GB2065382A - Flexible resistance film for use in variable resistance devices - Google Patents

Abstract

A method of making a flexible resistance film for use in multiple volume control or other variable resistance devices comprises coating a flexible plastics film (1) with a conductive material (2) to provide a uniform conductive coating, and then separating the conductive film (2) into portions to provide adjacent conductive elements (2a, 2b). The film portions may be separated by punching elongate holes 3 through the film and substrate, or by providing a removable separator element on the film before it is coated so that a gap is left when the element is removed. Terminals 9 are formed by conductive strips screen printed on uncoated film portions 8, and the substrate is finally divided along lines 5. The resultant resistor tracks are closely matched, and the film may be curved and placed in a single housing to provide a multiple track potentiometer. <IMAGE>

Description

SPECIFICATION Flexible resistance film for use in variable resistance devices The invention relates to a resistance film.

More particularly, the invention relates to a flexible resistance film for use in variable resistance devices such as volume control devices, and a method of manufacturing the flexible resistance film.

Heretofore, individual resistance bands of a knob controlled volume dial for example are generally each made of a rigid metal plate, which is circular in shape; one side of the rigid plate is coated with carbon, and terminals are provided which are located at each end of the band. A press is used to stamp out individual bands from the metal plates.

Various problems have arisen when the resistance bands of the aforesaid type are employed in volume control devices. The carbon coating process has inevitably resulted in differences occurring from one plate to another as well as from one band to another on the same plate. There has been a lack of consistency or uniformity. Furthermore, when two or more resistance bands are required for use in multiple volume control devices, the variations in the applied coatings require that the resistance variation between the different resistance bands be corrected. In addition, each resistance band requires its own individual housing.

It is therefore an object of the present invention to provide the resistance bands with uniform resistance values in corresponding positions as well as to reduce the number of volume control unit housings in the multiple volume control device.

In order to overcome these problems and in accordance with the present invention a method of making a flexible resistance film for use in a variable resistance device, comprises coating a flexible plastics film with a conductive material to form a uniform conductive coating, and separating the conductive film to provide a plurality of conductive resistance elements.

Preferably, the flexible plastics film is coated with carbon except for the terminal ends. In order to form separate resistance elements adjacent to each other, the coated portion of the plastics film may be punched to form rectangular slots, thereby isolating adjacent resistance elements from each other. The plastics film has properties conductive to achieving relatively even coating and plural elements from the same film only can be used for the same volume control device, so that it is possible to obtain adjacent elements which have the same resistance value as well as resistive characteristics in corresponding positions. To provide for connections to the separate adjacent resistance elements, separate pairs of wire connectors can be provided for each band.

Thus the requirement for correcting the resistance variation and the addition of further housings to the volume control device can be dispensed with.

In addition, a volume control device or other variable resistance device having two or more variators can be contemplated which is of reduced size because the resistance films comprising the individual separate resistance elements take less space and are more compact than the separate resistance bands of the prior known devices, the resistance film requiring only one housing.

Examples of the invention and prior art devices are shown in the accompanying drawings in which: Figure 1 is a plan view of an example of a flexible resistance film for use in a dual control resistance device; Figures 2 and 3 show the way in which the resistance film of Fig. 1 is used for a dual control device; Figures 4, 5 and 6 show another example for use in a quadruple control device similar to that of Figs. 1, 2 and 3; Figure 7 illustrates a dual volume control device according to the invention employing two resistance elements of the type of Fig. 3; Figure 8 is a plan view of plate used for manufacturing conventional resistance bands; Figure 9 shows a single conventional resistance band, and; Figure 10 illustrates the conventional volume control device with two housings employing two resistance bands of the type of Fig. 9.

Referring now to the Figs. 1, 2 and 3 of the drawings, there is shown a flexible plastics film 1 onto which is uniformly coated a conductive material 2, such as carbon to form a uniform and continuous carbon resistance. A portion 8 on each side of the flexible plastic film 1 is left uncoated for the formation of a terminal end. Separate bands of resistance elements 2a and 2b etc. are formed by punching elongate holes 3 or by providing a separator element on the plastic film 1 before it is coated so that when it is removed a space is left therebetween, isolating resistance elements 2a and 2b from each other. In use pairs of elements 2a and 2b are separated by cutting along line 5, and leads 4 are connected with elements 2a, 2b through terminals 9 formed at the ends of the resistance elements 2a, 2b.

The flexible plastic film 1 is thus used as a base material to make the carbon resistance elements. The elements 2a, 2b comprise the plastic film 1, and the carbon 2 with which the film is coated.Terminals 9 are provided on each end connected with the bands 2a, 2b, and the holes or spacing between the elements provides the insulation therebetween.

The connection of terminals 9 to the resis tance elements is formed by silk screen printing, and the elongate holes 3 are made by punching the coated part between each band to demarcate each resistance element. Of course, the aiternative procedure of providing a removable material can be used to leave a free space 3 after the material is removed.

The plastic film can be coated with the carbon so as to have the same uniform resistance value in each element and each of the resistance elements is separated from the other one of its pair by the punched hole or spacing 3.

All of the resistance elements have the same resistance value at parallel corresponding positions, while it is substantially impossible for the conventional resistance band to be coated under the same conditions, and the correction of the resistance variation, as well as the addition of housings, proportional to the number of the bands used, is needed for the multiple volume control device of Fig. 10.

Fig. 7 shows a volume control device 30 which includes a single housing 32 and contains a pair of the resistance elements 2a, 2b of Fig. 2. This provides for a more compact volume control device in addition to uniformity of adjacent resistance elements 2a, 2b.

In the prior art as best seen in Fig. 8 and 9, a metal plate 11 is provided onto which a resistance 1 2 is coated and to which connectors 1 4 are connected. Since the resistance bands 1 5 are separately formed with the resistance coating 12, there can be a lack of uniformity among the resistance bands 1 5.

In Fig. 10, a conventional volume control device 20 is shown which includes separate housings 22 for each of the resistance bands 15.

As will be evident from a comparison of the devices illustrated in Fig. 7 and 10, the multiple volume control device of this invention is manufactured in a relatively small size in comparison with the conventional one.

Also, this invention requires only one housing whether the device is intended for dual, triple or quadruple control. One housing can accommodate an unlimited number of resistance elements, with the only adjustment being the enlargement of the housing itself.

Referring now again to Fig. 1, it will be noted that a single continuous film 1 can be uniformly coated over its entire extent to provide for triple, quadruple, etc. resistance elements. For a dual control device, the film is punched out to form two resistance elements with one spacing 3 and detached at line 5 as shown in Figs. 1, 2 and 3. For a quadruple control device, the film is punched to form four resistance elements with three spacings 3 and detached at line 5 as shown in Figs. 4, 5 and 6.

Claims (8)

1. A method of making a flexible resistance film for use in a variable resistance device, comprising coating a flexible plastics film with a conductive material to form a uniform conducitve coating, and separating the conductive film to provide a plurality of conductive resistance elements.

2. A method according to claim 1, which includes connecting a pair of external leads to each of the adjacent conductive elements.

3. A method according to claim 2, which includes leaving a portion at each end of the plastic film uncoated, silk screen printing a conductive portion to each end of each adjacent conductive element, and connecting the external lead to each of the conductive portions.

4. A method according to any of claims 1 to 3, wherein the conductive coating is separated by punching an elongate opening to provide a free nonconductive spacing between adjacent conductive elements.

5. A method according to any of claims 1 to 3, wherein the conductive coating is separ ated by providing removable strips on the plastics film prior to coating and removing the removable strips after coating to leave a space between adjacent conductive elements.

6. A method according to claim 1, substantially as described with reference to the accompanying drawings.

7. A flexible resistance film formed by a method according to any of claims 1 to 6.

8. A variable resistance device, comprising a single housing, the housing containing a flexible resistance film according to claim 7.