Trimmer capacitor

Details Trimmer capacitor Trimmer capacitor

2000-12-22

2002-12-31

Reichard, Dean A. (Department: 2831)

Electricity: electrical systems and devices

Electrostatic capacitors

Variable

C361S292000, C361S287000

Reexamination Certificate

active

06501637

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a capacitor, and more particularly, the present invention relates to a trimmer capacitor in which fine adjustment of the capacitance can be made.
2. Description of the Related Art
As a conventional trimmer capacitor, there is, for example, a chip-type trimmer capacitor disclosed in Japanese Unexamined Patent Application Publication No. 6-20872. This trimmer capacitor, as shown in
FIG. 5
, includes a stator
31
that is integrally molded with a nearly semicircular fixed electrode
32
having anchor portions
40
a
and
40
b
disposed in the circumferential portion of the fixed electrode
32
using a resin
31
a
and a dielectric ceramic plate
33
defined by a ceramic plate
33
a
made of a dielectric material with a movable electrode
34
. The upper surface of the stator
31
on which the fixed electrode is provided and the lower surface of the dielectric ceramic plate
33
on which no movable electrode
34
is provided are arranged to rotatably contact with each other. A metal adjustment shaft
35
is arranged to pass through a shaft hole
38
of the stator and a through-hole
39
of the dielectric ceramic plate
33
. The tip portion of the metal adjustment shaft
35
and a metal spring (rotor spring washer)
36
are joined so that they mate with each other.
Then, in this trimmer capacitor, by rotating the dielectric ceramic plate
33
in a state in which the upper surface of the stator
31
is in contact with the lower surface of the dielectric ceramic plate
33
and by changing the area of the fixed electrode
32
opposed to the movable electrode
34
, that is, the overlapping area, the amount of capacitance generated between the fixed electrode
32
and the movable electrode
34
can be adjusted.
However, in the trimmer capacitor as described above, after the fixed electrode has been integrally embedded in the resin
31
, the flatness of the upper surface of the stator
31
and the surface of the fixed electrode
32
exposed over the stator is increased to improve the characteristics of the trimmer capacitor, and accordingly a process for polishing the upper surface of the stator
31
is generally required. However, in the above-described trimmer capacitor, since the stator
3
is molded using a resin and is soft, it is difficult to reliably and accurately perform the polishing, and by the process of polishing, there is in particular a problem that the fixed electrode may be removed. The removal of the fixed electrode
32
is caused by weak adhesion of the fixed electrode
32
to the resin
31
a
, although the fixed electrode
32
is embedded in the stator
31
, and when polishing is performed while the fixed electrode
32
b
is removed, excessive polishing is performed, and as a result, a problem of a decrease in the capacitance of the trimmer capacitor occurs.
In the above-described trimmer capacitor, by embedding the anchor portions
40
a
and
40
b
provided on the fixed electrode
32
in addition to the lead-out portion
37
of the fixed electrode in the stator, the fixed electrode
32
is fixed at the three points and the mounting strength of the fixed electrode
32
to the stator
31
is increased.
Here, the anchor portions
40
a
and
40
b
are provided in the circumferential portion of the fixed electrode
32
and are nearly at a right angle relative to the surface of the fixed electrode
32
, and the farther toward the tip portion, the larger is at least one of the width and the thickness. This is to decrease stray capacitance caused by the anchor portions and to prevent reduction of the bending strength of the stator
31
.
However, in the above-described conventional trimmer capacitor, as shown in
FIG. 5
, the anchor portions
40
a
and
40
b
are disposed in the circumferential portion of the fixed electrode
32
and at a location where the line connecting the anchor portions
40
a
and
40
b
does not pass through the shaft hole
38
of the stator. Therefore, the tip portions
41
a
and
41
b
of the fixed electrode
32
are to be located outside a triangular area defined by connecting the anchor portions
40
a
and
40
b
and the lead-out portion
37
of the fixed electrode, and there is the possibility that the removal of the tip portions
41
a
and
41
b
of the fixed electrode cannot be prevented merely by affixing the fixed electrode
32
at the three points.
In order to solve this problem, a method of providing additional anchor portions at the tip portions
41
a
and
41
b
of the fixed electrode
32
may be considered. As a method for providing these anchor portions, there is, for example, a method disclosed in Japanese Unexamined Patent Application Publication No. 57-140731, and in this method, as shown in
FIG. 6
, a fixed electrode
51
is firmly affixed in a stator
53
by performing press working on the circumferential portion
52
of the fixed electrode
51
so that the fixed electrode
51
cuts into the resin material. A trimmer capacitor in which the method is used in the tip portions of a fixed electrode and anchor portions
50
a
and
50
b
are further provided to the tip portions
41
a
and
41
b
of the fixed electrode is shown in FIG.
7
. In the trimmer capacitors in
FIGS. 5 and 7
, the same reference numerals are applied to equivalent portions. In the trimmer capacitor, because the anchor portions
50
a
and
50
b
are further disposed at the tip portions
41
a
and
41
b
of the fixed electrode, it is believed that the fixed electrode
32
is also firmly affixed at the tip portions to the stator
31
and that the floating of the fixed electrode
32
can be reliably prevented.
However, the trimmer capacitor in which the anchor portions
50
a
and
50
b
are disposed at the tip portions
41
a
and
41
b
of the fixed electrode by the above method has the following problem.
FIG. 8
is an enlarged sectional view taken along line Y-Y′ of the fixed electrode
32
embedded in the molded stator
31
in
FIG. 7
, which has not been polished. As shown in the drawing, the anchor portion
50
b
extends obliquely downward from the surface
32
a
of the fixed electrode. Accordingly, in the process of forming the stator
31
, when the upper surface of the stator
31
and the surface
32
b
of the fixed electrode embedded in the stator
31
are polished along line A-A′, the length of the fixed electrode
32
is extended in the direction of Y-Y′ by L, that is, the area of the fixed electrode
32
is increased. Here, as the anchor portions
50
a
and
50
b
are located in the direction in which the movable electrode
34
opposed to the anchor portions
50
a
and
50
b
rotates, the area of the fixed electrode
32
becomes larger in the direction of the anchor portions
50
a
and
50
b
, and this means that the area opposed to the movable electrode
34
, that is, the overlapping area, becomes larger, and as a result, the problem of varied capacitance in the trimmer capacitor occurs. In the process of polishing stators, since it is difficult to maintain the amount of polishing exactly constant among stators, the capacitance varies due to the polishing, and accordingly, variations in the capacitance of each stator occurs.
SUMMARY OF THE INVENTION
In order to overcome the problems described above, preferred embodiments of the present invention provide a trimmer capacitor in which in the process of forming a stator, even if the upper surface of the stator is polished in order to increase the flatness of the upper surface of the stator and the surface of the fixed electrode embedded in the stator, the capacitance does not change, and the trimmer capacitor has stable characteristics.
According to one preferred embodiment of the present invention, a trimmer capacitor includes a stator on the upper surface of which a substantially semicircular fixed electrode is mounted, and a dielectric ceramic plate on the upper surface of which a movable electrode is mounted, the lower surface of the dielectric ceramic plate contacting with the upper surface of the sta

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