JPS593466Y2 - Proximity switch - Google Patents

Description

[Detailed explanation of the idea] This invention relates to a high frequency oscillation type proximity switch.

In general, the higher the sensitivity of this type of proximity switch, the more easily it is affected by surrounding noise.

Noise that enters through the stray capacitance that exists between the detection coil and surrounding conductors cannot be ignored, which can cause malfunctions, and the influence of stray capacitance changes depending on the grounding condition of the surrounding conductors, causing loss in the detection coil. This may lead to changes in characteristics such as operating distance.

In particular, in the case of proximity switches housed in a metal case, the metal case is electrically connected to the surrounding conductor via the mounting member, so stray capacitance is formed between the coil and the metal case. Since the gap between them is usually extremely small, the stray capacitance is large.
The above-mentioned disadvantages may become noticeable.

Therefore, in order to eliminate the above-mentioned disadvantages, measures such as attaching an electrostatic shield ring to the detection coil portion have been taken in conventional proximity switches.

Figure 1 shows a conventional proximity switch. In this figure, a detection coil 11 is wound around a coil bobbin 12 made of insulating synthetic resin, etc., and this is a pot-shaped ferrite core with an E-shaped cross section. It is built in 13 grooves.

The circuit section 21 has a circuit configuration as shown in FIG. 2, and is mounted on a printed circuit board 22.

The ferrite core 13, the circuit section 21, etc. are housed in a bottomed cylindrical synthetic resin case 31, and this synthetic resin case 31 is further connected to a cylindrical metal case 33 with both ends open.
It is housed and fixed inside.

The ferrite core 13, circuit section 21, etc. are made of synthetic resin 32.
It is fixed internally by filling it with.

Then, the inside of the case 31 is sealed by the rubber backing 34 and the presser plate 35.

The cable 23 is attached to this rubber backing 34 and the holding plate 3.
5 and is drawn out.

A male thread is formed on the outer surface of the metal case 33, so that it can be fixed by attaching a nut or the like to the outer surface.

The circuit section 21 is configured as shown in FIG.
Reference numeral 41 includes an oscillation circuit including a detection coil 11 and a resonant capacitor 42, and a switching circuit that performs switching according to the oscillation state of this oscillation circuit.

Capacitor 43 is for integration, and capacitor 44 is for smoothing.

An electrostatic shield ring 25 made of conductive metal as shown in FIG.
connected to ground.

As a result, the electrostatic shield ring 25 acts as an electrostatic shield, and since the ferrite core 13 also has a certain degree of conductivity, it acts as an electrostatic shield plate.

As described above, in the conventional proximity switch, the detection coil 11 is electrostatically shielded.

However, in this case, if the plate thickness of the electrostatic shield ring 25 is thick, the outer diameter of the ferrite core 13 becomes relatively small, and the detection area (detection distance) as a proximity switch
This is not preferable because it reduces the size of the image.

Furthermore, if the thickness of the ring 25 is made thinner, the above-mentioned problem will disappear, but the work of inserting and installing it into the case 31 together with the ferrite core 13 becomes troublesome. Especially when the ring 25 is formed of metal foil, the above-mentioned insertion and installation work becomes troublesome. It becomes difficult to do this stably.

On the other hand, since the electrostatic shield ring 25 is made of a conductive metal, its resistance value is low, and eddy current may flow therein, increasing the loss of the detection coil 11 and reducing the rate of change in sensitivity.

Therefore, it has been difficult to accurately and stably set the detection area (detection distance).

To solve this problem, it is possible to form a conductive vapor deposited film on the back surface of the ferrite core 13 and use this as an electrostatic shield, but it is generally difficult to form a vapor deposited film firmly on the ferrite core, and It is also difficult to reliably connect lead wires to this.

In view of the above, the object of this invention is to provide a proximity switch in which a conductive film can be firmly deposited on a ferrite core and a lead wire can be connected reliably.

According to this invention, in order to achieve the above object, a conductive vapor-deposited film is formed of a metal-deposited film that is vapor-deposited on the ferrite core and serves as a binder, palladium, nickel, etc. that is vapor-deposited on the ferrite core via this metal-deposited film, It is characterized by having a two-layer structure having a metal vapor deposited film of either gold or silver.

Hereinafter, one embodiment of this invention will be described with reference to the drawings from FIG. 4 onwards.

As shown in FIG. 4, FIG. 5, and FIG.
It is connected to ground number 1.

The conductive thin film 27 has a two-layer structure in which chromium is deposited on the ferrite core 13 in advance, and palladium is deposited on the chromium deposited film.

That is, the underlying chromium vapor-deposited film serves as a binder so that the palladium vapor-deposited film is firmly formed on the ferrite core 13.

And palladium is easy to solder and lead wire 2
6 can be easily soldered, and the soldered parts have sufficient connection strength.

By grounding the conductive thin film 27 formed of chromium and palladium vapor deposited films in this way, the conductive thin film 27 itself acts as an electrostatic shield plate for the detection coil 11.

If the thickness of the ROM vapor-deposited film is approximately 300 to 400 A, and the palladium vapor-deposited film is formed to a thickness of approximately 600 to 800 A, an appropriate resistance value can be obtained as the conductive thin film 27, and the eddying can be achieved without impairing the electrostatic shielding effect. Loss in the detection coil 11 due to current generation can be prevented, and sensitivity changes will not occur.

On the other hand, compared to the electrostatic shield ring 25 described above, the conductive thin film 27 is formed even on the back surface of the ferrite core 13, so that the electrostatic shielding effect is more effectively performed.

As mentioned above, in this proximity switch, the ferrite core 13
The detection coil 11 is effectively electrostatically shielded by the extremely thin conductive thin film 27 firmly formed thereon.

Therefore, there is no fear that the outer diameter of the ferrite core 13 will be reduced due to the thickness of the electrostatic shielding member, and the insertion and installation work into the case 31 and wiring work can be easily performed.

Note that the same effect can be obtained by forming a metal vapor deposition film of gold, silver, nickel, etc. other than palladium.

In this case, the material of the metal vapor-deposited film serving as the binder is appropriately selected.

Furthermore, if one lead wire of the detection coil 11 is connected to the conductive thin film 27 as shown in FIG. 7, the circuit configuration will not change and the wiring work for this lead wire can be streamlined, which is economical. .

Note that the configuration of other parts such as the circuit section 21 in FIG.
Since it is substantially the same as the figure, corresponding numbers will be given to corresponding parts and explanations will be omitted.

As described above for the first embodiment, according to this invention, a conductive vapor deposited film is formed by a metal vapor deposited film which is vapor deposited on the ferrite core and serves as a binder, and a palladium vapor deposited film which is vapor deposited on the ferrite core via this metal vapor deposition film. , palladium, nickel or gold.

Silver is vapor-deposited on the ferrite core via a metal vapor-deposited film serving as a binder, and these metal vapor-deposited films are firmly formed on the ferrite core.

Therefore, when connecting the lead wire by soldering and grounding, soldering can be done easily, and
By soldering the lead wires, it is extremely unlikely that the metal vapor deposited film at the rear lead wire connection portion will be damaged, resulting in a poor connection to the ground, and the yield will be improved.

[Brief explanation of drawings]

Fig. 1 is a longitudinal sectional view showing a conventional example, Fig. 2 is a circuit diagram thereof, Fig. 3 is a perspective view showing an electrostatic shield ring, and Figs. 4 and 5 are both related to one embodiment of the present invention. FIG. 6 is a longitudinal sectional view of the proximity switch; FIG. 7 is a sectional view showing the detection coil portion of the proximity switch and explaining the wiring relationship. . 11...Detection coil, 13...Ferrite core, 21...Circuit section, 25...
Electrostatic shield ring, 27... Conductive thin film, 33
・・・・・・Metal case.

Claims (1)

[Scope of utility model registration request] A detection coil that responds to the approach of a detection object, a ferrite core arranged to surround this detection coil, and the detection coil together form an oscillation circuit, and the oscillation state changes as the detection object approaches. and a conductive vapor deposited film deposited on the ferrite core, and by soldering a lead wire to the conductive vapor deposited film, the conductive vapor deposited film can be connected to the circuit portion. In the proximity switch connected to ground, the conductive vapor deposited film includes a metal vapor deposited film that is vapor deposited on the ferrite core and serves as a binder, and palladium, nickel, gold, and the like that are vapor deposited on the ferrite core via this metal vapor deposition film. 1. A proximity switch characterized by having a two-layer structure comprising a metal vapor-deposited film of silver.