JPH03225222A - Electrostatic capacity type displacement detector - Google Patents

Abstract

PURPOSE:To surely position and support respective electrodes and to hold high accuracy for a long period by supporting a common electrode at least on two positions in the axial direction with a supporting member and positioning a variable electrode, a reference electrode and the supporting member by using an inner cylinder face as a reference. CONSTITUTION:When respective AV voltages having the same frequency and potential and opposite phases are impressed to the variable electrode 2 and the reference electrode 3, capacities C1, C2 are respectively formed between the electrodes 2, 20 and between the electrodes 3, 20 and a current relating to a capacitance difference (C2 - C1) is detected from the electrode 20. When a screen 32 is positioned on the leftmost side, the electrode 3 is adjusted by an adjusting screw or the like fitted to the electrode so that both capacitances C1, C2 are made equal and setup a current obtained from the electrode 20 is turned to zero. When a spindle 33 is pressed into a stem 34, the head 32a of the screen 32 is moved in the right direction in a gap between the electrodes 2, 20. As the result of the movement, the opposed area of the electrodes 2, 20 is changed and the capacitance C1 is changed. At this time, the capacitance C2 is held at a fixed value. Thus, the capacity difference (C2 - C1) is generated by the movement of the spindle 33 and the moving amount of the spindle 33 can be detected.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a structure of a capacitive displacement detector that converts a mechanical displacement amount into an electrical signal as a capacitance variation. In particular, it relates to a plurality of ring-shaped cylindrical electrodes provided close to each other on the same center line, a common electrode coaxially arranged with each of these cylindrical electrodes with a certain gap, and a plurality of cylindrical electrodes. It includes a cylindrical screen integrated with a spindle that is supported so as to be movable in the axial direction within the gap between one of the variable electrodes and a common electrode, and the mechanical displacement of this screen is shared with the cylindrical electrode. This invention relates to an improvement in the structure of a capacitive displacement detector that electrically detects the amount of change in capacitance formed by electrodes.

<Prior Art> A conventional capacitive displacement detector of this type is disclosed in British Patent No. 1347235, for example.

FIG. 4 is a sectional view showing the structure of this conventional capacitive displacement detector.

As shown in the figure, on the inner surface of the inner cylinder 51a of the cylindrical case 51, cylindrical first
The electrode 52 and a cylindrical second electrode Th53 are provided coaxially.

This electric ffi! A guard ring 55 insulated from the electrode 53 by an insulating member 56 is provided on the right side in the figure opposite to the electrode 52 of 53 .

The common electrode 57 is made of a cylindrical rod, and its right end in the figure is connected to an insulating member 58 on the small-diameter stepped inner cylinder 51b of the case 51.
It is attached so as to be coaxial with respect to the electrodes 52 and 53 via.

A screw hole 59 is bored in the axis of the common electrode 57, into which a set o and a white o are screwed. Further, a plurality of holes 661 are bored on the side surface of this common electrode 57 so as to meet the screw holes 59, and set screws 60
By adjusting the position of the common electrode 5 facing the electrode 53
By adjusting the area of 7, it is possible to adjust the capacitance between electric fi 53 and fi 57 depending on the purpose.

The screen 62 is slidably supported by a bearing 63 at the end of the case 51 so that it can move axially within the gap between the electrodes 52,57. This bearing 63
is insulated from the electrode 52 by an insulating member 64.

Further, the lead wires 65, 66 from the electrodes 52, 53 pass through the gaps between the inner tube 51a of the case 51 and the outer periphery of each electrode and insulating member to the case 5 on the opposite side of the housing side of the screen 62.
It is pulled out at the right end in Figure 1 so that it can be connected to a cable 70 of an electrical measuring device.

Furthermore, since the lead wire 67 from the guard ring 55 is connected to the ground potential, the lead wire 67 from the guard ring 55 is connected to the case 5 like the other wires.
It is pulled out to the right end in Figure 1.

Also, the lead wire 69 from the common electrode 57 is also connected to the case 5.
1 is connected to a cable 71 at the right end in the figure.

A cover 72 is attached to the right end of the case 51 in the figure, and this cover 72 allows the lead wire 65 to be
．． 66, 67 and 69 are protected.

In the detector having the above structure, a capacitance C1 is formed between the common electrode 57 and the first electrode i52, and the common type fi5
A capacitor C2 is formed between the second electrode 7 and the second electrode 53.

This capacitance CI is varied as the screen 62 moves axially within the gap between the electrodes 57,52.

On the other hand, the capacitor C2 has a screen 62 of 8i! 57.5
3, so it remains constant without changing.

Therefore, the capacitances C1 and c2 detected from the common electrode 57
The difference (C2C1) changes in proportion to the displacement of the screen 62, thereby detecting the displacement of the screen 62.

<Problems to be Solved by the Invention> In order to ensure the accuracy of the detector made of the above-mentioned tI structure, it is necessary to ensure that the cylindrical electrodes, especially the first electrode 52 and the common electrode 57, are always coaxial with high accuracy. It is preferable to place and hold it. However, in the conventional structure, the common electrode 57 is fixed only at one location on one end thereof, and each cylindrical electrode 52.53 is also fixed to the insulating member 54.53.
．． 64 and the guard ring 55, the structure is such that positioning is performed in the axial direction and the radial direction, and in particular, the structure is not such that positioning is performed from the same reference plane in the radial direction. Therefore, during assembly, the common electrode 57 and each cylindrical electrode 52.5
It was extremely difficult to position 3 on the same axis.

In addition, in the conventional detector, the common type VF157 is supported in a cantilevered state, so the open end side of the common electrode 57 tends to shift position even when subjected to vibrations or shocks after assembly, making it unstable. In particular, when the measurement range is lengthened, the length of the common electrode 57 from its support point must also be increased, making it even more likely that the position will shift, making it difficult to maintain stable accuracy over a long period of time. It also had the disadvantage of being difficult to maintain.

Furthermore, the gap between the common electrode 57 and the screen 62 in the conventional detector is determined by taking into account workability during assembly and subsequent radial positional deviation of the common electrode 57. This also has the disadvantage that the radial dimension of the detector increases accordingly, as the detector must be set with a sufficient margin so that the detector does not come into contact with each other.

In addition, since a guard ring 55 was provided for positioning the cylindrical electrode in the axial direction, it had to be brought to ground potential via a lead wire, which complicated the structure and increased costs. It was up.

An object of the present invention is to provide a capacitive displacement detector that can maintain high accuracy for a long period of time by ensuring the positioning and support of each electrode.

Means for Solving the Problems The capacitive displacement detector of the present invention includes a cylindrical case having an inner cylindrical surface, and a cylindrical variable case disposed coaxially with the inner cylindrical surface as a reference. An electrode and a reference electrode, a cylindrical common electrode arranged with a certain gap from the inner peripheral surfaces of the variable electrode and the reference electrode, and a cylindrical common electrode positioned with the inner cylindrical surface as a reference and with the common electrode at least in the axial direction. It consists of a support member supported at two locations, and a screen supported so as to be movable in the axial direction within the gap between the variable electrode and the common electrode.

Effects> The common electrode in the detector of the present invention is supported by a support member at at least two locations in its axial direction. Therefore, the positional accuracy is improved over a long period of time compared to the case of supporting at a negative point, and the position can be maintained with high precision without positional deviation even in the face of vibrations or shocks.

Furthermore, since the variable electrode, the reference electrode, and the support member are all positioned with the inner cylinder surface as a reference, their positioning is easy and the precision of their relative positions is improved.

Therefore, when detecting the displacement of the screen by detecting the amount of change in capacitance formed between multiple ring-shaped cylindrical electrodes and the common electrode, the positional accuracy of each electrode is improved, resulting in high accuracy. It becomes possible to perform displacement detection for a long period of time.

<Example> Hereinafter, preferred examples of the present invention will be described based on the drawings.

FIG. 1(A) and FIG. 1(B) are half-sectional views of a capacitive displacement detector according to an embodiment of the present invention, cut at the center, and FIG. FIG. 3 is an enlarged view of the vicinity of the insulating member 10 shown in FIG.

1 is a cylindrical case with openings on the left and right sides in the figure.
Threaded portions 1a and 1c are provided on the inner surfaces of the left and right opening ends, respectively.

2 is a cylindrical variable electrode, 3 is a cylindrical reference electrode, and these two electrodes 2.3 are connected to three substantially ring-shaped insulating members 4 guided by the inner cylindrical surface 1d of the case l. .10.5 and are coaxially supported and insulated from each other.

One end of each of the variable electrode 2 and the reference electrode 3 is inserted into the insulating member 4.5, and each end of the variable electrode 2 and the reference electrode 3 is inserted into the insulating member 10 from the left and right in the figure. has been done. Ring-shaped protrusions 10d and 10e protrude from the left and right end faces of the insulating member 10 in the figure.
d, supporting the end of each electrode by tucking the end of the electrode 2.3 into 10e.

The inner cylindrical surface 1d of the case 1 serves as the same standard guide surface in the radial direction for the members housed in the case, and the insulating member 4.10.5 also comes into contact with this inner cylindrical surface 1d, so that the radial direction is positioned.

6 is a shield ring made of metal material, and the insulating member 5
It is fitted on the right end in the figure, and its outer periphery abuts and is guided by the inner cylinder surface 1d. The left end face of the shield ring 6 in the figure is fitted onto the insulating member 5 so as not to come into contact with the right end face of the reference electrode 3 in the figure.

Reference numeral 7 denotes a support ring made of an insulating member, whose outer periphery abuts and is guided by the inner cylindrical surface 1d of the case 1, and whose left end surface in the figure contacts the right end surface of the shield link 6 in the figure.

8 is a shield plate made of metal material, and its outer periphery is also similar to case 1.
The left end surface in the figure is in contact with the right end surface of the support ring 7 in the figure.

Reference numeral 9 denotes a ring screw made of a metal material, which has a threaded portion formed on its outer periphery, and is screwed into the threaded portion 1a of the case 1. This ring screw 9 is attached to the case 1 so as to come into contact with the shield plate 8 and press it to the left in the figure, and a ring that protrudes inward is provided at the left end of the inner cylinder surface 1d in the figure. A component inserted between the stepped portion 1b and the ring screw 9 is held between them to regulate its axial position.

Note that the radial position of the component interposed between the step portion 1b and the ring screw 9 is regulated by the inner cylindrical surface 1d.

Reference numeral 20 denotes a cylindrical common electrode, and a small diameter stepped portion 20a is provided at the right end in the figure. The small-diameter stepped portion 20a of the common electrode 20 is inserted into the center of the support ring 7 with a slight tightening margin that allows for disassembly and assembly without damaging the components. A nut 21 is attached to and fixed to the support ring 7.

Furthermore, this common electrode 20 is connected to the center hole 10 of the insulating member 10.
a, and this insulating member 10
The middle part in the axial direction is supported by. Note that the fitting state between the common electrode 20 and the center hole 10a of the insulating member 10 is also as follows.
The fit is set to such an extent that parts can be disassembled and assembled without damaging each other.

As a result, the common voltage &20 is connected to the support ring 7 and the insulating member 10.
The common electrode 20 is supported at two locations, and the support ring 7 and the insulating member 10 constitute a support member that supports the common electrode 20.

A fixing screw 11 is screwed into a screw hole 10b provided from the outer periphery of the insulating member 10 to the center hole 10a, and is provided to prevent the common electrode 20 from moving in the axial direction. However, this fixing screw 11 is used when the clamping force of the common electrode 20 by the inner surface of the center hole 10a is weak, and is not necessarily necessary.

Reference numeral 22 denotes an insulating cap having a U-shaped cross section, which is fitted into the center hole of the shield plate 8 to insulate the nut 21 from the shield plate 8.

A spring receiver 23 is made of an insulating material and is screwed to the left end surface of the common electrode 20 in the figure.

Reference numerals 24, 25, and 26 denote lead wires coated with insulation, and one end of the lead wire 24 passes through a hole drilled inward from the center of the right end surface of the common electrode 20 in the axial direction.
It is electrically connected within the electrode 20 by a screw 27.

Further, one end of the lead wire 25 passes through the support ring 7, the shield ring 6, the reference electrode 3, and the insulating member 10, respectively, and reaches the right end of the variable electrode 2 in the figure, where it is electrically connected to the variable electrode 2 by a screw 28. Connected. Furthermore, the lead wire 26
One end side passes through the support ring 7 and the shield ring 6, respectively, and reaches the inside of the reference electrode 3, where it is electrically connected to the reference electrode 3 by a screw 29. The other end of each lead wire 24, 25, 26 is pulled out to the right in the figure from the shield plate 8, and is connected to a connector cap 30 screwed to the threaded portion 1a of the case 1 on the left open end side in the figure. It is detachably connected to the side lead wire 31 within the cap 30 by a connector (not shown).

32 is a cylindrical screen that is integrally formed with the spindle portion 33, and has two bearings 35. It is slidably supported by 36.

Reference numeral 37 denotes a guide pin, which is press-fitted into the stem 34 and whose tip is set to pass through the bearing 36 and enter the guide groove 2a provided in the screen 32. The guide groove 32a of this screen 32 is formed in the moving direction of the screen 32.
By inserting the guide pin 37 into the inside a, the screen 32 is guided by the guide pin 37 during axial movement and its rotation is also prevented.

38 is a compression coil spring, which is the same type as the inner bottom 32b of the screen 32 [! The screen 32 is interposed between the spring receiver 23 screwed into the end surface of the screen 32
And the spindle part 33 is always pressed outward of the stem 34.

Three are measuring heads, which are screwed to the tip of the spindle portion 33.

In FIG. 2, reference numeral 12 denotes a ring plate-shaped shield plate made of a metal material, and has a pipe 13 made of metal installed perpendicularly to the end face thereof. The shield plates 1 and 12 are fitted onto the common electrode 20 with a gap, and the pipe 13 is inserted into a small hole 10c provided in the insulating member 10. Inside this pipe 13,
The lead wire 25 of the variable electrode 2 is inserted, and the pipe 1
The lead wire 25 inside the pipe 3 is shielded by this pipe 13.

Reference numeral 14 denotes a ring-shaped insulating sheet made of a plastic sheet, which is provided between the shield plate 12 and the left end of the reference electrode 3 in the figure to insulate them.

15 is a conductive screw that is connected to a screw hole in case 1 and reaches inside the case, and its tip contacts pipe 13 to bring pipe 13 and shield plate 12 to the same potential as case 1 (earth potential). It is something. Therefore, by positioning the shield plate 12 on the electrode 2.3 and further bringing it to earth potential, the electrode 2.3 is shielded.

The variable electrode 2, the reference electrode 3, and the common f! 20 is the insulating member 4 as described above.
．． 10.5, it is held between the step portion 1b of the case 1 and the ring screw 9 together with the support ring 7 and the shield plate 8, and is positioned in the axial direction.

These electrodes 2.3.20 are also connected to insulating members 4.10.
5 and the support ring 7 are both positioned in the radial direction with the inner cylinder surface 1d of the case 1 as a reference, so they are all positioned coaxially with the same surface as a reference.

In this embodiment, two cylindrical electrodes, the variable electrode 2 and the reference electrode 3, are illustrated and explained, but it is also possible to determine the number of cylindrical electrodes to be three or more. This is set as necessary and is not limited to the example.

Further, the shield ring 6 made of a metal material has the same potential (earth potential) as the case 1 because its outer peripheral surface is in contact with the inner cylindrical surface 1d, and the shield plate 8 is connected to the ring screw 9.
It is at the same potential (earth potential) as case 1 through. Therefore, the parts made of metal between the step portion 1b of the case 1 and the ring screw 9 are all at the same potential as the case 1 except for the electric potential i2.3.

Next, the operation and characteristics of the detector according to this embodiment will be explained.

Variable tF! in the above detector! 2 and the reference electrode 3, when an AC voltage of the same frequency and the same potential and opposite phase is applied to each, the variable f! 2 and the common type 120 and between the reference electrode 3 and the common electrode 20, capacitors Jic and C2 are formed, respectively, and a current related to the capacitance difference (C2-CI) is detected from the common type [20]. Ru.

Now, as shown in FIGS. 1(A) and 1(B), when the screen 32 is located at the leftmost position in the figures, the adjustment screw (not shown) provided on the reference electrode 3, etc. Adjust the capacitances C1 and 02 to be equal, and connect the common electrode 20
Set so that the current obtained from is zero.

Then, when the spindle 33 is pushed into the stem 34,
The tip 32a of the screen 32 is connected to the variable electrode 2 and the common electrode 2.
0 in the right direction in the figure as shown by the dotted line.

When the screen 32 moves in this way, the opposing area between the variable electrode 2 and the common electrode 20 changes (in this case, decreases).
Then, the capacitance C1 changes (decreases).

At this time, the capacitance C2 does not change and is kept constant because the opposing area between the reference electrode 3 and the common electrode 20 does not change.

Therefore, the capacitance difference (C2Ct) is caused by the movement of the spindle 33, and changes depending on the amount of movement of the spindle 33.

Therefore, the common type [!] changes in proportion to the capacitance difference (C2ct). The amount of movement of the spindle 33 can be detected by the current from the spindle 20.

In the above-mentioned detector, it is extremely important in evaluating the detector that the amount of change in capacitance obtained when the spindle section 33 is displaced by a unit length is a constant value throughout the measurement range. It is an item.

In order to configure this, it is necessary to position the variable electrode 2 and the common electrode 20 so that they are coaxial without error, and furthermore, it is necessary to position the variable electrode 2 and the common electrode 20 so that they are coaxial with each other, and furthermore, the coaxiality is not impaired by vibration or shock and can be maintained for a long period of time. It needs to be stable.

Regarding this point, in this embodiment, by supporting the common electrode 20 at two places, the common electrode 20 and the variable electrode 2
This ensures coaxiality with the That is, one of the locations is the small diameter stepped portion 20 on the opposite side to the side through which the screen portion 33 is inserted.
The support ring 7 that supports a is provided with a support part, and the other part is located as far away as possible from this small diameter stepped part 20a and does not interfere with the movement of the screen part 33, and the variable electrode 2 and the reference voltage [! A supporting portion is provided on the insulating member 10 located between the insulating member 3 and the insulating member 3.

In this way, the center hole of the support ring 7 and the insulating member 10, which serve as supporting members that support the common electrode 20 at two locations, and the outer periphery of the common electrode 20 can be precisely coaxially secured in advance in the state of the parts. It is possible. Further, the outer peripheral surfaces of the support ring 7 and the insulating member 10 are connected to two electric currents 8ii2.3
Similarly to the insulating member 4.5 supporting the insulating member 4.5, it is guided by the inner cylindrical surface 1d of the case 1. For this reason, the common electrode 2
0 is coaxially and precisely supported with the inner cylinder surface 1d as a reference.

<Effects of the Invention> According to the present invention, the common electrode is supported in its axial direction by two supporting members, and the two supporting members are used as reference guide surfaces inside the case in the same way as supporting members for other electrodes. Since positioning is performed using the cylindrical surface as a reference, coaxiality of the electrodes can be easily and precisely obtained by simply assembling each component within the case.

Furthermore, since the common electrode is supported by two supporting members, it is possible to prevent positional deviation between the electrodes due to vibration or impact, and the performance obtained during assembly is maintained well over a long period of time. be able to. Therefore, it is also possible to use the detector directly attached to a machine tool, etc., in an environment where vibrations occur.

In addition, since the positional accuracy between the electrodes can be strongly maintained, the gap between the common electrode and the variable electrode can be made smaller compared to conventional detectors, and the radial dimension of the detector can be reduced accordingly. It is also possible to further increase the rigidity of the entire detector by making it smaller, or by increasing the thickness of the case.

[Brief explanation of drawings]

1(A) and 1(B) are cross-sectional views of a capacitive displacement detector according to an embodiment of the present invention, cut in half at the center, and FIG. B) is an enlarged view of the vicinity of the insulating member 10, FIG. 3 is a view taken along the line I-1 in FIG. 2, and FIG. 4 is a sectional view showing the structure of a conventional capacitive displacement detector. It is. DESCRIPTION OF SYMBOLS 1... Case, 1d... Inner cylinder surface, 2... Variable electrode, 3... Reference electrode, 4.5.10... Insulating member, 7... Support ring, 9... Ring screw, 10a・
... center hole, 10d, 10e... protrusion, 20... common electrode, 20a... small diameter stepped portion, 21... nut, 32... screen, 33...
...Spindle part.

Claims (3)

[Claims] (1) A cylindrical case having an inner cylindrical surface, a cylindrical variable electrode and a reference electrode arranged coaxially with respect to the inner cylindrical surface, and a cylindrical case with respect to the inner peripheral surface of the variable electrode and reference electrode. a cylindrical common electrode disposed with a certain gap between them; a support member positioned with respect to the inner cylindrical surface and supporting the common electrode at at least two points in the axial direction; and a support member common to the variable electrode. A capacitive displacement detector that includes a screen supported so as to be axially movable within a gap between the electrodes. (2) The common electrode is characterized in that an end portion adjacent to one end of the reference electrode and a portion located between the reference electrode and the variable electrode are supported by the support member. The capacitive displacement detector described. (3) A support member that supports a portion of the common electrode located between the reference electrode and the variable electrode is provided with a ring-shaped protrusion that protrudes from both end faces in the axial direction, and the ring-shaped protrusion 3. The capacitive displacement detector according to claim 2, wherein the capacitive displacement detector supports one end of each of the variable electrode and the reference electrode.