Electrical resistors – Mechanically variable – Movable contact electrically adjustable over length of...
Reexamination Certificate
2000-05-24
2001-01-09
Easthom, Karl D. (Department: 2832)
Electrical resistors
Mechanically variable
Movable contact electrically adjustable over length of...
C338S308000, C252S511000
Reexamination Certificate
active
06172595
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a resistor excellent in micro-linearity characteristic and in wear resistance and a variable resistor that uses the resistor.
2. Description of the Related Art
A conventional resistor used for a variable resistor of various sensors contains resin serving as based material of the resistor, carbon fiber serving as structural material, and carbon black serving as conducting particle, and a slider moves in contact with a resistor pattern consisting of the resistor. At that time, because hard carbon fiber receives the load of the slider in the diametral direction and distributes the load along the long carbon fiber, the load wears the resistor very little. Therefore, the wear resistance of the variable resistor that uses this type of resistor is excellent in comparison with the variable resistor that uses another type of resistor that contains only conducting particles such as carbon black or graphite.
However, in the case of a conventional resistor that uses carbon fiber, because carbon fiber has high conductivity in the fiber direction, the resistivity varies in a small range of the resistor depending on the fiber orientation of carbon fiber, and the micro-linearity characteristic is poor, and the poor micro-linearity is a problem.
The micro-linearity characteristic is described herein under.
FIG. 14
shows a graph obtained in a test. In the test, a rating voltage V
in
is applied in the length L direction of a resistor pattern, and the vertical axis represents the output V of a slider that slides on the resistor pattern in the longitudinal direction and the horizontal axis represents the position X of the slider on the resistor pattern. The output change concomitant with displacement &Dgr;X of the slider from an arbitrary point on the resistor is represented by an ideal straight line P having a gradient V
in
/L on the assumption that the resistivity of the resistor is constant not depending on the position.
On the ideal straight line P, the normal output voltage obtained when the slider moves from A point to B point by &Dgr;X is represented by &Dgr;V=(&Dgr;X/L)×V
in
, but the actual output S deviates from the ideal straight line P. As shown in the equation (1), the micro-linearity characteristic is calculated as described herein under. The normal output variation is subtracted from the output variation V
A
−V
B
(V
A
is the actual output at the point A and V
B
is the actual output at the point B) to obtain the difference, the difference is divided by the applied voltage, and the obtained value is multiplied by 100 to obtain percent expression. In the case of high performance position sensor, particularly excellent micro-linearity characteristic, which shows actual output S is similar to the ideal straight line P, is required.
[Equation 1]
micro-linearity
(
V
B
-
V
A
)
-
(
Δ
X
L
)
V
i
n
V
i
n
×
100
V
A
: output value obtained when the slider is positioned at the point A
V
B
: output value obtained when the slider is positioned at the point B
V
in
: applied voltage in the resistor length L direction
&Dgr;X: distance between the point A and the point B
L: resistor length
SUMMARY OF THE INVENTION
The resistor in accordance with the present invention contains 15 to 20% by volume of carbon black and 15 to 20% by volume of carbon fiber in the resistor base material. The particle diameter distribution of the carbon fiber is approximately according to the normal distribution, and 80% by volume or more carbon fiber of the whole carbon fiber is included in the particle size range from 1 to 20 &mgr;m.
The material to be used as the resistor base material is not limited as long as carbon black and carbon fiber are dispersed homogeneously and bonded. For example, thermosetting resins such as phenol-aldehyde resin, xylene-modified phenol resin, epoxy resin, polyimide resin, melamine resin, acrylic resin, acrylate resin, and furfuryl resin may be used.
Carbon black functions to render the resistor conductive. The carbon black content in the resistor lower than 15% by volume results in low conductivity as the resistor and poor micro-linearity characteristic, and on the other hand the carbon black content of higher than 20% by volume results in poor screen printability of the resistor and poor moldability of the resistor pattern.
Carbon fiber functions to distribute the load exerted from a slider and support the slider. Therefore, carbon fiber is served as the structural material for improving the wear resistance of the resistor due to the load of a slider and also functions to stabilize the electrical contact with the slider of the resistor at the contact point.
The carbon fiber content in the resistor lower than 15% by volume results in reduced points that support the load of a slider and results in poor support, the wear resistance is reduced. On the other hand, the carbon fiber content of higher than 20% by volume results in poor bonding power of resin that is used as the base material of the resistor and carbon fiber leaves off from the resistor surface, and the wear resistance of the resistor is reduced.
The particle size distribution of carbon fiber is prescribed so that carbon fiber fills the above-mentioned role and renders the resistor excellent in micro-linearity. The percentage of carbon fiber in the particle size range from 1 to 20 &mgr;m of 80% by volume or lower, namely the case that the particle size distribution is broad or the case that the distribution curve deviates significantly from the normal distribution or is asymmetric distribution, in other words carbon fiber contains much carbon fiber having long length and/or much carbon fiber having short length, results in poor micro-linearity characteristic due to existence of long carbon fiber, and/or results in poor wear resistance due to existence of short carbon fiber that does not function to support the load of the slider.
In the resistor in accordance with the present invention, the particle size distribution of carbon fiber has the peak at the particle size in the range from 1 to 3 &mgr;m. The carbon fiber in accordance with the present invention is granular, the high conductivity of carbon fiber in the fiber length direction does not affect the micro-linearity. The granular carbon fiber receives the load of the slider on several groups, and the load is distributed to adjacent many carbon fibers, and the carbon fiber renders the resistor wear resistant.
In the case of another resistor in accordance with the present invention, the particle size distribution of carbon fiber has the peak at the particle size in the range from 6 to 10 &mgr;m. In the case of carbon fiber having short fiber length as described herein above, the high conductivity in the fiber length direction does not affect the micro-linearity characteristic, carbon fiber receives the load of a slider in the fiber diameter direction, the load is distributed along the fiber length direction, and the load is supported. Therefore, the resistor is excellent in wear resistance, and the performance is maintained in the various environmental temperatures.
The resistor in accordance with the present invention contains carbon fiber that is desirably subjected to coupling treatment. Silanate base, titanate base, or alumina base coupling agents may be used as the coupling agent. The dispersibility of carbon fiber in the resistor base material is improved by means of such coupling agent, carbon fiber is prevented from leaving off from the resistor surface, and the wear resistance is improved.
The resistor of the present invention is excellent in micro-linearity characteristic and wear resistance in a wide environmental temperature range, as the result, the variable resistor of the present invention is also excellent in these performances, and desirably used for the position sensor to be mounted on an engine controller of a vehicle.
REFERENCES:
patent: 5111178 (1992-05-01), Bosze
pat
Fujita Takayuki
Komatsu Hisashi
Osada Katsuhisa
Taguchi Yoshihiro
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Easthom Karl D.
LandOfFree
Resistor excellent in micro-linearity characteristic and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Resistor excellent in micro-linearity characteristic and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Resistor excellent in micro-linearity characteristic and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2468722