JPH0422815A - Electrostatic capacity type displacement detector - Google Patents

Abstract

PURPOSE:To eliminate influence by floating capacity between plural electrodes on detection accuracy by providing a shield member between each confronting plane of plural cylindrical electrodes arranged coaxially via a constant gap on a common electrode. CONSTITUTION:The internal plane 1d of a case 1 is set as a reference guide plane, and a shield plate 12 that is the shield member is provided between the confronting planes of a variable electrode 2 and a reference electrode 3 mounted on the common electrode 20. Since the potential of the shield plate 12 is set at ground potential same as that of the case 1, an electric line of force generated between the confronting planes of the variable electrode 2 and the reference electrode 3 is shielded with the shield plate 12. Therefore, the electric line of force via the confronting planes of the electrodes can be prevented from functioning directly. Thereby, the flow-in of the current via the floating capacity to the electrodes can be eliminated by the shield plate 12 by grounding.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention uses mechanical displacement as a change in capacitance,
It relates to the structure of a capacitive displacement detector that converts it into an electrical signal, and in particular, it includes a plurality of cylindrical electrodes arranged close to each other on the same central axis, and a constant distance between each of these electrodes. a cylindrical screen supported movably in the axial direction within the gap between one of the cylindrical electrodes and the common electrode; The present invention relates to an improvement in the structure of a capacitive displacement detector that electrically detects the amount of mechanical displacement of an integral spindle as the amount of change in capacitance made up of a cylindrical electrode and a common electrode.

[Conventional technology]

FIG. 4 is a sectional view showing the structure of a conventional capacitive displacement detector, which is disclosed in, for example, British Patent No. 1,347,235.

In FIG. 4, inside the cylindrical case 51, there are cylindrical first 'g1
A pole (variable electrode) 52 and a second electrode (reference electrode) 53, which is also cylindrical, are provided coaxially. Second electrode 53
A guard ring 55 insulated from the 21i-th pole 53 by an insulating member 56 is provided on the opposite side of the 111-th pole 52 . The common electrode 57 is connected to the first electrode 5 at its right end via an insulating member to the small diameter stepped inner cylinder 51b of the case 51.
2 and the second i-pole 53 in a cylindrical shape. A screw hole 59 is bored in the axis of the common electrode 57, and a set screw 60 is screwed into the screw hole 59. The plurality of holes 61 are drilled from the side surface of the common electrode 57 so as to meet the screw holes 59, and set screws 60
By adjusting the position of , the area of the common electrode 570 facing the second electrode 53 is adjusted, and the capacitance between the second electrode 53 and the common electrode 57 can be adjusted depending on the purpose.

The screen 62 is pivotally supported by a bearing 63 at the end of the case 51 so as to be movable in the axial direction of arrow a within the gap between the first electrode 52 and the common electrode 57, and is integrally provided. A spindle 62a projects outward from the bearing 63. The bearing 63 is connected to the 111th pole 5 by the insulating member 64.
2, and is attached to the left open end of the case 51. Lead wires 65 from the first and second electrodes 52,53
．． 66 passes through the gap between the inner surface 51a of the case 51 and the outer periphery of each electrode 52.53 and the insulating member 54.56, and passes through the hole 51c in the end wall of the case 51 on the opposite side of the storage side of the screen 62 to the outside. It can be connected to a cable 70 of an electrical measuring device (not shown). Further, the lead wire 67 from the guard ring 55 is connected to the lead wire 65.66.
Similarly, it is connected to the ground potential through the hole 51c of the case 51. A node vA68 from the common electrode 57 is also connected to the cable 71 at the end of the case 51 opposite to the screen 62. A cover 69 protects the lead wires 65, 66, 67, and 68.

Insulating member 64. First electrode 52. Insulating member 54 second electrode 5
3. The insulating member 56 and the guard ring 55 are connected to each other in this order toward the right by means such as II@next press-fitting, and finally the left end side of the left end insulating member 64 is connected to the bearing 63, so that A series of members from the insulating member 64 to the guard ring 55 are supported by a bearing 63 in a cantilevered state.

Next, the operation will be explained.

In FIG. 4, two cylindrical first . Second electrode 52.
The first electrode 5
a variable capacitance C1 between the second electrode 57 and the common electrode 57;
A reference capacitance C2 between the common electrode 57 and the common electrode 57 is formed. The screen 62 moves in the axial direction only within the gap between the first pole 52 and the common electrode 57, changing the capacitance C1. On the other hand, the capacitance C2 does not change because the screen 62 does not enter the gap between the second-l pole 53 and the common electrode 57, and is kept constant and becomes the reference capacitance.

Therefore, the arrow a of the spindle 62a and the screen 62
The capacitance CI changes in accordance with the displacement in the direction, and the difference in capacitance between the reference capacitance C2 and the variable capacitance C1 (C2-CI) is detected by the common electrode 57 in proportion to the displacement of the screen 62.

[Problems to be Solved by the Invention] In this type of displacement detector, the linearity, that is, the amount of change in capacitance obtained when the spindle 62a (screen 62) is displaced by a unit length, is a constant value throughout the measurement range. This fact and the stability and accuracy of the detected value when the spindle 62a is stationary are extremely important items in evaluating the detector.

This requirement becomes more severe as the detector has a high resolution and high precision on the submicron order.

In the conventional capacitive displacement detector described above, the first electrode 52
The gap between the opposing surfaces of the first electrode 53 and the second electrode 53 is narrower than the gap between the respective common electrodes 57, and no measures have been taken to prevent stray capacitance occurring near the opposing surfaces. The flow of current through the stray capacitance due to the alternating current voltage applied to the second electrodes 52, 53 is difficult, and is a major cause of errors in linearity and stability.

In addition, the guard ring 55 provided to prevent the influence of stray capacitance on the right end side of the second electrode 53 has to be provided with a lead wire 67 to connect it to the ground potential, which leads to a reduction in the diameter of the detector. There was a problem with workability.

This invention was made to solve the above-mentioned problems, and its purpose is to provide a capacitive displacement detector that eliminates the influence of stray capacitance between multiple electrodes on detection accuracy. It is said that

(Means for Solving the Problems) In the present invention, a shield member is provided between each opposing surface of a plurality of cylindrical electrodes arranged coaxially with a certain gap between them with respect to a common electrode.

[For production]

The capacitive displacement detector according to the present invention is constructed by providing a shield member between the opposing surfaces of the cylindrical electrodes, which are attached using the inner cylinder of the case as a reference guide surface. The negative influence on accuracy can be eliminated, and the ground potential can be obtained by bringing the shield member into direct or indirect contact with the inner surface of the case.

〔Example〕

FIG. 1(A) and FIG. 1(B) are cross-sectional side views showing a preferred embodiment of a capacitive displacement detector according to the present invention. FIG. 2 is an enlarged view of the vicinity of the insulating member 10 shown in FIG. 1(B).

In Figures 1 and 2, 1 is a cylindrical case;
It is open on the left and right, and there is a threaded part 1a on the left and right opening ends.
, lc. 2 is a cylindrical variable electrode;
is also a cylindrical reference electrode, and these two electrodes 2.3
are three insulating members 4 guided on the inner surface 1d of the case 1.
, 10 and 5, it is electrically insulated from other members and supported coaxially with the case 1. The inner surface 1d of the case 1 is the same reference guide surface in the radial direction of the members housed in the case 1, and the inner surface 1d and the outer peripheral surface of the guided member can be disassembled and assembled without damaging each other. It is assembled with a slight tightening allowance allowed.

Reference numeral 6 denotes a shield ring made of a metal material, the left step portion of which fits into the right end of the insulating member 5, and the outer circumferential surface of which is guided by the inner surface ld. There is a slight gap between the left end surface of the shield ring 6 and the right end surface of the reference electrode 3 so that the left end surface does not come into contact with the right end surface of the reference electrode 3. Reference numeral 7 denotes a support ring made of an insulating material, the outer peripheral surface of which is guided by the inner surface 1d, and the left end surface of which is in contact with the right end surface of the shield ring 6. Reference numeral 8 denotes a shield plate made of a metal material, the outer peripheral surface of which is guided by the inner surface 1d, and the left end surface of which is in contact with the right end surface of the support ring 'l. Reference numeral 9 denotes a ring screw made of a metal material, which is screwed into a threaded portion 1c provided on the right opening end side of the case 1, and includes a ring-shaped step portion 1b protruding radially inward from the left end of the inner surface 1d. The member between the shield plate 8 and the insulating member 4 interposed between the ring screw 9 and the stepped portion 1b is held, and the axial position is regulated. Further, the radial direction of the member between the step portion 1b and the ring screw 9 is regulated by the inner surface 1d.

20 is a cylindrical common electrode, and on the right end side there is a small diameter stepped portion 2.
0a is attached to the center hole of the support ring 7 with a slight tightening margin that allows for disassembly and assembly without damaging the parts, and a nut 21 is attached to the threaded part provided at the tip. The support ring 7 is firmly fixed to the right end side of the common electrode 20. Further, the common electrode 20 has a center hole 1 in the insulating member 10 which serves both to support and insulate the variable electrode 2 and the reference electrode 3 at its axial middle.
The outer peripheries are supported at 0a with a slight tightening margin that allows for disassembly and assembly without damaging each other. Therefore,
The common electrode 20 as a whole is supported at two places, and the outer peripheral surfaces of the two support members, the insulating member 10 and the support ring 7, are guided by the inner surface 1d, which is the same reference guide surface as the electrode 2.3. ing.

Reference numeral 11 denotes a fixing screw screwed into the screw hole 10b of the insulating member 10, which is provided to further restrict the movement of the common electrode 20 in the axial direction. This is provided for use when the tightening force is weak, and is not necessarily required. 22 is an insulating cap made of insulating material with a U-shaped cross section;
The NAND 21 and the shield plate 8 are insulated from each other. Reference numeral 23 denotes a spring receiver made of an insulating material, which is fixed to the common electrode 20 by screw connection at the left end surface position of the common electrode 20. 2425.26 is an insulated lead wire, and one end of the lead wire 24 passes through a hole provided inward in the axial direction at the center of the right end of the common electrode 20, and is connected to the common electrode 20 by a set screw 27. electrically connected. One end side of the lead wire 25 is connected to the shield plate 8
, the support ring 7, the shield ring 6, the reference electrode 3, and the insulating member 10, respectively, and reach the right end of the variable electrode 2, where it is electrically connected to the variable electrode 2 by a set screw 28. One end side of the lead wire 26 is connected to the lead wire 25
At equidistant positions rotated approximately 180 degrees on the circumference,
The shield plate 8, the support ring 7, and the shield ring 6 are penetrated into the common electrode 3, where the set screw 29 is inserted.
It is electrically connected to the common electrode 3 by. Also,
The other end of each lead wire 24, 25 and 26 is pulled out to the right from the shield plate 8, and there the connector cap 3 is screwed to the threaded portion 1c of the right open end of the case 1.
They are each electrically shielded and removably connected to the 0-side glue 131 by a connector (not shown) inside the cap 30.

Reference numeral 32 denotes a cylindrical screen, which is integrally formed with the spindle part 33, and has two screws in the stem 34, which is screwed to the threaded part 1a provided on the left open end side of the case 1 via the threaded part 34a. It is supported by bearings 35, 36. Reference numeral 37 denotes a guide bin, which is fixed to the stem 34 in the correct size, and its tip passes through the bearing 36 and enters the guide groove 2a provided in the screen 32, where it guides and rotates the screen 32 when it moves in the axial direction. regulations. A compression coil spring 38 is interposed between the left bottom surface 32b of the screen 32 and the spring receiver 23 of the common electrode 20, and constantly presses the screen 32, that is, the spindle 33, to the outside of the stem 34 (in the direction indicated by the arrow). ing.

Reference numeral 39 denotes a known probe, which is screwed to the tip of the spindle 33.

12 is a shield plate as a shield member made of a metal material, and is located within the right recess 1°e of the insulating member 10! death,
On the upper side, a metal pipe 13 installed perpendicularly to this shield plate 12 is connected to a small hole 1 above the insulating member 10.
It is inserted in 0c. There is a variable electrode 2 inside the pipe 13.
A lead wire 25 is inserted through the pipe 13, and a portion of the lead wire 25 inside the pipe 13 is shielded by the pipe 13. Reference numeral 14 denotes an insulating sheet made of a plastic sheet, which is located between the facing surfaces of the shield plate 12 and the reference electrode 3 to insulate these two members from each other.

Reference numeral 3a denotes a shield pipe made of a metal material, which passes through the inside of the reference electrode 3 and covers the inside of this electrode 3, and its left end surface is in contact with the shield plate 12 and is electrically conductive. ing. 3b is an insulating pipe made of an insulating material, and the reference electrode 3 and the shield pipe 3a are insulated by shield-by 13a+MFM. Reference numeral 15 denotes a conductive screw connected to a screw hole in the case L, the tip of which is in contact with the pipe 13, so that the pipe 13. Shield plate】2. Keep the shield pipe 3a at the same potential (earth) as the case 1. Note that the conduction screw 15 and the pipe 13 constitute a conduction member. 7a (FIG. 1(B)) is a stepped pipe made of metal material, and a lead wire 25 passing through the support ring 7.
．． 26, and the left end side thereof is in contact with the shield ring 6 to shield the lead wires 25 and 26 passing through the support ring 7. Further, the outer circumferential surface of the shield plate 8 also contacts the inner surface 1d, and is maintained at the same potential as the case 1 via the ring screw 9.

In the explanation so far, the case where the shield plate 12 is provided in the recess 10e of the insulating member 10 has been illustrated and explained. Of course it's good too. In that case, the flange portion 10d on the right end side of the insulating member 10 is connected to the insulating member 10 by this shield plate having a larger outer diameter.
It is separated from 0 and is similar in shape to the insulating member 5.

Next, the operation will be explained.

When an AC voltage of the same frequency, same potential, and opposite phase is applied to the variable electrode 2 and the reference electrode 3, capacitances are created between the variable electrode 2 and the common electrode 20 and between the reference electrode 3 and the common electrode 20, respectively. C1 and C2 are formed, and a current proportional to the capacitance difference (C2-CI) is detected from the common electrode 20. Now, in the state shown in Fig. 1 (A) and (B), the capacitance C
1 and C2 are adjusted to be equal to each other, the sum of the currents obtained from the common electrode 20 will be zero. Then, when the spindle 33 is pushed into the stem 34 in the direction of arrow C against the spring 38, the tip of the screen 32
2a moves the gap between the variable electrode 2 and the common electrode 20 toward the insulating member 10 side and changes (in this case, decreases) the opposing area between the variable electrode 2 and the common electrode 20, so that the capacitance C
1 changes (decreases). At this time, the capacitance C2 does not change and remains at a constant value. Therefore, the capacitance difference (C2-CI) depends on the amount of movement of the spindle 33,
The amount of displacement of the spindle 33 can be electrically detected as the amount of change in capacitance.

In the capacitive displacement detector according to the present invention, a shield plate, which is a shielding member, is installed between the opposing surfaces of two cylindrical electrodes 2 and 30, which are attached using the inner surface 1d of the case 1 as a reference guide surface. 12 is provided, and since this shield plate 12 is set to the same ground potential as the case 1, the lines of electric force generated between the opposing surfaces of the variable electrode 2 and the reference electrode 3 are shielded by this shield plate 12. Therefore, lines of electric force do not act directly between the opposing surfaces of the electrodes. Therefore, the current flowing into each electrode through the stray capacitance is grounded by the shield plate 12, and is therefore eliminated. Furthermore, the side surfaces and outer peripheries of the electrodes 2 and 3 opposite to the opposing surfaces are completely shielded by the stepped portion 1b, the inner surface 1d, and the shield ring 6 guided by the inner surface 1d.

FIG. 3 shows another embodiment, and is a partial sectional view of a main part when a third cylindrical electrode 40 is further provided on the right side of the reference electrode 3 in FIG. 1(B). Note that the same parts as in FIG. 1(B) are denoted by the same reference numerals, and the description thereof will be omitted.

Even if a cylindrical electrode 40 is further added to provide three electrodes 2, 3, 40 as shown in FIG. electrically insulated by insulating members 5a and 5b,
It is arranged coaxially with the other electrode 2.3, and the opposing surfaces of the electrode 3 and the electrode 40 are shielded by a shield ring 41, which is a shield member in contact with the inner surface 1d. ), the adverse effects of stray capacitance occurring between the opposing surfaces of the electrodes are eliminated, similar to the case between the opposing surfaces of the electrodes 2.3.

Therefore, in addition, the fourth. Even when a fifth cylindrical electrode is added, as can be seen from FIG. 3, by providing a shield member that contacts the inner surface of the case between the opposing surfaces of each electrode, the influence of stray capacitance between these electrodes can be reduced. It can be prevented.

[Effects of the Invention] As explained above, according to the capacitive displacement detector according to the present invention, the opposing surfaces of the plurality of cylindrical electrodes coaxially incorporated in the case through the insulating member, Since a shield member maintained at the same potential as the case is provided between the electrodes, it is possible to prevent stray capacitance between the electrodes from having an adverse effect on detection accuracy, improving linearity and stability. You can get the desired effect. Furthermore, since there is no longer a need for a glue wire to keep the shield member at ground potential as in the past, there is no need for space for this, the detector can be made smaller in diameter, and there are other benefits such as improved assembly work efficiency. It will be done.

[Brief explanation of the drawing]

FIG. 1 (AL (B) is a cross-sectional side view showing a capacitive displacement detector according to an embodiment of the present invention, and FIG.
(B) is an enlarged cross-sectional side view of the main part, FIG. 3 is a cross-sectional side view of the main part showing a capacitive displacement detector according to another embodiment of the present invention, and FIG. 4 is a conventional capacitive displacement detector. It is a sectional side view showing a container. In the figure, 1 is a case, 2 is a variable electrode, 3 is a reference electrode, 4, 5.10 is an insulating member, 12 is a shield plate,
13 is a pipe, 20 is a common electrode. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (2)

[Claims] (1) A cylindrical case, a plurality of cylindrical electrodes coaxially arranged via an insulating member with the inner surface of the case as a reference guide surface in the radial direction, and a constant a common electrode arranged coaxially through a gap; a screen arranged movably in the axial direction within a gap between one of the plurality of cylindrical electrodes and the common electrode; A capacitive displacement detector comprising a shield member provided between opposing surfaces of a plurality of cylindrical electrodes. (2) A capacitive displacement detector, wherein the shield member is provided within the insulating member and electrically connected to the case via a conductive member.