JPH1140022A - Capacitance proximity sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To position a sensing electrode inside a case properly and eliminate the dispersion due to the intrusion of resin of the like by composing a proximity sensor by bonding the sensing electrode to the inside surface of the case using a pressure sensitive adhesive double coated tape having an adhesive layer each on both surfaces of its base of high insulating property. SOLUTION: A double-sided printed circuit board 22 on one side of which a sensing electrode pattern is formed is fixed in a case 21; an electronic circuit part 23 is packaged on the upper side of the printed circuit board 22. By bonding the printed circuit board 22 to the inside of a sensing surface of the case 21 tightly using a pressure sensitivity adhesive double coated tape 24, the dispersion in the thickness direction can be reduced. In this case, the adhesive double coated tape 24 is made of a thin film comprising a material having a high insulating property such as polyester, fluoro resin or polyimide. Thereby, the influence on the sensing characteristics can be reduced; because the part in between te sensing electrode and the sensing surface of the case is covered by the pressure sensitive adhesive double coated tape 24, resin is prevented form intruding there when the resin is filled into the case so that the characteristics of a proximity sensor can be stabilized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitance type proximity sensor, and more particularly to a capacitance type proximity sensor characterized by a method of fixing a detection electrode in a case.

[0002]

2. Description of the Related Art As shown in FIG. 5, a capacitance type proximity sensor has a detection electrode 1 made of a conductive thin plate such as brass or copper disposed on a front surface of a case or the like, and is connected between the detection electrode 1 and a circuit power supply. The oscillation circuit 2 is configured such that the oscillation condition changes with the capacitance of the oscillation circuit 2. When the object 3 approaches the vicinity of the detection electrode 1 of the oscillation circuit 2, the capacitance value between the detection electrode 1 and the circuit power supply changes.

FIG. 5 (a) shows a capacitance Co between the detection electrode 1, the oscillation circuit 2 and the circuit power supply. When the detection target 3 approaches, the capacitance between the detection electrode 1 and the circuit power supply becomes Co '. . Co ′ is the capacitance C2 between the detection electrode 1 and the detection target 3
Further, assuming that the capacitance between the power supply line and the ground is C1, it is expressed by the following equation. Co '= Co + C2 // C1 When C1 is sufficiently larger than C2, Co' ≒ Co + C2
Becomes Thus, the oscillation state of the oscillation circuit 2 changes due to the approach of the detection target 3.

A change in the oscillation state is detected by a subsequent signal processing circuit, and a detection signal is output. The capacitance type proximity sensor can be classified into various modes such as an oscillation start type, an oscillation stop type, an amplitude change type, and a frequency change type according to a change in the oscillation state.

FIG. 6 is a block diagram showing an example of an amplitude change type proximity sensor. The oscillation circuit 2 is connected to the detection electrode 1 as described above, and the output of the oscillation circuit 2 is integrated by the integration circuit 4. Then, the amplitude level is discriminated by the discrimination circuit 5, and the output of the discrimination circuit 5 is output to the logic processing circuit 6.
Give to. The logic processing circuit 6 determines the proximity of an object and outputs an object detection signal to the outside via the output circuit 7. Reference numeral 8 denotes a power supply circuit that supplies a voltage to each unit.

FIG. 7 is a sectional view showing an example of a conventional capacitance type proximity sensor. In this figure, the lower surface of the case 11 is a detection surface, and the inner surface thereof has protrusions 12 at a plurality of locations.
are formed. The above-mentioned detection electrode 1 is provided with an opening at the position of the projection. The opening of the detection electrode 1 is positioned in accordance with the projections 12a, 12b,... And fixed by heat caulking or the like. And the printed circuit board 13
The oscillation circuit 2 and another detection circuit are mounted thereon, and the gap is covered with the filling resin 14 to constitute a proximity sensor.

[0007]

In such a conventional proximity sensor, a projection is formed on the inner surface of the case 11 so that the detection electrode 1 is positioned. Between the case and the case. Further, since the resin is filled, the resin sometimes enters between the detection electrode and the case. Such a variation in the distance between the detection electrode 1 and the case and a large variation in the capacitance due to the resin entering between the detection electrode 1 and the inside of the case are large, which has a disadvantage that the detection characteristics are greatly affected. . In recent years, the size and thickness of the proximity sensor have been reduced, and it is necessary to reduce the thickness of the case detection surface. For this reason, it may not be possible to provide projections for press-fitting and swaging. Even when the projection is provided on the inner surface of the case, since the case is made thinner, stress is concentrated on the projection and there is a disadvantage that a crack may be caused.

The present invention has been made in view of such a conventional problem, and it is an object of the present invention to accurately position a detection electrode inside a case so as to eliminate variations caused by resin or the like entering. With the goal. It is another object of the present invention to provide a capacitive proximity sensor in which a crack is hardly generated even when a thin case is used, and is hardly affected by the crack.

[0009]

According to a first aspect of the present invention, there is provided an oscillation circuit which oscillates according to a capacitance between a detection electrode, the detection electrode and a circuit power supply, and detects an oscillation state of the oscillation circuit. And a signal processing circuit, wherein the detection electrode is bonded to the inner surface of the case using a double-sided adhesive tape.

According to a second aspect of the present invention, in the capacitive proximity sensor according to the first aspect, the double-sided adhesive tape has a highly insulating base material and adhesive layers on both surfaces thereof. It is.

According to the first aspect of the present invention having such a feature, it is difficult for the filling resin to enter between the detection electrode and the inner surface of the case, and the gap therebetween can be kept constant. According to the second aspect of the present invention, a double-sided adhesive tape having a high insulating base material is provided so that even if a crack occurs, the signal processing circuit and the oscillation circuit on the printed circuit board are not affected.

[0012]

FIG. 1 is a sectional view showing a configuration of a capacitance type proximity sensor according to an embodiment of the present invention, and FIG. 2 is a diagram showing a detection surface and a component mounting surface of a double-sided printed circuit board. In the proximity sensor according to this embodiment, a double-sided printed circuit board 22 is fixed to a case 21. As shown in FIG. 2A, one surface of the printed circuit board 22 has the pattern 2 of the detection electrode.
2a are formed, and an annular shield electrode pattern 22b is formed therearound. A circuit pattern 22c for mounting components is formed on the other surface. On the upper surface of the printed circuit board 22, an electronic circuit section 23 composed of a chip component is mounted as shown in the figure, and blocks including the oscillating circuit 2 and the integrating circuit 3 of the capacitive proximity sensor described above are formed.

FIG. 3A is a front view showing an example of the case 21, FIG. 3B is a sectional view, and FIG. 3C is a rear view. As shown in these figures, the L-shaped linear projections 21a, 21b, 21c and the square projections 21 are formed at three places on the inner surface of the case 21.
d is formed, and the corners of the printed circuit board 22 are fixed by the projections. An opening 21e for introducing a cable is provided at the right end of the case. Then, the printed circuit board 22 is closely adhered to the inner side of the detection surface of the case by the double-sided adhesive tape 24. In FIG. 1, the component mounting surface on the upper part of the printed circuit board 22 is covered with a shield plate 25. The gap is filled with the resin 26, and the upper portion of the case 21 is covered with the lid 27 to form a proximity sensor.

FIG. 4 is a sectional view showing an example of a double-sided adhesive tape 24 used for bonding the printed circuit board 22. As shown in FIG. The double-sided adhesive tape 24 is formed of a support 24a made of a thin film of a highly insulating material such as polyester, fluororesin, or polyimide, and adhesive layers 24b and 24c on both surfaces thereof. The adhesive layers 24b and 24c are made of an adhesive material such as a resin-based or silicone-based rubber, and the whole is from 0.03 to
It has a thickness of 0.2 mm. The printed circuit board 22 is adhered to the case 21 using a double-sided adhesive tape 24 having a certain thickness, having substantially the same shape as the printed circuit board 22, and at least covering the detection electrode surface.

In this case, the printed circuit board 2 is
It is not necessary to attach a detection electrode separately from the above-mentioned example 2, and the attachment of the detection electrode is facilitated, so that a thin capacitive proximity sensor can be configured. Further, since the printed circuit board 22 is adhered to the case with the double-sided adhesive tape 24, the resin 26 is
1 and the detection electrode can be prevented from entering, and the variation in the detection characteristics can be eliminated.

In order to secure insulation when a crack occurs in the case 21, a double-sided adhesive tape using a material having high insulation resistance as a base material is used, but in order to reduce the influence on detection characteristics. Preferably, the double-sided adhesive tape is a thin double-sided adhesive tape. Further, in order to secure more insulating properties, it is also possible to use a double-sided adhesive tape having a thick support 24a.

In this embodiment, all the blocks of the capacitive proximity sensor are mounted on the printed circuit board 22, but only the oscillation circuit and the integration circuit of the capacitive proximity sensor are mounted on the printed circuit board. And a signal processing unit. Furthermore, the present invention may be applied to a capacitance type proximity sensor having a detection electrode on the front surface of a cylindrical case, and the detection electrode may be attached to the front inner surface of the case via a double-sided adhesive tape to form a capacitance type proximity sensor.

[0018]

As described above in detail, according to the present invention, since the detection electrode is adhered to the back side of the case detection surface by using a double-sided adhesive tape having an adhesive layer, the thickness direction is reduced. Can be reduced, and the influence on the detection characteristics can be reduced. Further, since the space between the detection electrode and the case detection surface is covered with the double-sided adhesive tape, even when the resin is filled, the resin does not enter into the space therebetween, and the effect that the characteristics can be stabilized can be obtained. . Further, the effect that the entire proximity sensor can be reduced in thickness can be obtained. According to the second aspect of the present invention, in addition to this, even if a crack occurs in the case, there is an effect that the internal circuit is hardly affected.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a configuration of a capacitance type proximity sensor according to an embodiment of the present invention.

FIG. 2 is a diagram showing a pattern of a printed circuit board of the capacitance type proximity sensor according to the embodiment.

3A is a front view of a case of the capacitive proximity sensor according to the embodiment, FIG. 3B is a rear view, and FIG. 3C is a cross-sectional view.

FIG. 4 is a cross-sectional view showing an example of a double-sided adhesive tape.

FIG. 5 is a diagram illustrating a detection principle of a capacitance type proximity sensor.

FIG. 6 is a block diagram illustrating a configuration of a capacitance type proximity sensor.

FIG. 7 is a cross-sectional view illustrating an example of a conventional capacitive proximity sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Detection electrode 2 Oscillation circuit 3 Detected object 4 Integration circuit 5 Discrimination circuit 6 Logic processing circuit 7 Output circuit 21 Case 22 Printed board 22a Detection electrode pattern 23 Electronic circuit part 24 Double-sided adhesive tape 25 Shield plate 26 Filling resin

Claims (2)

[Claims] 1. An electrostatic proximity device comprising: a detection electrode; an oscillation circuit that oscillates according to a capacitance between the detection electrode and a circuit power supply; and a signal processing circuit that detects an oscillation state of the oscillation circuit. In the sensor, the detection electrode is configured to be adhered to an inner surface of a case using a double-sided adhesive tape. 2. The electrostatic capacitance type proximity sensor according to claim 1, wherein the double-sided adhesive tape has a highly insulating base material and an adhesive layer on both surfaces thereof.