JPH0522104A - Adjacent switch - Google Patents

Abstract

PURPOSE:To prevent mutual interference in the case of adjacently arranging the plural adjacent switches. CONSTITUTION:A comparator 7 is provided with a threshold value at a level higher than the normal oscillation level of an oscillation circuit 2. Since the threshold value exceeds this level with a beat phenomenon when there is the mutual interference, the mutual interference is discriminated according to an output from the comparator 7. The oscillation frequency of the oscillation circuit 2 is changed by a frequency control circuit 11 through a control circuit 10, and the frequency is switched to a frequency having no mutual interference.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a proximity switch having a function of detecting mutual interference when the proximity switches are arranged in parallel.

[0002]

2. Description of the Related Art A high frequency oscillating proximity switch oscillates a high frequency of a constant frequency from an oscillating coil. When a metal object approaches, the oscillating level decreases. Therefore, an object is detected based on the level change. There is. However, when a plurality of proximity switches are arranged in parallel, magnetic fields generated by the oscillating coils are interlinked with each other to cause a beat phenomenon or the like, which may cause false detection of an object. Also, chattering may occur when the signal is inverted.

[0003]

Therefore, it is conceivable to make the frequency of the detection switch different in order to prevent mutual interference. In addition, different frequency type proximity switches having different oscillation frequencies may be prepared in order to reduce the mutual interference distance. However, this proximity switch also has variations in frequency, and a plurality of proximity switches cannot be attached in close contact with each other. Further, there is a drawback in that the margin for mutual interference is unknown even when the device is mounted within the specified distance.

The present invention has been made in view of such conventional problems, and it is a technical object to detect the occurrence of mutual interference and display it, and to change the oscillation frequency. .

[0005]

According to a first aspect of the present invention, there is provided a proximity switch having an oscillating circuit and a first comparing means for detecting a decrease in output level of the oscillating circuit. Second comparing means having a threshold level exceeding an output level in a state where they are not close to each other, and outputting a warning of mutual interference when the output of the oscillation circuit exceeds the threshold level. Frequency adjusting means for changing the oscillation output of the oscillation circuit when the comparison signal is obtained.

According to a second aspect of the present invention, there is provided a proximity switch having an oscillating circuit and a first comparing means for detecting a decrease in the output level of the oscillating circuit. Second comparing means having a threshold level exceeding the level and outputting a warning of mutual interference when the output of the oscillation circuit exceeds the threshold level.
The display means is operated by the output of the comparing means and the frequency adjusting means for changing the oscillation output of the oscillation circuit.

[0007]

According to the invention of claim 1 of the present application having such a feature, when another proximity switch approaches the proximity switch, a beat phenomenon occurs if the difference in oscillation frequency is small. Therefore, the amplitude of the oscillator circuit varies from the steady state depending on the beat frequency. Therefore, the presence or absence of the beat phenomenon is discriminated by the second comparing means having a threshold level higher than that in the steady state, and mutual interference is output by this. Then, if mutual interference is detected, the mutual interference can be prevented by changing the oscillation frequency of the oscillation circuit. In the invention of claim 2 of the present application, mutual interference is notified to the outside and the oscillation frequency of the oscillation circuit can be changed from the outside.

[0008]

1 is a block diagram showing the overall construction of a proximity switch 1A according to a first embodiment of the present invention. In the figure, the proximity switch 1A has an oscillating circuit 2 including an oscillating coil L, and its output is given to a detecting circuit 3. The detection circuit 3 detects this signal, and the integration circuit 4
Is given to the comparator 5 which is the first comparing means. The comparator 5 has a threshold value Vref1 at a level corresponding to an integrated output that is lower than the steady output level of the oscillator circuit 2. If a signal below this level is detected, an object is detected externally via the output circuit 6. It outputs a signal. Further, the oscillator circuit 2 is connected to a comparator 7 which is a second comparing means. The threshold Vref2 of the comparator 7 is set to a level higher than the steady oscillation level of the oscillator circuit 2, and a signal is given to the integrating circuit 8 when the threshold Vref2 exceeds the threshold. The integrating circuit 8 converts this signal into a DC component and gives its output to the comparator 9. A predetermined threshold value Vref3 is set in the comparator 9, and when it exceeds this level, a signal for notifying the mutual interference state is given to the control circuit 10. The control circuit 10 has a random on-delay circuit, and supplies a frequency switching signal to the frequency adjusting circuit 11 until the output from the comparator 3 stops. The frequency adjustment circuit 11 sequentially changes the oscillation frequency of the oscillation circuit 2 in a predetermined direction.

2A and 2B show a frequency adjusting circuit 11
3 is a block diagram showing another example of the oscillator circuit 2. FIG.
In FIG. 2 (a), the oscillation circuit 2 has a resonance circuit formed by the oscillation coil L and the capacitor C0, and in parallel with this, a switch circuit including a capacitor C1, a transistor Q1, ... It is connected. And these transistors Q1
.. Q2 is a switching transistor, and in the ON state, capacitors C1 ... C2 connected in series to the transistor are added as capacitors of the resonance circuit, thereby changing the resonance frequency. A code conversion circuit 110 is connected to the transistors Q1 and Q2 as shown. The code conversion circuit 110 has, for example, a clock oscillator and a binary counter that counts its output, and the parallel outputs of the binary counters are transistor Q respectively.
It is given to Q2. Then, the oscillation is started by the frequency control signal, the transistors Q1 to Q2 are sequentially turned on by the count output, and the oscillation is stopped by the latch signal. In this way, the oscillation frequency of the oscillation circuit 2 changes intermittently at every predetermined time.

FIG. 2B is a diagram showing the configuration of a frequency switching circuit according to another example. In this embodiment, a series connection body of a switch C3 and a variable capacitance diode D1 is connected in parallel to the coil L and the capacitor C0. The voltage adjustment circuit 111 is connected to the variable capacitance diode D1. When the control signal from the control circuit 10 is applied, the voltage adjusting circuit 111 generates a sawtooth signal to gradually increase the terminal voltage of the variable capacitance diode D1. Then, if a holding signal is obtained after a fixed time after the output from the comparator 9 is stopped, the voltage is held to hold the capacitance value of the variable capacitance diode.
In this case, the voltage adjustment circuit 111 continuously changes the DC voltage applied to the variable capacitance diode D1 to change its capacitance and thus the oscillation frequency.

Next, the operation of this embodiment will be described with reference to the time chart of FIG. In this figure, (a)-
(F) shows the waveform of each part of a to f shown in FIG.
If there is no other proximity switch in the vicinity of the proximity switch 1A shown in FIG. 1, the oscillation circuit 2 continues to oscillate steadily as shown between times t _{0 and} t ₁ in FIG. If there is no object in the vicinity, the output of the oscillation circuit 2 is constant, no output is obtained from the comparator 5, and no object detection signal is output.

Now, it is assumed that another high-frequency oscillation type proximity switch 20 approaches the proximity switch 1. Then, the oscillation coil L of the proximity switch 1A receives the induced voltage from the other proximity switch 20 as shown in FIG. 3 (b). Therefore, the oscillation amplitude of the oscillation circuit 2 fluctuates due to the beat phenomenon, as shown after time t _{2 in} FIG.
The cycle of this variation corresponds to the difference between the oscillation frequencies of the proximity switches 1A and 20. If such a beating phenomenon occurs, the output level obtained through the detection circuit 3 and the integrator circuit 4 also periodically drops because there is a moment when the oscillation amplitude drops, and the output level obtained through the comparator 5 is output to the outside. An erroneous object detection signal as shown in 3 (c) is output. On the other hand, the threshold value V
Since there is a time zone that exceeds ref2, the signal as shown in FIG. 3D is periodically obtained from the comparator 7. If this signal is integrated by the integrator circuit 8, FIG.
The signal becomes as shown in (e), and the signal shown in FIG. 3 (f) is obtained by discriminating by the threshold value Vref3. This signal is given to the control circuit 10. The control circuit 10 has a random on-delay timer as described above,
A signal is provided from the output to the frequency adjusting circuit 11, for example, the code converting circuit 110 shown in FIG. Therefore, a binary output is given to the transistors Q1 ... Q2 every cycle, and the oscillating frequency of the oscillating circuit 2 is changed by sequentially conducting these. Then, mutual interference with the adjacent proximity switch is eliminated, and the output of the oscillation circuit 2 becomes the threshold value Vref2.
If the following occurs, no output can be obtained from the comparator 7, so that the oscillation frequency is fixed in that switch state. Therefore, the mutual interference state between the proximity switches can be automatically prevented.

In this embodiment, a control circuit having a random on-delay time is used as the control circuit 10. However, this has a structure in which the proximity switch 20 switches the frequency similarly to the proximity switch 1A of this embodiment. If so, the frequencies are switched at the same timing, and it is possible to prevent mutual interference from being stopped. See also Figure 2
Mutual interference can be similarly prevented even if the oscillation frequency is continuously changed by using the variable capacitance diode D1 as shown in (b).

FIG. 4 is a block diagram showing the configuration of the proximity switch 1B according to the second embodiment of the present invention.
The same parts as those in the embodiment are designated by the same reference numerals and detailed description thereof will be omitted. In this embodiment, the output of the comparator 9 is the display 12
Given to. The display device 12 displays the mutual interference state on the outside. A frequency adjusting circuit 11 is connected to the proximity switch 1B via an external adjusting terminal 13. The frequency adjustment circuit 11 may be, for example, one shown in FIGS. 2A and 2B, and the variable capacitor oscillation circuit 2
The oscillation frequency of can be directly switched. In this case, the operator can arbitrarily change the oscillation frequency based on the display on the display 12 to change the oscillation frequency until the display 12 is no longer lit, thereby preventing the mutual interference state.

[0015]

As described in detail above, according to the present invention, the second comparison means having the threshold value at a level higher than the oscillation level of the oscillation circuit is used, and the oscillation circuit is automatically generated based on this output. The oscillating frequency is changed or the display is turned on to prompt the adjustment of the oscillating frequency. Therefore, the mutual interference state can be prevented by changing the oscillation frequency, and the effect that the safety during use can be improved is obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a proximity switch according to a first embodiment of the present invention.

2A and 2B are block diagrams showing different examples of the frequency adjusting circuit 11, respectively.

FIG. 3 is a time chart showing the operation of the first embodiment.

FIG. 4 is a block diagram showing a configuration of a proximity switch according to a second embodiment of the present invention.

[Explanation of symbols]

1A, 1B, 20 Proximity switch 2 oscillator circuits 3 Detection circuit 4,8 Integrator circuit 5,7,9 Comparator 10 Control circuit 11 Frequency adjustment circuit 12 Display 13 Frequency adjustment terminal

Claims (2)

[Claims] 1. A proximity switch having an oscillating circuit and a first comparing means for detecting a decrease in the output level of the oscillating circuit, wherein a threshold level exceeding an output level in a state where an object of the oscillating circuit does not approach is set. Second comparison means for outputting a warning of mutual interference when the output of the oscillation circuit exceeds the threshold level and the oscillation when the comparison signal is obtained from the second comparison means. A proximity switch, comprising: a frequency adjusting unit that changes an oscillation output of the circuit. 2. A proximity switch having an oscillating circuit and a first comparing means for detecting a decrease in output level of the oscillating circuit, wherein a threshold level exceeding an output level in a state where an object of the oscillating circuit is not in proximity is set. Second comparing means for outputting a warning of mutual interference when the output of the oscillating circuit exceeds the threshold level, the display means operating by the output of the second comparing means; A proximity switch, comprising: a frequency adjusting unit that changes an oscillation output of the circuit.