JPH07283712A - Proximity switch - Google Patents

Abstract

PURPOSE:To detect only a nonmagnetic specimen with a long detection distance. CONSTITUTION:A proximity switch consists of a 1st oscillation circuit 1 which has a resonance circuit 13 including a detection coil 11 and a 2nd oscillation circuit 7 which has a connection coil 71 connected to the coil 11 and sets its oscillation frequency at a level slightly higher than the resonance frequency of the circuit 13, and a detector means 8 which detects the humming that is superposed on the oscillation output of the circuit 1. When a specimen is put close to the switch, the resonance frequency of the circuit 13 increases up to a level approximate to the oscillation frequency of the circuit 7. Thus the specimen is detected from the humming superposed on the circuit 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high frequency oscillation type proximity switch which is widely used for detecting an object in a production line or the like.

[0002]

2. Description of the Related Art FIG. 5 is a circuit diagram showing a conventional example of this type of high frequency oscillation type proximity switch. In FIG. 5, this proximity switch is represented by the detection coil 11 and the detection coil 11.
An oscillation circuit 1 having a resonance circuit 13 including a resonance capacitor 12 connected in parallel with the detection circuit 2, a detection circuit 2, an integration circuit 3, a comparator 4 and an output circuit 5 sequentially connected to the oscillation circuit 1. The circuit 2, the integrating circuit 3 and the comparator 4 constitute the amplitude detecting means 9.

The operation of this proximity switch will be described with reference to the time chart shown in FIG. In FIG. 6, time t
_When the subject is not close to the detection coil 11 at ₀ ,
The impedance of the resonance circuit 13 has a high value, and the oscillation circuit 1 outputs the oscillation output a having a large amplitude corresponding to the impedance value of the resonance circuit 13 at the oscillation frequency determined by the resonance frequency of the resonance circuit 13. The oscillation output a is detected by the detection circuit 2, smoothed by the integration circuit 3, and the integration circuit 3 outputs an output b proportional to the amplitude of the oscillation output a. This output b is compared by the comparator 4 with a preset threshold value h. In this case, since this output b is higher than the threshold value h, the output from the comparator 4, that is, the amplitude detecting means 9 is output. The signal c is turned off. Next, when the subject approaches at time t ₁ , the impedance of the resonance circuit 13 decreases, so the amplitude of the oscillation output a of the oscillation circuit 1 decreases, and the output b of the integrating circuit 3 also decreases accordingly. Then, at time t ₂ , this output b
Is reduced to the threshold value h of the comparator 4 or less, the output signal c from the comparator 4, that is, the amplitude detection means 9 is turned on, and the detection signal d for detecting the approach of the subject from the terminal P is output through the output circuit 5. Is output.

[0004]

In the proximity switch described above, there is no problem when the subject is a magnetic substance, but when the subject is a non-magnetic substance, the detection distance becomes short and in some cases it cannot be detected. That is, FIG. 7 shows an example of measuring the impedance of the resonance circuit with respect to the distance between the detection coil and the object when the object is a magnetic material and a non-magnetic material, and the impedance of the resonance circuit is when there is no object. The impedance Z ₀ of the magnetic substance decreases rapidly when the subject of the magnetic substance approaches, but decreases relatively slowly when the subject of the non-magnetic substance approaches. The amplitude of the oscillation output of the oscillation circuit corresponds to the impedance value of the resonance circuit. If the amplitude of this oscillation output drops to a level corresponding to the threshold value of the comparator, a signal for detecting the approach of the subject is output. Therefore, the detection distance in the case of a non-magnetic substance is shorter than the detection distance in the case of a magnetic substance, and in some cases it cannot be detected.

Further, in a production line or the like, there are cases where it is desired to detect only a non-magnetic substance from mixed magnetic substance and non-magnetic substance. An object of the present invention is to solve the above-mentioned problems and to provide a proximity switch that detects only a non-magnetic object with a long detection distance, like a magnetic object.

[0006]

In order to achieve the above-mentioned object, the invention according to claim 1 is electromagnetically coupled to a first oscillation circuit having a resonance circuit including a detection coil, and the detection coil. A beat detecting means for detecting a beat superposed on the oscillation output of the second oscillation circuit, which has a coupling coil and whose oscillation frequency is set slightly higher than the resonance frequency of the resonance circuit, and the oscillation output of the first oscillation circuit. To consist of.

The invention according to claim 2 has a first oscillation circuit having a resonance circuit including a detection coil, and a coupling coil electromagnetically coupled to the detection coil, the oscillation frequency of which is the resonance circuit. Approaching the resonant frequency of the first
A second oscillating circuit set so that the beat is superimposed on the oscillating output of the oscillating circuit, and beat detecting means for detecting the beat to be superimposed on the first oscillating output.

Furthermore, in these inventions, the beat detecting means changes from the change of the amplitude of the oscillation output of the first oscillation circuit,
It is convenient to detect the beat that is superimposed on the oscillation output.

[0009]

The resonance frequency of the resonance circuit including the detection coil is shown in FIG.
As shown in, the frequency of the magnetic body is almost unchanged with respect to the resonance frequency F ₀ in the absence of the body of the object, but when the body of the non-magnetic body approaches, the frequency is not changed. It rapidly rises from a long distance from the subject. Therefore, according to the first aspect of the present invention, by setting the oscillation frequency of the second oscillation circuit slightly higher than the resonance frequency of the resonance circuit, the resonance frequency of the resonance circuit rises due to the approach of the subject, The oscillating frequency of the oscillating circuit approaches and the beat is superimposed on the oscillating output of the first oscillating circuit. By detecting this superposition of beats with the beat detection means, it is possible to detect only the nonmagnetic object under a long detection distance. In the invention according to claim 2, the oscillation frequency of the second oscillation circuit is brought close to the resonance frequency of the resonance circuit, and
By setting the beat to be superposed on the oscillation output of the oscillation circuit, the resonance frequency of the resonance circuit rises due to the approach of the subject and deviates from the oscillation frequency of the second oscillation circuit, and the oscillation of the first oscillation circuit Beats superimposed on the output will disappear. By detecting the disappearance of the beat with the beat detection means, it is possible to detect only the non-magnetic object under a long detection distance. Furthermore, in these inventions, when a beat is superimposed on the oscillation output of the first oscillation circuit, its amplitude changes based on this beat, so the beat detection means detects the beat from the change in the amplitude of this oscillation output. be able to.

[0010]

1 is a circuit diagram showing an embodiment of a high frequency oscillation type proximity switch of the present invention. In FIG. 1, this proximity switch is a resonance circuit 1 including a detection coil 11 and a resonance capacitor 12 connected in parallel with the detection coil 11.
A first oscillating circuit 1, a first comparator 6, an integrating circuit 3, a second comparator 4, an output circuit 5, and a first oscillating circuit 1 which are sequentially connected to the oscillating circuit 1.
Coupling coil 7 electromagnetically coupled to the detection coil 11 of
And a second oscillating circuit 7 having 1 and a first comparator 6, an integrating circuit 3, and a second comparator 4 to constitute the detecting means 8.

The operation of this proximity switch will be described with reference to FIGS.
Will be described with reference to. FIG. 2 shows the operation of the proximity switch, and FIGS. 3 and 4 show the resonance frequency of the resonance circuit 13 with respect to the distance between the detection coil 11 and the object when the object is a magnetic body and a non-magnetic body, and FIG. An example of measuring impedance is shown. In FIG. 4 (this figure is the same as FIG. 7), the impedance of the resonance circuit 13 rapidly decreases when the magnetic object is approaching the impedance Z _{0 in the} absence of the object. However, when the subject of non-magnetic material approaches, it decreases relatively slowly. However, as shown in FIG. 3, the resonance frequency of the resonance circuit 13 is almost the same as the resonance frequency F ₀ when there is no subject, but when the subject of a magnetic body approaches, the resonance frequency is almost non-magnetic. When the subject of the body approaches, the distance between the detection coil and the subject is long (see FIG. 5).
The distance from the magnetic substance of the conventional proximity switch shown in FIG.

Here, the oscillation frequency F ₀ of the first oscillation circuit 1 when the object is not close to the oscillation frequency of the second oscillation circuit 7, that is, the resonance frequency F ₀ of this resonance circuit 13.
The oscillation frequency F ₁ is set to be slightly higher. Then, in FIG. 2, at time t ₀ , the nonmagnetic object is the detection coil 1
When it is not close to 1, the impedance of the resonance circuit 13 is at a high value of Z ₀ and its resonance frequency is F ₀ , so the first oscillation circuit 1 outputs an oscillation output with a large amplitude at the oscillation frequency F _0. Output a. This oscillation output a is compared by the first comparator 6 with a threshold value i set in advance in this comparator. In this case, since the amplitude of the oscillation output a is lower than the threshold value i, the first comparator 6 outputs Output of the second comparator 4, that is, the output signal c from the beat detecting means 8 is turned off. Next, at time t ₁ , when the subject of non-magnetic material approaches, the resonance frequency of the resonance circuit 13 rises, and when approaching the oscillation frequency F ₁ of the second oscillation circuit, interference occurs between these frequencies, and oscillation occurs. The beat amplitude is superimposed on the amplitude of the oscillation output a from the circuit 1. Therefore, the amplitude of the oscillation output a exceeds the threshold value i of the first comparator 6, and the first comparator 6 outputs the pulsed output e. This output e is smoothed by the integrating circuit 3, and the integrating circuit 3 outputs an output b proportional to the magnitude of the beat. This output b is compared in the comparator 4 with the threshold value h set in advance in the comparator 4, and when the output b exceeds the threshold value h of the comparator at time t ₂ , the output from the comparator 4, that is, the beat detecting means 8 is detected.
Is turned on, and a detection signal d for detecting the approach of the subject is output from the terminal P through the output circuit 5.

In this proximity switch, when the magnetic object is approaching, the resonance frequency of the resonance circuit 13 hardly changes as shown in FIG. 3, so that the magnetic object is not detected. Therefore, only the non-magnetic object can be detected at a long detection distance (about the detection distance of the magnetic object of the conventional proximity switch shown in FIG. 5). In the above example, the oscillation frequency of the second oscillation circuit 7 is set to a slightly higher oscillation frequency F ₁ than the resonance frequency F ₀ of the resonance circuit 13 of the first oscillation circuit 1 in the absence of the subject, When the resonance frequency of the resonance circuit 13 rises due to the approach of the specimen and approaches the oscillation frequency F ₁ of the second oscillation circuit 7, the beat superimposed on the oscillation output of the first oscillation circuit 1 is detected. However, conversely, the first oscillation circuit 1 when there is no subject
The resonance frequency F ₀ of the resonance circuit 13 is set so that the oscillation frequency of the second oscillation circuit 7 approaches the resonance frequency F ₀ so that the beat is superimposed on the oscillation output of the first oscillation circuit 1. When the subject approaches, the resonance frequency of the resonance circuit 13 rises, and when it departs from the oscillation frequency of the second oscillation circuit 7, it is superimposed on the oscillation output of the first oscillation circuit 1. May be detected to detect the subject.

[0014]

In the proximity switch of the present invention, only the non-magnetic object is detected at a long detection distance, so that only non-magnetic objects can be selected from mixed magnetic and non-magnetic objects in a production line. Can be detected and its effect is great.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a proximity switch of the present invention.

FIG. 2 is a time chart showing the operation of the proximity switch of the present invention shown in FIG.

FIG. 3 is a characteristic diagram showing a change in the resonance frequency of the resonance circuit of the first oscillation circuit when a magnetic or non-magnetic object is brought close to the detection coil in the proximity switch of the present invention shown in FIG.

FIG. 4 is a characteristic diagram showing a change in impedance of a resonance circuit of a first oscillation circuit when a magnetic or non-magnetic object is brought close to a detection coil in the proximity switch of the present invention shown in FIG.

FIG. 5 is a circuit diagram showing an example of a conventional proximity switch.

FIG. 6 is a time chart showing the operation of the conventional proximity switch shown in FIG.

7 is a characteristic diagram showing changes in impedance of a resonance circuit of an oscillation circuit when a magnetic or non-magnetic object is brought close to a detection coil in the conventional proximity switch shown in FIG.

[Explanation of symbols]

 1 1st oscillation circuit 11 detection coil 13 resonance circuit 7 2nd oscillation circuit 71 coupling coil 8 beat detection means

Claims (3)

[Claims] 1. A first oscillation circuit having a resonance circuit including a detection coil, and a coupling coil electromagnetically coupled to the detection coil, the oscillation frequency of which is set slightly higher than the resonance frequency of the resonance circuit. Proximity switch, which comprises a beat-up second oscillating circuit and beat detection means for detecting a beat superimposed on the oscillation output of the first oscillating circuit. 2. A first oscillation circuit having a resonance circuit including a detection coil, and a coupling coil electromagnetically coupled to the detection coil, the oscillation frequency of which approaches the resonance frequency of the resonance circuit. It is characterized by comprising a second oscillating circuit set so that a beat is superimposed on the oscillation output of the first oscillating circuit, and a beat detecting means for detecting a beat superimposed on the first oscillating output. Proximity switch. 3. The proximity switch according to claim 1 or 2, wherein the beat detection means detects a beat superimposed on the oscillation output from a change in the amplitude of the oscillation output of the first oscillation circuit. Proximity switch to.