JPH0746112A - Proximity switch - Google Patents

Abstract

PURPOSE:To simplify the installation work at the time of arranging a proximity switch adjacently to another and to reduce the cost. CONSTITUTION:An oscillation circuit 11 is so constituted that the oscillation frequency can be varied by switching of an auxiliary capacitor 15, and a beat detecting circuit 21 is provided which compares the oscillation amplitude of the oscillation circuit 11 with a prescribed interference detection level higher than its saturation level. If the mutual interference with another adjacently arranged proximity switch is brought about, the oscillation amplitude of the oscillation circuit 11 is periodically varied by the beat phenomenon to exceed the interference detection level, and therefore, an interference detection signal Si is outputted to turn on a switch 16. Thus, the oscillation frequency of the oscillation circuit 11 is changed to a different value to suppress the 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 that copes with mutual interference when a plurality of adjacent switches are arranged.

[0002]

2. Description of the Related Art Generally, a high-frequency oscillation type proximity switch supplies a high-frequency current to a detection coil by an oscillation circuit, integrates the output of the oscillation circuit, and compares the integrated output with a predetermined detection level in a discrimination circuit. It is a composition. When there is no object near the detection coil, the oscillation circuit oscillates at a certain saturation level, and when a metal object approaches it, the oscillation amplitude decreases and the integrated output decreases, so this is detected by the discrimination circuit. To be done.

However, when a plurality of proximity switches of this type are arranged adjacent to each other, the high frequency magnetic fields generated by the respective detection coils may interfere with each other to cause a beat phenomenon. Figure 6 (A) shows the stable oscillation waveform when placed alone.
When the beat phenomenon occurs, the oscillation amplitude periodically changes as shown in FIG. In this state, when the detected object approaches and the oscillation amplitude becomes small as a whole, the integrated output thereof alternately crosses the ON reference level Von and the OFF reference level Voff in the discrimination circuit as shown in FIG. As a result, the output signal of the discrimination circuit causes an erroneous operation in which it is repeatedly turned on and off as shown in FIG.

In order to prevent such malfunctions, a plurality of types are manufactured with a combination of oscillation frequencies that do not cause mutual interference, and the frequency types are appropriately selected and installed at the time of adjacent arrangement. Or, for example, the actual Kaihei 3
As disclosed in JP-A-58040, a configuration is provided in which an oscillation frequency switching terminal is provided in an oscillation circuit, and when a malfunction occurs due to an adjacent arrangement, the oscillation frequency is switched by changing the connection state of the switching terminal. It is provided.

[0005]

However, if a product of a type having a different oscillation frequency is manufactured to cope with the problem, the manufacturing cost and the management cost increase. On the other hand, in the case of switching the oscillation frequency by changing the connection of the switching terminal, it is necessary to perform the frequency setting work one by one so that mutual interference does not occur at every installation,
Installation work is very troublesome. Further, when changing the installation state of the proximity switch, it is necessary to check the frequencies of the other proximity switches and set the frequency again so as not to interfere with this, which is very time-consuming.

The present invention has been made in view of the above circumstances, and therefore an object thereof is to manufacture at low cost, and
An object of the present invention is to provide a proximity switch that can be easily installed.

[0007]

A proximity switch according to the present invention comprises an oscillating circuit for flowing a high frequency current in a detecting coil, and detects the approach of an object to the detecting coil based on a change in the oscillation amplitude of the oscillating circuit. In addition to configuring the oscillation circuit as an oscillation frequency variable type, a beat detection circuit that detects an interference beat with another proximity switch based on the oscillation amplitude of the oscillation circuit is provided, and the beat detection circuit detects the interference beat. In this case, the oscillation frequency of the oscillation circuit is made different (the invention of claim 1).

An oscillation frequency stabilizing section may be provided in the oscillation circuit, and a high frequency current having a frequency stabilized by the oscillation frequency stabilizing section may be made to flow through the detection coil (the invention of claim 2). .

[0009]

When there is no mutual interference with other proximity switches, the oscillation amplitude of the oscillation circuit is constant. However, when mutual interference with other adjacent switches arranged adjacently occurs, the beat amplitude causes the oscillation amplitude of the oscillation circuit to periodically change. Therefore, the beat detection circuit detects the interference beat due to the change in the oscillation amplitude, and the oscillation frequency of the oscillation circuit is changed to a different value. As a result, the mutual interference state disappears, and the malfunction is automatically suppressed.

According to a second aspect of the present invention, in which the oscillation frequency stabilizing portion is provided in the oscillation circuit, the frequency of the oscillation circuit does not change even when the object to be detected approaches, and not only high permeability materials such as iron,
Mutual interference can be suppressed stably even with non-magnetic materials such as copper and aluminum.

[0011]

As described above, according to the proximity switch of the present invention, it is possible to detect the interference state, switch the oscillation frequency, and automatically cancel the mutual interference with other proximity switches. Therefore, it is not necessary to check the frequency of another proximity switch and set the frequency each time the proximity switch is installed, and the installation work of the proximity switch is simplified. Of course, since it is not necessary to manufacture multiple types having different oscillation frequencies, it is possible to mass-produce and to reduce the manufacturing cost. Further, the invention of claim 2 has an effect that it is possible to stably cope with mutual interference regardless of the material.

[0012]

<First Embodiment> FIG. 1 shows a first embodiment of the present invention. In this embodiment, the oscillator circuit 11 has a configuration in which a detection coil 12 and a capacitor 13 are connected in parallel and these are connected to an amplifier circuit 14. A sub-capacitor 15 is connected in parallel to the capacitor 13 via a switch 16, and the oscillation circuit 11 is of an oscillation frequency variable type in which the oscillation frequency can be changed by opening / closing the switch 16. Note that as the switch 16, an analog switch, a transistor, a relay, or the like can be used.

The output signal of the amplification circuit 14 is the detection integration circuit 1
Detection integration is performed at 7, and the output is given to the discrimination circuit 18. The discrimination circuit 18 outputs the output circuit 1 when the output from the detection integration circuit 17 falls below a predetermined object detection ON level.
A signal is output to 9 and the object detection signal is output from the output circuit 19 to the output terminal 20. Note that this object detection on-level is set to a value lower than the saturation level of the oscillation amplitude of the oscillation circuit 11 in the steady state, as in the conventional case, and is smaller than the object detection on-level by a predetermined hysteresis width. When the object detection off level is set to a high level and the output from the detection integration circuit 17 rises to exceed the object detection off level, the object detection signal from the output circuit 19 is turned off.

The output signal of the detection integration circuit 17 is also given to the beat detection circuit 21, where the detection integration output from the detection integration circuit 17 is a predetermined interference detection ON level I.
When it exceeds ON, T-type flip-flop 22
And outputs a high level interference detection signal Si. The output terminal of the flip-flop 22 is connected to the switch 16 of the oscillation circuit 11, and the switch 16 is opened when this output terminal is at a low level. In the initial state, the flip-flop 22 has its output terminal at a low level and the switch 16 is open.

Here, the interference detection ON level ION is
As shown in FIG. 2, the oscillation circuit 11 is set to a value higher than the saturation level of the oscillation amplitude in the steady state. Also,
The interference detection off level IOFF is set to a level lower than the interference detection on level ION by a predetermined hysteresis width and higher than the saturation level, and when the output from the detection integration circuit 17 falls below the interference detection off level IOFF. , Drop the interference detection signal Si to a low level. In addition,
The interference detection signal Si from the beat detection circuit 21 is also given to the interference detection output circuit 23, and when an interference beat is detected, a signal can be output from the output terminal 24 to the outside.

Next, the operation of this embodiment will be described. When there is no mutual interference with other proximity switches In the oscillation circuit 11, oscillation is performed at a frequency determined by L of the detection coil 12 and the capacitance C of the capacitor 13, and its oscillation amplitude is constant at the saturation level. (Fig. 6
(See (A)). Here, when the detection object made of metal approaches the detection coil 12, the detection object is magnetically coupled to the detection coil 12 via the high-frequency magnetic field, so that the loss seen from the detection coil 12 side increases. As a result, the oscillation amplitude of the oscillator circuit 11 becomes smaller. For this reason, the signal level from the detection integration circuit 17 also becomes low, and when this falls below the object detection ON level, the discrimination circuit 18 outputs the object detection signal via the output circuit 19. When the object moves away from the detection coil 12, the oscillation amplitude increases and returns to the saturation level, so the signal level from the detection integration circuit 17 also increases, and when the object detection off level is exceeded, the object detection signal is output. Turns off. Since the oscillation amplitude is below the saturation level during such normal operation, the beat detection circuit 21 does not output the interference detection signal Si, and the switch 16 is in the open state.

When Mutual Interference with Other Proximity Switches Occurs When the proximity switches having similar oscillation frequencies are arranged adjacent to each other, the detection coils 12 of the proximity switches are magnetically coupled to each other, so that mutual interference occurs. To do. As a result, FIG.
As shown in (B), a beat phenomenon occurs in which the oscillation amplitude of the oscillation circuit 11 periodically changes up and down across the saturation level, and the output signal of the detection integrator circuit 17 has a periodical pattern as shown in FIG. It will change up and down. However, in the present embodiment, the beat detection circuit 21 is provided, and when the output level of the detection integration circuit 17 exceeds the interference detection ON level ION set higher than the saturation level of the oscillation amplitude in the steady state, the interference detection signal is detected. Si is output. Therefore, when the beat phenomenon occurs, the output level of the detection integrator circuit 17 becomes higher than the saturation level of the oscillation amplitude in the steady state, and when the beat level exceeds the interference detection ON level ION, the interference detection signal Si outputs the flip-flop 22. Is output (see FIG. 2A). As a result, the output of the flip-flop 22 is inverted from low level to high level, the switch 16 is turned on, and the sub capacitor 15 is turned on.
Are connected in parallel to the capacitor 13. Therefore, the oscillation frequency of the oscillation circuit 11 is switched to a low frequency, and
As shown by the solid line in (A), the beat phenomenon subsides, mutual interference is eliminated, and normal operation is resumed.

After that, assuming that the adjacent proximity switch is replaced with one of another frequency type and a beat phenomenon occurs again due to the mutual interference, the beat detection circuit 21 as shown in FIG. 2B. Since the interference detection signal Si is output from the output, the output of the flip-flop 22 is inverted to the low level, the switch 16 is opened, and the oscillation frequency is switched to the original high value. As a result, mutual interference is eliminated, the beat phenomenon is subsided, and normal operation is restored.

Generally, in a high-frequency oscillation type proximity switch, when an object approaches the detection coil, not only the oscillation amplitude decreases but also L changes, so the oscillation frequency may change. However, in an object to be detected made of magnetic material such as iron, there is a frequency range in which L tends to increase and L tends to decrease due to the contribution of eddy current loss, and L hardly changes. Setting the oscillation frequency in the frequency range prevents the oscillation frequency from changing due to the approach of the object to be detected. Therefore, if the interference beat is detected and the oscillation frequency of the oscillation circuit 11 is switched, the oscillation frequency changes to a value close to the original frequency due to the approach of the detected object, and mutual interference occurs again. This can be reliably prevented.

As described above, according to the present embodiment, when mutual interference with another proximity switch occurs, an interference beat is detected and the oscillation frequency of the oscillation circuit 11 is automatically changed. Mutual interference can be immediately eliminated. This eliminates the need to check the frequency of another proximity switch and set the frequency each time the proximity switch is installed, and the installation work when a plurality of proximity switches are adjacently arranged becomes extremely simple. In addition, since there is no need to manufacture multiple types of different types having different oscillation frequencies, mass production is possible and the manufacturing cost can be significantly reduced.

<Second Embodiment> FIG. 3 shows a second embodiment of the present invention. In the second embodiment, the oscillation frequency of the oscillation circuit 11 can be switched to four types. For that purpose, a counter 31 is provided in place of the flip-flop 22 of the first embodiment, and the interference detection signal Si is counted by the counter 31. Each time it is input to 31, the output terminals Q1 to Q3 are inverted to a high level so that the switches 35 to 37 connected in series to the sub capacitors 32 to 34 are inverted from the off state to the on state. Other points are the same as in the first embodiment,
The same parts are designated by the same reference numerals, and detailed description thereof will be omitted. With this configuration, since the oscillation frequency can be switched in various ways, mutual interference can be surely prevented with respect to a wider range of types of proximity switches.

<Third Embodiment> FIG. 4 shows a third embodiment of the present invention. In the third embodiment, a resonance coil 43 different from the detection coil 42 is provided in the oscillation circuit 41, and a resonance circuit of the resonance coil 43 and the capacitor 44 constitutes an oscillation frequency stabilizing section 47, which constitutes the oscillation frequency. Is stabilized. The resonance coil 43 can be magnetically closed so as not to couple with the object to be detected, and the oscillation frequency does not change even when the object to be detected approaches the detection coil 42. Also in this embodiment, the sub-capacitor 45 is connected in parallel to the capacitor 44 through the switch 46,
The output of the flip-flop 22 opens and closes the switch 46. Others are the same as those in the first embodiment.

With this configuration, the oscillation frequency does not change even when the object to be detected approaches, so that reliable interference can be achieved not only with magnetic materials such as iron but also with objects made of non-magnetic materials such as aluminum and copper. Preventive action is possible.

<Fourth Embodiment> FIG. 5 shows a fourth embodiment of the present invention, in which an oscillation frequency stabilizing unit 56 utilizing crystal oscillators 51 and 52 is configured to stabilize the oscillation frequency. It is a thing. The two crystal oscillators 51 and 52 are connected via switches 53 and 54, and the crystal oscillators 51 and 52 are selectively switched by the output of the counter 55. With this configuration, the same effect as that of the third embodiment can be obtained.

The present invention is not limited to the embodiments described above and shown in the drawings. For example, the following modifications are possible, and various modifications can be carried out without departing from the scope of the invention.

(A) In each of the above embodiments, the interference detection signal Si from the beat detection circuit is output to the outside through the interference detection output circuit 23. However, this is not essential, and the oscillation circuit oscillates only. It is sufficient to change the frequency. In addition, for example, an indicator lamp may be turned on at the same time that the oscillation frequency of the oscillation circuit is changed, and this can notify the user of the occurrence of mutual interference. Moreover,
When the interference detection signal Si is output to the outside or the indicator lamp is turned on, an off-delay timer may be provided in order to make the pulse width of the interference detection signal Si sufficiently wide.

(B) In order to make the oscillation frequencies different, it is not limited to switching the capacitor to change C as in the above embodiment, but L may be changed by switching the coil.
Further, when switching the capacitors or the coils, a configuration may be adopted in which an effective capacitor or coil is added in response to the interference detection signal, or conversely, the configuration may be reduced. Further, a variable capacitor whose capacitance is changed according to an applied voltage may be used as the capacitor to make the oscillation frequency different.

(C) In order to detect the interference beat, the oscillation amplitude of the oscillation circuit is not necessarily compared with the interference detection level higher than the saturation level, but the oscillation amplitude is compared with the interference detection level lower than the saturation level. However, when both levels cross each other alternately with the periodicity peculiar to the interference beat, it may be determined that the interference beat is generated, that is, based on the mutual interference with other proximity switches. It is only necessary to detect the interference beat.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a waveform diagram showing a state in which an interference beat is detected and the oscillation frequency is switched.

FIG. 3 is a block diagram showing a second embodiment of the present invention.

FIG. 4 is a block diagram showing a third embodiment.

FIG. 5 is a block diagram showing a fourth embodiment.

FIG. 6 is a waveform diagram illustrating mutual interference caused by proximity switches.

[Explanation of symbols]

 11 ... Oscillation circuit 12 ... Detection coil 13 ... Capacitor 17 ... Detection integration circuit 18 ... Discrimination circuit 21 ... Beat detection circuit 45, 56 ... Oscillation frequency stabilizing unit

Claims (2)

[Claims] 1. An oscillation frequency variable type detector for detecting the approach of an object to the detection coil based on a change in an oscillation amplitude of the oscillation circuit, the oscillation circuit including a high frequency current flowing through the detection coil. And a beat detection circuit for detecting an interference beat with another proximity switch based on a change in the oscillation amplitude of the oscillation circuit, and when the beat detection circuit detects the interference beat, the oscillation of the oscillation circuit Proximity switch characterized by different frequencies. 2. The proximity switch according to claim 1, wherein the oscillating circuit includes an oscillating frequency stabilizing section, and a high frequency current having a frequency corresponding to the oscillating frequency stabilizing section is passed through the detection coil.