JPS6231773B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a capacitive proximity switch,
Especially regarding its structure.

The operating principle of a capacitive proximity switch is that the circuit operates when the capacitance that the detection electrode has between the ground changes when an object approaches. Compared to switches, it is often used because it is advantageous in terms of detection distance for non-magnetic metals and detection of objects other than metals.

FIG. 1 shows a typical conventional example of a capacitive proximity switch. As shown in this figure, a printed circuit board 3 on which a detection electrode 2 is arranged is arranged at the bottom of a bottomed cylindrical resin case 1, and a printed circuit board 5 on which a circuit section 4 is mounted, the electrode 2 and a cable 6 are connected to each other. After electrically connecting and placing the printed circuit board 5 inside the case 1, a resin 7 such as epoxy is filled in to protect the circuit section 4 and the like from vibrations, shocks, etc., and to maintain sealing properties. Thereafter, the cable holding member 8 which also serves as a lid is attached to the case 1.

By the way, when the resin 7 is filled up to the periphery of the detection electrode 2, the detection change rate decreases due to the dielectric detection function of this electrode 2, and minute capacitance changes are stably detected (especially with respect to changes in ambient temperature). Therefore, conventionally, as shown in this figure, a hollow member 9 is used to connect the electrode 2 and a part 41 of the oscillation circuit of the circuit section 4 into the cavity 91 of the hollow member 9. It is arranged to keep the filled resin 7 away. Further, the hollow member 9 may be made of metal and also have an electrostatic shielding function.

However, using such a separately manufactured hollow member 9 only unnecessarily complicates the structure, takes time and effort to assemble, and increases the price.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a capacitive proximity switch which eliminates the above-mentioned drawbacks, has a simple structure, is easy to assemble, and can be manufactured at a low cost.

An embodiment of the present invention will be described below with reference to FIG. In this figure, a printed circuit board 3 having a detection electrode 2 formed of copper foil or the like and a printed circuit board 5 on which a circuit section 4 is mounted are connected in advance with a terminal member 31, and the printed circuit board 5 is connected in advance with a terminal member 31.
After connecting the cable 6 to the cylindrical resin case 1, the cable 6 is inserted into the bottomed cylindrical resin case 1 through its opening. Then, the opening is first filled with foamed resin 71 and then with resin 7 such as non-foamed epoxy. There are various types of foamed resin, but polyurethane-based ones in particular are 50 to 90% gaseous.
Even if the area around the electrode 2 is filled, there is little effect on detection sensitivity. In this case, the closed cell type has good sealing properties against the subsequent epoxy resin 7 and others. Moreover, the hard form is advantageous in terms of mechanical strength from the outside of the case 1. Filling with the epoxy resin 7 is effective in improving the tensile strength and external mechanical strength of the cable 6. If the material of the case 1 is epoxy, ABS, etc., it is particularly effective in terms of adhesive strength, water resistance, etc. in combination with a bottomed cylindrical shape.

If the terminal member 31 is press-fitted into the printed circuit boards 3, 5 by providing flanges at both ends thereof and bringing the flanges into contact with the printed circuit boards 3, 5, the positional relationship between the two circuit boards 3, 5 can be changed. Variations are eliminated, and variations in operating distance settings are also reduced. Also case 1
If the thickness and material are such that it will not bend when inserted, it will be easier to handle.

As shown in FIG. 2, when a shield tube 92 is provided as required, handling can be facilitated by soldering small protrusions to the substrate 3. Further, the shield cylinder 92 is not a complete cylinder, but may be a cylinder with a portion cut out, such as a plate pressed (rolled).

For example, in the case of a fixed operating distance type, after connecting the printed circuit boards 3 and 5, the circuit section 4 etc. may be adjusted in advance to set a predetermined operating distance, and then the case 1 may be housed and filled with resin. When adjusting the operating distance, a part of the electrode 2 vicinity may be partially molded with foamed resin and stored, and the foamed resin 71 and epoxy resin 7 may be newly filled.

As described above, by filling the area around the electrode at the bottom of the case with foamed resin, the present invention can stably detect minute capacitance changes without reducing the detection rate of change, similar to the case using a hollow member. Therefore, there is no possibility of malfunction. In addition, compared to the case where hollow members are used, there is no cavity for creating a space, and the circuit parts can be gathered in one place, so the structure and assembly are simplified, and the cost of parts and assembly can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of a conventional example, and FIG. 2 is a longitudinal sectional view of an embodiment of the present invention. 1... Bottomed cylindrical resin case, 2... Detection electrode,
3, 5... Printed circuit board, 31... Terminal member, 4... Circuit portion, 6... Cable, 7... Non-foamed resin, 71... Foamed resin, 8... Cable holding member that also serves as a lid, 9... Cavity member, 92... Shield tube.

Claims (1)

[Claims] 1 A detection electrode is arranged at the bottom of a bottomed cylindrical resin case, a circuit section connected to the detection electrode is housed in the case, and foamed resin is filled around the electrode at the bottom. Features: Capacitive proximity switch.