JPH02232585A - Capacitance type detector - Google Patents

Abstract

PURPOSE:To enable highly accurate detection without requiring a high accuracy for a shape and position of an electrode or the like by arranging a pair of screens moving integral axially at a fixed interval. CONSTITUTION:Cylindrical common electrodes 34 are arranged at a fixed interval with a fixed clearance on the inner circumference of first and second electrodes 14 and 16 disposed in proximity within a cylindrical case 12. A pair of screens 50 and 52 is so arranged that it can move integral axially within the clearance while a fixed ring-shaped space is formed axially. Then, as a spindle 54 is shifted axially, the screens 50 and 52 are shifted axially together, when capacities of the electrodes 14 and 16 and the electrode 34 developed through the ring-shaped space changes with a movement of the space. Such a capacity difference between the electrodes 14, 16 and 34 is picked up from a lead 48 to be detected as variation of a movement of the spindle 54. An apparatus thus obtained is inexpensive because there is no need for securing a dimensional shape accuracy and an assembling position relationship of the electrodes and enables highly accurate detection.

Description

Detailed Description of the Invention Industrial Field of Application The present invention provides a common electrode with a certain gap between the first and second fixed electrodes, and A movable screen is provided between the common electrode 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 this screen. The present invention relates to 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. 5 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 electrode 2 and a second cylindrical fixed electrode 3 are arranged on the outside thereof with a constant gap from the common electrode 1.

The capacitance between these electrodes, that is, the capacitance between the first fixed electrode 2 and the common electrode 1 and the capacitance between the second fixed electrode 3 and the common electrode 1, is It changes depending on the position of the cylindrical screen 6 that moves along. This screen 6 includes first and second fixed electrodes 2,
3 and the common electrode 1 located inside it. The rods 4 and 5 supporting the screen 6 have a uniform diameter and are constructed so as not to affect the change in capacity due to the movement of the screen 6. Further, the common t-pole 1 is insulated and supported by a support shaft 7. This support shaft 7 is firmly fixed to the housing 8,
Furthermore, first and second insulated fixed electrodes 2.3 are fixed to this housing 8. The housing 8 functions as an electrical shield, a support means for the detection part, and a bearing for the rods 4 and 5, supporting each part so that the screen 6 does not touch the electrodes. Further, the common electrode 1 and the first and second fixed electrodes 2.3 are connected to terminals 9, respectively.
, 10.11, and the amount of movement is detected by changes in the output from these terminals. Problems 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 part shielded by the screen 6 spanning the first and second fixed electrodes 2 and 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 fi1 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 capacitance between the first fixed electrode 2 and the common electrode 1 without the screen 6 is 01, and the capacitance of the second fixed electrode 1f! 3 and the common electrode 1 is set as C2, and if the screen 6 is further inserted and the capacitance change at a certain position is ΔC, the differential capacitance change f is {C1+ΔC)−(CZ−ΔCl =
(c, -C2)+2ΔC, where C r C
During the period 2 > 2ΔC, the original difference c, -C2 is larger than the differential change 2ΔC, making it difficult to detect the change. Therefore, in this structure, it was necessary to improve the precision of parts and the precision of mounting positions so that each capacitance would match exactly without the screen 6.
However, in reality, this was extremely difficult and caused an increase in costs. In addition, 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 and the rods 4.5. Housing 8
The operation of the screen 6 had to be machined with great precision to attach it to the screen 6. 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. The present invention aims to provide an inexpensive and highly accurate detector without requiring high precision in the shape and position of electrodes, etc. 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 circumferential surfaces of the first and second fixed electrodes, and integrally spaced apart from each other by a certain distance in the axial direction and said gap. A pair of cylindrical screens are supported so as to be movable in the axial direction, and the first and second fixed electrodes and the common electrode are connected to each other through a ring-shaped constant space formed by the pair of screens. It is characterized by differentially detecting the ratio of the capacitances formed between the two. Function> The screen in the present invention is composed of a pair of screens that move together at a constant interval in the axial direction. Therefore, the first and second fixed electrodes and the common electrode each face each other via the ring-shaped space between the pair of screens to form a capacitance.

When the pair of screens moves, the ring-shaped fixed space also moves accordingly, and the ratio of the areas where the first and second fixed electrodes and the common electrode face each other changes. Each capacitance changes and the ratio is output differentially. A sinusoidal voltage with 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 difference between the capacitance formed between the first fixed electrode and the common electrode and the capacitance formed between the second fixed electrode and the common electrode as described above increases. changes in proportion to the displacement of the screen. By obtaining this change as an output from the common electrode, the amount of displacement of the screen is converted into an electrical signal and detected. Embodiments> Preferred embodiments of the present invention will be described below based on the drawings. FIG. 1 is a sectional view of a capacitance type detector according to an embodiment of the present invention, FIG. 2 is a sectional view taken along the line II' in FIG. FIG. 4 is a side view showing one screen shown in FIG. 1;

Reference numeral 12 denotes a cylindrical case, which is open to the left and right in FIG.

Reference numerals 14 and 16 designate first and second fixed electrodes having a cylindrical shape and arranged adjacent to each other. 6 These first and second fixed electrodes 14.1 are arranged so as to be in contact with each other via ring-shaped insulating sheets 1 to 20.
6 is a disc-shaped receptacle f fitted into the case 12.
It is fixed by being inserted between the base plates 22 and 24 via spacers 26 and 28.

Note that a ring-shaped insulating sheet 30.32 is also provided between the first and second fixed electric currents 114.16 and the spacer 26.28.
34 is a cylindrical common electrode.

This common electrode 34 is externally fitted and fixed to a cylindrical support shaft 38 via an insulating ring 36. This support shaft 3
8 is fixed by fitting the extending end on the right side in the figure into a hole provided in the center of the mounting plate 22,
The common electrode 34 is connected to the mounting plate 22 via this support shaft 38.
Fixed. At this time, the common electrode 34 is fixed coaxially with the central axis of the case 12. Note that the common electrode 34 in this embodiment is attached to the mounting plate 22.
The left end in the figure is also supported by a plurality of support rods 40 (three at 120 degree intervals in the example figure) made of an insulating material such as ceramic rods or plastic that extend from the mounting plate 24 facing the Although it has been
It is not necessary to provide this support rod 40.

Further, in this embodiment, a ring-shaped spacer 42 is also fitted around the support shaft 38, and is interposed between the opposing end surfaces of the common electrode 34 and the mounting plate 22 to determine the position of the common electrode 34. There is.

A ring-shaped insulating sheet 41 is placed between the spacer 42 and the common electrode 34 to provide electrical insulation. 43 is also a ring-shaped insulating sheet, and insulating sheet 41
It is arranged on the end surface side of the common electrode 34 on the opposite side.

The first and second fixed electrodes 14, 16 and the common electrode [!
34, a total of three lead wires 44, 46.4, one each passing through the mounting plate 24, spacer 28, etc.
8 is installed. This first and second fixed voltage f
The inner diameters of the first and second fixed electrodes 14 and 16 and the outer diameter of the common electrode 34 are adjusted so that a uniform gap is formed between the inner circumferential surface of the fi 14.16 and the outer circumferential surface of the common electrode 34. and their mounting positions are determined.

A pair of cylindrical screens 50.52 are arranged in the gap formed between the first and second fixed electrodes 14.16 and the common electrode 34, and are movable in the axial direction. is supported by

As shown in FIGS. 3 and 4, this one screen 50 has two claw portions 50b and 50c that integrally extend in the axial direction from a ring-shaped cylindrical portion 50a. 50b and 50c are inserted into holes 22a and 22b provided in the mounting plate 22, respectively, and the tip of the claw portion protruding through each hole is fixed to the spindle 54. In this embodiment, the claws 50b and 50c are not directly fixed to the spindle 54, but two mounting screws 58 are attached to the screen support block 56, which is fixed to the spindle 54 with one screw or with adhesive. They are each secured with screws. Therefore, the screen 50 moves axially together with the spindle 54, and in particular the ring-shaped cylindrical part 50a of this screen 50 is formed by the first and second fixed poles 14, 16 and the common electrode. You will have to move within the gap.

Incidentally, the opening 12a made in the vicinity of the mounting screw 58 position of the case 12 is provided for inserting a tool such as a screwdriver when screwing the claw portion of the screen 50 to the screen support block 56. be. Further, although the screen 50 has two claws in this embodiment, there may be two or more claws. Also, the other screen 5
2 has a U-shaped cross section, has a bottom portion 52a at the left end in the figure, and its cylindrical portion 52b is machined to have the same inner and outer diameter dimensions as the ring-shaped cylindrical portion 50a of the screen 50 described above. 6 This screen 52 has a cylindrical portion 52.
The end face of the cylindrical portion 50a of the screen 50 is positioned such that there is a constant spatial distance t between the end face of the screen 50, and the end face of the cylindrical portion 50a of the screen 50 is fixed to the screen shaft 60.

One end 60a of the screen shaft 60 is firmly fixed to the screen support block 56 by means such as press fitting, and the other end 60b, which passes through the support shaft 38 and protrudes to the left end in the figure, is attached to the screen support block 56. The center hole of the bottom 52a of 52 has a dimension of f. Accordingly, this screen 52 is connected to the first and second fixed electrodes 14,16 and the common voltage 8 as the spindle 54 moves with the screen 50.
i! It will move within the gap between 34 and 34. A ring-shaped space with a constant spatial distance 1t is formed between the screen 50.52 configured in this way, and as the screen 50.52 moves, this ring-shaped space also moves. Become. Next, the operation of the characteristic parts of the capacitance type detector in this example will be explained. When an axial displacement is applied to the spindle 54 of the detector having the above configuration, the screen 54 is moved by the amount of the applied displacement.
0.52 is integrally displaced in the axial direction. At this time, the ring-shaped space between the screens 50.52 will be displaced as the screens 50.52 are displaced. Therefore, the capacitance between the first fixed electrode 14 and the common electrode 34 and the capacitance between the second fixed electrode 16 and the common electrode 34 formed through this ring-shaped space change as the ring-shaped space moves. become. For example, when the screen 50, 52 in the state shown in FIG. 1 moves in the direction shown in the figure,
The capacitance formed between the first fixed electrode 14 and the common electrode 34, which face each other with a ring-shaped space in between, is gradually blocked by the screen 50 and decreases. The capacitance formed between the two fixed electrodes 16 and the common electrode 34 increases because the portions facing each other through the ring-shaped space gradually increase. This difference in capacitance between each electrode is taken out from the lead wire 48 and detected as the amount of change in movement of the spindle. 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 ring-shaped fixed space formed by the pair of screens. It will be done. In other words, the area other than the part facing the ring-shaped constant space is shielded by the screen, so there is no effect on the capacitance change. Therefore, in a state where there is no screen as in the conventional example, the dimensions and shape of each electrode are adjusted such that the capacitance between the first fixed electrode and the common electrode completely matches the capacitance between the second fixed electrode and the common electrode. Since there is no need to ensure accuracy and assembly location, an inexpensive and highly accurate detector can be obtained. In addition, unlike the conventional screens, the screen constructed according to the present invention does not have both ends of the screen pivotally supported by rods, etc., so the overall length of the detector is shortened, making it more compact. Furthermore, since the screen itself can move through the gap between the electrodes in a completely frictionless state, stable accuracy can be ensured over a long period of time.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a capacitance type detector according to an embodiment of the present invention, FIG. 2 is a sectional view taken along the line II' in FIG.
4 is a side view showing one of the screens shown in FIG. 1, and FIG. 5 is a sectional view showing the configuration of a conventional n-capacitance type detector. l2... Case, 14... First fixed electrode, 16... Second fixed electrode, 34... Common electrode, 50.52... Screen, 54... Spindle.

Claims (1)

[Claims] (1) A cylindrical case, first and second cylindrical fixed electrodes installed in the case and arranged adjacent to each other, and inner circumferential surfaces of the first and second fixed electrodes. comprising a cylindrical common electrode arranged with a certain gap, and a pair of cylindrical screens that are spaced apart from each other by a certain distance in the axial direction and supported so as to be integrally movable in the axial direction within the gap, Differentializing 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 through a ring-shaped fixed space formed between the pair of screens. A capacitance type detector that is characterized by its ability to detect