JPH04142111A - Contactless switch - Google Patents

Abstract

PURPOSE:To simplify structure and to effectively prevent mutual interference from occurring by providing a Hartley oscillation circuit which supplies a constant current to a resonance circuit and feeds back the current to a coil on one side connected in series. CONSTITUTION:The collector of a transistor Tr3 is connected to the common connection terminal of detection coils L1, L2, and it is grounded via a capacitor C2 to help the growth of oscillation, and also, the emitter of a transistor Tr1 is grounded via a resistor R1 for sensitivity adjustment, and is connected to a comparator 11. The comparator 11 outputs the detection signal of a material by rectifying a voltage obtained at the base of the transistor Tr1, and discriminating a signal by a constant level. in such a way, since the approach of two materials in a detecting area can be detected by separating the detection coils L1, L2 by using one oscillation circuit, a price can be reduced, and also, since oscillation is performed at the same oscillation circuit, to mutual interference occurs, and an abnormal operation due to the mutual interference can be prevented from occurring.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a proximity switch with two coils.

[Prior art] Conventional high-frequency oscillation type proximity switches oscillate at a constant frequency using an oscillation circuit that includes a coil and a capacitor.
When an object such as a metal object approaches and the oscillation output decreases,
Objects are detected by detecting a decrease in the output. FIG. 5 is a circuit diagram showing an example of an oscillation circuit of such a proximity switch. In this figure, a constant current source 1 and a voltage a! are connected to a resonant circuit consisting of a coil and a capacitor C. A constant current is supplied via 2. One end of the hot end of the resonant circuit is connected to the base of the transistor Tri via the voltage source 2, and a current mirror circuit consisting of transistors Tr2 and Tr3 is connected to the collector of the hot end, and the mirror current is fed back to the resonant circuit. It is configured as follows. The emitter of the transistor Tri is grounded via an emitter resistor R1, and the emitter terminal serves as an output terminal to output an oscillation output to the outside.

[Problems to be Solved by the Invention] FIG. 6 is a schematic diagram of two such conventional proximity switches arranged close together for use in detecting pachinko balls. In this figure, when two proximity switches 3.4 are operated simultaneously to cause the oscillation circuit to oscillate, mutual interference may occur. Therefore, there was a drawback that it became impossible to accurately detect the passage of the metal sphere. In order to eliminate such drawbacks, it is necessary to provide a shield between the two proximity switches, but this also has the drawback of complicating the structure.

The present invention has been made in view of these conventional problems, and aims to simplify the structure of a proximity switch for detecting multiple objects and to effectively prevent mutual interference. Consider it a technical issue.

[Means for Solving the Problems] The present invention includes a resonant circuit composed of a plurality of series-connected coils and a capacitor, and a system that supplies a constant current to the resonant circuit and directs the current to one of the series-connected coils. The present invention is characterized by comprising a Hartley-type oscillation circuit for returning.

[Effect]

According to the proximity switch of the present invention having such characteristics, the separated Hartley type oscillation circuit having a plurality of coils always oscillates at a constant frequency. When a metal body comes close to at least one of the coils, the oscillation level decreases. Therefore, the proximity of a metal object is detected based on a decrease in the oscillation level.

[Embodiment] FIG. 1 is a circuit diagram showing the configuration of a high frequency oscillation type proximity switch according to a first embodiment of the present invention. In this figure, the same parts as those in the conventional example described above are given the same reference numerals, and detailed explanation will be omitted. Now, in this embodiment as well, a constant current source 1 and a voltage source 2 are connected to the power source Vcc, and one end of the voltage source 2 is connected to the coil L.
It is connected to a series connection body of L and L2 and a capacitor C1 connected in parallel thereto. The coils Ll and L2 are detection coils having the same inductance. The other ends of these are commonly connected and connected to a ground end. Further, one end of the voltage source 2 is connected to the base of the transistor Trl. The transistor Tri is a transistor for converting voltage into current, and has transistors Tr2. A current mirror circuit consisting of Tr3 is connected. Now, in this embodiment, the transistor T
The collector of r3 is connected to the common connection end of the detection coils LL and L2, and a capacitor C2 is connected to the common connection end of the detection coils LL and L2.
is grounded through. The emitter of the transistor Tri is grounded via a sensitivity adjustment resistor R1, and is also connected to a comparator circuit 11. The comparator circuit 11 rectifies the voltage obtained at the base of the transistor Tri and outputs an object detection signal by discriminating the signal at a constant level.

Now, the structure of the proximity switch according to this embodiment will be explained with reference to FIG. In this embodiment, a case is shown in which this proximity switch is used as a proximity switch for detecting a metal ball. In this embodiment, two through holes 1314 are provided close to the case 12 as shown in the figure. The through holes 13, 14 are provided at positions through which the metal balls pass. Now, the above-mentioned detection coils L1 and L2 are arranged in the case in close proximity to these through holes 13 and 14, and the other circuit parts are arranged in the detection circuit section 15 on the printed circuit board in the case. The detection circuit section 15 may be configured using an IC-based detection circuit.

Next, the operation of this embodiment will be explained. First, Figure 3 (a
), as shown in (b), which detection coil LIL2
If there is no object nearby, the Hartley type oscillation circuit oscillates at a constant frequency as shown in FIG. 3(C), and a constant high frequency signal is output from the emitter of the transistor Tri. By rectifying and discriminating this signal by the comparator circuit 11, a signal as shown in FIG. 3(d) is output.

Now, one of the detection coils, for example, detection coil L1
When an object approaches, the oscillation by the oscillation circuit stops, and the output of the comparison circuit 11 is also turned off as shown in FIG. 3(d), making it possible to detect the object. Then, when the object separates from the detection coil L1, oscillation starts again. Similarly, when an object approaches one or both of the detection coils LL and L2, the oscillation will be stopped as shown.

Therefore, when an object approaches one of the coils, the object can be detected, and a logical OR detection signal can be obtained.

FIG. 4 is a circuit diagram of a proximity switch according to a second embodiment of the present invention. Also in this embodiment, the detection coils LL, L2
Similarly to the first embodiment described above, a resonant circuit is formed by the capacitor C1 and the capacitor C1. In this embodiment, power is supplied from the power supply to the resonant circuit via the resistor R2 and the transistor Tr4, and the voltage at the hot end of the resonant circuit is applied to the base of the transistor Tr5. The transistor Tr5 converts this voltage into a current value, which is returned to the connection point between the detection coils LL and L2 of the resonant circuit via the resistor R3. The emitter terminal of the transistor Tr5 is connected to the comparator circuit 1.
1 is the same as in the first embodiment described above. Also in this embodiment, when an object approaches one or both of the detection coils LL and L2, an object detection signal can be outputted by the logical sum thereof.

〔Effect of the invention〕

As described above in detail, according to the present invention, the proximity of an object in two detection areas can be detected by separating the detection coils using one oscillation circuit. Therefore, compared to the case where a plurality of proximity switches are used, the cost can be significantly reduced. Further, since the detection sensitivity of each coil is determined only by the precision of the coil, adjustment becomes easy. Furthermore, since they oscillate in the same oscillation circuit, there is no mutual interference.
It is possible to prevent abnormal operations due to mutual interference, and it is possible to obtain the effects that a mechanism such as a shield can be made unnecessary.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the configuration of a proximity switch according to a first embodiment of the present invention, FIG. 2 is a schematic diagram showing its structure, FIG. 3 is a time chart showing the operation of this embodiment, and FIG. A circuit diagram showing the configuration of a proximity switch according to a second embodiment of the present invention, FIG. 5 is a circuit diagram of an oscillation circuit of a conventional proximity switch, and FIG. 6 is a schematic diagram of a case where conventional proximity switches are arranged in parallel. be. LL, L2...--Detection coil C1--Capacitor 1--Constant current source 2--Voltage source 11 Comparison circuit case detection circuit section

Claims (1)

[Claims] (1) A resonant circuit composed of a plurality of series-connected coils and capacitors, and a Hartley-type oscillation circuit that supplies a constant current to the resonant circuit and returns the current to one of the series-connected coils. A proximity switch comprising: