JPH0810825B2 - High frequency oscillation type proximity switch - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a high-frequency oscillation type proximity switch with improved response speed for object detection.

[Outline of Invention]

In the proximity switch according to the present invention, when a voltage control resistance element is connected in parallel to a resistance that determines the conductance of the oscillation circuit and the detection output of the oscillation circuit is inverted and amplified to control the voltage control resistance element, an object is brought into proximity. In particular, the oscillation is continued with a small constant amplitude value to improve the response speed of object detection.

[Prior art and its problems]

(Prior Art) Conventionally, an oscillating circuit as shown in FIG. 8 has been used for a high-frequency oscillation type proximity switch. In this oscillation circuit, the collector of one transistor 1 of the current mirror circuit 3 composed of transistors 1 and 2 is connected to a resonance circuit composed of a coil L and a capacitor C1. The emitters of the transistors 1 and 2 have emitter resistors R1 and R2 having the same resistance value connected to the power supply terminal. A resistor R3, diodes 4, 5 and a resistor R4 are further connected to the resonance circuit from the power source end. The collector of the transistor 2 is connected to the bases of the transistors 1 and 2, and is grounded via the transistor 6 and the resistor R5. A transistor 7 is provided at the connection point between the resistor R3 and the diode 4.
The base of is connected. The transistor 7 is an emitter follower type transistor, and the emitter resistance R6 is given to the base of the transistor 6. The oscillation output from the emitter of the transistor 7 is taken out through the transistor 8 connected to the emitter follower and rectified, and the output is given to the comparator 9 and the output circuit 10.

In such a conventional high frequency oscillation type proximity switch, the current flowing in the resonance circuit is converted into a voltage by the transistor 7, and the emitter follower output is fed back to the transistor 6. Therefore, the current flowing through the transistor 6 is positively fed back to the resonance circuit via the current mirror circuit 3 to continue the oscillation. Then, as shown in FIGS. 9 and 10, when an object approaches the coil L of the resonance circuit, the conductance g _{a of the} resonance circuit
Becomes larger (g _a = g _a1 ), and the conductance g _{a of the} resonant circuit becomes smaller when there is no object (g _a = g _a2 ). Object by the presence or absence of the oscillation for a change in conductance g _a is not greater than the negative conductance g _x0 of the oscillation circuit defined by the reciprocal of the resistor R5 stops oscillating, oscillation becomes smaller than the conductance g _x0 of the resonant circuit Can be detected.

(Problems to be Solved by the Invention) In such a conventional proximity switch, as shown in FIG. 10, oscillation is stopped when an object approaches, and oscillation is restarted 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 the oscillation stop speed. In general, the oscillation circuit has a very slow rising (starting) speed and a relatively high stopping speed. Therefore, there is a problem that the response speed of the proximity switch is limited by the oscillation start speed.

Therefore, for example, in Japanese Utility Model Laid-Open No. 60-145742, an oscillation circuit is proposed in which the amplitude of the oscillation output is discriminated at a predetermined level, and when the oscillation output decreases, a switching circuit for amplitude adjustment is operated to continue oscillation. Has been done. With such an oscillation circuit, oscillation can be continued when an object approaches, but since the resistance value of the oscillation state control resistor of the resonance circuit is switched by switching operation, oscillation can be continued with a constant amplitude. There wasn't. And when the object gets closer, the oscillation may stop. Therefore, there is a problem that it takes a predetermined time to start the oscillation from the state where the oscillation is stopped, and the response speed may not be so fast.

[Object of the Invention]

The present invention has been made in view of the above problems of the conventional proximity switch, and it is a technical object to continue oscillation at a constant level when an object approaches.

[Constitution and effect of the invention]

(Structure) The present invention is a high-frequency oscillation type proximity switch having an oscillation circuit and a detection circuit for detecting an object due to a decrease in the output of the oscillation output, and as shown in FIG. R5) and a voltage control resistance circuit (25) in which the resistance value changes continuously according to the input voltage are connected in parallel, and the detection output of the oscillation circuit is inverted and amplified to obtain its analog amplified output. To the voltage control resistance circuit (25) as a control signal, the voltage control circuit (25) continuously increases the conductance of the oscillation circuit when the oscillation level decreases.

(Operation) According to the present invention having such a feature, a control voltage is applied to the voltage control resistor circuit that determines the conductance of the oscillation circuit when an object approaches and the conductance of the resonance circuit becomes equal to or higher than a predetermined level. Is automatically controlled to be constant. When the object goes away and the conductance of the resonance circuit becomes lower than this level, voltage control is not performed on the voltage control resistor circuit of the oscillation circuit, and the oscillation amplitude sharply increases. Therefore, even if an object approaches and the conductance of the resonance circuit increases, the oscillation can be continued at a substantially constant level.

(Effect) Therefore, according to the present invention, when the object approaches the proximity switch, the oscillation amplitude hardly changes even if the distance changes, and the oscillation is continued at a substantially constant level. Moreover, since the conductance of the oscillation circuit is larger than that of the conventional circuit, the oscillation rapidly rises when the object moves away, and the amplitude can be increased to a required amplitude level in an extremely short time. Therefore, according to the present invention, it is possible to always obtain a high response speed by adding a relatively simple circuit.

[Explanation of Example]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. In this figure, the same parts as those of the conventional example are denoted by the same reference numerals. Also in this embodiment, the current mirror circuit 3 including the transistors 1 and 2 is provided in the resonance circuit including the oscillation coil L and the capacitor C1.
Is connected, and its oscillation output is converted into a voltage signal by the transistor 7 connected in the emitter follower type, which is further given to the base of the transistor 6 and positively fed back to the resonance circuit via the current mirror circuit 3 by its collector current. There is.

In this embodiment, the emitter resistances R7 and R7 of the transistor 8 are
Connect the input terminal of the operational amplifier 21 with the amplification factor α to the middle point of 8,
Further, the amplified output is given to the inverting input terminal of the inverting amplifier 22 for amplification. It is assumed that the non-inverting input terminal of the inverting amplifier 22 is supplied with a reference voltage signal composed of the voltage E. And amplifier 2
The output of the voltage control circuit 23 composed of 1, 22 is used as a voltage control resistance element, for example, a field effect transistor (hereinafter referred to as FET) 2
Give to the gate terminal of 4. The resistor R9 is connected in series to the FET24, and the series connection body of the resistor R9 and the FET24 is connected in parallel to the emitter resistor R5 of the transistor 6 to form the voltage control resistor circuit 25.

Similarly to the above-mentioned conventional example, the comparator 9 is connected to the middle point of the emitter resistances R7 and R8 of the transistor 8, and the voltage signal of a predetermined level is discriminated and given to the output circuit 10. The output circuit 10 amplifies this output and gives it to the outside as a switch output.

(Operation) Next, the operation of this embodiment will be described. When this oscillator circuit is operated, the current flowing in the resonance circuit causes the transistor 7
Is converted into a voltage signal by the voltage signal, and the voltage signal flows to one transistor 2 of the current mirror circuit 3 through the emitter follower of the transistor 6, and the same current is fed back from the transistor 1 to the resonance circuit to start oscillation. To be done. The voltage at the midpoint of the emitter resistances R7 and R8 of the transistor 8 is smoothed by the capacitor C2, and the detected voltage Vd
Is given to the voltage control circuit 23 and the comparator 9. Second
The figure shows the output voltage of the voltage control circuit 23 with respect to this detection voltage Vd.
The voltage control circuit 23 is a characteristic curve showing V _G
The output voltage (that is, E-αVd) of the FET 24 is set as the control voltage V _G.
Is giving to the gate. Therefore, as shown in FIG. 3, the resistance of the voltage control resistance circuit 25 with respect to the detection voltage Vd is
A constant resistance value of resistor R5 that does not depend on Vd
It becomes the resistance value given by the curve R _X as the parallel combined resistance with the sum R9 + R _FET of the resistance R _FET determined by the detection voltage Vd of T24. Then, as shown in FIG. 4, the reciprocal of this resistance value becomes the combined conductance g _X of the voltage control resistance circuit 25 with respect to the detection voltage Vd. Then, as shown in FIG. 3, the detected voltage Vd is Vd
If it becomes ₁ or less, the gate voltage V _G given to the FET 24 rises, so that the FET 24 is turned on and the combined resistance of the voltage control resistance circuit 25 becomes a parallel combined resistance of the resistor R5 and the resistor R9, and the detected voltage becomes Vd ₂ If it exceeds, the control voltage is not applied to the gate terminal of the FET 24, so that the FET 24 is turned off and the combined resistance of the voltage control resistance circuit 25 is only the original emitter resistance R5. Therefore, when the detection voltage Vd is between Vd ₁ and Vd ₂ , the FET 24 performs an analog operation, and is the combined resistance R _X of the voltage control resistance circuit 25 and its reciprocal as shown in FIGS. 3 and 4. The negative conductance g _X of the oscillator circuit changes continuously as shown in the figure.

On the other hand, when an object comes close to the detection coil L, eddy current loss occurs, so that the loss resistance of the resonance circuit increases, and the conductance g _{a of the} resonance circuit becomes large with respect to the distance l from the proximity switch to the object as shown in FIG. Become. And the predetermined distance l ₂
When the distance is further, the conductance g _{X of the} oscillation circuit becomes larger than the conductance g _{a of the} resonance circuit. Therefore, as shown in FIG. 6, the oscillation amplitude increases and the detection output Vd also increases until the oscillation circuit is saturated. If the distance is closer than l ₂ , the detection voltage
The decrease in Vd is controlled so that the conductance g _{X of the} oscillator circuit follows the conductance g _{a of the} resonance circuit.
As shown in FIG. 7 and FIG. 7A, even when an object approaches the proximity switch, oscillation can be continued with a substantially constant amplitude. By setting the predetermined value Vref of Vd ₂ or more for the detection output Vd as the threshold level of the comparator 9, it is possible to detect an adjacent object. Then, as shown in FIG. 7, when the object approaches the vicinity of the proximity switch from the distance l ₂ , the amplitude of oscillation increases from the predetermined amplitude level. Therefore, the amplitude of the oscillation circuit rises quickly, and it becomes possible to reach the level at which the proximity of an object is detected in an extremely short time, and the response speed of the proximity switch can be greatly improved.

[Brief description 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 characteristics of an output voltage V _G of an amplifier circuit with respect to a detection voltage Vd, and FIG. 3 is a voltage with respect to a detection voltage Vd. Graph showing combined resistance of control resistance circuit, 4th
FIG. 5 is a graph showing the combined conductance (conductance of the oscillating circuit) g _X of the voltage controlled resistance circuit with respect to the detection voltage Vd, and FIG. 5 is a graph showing the conductance g _{a of the} resonant circuit with respect to the distance 1 from the proximity switch to the object. Figure is a graph showing the detection output Vd with respect to the distance l to the object. Figure 7 is the conductance g _{a of the} resonant circuit with respect to the position of the object
And a graph showing changes in the conductance g _X and the oscillation amplitude of the oscillation circuit, FIG. 8 is a circuit diagram showing an example of a conventional high-frequency oscillation type proximity switch, and FIG. 9 is an oscillation amplitude of the conventional proximity switch with respect to the object distance. FIG. 10 is a graph showing changes, and FIG. 10 is a graph showing changes in the conductance g _{a of the} resonance circuit and the conductance g _X0 of the oscillation circuit and changes in the oscillation amplitude with respect to the position of the object of the conventional proximity switch. L: coil, 1,2,6 to 8 ... transistor, 3 ... current mirror circuit, 9 ... comparator, 10 ... output circuit, 21 ...
Amplifier, 22 ... Inverting amplifier, 23 ... Voltage control circuit, 24 ...
… FET, 25 …… voltage control resistor circuit

Claims (2)

[Claims] 1. A high frequency oscillation type proximity switch having an oscillating circuit and a detection circuit for detecting an object when the output of the oscillating circuit is lowered, wherein the resistance value is continuously changed by a resistance defining a conductance of the oscillating circuit and an input voltage. And a voltage control resistance circuit in which a voltage control resistance element is connected in parallel, and a detection output of the oscillation circuit is inverted and amplified and its analog amplified output is given as a control signal to the voltage control resistance circuit, thereby lowering the oscillation level. And a voltage control circuit for continuously increasing the conductance of the oscillation circuit, the high-frequency oscillation type proximity switch. 2. The high frequency oscillation type proximity switch according to claim 1, wherein the voltage controlled resistance element is a field effect transistor.