Variable resistor

Details Variable resistor Variable resistor

2000-11-08

2004-09-28

Easthom, Karl D. (Department: 2832)

Electrical resistors

Mechanically variable

Movable contact electrically adjustable over length of...

C338S202000, C338S163000

Reexamination Certificate

active

06798333

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a variable resistor used in devices such as a hearing aid, a measuring instrument, communications equipment, a sensor, or other such electronic apparatus, and in particular, the present invention relates to a miniaturized variable resistor.
2. Description of the Related Art
In recent years, reduction in the size and the weight of electronic equipment has been desired, and the reduction in the size and the weight of the circuit components provided within such electronic equipment has also been desired. An ultra-miniature variable resistor having a diameter or side length of about 2 mm has been used as a circuit component. A variable resistor requires a slider which is a spring component. However, the miniaturization of the slider makes it difficult to achieve good electrical contact and sliding characteristics.
FIGS. 1 and 2
show a conventional ultra-miniature variable resistor having a structure in which a shaft
2
, a rotor
3
, a slider
4
, and a substrate
5
are provided in a case
1
and which are sealed by filling a sealing resin
6
such as epoxy resin in the bottom opening of the case
1
. Lead terminals
71
,
72
, and
73
are fixed on the substrate
5
. The lead terminals are electrically connected to both sides of an arcuate resistor
51
and a collector electrode
52
, respectively.
As shown in
FIG. 3
, the slider
4
is defined by a thin metallic plate having a annular arm portion
41
making sliding contact with the arcuate resistor
51
of the substrate
5
and an I-shaped arm portion
42
arranged to contact the collector electrode
52
of the substrate
5
. The annular arm portion
41
is bent up at the portion corresponding to the diameter, and the I-shaped arm portion
42
extends in a direction that is substantially perpendicular to the bent-up line of the annular arm portion
41
and is located inside of the annular arm portion
41
. In the left side view of
FIG. 3
, the solid line designates the slider under a load, and the two-dot chain line designates the slider without a load. In the slider
4
, a pair of through holes
44
for fitting the protrusions
31
(see
FIG. 4
) of the rotor
3
are provided at bilaterally symmetrical positions around the I-shaped arm portion
42
. The slider
4
is mounted on the rotor
3
so as to he rotatable together with the rotor
3
, by fitting the protrusions into the through holes
44
and then crushing the protrusions
31
by weld-caulking.
As shown in
FIGS. 5A and 5B
when the substrate is mounted in the variable resistor, both of the annular arm portion
41
and the I-shaped arm portion
42
are subjected to a load. As a result, a moment M in the backward-tilting direction of the slider
4
occurs about the bending-up line
43
(see FIG.
5
B). The distance between the the protrusions
31
and the bending-up line
43
define the fulcrum about which the moment M acts. Once a backward-tilting of the slider
4
occurs, a problem arises that the contact between the resistor
51
and the annular arm portion
41
and the contact between the collector electrode
52
and the I-shaped arm portion
42
become unstable, resulting in a reduction in the reliability of the variable resistor.
In order to prevent the slider
4
from backwardly tilting, the protrusions
31
of the rotor
3
are weld-caulked. However, because the two protrusions
31
are arranged in the vicinity of the bending-up line
43
, the distance between the protrusions
31
and the bending-up line
43
defining the fulcrum is small. Because the distance defining the fulcrum is small, the backward-tilting of the slider
4
cannot be effectively prevented. Furthermore, in the case of very small components, protrusions
31
having a sufficient size cannot be formed on the rotor
3
, and the weld-caulking of the protusions
31
is very difficult. For example, when the diameter of the slider
4
is 1.5 mm, the diameter of the protrusions needs to be about 0.2 mm to effectively prevent the backward-tilting of the slider
4
. The process of welding such small protrusions
31
is thus very difficult, and a desired fixing strength cannot be reliably achieved even though welding is executed.
SUMMARY OF THE INVENTION
In order to overcome the problems described above, the preferred embodiments of the present invention provide a variable resistor arranged to effectively and reliably prevent a slider from backwardly tilting toward a rotor, thereby maintaining a stable contact between the slider and a substrate.
According to one of the preferred embodiments of the present invention, a variable resistor includes a case, a rotor rotatably accommodated in the case, the rotor being rotationally operated from the outside of the case, a substrate located in the case, the substrate having a collector electrode at an approximate central portion of the surface thereof, and having an arcuate resistor disposed around the collector electrode so as to be substantially concentric therewith, a slider mounted on the rotor so as to be rotatable together with the rotor. The slider having an annular arm portion arranged to achieve sliding contact with the arcuate resistor on the substrate, a substantially I-shaped arm portion arranged to contact the collector electrode, and a base portion that is integral with the slider. The base portion being coupled at one end thereof with the annular arm portion and the substantially I-shaped arm portion by a folded back structure. The base portion extends up to the vicinity of the position corresponding to the tip portion of the annular arm portion. The rear surface of the base portion is supported by the rotor. In this variable resistor, the annular arm portion is bent up at the portion corresponding to the diameter or at the portion in the vicinity of the diameter. The substantially I-shaped arm portion extends in a direction that is substantially perpendicular to the bent-up line of the annular arm portion and is located inside the annular arm portion.
The annular arm portion of the slider rotates and makes sliding contact with the arcuate resistor of the substrate. The substantially I-shaped arm portion makes contact with the collector electrode of the substrate. When both the annular arm portion and the substantially I-shaped arm portion are under a load, a moment about the bent-up line of the annular arm portion and in the backward-tilting direction acts on the slider. In the slider in accordance with a preferred embodiment of the present invention, a base portion is integral with the slider. The base portion is coupled with the annular arm portion and the substantially I-shaped arm portion by a folded back structure. The base portion extends up to the vicinity of the position corresponding to the tip portion of the annular arm portion. With this configuration, the base portion supports the moment in the backward-tilting direction and prevents the slider from backwardly tilting. This stabilizes the contact between the resistor and the annular arm portion and the contact between the collector electrode and the substantially I-shaped arm portion, which leads to an improvement in the reliability of the variable resistor.
Preferably, the annular arm portion, the substantially I-shaped arm portion, and the base portion are coupled such that the base portion is folded back, and the annular arm portion, the substantially I-shaped arm portion, and the base portion are closely contacted by the folded-back structure. Thereby, the height dimension of the slider can be made smaller than the structures of the prior art. This allows variable resistors of the preferred embodiments of the present invention to have lower profiles.
It is preferable that the substantially I-shaped arm portion is raised without folding the substantially I-shaped arm portion. This is accomplished by bending a portion of the folded-back portion in the direction opposite to the bending-up direction of the annular arm portion. In the slider having a conventional structure, because the substantia

Affiliated with

Also associated with

Rating

Variable resistor does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Variable resistor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Variable resistor will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3260788