JP3654356B2 - Photoelectric switch - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a photoelectric switch with noise countermeasures applied to, for example, an inverter type fluorescent lamp, and in particular, prior to on / off determination processing, defines a level of a light reception signal at a timing immediately before a pulsed detection light will arrive. The present invention relates to a photoelectric switch that eliminates the influence of fluorescent lamp noise as much as possible by adjusting the level.
[0002]
[Prior art]
As is well known, this type of photoelectric switch includes a light projecting means, a light receiving means, and a signal processing means. In the case of a reflective photoelectric switch, the light projecting means and the light receiving means are generally housed in the same housing. In the case of a transmissive photoelectric switch, the light projecting means and the light receiving means are generally housed in separate housings that are separated from each other.
[0003]
The light projecting means outputs a driving pulse signal (hereinafter referred to as a light projecting pulse) at a timing indicated by the light projecting control signal, and detects a pulse in response to the light projecting pulse output from the driving means. And a light emitting element that projects light onto a target region. The light receiving means includes a light receiving element that receives and photoelectrically converts pulsed detection light coming from the target region, and an amplifier that amplifies the output of the light receiving element and generates a light reception signal. The signal processing means generates an on / off determination output based on the light receiving signal output from the light receiving means.
[0004]
Specific examples of the light projection pulse PD and the light reception signal VS2 are shown in the waveform diagrams of FIG. As can be seen from the figure, the light projection pulse PD is a rectangular wave having a time width corresponding to the light emission period, and repeatedly appears every period T. The light reception signal VS2 rises steeply from the time corresponding to the front edge of the light projection pulse PD to the time corresponding to the rear edge, reaches the peak pk, then immediately falls and overshoots to reach the bottom bm. After that, it has a characteristic chevron waveform that rises relatively slowly and converges to zero level. The overshoot portion in the characteristic chevron waveform appears due to the capacitance component of the amplifier constituting the light receiving means.
[0005]
As shown in FIG. 12, if the base level of the chevron waveform of the light reception signal VS2 is always stable, for example, the light reception signal VS2 is sampled at a timing slightly delayed from the timing of the light projection pulse PD, and By comparing the level of the sampled light reception signal VS2 with a prescribed threshold value, it should be possible to easily perform the on / off determination.
[0006]
[Problems to be solved by the invention]
A specific example of the projection pulse PD, the variation range Δt of the sampling pulse generation timing, and the noise component VN2 due to the inverter fluorescent lamp is shown in the waveform diagram of FIG.
[0007]
The value of the light projection period T in this type of photoelectric switch is relatively close to the blinking period of an inverter type fluorescent lamp that is often used in factory lighting in Europe. This is because, when this type of photoelectric switch is installed in an environment in which such an inverter fluorescent lamp is installed, the light reception signal VS2 (see FIG. 12) and the noise component VN2 due to the fluorescent lamp are superimposed. Since the base level of the VS2 chevron waveform fluctuates greatly every light projection period, on-off determination is simply performed by comparing the level of the light reception signal VS2 at a timing delayed by a certain time from the light projection pulse PD with a prescribed threshold value. Means that it cannot be done accurately.
[0008]
Even if the noise component VN2 due to the fluorescent lamp does not exist, the generation timing of the sampling pulse can be determined based on the generation timing of the light projection pulse PD, etc., so that the generation timing varies depending on the capacitance component of the circuit element. It is difficult to suppress completely. In particular, in the case of a transmissive photoelectric switch, the light projection pulse PD is transmitted from the light-receiving side device to the light-projecting side device via the communication means. Therefore, the sampling pulse is generated due to the variation in the transmission time due to this communication. The variation range Δt with timing is hard to ignore.
[0009]
Therefore, in the signal processing technique previously proposed by the present inventors in Japanese Patent Laid-Open Nos. 5-145395 and 6-152364, the received light signal at the timing immediately before the pulsed detection light will arrive. The level shift is performed by shifting the level of the received light signal included in the period in which the received light signal waveform of the pulsed detection light is obtained by an amount corresponding to the difference between the level and the specified level in a direction approaching the specified level. Based on the level of the received light signal later, a signal processing technique is adopted in which satisfaction of the on / off 1 condition is determined.
[0010]
According to such a signal processing method, an algorithm is adopted in which a noise component is removed from the level of the received light signal and then compared with a threshold value. Therefore, the influence of the noise component due to the fluorescent lamp is removed, and the reliability is high. It was expected that an on / off judgment result could be obtained.
[0011]
However, according to the earnest research by the present inventors, even in the signal processing method with the noise component removal function by the level shift described above, there is still a problem in the reliability of the on / off determination due to the following reasons. Turned out to be left.
[0012]
First, for the same reason as described above, it is difficult to accurately determine the timing immediately before the pulsed detection light will arrive. In particular, in the case of a transmissive photoelectric switch, the light projection pulse PD is transmitted from the light receiving side device to the light emitting side device via the communication means. It is not possible to accurately determine the timing immediately before light will arrive. When there is a large variation in the timing immediately before the pulsed detection light will arrive, even if the determination threshold is appropriate, accurate on / off determination cannot be performed.
[0013]
Second, even if the timing immediately before the arrival of the pulsed detection light can be accurately determined, the determined timing has a large rate of change on the waveform of the noise component VN2 due to the fluorescent lamp. If the received light signal level of the pulsed detection light at that time happens to be near the upper and lower sides of the determination threshold when coincident with the portion (phase 0 degree, 180 degrees, 360 degrees, etc.), the received light signal level is affected by the noise component VN2. May not exceed the threshold value by mistake, or cannot be accurately determined.
[0014]
The present invention has been made to solve the above-described problems in the photoelectric switch having the level shift function.
[0015]
That is, an object of the present invention is to provide a photoelectric switch with a level shift function that can further improve the reliability in on / off determination.
[0016]
Another object of the present invention is to provide a photoelectric switch with a level shift function capable of obtaining a reliable on / off determination result even if the sampling timing of the received light signal for performing the on / off determination is slightly shifted. Is to provide.
[0017]
Another object of the present invention is to obtain a reliable on / off determination result even if the sampling timing of the received light signal for performing the on / off determination coincides with a steep portion of the received light signal waveform due to a noise component. An object of the present invention is to provide a photoelectric switch with a level shift function.
[0018]
Still other objects and operational effects of the present invention will be easily understood by those skilled in the art based on the following description of the specification.
[0019]
[Means for Solving the Problems]
The photoelectric switch of the present invention is output from a light projecting unit that periodically projects pulsed detection light, a light receiving unit that photoelectrically converts the pulsed detection light and outputs a corresponding light reception signal, and a light receiving unit. Signal processing means for generating an on / off determination output based on the received light signal.
[0020]
The signal processing means obtains a received light signal waveform of the pulsed detection light by an amount corresponding to a difference between the level of the received light signal and a specified level immediately before the arrival of the pulsed detection light. A level shift means for level-shifting the level of the received light signal included in the expected period to a direction approaching the specified level, and on-off determination based on the received light signal after the level shift by the level shift means. And condition determination means for determining whether or not at least one of the existing conditions is satisfied.
[0021]
Here, the function of the level shift means may be realized by software using a microprocessor, or may be realized by hardware using a dedicated analog circuit as in an embodiment described later. .
[0022]
A person skilled in the art will be able to conceive several methods for realizing in software. As one of those methods, the level of the received light signal output from the light receiving means is continuously A / D converted at a predetermined sampling period and stored in a memory in time series, and then used for on / off determination. The value of the data at the timing just before the timing at which the pulsed detection light will arrive is subtracted from or added to the data value at one or more timings.
[0023]
Also, the function of the condition determination means may be realized by software using a microprocessor, or may be realized by hardware using a comparator, a dedicated logic circuit, or the like.
[0024]
The photoelectric switch of the present invention further has the following characteristics in the above basic configuration.
[0025]
In other words, the condition determination means includes a level of the light reception signal at a first timing at which a peak of the light reception signal waveform of the pulsed detection light will arrive and a bottom due to an overshoot of the light reception signal waveform of the pulsed detection light. The determination is made at least on the condition that the comparison result with the level of the received light signal at the second timing at which the second signal will arrive is a predetermined magnitude relationship.
[0026]
As described above, the function of the condition determination means may be realized by hardware using an analog comparator and a logic circuit, or after A / D conversion of the level-shifted received light signal, You may make it implement | achieve in software using a processor.
[0027]
In the present invention, “determining whether or not at least one of the conditions used for on / off determination is satisfied” is used for this type of photoelectric switch for the final on / off determination. This is because it is usually considered that a plurality of determination conditions are satisfied. Examples of other judgment conditions that are often employed include those for judging on or off on the condition that the on / off judgment result is continued a plurality of times.
[0028]
According to the above configuration, the peak of the light reception signal waveform of the pulsed detection light at which the peak of the light reception signal waveform will arrive and the bottom due to the overshoot of the light reception signal waveform of the pulsed detection light arrive. Since the comparison result with the level of the received light signal at the second timing is a predetermined magnitude relationship, the satisfaction determination of the first condition is performed, so that the first timing and the second timing are satisfied. Is slightly deviated from the peak or bottom timing of the received light signal waveform, as long as a chevron waveform peculiar to the received light signal waveform of the pulsed detection light exists in the sampling region, the received light level at the first timing and the second timing. Since the magnitude relationship between the two is almost immobile, it is possible to make a reliable on / off determination based on the relationship.
[0029]
More specifically, the first timing and the second timing may not be set strictly in accordance with the peak or bottom timing of the received light signal waveform due to variations in circuit characteristics (constants) related to the received light signal. Absent. Moreover, it is not necessary to match exactly. If there is no noise component, the difference between the signal value in the vicinity of the peak of the received light signal waveform and the signal value in the vicinity of the bottom is large. Any deviation from the peak and bottom timings of the received light signal waveform at the first timing and the second timing is allowed as long as it does not deviate from the principle.
[0030]
In a preferred embodiment, the condition determining means has a predetermined magnitude relationship between a comparison result between the level of the light reception signal at the first timing and the level of the light reception signal at the second timing, The determination is made on the condition that the comparison result between the level of the received light signal at the first timing and the specified level has a predetermined magnitude relationship.
[0031]
According to such a configuration, the timing immediately before the pulsed detection light will arrive coincides with the steep fall timing of the received light signal waveform due to the noise component, and there is no reflected light of the pulsed detection light. Or, since there is almost no presence, normal reflected light exists even if a situation in which it is difficult to accurately perform the on / off determination occurs only by the magnitude relationship between the light reception level at the first timing and the light reception level at the second timing. There is a clear difference in the comparison result between the light reception level at the first timing and the specified level between the case and the case where it does not exist. Therefore, by adding this as a reference for determination, a reliable on / off determination result Will be obtained.
[0032]
The photoelectric switch of the present invention viewed from another aspect includes a light projecting unit that periodically projects pulsed detection light, a light receiving unit that photoelectrically converts the pulsed detection light and outputs a corresponding light reception signal, Signal processing means for generating an on / off determination output based on a light receiving signal output from the light receiving means.
[0033]
The signal processing means obtains a received light signal waveform of the pulsed detection light by an amount corresponding to a difference between the level of the received light signal and a specified level immediately before the arrival of the pulsed detection light. A level shift means for level-shifting the level of the received light signal included in the expected period to a direction approaching the specified level, and on-off determination based on the received light signal after the level shift by the level shift means. And condition determination means for determining whether or not at least one of the existing conditions is satisfied.
[0034]
Here, the function of the level shift means may be realized by software using a microprocessor, or may be realized by hardware using a dedicated analog circuit as in an embodiment described later. .
[0035]
A person skilled in the art will be able to conceive several methods for realizing in software. As one of those methods, the level of the received light signal output from the light receiving means is continuously A / D converted at a predetermined sampling period and stored in a memory in time series, and then used for on / off determination. The value of the data at the timing just before the timing at which the pulsed detection light will arrive is subtracted from or added to the data value at one or more timings.
[0036]
Further, as will be described later, the function of the condition determination means may be realized by software using a microprocessor, or may be realized by hardware using a comparator, a dedicated logic circuit, or the like. good.
[0037]
The photoelectric switch of the present invention further has the following characteristics in the above basic configuration.
[0038]
That is, the light projecting means is structured to perform light projection at least three times within the blinking cycle of the inverter fluorescent lamp in the installation environment. Incidentally, in the case of the current inverter fluorescent lamp, the shortest blinking period is about 60 to 70 μsec.
[0039]
In addition, the condition determination means obtains a comparison result by comparing the level of the received light signal at a timing when the peak of the pulsed detection light will arrive with a predetermined threshold value, and all comparisons obtained within the light projection period. The determination is made in accordance with the comparison result that occupies the majority of the results.
[0040]
As described above, the function of the condition determination means may be realized by hardware using an analog comparator and a logic circuit, or after the A / D conversion is performed on the received light signal after the level shift, the microprocessor It may be realized in software using
[0041]
Note that “determining whether or not at least one of the conditions used for the on / off determination is satisfied” is generally used in this type of photoelectric switch for final on / off determination. This is because it is often considered that the determination condition is satisfied as a requirement. Examples of other requirements that are often adopted include those that determine ON or OFF on the condition that the ON or OFF determination result is continued a plurality of times.
[0042]
According to the above configuration, since the noise waveform due to the inverter fluorescent lamp is substantially sinusoidal, there are only two places (for example, phase 0 degree and 180 degree) where the waveform slope is steep within one blinking period of the fluorescent lamp. Therefore, if light projection is performed at least three times within one blinking cycle, the light projection timing of the two will almost coincide with the timing of the steeply rising portion and the steeply falling portion of the noise waveform. Thus, even if an incorrect level determination result is obtained at any timing, the other light projection timings correspond to relatively gentle portions. Therefore, a comparison result is obtained by comparing the level of the received light signal at the timing when the peak of the pulse-shaped detection light will arrive with a predetermined threshold value, and occupies a large number of all the comparison results obtained within the light projection period. If the determination of satisfaction of the one condition is performed according to the comparison result, a reliable on / off determination result can be obtained.
[0043]
As a more specific form, the photoelectric switch of the present invention includes a driving unit that outputs a driving pulse signal at a timing indicated by a light projection control signal, and a pulse detection in response to the driving pulse signal output from the driving unit. Light projecting means including a light emitting element that projects light to the target area, a light receiving element that receives and photoelectrically converts reflected light of the pulsed detection light coming from the target area, and amplifies the output of the light receiving element A light receiving means including an amplifier for generating a light reception signal, and a signal processing means for generating an on / off determination output based on the light reception signal output from the light reception means.
[0044]
The signal processing means obtains a received light signal waveform of the pulsed detection light by an amount corresponding to a difference between the level of the received light signal and a specified level immediately before the arrival of the pulsed detection light. A level shift means for level-shifting the level of the received light signal included in the expected period to a direction approaching the specified level, and on-off determination based on the received light signal after the level shift by the level shift means. And condition determination means for determining whether or not at least one of the existing conditions is satisfied.
[0045]
The above-described reflective photoelectric switch has the following features in the above basic configuration.
[0046]
In other words, the condition determination means includes a level of the light reception signal at the first timing at which a peak of the light reception signal waveform of the pulsed detection light will arrive and a bottom due to an overshoot of the light reception signal waveform of the pulsed detection light The determination is made at least on the condition that the comparison result with the level of the received light signal at the second timing at which the second signal will arrive is a predetermined magnitude relationship.
[0047]
In a preferred embodiment, the condition determining means has a predetermined magnitude relationship between a comparison result between the level of the light reception signal at the first timing and the level of the light reception signal at the second timing, The determination is made on the condition that the comparison result between the level of the received light signal at the first timing and the specified level has a predetermined magnitude relationship.
[0048]
Another specific form of the photoelectric switch of the present invention is a driving means for outputting a driving pulse signal at a timing indicated by a light projection control signal, and a pulse in response to the driving pulse signal output from the driving means. A light projecting means including a light emitting element for projecting the detection light to the target area, a light receiving element for receiving and reflecting the reflected light of the pulsed detection light coming from the target area, and an output of the light receiving element And a signal processing means for generating an ON / OFF determination output based on the light reception signal output from the light reception means.
[0049]
The signal processing means obtains a received light signal waveform of the pulsed detection light by an amount corresponding to a difference between the level of the received light signal and a specified level immediately before the arrival of the pulsed detection light. A level shift means for level-shifting the level of the received light signal included in the expected period to a direction approaching the specified level, and on-off determination based on the received light signal after the level shift by the level shift means. And condition determination means for determining whether or not at least one of the existing conditions is satisfied.
[0050]
The above-described photoelectric switch has the following features in the above basic configuration.
[0051]
That is, the light projecting means is structured to perform light projection at least three times within the blinking cycle of the inverter fluorescent lamp in the installation environment.
[0052]
In addition, the condition determination means obtains a comparison result by comparing the level of the received light signal at a timing when the peak of the pulsed detection light will arrive with a predetermined threshold value, and all comparisons obtained within the light projection period. The determination is made in accordance with the comparison result that occupies the majority of the results.
[0053]
In a preferred embodiment, the level shift means has a function of transmitting an AC component of the input side signal to the output side and initializing a DC potential to be superimposed on the output side AC component to a specified potential. The direct current potential to be superimposed on the output side alternating current component of the alternating current signal transmission circuit is repeatedly set to a specified potential immediately before the timing at which the pulsed detection light will arrive. Will be fixed.
[0054]
According to such a configuration, the received light signal waveform of the pulsed detection light can be obtained by an amount corresponding to the difference between the level of the received light signal and the specified level immediately before the pulsed detection light will arrive. The function of level-shifting the level of the received light signal included in the period that is likely to approach the specified level can be realized by hardware using an analog circuit.
[0055]
In a preferred embodiment, the AC signal transmission circuit includes a coupling capacitor interposed between the input and output terminals, and a switch interposed between the output side terminal and the specified potential point. On / off control is performed by a gate control signal synchronized with the timing signal.
[0056]
In a preferred embodiment, an operation such as a comparison between the level of a received light signal and a threshold value performed in the condition determination means is performed on digital data acquired by A / D converting the output signal of the AC signal transmission circuit. Based on this, it is realized in software by a microprocessor.
[0057]
In a preferred embodiment, the photoelectric switch is realized as a transmissive photoelectric switch having a light emitting side device and a light receiving side device that are arranged apart from each other.
[0058]
In this transmissive photoelectric switch, the light projecting means is built in the light projecting side device. The light receiving means and the signal processing means are built in the light receiving side device. The light projection control signal is transmitted from the light receiving side device to the light projecting side device via communication.
[0059]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a preferred embodiment of a photoelectric switch according to the present invention will be described in detail with reference to the accompanying drawings.
[0060]
As described above, the photoelectric switch of the present invention includes a light projecting unit that periodically projects pulsed detection light, a light receiving unit that photoelectrically converts the pulsed detection light and outputs a corresponding light reception signal, Signal processing means for generating an on / off determination output based on a light receiving signal output from the light receiving means.
[0061]
In the signal processing means, the light reception signal waveform of the pulse detection light is obtained in an amount corresponding to the difference between the level of the light reception signal and the specified level immediately before the pulse detection light will arrive. Level shift means for level-shifting the level of the received light signal included in the wax period in a direction approaching the specified level, and at least of the conditions used for on / off determination based on the received light signal after the level shift by the level shift means And condition determination means for determining whether one is satisfied.
[0062]
Here, the function of the “level shift means” may be realized by software using a microprocessor, or may be realized by hardware using a dedicated analog circuit as in an embodiment described later. Also good.
[0063]
A person skilled in the art will be able to conceive several methods for realizing in software. As one of those methods, the level of the received light signal output from the light receiving means is continuously A / D converted at a predetermined sampling period and stored in a memory in time series, and then used for on / off determination. The value of the data at the timing just before the timing at which the pulsed detection light will arrive is subtracted from or added to the data value at one or more timings.
[0064]
The photoelectric switch of the present invention further has the following characteristics in the above basic configuration. Here, as the feature items, a first feature item and a second feature item that can be adopted alternatively or in combination are prepared.
[0065]
The first characteristic item relates to “condition determination means”. That is, in this first feature matter, the condition determining means receives the level of the light reception signal at the first timing at which the peak of the light reception signal waveform of the pulsed detection light will arrive and the light reception of the pulsed detection light. The determination is made at least on the condition that the comparison result with the level of the received light signal at the second timing at which the bottom due to the overshoot of the signal waveform will arrive is a predetermined magnitude relationship. In other words, this first characteristic item is intended to improve the reliability of the on / off determination by paying attention to the characteristic chevron waveform generated only when the pulse-shaped detection light is received.
[0066]
The second characteristic item relates to “light projection means” and “condition determination means”. That is, in this second feature, the light projecting means has a light projecting period shorter than the blinking period of the inverter fluorescent lamp in the installation environment, and performs light projection at least three times within the light projecting period. It is structured to do. In addition, the condition determination means obtains a comparison result by comparing the level of the received light signal at a timing when the peak of the pulsed detection light will arrive with a predetermined threshold value, and all comparisons obtained within the light projection period. The determination is made in accordance with the comparison result that occupies the majority of the results. In other words, this second feature is intended to improve the reliability of the on / off determination by focusing on the fact that there are only two steep portions in one period of the fluorescent lamp noise waveform. It is. The first feature item may be applied in order to obtain a comparison result for the received light signal corresponding to each light projection in the second feature item.
[0067]
The function of the condition determining means may be realized by hardware using an analog comparator and a logic circuit, or after performing A / D conversion on the level-shifted received light signal, software using a microprocessor. You may make it implement | achieve.
[0068]
Next, FIG. 1 shows an electrical basic configuration of the photoelectric switch according to the first embodiment of the present invention. The illustrated photoelectric switch is a reflective photoelectric switch. Further, the function of the “level shift means” is realized by hardware using a dedicated analog circuit. Further, the first feature item is adopted as the feature item. For this reason, the condition determining means receives the level of the light reception signal waveform at the first timing at which the peak of the light reception signal waveform of the pulse detection light and the bottom due to the overshoot of the light reception signal waveform of the pulse detection light arrive. The determination is made at least under the condition that the comparison result with the level of the received light signal at the second timing is a predetermined magnitude relationship.
[0069]
As shown in the figure, the photoelectric switch 1 includes a light projecting unit 2, a light receiving unit 3, a filter unit 4, an A / D conversion unit 5, and a CPU 6. Details of these basic components 1 to 6 are as follows.
[0070]
The light projecting unit 2 includes a driving unit 7 and a light emitting element 8. Their configuration and operation are as follows.
[0071]
The drive means 7 is composed of an LED drive circuit such as a constant current source. This drive means 7 is based on a light projection control signal CD having a pulse waveform with a constant period T provided from the light projection control means 13 realized by software in the CPU 6, and has a pulse width TP and a rest period TK (T = A light projection pulse (drive pulse signal) PD having TP + TK is supplied to the light emitting element 8 (see FIG. 5A).
[0072]
The light emitting element 8 is configured by a light emitting diode (LED) in this example. The light emitting element 8 emits light only during a period corresponding to the pulse width of the light projection pulse PD supplied from the driving means 7 (see FIG. 4A), and the pulsed detection light LS can be present in the object 20. Flood light toward the area.
[0073]
The light receiving means 3 includes a light receiving element 9 and an amplifier 10. Their configuration and operation are as follows.
[0074]
In this example, the light receiving element 9 is composed of a photodiode (PD). The light receiving element 9 receives the reflected light LR reflected by the object 20 and the noise light LN from the inverter fluorescent lamp, and performs photoelectric conversion. The electric signal VS1 obtained by photoelectric conversion of the reflected light LR from the object 20 and the electric signal VN1 obtained by photoelectric conversion of the noise light LN from the fluorescent lamp are superimposed on each other and then supplied to the amplifier 10. Supplied.
[0075]
In this example, the amplifier 10 is composed of an operational amplifier capable of changing the gain. The amplifier 10 amplifies the electric signal (VS1, VN1) output from the light receiving element 9 with a specified gain, and generates and outputs a light receiving signal (VS2, VN2). Signal VS2 is a signal obtained by amplifying signal VS1, and signal VN2 is a signal obtained by amplifying signal VN1. The light reception signals (VS2, VN2) generated and output in this way are supplied to the filter means 4 arranged at the subsequent stage.
[0076]
The filter means 4 functions as “level shift means” which is one of the constituent features of the present invention. Note that the name “filter means” is a signal in a received light signal including a signal component VS2 corresponding to the reflected light LR that is periodic pulsed light and a signal component VN2 corresponding to the noise light LN from the fluorescent lamp. This is because the function of allowing only the component VS2 to pass is similar to the function of a so-called comb filter from a macro viewpoint.
[0077]
The filter means 4 determines the difference between the level of the light reception signal (VS2 + VN2) and the specified level (GND level in this example) at the timing T0 (see FIG. 5) immediately before the reflected light LR of the pulse-shaped detection light arrives. It functions as level shift means for shifting the level of the received light signal (VS2 + VN2) included in the period during which the reflected light LR of the pulse-shaped detection light will arrive by a corresponding amount in a direction approaching the specified level. The timing T0 is generated by the CPU 6.
[0078]
FIG. 3 shows an example of a circuit configuration for realizing the filter means 4 in hardware by a dedicated analog circuit. The analog circuit constituting the filter means 4 shown in the figure includes a coupling capacitor C1 interposed between the input and output terminals, and an analog switch Q1 interposed between the output side terminal and a specified potential point (GND in this example). Have. When the analog switch Q1 is in the OFF state, the output side is in a floating state, and the AC component of the input side signal is transmitted to the output side. When the analog switch Q1 is in the on state, the output-side potential is restricted to the GND potential that is the specified potential. When the analog switch Q1 is switched from the on state to the off state, the output side potential is unconstrained and the floating state is established. At the same time, transmission of an alternating current between the input and output is possible, so the potential of the output signal VO is A GND potential that is a specified potential is superimposed on the AC component on the input side. Note that any potential other than the GND potential can be employed as the specified potential.
[0079]
In other words, the analog circuit starts the transmission of the AC component from the input side to the output side by switching the analog switch Q1 from the ON state to the OFF state, and after the AC component transmission is started. In this case, the direct-current potential to be superimposed on the output-side alternating current component can also be expressed as an alternating-current signal transmission circuit having a function that is always initially set to the GND potential (specified potential).
[0080]
The A / D conversion means 5 performs A / D conversion on the output signal VO of the filter means 4 at a first timing T1 and a second timing T2, which will be described later (see FIG. 5). Here, the first timing T1 is the timing at which the peak of the light reception signal waveform of the pulsed detection light will arrive, and the second timing T2 is due to the overshoot of the light reception signal waveform of the pulsed detection light. This is the timing when the bottom will come. These timings T1 and T2 are generated by the CPU 6 as will be described later. On the output side of the A / D conversion means 5, the digital data DMX corresponding to the peak value obtained by the A / D conversion at the first timing T1 and the A / D conversion at the second timing T2 are obtained. The digital data DMN corresponding to the bottom value is output.
[0081]
The CPU 6 is mainly composed of a microprocessor. In the figure, the functions of the condition determination means 11, the sampling pulse generation means 12, and the light projection control means 13 depicted in the CPU 6 are realized by software by a microprocessor.
[0082]
Each function of the sampling pulse generation means 12 and the light projection control means 13 will be described with reference to the waveform diagram of FIG.
[0083]
The light projection control unit 13 generates a reference timing signal (not shown) having a period T based on a reference clock built in the CPU 6. Based on this reference timing signal, a light projection control signal CD and a sampling control signal CS are generated. The light projection control signal CD is a pulse signal having a period T synchronized with the reference timing signal, and its pulse width corresponds to the light emission time of the light emitting element 8. FIG. 5A shows the waveform of the light projection pulse PD generated as a result of the operation of the driving means 7 in response to the light projection control signal CD. As is apparent from the figure, the light projection pulse PD is a pulse signal having a period T and a pulse width TP. The sampling control signal CS is also a pulse signal having a period T synchronized with the reference timing signal. The sampling control signal CS is supplied to the sampling pulse generating means 12 and used for generating a gate pulse GP and a sampling pulse PS, which will be described later.
[0084]
The sampling pulse generator 12 generates a gate pulse signal GP and a sampling pulse signal PS based on the sampling control signal CS supplied from the light projection controller 13. The gate pulse signal GP obtained in this way is shown in FIG. As is apparent from the figure, the gate pulse signal PG is a pulse signal having a period T (= TOF + TON) synchronized with the reference timing signal. The gate pulse signal PG has a period TOF of “L” from the timing T0 immediately before the reflected light LR arrives until at least the signal component VS2 corresponding to the reflected light LR disappears, and then immediately before the next reflected light LR arrives. The period TON up to timing T0 is “H”. The gate pulse signal PG is supplied to the analog switch Q1 included in the AC signal transmission circuit constituting the filter unit 4. The analog switch Q1 is turned off when the signal level of the gate pulse signal PG is “L”, and turned on when it is “H”. The output of the AC signal transmission circuit functioning as the filter means 4 changes following the AC component on the input side when the analog switch Q1 is OFF, while GND regardless of the AC component on the input side when the analog switch Q1 is ON. It is fixed at a potential (0 potential).
[0085]
On the other hand, the sampling pulse signal PS includes a timing signal indicating the first timing T1 and a second timing signal indicating the second timing T2, although not shown. These timing signals are set so as to have a certain time difference from the timing signal indicating the timing T0 immediately before the arrival of the reflected light. These two timing signals are supplied to the A / D conversion means 5. The A / D conversion means 5 generates and outputs digital data DMX and digital data DMN by executing A / D conversion processing at the first timing T1 and the second timing T2. The digital data DMX and DMN obtained in this way are subjected to an on / off condition determination process in the condition determination means 11.
[0086]
FIG. 4 shows a conceptual description of the function of the condition judging means 11 realized by software by the microprocessor of the CPU 6 using logic symbols. As shown in the figure, the function of the condition determination means 11 can be expressed by two comparators COM1 and COM2 and one AND gate AND. That is, the function of the condition determination means 11 is that the first comparator COM1 that compares the digital data DMX and the digital data DMN with each other, and the second comparator COM2 that performs a size comparison between the digital data DMX and 0 (specified level). And an AND gate AND that outputs a logical product of the output HA of the first comparator COM1 and the output HB of the second comparator COM2. The output HO of the AND gate AND becomes “H” indicating that the reflected light LR is received only when the digital data DMX is larger than the digital data DMN and the digital data DMX is larger than 0 (specified level). .
[0087]
The input signal waveform of the AC signal transmission circuit functioning as the filter means 4 is shown in FIG. 5B, and the output signal waveform is shown in FIG. 5D. As is clear from the comparison between FIG. 5B and FIG. 5D, in the TOF period, the input signal level is set to 0 level at the period start timing (timing immediately before the arrival of reflected light) T0. The signal waveform (b) is level-shifted as a whole to become an output signal waveform (d). More specifically, in the example shown in the waveform diagram of FIG. 5, the input side signal waveform (b) is level-shifted downward as a whole in the first period, the second period, and the fifth period. The output side signal waveform (d). On the other hand, in the third period and the fourth period, the input side signal waveform (b) is level-shifted upward as a whole to become the output side signal waveform (d). As is apparent from the waveform diagram of FIG. 5D, in the received light signal waveform after the level shift, the mountain-shaped waveform peculiar to the reflected light LR always has a base level of 0 within a certain time width immediately after the start of the TOF period. Appears in a state aligned with the level (regular level).
[0088]
More specifically, as long as the reflected light LR having a predetermined light amount is received, the signal level (DMX) at the first timing T1 is necessarily higher than the signal level (DMN) at the second timing T2. To establish. Of course, such a relationship appears even when the reflected light LR is not received and the timing T0 immediately before receiving the reflected light coincides with the sharply falling portion of the fluorescent lamp noise received waveform. The polarity of the signal level (DMX) at the first timing T1 is always smaller than the 0 level that is the specified level. Therefore, even if a relationship is found in which the signal level at the first timing T1 is higher than the signal level at the second timing T2, at that time, the signal level at the first timing T1 is the 0 level, which is the specified level If it is smaller than this, such misperception can be avoided by determining that the reflected light LR is not received.
[0089]
Therefore, if the digital data DMX and DMN obtained from the A / D conversion means 5 are supplied to the condition determination means 11 described above with reference to FIG. 4, it is determined without error whether or not the reflected light LR is received. can do. Moreover, in this condition determination process, even if the first and second timings T1 and T2 vary in the timing variation range indicated by ΔT1 and ΔT2 in the waveform diagram of FIG. Since the relationship is almost immobile and the data DMX is larger than the prescribed level 0, it is ensured whether the reflected light LR is received regardless of the timing variation of the gate pulse signal PG and the sampling pulse signal PS. It has a special effect that it can be determined.
[0090]
According to the first embodiment described above, the level (DMX) of the light reception signal at the first timing T1 at which the peak of the light reception signal waveform of the pulsed detection light will arrive, and the light reception signal waveform of the pulsed detection light. Of the condition used for the on / off determination, at least on the condition that the comparison result with the level (DMN) of the received light signal at the second timing T2 at which the bottom due to the overshoot of Since it is determined whether one is satisfied or not, even if the sampling timings T1 and T2 of the received light signal for performing the on / off determination are slightly shifted, the received light signal waveform peculiar to the pulsed detection light (see FIG. 12). ) Exists in the sampling region, the received light level (DMX, D) at the first timing T1 and the second timing T2. Since most immobile for the magnitude relationship of N), it is possible to highly-off determination reliability based on their relationship.
[0091]
In addition, in addition to the comparison result between the light reception signal level (DMX) at the first timing T1 and the light reception signal level (DMN) at the second timing T2, the condition determination unit adds the light reception signal level (DMX) at the first timing T1. Under the condition that the level of the received light signal is larger than the prescribed level 0, the condition T1 is satisfied so that the timing T0 immediately before the pulsed detection light arrives is determined. The first timing occurs because it coincides with the steep fall timing (180 degrees in FIG. 9) of the received light signal waveform due to the noise component, and the reflected light (projection signal) of the pulsed detection light does not exist or hardly exists. Only the magnitude relationship between the light reception level (DMX) at T1 and the light reception level (DMN) at the second timing T2 is determined as ON / OFF judgment. Even if a situation occurs in which it is difficult to accurately perform the measurement, there is a clear difference in the magnitude relationship between the light reception level (DMX) and the zero level at the first timing T1 between the case where there is normal reflected light and the case where there is no normal reflected light. Therefore, by adding this as a reference for judgment, a reliable on / off judgment result can be obtained.
[0092]
In the above description, the type of the photoelectric switch to which the present invention is applied is a reflection type, but the present invention can of course be applied to a transmission type photoelectric switch. An example of an electrical basic configuration diagram of a transmissive photoelectric switch to which the present invention is applied is shown in FIG. 2 just in case. In the figure, the same components as those of the reflective photoelectric switch of FIG.
[0093]
As shown in the figure, the transmissive photoelectric switch 15 includes a light emitting side device 100 and a light receiving side device 200 which are provided apart from each other. The light projecting device 100 includes a light projecting means 2. The light receiving side device 200 includes a light receiving means 3, a filter means 4, an A / D conversion means 5, and a CPU 6. The drive control signal CD is transmitted from the CPU 6 in the light receiving side device 200 to the light projecting means 2 in the light projecting side device 100 via communication. In such a transmission type photoelectric sensor, since the drive control signal CD is transmitted from the light receiving side device 200 to the light projecting side device 100 via communication, the actual light projecting timing and the sampling timing are synchronized. Since it is difficult to obtain accurately, the on / off determination process of the present invention, which is less affected by variations in sampling timing, is particularly effective.
[0094]
Next, an electrical basic configuration of a photoelectric switch according to the second embodiment of the present invention is shown in FIG. The illustrated photoelectric switch is a reflective photoelectric switch. Further, the function of the “level shift means” is realized by hardware using a dedicated analog circuit. Further, the second feature item is adopted as the feature item. For this reason, the light projecting means is configured to perform light projection at least three times within the blinking period (fluorescent lamp noise period) TN of the inverter fluorescent lamp in the installation environment. In addition, the condition determination means obtains a comparison result by comparing the level VMX of the received light signal at the timing T1 at which the peak of the pulsed detection light LS will arrive with a predetermined threshold value Vth, and obtains it within the period TN. The determination is performed in accordance with the comparison result that occupies the majority of all the comparison results.
[0095]
As shown in the figure, the photoelectric switch 1 includes a light projecting unit 2, a light receiving unit 3, a filter unit 4, an A / D conversion unit 5A, and a CPU 6A. The CPU 6A includes a condition determination unit 11A, a sampling pulse generation unit 12A, and a light projection control unit 13A. Of these, the same components as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.
[0096]
The projection control means 13A generates a reference timing signal (not shown) that defines the projection cycle based on a reference clock built in the CPU 6A. The period of this reference timing signal is set to be approximately the same as the expected shortest fluorescent lamp noise period (for example, 60 to 70 μsec). Further, the light projection control means 13A generates a light projection control signal CD for controlling the light projection means 2 based on this reference timing signal. The light projection control signal CD has at least three timing components. Specifically, when the light projection control signal CD is supplied to the driving means 7, as shown in FIGS. 7 and 8, at least three or more (see FIG. 7) from the driving means 7 within one noise period TN. In this case, three light projection pulses P1, P2, and P3 are sequentially output at predetermined intervals. The light emitting element 8 is driven by these light projection pulses P1, P2, and P3, and three pulsed detection lights LS are projected from the light emitting element 8 to a region where the target object 20 will exist at predetermined intervals. The The reflected light LR of the pulsed detection light reflected by the object 20 reaches the light receiving element 9. Thereafter, as described in the first embodiment, the reflected light LR and the noise light LN are photoelectrically converted via the light receiving element 9, and the obtained electric signals VS1 and VN1 are amplified via the amplifier 10 to obtain the light receiving signal. VS2 and VN2 are generated and output.
[0097]
FIG. 9 shows the relationship between the light projection signal VS2 generated in this way and the fluorescent lamp noise signal VN2. As shown in the figure, the interval between the three light projection signals VS21, VS22, and VS23 is the presence of fluorescent lamp noise VN2, so that the two light projection signals VS21 and VS23 located on both sides are Even in the worst situation where the phase coincides with the phase 0 degree and the phase 180 degree, the light projection signal VS22 located in the middle is set so as to coincide with the 90 degree portion of the noise waveform having a relatively gradual change. Has been.
[0098]
The filter unit 4 shifts the level of the light reception signals VS2 and VN2 obtained from the light reception unit 3 by the same operation as described in the first embodiment. The received light signal thus level-shifted is shown in FIG. The three light projection signals VS21, VS22, and VS23 shown in the figure must originally exceed the threshold value Vth at the first timing T1 when the reflected light LR is incident. In the worst case described above, the light emission signals VS21 and VS22 whose timings coincide with each other at the phase of 0 degrees and 90 degrees of the noise waveform exceed the threshold value Vth, whereas the phase of the noise waveform is 180 degrees. As for the light projection signal VS23 whose timing coincides with the threshold value, the value cannot exceed the threshold value Vth. On the other hand, although not shown in the figure, assuming that the three light projection signals VS21, VS22, and VS23 are incident only with the noise light LN that should not exceed the threshold Vth, the phase is 90 degrees and 180 degrees. The values of the projection signals VS22 and VS23 having the same timing do not exceed the threshold value Vth, whereas the value of the projection signal VS21 having the same timing at phase 0 exceeds the threshold value Vth. It will be. Therefore, of the three determinations performed within one noise period (TN), if two or more times exceed the threshold value, the on-qualification is performed. If the second time or more does not exceed the threshold value, the off-qualification and the majority rule are followed. If it is assumed, a reliable on / off determination result can be obtained.
[0099]
The condition determination unit 11A performs on / off determination based on the data DMX obtained from the A / D conversion unit 5A by the above-described determination algorithm. FIG. 11 is a flowchart showing a process for realizing the function required for the condition determining means 11A by software using a microprocessor.
[0100]
In the figure, when the process is started, an initialization process is first executed, and various counters and registers necessary for the operation are initialized (step 1101). Subsequently, the first digital data DMX read from the A / D conversion means 5A is compared with the threshold value Dth (step 1102). If it is determined that DMX> Dth (step 1102 YES), the predetermined ON counter is incremented by +1 (step 1103). On the other hand, when it is determined that DMX <Dth (NO in step 1102), the predetermined OFF counter is incremented by +1 (step 1104). Thereafter, the data number counter N is incremented by +1 to confirm that the third data has been reached (step 1106). The above processing (steps 1102 to 1105) is repeated until the value of the data number counter N becomes “3”.
[0101]
If the value of the data number counter N reaches “3” (YES at step 1106), the count value of the ON counter is compared with the count value of the OFF counter (step 1107). If it is determined that ON counter value> OFF counter value (YES in step 1107), ON determination is made (step 1108). On the other hand, when it is determined that the ON count value <the OFF count value (step 1109), the OFF determination is made. A determination result according to these majority rules is one of the determination elements for making a final on / off determination.
[0102]
According to the second embodiment described above, since the noise waveform due to the inverter fluorescent lamp is substantially sinusoidal, there are only two steep portions of the waveform inclination within one flashing period (TN) of the fluorescent lamp, so that one flashes. If light projection is performed at least three times within the period, the timing of the two light projections of these is almost the same as the timing of the steeply rising portion and the steeply descending portion of the noise waveform. Even if an incorrect level determination result is obtained at this timing, the other light projection timings correspond to relatively gentle portions. Therefore, a comparison result is obtained by comparing the level (VMX) of the received light signal at the timing T1 at which the peak of the pulsed detection light will arrive, with a predetermined threshold (Vth), and all comparisons obtained within the light projection period. If it is determined whether or not one of the conditions used for the on / off determination is satisfied according to the comparison result occupying a large number of the results, a reliable on / off determination result can be obtained.
[0103]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a photoelectric switch with a level shift function that can further improve the reliability in on / off determination.
[0104]
In addition, according to the present invention, there is provided a photoelectric switch with a level shift function capable of obtaining a reliable on / off determination result even if the sampling timing of the received light signal for performing the on / off determination is slightly shifted. be able to.
[0105]
Furthermore, according to the present invention, a reliable on / off determination result can be obtained even if the sampling timing of the received light signal for performing the on / off determination coincides with a steep portion of the received light signal waveform due to the noise component. A photoelectric switch with a level shift function can be provided.
[Brief description of the drawings]
FIG. 1 is a basic configuration diagram of a reflective photoelectric switch according to a first embodiment.
FIG. 2 is a basic configuration diagram of a transmissive photoelectric switch according to the first embodiment.
FIG. 3 is a circuit diagram of filter means configured by a dedicated analog circuit.
FIG. 4 is a diagram conceptually showing the function of condition determination means using logic symbols.
FIG. 5 is a waveform diagram showing signal states at various parts in FIG. 1;
FIG. 6 is a basic configuration diagram of a reflective photoelectric switch according to a second embodiment.
FIG. 7 is a waveform diagram showing a relationship between a fluorescent lamp noise waveform and a light projection pulse.
FIG. 8 is a waveform diagram showing the relationship between the generation timing of a fluorescent lamp pulse and the cycle of the fluorescent lamp pulse.
FIG. 9 is a waveform diagram showing a relationship between fluorescent lamp noise and a projection signal.
FIG. 10 is a waveform diagram showing a relationship between a light reception signal (light projection part) after a level shift and a threshold value.
FIG. 11 is a flowchart showing processing for realizing a condition determination unit.
FIG. 12 is a waveform diagram showing a relationship between a light projection pulse and a light reception signal in a state where there is no fluorescent lamp noise.
FIG. 13 is a waveform diagram showing a relationship between a light projection pulse and A / D conversion timing in a state where fluorescent lamp noise exists.
[Explanation of symbols]
1,15 photoelectric switch
2 Projection means
3 Light receiving means
4 Filter means
5,5A A / D conversion means
6,6A CPU
7 Drive means
8 Light emitting elements
9 Light receiving element
10 Amplifier
11, 11A Condition determining means
12, 12A Sampling pulse generating means
13, 13A Light emission control means
LS Light projection
LR Reflected light
C1 capacitor
Q1 Analog switch
COM1, COM2 comparator
AND ANDGATE
PD Flood pulse
PG gate pulse signal
PS sampling pulse signal
VS1, VS2 detection light signal (light projection signal)
VN1, VN2 Noise component signal
VO (= VS2 + VN2) Output signal
DMX, DMN Digital data (A / D conversion value)
Timing just before T0
T1 first timing
T2 Second timing
P1, P2, P3 Projection pulse

Claims (10)

On / off determination based on light receiving means for periodically projecting pulsed detection light, light receiving means for photoelectrically converting the pulsed detection light to output a corresponding light receiving signal, and a light receiving signal output from the light receiving means Signal processing means for generating an output, and
The signal processing means includes
Included in the period during which the light-receiving signal waveform of the pulse-shaped detection light will be obtained by an amount corresponding to the difference between the level of the light-receiving signal and the specified level immediately before the pulse-shaped detection light will arrive Level shift means for shifting the level of the received light signal in a direction approaching the specified level;
A condition determining means for determining whether or not at least one of the conditions used for the on / off determination is satisfied based on the light-receiving signal after the level shift by the level shift means; There,
The condition judging means has a light receiving signal level at a first timing at which a peak of the light receiving signal waveform of the pulsed detection light will come, and a bottom due to an overshoot of the light receiving signal waveform of the pulsed detection light. A photoelectric switch configured to perform the determination at least on the condition that the comparison result with the level of the received light signal at the second timing that is likely to be a predetermined magnitude relationship. The condition determining means has a predetermined magnitude relationship between the result of comparison between the level of the light reception signal at the first timing and the level of the light reception signal at the second timing, and the light reception signal at the first timing. The photoelectric switch according to claim 1, wherein the determination is made on the condition that a comparison result between the level and the specified level has a predetermined magnitude relationship. On / off determination based on light receiving means for periodically projecting pulsed detection light, light receiving means for photoelectrically converting the pulsed detection light to output a corresponding light receiving signal, and a light receiving signal output from the light receiving means Signal processing means for generating an output, and
The signal processing means includes
Included in the period during which the light-receiving signal waveform of the pulse-shaped detection light will be obtained by an amount corresponding to the difference between the level of the light-receiving signal and the specified level immediately before the pulse-shaped detection light will arrive Level shift means for shifting the level of the received light signal in a direction approaching the specified level;
A condition determining means for determining whether or not at least one of the conditions used for the on / off determination is satisfied based on the light-receiving signal after the level shift by the level shift means; There,
The light projecting means is structured to perform light projection at least three times within the blinking cycle of the inverter fluorescent lamp in an installation environment, and the condition determining means has a peak of the pulsed detection light. A comparison result is obtained by comparing the level of the received light signal at a timing at which it will be performed with a predetermined threshold value, and the determination is performed according to a comparison result that occupies a majority of all the comparison results obtained within one light projection period. A photoelectric switch that is built. Drive means for outputting a drive pulse signal at a timing indicated by the light projection control signal, and a light emitting element for projecting pulsed detection light to a target region in response to the drive pulse signal output from the drive means Including floodlight means,
A light receiving means including a light receiving element that receives and photoelectrically converts reflected light of the pulsed detection light coming from the target region, and an amplifier that amplifies an output of the light receiving element to generate a light reception signal;
Signal processing means for generating an on / off determination output based on a light reception signal output from the light receiving means,
The signal processing means includes
Included in the period during which the light-receiving signal waveform of the pulse-shaped detection light will be obtained by an amount corresponding to the difference between the level of the light-receiving signal and the specified level immediately before the pulse-shaped detection light will arrive Level shift means for shifting the level of the received light signal in a direction approaching the specified level;
A condition determining means for determining whether or not at least one of the conditions used for the on / off determination is satisfied based on the light-receiving signal after the level shift by the level shift means; There,
The condition judging means has a light receiving signal level at a first timing at which a peak of the light receiving signal waveform of the pulsed detection light will come, and a bottom due to an overshoot of the light receiving signal waveform of the pulsed detection light. A photoelectric switch configured to perform the determination at least on the condition that the comparison result with the level of the received light signal at the second timing that is likely to be a predetermined magnitude relationship. The condition determining means has a predetermined magnitude relationship between the result of comparison between the level of the light reception signal at the first timing and the level of the light reception signal at the second timing, and the light reception signal at the first timing. The photoelectric switch according to claim 4, wherein the determination is made on the condition that a comparison result between the level and the specified level has a predetermined magnitude relationship. Drive means for outputting a drive pulse signal at a timing indicated by the light projection control signal, and a light emitting element for projecting pulsed detection light to a target region in response to the drive pulse signal output from the drive means Including floodlight means,
A light receiving means including a light receiving element that receives and photoelectrically converts reflected light of the pulsed detection light coming from the target region, and an amplifier that amplifies an output of the light receiving element to generate a light reception signal;
Signal processing means for generating an on / off determination output based on a light reception signal output from the light receiving means,
The signal processing means includes
Included in the period during which the light-receiving signal waveform of the pulse-shaped detection light will be obtained by an amount corresponding to the difference between the level of the light-receiving signal and the specified level immediately before the pulse-shaped detection light will arrive Level shift means for shifting the level of the received light signal in a direction approaching the specified level;
A condition determining means for determining whether or not at least one of the conditions used for the on / off determination is satisfied based on the light-receiving signal after the level shift by the level shift means; There,
The light projecting means is controlled by the light projecting control signal so as to perform light projection at least three times within the blinking cycle of the inverter fluorescent lamp in an installation environment, and the condition judging means The comparison result is obtained by comparing the level of the received light signal at the timing when the peak of the state detection light is expected with a predetermined threshold value and occupying a large number of all the comparison results obtained within one light projection period. A photoelectric switch, which is structured to make the determination according to: The level shift means is an AC signal transmission circuit having a function of initializing the DC potential to be superimposed on the output side AC component to a specified potential while transmitting the AC component of the input side signal to the output side. The DC potential to be superimposed on the output side AC component of the AC signal transmission circuit is reinitialized to a specified potential repeatedly immediately before the timing at which the pulsed detection light will arrive. The reflective photoelectric switch according to any one of 6. The AC signal transmission circuit includes a coupling capacitor interposed between the input and output terminals, and a switch interposed between the output side terminal and the specified potential point, and the switch is synchronized with the projection timing signal. The reflective photoelectric switch according to claim 7, which is on / off controlled by a gate control signal. Computations such as comparison between the level of the received light signal and the threshold value performed in the condition determining means are performed by software by a microprocessor based on digital data obtained by A / D conversion of the output signal of the AC signal transmission circuit. The reflective photoelectric switch according to claim 7 or 8, which is executed automatically. A light emitting side device and a light receiving side device that are spaced apart from each other;
The light projecting means is built in the light projecting side device,
The light receiving means and the signal processing means are built in the light receiving side device, and the light projection control signal is transmitted from the light receiving side device to the light emitting side device via communication. The photoelectric switch described in 1.

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