WO1999035654A1

WO1999035654A1 - Adjustable resistor with slider made from elastomeric material

Info

Publication number: WO1999035654A1
Application number: PCT/NL1998/000020
Authority: WO
Inventors: Cornelis Gerardus Bressers
Original assignee: Capax BV
Current assignee: Capax BV
Priority date: 1996-07-16
Filing date: 1998-01-09
Publication date: 1999-07-15
Anticipated expiration: 2000-07-09
Also published as: NL1003612C2

Abstract

The invention relates to an adjustable resistor comprising a strip of resistance material arranged on an insulating carrier and a slider made of conductive material guidable along the strip and contacting the strip, wherein the slider is manufactured from elastomeric material. A slider manufactured from an elastomeric material will, as a result of its flexibility, make contact with the resistance strip over a relatively large part of the width of the resistance strip so that the problems of an uneven current distribution associated with one-point contact are avoided. The use of an elastomeric material further provides the option of dimensioning and shaping the slider such that it can be handled easily by means of a positioning machine, and the problems of the usually elongate rigid sliders on the production line are avoided. The slider is preferably manufactured from conductive rubber or a conductive plastic. According to yet another embodiment the slider is clamped in a carriage movable parallel to the strip.

Description

ADJUSTABLE RESISTOR WITH SLIDER MADE FROM ELASTOMERIC MATERIAL

The present invention relates to an adjustable resistor comprising a strip of resistance material arranged on an insulating carrier and a slider made of conductive material movable along the strip and contact- ing the strip.

Such adjustable resistors are generally known, for instance in the form of potentiometers, wherein the slider is formed by an element usually made of copper or silver which is movable along a carbon strip. Such ad- justable resistors are also known in the form of for instance ceramic printed circuit boards on which strips of resistance material are arranged along which a slider made of copper or silver is movable and which can be used in particular to adjust the speed of an electrical hand- tool. In both cases a slider of a rigid, though slightly resilient material is moved along a resistance strip. The resilience of the material is necessary herein to press a contact surface of the slider against the resistance strip. it is noted here that while such a material is resilient, it is hardly flexible. This has the consequence that generally only one point of the slider is in contact with the resistance strip. A current can thus flow only at this one point between the slider and the resistance strip. The current flowing through the resistance strip to the slider will, starting from one end of the resistance strip, initially be fully distributed over the width of the resistance strip, but in the vicinity of the contact position of the slider will be distributed with a greater current density to this contact position. This results in an uneven current distribution and thus to a locally higher current density and a locally greater resistance. The curve of the adjustable resistor is thus not linear. This problem otherwise occurs both when the adjustable resistor is used purely as an adjustable resistor and when it is used as a potentiometer. In the case of a potentiometer, a current flowing from the one end of the resistance strip to the other end of the resistance strip is superimposed on the said current.

In the adjustable resistors of the prior art this problem is avoided by making use of two parallel resistance strips which are mutually connected on both sides and on each of which a slider is simultaneously movable. This results however in a more complicated and thus more expensive construction.

The object of the present invention is to avoid the above stated problem. Another problem of the prior art adjustable resistors is that the rigid sliders used therein are components which are difficult to handle during assembly and soon result in disruption of the assembly process, and which can be processed only with the greatest difficulty using mechanical positioning machines. Due to the greater thickness thereof, the sliders according to the invention become easier to handle mechanically. The object of the present invention is to provide such an adjustable resistor wherein the above stated problems are avoided.

This object is achieved in that the slider is manufactured from elastomeric material .

A slider manufactured from an elastomeric material will, as a result of its flexibility, make contact with the resistance strip over a relatively large part of the width of the resistance strip, so that the problems of an uneven current distribution associated with one-point contact are avoided.

The use of an elastomeric material further provides the option of dimensioning and shaping the slider such that it can be handled easily by means of a positioning machine, and the problems of the usually elongate rigid sliders on the production line are avoided. The slider is preferably manufactured from conductive rubber or a conductive plastic. According to yet another embodiment the slider is clamped in a carriage movable parallel to the strip. The present invention will be elucidated hereinbelow with reference to the annexed drawings, in which: figure 1 shows a schematic perspective view of a first embodiment of an adjustable resistor according to the present invention; figure 2 shows a sectional view of the adjustable resistor depicted in figure 1; figure 3 shows a sectional view of a variant of the adjustable resistor depicted in figures 1 and 2 ; figure 4 shows a sectional view of a second variant of an adjustable resistor according to the invention; and figure 5 is a top view of resistance strips of the variant shown in figure 4. Figure 1 shows a base plate 1 which is manufactured from insulating material, for instance from ceramic insulating material . This support plate serves as carrier for the components arranged thereon which, in addition to a resistance strip 2 arranged thereon, generally also include other elements such as semiconductors . Such a carrier usually forms part of control electronics for adjusting the rotation speed and/or the torque of electrically driven hand-tools in which such a support plate is arranged. As stated, a strip 2 of resistance material is arranged on support plate 1. This resistance material is formed by a material which includes conductive particles, for instance carbon, and the specific resistance of which has a value such that the total resistance of the strip acquires the required value. On at least one side the resistance strip 2 is connected to a conductive strip 3 manufactured from conductive material, for instance of copper or of silver. This strip forms the connection to Hi

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using a slider made from an elastomeric material which extends over a substantial part of the width of the resistance strip.

Claims

1. Adjustable resistor comprising a strip of resistance material arranged on an insulating carrier and a slider made of conductive material guidable along the strip and contacting the strip, characterized in that the slider is manufactured from elastomeric material.

2. Adjustable resistor as claimed in claim 1, characterized in that the slider is manufactured from conductive rubber or conductive plastic.

3. Adjustable resistor as claimed in claim 1 or 2, characterized in that the slider is clamped into a carriage movable parallel to the strip.

4. Adjustable resistor as claimed in claim 3, characterized in that the carriage comprises a sleeve which encloses the slider and in which an end of the slider is fixedly clamped.

5. Adjustable resistor as claimed in claim 3, characterized in that the slider is rod-shaped and is fixedly clamped in the carriage on both its ends, wherein the slider contacts the strip between its two ends.

6. Adjustable resistor as claimed in claim 1, 2 or 3, characterized in that the slider has a contact surface with which it contacts the strip, and that the contact surface of the slider makes contact with the strip over its full width.

7. Adjustable resistor as claimed in any of the foregoing claims, characterized in that the slider is rounded on its contact surface.

8. Adjustable resistor as claimed in any of the foregoing claims, characterized in that the resistance strip is divided into two parallel extending strips of equal width, the contact surface of the slider is inter- rupted and each of the thus formed parts of the contact surface makes contacts with a strip.

9. Adjustable resistor as claimed in claim 8, characterized in that the strips are mutually connected on at least one of their ends .

10. Adjustable resistor as claimed in any of the foregoing claims, characterized in that the adjustable resistor forms part of a circuit for adjusting the rotation speed of an electrical hand-tool.

11. Adjustable resistor as claimed in any of the foregoing claims, characterized in that a lubricant is applied to the contact surface of the slider.