JP2889646B2 - Capacitive detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an improvement in the structure of a capacitance type detector that converts a minute mechanical displacement into an electric signal as a change in capacitance. It is about.

<Prior Art> A conventional detector of this type is disclosed in a patent application filed on March 9, 1999 by the present applicant.

As shown in FIG. 2, the detector accommodates a detection section A having a parallel leaf spring structure in a cylindrical case 2 made of a metal material.

The detecting unit A includes two plate springs 4 and 6 formed of two metal members mounted in the cylindrical case 2 and the above-described parallel plate so as to be movable substantially on the axial center line of the cylindrical case 2. A metal core shaft 8 supported by springs 4 and 6 and a cylindrical metal core electrode 10 attached to the core shaft 8 between parallel leaf springs via an insulating pipe 9 made of a cylindrical plastic material. And a pair of ring-shaped fixed electrodes made of metal attached to the inner peripheral wall of the cylindrical case 2 via an insulating cylinder 3 made of a plastic material between the leaf springs with a certain gap from the outer peripheral surface of the core electrode 10. 12 and 14, the displacement of the core shaft 8 is controlled by the core electrode 10 and the pair of fixed electrodes 1
The signals are converted differentially into electric signals as the amount of change in capacitance by the signals 2 and 14.

The fixed electrodes 12 and 14 of the detection section A are made of spacers 16, 18, 20 and 22 made of a metal material with reference to a ring-shaped projection 2a below the inner peripheral wall of the cylindrical case 2, and a plastic sheet such as polyester. Insulating sheets 5a, 5b and 5c
And is fixed between the first case nut 50 fitted into the opening 2b of the case 2 and the projecting portion 2a of the case 2. The core electrode 10 is formed by spacers 24, 26, 28, and 30 made of a metal material and insulating sheets 7a and 7b made of a plastic sheet material such as polyester with reference to the upper surface 8b of the lower step portion 8a of the core shaft 8. The core shaft 8 is positioned and fixed between the first shaft nut 52 and the step 8a of the core shaft 8, which is screwed to the screw portion on the distal end side of the core shaft 8. After the detection unit A is inserted into the case 2 and fixed by the first case nut 50 and the first shaft nut 52 in this manner, foreign matter (moisture,
For the purpose of preventing invasion of abrasives, dust, etc.), a moisture-proof film 32 made of a thin, flexible, chemically stable polyethylene film or the like is provided inside the case so as to close the opening 2b of the cylindrical case 2. On the side of the peripheral wall and the side of the core shaft, packings 34, 36 and 38, 40, such as Teflon, which have a small coefficient of friction and a high elasticity with the moisture-proof film 32, respectively.
And is fixed between the first case nut 50 and the second case nut 54 on the inner peripheral wall side of the case, and is fixed by the second shaft nut 56 on the core shaft side. It is sandwiched and fixed between the first shaft nut 52.

That is, focusing on the detection unit A in the above structure, this detection unit A is a fixing member (a second case nut 54 and a second shaft nut 56) different from the fixing members (the second case nut 54 and the second shaft nut 56) of the moisture-proof film 32 and the packings 34 to 40. Since the first case nut 50 and the first shaft nut 52) are fixed in the case 2 at a stage before the moisture-proof film 32 and the packings 34 to 40, the coefficient of linear expansion of iron with respect to a change in ambient temperature is reduced. The influence of temperature change of the moisture-proof film 32 and the packings 34 to 40 made of polyethylene and Teflon, such as 10 to 20 times, on the inside of the detection unit A is avoided.

<Problems to be Solved by the Invention> However, even in the above structure, the insulating sheets 5a, 5b, 5c and 7a, 7b made of a polyester film having a coefficient several times larger than the linear expansion coefficient of iron in the detecting section A, and the insulating pipe 9 Since the insulating cylinder 3 is interposed, for a large temperature change, for example, as a temperature difference of 10 ° C. or even 20 ° C., a slight error in the indication of the detector before and after the temperature change, so-called temperature hysteresis occurs. I have.

Therefore, in the present invention, before the moisture-proof film and the packing, the detection portion A fixed in the case by a fixing member separate from the moisture-proof film and the packing is entirely made of a metal material and a linear expansion of the metal material. An object of the present invention is to provide a more stable and high-accuracy capacitance type detector even with a large temperature change due to a ceramic material having substantially the same coefficient.

<Means for Solving the Problems> A capacitance type detector according to the present invention includes a cylindrical case,
A cylindrical core electrode movably supported via a core axis on the center side between two parallel leaf springs, and a ring-shaped opposed face of the core electrode between the leaf springs with a fixed gap to the outer peripheral surface of the core electrode. Having a pair of fixed electrodes, a detection unit housed in the case, a moisture-proof film disposed via a packing member so as to close one open end of the case, and the detection unit includes a moisture-proof film and In the capacitance type detector fixed in the case at a stage preceding the moisture-proof film and the packing member by a fixing member different from the fixing member of the packing member, the detection unit is entirely formed of a metal material and a ceramic material. It is characterized by the following.

<Operation> The detection unit in the capacitance type detector according to the present invention is fixed in the case by a fixing member different from the moisture-proof film and the packing member, and is entirely formed of a metal material and a ceramic material. Therefore, the expansion and contraction of the moisture-proof film and the packing member do not directly affect the fixed portion of the detection unit, and the detection unit performs almost the same expansion and contraction as the detection unit integrally,
It is possible to maintain high accuracy with respect to temperature changes.

<Example> Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view showing the structure of a capacitance type detector according to a preferred embodiment of the present invention.

The same parts as those of the capacitance type detector shown in FIG. 2 are denoted by the same reference numerals.

The detector in this embodiment is substantially the same as the detector shown in FIG. 2 except that the structure and constituent members of the detection unit A are different.

That is, the detection unit A in the present embodiment includes the parallel leaf springs 4 and 6, the core electrodes 110, and the spacers 24 and 3, which are members on the core shaft 8 side.
0, The insulating spacers 126 and 128 of the core electrode 110 are sandwiched and fixed between the first shaft nut 52 attached to the core shaft 8 and the step 8a of the core shaft 8. The parallel leaf springs 4 and 6, the fixed electrodes 112 and 114, the spacers 16 and 22, and the insulating spacers 118, 119 and 120 of the fixed electrodes 112 and 114, which are members on the inner peripheral wall side of the case 2 of the detection unit A, fit into the opening 2b of the case 2. The first case nut 50 and the projecting portion 2a of the case 2 are sandwiched and fixed. Then, the insulating spacers 126 and 12
8 and 118, 119, and 120 are formed of a ceramic material substantially equal to the coefficient of linear expansion of iron, and the core electrode 8 and the fixed electrode
112 and 114 are electrically insulated from each other. Members other than the insulating spacers are formed of a metal material. Therefore, the detection section A in this embodiment is entirely formed of a metal material and a ceramic material.

<Effects of the Invention> According to the present invention, only the detection unit is fixed in the case without the interposition of the moisture-proof film and the packing member, that is, all the members having a large linear expansion coefficient are removed, and the detection unit has substantially the same linear expansion. Since it is formed only with a member having a coefficient, the detection part itself is of course, even for a large temperature change such as a temperature change of 10 ° C. or more, a large expansion of the moisture-proof film and the packing member, The shrinkage has no effect on the detection unit, and stable high accuracy can be ensured for a long period of time.

[Brief description of the drawings]

FIG. 1 is a sectional view of a capacitance type detector according to an embodiment of the present invention, and FIG. 2 is a sectional view of a conventional capacitance type detector. 2 ... case, 4, 6 ... parallel leaf spring, 8 ... core shaft, 110
…… Core electrode, 112,114 …… Fixed electrode, 16,22,24,30 ……
Spacers, 118, 119, 120, 126, 128 ... Insulating spacers, 32
…… Moisture proof film, 34,36,38,40 …… Packing, 50 ……
1st case nut, 52 ... 1st shaft nut, 54 ... 2nd case nut, 56 ... 2nd shaft nut.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01B 7/00-7/34 G01D 5/24

Claims (1)

(57) [Claims] 1. A cylindrical case, a cylindrical core electrode movably supported via a core shaft at a center side between two parallel leaf springs, and the core electrode within the leaf spring. It has a pair of ring-shaped fixed electrodes opposed to the outer peripheral surface with a certain gap, and is disposed via a packing member so as to close a detection portion housed in the case and one open end of the case. The moisture-proof film and the detection unit are fixed in the case at a stage preceding the moisture-proof film and the packing member by a fixing member different from the fixing member for the moisture-proof film and the packing member. , Wherein the detection section is formed entirely of a metal material and a ceramic material.