JPH059037U - Photoelectric switch - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a photoelectric switch that eliminates the influence of spike noise and the like and prevents malfunction. [Structure] The signals from the pulse generation circuit 4 are fed to FF ₁ to FF.
Divide by ₃ to obtain the first signal (d) and the second signal (e)
Among them, the first signal (d) is used as a light emitting pulse to drive the light emitting element 1, and the second signal (e) is used as a gate pulse. In the gate circuit 10, the light receiving signal i of the light emitting element 1 is passed only during the gate pulse period and is guided to the light receiving signal processing circuit.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a photoelectric switch, and more particularly to improvement of a photoelectric switch that detects an object by using modulated light and obtains a switching output.

[0002]

[Prior Art]

 As is well known, this type of photoelectric switch pulse-drives a light-emitting diode, which is a light-emitting element, receives pulsed light that has undergone changes such as blocking, reflection, transmission, and absorption by a detection object, and amplifies the received light signal. -Signal processing such as discrimination is performed and binarized to generate switching output. Then, the current value of the light emitting diode drive pulse current is increased to increase the light output so that even a distant object can be reliably detected.

[0003]

[Problems to be solved by the device]

 However, in such a conventional photoelectric switch, the line for supplying the drive pulse current to the light emitting diode and the line for guiding the weak light receiving signal of the light receiving element to the amplifier circuit (this line is called A line) are very close to each other. It is customary to be arranged as. Therefore, a spike-like noise voltage is induced in the A line due to the electromagnetic induction effect due to changes in the rise and fall of the drive pulse current. In other words, a signal of a certain level is output to the output of the amplifier circuit even though there is no light reception signal. In particular, in the large-current-driven photoelectric switch targeted by the present invention, spike noise was also large, and the output of the amplifier circuit appeared as a regular light-receiving signal, which was a cause of malfunction.

On the other hand, the applicant of the present application has previously constructed a configuration using a NOT circuit in which an output pulse obtained by inverting a drive pulse is used as a gate pulse, thereby preventing the influence of ambient light noise and causing a malfunction. We proposed a photoelectric detection device that does not include this (see Japanese Examined Patent Publication No. 52-33308), but in this example, the gate pulse is a pulse that is the inverted drive pulse (duty ratio 1: 1). The effect of spike noise can be eliminated by the rise and fall of the pulse current, but all disturbance light such as sunlight when the emission pulse is not rising is received as noise. However, there is a problem in that it is easy to malfunction.

The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a photoelectric switch that removes the influence of the spike noise described above and prevents malfunction. Is.

[0006]

[Means for Solving the Problems]

 In order to achieve the above object, the present invention provides a pulse generating circuit, a light emitting element, a frequency dividing unit for dividing a signal from the pulse generating circuit, and a logic of a plurality of signals from the frequency dividing unit. And a drive circuit for intermittently driving the light emitting element to emit light using the first signal (d) obtained by the logic circuit as a light emitting pulse, and an output signal based on the light receiving signal of the light receiving element. Is provided between the light receiving element and the light receiving signal processing circuit for generating the light receiving signal processing circuit, and the second signal (e) obtained by the logic circuit is used as a gate pulse, and the light receiving is performed only during this pulse period. A gate circuit that allows a signal to pass therethrough.

[0007]

[Action]

 The signal from the pulse generating circuit is divided by a dividing means to generate a first signal (d) and a second signal (e). Of these, the first signal (d) is emitted as a light emitting pulse. The element is driven, and the second signal (e) is a gate pulse. Then, in the gate circuit, the light receiving signal of the light emitting element is passed only during the gate pulse period and is guided to the light receiving signal processing circuit.

[0008]

【Example】

 Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic diagram showing an electrical configuration of a reflection type photoelectric switch to which the present invention is applied, and FIGS. 2 and 3 are time charts showing signal waveforms of respective parts.

In FIG. 1, the reflection type photoelectric switch detects the presence of the object 2 by detecting the light emitted from the light emitting diode 1 by the detection object 2 and receiving the reflected light by the photodiode 3.

A drive circuit for intermittently driving the light emitting diode 1 to emit light is a pulse generation circuit 4, three T-type flip-flops FF ₁ , FF ₂ and FF ₃ forming a frequency divider circuit, and a drive pulse d. An AND circuit 5 to be formed and a driver circuit 6 which supplies a drive pulse current to the light emitting diode 1 in response to the drive pulse d.

The received light signal processing circuit for processing the received light signal of the photodiode 3 includes an amplifier circuit 7, a comparator 8, a gate circuit 9, a flip-flop circuit 10, and five D-type flip-flops which form a shift register. It is composed of FF ₅ , FF ₆ , FF ₇ , FF ₈ and FF ₉ , AND circuits 11 and 12, an RS flip-flop FF _10, and an output circuit 13.

The AND circuit 14 creates a gate pulse e. This gate pulse e occurs from the trailing edge of the gate pulse e so as not to overlap with the drive pulse d, and is a constant pulse like the drive pulse d. It has a width (see Fig. 2). It should be noted that the NAND circuit 15 produces the signal k for resetting the flip-flop circuit 10.

Next, the operation of the reflection type photoelectric switch having such a configuration will be described with reference to FIGS. 2 and 3.

The light emitting diode 1 is pulse-driven based on the drive pulse d, and as described above, spike noise is input to the amplifier circuit 7 together with the light reception signal from the photodiode 3. In addition to the regular reflected light, light from the surroundings is input to the photodiode 3, so that various signals appear at the output of the amplifier circuit 7. That is, (a) is spike noise that is synchronized with the rising and falling edges of each drive pulse d, (b) shows the received light signal superimposed on spike noise, and the received light signal is the same as the falling portion of the drive pulse d. Of the driving pulse d, and the peak portion is at the trailing edge of the drive pulse d, and only the light reception signal is present at the portion after the trailing edge of the driving pulse d. Further, the signal (c) is noise due to ambient light that the photodiode 3 appropriately receives. A is the discrimination level of the comparator 8, and the output h of the comparator 8 is the binarization of the signals (a), (b) and (c) at the discrimination level A. The binarized signal waveform corresponding to the signal (b) is the signal (d) due to the rising portion of spike noise, the signal (e) that is within the pulse width of the drive pulse d and is the first half of the received light signal, and the drive pulse It is present after the fall of d and is composed of the signal (f) which is the latter half of the received light signal. Therefore, when the gate circuit 9 takes the logical product of the gate pulse e generated from the falling portion of the drive pulse d and the signal h, only the signal (f) is valid. In this way, only the received light signal i can be extracted by removing the influence of force majeure spike noise that is surely generated in synchronization with each drive pulse d.

Further, in this embodiment, it is monitored that the light reception signal i thus extracted continues for a fixed number (five), and the output circuit 13 operates accordingly. That is, as shown in FIG. 3, when all the Q outputs of FF ₅ , FF ₆ , FF ₇ , FF ₈ and FF ₉ constituting the 5-stage shift register become “H”, the Q of FF ₁₀ is changed. The output becomes "H". When the number of received light signals i is 4 or less, the set input S of the FF ₁₀ is "L", the Q output is "L", and the output circuit 13 does not operate. That is, the output circuit 13 does not operate due to the function of the shift register even if the one-time noise is included in the timing light reception signal i of the gate pulse e. This further ensures the normal operation of the device.

As shown in FIG. 2, in this embodiment, the gate pulse e is 1/7 of the oscillation period of the drive pulse d, so (1) the influence of external noise can be eliminated. ) The power of the light projection pulse can be increased, and (3) the current consumption can be reduced.

Even if the technique described in Japanese Patent Publication No. 52-33308 shown in the above-mentioned conventional example is applied to the one having a small duty ratio as in this embodiment (that is, the driving pulse is subjected to NOT), The gate is applied to all the periods when the light is off, and light can be received during that period, which makes it easier to receive external noise such as ambient light, and as a result, malfunctions are likely to occur.

As is clear from the above description, the photoelectric switch according to the present embodiment increases the power of the light-emission pulse from the light-emitting element, which makes it possible to reduce the current consumption and the disturbance light. It is possible to reliably remove the effect of spike noise, etc., and thereby prevent malfunction.

Further, in the present embodiment, since the drive pulse d and the gate pulse e can be generated by dividing the frequency of the output signal of one pulse generating circuit 4 and performing the logical operation, this kind of one-chip IC is formed. The cost and size of the photoelectric switch can be reduced.

[0021]

[Effect of the device]

 As described above, the photoelectric switch according to the present invention has the following effects. (1) The influence of external noise can be reduced. (2) The power of the light emitting pulse can be increased. (3) Current consumption can be reduced. (4) Since the light emitting pulse signal and the gate signal are generated from one oscillator, the cost can be reduced. It should be noted that the IC can be downsized because the mounting area can be reduced in the case of an IC. (5) By taking the logic of the signal from the frequency dividing means, a desired pulse can be easily and accurately created.

[Brief description of drawings]

FIG. 1 is a schematic block diagram showing an electrical configuration of a reflective photoelectric switch to which the present invention is applied.

FIG. 2 is a time chart showing signal waveforms at various parts of the switch shown in FIG.

3 is a time chart showing signal waveforms of various parts of the switch shown in FIG.

[Explanation of symbols]

1 Light emitting diode (light emitting element) 3 Photo diode (light receiving element) 4 Pulse generation circuit 5 AND circuit 6 Driver circuit 7 Amplifying circuit 8 Comparator 9 Gate circuit FF ₁ , FF ₂ , FF ₃ , FF ₁₀ Flip flop d Drive pulse e Gate pulse i Light reception signal (b) Light reception signal superimposed on spike noise

Claims (1)

Claims for utility model registration: 1. A pulse generating circuit, a light emitting element, frequency dividing means for dividing the signal from the pulse generating circuit, and logic for a plurality of signals from the frequency dividing means. And a drive circuit for intermittently driving the light emitting element to emit light by using the first signal (d) obtained by the logic circuit as a light emitting pulse, and an output signal is generated based on the light receiving signal of the light receiving element. Which is provided between the light receiving signal processing circuit and the light receiving element and the light receiving signal processing circuit. A photoelectric circuit having a gate circuit for passing through