JPH01129529A - High frequency oscillation type proximity switch - Google Patents

Abstract

PURPOSE:To continue the oscillation at a prescribed level even at the time of proximity of an object by a simple constitution by connecting in parallel a small amplitude oscillation control circuit to an oscillating circuit having a resonance circuit brought to current driving by a current mirror circuit with a first feedback circuit brought to positive feedback to the current mirror circuit and controlling the feedback current of a second feedback circuit. CONSTITUTION:The negative conductance gx of an oscillating circuit which has synthesized original negative resistance values of a voltage control resistance circuit 28 and the oscillating circuit is varied by following up the conductance ga of a resonance circuit. Accordingly, when a distance (l) between a proximity switch and an object is shorter than a distance lon for detecting the object, the amplitude of the oscillating circuit becomes constant irrespective of a position of the object. When the object goes away from the lon point and the conductance ga of the resonance circuit becomes smaller than a fixed negative conductance gxon of the oscillating circuit, the negative conductance gx of a small amplitude oscillation control circuit 20 becomes zero. Therefore, when the object goes away, the oscillation amplitude increases suddenly, but the oscillation is led from a prescribed level, therefore, its leading edge is very quick and high speed responsiveness can be realized.

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.

[Prior art and its problems]

(Prior Art) Conventionally, a high frequency oscillation type proximity switch uses an oscillation circuit as shown in FIG. 10, 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 CI. Emitter resistors R1 and R2 each having the same resistance value are connected to the power source end of the emitter of the transistor 1.2. The resonant circuit further includes a resistor R3 and a diode 4 from the power supply end.
5 and resistor R4 are connected. The collector of transistor 2 is connected to the base of transistor 1.2, and is also grounded via transistor 6 and resistor R5.

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 has an emitter resistor R6, the output of which is given to the base of transistor 6. The oscillation output from the emitter of the transistor 7 is detected by a transistor 8 connected as an emitter follower, and its output is given to a comparator 9. A predetermined darkness value level is set in the comparator 9, and when this level is exceeded, an object detection signal is outputted from the output circuit 10 to the outside.

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 11.12, when an object approaches the coil of the resonant circuit and the distance β to the object becomes small (then the conductance g8 of the resonant circuit increases (ga
=g, +), when the object disappears, the conductance g8 of the resonant circuit becomes smaller (g-"gRz).

If the change in the conductance g8 of this resonant circuit is larger than the negative conductance gxo of the oscillation circuit determined by the reciprocal of the resistor R5 (if it becomes, oscillation is stopped and this conductance gxo
If it becomes smaller, it will oscillate, so the proximity of an object can be detected based on the presence or absence of oscillation.

(Problems to be Solved by the Invention) In such a conventional proximity switch, as shown in FIG. 12, 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. -The oscillation circuit used in boat fishing has a very slow oscillation rise (start) speed and a relatively fast oscillation 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 No. 60-145742, 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. First, the amplitude changes depending on the position of the object. 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 the conventional high frequency oscillation type proximity switch, and its technical problem is to continue oscillation at a constant level even when an object approaches.

[Structure and effects of the invention]

(Means for Solving the Problems) The present invention includes a resonant circuit, a current mirror circuit whose one end is connected to the resonant circuit and drives the resonant circuit with current, and a current of the current mirror circuit that is positively fed back by an oscillation output. an oscillation circuit having a first feedback circuit; a first detection circuit that detects the oscillation output of the oscillation circuit; a comparator that detects an object by comparing the detection output of the detection circuit with a predetermined level; This is a high-frequency oscillation type proximity switch that has an output circuit that outputs an object detection signal based on the comparative output of the device, and as shown in FIGS. 1 and 9, the conductance of the oscillation circuit is connected to the current control end of the current mirror circuit. A second circuit includes a voltage controlled resistance circuit connected as a controlled resistor and whose resistance value is changed by a control voltage, converts the resonant voltage of the resonant circuit into a voltage signal, and positively feeds back the current of the current mirror circuit by an oscillation output. A feedback circuit, a second detection circuit that detects the oscillation voltage of the oscillation circuit to obtain a DC voltage corresponding to the amplitude, and a detection output of the second detection circuit is given to the base, and the output is inverted and amplified to control the voltage. The oscillation circuit is characterized in that a small amplitude oscillation control circuit having a transistor that supplies a signal to the voltage controlled resistance circuit is attached to the oscillation circuit.

(Function) According to the present invention having such characteristics, an oscillation circuit that is current-driven by a current mirror circuit and has a resonant circuit and a first feedback circuit that converts the oscillation output into a voltage and provides positive feedback to the current mirror circuit. A small amplitude oscillation control circuit is connected in parallel to the circuit. The small amplitude oscillation control circuit converts the amplitude level of the oscillation into a voltage using a detection circuit, inverts and amplifies it using a transistor, and controls the feedback current of the second feedback circuit.
As the detection voltage increases, the feedback current is lowered. Therefore, the conductance of the oscillation circuit to which the small amplitude oscillation control circuit is attached will follow the change in the conductance of the resonant circuit that corresponds to the proximity of the object, and the oscillation will continue at a constant small amplitude even when the object is close. can be continued. When the object moves away, the small amplitude oscillation control circuit stops operating, and its amplitude changes based on the object's position. A nearby object is detected by detecting the oscillation output and discriminating the amplitude level using a comparator set to a constant darkness value.

(Effects of the Invention) Therefore, according to the present invention, when an object is in close proximity, the amplitude of the oscillation circuit hardly changes and can be maintained at a substantially constant low level regardless of its position. When the object moves away, the oscillation rises rapidly and the amplitude can be increased to a large amplitude level in an extremely short period of time. As described above, according to the present invention, oscillation can be continued at a constant level even when an object approaches with a simple configuration of adding a small amplitude oscillation control circuit to the oscillation circuit, and the response speed of object detection can be improved. Can be done. During large amplitude oscillation when the small amplitude oscillation control circuit is not operating, the feedback circuit is
Any circuit with B-class operation can be used, increasing the degree of freedom in circuit selection.

[Explanation of Examples]

(Configuration of Embodiment) FIG. 1 is a circuit diagram showing a proximity switch having an oscillation circuit operating in class B according to a first 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 made up of transistors 1 and 2 is connected to a resonant circuit made up of an oscillation coil L and a capacitor CI, 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. Here, the resistors R3 to R6, the diode 4.5, and the transistor 6.7 constitute a first feedback circuit 11 that controls the positive feedback current of the current mirror circuit 3 using an oscillation output. The voltage across resistor R6 is then applied to the base of resistor R8. The resistor R8 operates as an emitter follower with the resistor R7°R8 connected to its emitter, as in the conventional example described above. A capacitor C2 is connected in parallel to the resistor R8 to constitute a first detection circuit 12 that detects the oscillation output and converts it to a DC level according to its amplitude. The output of this detection circuit 12 is given to a comparator 9 in which a predetermined dark value level is set.

The comparator 9 detects the proximity of an object when the voltage changes to a level lower than the darkness value level, and its output is outputted to the outside as an object detection output via the output circuit 10.

Now, as shown in the figure, the oscillation circuit according to this embodiment is a conventional oscillation circuit to which a small amplitude oscillation control circuit 20 shown by a dashed line is added. The small amplitude oscillation control circuit 20 is connected to the power supply V
A resistor R9, a diode 21, 22, and a resistor RIO are connected in series between cc and the hot end of the resonant circuit in the same manner as resistors R3 to R4, and the core of the transistor 23 is connected to the power supply terminal like the transistor 7, and the base is connected to the resistor R9. and the diode 21 at a common connection point. Further, a series connection body of a transistor 24, a resistor R11, and an FET 25 is connected between the collector of the transistor 2 and the ground terminal. Transistor 23 is an emitter follower connected transistor having emitter resistor R12, and its output is given to the bases of transistor 24 and transistor 26. The transistor 26 has a collector connected to the power supply terminal, an emitter connected to a series circuit consisting of a resistor R13 and a capacitor C3, and a resistor R14 connected in parallel to the capacitor C3. Further, the base of the transistor 27 is connected to the common connection point of the resistors R13 and R14 via the resistor R15. The emitter of the transistor 27 is grounded, and the collector is connected to the power supply terminal via a resistor R16, and its collector output is applied to the FET 25 as a voltage control signal VG. Here, resistor R1,1 and FET25 are voltage controlled resistance circuit 28 whose resistance value is changed by control voltage.
It consists of resistors R9 to R12, diode 21,
22 and transistors 23 and 24 and voltage controlled resistance circuit 2
Reference numeral 8 constitutes a second feedback circuit 29 that positively feeds back the current of the current mirror circuit using an oscillation output. The transistor 26, the resistors R13 and R14, and the capacitor C3 constitute a second detection circuit 30 that detects the oscillation output and obtains a DC voltage proportional to the amplitude. The output is controlled by the voltage controlled resistance circuit 28 by the transistor 27. It is given as an In voltage. A small amplitude oscillation control circuit 20 added to these oscillation circuits provides a positive feedback voltage corresponding to the amplitude to the FET 25 when an object approaches and the conductance of the resonant circuit increases, thereby generating a constant low level. This allows the oscillation to continue.

Next, the operation of this embodiment will be explained. When this oscillation circuit is operated, the current flowing through the resonant circuit flows to the first feedback circuit 1.
One transistor 7 converts the current into a voltage signal, and the voltage signal flows through transistor 6 to one transistor 2 of current mirror circuit 3 . Similarly, the current flowing through the resonant circuit is converted into a voltage signal by the transistor 13 of the second feedback circuit 29, and the voltage is transferred to the transistor 24.
join the base of This voltage is also applied to the base of transistor 26, and capacitor C3 is charged only while transistor 26 is on. Therefore, the transistor 26 and the capacitor C3 operate as a kind of detection circuit, and a DC voltage corresponding to the amplitude of the high frequency is obtained across the capacitor C3. When this detected voltage V is small and is less than 0.6V, the voltage applied to the transistor 27 is also less than 0.6V. Therefore, the transistor 27 is off when the resonance circuit stops oscillating or when the amplitude is small, and the control voltage V applied from its collector to the FET 25 has a high value equal to the power supply voltage. Therefore, the resistance value of the voltage controlled resistance circuit 28 is determined only by the resistor R11. Therefore, when a slight high frequency voltage flows through the resonant circuit, positive current feedback is performed with a high amplification factor and is fed back to the resonant circuit. Here, the control voltage V with respect to the detected voltage Vd detected by the transistor 26 and obtained at the capacitor C3, as shown in FIG. A base current begins to flow through 27 and rapidly decreases to near zero level.

The combined resistance RX of the voltage controlled resistance circuit 28 changes as shown in FIG. 3 in response to the detected voltage (2). Therefore, the conductance gx of the voltage controlled resistance circuit 28 takes the reciprocal of the combined resistance RX shown in FIG. 3, and the detected voltage Vd at which the FET 25 turns off as shown in FIG. 4. It increases rapidly below, and the detected voltage changes to zero as Vao becomes larger. The collector current flowing out from the transistor 2 of the current mirror circuit 3 is the sum of the current flowing to the second feedback circuit 11 connected in parallel with the small amplitude oscillation control circuit 20, and also includes the conductance due to the resistor R5. The negative conductance gx' of the oscillation circuit is the sum of the conductance g and the reciprocal of the resistor R5, that is, . Figure 5 shows the negative conductance gX' of the oscillation circuit.
This shows the relationship between the detection voltage and the detection voltage.

Actually, as the object approaches, the conductance g3 of the resonant circuit changes as shown by the broken line in FIG. At a position where an object is close to the coil, the conductance g3 of the resonant circuit, that is, the loss of the coil, is large and it is difficult to oscillate, but if there is noise in the resonant circuit, it will cause a high amplification factor as described above. is amplified and positive feedback is applied to the resonant circuit. Therefore, the oscillation rises and the amplitude increases, but as the amplitude increases, the detected voltage (2) also increases, and the transistor 27 gradually turns on from off. Therefore, the control voltage V.

decreases, and the resistance value of the FET 25 increases. Therefore, in reality, the negative conductance gx' of the oscillation circuit, which is a combination of the voltage controlled resistance circuit 28 and the original negative resistance value of the oscillation circuit, follows the conductance g11 of the resonant circuit, as shown in FIG. Changes to Therefore, the seventh
As shown in the figure, if the distance l from the proximity switch to the object is shorter than the object detection distance j2oゎ, the amplitude of the oscillation circuit will be constant regardless of the object position, and the detection voltage V6
remains constant, and oscillation continues at a low level even when an object approaches the coil. If the value of the resistor R11 is made small, the oscillation will continue at a constant low amplitude until the object comes into contact with the detection coil, but if the resistance value of the resistor R11 is made large, the oscillation will continue at a certain position as shown by the broken line in Figure 7. The oscillation will stop at this point. In FIG. 7, Vref indicates the dark value level of the comparator 9. In this manner, in this embodiment, oscillation continues even when the object is extremely close to the detection distance.

And the object is l. Farther away from point n, the conductance gs of the resonant circuit becomes the fixed negative conductance g of the oscillation circuit.
When it becomes smaller than xon', the negative conductance gx of the small amplitude oscillation control circuit 20 becomes zero, and the amplitude cannot be controlled to a constant value. As a result, the amplitude value increases rapidly, and B
This will enter the operating range of the class. Therefore, Fig. 8 (al,
(As shown in bl, when an object moves between a point at a position β1 closer to the detection distance l.7 and a point at a distance 12 farther away from β. The changes in the oscillating circuit's eclipsing conductance g xon' are as shown in the figure.Here, V 4 I, V 4 in Fig. 8)
2 is distance 7! , 7!2. Therefore, as the object moves away, the oscillation amplitude increases rapidly, but since the oscillation rises from a constant level, the rise is extremely fast, making it possible to achieve high-speed response.

(Description of the second embodiment) In the first embodiment described above, class A operation is performed at the start of oscillation, and when the oscillation amplitude increases rapidly as the object moves away, class B operation is performed.
Although the oscillation circuit is configured to switch to class A operation, the temperature characteristics of the circuit can be improved by performing all operations in class A operation. FIG. 9 is a circuit diagram showing the configuration of a proximity switch having such an oscillation circuit. In this figure, the same parts as in the embodiment described above are given the same reference numerals. This embodiment has a small amplitude oscillation control circuit 20 similar to the embodiment described above, but the configuration of the first feedback circuit 11' of the oscillation circuit is different. That is, the hot end of the resonant circuit is connected to the common connection point of resistors R17 and R18 via capacitor C4.

Resistors R17 and R18 are voltage dividing circuits that divide the power supply voltage, and a connection point thereof is connected to the transistor 31. The oscillation bias point can be arbitrarily determined by this divided voltage. Now, the transistor 31 is an emitter follower type transistor having a collector connected to a power supply and an emitter resistor R19, and its emitter end is connected to the base of the transistor 6. Further, the terminal voltage of the resistor R19 is applied to the first detection circuit 12 similar to the embodiment described above. The first detection circuit 12 detects the emitter voltage of the transistor 31, and its output is given to the comparator 9 similar to the embodiment described above. The comparator 9 compares the input signal with a predetermined dark value level Vref, and its output is given to the output circuit. In this embodiment, unlike the first embodiment described above, the base voltage of the transistor 31 corresponding to the transistor 7 is the resistance R], 7. Selected arbitrarily by R18, only high frequency signals are connected to capacitor C.
4, and only the alternating current component is amplified at an arbitrary bias point. Therefore transistor 3
By selecting base voltage 1 to be 2, which is the power supply voltage, for example, class A operation can always be performed even when the amplitude becomes large, and the temperature characteristics of the proximity switch can be improved.

[Brief explanation of the drawing]

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 the detected voltage V, FIG. 4 is a graph showing the combined resistance RX of the voltage controlled resistance circuit with respect to the detected voltage V, FIG. 5 is a graph showing the conductance gx of the voltage controlled resistance circuit with respect to the detected voltage V. FIG. 6 is a graph showing the conductance ga of the resonant circuit and the negative conductance gx' of the oscillation circuit as a function of the distance l from the proximity switch to the object. Graph showing changes in detection voltage v7 with respect to distance β, Figure 8 shows conductance g of the resonant circuit with respect to the position of the object.
FIG. 9 is a time chart showing a, conductance gx' of the oscillation circuit, and oscillation amplitude, and FIG. 9 is a circuit diagram of a proximity switch according to a second embodiment of the present application. Also, Fig. 10 is a circuit diagram showing an example of a conventional high frequency oscillation type proximity switch, Fig. 11 is a graph showing changes in oscillation amplitude with respect to object distance of a conventional proximity switch, and Fig. 12 is a graph showing a change in oscillation amplitude with respect to object distance of a conventional proximity switch. The conductance of the resonant circuit g8 with respect to the position of
2 is a graph showing changes in conductance gxo and changes in oscillation amplitude of the oscillation circuit. L-------Coil 1. ．． 2.6-8, 23.2
4゜26, 27, 31------) transistor 3--------Current mirror circuit 9-=--
---Comparator 1o------Output circuit 11
'--First feedback circuit 12--First detection circuit 20--Small amplitude oscillation control circuit 25--
--FET 28-111--Voltage control resistance circuit 29--1 Second feedback circuit 30--1 2nd
detection circuit

Claims (2)

[Claims] (1) An oscillation circuit that includes a resonant circuit, a current mirror circuit whose one end is connected to the resonant circuit and drives the resonant circuit with current, and a first feedback circuit that positively feeds back the current of the current mirror circuit using an oscillation output. a first detection circuit that detects the oscillation output of the oscillation circuit; a comparator that detects an object by comparing the detection output of the detection circuit with a predetermined level; and a first detection circuit that detects an object by comparing the detection output of the detection circuit with a predetermined level; a high-frequency oscillation type proximity switch having an output circuit that outputs a signal, a voltage control resistor connected to a current control end of the current mirror circuit as a resistor for controlling the conductance of the oscillation circuit, and whose resistance value is changed by a control voltage. a second feedback circuit that converts the resonant voltage of the resonant circuit into a voltage signal and positively feeds back the current of the current mirror circuit using an oscillation output; a direct current that detects the oscillation voltage of the oscillation circuit and corresponds to the amplitude; A small amplitude oscillation control comprising: a second detection circuit that obtains a voltage; and a transistor whose base receives the detection output of the second detection circuit, inverts and amplifies the output and supplies it as a voltage control signal to the voltage control resistance circuit. A high frequency oscillation type proximity switch, characterized in that a circuit is provided alongside the oscillation circuit. (2) The high frequency oscillation type proximity switch according to claim 1, wherein the voltage controlled resistance circuit includes a field effect transistor.