JPH02200007A - Photoelectric switch - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] (b) Industrial application field The present invention relates to a pulse modulation type photoelectric switch.

(B) Prior Art Conventionally, some photoelectric switches are of a pulse modulation type in which a light emitting element is lit in pulses. FIG. 6 shows this type of pulse modulation type, reflection type photoelectric switch. In the figure, a light projecting circuit 1 includes a light projecting element such as an LED, and in response to a pulse signal η from an oscillation circuit 2, the light projecting element projects pulse modulated light having a constant pulse width and period. The light reflected by the detection object 7 is received by the light receiving circuit 3, amplified by the amplifier circuit 4, and input to the signal processing circuit 5. The signal processing circuit 5 first determines the input signal at a certain slice level,
If the input signal exceeds the slice level, a pulse signal is generated. This pulse signal is ANDed with a gate signal created based on the oscillation signal of oscillation circuit 2 to remove noise, and in the 0th stage, which is transmitted to the next stage, the pulse signal is shifted to further improve noise resistance. Count using a signal delay circuit such as a register. The output signal is then transmitted to the output circuit 6 and output as a binary output.

(C) ↓11 Problem-C that the invention seeks to solve: Photoelectric switches are used in various environments, and the required noise resistance is also various. Furthermore, the response speed of the photoelectric switch required to detect the object to be detected also varies. Therefore, it is desired that the noise resistance and response speed of the photoelectric switch can be freely set depending on the environment of use and the object to be detected. However, the conventional photoelectric switch described above has a problem in that the response speed and noise resistance are fixed to fixed values and cannot be set freely by the user.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a photoelectric switch whose noise resistance and response speed can be freely set.

(d) Means and operation for solving the problems The photoelectric switch of the present invention includes a light projecting circuit including a light projecting element and a pulse oscillator, and the light projecting element is pulse-lit by a pulse signal from the pulse oscillator. The apparatus is characterized in that it includes an oscillation cycle control circuit' having a manual operation device that varies the pulse cycle of the pulse oscillator.

In this photoelectric switch, the pulse period can be freely set by adjusting the manual operation device. By changing the pulse period, the duty changes, so the noise resistance can be changed. Furthermore, since the number of pulses within a predetermined time period changes when the pulse period changes, the response speed can also be changed.

(e) Examples Hereinafter, the present invention will be explained in more detail with reference to Examples.

FIG. 1 is a circuit block diagram of a photoelectric switch showing one embodiment of the present invention.

This photoelectric switch consists of a light projection circuit 1, an oscillation circuit 2 that oscillates a pulse signal, and a light emitted from the light projection circuit 1 to a detection object 7.
The basic configuration is the same as the conventional photoelectric switch shown in FIG. 6 in that it includes a light receiving circuit 3 for receiving light reflected by a light receiving circuit, an amplifier circuit 4, a signal processing circuit 5, and an output circuit 6.

This photoelectric switch is further characterized in that it includes an oscillation cycle control circuit 8 that can vary the oscillation cycle of the pulse signal of the oscillation circuit 2.

The oscillation cycle control circuit 8 includes variable resistors 3 and 39 for manually adjusting the oscillation cycle. The resistance of the variable resistor 9 can be adjusted manually using a knob, for example.

A specific circuit example of the oscillation circuit 2 is shown in FIG. The configuration itself of this oscillation circuit 2 is already well known.

In this oscillation circuit 2, resistor R11 and capacitor C8
The period of the pulse signal is determined by the resistor R1 and capacitor C.
0 determines the pulse width. Therefore, this resistance Rl 1
In the present invention, it is possible to change the oscillation frequency by changing the internal resistance value using another oscillation circuit.

In this example photoelectric switch, the value of the variable resistor 9 is now set to a predetermined value, and the waveform of the current flowing through the light projecting circuit 1 in response to the pulse signal output from the oscillation circuit 2 is shown in (n) in FIG. Assume that the waveform is shown in

A pulse signal generated by this light emitting current is reflected from the light emitting circuit 1 by the detection object '7, and is received by the light receiving circuit 3.

This light reception signal is shown in (■) in FIG. Light receiving circuit 3
While the pulse signal obtained by is being output, the pulsed light is reflected by the detection object 7 and is incident.

(C) in FIG. 3 is the output signal of the output circuit 6. Here, the signal processing circuit 5 counts four pulses, and the output of the output circuit 6 rises from low to high at the fourth pulse. It is composed of

Now, the variable resistor 23 of the photoelectric switch set in this way
Assuming that the period of the pulse signal is further increased by adjusting 9, when the period is doubled, the light emitting current becomes as shown in FIG. 3(d).

Accordingly, the light receiving signal of the light receiving circuit 3 is shown in (e) in FIG.
Therefore, if this pulse signal is counted by the signal processing circuit 5 and the output circuit rises at the fourth pulse, its output will have the waveform shown in FIG. 3(f).

The waveforms (a) to (C) in Fig. 3 and the waveforms (d) in Fig. 3
Comparing the waveforms l to (f), it is found that the ratio of the pulse period and pulse width of the light emitting current fa) in the former is (fa) in Fig. 3.
The ratio of the light projection signal in d) is larger.

That is, the pulse period is large relative to the pulse width. In this photoelectric switch, a signal from an oscillation circuit 2 is used as a gate signal to cause a signal processing circuit 5 to operate.
Since it derives a pulse signal, it will not malfunction even if an optical signal is mixed in when the pulse signal is off.
In other words, such noise resistance, which has no influence on noise, is better as the interval width becomes larger with respect to the pulse ψM, that is, as the duty becomes smaller, so by making the period variable,
By increasing the pulse period, noise resistance can be improved. It can also be seen that the rise of the waveform (r) in FIG. 3 lags behind the rise of the waveform (C) in time, which also changes the response speed.

FIG. 2 is a circuit block diagram of a photoelectric switch showing another embodiment of the invention.

The basic circuit shown in the same figure is also the same as that shown in FIG. The light emitting current control circuit 10 is similar to the example photoelectric switch, and additionally includes a light emitting current control circuit 10 that controls the light emitting current of the light emitting circuit 1 in conjunction with changes in the variable resistor 9.

In this example photoelectric switch, when the waveforms (a) to (C) in FIG. 3 are changed to the waveforms (d) to (f), that is, when the pulse period is doubled, the pulse In accordance with doubling the period, the level value of the light emitting current is doubled as shown in FIG. 3 (8). The upper limit of the average light emitting current of the photoelectric switch is determined by the maximum power rating of the light emitting element. Therefore, as shown in FIG. 3(d) above, when the light projection period becomes twice that of (a), the average current becomes 1/2, so it can be further doubled accordingly. Therefore, the light emitting current is also set to double in conjunction with the change in the variable resistor 2'j19. It is clear that this makes it possible to increase the detection distance while satisfying the maximum rating of the light projecting element. In other words, the stronger the light projection signal, the greater the distance it can reach, and therefore even if weak noise is mixed in, it will not be affected by this noise. In other words, noise resistance is also improved.

Furthermore, by changing the resistance of the variable resistor 9 using the above-mentioned photoelectric switch and making the light emitting period variable, the following becomes possible. is flowing, in a photoelectric switch whose cycle is set as shown in (h) in Fig. 4, (i) in Fig. 4
When a total of six reflected lights are obtained from the detection object as shown in (j) of Fig. 4, the signal of the output circuit 6 rises at the fourth shot as shown in (j) of Fig. 4, so this object can be detected. However, if the period is made twice as long as (h) in Fig. 4, as shown in Fig. 4 (provisional), then at the same speed, (1)
As shown in (e), only three pulse signals are reflected, and therefore, the signal of the output circuit does not rise as shown in (e). In other words, even if the object is flowing at the same speed, by changing the period, it is possible to make the object detectable or not. This makes it possible to distinguish between detection objects of different sizes flowing along the same line.

Further, contrary to the case described above, when the detected object has a constant size, the moving speed of the detected object can be determined by adjusting the light projection period.

(f) Effects of the Invention According to the present invention, since the oscillation cycle control circuit is provided with a manual operation device that changes the pulse period of the pulse oscillator, the user can freely project light using the hand aJ operation device. The oscillation period of the light emitting signal output from the circuit can be changed,
This allows the duty to be changed, thereby improving noise resistance, and since the pulse signal value counted during a predetermined period of time can be changed, the response speed can be changed.

Further, when the conveyor speeds are the same, it is possible to determine the size of the detected object, and conversely, when the same detection and object are detected, it is also possible to determine the moving speed of the detected object.

[Brief explanation of the drawing]

FIG. 1 is a circuit block diagram of a photoelectric switch showing one embodiment of the invention, FIG. 2 is a circuit block diagram of a photoelectric switch showing another embodiment of the invention, and FIG. 3 is a circuit block diagram of a photoelectric switch showing another embodiment of the invention. FIG. 4 is a waveform diagram for explaining the operation when the photoelectric switch of the above embodiment is installed in a line, and FIG. 5 is a waveform diagram of the oscillation circuit of the photoelectric switch of the above embodiment. FIG. 6, which shows an example, is a block diagram showing the configuration of a conventional photoelectric switch. 1: Light projection circuit, 2: Oscillation circuit, 8: Oscillation cycle control circuit, 9: Variable resistor, 10: Light projection current control circuit. Patent Applicant Tateishi NR Co., Ltd. Agent Patent Attorney Shigeru Nakamura Amendment to Diagram Procedures (Voluntary) September 18, 1999

Claims (2)

[Claims] (1) A photoelectric switch comprising a light emitting circuit including a light emitting element and a pulse oscillator, and lighting the light emitting element in pulses according to a pulse signal from the pulse oscillator, wherein the light emitting element is manually controlled to vary the pulse period of the pulse oscillator. A photoelectric switch characterized by comprising an oscillation period control circuit having an operation device. (2) A photoelectric switch that includes a light projecting circuit including a light projecting element and a pulse oscillator, and lights the light projecting element in pulses according to a pulse signal from the pulse oscillator, wherein a manual operation that varies the pulse period of the pulse oscillator is provided. 1. A photoelectric switch comprising: an oscillation cycle control circuit having an operating device; and a light projection current control circuit that controls a light projection current of the light projection circuit in conjunction with changes in the pulse period.