JP2002319851A - Photoelectric switch - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide photoelectric switch with a level shift function that can furthermore enhance the reliability at on-off judgment. SOLUTION: After eliminating a noise component of a fluorescent lamp by shifting a level of a light detection signal at a period immediately before the waveform of the light detection signal of a pulsed detection light is expected to arrive towards a specific level by an amount corresponding to the difference between the specified level and the level of the light detection signal at a time immediately before the pulsed detection light is expected to arrive, on-off judgment is made under conditions where at least a plurality of quantity correlations can be obtained from result of comparison between the level of the light detection signal in a 1st timing when a peak of the light detection signal waveform of the pulse detection light is expected to arrive and a level of the light detection signal in a 2nd timing when a bottom by an overshoot of the light detection signal waveform of the pulse detection light is expected to arrive.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photoelectric switch in which noise suppression is applied to, for example, an inverter type fluorescent lamp, and in particular, prior to on / off determination processing, a timing immediately before pulsed detection light will arrive. The present invention relates to a photoelectric switch in which the influence of fluorescent lamp noise is eliminated as much as possible by adjusting the level of the light receiving signal at a specified level.

[0002]

2. Description of the Related Art As is well known, this type of photoelectric switch includes a light projecting unit, a light receiving unit, and a signal processing unit. 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 transmission type photoelectric switch, the light projecting means and the light receiving means are generally housed in separate housings separated from each other.

[0003] The light emitting means generates a driving pulse signal (hereinafter referred to as a light emitting pulse) at a timing specified by a light emitting control signal.
And a light emitting element that emits the pulsed detection light to the target area in response to the light emission pulse output from the drive means. The light receiving means includes a light receiving element that receives the pulse-like detection light arriving from the target area and performs photoelectric conversion, and an amplifier that amplifies an output of the light receiving element and generates a light receiving 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 projecting pulse PD and the light receiving signal VS2 are shown in waveform diagrams of FIG.
As is clear from the figure, the light projecting pulse PD is a rectangular wave having a time width corresponding to the light emission period, and appears repeatedly in each cycle T. The light receiving signal VS2 rises sharply from the time corresponding to the leading edge of the light projection pulse PD to the time corresponding to the trailing edge thereof, reaches a peak pk, immediately drops, overshoots and reaches a bottom bm, Thereafter, it has a characteristic mountain-shaped waveform that rises relatively slowly and converges to zero level. Note that the overshoot portion in the characteristic chevron waveform appears due to the capacitance component of the amplifier constituting the light receiving means.

As shown in FIG. 12, the light receiving signal VS2
If the base level of the chevron waveform is always stable, for example, the light receiving signal VS2 is sampled at a timing slightly delayed from the timing of the light projection pulse PD, and the level of the sampled light receiving signal VS2 is specified. By comparing with the threshold value, the on / off determination should be easily performed.

[0006]

A variation range Δt of the generation timing of the projection pulse PD and the sampling pulse,
Further, a specific example of the noise component VN2 due to the inverter fluorescent lamp is shown in the waveform diagram of FIG.

The light emitting period T of this type of photoelectric switch
Is relatively close to the blinking cycle of an inverter-type fluorescent lamp, which is often used for factory lighting in Europe. This means that if this type of photoelectric switch is installed in an environment where such an inverter fluorescent lamp is installed, the received light signal V
As a result of superimposition of S2 (see FIG. 12) and the noise component VN2 due to the fluorescent lamp, the base level of the chevron waveform of the received light signal VS2 fluctuates greatly in each light projection cycle, and thus is simply delayed by a certain time from the light emission pulse PD. This means that a simple method of comparing the level of the light receiving signal VS2 at the timing with a prescribed threshold value cannot accurately determine the on / off state.

Further, even if the noise component VN2 due to the fluorescent lamp does not exist, the generation timing of the sampling pulse is determined based on the generation timing of the projection pulse PD and the like. It is difficult to completely suppress the variation of the data. In particular, in the case of a transmission type photoelectric switch, the light emitting pulse PD is transmitted from the light receiving side device to the light emitting side device via the communication means. The variation range Δt from the timing is not negligible.

Therefore, the present inventors have disclosed in Japanese Patent Laid-Open No.
In the signal processing method proposed in Japanese Patent Application Laid-Open No. 5395, Japanese Patent Application Laid-Open No. 6-152364, etc., an amount corresponding to the difference between the level of the received light signal and the specified level at the timing immediately before the pulsed detection light is likely to arrive is obtained. The level of the light receiving signal included in the period in which the light receiving signal waveform of the pulsed detection light will be obtained is level-shifted in a direction approaching the specified level, and based on the level of the light receiving signal after the level shift,
A signal processing method of performing a satisfaction determination of one on-off condition was employed.

According to such a signal processing method, an algorithm is employed in which a noise component is removed from the level of a received light signal and then compared with a threshold value. It was expected that a highly reliable on / off determination result would be obtained.

However, according to the inventor's earnest research, even in the above-described signal processing method with a noise component removing function by level shift, the following reasons are given.
It has been found that the reliability of the on / off judgment still has a problem.

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 transmission type photoelectric switch, the light emitting pulse PD is transmitted from the light receiving side device to the light emitting side device via the communication means. The timing just before the light will arrive cannot be determined accurately. If there is a large variation in the timing immediately before the pulsed detection light will arrive, accurate on / off determination cannot be performed even if the determination threshold is appropriate.

Second, even if the timing immediately before the pulsed detection light is likely to arrive can be accurately determined, the determined timing varies on the waveform of the noise component VN2 due to the fluorescent lamp. If the rate coincides with a large portion (phase 0 degree, 180 degree, 360 degree, etc.), if the light receiving signal level of the pulsed detection light at that time happens to be near the upper and lower sides of the determination threshold, the influence of the noise component VN2 causes If the light receiving signal level erroneously exceeds or does not exceed the threshold value, accurate on / off determination cannot be performed.

The present invention has been made to solve the above-described problems in the photoelectric switch having the level shift function.

That is, an object of the present invention is to provide a photoelectric switch with a level shift function, which can further improve the reliability in ON / OFF determination.

Another object of the present invention is to provide a level shift function capable of obtaining a highly reliable on / off determination result even if the sampling timing of the light receiving signal for performing the on / off determination is slightly shifted. To provide a photoelectric switch.

Another object of the present invention is to provide a highly reliable on / off determination result even if the sampling timing of the received light signal for performing the on / off determination happens to coincide with a steep portion of the received light signal waveform due to a noise component. To provide a photoelectric switch with a level shift function capable of obtaining the following.

Still other objects, functions and effects of the present invention will be easily understood by those skilled in the art based on the following description of the specification.

[0019]

A photoelectric switch according to the present invention comprises: a light projecting means for periodically projecting pulsed detection light; and a light receiving means for photoelectrically converting the pulsed detection light and outputting a corresponding light reception signal. Means, and signal processing means for generating an on / off determination output based on a light receiving signal output from the light receiving means,
Is provided.

[0020] The signal processing means includes a light receiving signal of the pulsed detection light in an amount corresponding to a difference between a level of the light receiving signal and a prescribed level at a timing immediately before the pulsed detection light will arrive. Level shift means for level-shifting the level of the received light signal included in the period in which a waveform will be obtained in 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. Condition determination means for determining whether at least one of the used conditions is satisfied.

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. May be.

For realization by software, those skilled in the art can think of several methods. As one of those methods, the level of a light receiving signal output from the light receiving means is continuously adjusted at a predetermined sampling period.
/ D converted and stored in a memory in a time-series manner, and then, based on one or two or more timing data values used for the on / off determination, the timing immediately before the timing at which the pulsed detection light is likely to arrive will be described. Examples include subtracting or adding data values.

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.

The photoelectric switch of the present invention has the following features in the above basic configuration.

That is, the condition determining means determines whether the level of the light reception signal waveform at the first timing when the peak of the light reception signal waveform of the pulsed detection light will arrive, and the level of the light reception signal waveform of the pulsed detection light. The determination is made on the condition that the result of comparison with the level of the light receiving signal at the second timing at which the bottom due to the shot will arrive has a predetermined magnitude relationship.

As described above, the function of the condition judging means may be realized by hardware using an analog comparator and a logic circuit, or A / D-converted the level-shifted light-receiving signal. After that, it may be realized by software using a microprocessor.

In the present invention, "determining whether or not at least one of the conditions used for the on / off determination is satisfied" is the reason for the final on / off determination in this type of photoelectric switch. This is because, in general, consideration is given to the condition that a plurality of determination conditions are satisfied. As other determination conditions that are often adopted, there may be mentioned those that determine ON or OFF on condition that the ON or OFF determination result is repeated a plurality of times.

According to the above configuration, the level of the light receiving signal at the first timing when the peak of the light receiving signal waveform of the pulsed detection light will arrive, and the bottom of the light receiving signal waveform of the pulsed detection light due to overshoot. Is satisfied under the condition that the result of comparison with the level of the light-receiving signal at the second timing when the signal arrives at a predetermined magnitude relationship is determined, so that the first condition and the second timing are determined. Even if the timing of 2 is slightly shifted from the peak or bottom timing of the light-receiving signal waveform, the first timing and the second timing as long as the peak waveform peculiar to the light-receiving signal waveform of the pulsed detection light exists in the sampling area. Since the magnitude relation of the light receiving level at the point is almost fixed, reliable on / off judgment based on those relations It can become.

More specifically, the first timing and the second timing can be set strictly in accordance with the peak and bottom timings of the light receiving signal waveform due to variations in the characteristics (constants) of the circuit relating to the light receiving signal. Not necessarily. Also, there is no need to exactly match. The present invention solves the problem of utilizing the fact that the difference between the signal value near the peak and the signal value near the bottom of the received light signal waveform is large if there is no noise component, and that the magnitude relationship is unlikely to be inverted even with the noise component. As long as the principle is not deviated, deviation from the peak or bottom timing of the light receiving signal waveform at the first timing and the second timing is allowed.

In a preferred embodiment, the condition determining means determines that a comparison result between the level of the light receiving signal at the first timing and the level of the light receiving signal at the second timing has a predetermined magnitude relationship. in addition,
The determination is made on condition that the comparison result between the level of the light receiving signal at the first timing and the specified level has a predetermined magnitude relationship.

According to such a configuration, the timing immediately before the pulse-like detection light will arrive coincides with the steep fall timing of the light-receiving signal waveform due to the noise component, and the reflected light of the pulse-like detection light is not reflected. Due to the non-existence or almost non-existence, even if a situation where it is difficult to accurately determine the on / off state only by the magnitude relation between the light reception level at the first timing and the light reception level at the second timing occurs, the normal reflected light 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 where there is and the case where it does not exist, so by adding this as a reference for judgment,
A highly reliable on / off determination result is obtained.

According to another aspect of the present invention, there is provided a photoelectric switch of the present invention comprising: a light projecting means for periodically projecting pulsed detection light; and a light receiving means for photoelectrically converting the pulsed detection light and outputting a corresponding light reception signal. Means, and signal processing means for generating an on / off determination output based on a light receiving signal output from the light receiving means,
Is provided.

[0033] The signal processing means includes a light receiving signal of the pulsed detection light in an amount corresponding to a difference between a level of the light receiving signal and a prescribed level at a timing immediately before the pulsed detection light will arrive. Level shift means for level-shifting the level of the received light signal included in the period in which a waveform will be obtained in 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. Condition determination means for determining whether at least one of the used conditions is satisfied.

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. May be.

For software implementation, those skilled in the art will be able to conceive of several approaches. As one of those methods, the level of a light receiving signal output from the light receiving means is continuously adjusted at a predetermined sampling period.
/ D converted and stored in a memory in a time-series manner, and then, based on one or two or more timing data values used for the on / off determination, the timing immediately before the timing at which the pulsed detection light is likely to arrive will be described. Examples include subtracting or adding data values.

As will be described later, the function of the condition determining means may be realized by software using a microprocessor, or may be realized by hardware using a comparator or a dedicated logic circuit. You may.

The photoelectric switch of the present invention has the following features in the above basic configuration.

That is, the light projecting means is designed to emit light at least three times within a blinking cycle of the inverter fluorescent lamp in an installation environment. Incidentally, in the case of the current inverter fluorescent lamp, the shortest blinking cycle is about 60 to 70 μsec.

Further, the condition determining means compares the level of the received light signal at a timing when the peak of the pulsed detection light is likely to arrive with a predetermined threshold to obtain a comparison result, and obtains the comparison result within the light projection period. It is designed to make the determination according to the comparison results that occupy the majority of all the comparison results obtained.

As described above, the function of the condition determining means may be realized by hardware using an analog comparator and a logic circuit, or after A / D conversion of a level-shifted light receiving signal. Alternatively, it may be realized by software using a microprocessor.

The reason why "it is determined whether or not at least one of the conditions used for the on / off determination is satisfied" is that in this type of photoelectric switch, the final on / off determination is This is because, in general, it is necessary to satisfy a plurality of determination conditions. Other requirements that are often adopted include those that determine on or off on the condition that the result of on or off determination is repeated a plurality of times.

According to the above configuration, since the noise waveform due to the inverter fluorescent lamp is substantially sinusoidal, there are two steep portions of the waveform gradient within one blinking cycle of the fluorescent lamp (for example, a phase of 0 degree and 180 degrees). Therefore, if light emission is performed at least three times within one blinking period, if two of the light emission timings are set at the timing of the steep rising portion and the timing of the steep falling portion on the noise waveform, Even if the levels substantially coincide with each other and an erroneous level determination result is obtained at any one of the timings, the other light emission timings correspond to relatively gentle portions. Therefore, the level of the received light signal at the timing when the peak of the pulsed detection light will arrive is compared with a predetermined threshold value to obtain a comparison result, and accounts for a large number of all the comparison results obtained within the light emission period. If the satisfaction determination of the one condition is performed according to the comparison result, a highly reliable on / off determination result can be obtained.

A photoelectric switch according to the present invention as a more specific form includes a driving means for outputting a driving pulse signal at a timing designated by a light emitting control signal, and a driving pulse signal output from the driving means in response to the driving pulse signal. A light projecting unit including a light emitting element for projecting the pulsed detection light to the target area, a light receiving element for receiving reflected light of the pulsed detection light coming from the target area and performing photoelectric conversion, and The light-receiving unit includes an amplifier that amplifies an output to generate a light-receiving signal, and a signal processing unit that generates an on / off determination output based on the light-receiving signal output from the light-receiving unit.

The signal processing means includes a light receiving signal of the pulsed detection light in an amount corresponding to a difference between a level of the light receiving signal and a specified level at a timing immediately before the pulsed detection light will arrive. Level shift means for level-shifting the level of the received light signal included in the period in which a waveform will be obtained in 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. Condition determination means for determining whether at least one of the used conditions is satisfied.

The above-mentioned reflection type photoelectric switch has the following features in the above basic configuration.

That is, the condition judging means determines whether the level of the light receiving signal waveform at the first timing when the peak of the light receiving signal waveform of the pulsed detection light will arrive, and the level of the light receiving signal waveform of the pulsed detection light. The determination is made on the condition that the result of comparison with the level of the light receiving signal at the second timing at which the bottom due to the shot will arrive has a predetermined magnitude relationship.

In a preferred embodiment, the condition determining means determines that a comparison result between the level of the light receiving signal at the first timing and the level of the light receiving signal at the second timing has a predetermined magnitude relationship. in addition,
The determination is made on condition that the comparison result between the level of the light receiving signal at the first timing and the specified level has a predetermined magnitude relationship.

According to another embodiment of the present invention, there is provided a photoelectric switch which outputs a driving pulse signal at a timing designated by a light emitting control signal, and which responds to the driving pulse signal output from the driving means. A light-emitting element including a light-emitting element for projecting the pulsed detection light to the target area, and a light-receiving element for receiving reflected light of the pulsed detection light coming from the target area and photoelectrically converting the reflected light; Light receiving means including an amplifier for amplifying the output of the element to generate a light receiving signal, and signal processing means for generating an on / off determination output based on the light receiving signal output from the light receiving means.

The signal processing means includes a light receiving signal of the pulsed detection light in an amount corresponding to a difference between a level of the light reception signal and a prescribed level at a timing immediately before the pulsed detection light will arrive. Level shift means for level-shifting the level of the received light signal included in the period in which a waveform will be obtained in 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. Condition determination means for determining whether at least one of the used conditions is satisfied.

The above-described photoelectric switch has the following features in the above basic configuration.

That is, the light projecting means is designed to emit light at least three times within the blinking cycle of the inverter fluorescent lamp in the installation environment.

The condition determining means compares the level of the received light signal at a timing when the peak of the pulsed detection light will arrive with a predetermined threshold to obtain a comparison result, and obtains the comparison result within the light projection period. It is designed to make the determination according to the comparison results that occupy the majority of all the comparison results obtained.

In a preferred embodiment, the level shift means transmits an AC component of the input side signal to the output side and can initialize a DC potential to be superimposed on the output side AC component to a specified potential. The DC potential to be superimposed on the output side AC component of the AC signal transmission circuit is repeatedly set to the specified potential immediately before the timing when the pulsed detection light will arrive. Initialized again.

According to such a configuration, the light-receiving signal waveform of the pulse-like detection light has an amount corresponding to the difference between the level of the light-receiving signal and the prescribed level at the timing immediately before the pulse-like detection light will arrive. The function of shifting the level of the light receiving signal included in the period in which is likely to be obtained in the direction approaching the specified level can be realized by hardware using an analog circuit.

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 terminal and a specified potential point. Are controlled on and off by a gate control signal synchronized with the light emission timing signal.

In a preferred embodiment, the operation of comparing the level of the light receiving signal with a threshold value performed by the condition determining means is performed by converting the output signal of the AC signal transmitting circuit to A
The software is realized by a microprocessor based on digital data obtained by performing the / D conversion.

In a preferred embodiment, the above photoelectric switch is realized as a transmission type photoelectric switch having a light emitting side device and a light receiving side device which are arranged apart from each other.

In this transmission type photoelectric switch, the light emitting means is built in the light emitting side device. Further, the light receiving means and the signal processing means are built in the light receiving side device. The light emitting control signal is transmitted from the light receiving side device to the light emitting side device via communication.

[0059]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a photoelectric switch according to the present invention will be described below in detail with reference to the accompanying drawings.

As described above, the photoelectric switch of the present invention comprises: a light projecting means for periodically projecting pulsed detection light;
The light receiving device includes a light receiving unit that photoelectrically converts the pulsed detection light and outputs a corresponding light receiving signal, and a signal processing unit that generates an on / off determination output based on the light receiving signal output from the light receiving unit.

The signal processing means obtains the received light signal waveform of the pulsed detection light by an amount corresponding to the difference between the level of the light reception signal and the specified level at the timing immediately before the pulsed detection light will arrive. Level shift means for shifting the level of the light receiving signal included in the period that is likely to be approached to the specified level, and is used for on / off determination based on the light receiving signal after the level shift by the level shifting means. Condition determination means for determining whether at least one of the conditions is satisfied.

Here, the function of the "level shift means" is as follows.
It 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.

For software implementation, those skilled in the art will be able to conceive of several techniques. As one of those methods, the level of a light receiving signal output from the light receiving means is continuously adjusted at a predetermined sampling period.
/ D converted and stored in a memory in a time-series manner, and then, based on one or two or more timing data values used for the on / off determination, the timing immediately before the timing at which the pulsed detection light is likely to arrive will be described. Examples include subtracting or adding data values.

The photoelectric switch of the present invention has the following features in the above basic configuration. Here, as the characteristic items, a first characteristic item and a second characteristic item that can be adopted alternatively or in combination are prepared.

The first characteristic relates to “condition determining means”. That is, in the first feature, the condition determining means determines the level of the light reception signal at the first timing when 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 on the condition that the result of comparison with the level of the light receiving signal at the second timing when the bottom due to the overshoot of the signal waveform will arrive at a predetermined magnitude relationship. That is,
The first feature is to improve the reliability of the on / off determination by focusing on a characteristic mountain-shaped waveform generated only when the pulsed detection light is received.

The second characteristic relates to "light emitting means" and "condition determining means". That is, this second
In the light emitting device, the light emitting means has a light emitting cycle shorter than a blinking cycle of the inverter fluorescent lamp in the installation environment, and is configured to emit light at least three times within the light emitting cycle. ing. The condition determining means may compare the level of the received light signal at a timing when the peak of the pulsed detection light will arrive with a predetermined threshold to obtain a comparison result, and perform all comparisons obtained within the light emitting cycle. It is designed to make the determination according to the comparison result that accounts for the majority of the results. In other words, the second feature is to improve the reliability of the on / off determination by focusing on the fact that there are only two steep portions in one cycle of the fluorescent lamp noise waveform. It is.
The first feature may be applied in order to obtain a comparison result of the light receiving signal corresponding to each light projection in the second feature.

The function of the condition judging means may be realized by hardware using an analog comparator and a logic circuit, or the level-shifted light-receiving signal may be converted to an A / D signal.
After the conversion, it may be realized by software using a microprocessor.

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 reflection type photoelectric switch. The function of the "level shift means" is realized by hardware using a dedicated analog circuit. Further, as the characteristic items, the first characteristic items described above are adopted. Therefore, the condition determining means determines that the level of the received light signal at the first timing when the peak of the received light signal waveform of the pulse-like detection light will arrive, and the bottom due to the overshoot of the light-receiving signal waveform of the pulse-like detection light arrives The determination is made on condition that the result of comparison with the level of the light receiving signal at the second timing that will be performed has a predetermined magnitude relationship.

As shown in the figure, the photoelectric switch 1 comprises a light projecting means 2, a light receiving means 3, a filter means 4
And A / D conversion means 5 and a CPU 6. The details of these basic components 1 to 6 are as follows.

The light projecting means 2 includes a driving means 7 and a light emitting element 8. The configuration and operation thereof are as follows.

The driving means 7 comprises an LED driving circuit such as a constant current source. The driving means 7 has a pulse width TP and a pause period TK (T = T) based on a light emission control signal CD having a pulse waveform of a constant period T provided from the light emission control means 13 realized by software in the CPU 6. A light emitting pulse (drive pulse signal) PD having TP + TK) is applied to the light emitting element 8.
(See FIG. 5A).

The light emitting element 8 is constituted 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 pulse-like detection light LS can be present on the object 20. Emits light toward the area.

The light receiving means 3 includes a light receiving element 9 and an amplifier 10. The configuration and operation thereof are as follows.

The light receiving element 9 is constituted by a photodiode (PD) in this example. This light receiving element 9 is
The reflected light LR reflected at 0 and the noise light LN from the inverter fluorescent lamp are received and photoelectrically converted. The electric signal VS1 obtained by photoelectrically converting the reflected light LR from the object 20 and the electric signal VN1 obtained by photoelectrically converting the noise light LN from the fluorescent lamp are superimposed on each other and then sent to the amplifier 10. Supplied.

The amplifier 10 in this example is constituted by an operational amplifier whose gain can be changed. The amplifier 10 amplifies the electric signals (VS1, VN1) output from the light receiving element 9 with a specified gain to generate and output light receiving signals (VS2, VN2). Note that the signal VS2 is a signal obtained by amplifying the signal VS1, and the signal VN2 is a signal obtained by amplifying the 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.

The filter means 4 is one of the constituent elements of the present invention.
Function as "level shift means". In addition,
The term "filter means" refers to a signal component VS2 of a light receiving signal including a signal component VS2 corresponding to reflected light LR which is a periodic pulse light and a signal component VN2 corresponding to noise light LN from a fluorescent lamp. From a macro point of view, the function of passing only a so-called comb filter (comb f
ilter).

The filter means 4 detects the timing T0 (FIG. 5) immediately before the reflected light LR of the pulsed detection light will arrive.
(See FIG. 2) and the amount corresponding to the difference between the level of the light receiving signal (VS2 + VN2) and the specified level (GND level in this example) in the period in which the reflected light LR of the pulsed detection light will arrive. VS2 + VN2) functions as a level shift means for shifting the level toward a specified level. Timing T0 is C
Generated by PU6.

FIG. 3 shows an example of a circuit configuration for realizing the filter means 4 by hardware using a dedicated analog circuit. The analog circuit constituting the filter means 4 shown in the figure is composed of a coupling capacitor C interposed between input and output terminals.
1 and an analog switch Q1 interposed between the output terminal and a specified potential point (GND in this example). 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 potential on the output side is restricted to the specified potential GND. When the analog switch Q1 switches from the ON state to the OFF state, the constraint on the output side potential is released and the output side potential becomes a floating state, and at the same time, the transmission of the alternating current between the input and the output becomes possible. The GND potential, which is a specified potential, is superimposed on the input side AC component. Note that an arbitrary potential other than the GND potential can be used as the prescribed potential.

In other words, the analog circuit starts transmitting 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 starts transmitting the AC component. Later, the DC potential to be superimposed on the output side AC component is always GN
It can also be expressed as an AC signal transmission circuit having a function of being initially set to a D potential (prescribed potential).

The A / D converter 5 performs A / D conversion on the output signal VO of the filter 4 at a first timing T1 and a second timing T2 described later (see FIG. 5). Here, the first timing T1 is a 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 overshoot of the light reception signal waveform of the pulsed detection light. It's time for the bottom to arrive. These timings T
1 and T2 are generated by the CPU 6 as described later. On the output side of the A / D conversion means 5, digital data DMX corresponding to the peak value obtained by the A / D conversion at the first timing T1 and A / D conversion at the second timing T2.
Digital data D equivalent to the bottom value obtained by D conversion
MN is output.

The CPU 6 is mainly composed of a microprocessor. In the figure, a condition judging means 11 and a sampling pulse generating means 1 drawn in a CPU 6 are shown.
2 and each function of the light projection control means 13 are realized by software by a microprocessor.

Each function of the sampling pulse generating means 12 and the light projecting control means 13 will be described with reference to the waveform diagram of FIG.

The light projecting control means 13 generates a reference timing signal (not shown) having a period T based on a reference clock incorporated 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 cycle 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 emitting pulse PD generated as a result of the operation of the driving means 7 in response to the light emitting control signal CD. As is clear 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 receives a gate pulse GP to be described later.
In addition, it is used to generate a sampling pulse PS.

The sampling pulse generation means 12 is provided with a sampling control signal CS supplied from the light emission control means 13.
, A gate pulse signal GP and a sampling pulse signal PS are generated. The gate pulse signal GP thus obtained is shown in FIG. As is clear 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 includes at least the reflected light L from the timing T0 immediately before the reflected light LR arrives.
Period TO until signal component VS2 corresponding to R disappears
F is "L", and the period TON until the timing T0 immediately before the next reflected light LR arrives is "H". The gate pulse signal PG is supplied to an analog switch Q1 included in an 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, and changes when the analog switch Q1 is on regardless of the AC component on the input side. It is fixed to the potential (0 potential).

On the other hand, although not shown, the sampling pulse signal PS includes a timing signal indicating a first timing T1 and a second timing signal indicating a second timing T2. 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 converter 5. The A / D converter 5 generates and outputs digital data DMX and digital data DMN by performing A / D conversion processing at the first timing T1 and the second timing T2. The digital data DMX and DMN thus obtained are subjected to an on / off condition determination process in the condition determination means 11.

FIG. 4 conceptually illustrates the function of the condition judging means 11 realized by software by the microprocessor of the CPU 6 using logic symbols.
Is shown in As shown in the figure, the function of the condition determining means 11 is that two comparators COM1, COM2
And one AND gate AND. That is, the function of the condition judging means 11 is as follows: a first comparator COM1 for comparing the magnitude of the digital data DMX and the digital data DMN; and a second comparator COM2 for comparing the magnitude of the digital data DMX and 0 (specified level). , The output HA of the first comparator COM1
And an AND gate AND that outputs a logical product of the output of the second comparator COM2 and the output HB of the second comparator COM2. And
The output HO of the AND gate AND is the digital data DM
Only if X is greater than digital data DMN and digital data DMX is greater than 0 (defined level)
It becomes "H" indicating that the reflected light LR has been received.

FIG. 5B shows the input signal waveform of the AC signal transmission circuit functioning as the filter means 4 and FIG. 5D shows the output signal waveform. As is clear from the comparison between FIG. 5B and FIG. 5D, in the TOF period, the input signal is set so that the output signal level at the period start timing (timing immediately before the arrival of the reflected light) T0 becomes 0 level. The signal waveform (b) is level-shifted as a whole to become an output signal waveform (d). More specifically, FIG.
In the example shown in the waveform diagram of the first cycle, the second cycle,
In the fifth period, the input-side signal waveform (b) is level-shifted as a whole to become 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 clear from the waveform diagram of FIG. 5D, in the light-receiving signal waveform after the level shift, the mountain-shaped waveform peculiar to the reflected light LR always has the base level of 0 within a certain time width immediately after the start of the TOF period.
Appears in the same level as the specified level.

More specifically, as long as a predetermined amount of reflected light LR is received, the signal level (DMX) at the first timing T1 is always higher than the signal level (DMN) at the second timing T2. The relationship to be established is established. However, such a relationship is established when the reflected light LR is not received and the timing T0 immediately before the reflected light is received.
The signal level (DMX) at the first timing T <b> 1 always becomes smaller than the specified level 0, although it also appears when the signal coincides with a steep falling point of the fluorescent lamp noise reception waveform. . Therefore, even if it is recognized that the signal level at the first timing T1 is higher than the signal level at the second timing T2, the signal level at the first timing T1 is 0 level, which is the specified level. If it is smaller than this, it is possible to avoid such erroneous recognition by determining that the reflected light LR has not been received.

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 whether or not the reflected light LR has been received. The determination can be made without error. 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 fixed and the data DMX is larger than the specified level 0, the gate pulse signal P
It has an extraordinary effect of being able to reliably determine whether or not the reflected light LR has been received, regardless of the timing variations of the G and the sampling pulse signal PS.

According to the first embodiment described above, the level (DM) of the light receiving signal at the first timing T1 at which the peak of the light receiving signal waveform of the pulsed detection light will arrive.
X) and that the comparison result of the level (DMN) of the received light signal at the second timing T2 at which the bottom due to the overshoot of the received light signal waveform of the pulsed detection light will arrive at a predetermined magnitude relationship at least. As a condition,
Since it is determined whether or not one of the conditions used for the on / off determination is satisfied, the sampling timings T1 and T of the light receiving signal for performing the on / off determination are determined.
Even if there is a slight shift in the light reception level (DMX, DMN) at the first timing T1 and the second timing T2, as long as the light reception signal waveform (see FIG. 12) peculiar to the pulsed detection light exists in the sampling area. Since the magnitude relation is almost immobile, highly reliable on / off determination can be performed based on the relation.

In addition, the condition determining means determines the level (DMX) of the light receiving signal at the first timing T1 and the second level.
(DMN) of light receiving signal at timing T2
In addition to the result of the comparison, the condition that the level of the light receiving signal at the first timing T1 is larger than the specified level 0 is performed so that the satisfaction determination of the above one condition is performed. The timing T0 immediately before the detection light will arrive is coincident with the steep fall timing of the light receiving signal waveform due to the noise component (180 in FIG. 9).
Degree) and the absence or almost no reflected light (projection signal) of the pulsed detection light, the light reception level (DMX) at the first timing T1 and the light reception level at the second timing T2 (DMN), the light reception level (DMX) at the first timing T1 depends on whether normal reflected light exists or not, even if it is difficult to make an accurate ON / OFF determination. Since there is a clear difference in the magnitude relationship between the level and the 0 level, by adding this as a reference for determination, a highly reliable on / off determination result can be obtained.

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 is of course applicable to a transmission type photoelectric switch. FIG. 2 shows an example of an electrical basic configuration of a transmission type photoelectric switch to which the present invention is applied. In the figure,
For the same components as the reflection type photoelectric switch of FIG.
The same reference numerals are given and the description is omitted.

As shown in the figure, the transmission type photoelectric switch 15 is provided with the light emitting side device 1 provided separately from each other.
00 and the light receiving side device 200. Light emitting side device 100
Includes light emitting 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. Then, the drive control signal CD is transmitted from the CPU 6 in the light receiving side device 200 to the light emitting means 2 in the light emitting side device 100 via communication.
In such a transmission type photoelectric sensor, the light receiving side device 2
Since the drive control signal CD is transmitted from the device 00 to the light emitting side device 100 via communication, it is very difficult to accurately synchronize the actual light emission timing with the sampling timing. The on / off determination processing of the present invention, which is less affected by the above, is particularly effective.

Next, FIG. 6 shows an electrical basic configuration of the photoelectric switch according to the second embodiment of the present invention. The illustrated photoelectric switch is a reflection type photoelectric switch. The function of the "level shift means" is realized by hardware using a dedicated analog circuit. Further, as the characteristic items, the above-mentioned second characteristic items are adopted. Therefore, the light emitting means is provided with a blinking cycle (cycle of fluorescent lamp noise) TN of the inverter fluorescent lamp in the installation environment.
It is designed to emit light at least three times in the interior. Further, the condition determining means may determine whether the peak of the pulsed detection light LS will arrive at the timing T1.
Is compared with a predetermined threshold value Vth to obtain a comparison result, and the determination is made in accordance with the comparison result that occupies a large part of all the comparison results obtained within the period TN.

As shown in the figure, the photoelectric switch 1 comprises a light projecting means 2, a light receiving means 3, a filter means 4
, A / D conversion means 5A, and CPU 6A. The CPU 6A includes a condition determination unit 11A, a sampling pulse generation unit 12A, and a light emission control unit 13A. In addition, among them, the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

The light emitting control means 13A generates a reference timing signal (not shown) for defining the light emitting cycle based on a reference clock incorporated in the CPU 6A. The cycle of the reference timing signal is set to be substantially the same as the assumed shortest cycle of fluorescent lamp noise (for example, 60 to 70 μsec). Further, the light emission control means 13A generates a light emission control signal CD for controlling the light emission means 2 based on the reference timing signal. This light projection control signal CD has at least three or more timing components. More specifically, when the light projecting control signal CD is supplied to the driving means 7, as shown in FIGS. 7 and 8, the driving means 7 outputs at least three or more signals within one noise period TN (FIG. 7). 3) light projection pulses P1, P2, P3
Are sequentially output at predetermined intervals. The light emitting element 8 is driven by the light emitting pulses P1, P2, and P3, and three pulsed detection lights LS are emitted from the light emitting element 8 at predetermined intervals to an area where the target object 20 will be present. You. 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 received light signal. VS2, VN
2 is generated and output.

FIG. 9 shows the relationship between the light projection signal VS2 and the fluorescent lamp noise signal VN2 generated in this manner. As shown in the figure, three light emission signals VS21 and VS2
2 and VS23, the presence of the fluorescent lamp noise VN2 causes the two light emission signals VS21 and V
Even in the worst case where S23 coincides with the fluorescent light noise phase of 0 ° and 180 °, the light emission signal VS22 located in the middle has a phase of 90 ° in the noise waveform with a relatively gentle change. Is set to match.

The filter means 4 shifts the level of the light receiving signals VS2 and VN2 obtained from the light receiving means 3 by the same operation as described in the first embodiment. The level-shifted light receiving signal is shown in FIG. The three projected light signals VS21, VS22, VS23 shown
In the case where the reflected light LR is incident, at the first timing T1, all of the light beams must originally exceed the threshold value Vth. In the worst case described above, the light emitting signals VS21 and VS22 whose timings coincide with the noise waveform phases 0 ° and 90 ° both exceed the threshold value Vth, whereas the noise waveform phase 180 ° For the light emission signal VS23 whose timing coincides with
Its value cannot exceed the threshold value Vth. On the other hand, although not shown, the three light emission signals VS21, VS22, VS
Assuming that only the noise light LN, which must not exceed the threshold value Vth, is incident on the phase shifter 23, the phase 9
Light projection signal V whose timing coincides with 0 ° and 180 °
The values of S22 and VS23 do not exceed the threshold value Vth, whereas the values of the light-emitting signal VS21 whose timing coincides with the phase of 0 degrees have the threshold value Vt.
h. Therefore, one noise period (TN)
Of the three determinations made in the above, if two or more times exceed the threshold, it is turned on, and if it does not exceed the threshold, it is turned off and the majority rule is followed. It can be seen that a high on / off determination result is obtained.

The condition judging means 11A makes an on / off judgment based on the data DMX obtained from the A / D converting means 5A by the above judgment algorithm. FIG. 11 is a flowchart showing a process for realizing the function required of the condition determining means 11A in a software manner using a microprocessor.

In the figure, when the process is started, first, an initialization process is executed, and various counters and registers required for the operation are initialized (step 11).
01). Subsequently, the first digital data DMX read from the A / D converter 5A is compared with the threshold value Dth in magnitude (step 1102). Where D
If it is determined that MX> Dth (step 1102
YES), the predetermined ON counter is incremented by +1 (step 1103). In contrast, DMX
<Dth (Step 1102N
O), the predetermined OFF counter is incremented by +1 (step 1104). Thereafter, the data number counter N is incremented by +1 to confirm that the data has reached the third data (step 1106). The above processing (steps 1102 to 1105) is repeated until the value of the data number counter N becomes “3”.

If the value of the data number counter N has reached "3" (step 1106: YES), the count value of the ON counter is compared with the count value of the OFF counter (step 1107). Here, ON counter value> O
If it is determined that the value is the FF counter value (step 110
7YES), an ON determination is made (step 110)
8). On the other hand, if it is determined that ON count value <OFF count value (step 1109),
A determination is made. The determination result according to the majority rule is one of the determination factors for making a final ON / OFF determination.

According to the second embodiment, since the noise waveform of the inverter fluorescent lamp is substantially sinusoidal, there are only two steep portions in the waveform gradient within one blinking period (TN) of the fluorescent lamp. If light emission is performed at least three times within one blinking cycle, the light emission timing of two of them will almost coincide with the timing of the steep rising portion and the timing of the steep falling portion on the noise waveform. Even if an erroneous level determination result is obtained at any one of the timings, the other light projection timings correspond to relatively gentle portions. Therefore, the level of the received light signal (VM) at the timing T1 when the peak of the pulsed detection light will arrive.
X) is compared with a predetermined threshold value (Vth) to obtain a comparison result, and one of the conditions used for the on / off determination according to the comparison result that occupies a large part of all the comparison results obtained within the light emitting cycle is satisfied. If it is determined whether or not the determination has been made, a highly reliable on / off determination result can be obtained.

[0103]

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 the on / off determination.

Further, according to the present invention, a photoelectric switch with a level shift function capable of obtaining a reliable ON / OFF determination result even if the sampling timing of a light receiving signal for performing ON / OFF determination is slightly shifted. Can be provided.

Further, according to the present invention, even if the sampling timing of the received light signal for performing the on / off determination happens to coincide with the steep portion of the received light signal waveform due to the noise component, a highly reliable on / off determination result can be obtained. It is possible to provide a photoelectric switch with a level shift function that can perform the above.

[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 the transmission type photoelectric switch according to the first embodiment.

FIG. 3 is a circuit diagram of a filter means constituted by a dedicated analog circuit.

FIG. 4 is a diagram conceptually showing the function of a condition determining means using a logic symbol.

FIG. 5 is a waveform chart showing signal states of respective units 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 a relationship between a generation timing of a fluorescent lamp pulse and a cycle of the fluorescent lamp pulse.

FIG. 9 is a waveform chart showing a relationship between fluorescent lamp noise and a projection signal.

FIG. 10 is a waveform diagram showing a relationship between a light receiving signal (light projection portion) after a level shift and a threshold.

FIG. 11 is a flowchart illustrating a process for realizing a condition determining unit.

FIG. 12 is a waveform diagram showing a relationship between a light emitting pulse and a light receiving signal in a state where no fluorescent lamp noise exists.

FIG. 13 is a waveform diagram showing a relationship between a light emission pulse and A / D conversion timing in a state where fluorescent light noise is present.

[Explanation of symbols]

 1,15 photoelectric switch 2 light emitting means 3 light receiving means 4 filter means 5,5A A / D conversion means 6,6A CPU 7 driving means 8 light emitting element 9 light receiving element 10 amplifier 11,11A condition determining means 12,12A sampling pulse generation Means 13, 13A Projection control means LS Projection of detection light LR Reflection of reflection light C1 Capacitor Q1 Analog switch COM1, COM2 Comparator AND AND gate PD Projection 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) T0 Timing immediately before T1 First timing T2 Second timing P1, P2, P3 Light pulse

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Tetsuya Akagi 801 Minami-Fudo-cho, Higashi-iri, Horikawa-Shioji, Shimogyo-ku, Kyoto F term in Omron Corporation (reference) 5J050 AA13 BB17 CC00 DD18 EE02 EE34 EE35 EE40 FF01

Claims (10)

[Claims] 1. A light projecting means for periodically projecting pulsed detection light, a light receiving means for photoelectrically converting the pulsed detection light to output a corresponding light receiving signal, and a light receiving signal outputted from the light receiving means. A signal processing means for generating an on / off determination output based on the signal, wherein the signal processing means has a level between the level of the light receiving signal and a specified level at a timing immediately before the pulsed detection light will arrive. Level shift means for level-shifting the level of a light receiving signal included in a period in which a light receiving signal waveform of the pulsed detection light is likely to be obtained by an amount corresponding to the difference in a direction approaching the specified level; Condition determining means for determining whether at least one of the conditions used for on / off determination is satisfied based on the light receiving signal after the level shift by the means. A photoelectric switch included therein, wherein the condition determining means comprises: a level of a light receiving signal at a first timing when a peak of a light receiving signal waveform of the pulsed detection light will arrive; The determination is made at least under the condition that the result of comparison with the level of the light receiving signal at the second timing at which the bottom due to the overshoot of the light receiving signal waveform will come to have a predetermined magnitude relationship. There is a photoelectric switch. 2. The condition determining means according to claim 1, wherein the comparison result between the level of the light receiving signal at the first timing and the level of the light receiving signal at the second timing has a predetermined magnitude relation. 2. The photoelectric switch according to claim 1, wherein the determination is performed on condition that the comparison result between the level of the light receiving signal at the timing and the prescribed level has a predetermined magnitude relation. 3. 3. A light projecting means for periodically projecting the pulsed detection light, a 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. A signal processing means for generating an on / off determination output based on the signal, wherein the signal processing means has a level between the level of the light receiving signal and a specified level at a timing immediately before the pulsed detection light will arrive. Level shift means for level-shifting the level of a light receiving signal included in a period in which a light receiving signal waveform of the pulsed detection light is likely to be obtained by an amount corresponding to the difference in a direction approaching the specified level; Condition determining means for determining whether at least one of the conditions used for on / off determination is satisfied based on the light receiving signal after the level shift by the means. A photoelectric switch, wherein the light emitting means is designed to emit light at least three times or more within a blinking cycle of the inverter fluorescent lamp in an installation environment, and the condition determining means Compares the level of the received light signal at a timing when the peak of the pulsed detection light will arrive with a predetermined threshold to obtain a comparison result, and a large number of all the comparison results obtained within one light emitting cycle. The photoelectric switch is configured to make the determination according to a comparison result occupying the following. 4. A driving means for outputting a driving pulse signal at a timing instructed by a light emitting control signal, and projecting the pulsed detection light to a target area in response to the driving pulse signal output from the driving means. A light-emitting element including a light-emitting element that performs light-receiving, a light-receiving element that receives reflected light of the pulsed detection light coming from the target area and performs photoelectric conversion, and an amplifier that amplifies an output of the light-receiving element and generates a light-receiving signal. And a signal processing unit that generates an on / off determination output based on a light receiving signal output from the light receiving unit. The signal processing unit receives the pulsed detection light. The level of the light receiving signal included in the period in which the light receiving signal waveform of the pulsed detection light will be obtained by an amount corresponding to the difference between the level of the light receiving signal and the prescribed level at the timing immediately before Level shifting means for shifting the level toward the prescribed level; and determining whether at least one of the conditions used for on / off determination is satisfied based on the light receiving signal after the level shift by the level shifting means. And a condition determining means for determining, wherein the condition determining means determines a light receiving signal at a first timing at which a peak of a light receiving signal waveform of the pulsed detection light will arrive. At least on condition that the result of comparison between the level and the level of the received light signal at the second timing when the bottom due to overshoot of the received light signal waveform of the pulsed detection light will arrive at a predetermined magnitude relationship. A photoelectric switch designed to make a determination. 5. The condition determining means according to claim 1, wherein the comparison result between the level of the light receiving signal at the first timing and the level of the light receiving signal at the second timing has a predetermined magnitude relation. 5. The photoelectric switch according to claim 4, wherein the determination is performed on condition that the comparison result between the level of the light receiving signal at the timing and the prescribed level has a predetermined magnitude relation. 6. 6. A driving means for outputting a driving pulse signal at a timing designated by a light emitting control signal, and projecting the pulsed detection light onto a target area in response to the driving pulse signal output from the driving means. A light-emitting element including a light-emitting element that performs reflection, a light-receiving element that receives reflected light of the pulsed detection light coming from the target area, and performs photoelectric conversion, and an amplifier that amplifies an output of the light-receiving element to generate a light-receiving signal And a signal processing unit that generates an on / off determination output based on a light receiving signal output from the light receiving unit. The signal processing unit receives the pulsed detection light. The level of the light receiving signal included in the period in which the light receiving signal waveform of the pulsed detection light will be obtained by an amount corresponding to the difference between the level of the light receiving signal and the prescribed level at the timing immediately before Level shifting means for shifting the level toward the prescribed level; and determining whether at least one of the conditions used for on / off determination is satisfied based on the light receiving signal after the level shift by the level shifting means. And a condition determining means for determining, wherein the light emitting means emits light at least three times or more within a blinking cycle of the inverter fluorescent lamp in an installation environment. It is controlled by a light emission control signal, and the condition determination means obtains a comparison result by comparing a level of a light reception signal at a timing when a peak of the pulsed detection light will arrive with a predetermined threshold value, A light configured to make the determination according to a comparison result that occupies a large part of all the comparison results obtained within one light emitting cycle; Switch. 7. An alternating current having a function of transmitting the alternating current component of the input side signal to the output side and initializing a DC potential to be superimposed on the output side alternating current component to a specified potential. The DC potential to be a signal transmission circuit and to be superimposed on the output side AC component of the AC signal transmission circuit is
The reflective photoelectric switch according to claim 4, wherein the reset potential is repeatedly reset to a specified potential immediately before the timing at which the pulse-like detection light will arrive. 8. The AC signal transmission circuit includes a coupling capacitor interposed between input and output terminals, and a switch interposed between an output terminal and a specified potential point, wherein the switch is a light emitting timing signal. 8. The reflection type photoelectric switch according to claim 7, wherein on / off control is performed by a gate control signal synchronized with the switch. 9. An operation, such as a comparison between a light receiving signal level and a threshold value, performed by the condition determining means, based on digital data obtained by A / D converting an output signal of the AC signal transmission circuit. 9. The reflection type photoelectric switch according to claim 7, wherein the reflection type photoelectric switch is executed by software by a microprocessor. 10. A light emitting side device and a light receiving side device which are arranged apart from each other, wherein the light emitting means is built in the light emitting side device, and wherein the light receiving means and the signal processing means are 5. The light-receiving side device, wherein the light-emitting control signal is transmitted from the light-receiving side device to the light-emitting side device via communication.
10. The photoelectric switch according to any one of items 1 to 9.