interference light is received when the comparing unit determines that the signal level of the light receiving signal from the light receiving unit does not exceed a predetermined reference level and when it determines that the signal level exceeds the predetermined reference level. 2. The photoelectric sensor according to claim 1, wherein it is determined that the detection is not detected when the detection is performed, and when it is determined that the interference light is not received when it is determined that the interference is exceeded, the detection is determined that the detection is performed.