JPH02228581A - Static capacitance-operated detector - Google Patents

Abstract

PURPOSE:To reduce the cost of a detector and to improve the precision thereof without necessitating high precision in the shape and position of electrodes and others by a method wherein first and second fixed electrodes and a common electrode are made to so face each other as to form a capacity with slits of a screen interposed therebetween. CONSTITUTION:When displacement in the axial direction is given to a measurer 49 provided at the fore end of a spindle 48 of a detector, a screen 46 is displaced in the axial direction by a given amount of displacement. On the occasion, slits 46d to 46f of the screen 46 are displaced in the axial direction. When the screen 46 is moved rightward, for instance, a capacity formed between a first fixed electrode 14 and a common electrode 34 facing directly each other through the slits 46d to 46f is shielded gradually by the screen 46 and decreases, and a capacity formed between a second fixed electrode 16 and the common electrode 34 also facing directly each other through the slits 46d to 46f increases with gradual expansion of the open areas of the slits 46d to 46f. By taking a difference of these capacities between the electrodes out of a lead wire 44, the amount of displacement of the spindle 48 can be detected.

Description

Detailed Description of the Invention <Industrial Application Field> The present invention provides a method for disposing a common electrode with a certain gap between the first and second fixed electrodes, and A movable screen is provided between the electrodes, and the ratio of the capacitance between the first fixed electrode and the common electrode and the capacitance between the second fixed electrode and the common electrode is differentially detected depending on the position of the screen. The present invention relates to such a capacitance type detector, and particularly relates to improvements in its structure.

<Prior Art> A conventional capacitive detector of this type is disclosed in British Patent No. 1,347,235, for example.

FIG. 10 is a sectional view showing the structure of this capacitance type detector.

The common electrode 1 is a cylindrical electrode, and a cylindrical first fixed type 8i! 2 and a second fixed electrode 3 are arranged with a certain gap between them. The capacitance between these electrodes, ie the first fixed tffi! 2 and the common electrode 1 and the capacitance between the second fixed electrode 3 and the common electrode 1 are determined by the position of the cylindrical screen 6, which is moved along the axis of the cylinder by the two rods 4, 5. Varies depending on This screen 6
moves in the gap between the first and second fixed electrodes 2.3 and the common electrode 1 located inside them. This screen 6
The rods 4 and 5 supporting the screen 6 have a diameter similar to that of -, and are constructed so as not to affect the change in capacity due to the movement of the screen 6. Also, common type f! 1 is insulated and supported by a support shaft 7.

The support shaft 7 is firmly fixed to a housing 8, and to the housing 8 are fixedly insulated first and second fixed molds i2, 3.

The housing 8 serves as an electrical shield and for the detection part.
It acts as a support means and also as a bearing for the rods 4 and 5, supporting each part so that the screen 6 does not touch the electrodes. Moreover, the common electrode 1 and the first . Second fixed type i2
．． 3 are connected to terminals 9, 10, and 11, respectively, and the amount of movement is detected by changes in output from these terminals.

<Problem to be solved by the invention> In the conventional capacitive detector having the above configuration,
The capacitance between the first fixed electrode 2 and the common electrode 1 other than the portion shielded by the screen 6 spanning the first and second fixed electrodes 2.3, and the capacitance between the second fixed electrode 3 and the common electrode 1 The difference with the capacitance is detected as a differential output. Therefore, if the capacitance of the first fixed electrode 2 and the common electrode 1 without the screen 6 and the capacitance of the second fixed electrode 3 and the common electrode 1 do not almost completely match, the screen 6 The difference in capacitance in the absence of the screen 6 is always added to the differential output obtained when the screen 6 is interposed, which adversely affects accuracy.

That is, the first fixed voltage, pole 2, without the screen 6
If the capacitance between the fixed electrode 3 and the common electrode 1 is set to 01, the capacitance between the second fixed electrode 3 and the common electrode 1 is set to 02, and the screen 6 is further inserted, and the capacitance change at a certain position is ΔC, the difference is The dynamic capacitance change is (C1+ΔC) +C2-ΔC)=(
CI C2)+2ΔC, where C,-02>2
During ΔC, the original difference C, - is smaller than the differential change 2ΔC.
C2 makes it more difficult to detect a larger lick change.

Therefore, in this structure, it was necessary to improve the precision of the parts and the mounting position so that each capacitance accurately matches without the screen 6. However, in reality, this was extremely difficult and caused an increase in costs.

Since the screen 6 is suspended from the left and right sides by two rods 4 and 5, it is difficult to attach the screen 6 to the rods 4 and 5, and furthermore, the screen 6 is suspended from the left and right sides by the two rods 4 and 5.
, 5 must be machined with high precision to attach them to the housing 8 without making any mistakes, otherwise the operation of the screen 6 would be hindered.

Furthermore, since the rods 4 and 5 move together with the screen 6, they must protrude left and right from the supporting portion of the housing 8 by the amount by which the screen 6 moves left and right, which increases the size of the entire detector. There was also.

An object of the present invention is to provide an inexpensive and highly accurate detector without requiring high precision in the shape and position of electrodes and the like.

Means for Solving the Problems> The capacitance type detector of the present invention includes a cylindrical case and a cylindrical first sensor mounted in the case and arranged close to each other.
and a second fixed electrode, a cylindrical common electrode arranged with a certain gap from the inner peripheral surfaces of the first and second fixed electrodes, and a gap between the first and second fixed electrodes and the common electrode. and a cylindrical screen supported movably in the axial direction and having slits at predetermined positions, and depending on the position of this screen, the capacitance between the first fixed electrode and the common electrode facing each other through the slit is the same. It is characterized by differentially detecting the ratio of the capacitances of the second fixed electrode and the common electrode that face each other through the slit.

Function> The screen in the present invention has a slit, and the first and second fixed electrodes and the common electrode face each other through the slit to form a capacitor.

When the screen moves, the position of the slit also moves, and the ratio of the areas where the first and second fixed electrodes and the common electrode face each other changes, which changes each capacitance. Output the ratio differentially.

The principle of this capacitance type detector is as follows.

A sinusoidal voltage having a phase difference of 180 degrees is applied to the first and second fixed electrodes from an oscillation circuit.

At this time, when the screen is displaced, the capacitance formed between the first fixed electrode and the common electrode as described above,
The difference in capacitance formed between the second fixed electrode and the common electrode changes in proportion to the displacement of the screen.

By obtaining this change as an output from the common electrode, the displacement amount of the screen is converted into an electrical signal and detected.

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

FIG. 1(A) and FIG. 1(B) together represent a cross-sectional view of a capacitance type detector according to an embodiment of the present invention, and FIG. -A' line arrow sectional view, Figure 3 is the 1st
It is a sectional view taken along the line BB' in Figure (B).

4 is a sectional view showing the screens of FIGS. 1(A) and 1(B), FIG. 5 is a sectional view taken along line C-C' in FIG. 4, and FIG. It is a sectional view taken along the I arrow in the figure.

Reference numeral 12 denotes a cylindrical case, which is open to the left and right in FIGS. 1(A) and 1(B).

Reference numerals 14 and 16 designate first and second fixed electrodes having a cylindrical shape, the outer circumferential surfaces of which are in contact with the inner circumferential surface of the case 12 via the insulating sheet 18, and each opposing end surface also has a ring-shaped insulating sheet 20. are arranged so as to come into contact with each other through the

The first and second fixed electrodes 14.16 are connected to the case 12.
It is fixed by being sandwiched between disk-shaped mounting plates 22 and 24 fitted therein via spacers 26 and 28. Note that the first and second fixed electrodes 14
．． A ring-shaped insulating sheet 30.degree. 32 is also inserted between the spacer 16 and the spacer 26.28.

34 is a cylindrical common electrode. This common electrode 34
have shaft portions 34a and 34b on their axial end faces, respectively, and are positioned and fixed on the axial center of the case 12 by fitting the shaft portions 34a and 34b into bushings 36 and 38.

The bushings 36 and 38 are made of an insulating material such as ceramic and plastic, and are attached to the mounting plates 22 and 24, respectively.
It is fixed by being fitted into the hole provided in the center.

Shield rings 39a and 39b are made of metal and are fitted around the outer periphery of the bushings 36 and 38 to electrically shield the shaft portions 34a and 34b of the common electrode 34.

35a and 35b are ring-shaped insulating sheets made of plastic, which are connected to both end surfaces of the common electrode 34 and the shield ring 39.
a, 39b, the common electrode 34
is interposed between the end face of the shield ring 39a and the shield ring 39b,
It is being pinched.

The nut 37 is screwed to the threaded end portion of the shaft portion 34b of the common electrode 34, thereby firmly fixing the entire common electrode 34 to the mounting plate 24 side.

Screw hole 3 provided in the other shaft portion 34a of the common electrode 34
Reference numeral 9 denotes a screw hole into which the mounting screw 80 shown by the dotted chain line in FIG. 1(B) is screwed. After assembling the members to be assembled in between, the mounting plate 2 is fixed with the mounting screws 80 and nuts 37.
2. It can be inserted into the case as it is by sandwiching between 24 and 24, making assembly easy. Since the mounting screws 80 are not required after being inserted into the case 12, they can be removed from the open end 12a side of the case 12 before assembling the screen 46 and screen fixing block 50, which will be described later.

40.42 and 44 are lead wires of the first and second fixed electrodes 14.16 and the common electrode 34, respectively.

The lead wire 40 includes an intermediate mounting plate 24, a spacer 28,
It passes through the second fixed electrode 16 and reaches into the first fixed electrode 14, and one end thereof is fixed to the first fixed electrode 14 by a screw 14a. The lead wire 42 passes through the attachment plate 24 and the spacer 28 and reaches the inside of the second fixed electrode 16, where one end thereof is fixed to the second fixed electrode 16 by a screw 16a. The lead wire 44 passes through the screw at the end of one shaft portion 34b of the common electrode 34 and connects to the shaft portion 3.
4b, and one end thereof is soldered within a horizontal hole 34c that passes through the shaft portion 34b in the radial direction.

The first and second fixed electrodes 14.16 are arranged so that a gap is formed between the inner peripheral surfaces of the first and second fixed electrodes 14.16 and the outer peripheral surface of the common electrode 34. The inner diameter of the common electrode 34, the outer diameter of the common electrode 34, and their mounting positions are determined.

A cylindrical screen 46 is disposed within the gap formed between the first and second fixed electrodes 14.16 and the common electrode 34, and is supported so as to be movable in the axial direction therein. There is. That is, as shown in FIGS. 2 and 3 or 4 and 6, this screen 46 has three claw portions 46a integrally extending in the axial direction from one end surface thereof;
46b.

46c, and the claws 46a, 46b and 46c are inserted into the holes 22a, 22b, 2 provided in the mounting plate 22.
2c, and the tips of the claw portions protruding through the multiple holes are fixed to the spindle 48. In this embodiment, the claws 46a, 46b, 46c are connected directly to the spindle 4.
8, but is fixed by three screen fixing screws 52 to a screen fixing block 50, which is fixed to the spindle 48 by screws or adhesive.

The opening 12b in the case 12 near the screen fixing screw position is provided for inserting a tool such as a screwdriver when screwing the claw part of the screen 46 to the screen fixing block 50. be.

The screen 46, which moves integrally with the spindle 48 in this manner, is provided with three slits 46d, 46e, and 46f as shown in FIG. 5 and the like. The slits 46d, 46e, 46f are provided at positions where the first and second fixed electrodes 14.16 and the common electrode 34 face each other, and the slits 46d, 46f are formed by moving the screen 46.
6e.

If the position of 46f is moved, the ratio of the vertices of the opposing surfaces of the first fixed electrode 14 and the common electrode 34 and the second fixed electrode 16 and the common electrode 34 that face each other through this slit will change.

The above-mentioned parts are the main parts constituting the detector of the present invention, but the actual detector also has the following structure added to it.

A cylindrical stem 54 is provided on one end 12a side of the case 12.
is attached, and a spindle guide 56 and a retainer 57 are provided in this stem 54. The spindle guide 56 fixed in the stem has a guide groove 56a in the direction of movement of the spindle 48, and guides a guide pin 58, which is installed in the spindle 48 and has a dimension f, along the guide groove 56a. There is. The retainer 57 holds the spindle 48 so as to be able to swing freely in the axial direction.

Further, a shield plate 60 having insulating bushings 62 for fixing the other ends of the three lead wires 40, 42, and 44 is fitted inside the other end of the case 12. . Further, this shield plate 60 or three terminal plates 64, 66, and 68 are arranged adjacent to each other. Lead wire 40
．． 42 and 44 are connected via these terminal plates 64, 66, 68 to a cable 72 drawn out into a cap 70 attached to the other end of the case 12.

Reference numeral 75 is an insulating sheet, which is incorporated between the mounting plate 24 and the nut 37 to electrically insulate the nut 37 and the mounting plate 24, and 76 is an insulating sheet between the nut 37 and the shield plate 60.
This is an insulating bushing made of plastic or the like that is arranged to electrically insulate the

The detector in this example is shown in Fig. 1 (A) and Fig. 1 (
Parts are sequentially added to case 1 from the right end of case 12 in B).
2, and by attaching the ring screw 74 and the cap 70 to the case 12, it is held within the case.

Next, the operation of the characteristic parts of the capacitance type detector in this embodiment will be explained.

When an axial displacement is applied to the four probes at the tip of the spindle 48 of the detector configured as described above, the screen 46 is displaced in the axial direction by the amount of the applied displacement.

At this time, the slit 46d of the screen 46.

46e and 46f are also displaced in the axial direction. For example, the screen 4 in the state shown in FIG. 1 (A) and FIG. 1 (B)
6 moves to the right in the figure, these slits 46d, 4
The first fixed electrodes 14 are directly opposed to each other via 6e and 46f.
The capacitance formed between the slit 46 and the common electrode 34 gradually decreases as it is shielded by the screen 46.
The capacitance formed between the second fixed electrode 16 and the common electrode 34, which are directly opposed to each other through the slits 46d, 46e, and 46f, increases as the opening areas of the slits 46d, 46e, and 46f gradually expand.

The amount of displacement of the spindle 48 is detected by taking out the difference in capacitance between each electrode from the lead wire 44.

As can be seen from the embodiments in FIGS. 1A and 1B, during the movement process of the screen 46, the first and second fixed Ef!14.16 and the common electrode 34 are opposed to each other. Capacitive coupling can be formed only through the slits 46d, 46e, and 46f of the screen 46, and the other parts are completely shielded by the screen 46, so that no capacitive coupling is formed.

FIG. 7 is a sectional view showing another example of the screen 46 shown in FIGS. 1(A) and 1(B), and FIG. 8 is a sectional view taken along the line DD in FIG.
9 is a cross-sectional view taken along the line {circle around (2)} in FIG. 7.

The screen 46 shown in FIG. 1 (A), FIG. 1 (B), or FIG.
6c and three slits 46d, 45e, and 46f, the screen 146 shown in FIG.
6d and 146e are provided.

In this way, the number of claws and slits provided on the screen 46, 146 can be arbitrarily determined as necessary.

Also, one claw portion 146 of the screen 146 shown in FIG.
A guide groove 146g is formed in b. The guide groove 146g is provided to guide a guide bin (not shown) attached to the case 12 so as to protrude inward from the case 12, and restricts rotation of the screen 146.

This guide groove 146g corresponds to the guide groove 56a of the spindle guide 56 shown in FIG. 1(A),
Guide grooves can also be provided in the screen 146 or 46 on the movable side.

<Effects of the Invention> According to the present invention, the capacitance between the first fixed electrode and the common electrode and the capacitance between the second fixed electrode and the common electrode are determined only by the slits formed in the screen. In other words, since the portion other than the portion facing the slit is shielded by the screen, there is no effect on the capacitance change f at all.

Therefore, in the state where there is no screen as in the example, the first
It is inexpensive because it is not necessary to ensure the dimensional shape accuracy and assembly positional relationship of each electrode so that the capacitance between the fixed electrode and the common electrode completely matches the capacitance between the second fixed electrode and the common electrode. A highly accurate detector can be obtained.

In addition, unlike the conventional screens, the screen of the present invention does not have both ends of the screen pivoted by rods, etc., so the overall length of the detector is shortened, and the detector is shaped like a wheel. Moreover, since the screen itself can move through the gap between the electrodes without any friction, stable accuracy can be ensured over a long period of time.

[Brief explanation of the drawing]

FIG. 1(A) and FIG. 1(33) are a cross-sectional view of a capacitance type detector according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view taken along A-A in FIG. 1(A). Figure 3 is a cross-sectional view taken along line B-B' in Figure 1 (B), Figure 4 is a cross-sectional view taken along line 1 (B).
5 is a sectional view taken along the line c-c' in FIG. 4, and FIG. 6 is a sectional view showing the screen shown in FIG.
FIG. 7 is a sectional view showing another example of the screen shown in FIG. 1, FIG. 8 is a sectional view taken along line D-D' in FIG. 7, and FIG.
10 is a cross-sectional view showing the configuration of a conventional capacitance type detector. 12... Case, 14... First fixed electrode, 16... Second fixed electrode, 34... Common electrode, 46.146... Screen, 48... Spindle. Figure Figure

Claims (4)

[Claims] (1) A cylindrical case, and a first and second cylindrical case installed in the case and arranged close to each other.
a fixed electrode, a cylindrical common electrode arranged with a certain gap from the inner peripheral surfaces of the first and second fixed electrodes, and a gap between the first and second fixed electrodes and the common electrode. and a cylindrical screen supported movably in the axial direction and having slits at predetermined positions, and depending on the position of the screen, there is a gap between the first fixed electrode and the common electrode facing each other via the slit. and a capacitance formed between the second fixed electrode and the common electrode facing each other via the slit. Detector. (2) The common electrode is supported by a mounting plate fixed within the case, and the screen is fixed to the spindle by passing through a hole provided in the mounting plate. A capacitance type detector according to claim 1. (3) The screen is fixed to the spindle with a screw, and an opening is provided in the case at a position corresponding to the screw into which a tool for screwing the screw is inserted. Capacitance type detector according to scope 2. (4) The capacitance type detector according to claim 1, wherein the screen has a guide groove that fits an inwardly protruding guide pin provided on the case.