EP0023276A1 - Potentiometer comprising at least two conducting tracks and a rolling contact bridge as electrical connection therebetween - Google Patents

Abstract

Potentiometer comprising at least two conducting tracks and a rolling contact bridge as electrical connection therebetween. A potentiometer is proposed which contains at least two conducting tracks (1, 2) between which a rolling contact bridge, designed as a contact roller (4), is provided as an electrical connection, which contact bridge consists of an inner part (5) of solid material and of a sleeve (8), attached to the surface of the inner part (5), of rubber or plastic that is made conductive. (Figures 1 + 5). <IMAGE> <IMAGE>

Description

The invention relates to a potentiometer, consisting of at least two conductor tracks, one of which is made of a good electrically conductive material and is used for power supply and the other conductor track is designed as a resistance track, with a rolling contact bridge being provided as the electrical connection between these tracks elastic, electrically conductive material.

Conductors in the sense of the present invention are those which are applied in the form of thin layers to an insulating base; but it can also consist of at least one conductor made of wire or metal tape on the insulating base, on which the contact bridge rolls.

Potentiometers, ie adjustable resistors, have been known for a long time. The formation of the contact bridge serving as an electrical connection between the conductor tracks ke in the form of a roll or roller is also known, as can be seen in this connection from DE-PS 532 674, 532 982, 716 563 and DE-OS 17 65 545. In these known potentiometers, the contact roller always consists of a metal ring or a metal roller, which can optionally also be ball-bearing. In most cases, this contact roller is pressed by spring force against the resistance track, which is usually made of wire, metal strip or carbon. The conductor track serving as a resistance track is usually located on rod-shaped insulating bodies or on flat surfaces, for example also in the form of a circle or on the inside of a cylinder (cf. DE-OS 17 65 545 or DE-PS 609 255).

DE-PS 538 301 describes a variable contact in the case of electrical variable resistors. Potentiometers and similar electrical apparatus described, which consists of circularly arranged resistance coils and in which an elastic metal ring is provided, which is between the resistance coil and either the axis of rotation of the device or a part connected to the axis of rotation. pressed, rolls under pressure on the resistance coil while rotating this axis and at the same time is held in position by a device, for example a disk attached to the axis of rotation. If a metal strip is arranged between the ring and the resistance coil, which is attached to the housing or is designed as a freely movable ring, the rolling ring can optionally consist of insulating material. The ring, which rolls under pressure on the resistance wheel, creates a certain contact surface with several edge turns due to its flattening; the result is a very low frictional resistance and consequently little wear and very easy mobility.

All these known contact rollers have the disadvantage that their surface - even if it is an elastic partial ring - only comes into contact with the bumps of the conductor track serving as a resistance layer and rolls on them. The contact transition is therefore naturally only point-shaped or at best linear. In order to obtain a vibration-proof contact, a certain contact pressure has to be applied, whereby on the one hand there is still a certain amount of abrasion on the resistance surface and on the other hand there are contact resistances at the point or line-shaped contact transitions because not the entire surface serves as contact. There is therefore a certain amount of abrasion and thus also a change in the contact transition, so that the potentiometer experiences changes in its electrical values after prolonged use. Furthermore, the contact is subject to certain changes due to its resilient support against vibrations and shock loads. In the case of very hard resistance layers, for example made of metal oxides or shiny coal, these conditions lead to metallic precipitation on the resistance track, which also causes changes in resistance.

The object of the present invention is to specify, while avoiding the disadvantages described, a potentiometer in which the contact transition is extensive, yet permits good rolling, and at. which does not change the electrical resistance value even with high change cycles and, if possible, also causes a cleaning effect of the resistance layers.

• a) Die Kontaktbrücke ist als Kontaktwalze ausgebildet und besteht aus einem Innenteil aus festem Material (Metall, Isolierstoff), der mittels einer konzentrischen Bohrung auf eine Achse aufgeschoben ist, und aus einem an der Oberfläche des Innenteils aufgebrachten Mantel, der aus unter Aufrechterhaltung seiner elastischen Zusammendrückbarkeit durch Zusatz leitfähiger Partikel (Metallstaub, Kohle) leitend gemachten Gummi oder Kunststoff besteht,
• b) die Leiterbahnen sind in der Art der Leitungszüge gedruckter Schaltungen auf einer ein- oder mehrlagigen Schaltplatte zueinander in gleicher Richtung verlaufend aufgetragen,
• c) die Kontaktwalze ist durch eine Kraft F gegen beide Leiterbahnen gedrückt.

To achieve this object, the potentiometer of the type specified at the outset is characterized by the following features:

• a) The contact bridge is designed as a contact roller and consists of an inner part made of solid material (metal, insulating material), which is pushed onto an axis by means of a concentric bore, and of a jacket applied to the surface of the inner part, which is made of while maintaining its elastic Compressibility due to the addition of conductive particles (metal dust, coal) made of conductive rubber or plastic,
• b) the conductor tracks are plotted in the same direction as the lines of printed circuits on a single or multi-layer circuit board,
• c) the contact roller is pressed by a force F against both conductor tracks.

The term "rubber" in the sense of the present invention is also understood to mean silicone rubber.

The force F can either be a spring force which results from the arrangement of a pressure spring, or the distance between the inner part or axis of the contact roller and the conductor tracks can be constant, the jacket being elastically deformed to a small amount and therefore the force F generated on the conductor tracks, that is, the elasticity of the contact roller also acts through its compression.

What is achieved by the invention is that the contact transition in this type of contacting can no longer take the form of a point or line, but rather a surface.

It is advantageous if the resistance track is applied to the circuit board as a discontinuous resistance surface.

In the previous potentiometers with discontinuous - resistance assignment, e.g. with logarithmic potentiometers, it was common to build up the resistance materials in different layers on the resistance track, e.g. wedge-shaped to realize a discontinuous resistance tap.

The discontinuous resistance tapping by simple and precise surface printing of the same thickness, but with a certain curve shape of the resistance surface contour, was difficult to achieve. At the same time, this would have required the resistance to be tapped at least linearly over the entire surface section.

In the case of precision potentiometers, it is only possible with considerable technical effort to combine the advantage of the discontinuous area with the disadvantage of the need to make contact in a linear manner.

However, if, according to the present invention, a potentiometer tap is carried out with elastic and conductive rollers on its surface, the construction can ensure that these two requirements described above are compatible, since the area-like contacting of this type of contacting can cover the entire area cut without difficulty .

In. DE-OS 20 47 904 describes an adjustable electrical device that can be changed by rotating its electrical values with rolling friction, but the construction of this device is extremely complicated and has no significance in practice. This device has three outer rollers arranged on the inside of a housing with an internally circular cross section, between which there is an endless belt which wraps around four inner rollers, three of which are arranged between the outer rollers and one in the center, at least one of these parts consisting partly of electrically insulating and partly of electrically conductive material. The endless band can consist of electrically insulating material and can have a resistance layer on one side, the resistance value of which varies along the band, the rollers that come into contact with the resistance layer at least superficially consist of electrically conductive material and the housing consists of electrically insulating material.

These various requirements and the complicated structure of this known device do not suggest the present invention.

Further preferred embodiments of the invention can be found in the subclaims.

It is particularly advantageous if, in addition to the conductor tracks, further conductor tracks are arranged, which serve as buttons for a switch actuated with a further contact roller, and this contact roller, like the contact roller of the potentiometer, consists of an inner part made of solid insulating material and a jacket made of conductive rubber built thereon or plastic.

A switch, as used here alongside the potentiometer, is already the subject of the unpublished German patent application P 29 09 585.0 dated March 12, 1979. The application of this contact roller principle to potentiometers opens up new, particularly advantageous and unpredictable applications in terms of design and properties (e.g. life duration, precision) of such potentiometers.

A decisive advantage of the present invention is also that it is easily possible to build tandem potentiometers of almost any selectable configuration either side by side or on an insulating plate provided on two sides with conductor tracks.

It has been confirmed by tests that the flexing work of the elastic contact rollers achieves a good cleaning effect of the contact elements, that is to say here the metal tracks and the resistance tracks on insulating material plates. The contradiction between wear of the contact parts and cleaning of the contact parts which is usually present in the case of potentiometers is thus eliminated or at least reduced by orders of magnitude by the present invention.

The following description in connection with the figures serves to explain the invention.

• Fig. 1 den Aufbau eines Potentiometers nach der Erfindung in schematischer Form;
• Fig. 2 den prinzipiellen Aufbau eines diskontinuierlichen Widerstandsstreifens mit unterschiedlicher Schichtstärke, links in Aufsicht und rechts in Seitenansicht;
• Fig. 3 ein Potentiometer mit diskontinuierlicher Widerstandsfläche bei gleicher Schichtstärke, links in Aufsicht und rechts in Seitenansicht;
• Fig. 4 ein Potentiometer mit ringförmig angeordneten Leiterbahnen;
• Fig. 5 eine Kombination von Potentiometer und Schalter;
• Fig. 6 ein Potentiometer nach der. Erfindung, bei dem die Widerstandsbahnen auf der inneren Oberfläche eines zylindrischen Körpers angeordnet sind.

Show it

• Figure 1 shows the structure of a potentiometer according to the invention in schematic form.
• Figure 2 shows the basic structure of a discontinuous resistance strip with different layer thickness, left in top view and right in side view.
• 3 shows a potentiometer with a discontinuous resistance surface with the same layer thickness, on the left in top view and on the right in side view;
• 4 shows a potentiometer with conductor tracks arranged in a ring;
• 5 shows a combination of potentiometer and switch;
• Fig. 6 is a potentiometer after. Invention in which the resistance tracks on the inner surface a cylindrical body are arranged.

In Fig. 1, 1 denotes the power supply conductor track, which consists of a good electrically conductive material. The resistance track 2 is arranged next to the conductor track 1 and runs in the same direction as this, is of uniform thickness and of a uniform cross section. The two conductor tracks are on the _. Isolierstoffplatte 3, which can be a one-sided or a multi-layer coated insulating carrier. The contact roller 4 consists of an inner part 5 made of solid material, for example metal or insulating material, preferably polyethylene terephthalate. The inner part 5 is pushed onto an axis 7, on which it slides well, by means of a concentric bore 6. On the surface of the inner part 5, a jacket 8 is applied, which, while maintaining the elastic compressibility by adding conductive particles, for example. Metal dust or coal dust, made of conductive rubber or plastic. The contact roller 4 is pressed onto the conductor tracks 1 and 2 by means of the pressing force F.

2 and 3, resistance tracks 2 are shown, in FIG. 2 in plan view as a rectangle (left side). The side view shown (right side) shows that the conductor track 2 is of increasing thickness, so that the contact roller 4 'can roll over this conductor track. The increasingly thick conductor track 2 can be constructed in such a way. that it is composed of layers of material with different specific conductivity (different specific resistance). The lowest and therefore longest layer is very high-resistance, and the top, shortest layer is very low-resistance. The intermediate layers are graded accordingly, so that the result is a logarithmic resistance characteristic.

3, the conductor track is of uniform thickness according to the side view (right side), but it increases in width according to the top view (left side), so that a correspondingly long contact roller 4 is also required. The use of a contact roller 4 with a conductive, elastic surface according to the invention results in a particularly advantageous embodiment of a potentiometer with a logarithmic characteristic over a range of several powers of ten. For this purpose, the conductor track 2 is preferably composed of individual narrow longitudinal strips 2a, which consist of materials with different specific resistances and are well contacted by the contact roller. The longest longitudinal stripe (left) is high-resistance, e.g. 5 M ohms over its entire length, the shortest longitudinal stripe (right) is low-resistance over its length, e.g. 1 k ohm. The longitudinal strips in between are graded accordingly, both with regard to the resistance value and with regard to the resulting boundary line, which is shown here in a curve. In this way it is e.g. possible to produce a potentiometer with a logarithmic characteristic of the resistance value, which covers the range from 1 k ohm to 10 k ohm.

According to FIG. 4, the conductor track 10 serving as a resistance track and the conductor track 11 serving as a power supply are applied in the form of concentric ring surfaces on the circuit board 3; the contact roller 12 is arranged rotatably about the center of the concentric rings 10 and 11 and has an increasing diameter in the radial direction. The pressure force F ensures that a sufficient Contact is given.

The pressing force F can be realized in various ways known per se, for example by spiral springs which are supported against the housing, or by a spring which interacts with a second axis, as is shown schematically in FIG. 5, or by the elastic properties of the contact jacket 8 itself.

5, in addition to the conductor tracks 1 and 2, further conductor tracks are arranged, which serve as buttons 13, 14, 15 and 16 of a switch actuated by a further contact roller 17. Like the contact roller 4, the contact roller 17 consists of an inner part 18 made of solid insulating material and a jacket 19 made of conductive rubber or plastic applied thereon. On the axis 7, a spring 20 is fixed, which cooperates with an axis 21. On this axis 21, a further contact roller 22 is attached, which interacts with conductor tracks 23 and 24 on the opposite side of the insulating plate 3. The contact roller 17 is also on the other side of the circuit board 3 opposite a contact roller, which, however, is not visible in the drawing. A spring 25 is attached to the axis of this contact roller and the axis 7 of the contact roller 17.

5, for example, a switch and a logarithmic potentiometer can be implemented. Use cases. there are numerous ways of doing this, for example in the case of measuring devices.

6, the conductor tracks 1 and 2 are on the inside. nenfläche a cylindrical housing 26 applied from insulating material. The pressing force F acts radially outward on the contact roller 4. One possibility for realizing this force F is described, for example, in DE-PS 609 255.

Claims (6)

1. Potentiometer, consisting of at least two conductor tracks, one of which is made of a highly conductive material and is used for power supply and the other conductor track is designed as a resistance track, with a rolling contact bridge being provided as an electrical connection between these tracks, which is made of elastic, electrical conductive material, characterized by the following features: a) The contact bridge is designed as a contact roller (4) and consists of an inner part (5) made of solid material (metal, insulating material), which is pushed onto an axis (7) by means of a concentric bore (6) and one on the surface the inner part (5) applied jacket (8), which consists of rubber or plastic made conductive while maintaining its elastic compressibility by adding conductive particles (metal dust, coal), b) the conductor tracks (1, 2) are applied in the manner of the lines of printed circuits on a single or multi-layer circuit board (3) to each other in the same direction, c) the contact roller (4) is pressed by a force (F) against both conductor tracks (1, 2). 2. Potentiometer according to claim 1, characterized in that the resistance track (2) is applied as a discontinuous resistance surface (9) on the circuit board (3) (Fig. 2 and 3). 3. Potentiometer according to claim 2, characterized in that the resistance track 2 from layers arranged one above the other or of narrow longitudinal strips (2a) arranged next to one another each consist of resistance material with different specific electrical conductivity. 4. Potentiometer according to claims 1, 2 or 3, characterized in that the conductor track (10) serving as a resistance track and the conductor track (11) serving as a power supply are applied in the form of concentric annular surfaces to the circuit board (3) and the contact roller (12 ) is arranged to be rotatable about the center of the concentric rings and has an increasing diameter in the radial direction (FIG. 4). 5. Potentiometer according to one of claims 1 to 4, characterized in that the conductor tracks (1, 2) on the inner surface of a cylindrical housing (26) made of insulating material and the force (F) on the contact roller (4) radially outwards acts (Fig. 6). 6. Potentiometer according to one of claims 1 to 5, characterized in that in addition to the conductor tracks (1, 2) further conductor tracks are arranged, which as buttons (13, 14, 15, 16) of a switch actuated by a further contact roller (17) serve and the contact roller (17) as well as the contact roller (4) consists of an inner part (18) made of solid insulating material and an applied coat (19) made of conductive rubber or plastic (Fig.5).

Images