GB2240885A - Potentiometer connector - Google Patents

Abstract

A variable resistance device, such as a potentiometer, has a housing (1) including an electrically insulating substrate (4) which carries a resistance element (6) and film electrical conductors (8, 11, 12). The film conductors extend to an edge region (9) of the substrate (4) and terminate in a side-by-side array (8A, 11A, 12A). A demountable electrical connector assembly (13, 14) locates with an apertured region (10) of the housing (1) and such that spring-biased terminals (14) in the connector assembly make electrical contact with the array (8A, 11A, 12A) of conductors on the edge region (9) of the substrate (4). This arrangement obviates the need for separate external terminal pins on the device and the risk of unreliable connections between these and the resistance element and conductors inside the device housing. <IMAGE>

Description

VARIABLE ELECTRICAL RESISTANCE DEVICE This invention relates to variable electrical resistance devices.

It is particularly, although by no means exclusively, applicable to variable resistance devices in the form of potentiometers, particularly for use in the automotive field, but it is to be understood that other applications are envisaged, such as in variable resistance devices adapted and arranged for force or pressure measurement.

Variable resistance devices in the form of potentiometers are well known, comprising a housing containing a substrate on which a film resistance element is provided and an electrically conductive wiper which is externally operable to traverse the resistance element. It is necessary to provide electrical connections from the ends of the resistance element and the wiper to the exterior of the potentiometer to enable a voltage supply to be applied to the resistance element and an output voltage to be obtained at the wiper, which is dependant upon the position of the wiper along the resistance element. Such potentiometers are finding increasing application in the automotive industry as engine throttle position sensors, wheel suspension movement monitors, steering wheel position sensors, etc.In prior art potentiometers it has been standard practice to provide metal terminal pins emerging from the housing and to provide a standard automotive-type of connector to fit onto the pins in order to connect the necessary external wires or cables to the potentiometer. Sealing means has to be provided to prevent contamination or corrosion of the terminal pins. The terminal pins are usually electrically connected to the resistance element, and to conductors associated with the wiper, by means of eyelets, rivets, conductive adhesives, or spring contacts, etc. These prior art arrangements are expensive and tend to be unreliable.

Similar problems can arise with other forms of variable resistance devices, eg with force or pressure sensors incorporating force or pressure sensitive film resistance elements on a deformable or deflectable substrate in a housing and where electrical connections to the outside of the housing are required to be made from the resistance elements.

It is an object of the present invention to overcome or minimise the aforementioned disadvantages of the prior art devices.

The present invention provides, in a variable electrical resistance device, an electrically insulating substrate having on a surface thereof a film electrical resistance element and film electrical conductors associated therewith, characterised in that the film electrical conductors extend to an edge region of the substrate and terminate in a side-by-side array thereat, the edge region of the substrate being profiled to receive a demountable electrical connector assembly such that the side-by-side array of the conductors make electrical contact with electrically conductive terminals on or in the connector assembly.

The electrical connector assembly suitably comprises an electrically insulating body of hollow or solid form having the said electrically conductive terminals secured therein or thereto and with means to connect the said terminals to external conductor leads. The said conductive terminals may be suitably spring-biased to ensure good electrical contact with the film electrical conductors.

The said edge region of the substrate may either be formed to present a straight edge to the said connector assembly or may be profiled to present an array of fingers to the connector assembly, with a film conductor extending along the surface of each finger.

In the latter case, a connector assembly may then be utilised having a portion thereof surrounding each finger and with a conductive terminal in each portion making electrical contact with a corresponding film conductor on each finger.

The fingers may, as an option, be provided with an additional coating of electrically conductive material on top of the film conductors and preferably completely surrounding the fingers, thereby providing improved contact with the conductive terminals in the connector assembly. Such additional coating may suitably be provided by dipping the fingers in a liquid electrically conducting polymer composition, followed by a usual heat treatment therefor.

For some applications, the said electrical connector assembly may conveniently comprise or be based upon a known standard form of printed circuit board edge connector which is arranged to be press-fitted on the edge region of the substrate.

For other applications the variable resistance device may be provided with a housing having an apertured portion into which the said edge region of the substrate extends, the said electrical connector assembly being adapted and arranged to fit in or over said apertured portion with electrically conductive terminals in the connector assembly making electrical contact with the conductors on the edge region of the substrate. If required, sealing means may be provided between the connector assembly and the housing.

Suitably the resistance element and conductors have been provided on the surface of the substrate by screen printing and suitably comprise materials selected from electrically conducting polymers or fired-on thick film metal glaze or cermet materials or metal resinate materials. Such materials are well-known. The electrically conducting polymer materials comprise electrically conducting particles dispersed in an organic polymer.

The substrate is selected according to its compatibility with the film resistance element and conductors and its ability to be suitably shaped. Examples of materials for selection are moulded plastics materials, plastics sheets, plastics laminates, ceramics and insulated metals.

In a particular embodiment, the variable electrical resistance device comprises a potentiometer and the film resistance element is of elongate arcuate or linear form and is arranged to be traversed by an electrically conductive wiper, three said film electrical conductors being provided, electrically connected respectively to opposite ends of the resistance element and to the wiper. By means of the electrical connector assembly a voltage may be applied from an external source to the ends of the resistance element and an output voltage obtained between the wiper and one end of the resistance element, the magnitude of the output voltage being dependant upon the position of the wiper along the resistance element.

This embodiment is particularly applicable in the automotive industry for applications such as engine throttle position sensing, road wheel suspension monitoring and steering wheel position sensing.

In a further embodiment the variable electrical resistance device comprises a force or pressure measuring device in which one or more said film electrical resistance elements are provided on the substrate and is or are adapted and arranged such that the substrate is mechanically deflectable or deformable by means of an externally applied force or pressure (eg fluid pressure), the resistance value of the electrical resistance element or elements changing in known manner as a function of the applied force or pressure. In such an embodiment a Wheatstone bridge network of the resistance elements may be provided and the said film electrical conductors serve to connect a voltage supply to and receive an output voltage from the network by way of the said electrical connector assembly.

By means of the present invention, external terminal pins of the prior art are eliminated, as is also the need to employ eyelets, rivets, conductive adhesives or spring contacts to connect such pins with the internal components of the variable resistance devices.

The invention is now described by way of example with reference to the accompanying drawings in which: Figure 1 represents a top plan view of a variable electrical resistance device according to the invention in the form of an electrical potentiometer, with its top cover and wiper assembly removed; Figure 2 represents a cross-sectional view of the device of Figure 1 in complete form and provided with an electrical connector assembly; Figure 3 represents a top plan view of a variable resistance device as in Figure 1 but with an alternative arrangement of edge region of the substrate for connection to an alternative electrical connector assembly; Figure 4 represents a cross-sectional view of the device of Figure 3 in complete form.

Referring to Figures 1 and 2, a variable electrical resistance device, embodied as a potentiometer, is constructed as follows. A housing 1, of moulded plastics material, provided with a cover 2 clipped thereto, and with a cylindrical aperture 3 through it, has a flat electrically insulating substrate 4 secured therein. The substrate 4 suitably comprises a plastics or ceramic material and has a hole in it to accommodate the aperture 3 through the housing.

Further holes are provided in the substrate 4 through which protrusions 5 on the housing 1 pass and are heat swaged to secure the substrate in the housing. An arcuate film resistance element 6 of well-known form, and suitably comprising an electrically conducting polymer material of appropriate electrical resistivity, is provided by screen printing on the surface of the substrate 4, followed by an appropriate heat treatment process. An electrically conductive wiper means (not shown) of well known form is secured to a rotatable carrier 7 which is rotatably mounted in the aperture 3 in the housing 1. The wiper means is arranged to traverse, in well known manner, the resistance element 6 and also an electrically conducting collector track 8 on the substrate 4 when the carrier 7 is rotated by suitable external means inserted through the aperture 3 in the housing 1.

The key feature of the invention is the provision on the substrate 4 of an edge region 9 which is suitably profiled to extend into an apertured portion 10 of the housing 1. The apertured portion 10 provides a rectangular aperture extending into the housing 1 with its cover 2. Film electrical conductors 11, 12, suitably of well-known electrically conducting polymer material are screen printed onto the surface of the substrate 4 and such that they extend onto the edge region 9 and form terminations lIA and 12A.

The collector track 8 is also suitably formed of a conducting polymer material by screen printing and is provided with a portion extending onto the edge region 9 of the substrate 4 to form a further termination 8A.

A side-by-side array of film terminations 8A, lIA and 12A is consequently provided on the edge region 9 of the substrate 4.

A demountable electrical connector assembly comprising a rectangular hollow body 13 (Figure 2) of a plastics material has three spring contacts 14 secured therein, each with an electrical lead wire 15 connected thereto. The connector assembly is arranged to fit over the apertured portion 10 of the housing and is retained in snap-fit manner by means of protrusions 16 on the portion 10 of the housing.

Alternatively, screws could be used to retain the connector assembly in position. The three spring contacts 14 make electrical contact at their ends with the film conductor terminations 8A, llA, 12 A.

The spring contacts 14 may be plated with a precious metal, if necessary, to provide improved electrical contact.

If required, a suitable sealing means (not shown) such as a gasket or O-ring of plastics or rubber material, can be provided between the body 13 of the connector assembly and the portion 10 of the potentiometer housing.

In operation a voltage is applied through the appropriate pair of wires 15 to conductors 11 and 12 at the ends of the resistance element 6 and an output voltage, dependant upon the position of the wiper along the resistance element 6, is obtained from a third wire 15 via the conductor 8, 8A.

Figures 3 and 4 illustrate a potentiometer which is the same as that shown in and described with reference to Figures 1 and 2 with the exception that a somewhat different arrangement is provided for the edge region 9 of the substrate 4. In the embodiment of Figures 3 and 4 the edge region 9 of the substrate 4 is profiled to form three fingers 17 on one surface of which the film conductor terminations 8A, llA and 12A are provided. An electrical connector assembly (not shown) of a type known to be used for fitting onto metal pin terminals can then be plugged into the apertured portion 10 of the housing and onto the fingers 17 to provide electrical connection to the conductor terminations 8A, lIA and 12A. If desired, a coating of electrically conducting material could be applied to completely surround each of the fingers 17, to provide improved electrical contact with the connector assembly. Such a coating conveniently comprises a known electrically conducting polymer material and is suitably applied by dipping the fingers into a liquid composition for producing such a material, followed by heat treatment in known manner to effect the necessary curing and/or polymerisation of the material.

Claims (18)

1A variable electrical resistance device comprising, an electrically insulating substrate having on a surface thereof a film electrical resistance element and film electrical conductors associated therewith, characterised in that the film electrical conductors extend to an edge region of the substrate and terminate in a side-by-side array thereat, the edge region of the substrate being profiled to receive a demountable electrical connector assembly such that the side-by-side array of the conductors make electrical contact with electrically conductive terminals on or in the connector assembly.

2 A device according to Claim 1, in which the electrical connector assembly comprises an electrically insulating body of hollow or solid form having the said electrically conductive terminals secured therein or thereto and with means to connect the said terminals to external conductor leads.

3 A device according to Claim 1 or 2, in which the said conductive terminals are suitably spring-biased to ensure good electrical contact with the film electrical conductors.

4 A device according to Claim 1, 2, or 3, in which the said edge region of the substrate is formed to present a straight edge to the connector assembly.

5 A device according to Claim 1, 2 or 3, in which the said edge region of the substrate is profiled to present an array of fingers to the connector assembly.

6 A device according to Claim 5, in which a connector assembly is utilised having a portion thereof surrounding each finger and with a conductive terminal in each portion making electrical contact with a corresponding film conductor on each finger.

7 A device according to Claim 5 or 6, in which the fingers are provided with an additional coating of electrically conductive material on top of the film conductors or completely surrounding the fingers, thereby providing improved contact with the conductive terminals in the connector assembly.

8 A device according to Claim 7, in which the additional coating is provided by dipping the fingers in a liquid electrically conducting polymer composition, followed by a usual heat treatment therefor.

9 A device according to any preceding Claim, in which the said electrical connector assembly comprises or is based upon a known standard form of printed circuit board edge connector which is arranged to be press-fitted on the edge region of the substrate.

10 A device according to any of Claims 1 to 8, in which the variable resistance device is provided with a housing having an apertured portion into which the said edge region of the substrate extends, the said electrical connector assembly being adapted and arranged to fit in or over said apertured portion with electrically conductive terminals in the connector assembly making electrical contact with the conductors on the edge region of the substrate.

11 A device according to Claim 10, in which sealing means is provided between the connector assembly and the housing.

12 A device according to any preceding Claim, in which the resistance element and conductors have been provided on the surface of the substrate by screen printing and comprise materials selected from electrically conducting polymers or fired-on thick film metal glaze or cermet materials or metal resinate materials.

13 A device according to Claim 12, in which the electrically conducting polymer materials comprise electrically conducting particles dispersed in an organic polymer.

14 A device according to any preceding Claim, in which the substrate comprises a material selected from moulded plastics materials, plastics sheets, plastics laminates, ceramics and insulated metals.

15 A device according to any preceding Claim, in which the variable electrical resistance device comprises a potentiometer and the film resistance element is of elongate arcuate or linear form and is arranged to be traversed by an electrically conductive wiper, three said film electrical conductors being provided, electrically connected respectively to opposite ends of the resistance element and to the wiper.

16 A device according to any of Claims 1 to 14 in which the variable electrical resistance device comprises a force or pressure measuring device in which one or more said film electrical resistance elements are provided on the substrate and is or are adapted and arranged such that the substrate is mechanically deflectable or deformable by means of an externally applied force or pressure, the resistance value of the electrical resistance element or elements changing in known manner as a function of the applied force or pressure.

17 A device according to Claim 16, in which a Wheatstone bridge network of the resistance elements is provided and the said film electrical conductors serve to connect a voltage supply to and receive an output voltage from the network by way of the said electrical connector assembly.

18 A variable electrical resistance device constructed and arranged substantially as hereinbefore described with reference to the accompanying drawings.