JPH04337921A - Adjacent switch - Google Patents

Abstract

PURPOSE:To prevent the mutual interference of an adjacent switch with simple circuit configuration by fluctuating the oscillation frequency of the adjacent switch with the lapse of time. CONSTITUTION:When a power source is turned on, the oscillation circuit 3 of a detection part 2 starts oscillation at a first frequency, the lamp waveform oscillation circuit 11 of a direct frequency modulation part 10 is simultaneously activated, the amplitude is changed with the lapse of time, and a second high-frequency signal lower than the first frequency is outputted to a vari-cap diode D. Based on the change of the signal, the vari-cap diode D modulates the first frequency of the detection aprt 2 to a direct frequency as the oscillation frequency to be fluctuated within a prescribed range. Then, a detection/integration circuit 4 detects the amplitude of the oscillation frequency modulated to the direct frequency, outputs a DC voltage integrated while responding to a frequency lower than the second frequency to a comparator circuit 5, compares the voltage with a reference level and detects the approach of a reagent. Namely, the oscillation frequency of the adjacent switch is fluctuated with the lapse of time, time for making adjacent the oscillation frequencies each other is shortened, and the mutual interference can be prevented.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a proximity switch, and more particularly to a proximity switch that can prevent mutual interference.

0002

[Prior Art] A conventional proximity switch uses an oscillation circuit that has at least a detection coil to oscillate at a predetermined frequency, and when an object to be detected approaches, the detection coil The Q of changes,
It was common to detect changes in the level of the oscillation amplitude.

Furthermore, when proximity switches are placed adjacent to each other, if their oscillation frequencies are close to each other, the oscillation circuit of the proximity switch will affect the oscillation frequency of the other proximity switch (
(hereinafter referred to as mutual interference), which may cause malfunctions.
Even if there were slight differences in shape, each was used by changing its oscillation frequency or by applying a shield.

0004

[Problems to be Solved by the Invention] In the conventional proximity switch as described above, changes in magnetic flux caused by eddy current generated in a nearby detected object by oscillating at a predetermined frequency cause
Since changes in the oscillation amplitude level are detected, for example, if multiple proximity switches are used adjacently, the oscillation circuits will interfere with each other and the oscillation amplitude level will change, resulting in malfunction. There was a problem with that.

In addition, in order to prevent mutual interference, if the oscillation frequency of the oscillation circuit of each proximity switch is changed, it is necessary to prepare two or more types of the same shape, and due to the circuit configuration, it is necessary to prepare two or more types of oscillation circuits. There were problems with product management and circuitry, such as not being able to prepare the oscillation frequency.

[0006] Furthermore, when mutual interference is prevented by using a shield or the like, there is a problem in that the oscillation is attenuated by the shield material, resulting in a shortened detection distance.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a proximity switch that can change the oscillation frequency and prevent mutual interference even with a simple circuit configuration.

[0008]

[Means for Solving the Problems] A proximity switch according to the present invention has a detection section consisting of a first oscillation circuit including at least a detection coil, and when the power is turned on, the oscillation circuit is switched to a predetermined first oscillation circuit. Based on the comparison result of the comparison circuit that compares the DC voltage with the integrated amplitude of the oscillation frequency and the reference level, the proximity switch that detects the approach of the detected object operates simultaneously with the oscillation. , a second oscillation circuit that outputs a signal of a second frequency whose amplitude changes with time and is lower than the first frequency; direct frequency modulation means that directly modulates the first frequency to produce an oscillation frequency that fluctuates within a predetermined range; detects the amplitude of the oscillation frequency directly frequency modulated from the detection section; It is equipped with a detection/integration circuit that responds and outputs the integrated DC voltage to a comparison circuit.

[0009]

[Operation] When the power is turned on, the detection unit causes the oscillation circuit to oscillate at a predetermined first frequency, and at the same time, the second oscillation circuit operates so that the amplitude changes with time and the first frequency The lower second high frequency signal is directly output to the frequency modulation means.

Then, the direct frequency modulation means directly frequency modulates the first frequency of the detection section based on the change in the amplitude of the signal from the second oscillation circuit, and makes the oscillation frequency fluctuate within a predetermined range. .

Next, the detection/integration circuit directly detects the amplitude of the frequency-modulated oscillation frequency, outputs the integrated DC voltage in response to a frequency lower than the second frequency to the comparison circuit, and compares it with the reference level. The comparison is made to detect the approach of the subject.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing a schematic configuration of a proximity switch according to the present invention. In the figure, numeral 1 indicates a proximity switch, which has at least the circuit described below.

Reference numeral 2 denotes a detection section, which is composed of an oscillation circuit 3 including a detection coil L. When the power is turned on, the oscillation circuit 3 starts oscillating, and a direct frequency modulation section described later changes the frequency of the oscillation frequency with time. It is something that changes. In addition, in this embodiment, the frequency of this oscillation is set to 100 KHz to 1 MHz.
degree.

4 is a detection/integration circuit, which detects the amplitude of the output of the detection section 2 and outputs the integrated DC voltage. , which is very large.

Furthermore, the response is set to be faster than that of the proximity switch 1 itself.

A comparison circuit 5 compares the level of the integrated wave inputted from the output level of the detection/integration circuit 4 with a preset reference level and outputs the comparison result.

Reference numeral 6 denotes an output circuit, which outputs the comparison result from the comparison circuit 5 as a detection signal.

Reference numeral 7 denotes an initial reset circuit which stops the output of the detection signal from the proximity switch 1 for a predetermined period of time to prevent erroneous output when the power is turned on.

Reference numeral 8 denotes a power supply circuit, 9 a load, and 10 a direct frequency modulation section, each of which has at least the circuit configuration described below.

Reference numeral 11 denotes a ramp waveform oscillator circuit, which outputs a ramp waveform signal which increases monotonically after a predetermined period when the power is turned on, obtains a constant increase, and then rapidly decreases. Moreover, in this embodiment, this ramp waveform signal is several 10
The frequency should be about KHz.

One side of C is connected to the detection coil L, and the other side is connected to the cathode of a varicap, which will be described later, to cut only the DC component from the detection section 2 and the ramp waveform oscillation circuit 11, and combine the capacitance of the varicap. It is a coupling capacitor that allows

D is a varicap diode (variable capacitance diode) whose cathode is connected to the capacitor C and the ramp waveform oscillation circuit 11, and whose anode is connected to ground, and the capacitance changes depending on the voltage level of the ramp wave signal. As a result, the oscillation frequency of the detection section 2 is changed.

The operation of the proximity switch configured as described above will be explained below. FIG. 2 is a timing chart explaining the operation of the present invention.

In the figure, a is the waveform of the oscillation frequency when the frequency is not directly modulated in the oscillation circuit 3, b is the ramp waveform from the ramp waveform oscillation circuit 11, and c is the waveform from the varicap diode D and the ramp waveform oscillation circuit 11. The waveform of the oscillation frequency when the oscillation frequency a is directly frequency-modulated by the ramp waveform b, and d is the waveform integrated by the detection/integration circuit 4.

Further, in this case, the detection distance of the proximity switch 1 is set to a distance corresponding to the amplitude level of f3.

When the power is turned on, the oscillation circuit 3 of the detection section 2 starts oscillation, and at the same time, the ramp waveform oscillation circuit 11 of the direct frequency modulation section 10 transmits the signal of the ramp waveform a shown in FIG. and send it to Varicap Died D.

Then, since the amplitude of the ramp waveform of the varicap diode D changes with time, the capacitance changes,
Let us assume that the oscillation frequency a shown in FIG. 2 is the oscillation frequency c obtained by directly frequency modulating the oscillation frequency a.

FIG. 3 is a diagram showing the relationship between oscillation frequency and amplitude level. As the oscillation amplitude changes between f1 and f2, the operating distance of the proximity switch 1 may be affected. Therefore, in order to eliminate the influence of the detection distance, the detection/integration circuit 4 detects and integrates the oscillation amplitude of the oscillation circuit 3, but since the time constant of the integration capacitor is made sufficiently larger than the frequency of the ramp wave, the detection/integration circuit 4 detects and integrates the oscillation amplitude of the oscillation circuit 3.・The responsivity of the integrating circuit 4 decreases, and as a result, the DC voltage becomes a solid line instead of the dotted line shown in Fig. 2, and the apparent (f1+
The amplitude level of the frequency similar to f2)/2 is output to the comparator circuit 5.

The reference level of the comparator circuit 4 is set to a predetermined level so that it can be determined whether metal has approached the proximity switch 1, so that when metal approaches, the output circuit outputs the detection result based on the DC voltage level. Output to 6.

In other words, the original oscillation frequency is directly frequency modulated and its amplitude level is detected (in this case, f1 to f
2) By making the response of the detection/integration circuit 4 smaller than the frequency of the ramp waveform, a DC voltage corresponding to (f1 to f2)/2 can be obtained, and the effect of distance due to frequency fluctuation can be ignored. At the same time, mutual interference is prevented.

Therefore, for example, even if several proximity switches 1 of the present invention are arranged adjacently, the direct frequency modulation at different frequencies may occur due to manufacturing errors, operation timings, etc. of the respective varicap diodes or ramp waveform oscillation circuits. Therefore, the frequencies do not change over time and interfere with each other, and the shapes can be made the same. Note that although a ramp waveform is used in the above embodiment, any signal whose amplitude changes with time may be used.

[0032]

As described above, according to the present invention, the first frequency oscillated from the oscillation circuit can be changed to the second frequency whose amplitude changes with time and which is lower than the first frequency. Based on this, by directly frequency modulating the oscillation frequency, for example, if the proximity switches of the present invention are used adjacently, the oscillation frequencies will fluctuate over time, and the time during which the oscillation frequencies are close to each other will be shortened. This has the effect of preventing mutual interference.

Furthermore, by detecting the amplitude of the oscillation frequency that has been directly frequency modulated, and then responding at a frequency lower than the second frequency to produce an integrated output, it is possible to vary the amplitude by varying the oscillation frequency. The effect is that a detection level corresponding to a fixed detection distance can be obtained.

Furthermore, since mutual interference is prevented with a simple circuit configuration, it is possible to use proximity switches with the same shape.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a schematic configuration of a proximity switch of the present invention.

[Fig. 2] Timing chart explaining the operation of the present invention

[Figure 3
] Diagram showing the relationship between oscillation frequency and amplitude level

[Explanation of symbols]

1 Proximity switch 2 Detection section 3 Oscillation circuit 4 Detection/integration circuit 5 Comparison circuit 6 Output circuit 7 Initial reset circuit 10 Direct frequency modulation section D Varicap diode

Claims (1)

[Claims] 1. A detection unit comprising a first oscillation circuit including at least a detection coil; when power is turned on, the oscillation circuit is caused to oscillate at a predetermined first frequency, and the amplitude of the oscillation frequency is Based on the comparison result of a comparison circuit that compares the integrated DC voltage and a reference level, a proximity switch that detects the approach of a detected object operates simultaneously with the oscillation, and changes amplitude with time, and A second oscillation circuit outputs a signal of a second frequency lower than the first frequency, and the first frequency of the detection section is directly set to the frequency based on a change in the amplitude of the signal from the second oscillation circuit. direct frequency modulation means that modulates the oscillation frequency to fluctuate within a predetermined range; and detects the amplitude of the oscillation frequency directly frequency modulated from the detection section, and integrates the response at a frequency lower than the second frequency. A proximity switch comprising a detection/integration circuit that outputs a DC voltage to the comparison circuit.