JPS62261223A - High frequency oscillation type proximity switch - Google Patents

Abstract

PURPOSE:To improve the resonse speed of the detection of an object by connecting a voltage control resistor circuit as a resistor deciding a conductance of an oscillation circuit, amplifying inversely the detection output of the oscillation circuit, controlling the voltage control resistance circuit so as to keep the amplitude of the oscillation circuit nearly constant thereby detecting the object based on the control signal of the voltage control circuit. CONSTITUTION:When an object approaches a proximity switch, an amplitude VL, of the oscillation circuit is lowered slightly, a detection voltage Vd is lowered attended therewith and a control voltage VG is increased remarkably. Thus, the conductance gx of the oscillation circuit is increased from a conductance gx2 into gx1. The position of the object is unchanged. the amplitude of the oscillation circuit is nearly constant and the control voltage VG of a voltage control circuit 23 is changed corresponding to the distance. That is, when the control voltage VG exceeds the threshold value level Vref of a comaprator 9 decided in response to the output level of the control voltage, an object detection output is outputted from an output circuit 10. Thus, the response speed of the proximity switch depends on the response speed of the voltage control circuit 23 to improve the response speed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a high frequency oscillation type proximity switch with improved response speed for object detection.

[Summary of the invention]

The proximity switch according to the present invention connects a voltage-controlled resistance circuit as a resistor that determines the conductance of the oscillation circuit, inverts and amplifies the detection output of the oscillation circuit, and controls the voltage-controlled resistance circuit, thereby creating an oscillation circuit regardless of the position of the object. The amplitude of the voltage control circuit is kept almost constant, and the object is detected based on the control signal of the voltage control circuit, thereby improving the response speed of object detection.

[Prior art and its problems]

(Prior Art) Conventionally, a high frequency oscillation type proximity switch uses an oscillation circuit as shown in FIG. 9, for example. In this oscillation circuit, the collector of one transistor 1 of a current mirror circuit 3 consisting of transistors 1 and 2 is connected to a resonant circuit consisting of a coil L and a capacitor C1. The emitters of transistors 1 and 2 each have an emitter resistor R1 having the same resistance value.
, R2 are connected to the power supply terminal. Further, a resistor R3, a diode 4.5, and a resistor R4 are further connected to the resonant circuit from the power source end. The collector of transistor 2 is transistor 1
．． 2 and is also connected to the base of transistor 6 and resistor R5.
is grounded through. The base of the transistor 7 is connected to the connection point between the resistor R3 and the diode 4. Transistor 7 is an emitter follower type transistor, and emitter resistor R6 is provided to the base of transistor 6. The oscillation output from the emitter of the transistor 7 is taken out via the emitter follower-connected transistor 8 and rectified, and the output is given to the comparator 9 and the output circuit 10.

In such conventional high frequency oscillation type proximity switches,
The current flowing through the resonant circuit is converted into a voltage by transistor 7, and the emitter follower output is fed back to transistor 6. Therefore, the current flowing through the transistor 6 is positively fed back to the resonant circuit via the current mirror circuit 3 to continue oscillation. As shown in Figure 10.11, when an object approaches the coil of a resonant circuit, the conductance g8 of the resonant circuit increases (ga=gs,), and when the object disappears, the conductance g of the resonant circuit decreases Cg- =g
s□). The change in the conductance g3 of this resonant circuit is determined by the reciprocal of the resistance R5, which is the negative conductance g of the oscillation circuit.
When the conductance becomes larger than xo, the oscillation is stopped, and when the conductance becomes smaller than the conductance gxo, the oscillation starts. Therefore, the proximity of an object can be detected based on the presence or absence of the oscillation.

(Problems to be Solved by the Invention) In such a conventional proximity switch, as shown in FIG. 11, oscillation stops when an object approaches, and oscillation resumes when the object moves away. Therefore, the response speed of the proximity switch can be considered to be the total time of the oscillation start speed and oscillation stop speed. Generally, an oscillation circuit has a very slow oscillation rise (start) speed and a relatively fast oscillation stop speed. Therefore, there is a problem in that the response speed of the proximity switch is limited by the oscillation start speed.

Therefore, for example, in Utility Model Application Publication No. 59-145742, an oscillation circuit was proposed in which the amplitude of the oscillation output is discriminated at a predetermined level, and if the oscillation output decreases, a switching circuit for adjusting the amplitude is operated to continue oscillation. ing. This kind of oscillation circuit can continue oscillating when an object approaches, but since the resistance value of the oscillation state control resistor of the resonant circuit is changed by a switching operation, it is not possible to continue oscillating with a constant amplitude. There wasn't. Furthermore, there is a problem in that it takes a certain amount of time to start up oscillation from an oscillation state where the level is relatively low, and the response speed may not be very fast.

[Purpose of the invention]

The present invention has been made in view of the problems of conventional high-frequency oscillation type proximity switches, and the oscillation level is constant regardless of the position of the object, and the response speed is determined regardless of the rise speed of the amplitude. The technical challenge is to do so.

[Structure and effects of the invention]

(Structure) The present invention is a high frequency oscillation type proximity switch that has an oscillation circuit and a detection circuit that detects an object by a change in the oscillation state, and as shown in FIG. 1, the switch is connected as a resistor to control the conductance of the oscillation circuit. voltage controlled resistance circuit (25
), a voltage control circuit (23) that inverts and amplifies the detected output of the oscillation circuit and supplies the amplified output as a control signal to the voltage control resistance circuit (25), and a voltage control circuit (23) that controls the control signal of the voltage control circuit (23) to a predetermined threshold value. The device is characterized in that it has a comparison circuit (9) for comparing with the level, and an output circuit (10) for outputting an object detection signal based on the comparison output of the comparison circuit (9).

(Function) According to the present invention having such characteristics, when an object approaches and the conductance of the resonant circuit increases, the oscillation output decreases, and based on this, the conductance of the voltage controlled resistance circuit (25) follows it. Therefore, the amplitude of the oscillation circuit is automatically controlled so that it always remains approximately constant regardless of the position of the object. Since this control voltage changes based on the position of the object, a comparison circuit (9)
Detects nearby objects by applying

(Effects) Therefore, according to the present invention, the amplitude of the oscillation circuit hardly changes and is kept almost constant regardless of the position of the object, and the object can be detected by changing the control voltage. The response speed of object detection is determined by the control voltage of the amplifier circuit, regardless of changes in the amplitude of oscillation. Since the response speed of the control circuit is usually sufficiently faster than the change in the oscillation amplitude, it is possible to obtain a response speed sufficiently faster than in a conventional proximity switch that detects the proximity of an object based on the change in the oscillation amplitude.

[Explanation of Examples]

(Configuration of Example) FIG. 1 is a circuit diagram showing an embodiment of the present invention.

In this figure, the same parts as in the conventional example are given the same reference numerals. In this embodiment as well, a current mirror circuit 3 consisting of a transistor 1.2 is connected to a resonant circuit consisting of an oscillation coil L and a capacitor C1, and the oscillation output is converted into a voltage signal by a transistor 7 connected in an emitter follower type. Further, the current is applied to the base of the transistor 6, and its collector current is positively fed back to the resonant circuit via the current mirror circuit 3.

In this actual example, the emitter resistor R7 of transistor 8
, R8 is connected to the non-inverting input terminal of an adding/subtracting amplifier 21 having an amplification factor α. A reference voltage E is applied to the inverting input terminal of the adding/subtracting amplifier 21. is given. and addition/subtraction amplifier 2
The output of 1 is applied to the inverting input terminal of the addition/subtraction amplifier 22. A reference voltage E is applied to the non-inverting input terminal of the adding/subtracting amplifier 22.
1 is given, and a voltage control circuit 23 is configured by amplifiers 21 and 22. Output voltage V of voltage control circuit 23
G is applied to the gate terminal of a voltage control element, for example, a field effect transistor (hereinafter referred to as FET) 24. FE
A resistor R9 is connected in series to T24.
A series connection body of FET 24 and FET 24 is connected as an emitter resistance of transistor 6 to form a voltage controlled resistance circuit 25. Then, the output of the voltage control circuit 23 is given to the comparator 9, and a voltage signal of a predetermined level is discriminated and the output circuit IO
given to. The output circuit 10 amplifies this output and provides it to the outside as a switch output.

(Operation) Next, the operation of this embodiment will be explained. When this oscillator circuit is operated, the current flowing through the resonant circuit is converted into a voltage signal by the transistor 7, and that voltage signal flows through the emitter follower of the transistor 6 to one transistor 2 of the current mirror circuit 3, and the current is the same as that current. The current is fed back from transistor 1 to the resonant circuit, and oscillation is started. Then, the voltage at the midpoint of the emitter resistors R7 and R8 of the transistor 8 is smoothed by the capacitor C2 and provided to the voltage control circuit 23 as the detected voltage Vd. FIG. 2 is a characteristic curve showing the output control voltage V6 of the voltage control circuit 23 with respect to the detected voltage Vd, and the control voltage VG is given by the following equation from the input and output voltages of the addition/subtraction amplifiers 21 and 22.

Vc"'El (r(Vd Eo) Therefore, the control voltage vG changes linearly with respect to the detection voltage Vd, and the resistance value of the FET 24 is determined by this control voltage. Therefore, the FE
The resistance value Rx of the voltage controlled resistance circuit 25 changes as shown in FIG. 3 due to the combined resistance of the resistor RFIT and the resistor R9 determined by the detected voltage Vd of T24. The reciprocal of this voltage becomes the conductance gx of the voltage controlled resistance circuit 25, as shown in FIG. In this way, the resistance value Rx of the voltage control resistance circuit 25 and the conductance gx of the oscillation circuit continuously change according to the detected voltage Vd.

On the other hand, when an object approaches the detection coil, eddy current loss occurs, which increases the loss resistance of the resonant circuit, and the conductance g3 of the resonant circuit increases as shown in Figure 5 with respect to the distance l from the proximity switch to the object. . Therefore, the distance at which the object is close to the proximity switch, ? 1III and nearly infinite distance 12
, the conductance ga of the resonant circuit is the fifth
As shown in the figure and FIG. 6(a), it changes like ga+ and g3□. When the object approaches the proximity switch from a distance I12, the amplitude 1 of the oscillation circuit decreases slightly as shown in FIG. 6 (bl), and the detection voltage Vd also decreases accordingly, but as shown in FIG. As the detection voltage Vd decreases, the control voltage (2) increases significantly.Therefore, the conductance gx of the oscillation circuit also increases from gxz to gx+ as shown in Figures 4 and 6. Regardless, the amplitude of the oscillation circuit remains almost constant as shown in FIG. 6 (bl) and FIG. 7, and the control voltage 6 of the voltage control circuit 23 changes as shown in FIG. The proximity of an object can be detected based on the level of this control voltage. Fig. 6(d) is a diagram showing the threshold level Vref of the comparator 9 determined in correspondence to the output level of the control voltage. If the control voltage (6) exceeds this threshold level Vref, the output circuit 10 outputs an object detection output.

In this way, the response speed of the proximity switch is detected based on the control voltage without directly detecting and comparing the amplitude value of the oscillation circuit, so the response speed of the proximity switch is determined by the response speed of the voltage control circuit 23. Therefore, compared to conventional proximity switches, it is possible to provide a proximity switch with almost no time delay in object detection and a faster response speed.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a high frequency oscillation type proximity switch according to an embodiment of the present invention, FIG. 2 is a graph showing the characteristics of the control voltage 6 of the voltage control circuit with respect to the detected voltage Vd, and FIG. 3 is a graph showing the characteristics of the control voltage 6 of the voltage control circuit with respect to the detected voltage Vd. A graph showing the combined resistance of the voltage controlled resistance circuit, Figure 4 shows the combined conductance of the voltage controlled resistance circuit (conductance of the oscillation circuit) g with respect to the detected voltage Vd.
Graph showing X, Figure 5 is a graph showing the conductance ga of the resonant circuit with respect to the distance β from the proximity switch to the object, Figure 6 (al to tel are the conductance g of the resonant circuit and the conductance of the oscillation circuit with respect to the position of the object) This is a time chart showing waveforms of gx and each part, and the seventh
The figure is a graph showing the amplitude of the oscillation circuit versus the distance l from the proximity switch to the object, Figure 8 is a graph showing the control voltage Vc of the voltage control circuit versus the distance l, and Figure 9 is a graph of the conventional high frequency oscillation type proximity switch. Circuit diagram showing an example of
Figure 0 is a graph showing the change in oscillation amplitude with respect to the object distance of a conventional proximity switch, and Figure 11 is a graph showing the change in the conductance g of the resonant circuit and the conductance gxo of the oscillation circuit and the oscillation amplitude with respect to the position of the object in the conventional proximity switch. It is a graph showing changes in. L-... Coil 1, 2.6-8------
Transistor 3-----One current mirror circuit
9-...-Comparator i' o-----One output circuit
21.22--1111 addition/subtraction amplifier 23--
---Voltage control circuit 24-----F E T2
5-----Voltage controlled resistance circuit Patent applicant Tateishi Electric Co., Ltd. Agent Patent attorney Yoshiki Okamoto (and one other person) Figure 3 Rx(n) t Figure 5 Figure 7 Figure 8 Figure 6 Figure 9 Figure 10 Figure 1i Figure 11

Claims (2)

[Claims] (1) A high frequency oscillation type proximity switch having an oscillation circuit and a detection circuit that detects an object based on a change in the oscillation state, the voltage controlled resistance circuit being connected as a resistor to control the conductance of the oscillation circuit, and the oscillation circuit. a voltage control circuit that inverts and amplifies the detection output of the circuit and supplies the amplified output as a control signal to the voltage control resistance circuit; a comparison circuit that compares the control signal of the voltage control circuit with a predetermined threshold level; and the comparison circuit. A high frequency oscillation type proximity switch characterized by having an output circuit that outputs an object detection signal based on a comparison output of. (2) The high frequency oscillation type proximity switch according to claim 1, wherein the voltage controlled resistance circuit includes a field effect transistor.