JPH02224523A - High frequency oscillation type proximity switch - Google Patents

Abstract

PURPOSE:To make the conductance of an oscillating circuit stable by giving a voltage signal to a voltage controlled varactor diode circuit so as to vary the capacitance of a varactor diode via an F/V converter when the oscillated frequency is changed because of the proximity of a surrounding metal. CONSTITUTION:The inductance of a coil L is changed due to the effect of the presence of a surrounding metal or the like and the oscillating frequency of an oscillation circuit 1 is changed. The change is given to a voltage controlled varactor diode circuit 22 as a change in a voltage signal by an F/V converter 21. Then the capacitance of the varactor diode 25 is changed to suppress the fluctuation in the oscillating frequency. Thus, the fluctuation of the oscillating frequency is suppressed and the conductance of the circuit 1 is made stable. When the tip of the proximity switch is used while being imbedded in the mount part, the effect of the surrounding metal is not almost received. Thus, an object is sensed with high sensitivity.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a high frequency oscillation type proximity switch that reduces the influence of surrounding metal.

[Conventional technology]

FIG. 6 is a block diagram showing an example of a conventional high frequency oscillation type proximity switch. In this proximity switch 100, a negative resistance type oscillation circuit 102 is connected to a resonant circuit 101 consisting of an LC, and the oscillation output thereof is given to a detection circuit 103. The detection circuit 103 outputs a signal corresponding to the oscillation amplitude, and its output is given to a comparison circuit 104'. The comparison circuit 104 discriminates the input signal based on a predetermined darkness value, outputs an object detection signal, and outputs it to the outside via the output circuit 105.

Now, as one type of conventional high-frequency oscillation type proximity switch, there is one that has a cylindrical shape and has mounting screws around it, as shown in Fig. 7 (81, (bl).When installing such a proximity switch, As shown in FIG. 7, the proximity switch 100 is inserted into the opening of the plate 106 without placing the tip end of the proximity switch close to the plate 106. However, when the proximity switch itself is embedded in the surrounding metal 107 as shown in FIG. 7(b), the influence of the surrounding metal increases. A proximity switch is used that measures the influence of surrounding metal by covering the core of the oscillation coil with a brass base metal.

[Problem to be solved by the invention]

However, in such conventional high-frequency oscillation type proximity switches, the influence of surrounding metal appears more greatly in high-sensitivity type proximity switches. The conductance of the resonant circuit 101 with respect to the distance β to the detection object changes in different directions depending on the type of surrounding metal. That is, in a state where the proximity switch is not embedded in the surrounding metal as shown in FIG. 8, if the conductance g of the resonant circuit 101 changes as shown by curve A with respect to the distance l to the object, then as shown in FIG. (If the surrounding metal of bl is iron, it will change as shown in curve B, and if it is aluminum or brass, it will change as shown in curve C. Therefore, simply covering the core in the proximity switch with a brass base metal will not allow such detection. This method has the disadvantage that it is not possible to sufficiently prevent variations in distance.

The present invention has been made in view of the problems of the conventional high frequency oscillation type proximity switch, and its technical object is to reduce the variation in detection distance due to the influence of surrounding metal.

[Means to solve the problem]

The present invention provides a high-frequency oscillator that has an oscillation circuit including a resonant circuit, a detection circuit that detects the output of the oscillation circuit, and a comparison circuit that outputs an object detection signal by comparing the detection output of the detection circuit with a predetermined level. The F/V converter is a type proximity switch, which is connected to the resonant circuit and includes an F/V converter that receives the output of the oscillation circuit and generates a voltage signal corresponding to the oscillation frequency, and a voltage-controlled variable capacitance diode. The present invention is characterized by comprising a voltage-controlled variable capacitance circuit that controls the resonant frequency of the resonant circuit based on the input voltage given by the resonant circuit and stabilizes the resonant frequency.

[Effect]

According to the present invention having such characteristics, a voltage controlled variable capacitance circuit including a variable capacitance diode is connected to the resonant circuit, and the oscillation output of the oscillation circuit is given to the F/V converter. When the oscillation frequency changes due to the influence of surrounding metal, etc., the change is converted into a voltage signal by the F/V converter, and the corresponding voltage signal is given to the voltage controlled variable capacitance circuit. Therefore, the capacitance of the variable capacitance diode changes, working to suppress changes in the oscillation frequency. By suppressing fluctuations in the oscillation frequency, the conductance of the resonant circuit is stabilized.

〔Effect of the invention〕

Therefore, according to the present invention, fluctuations in the oscillation frequency are reduced regardless of the influence of surrounding metals, and the conductance of the resonant circuit is stabilized, so the influence of surrounding metals can be significantly reduced.Therefore, the present invention The high-frequency oscillation type proximity switch of 2009 was applied to a cylindrical proximity switch with a mounting screw, and even when the tip of the proximity switch is embedded in the mounting part, it has high sensitivity and is almost unaffected by surrounding metal. In addition, since the distance change rate of conductance increases, the detection distance can be extended over a longer distance, and temperature characteristics can also be stabilized by suppressing fluctuations due to conductance frequency. This effect can be obtained.

[Explanation of Examples]

FIG. 1 is a circuit diagram of the main parts of a high frequency oscillation type proximity switch according to an embodiment of the present invention. In this oscillation circuit, a negative resistance type oscillation circuit 2 is connected to a resonance circuit 1 consisting of a coil L and a capacitor C1. The negative resistance type oscillation circuit 2 has a current mirror circuit 5 consisting of transistors 3 and 4, and the collector of the transistor 3 is connected to the resonant circuit 1.

Emitter resistors R1 and R2, each having the same resistance value, are connected to the power source terminal of the transistor 3.4. Further, a resistor R3, a diode 6.7, and a resistor R4 are further connected in series between the resonant circuit 1 and the power supply terminal. The collector of transistor 4 is connected to the base of transistor 3.4, and is also grounded via transistor 8 and resistor R5.

A transistor 90 is connected to the connection point between the resistor R3 and the diode 6.
The base is connected. Transistor 9 is an emitter follower type transistor and has an emitter resistor R6, and its output is given to the base of transistor 8. The oscillation output obtained from the emitter of the transistor 9 is detected by the transistor 11 connected as an emitter follower of the detection circuit 10, and the output thereof is given to the comparison circuit 12. A predetermined threshold level is set in the comparator circuit 12, and when the threshold level is exceeded, an object detection signal is outputted from the output circuit 13 to the outside.

In the present invention, an F/V converter 21 is connected to one end of the resonant circuit 1 to convert the oscillation frequency into a voltage signal.

The F/V converter 21 converts the oscillation output into a voltage signal corresponding to the oscillation frequency, and the output is given to the voltage controlled variable capacitance circuit 22. Voltage control variable capacitance circuit 2
2 has a voltage follower 23 as shown, the output of which is given to a variable capacitance diode 25 via a choke coil 24. The variable capacitance diode 25 is connected in parallel to the resonant circuit 1 via the capacitor C3.

Next, the operation of this embodiment will be explained. Figure 2 shows F/V
3 is a diagram showing the relationship between the human power frequency and the output voltage of the converter 21. FIG. As shown in this figure, the output voltage of the F/V converter 21 decreases as the input frequency increases. This voltage change is transmitted to the voltage controlled variable capacitance diode 2 via the voltage follower 23 and the choke coil 24.
given to 5.

FIG. 3 shows the voltage ■ applied to the variable capacitance diode 25.

FIG. 4 is a diagram showing a change in the resonance frequency with respect to a capacitance change in the junction capacitance CX. In this figure, the curve L0 is L when it is not affected by surrounding metal.

is a graph showing frequency changes with respect to junction capacitance Cx when surrounding metal exists and the inductance of the coil L changes. Now, in these figures, the junction capacitance of the variable capacitance diode 25 in a state where there is no surrounding metal is CXO, and in that state, the oscillation circuit 1 oscillates at a frequency f0 as shown in FIGS. 2 to 4.

In this state, the output of the F/V converter 21 is assumed to be V, and the voltage applied to the variable capacitance diode 25 is assumed to be VOO.

Now, when this proximity switch is embedded in the mounting metal as shown in Figure 7, and the inductance of the coil L changes from Lo to Changes to fl. Then, since the input frequency of the F/V converter 21 shown in FIG. 2 changes from fI to fI, its output voltage also changes from vo to vI. Then, by negative feedback, the voltage follower 23. The terminal voltage applied to the variable capacitance diode 25 via the choke coil 24 is also V. It is assumed that the junction capacitance of the variable capacitance diode 25 changes from CXO to CXI. Therefore, if the junction capacitance is C□ on the curve in Fig. 4, the frequency f,' will be lower than the original oscillation frequency f0, but
In reality, due to negative feedback, the junction capacitance is CXZ
, the oscillation frequency is a value f2 slightly higher than the original frequency f0
is the oscillation frequency. Since the frequency change of the resonant circuit is suppressed in this way, the accompanying change in the conductance g of the resonant circuit 1 is also reduced. Therefore, objects can be detected with almost no reduction in object detection sensitivity, detection distance, etc. That is, the change in inductance ΔL=L+
If no feedback is applied to Lo, the oscillation frequency is Δ
The frequency fluctuates by f+=f+fo, but by applying feedback, the frequency fluctuates only by Δf2=rz-fO, and the frequency fluctuation can be suppressed. Here, the frequency variation will be explained below.

(1) When there is no feedback, the resonant frequency ω is expressed by the following formula.

ω2= ・−・−・(1)
”L (C+ +Cxa) Here, dω/dL is determined.

d L L" (C+ + Cxo) Now, if dω/dL is when the inductance of the coil L is Lo, then K1 is expressed by the following equation.

Ru.

(2) Next, when there is feedback, using a linear approximation based on the relationships shown in FIGS. 2 and 3 above, the junction capacitance CX of the variable capacitance diode 25 is expressed by the following equation using the constant Q. .

Cx cow Pω-Q -... (3) In this case, the resonant frequency is expressed by the following equation.

L (C1+CX) L (CI+
Pω-Q) Here, dω/dL is determined.

dω 11 dL K23Pω" +2 (ct-Q)ω・-・
−(4) Here, when the inductance of the coil L is Lo, dω/
If dL is set to 2, K2 is expressed by the following formula.
) Therefore, the ratio between equation (2) and equation (5) is expressed by the following equation.

K, 1 Cxo<CI + CXO<<Q, then Kz
If 2Ct K, Q, that is, the constant Q is larger than 01, the frequency change with respect to the change in coil inductance is a sufficiently small value.

Next, a second embodiment of the present invention will be described with reference to FIG. In this embodiment, the same parts as in FIG. 1 are given the same reference numerals, and detailed explanation thereof will be omitted. In this embodiment, an F/■ converter 21 is connected to one end of the resonant circuit 1, and its voltage output is given to a voltage controlled variable capacitance circuit 31.

The voltage controlled variable capacitance circuit 31 has F/V as in the first embodiment.
a voltage follower 32 to which the output of the converter 21 is applied;
The output is given to a current mirror circuit 35 consisting of transistors 33 and 34 via resistors R9 and RIO. The collector of the transistor 33 is the constant current circuit 3
6, and the collector of the transistor 34 is connected to one end of the resonant circuit 1. Now, an operational amplifier 37 is connected to one end of the resonant circuit 1 via a DC blocking capacitor C3. The operational amplifier 37 attenuates the AC output of the resonant circuit 1 to 1/n, adds the DC component of the DC power supply 38, and provides the result to the inverting amplifier 39.

The inverting amplifier 39 inverts this output and supplies it to the variable capacitance diode 40. The collector of the transistor 33 described above is connected to the other end of the variable capacitance diode 40.

Now, a negative resistance type oscillation circuit 2 similar to that of the first embodiment is connected to this resonant circuit 1, and its oscillation output is detected by a detection circuit 10. Similar to the first embodiment described above, the detection output is compared with a predetermined dark value level by the comparator circuit 12 and outputted to the outside via the output circuit 13. In this embodiment, when the oscillation circuit 2 is operated, the resonance output of the resonance circuit 1 is 1 /
n, and is applied to the variable capacitance diode 40 in the same phase as the resonant circuit 1. At this time, the current flowing through the variable capacitance diode 40 is i, and the current flowing through the constant current circuit 36 is ■. Then, the transistor 3 of the current mirror circuit 35
The current flowing through 3 is ■. -1. Current mirror circuit 35
If the current amplification factor of is m, the current flowing into the resonant circuit l from the transistor 34 is m(1(,-i). Here, the output voltage of the operational amplifier 39 is ■, and the capacitance of the variable capacitance diode 40 is Assuming Cx, the collector current of the transistor 34 is given by the following equation, ignoring the DC component.

V m i = −−j ωCx Therefore, the impedance on the collector side of the transistor 34 is expressed by the following equation.

n Therefore, this is equivalent to a state in which a variable capacitance element of m CX 6 /n is connected to the resonant circuit l. In this way, in the second embodiment, the variable capacitance diode is not directly connected to the resonant circuit, but is connected to the resonant circuit by expanding its capacitance change. In this case, the voltage change applied to one end of the variable capacitance diode does not become too large, and the optimum operating point can be selected and the change can be fed back using the current mirror circuit, thereby reducing waveform distortion. Can be done.

The operation of this embodiment is the same as that of the first embodiment described above, except that the junction capacitance is multiplied by m/n. In this case as well, it is possible to reduce the influence of the surrounding metal by the amount by which the capacitance change of the variable capacitance diode is increased.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of a high frequency oscillation type proximity switch according to an embodiment of the present invention, Figure 2 is a graph showing the characteristics of an F/V converter according to this embodiment, and Figure 3 is a diagram of a variable capacitance diode. A graph showing the characteristics, FIG. 4 is a graph showing the relationship between capacitance change of a variable capacitance diode and oscillation frequency, and FIG. 5 is a circuit diagram of a high frequency oscillation type proximity switch according to a second embodiment of the present invention.
Fig. 6 is a block diagram showing a conventional high-frequency oscillation type proximity switch, Fig. 7 (a), Fig. 7 (bl) is a diagram showing its appearance and usage, and Fig. 8 is a block diagram showing the conventional high-frequency oscillation type proximity switch. It is a graph showing a change in conductance with respect to distance. 1--Resonance circuit 2 10--Detection circuit F/V converter variable capacitance circuit 25° de-- Negative Resistance type oscillator circuit 12 - Comparison circuit 21 22.31 - Voltage controllable 40 - Variable capacitance diode Patent applicant Tateishi Electric Co., Ltd. agent Patent attorney Okamoto Kan Ki (1 other person) Figure (a) Figure (b)

Claims (1)

[Claims] (1) It has an oscillation circuit including a resonant circuit, a detection circuit that detects the output of the oscillation circuit, and a comparison circuit that outputs an object detection signal by comparing the detection output of the detection circuit with a predetermined level. The high frequency oscillation type proximity switch includes: an F/V converter to which the output of the oscillation circuit is applied and generates a voltage signal corresponding to the oscillation frequency; and a voltage-controlled variable capacitance diode connected to the resonant circuit;
A high frequency oscillation type proximity switch comprising: a voltage controlled variable capacitance circuit that controls the resonant frequency of the resonant circuit based on the input voltage given from the /V converter and stabilizes the resonant frequency.