High current slipring for multi fiber brushes

A slipring comprises a slipring module rotating about a rotation axis, having a plurality of sliding tracks and at least one multi wire brush sliding thereon. The sliding tracks have a circular contact surface with its center located at the rotation axis and a convex shaped cross-section. Due to this convex shaped sliding track, the individual brush wires of the multi wire brush distribute over the sliding track surface and offer a higher number of contact points. This results in a higher current capacity, lower contact resistance and lower contact noise.

FIELD OF THE INVENTION

The invention relates to slip rings for the transmission of electrical signals and/or energy by means of sliding contacts between rotatable parts. In such a sliding contact, a brush is slidable on a sliding track, also called slipring track. The brush and the sliding track comprise electrically conductive materials. The contact between the brush and the sliding track establishes a galvanic connection by which the electric current may be transferred.

DESCRIPTION OF RELEVANT ART

A slip ring is disclosed in DE 14 89 080 A. Here, the brushes comprise solid single wires running in grooves of a track.

Another slip ring is disclosed in EP 0 662 736 A, having multi-wire brushes running in a V-shaped groove of a track. The multi-wire brushes have a plurality of brush wires providing a plurality of simultaneous contacts with the sliding track. This results in a lower contact resistance and a higher current capacity.

US 2011/0081789 discloses a slipring with V-shaped grooves and multi-contact brushes.

SUMMARY

The embodiments are based on the object of providing a slip ring further providing an improved capacity, further reduced contact resistance and contact noise, and further increased current capacity. A further object is to provide a sliding track having improved capacity, further reduced contact resistance and contact noise, and further increased current capacity.

In a first embodiment, a sliding track has a convex shape to provide a better distribution of the brush wires—also called contact wires—of a multi-fiber brush. Preferably, this convex shape protrudes outwards of the surface of a slipring module. Most sliding tracks known from the prior art have concave surfaces formed inwards into the surface of a slipring module, which are designed to guide at least one wire of a brush at a predetermined track. If there is a plurality of brush wires running in a concave sliding track, some of the brushes are directly sliding on the concave track surface, while other wires are located on the top of these sliding wires. These other wires do not establish an electric contact with the sliding track. Test series have shown, that in most cases 20 to 50%, and up to 80% of the available wires are not sliding on the sliding track surface. This is improved by said first embodiment, by using a convex sliding track surface. Here, the individual wires evenly distribute over the surface of the sliding track. If there would be one wire located above another wire, it simply would slide to the side of this other wire and contact the sliding track.

Using a convex sliding track is only useful in conjunction with multi-wire brushes having at least two wires. If there is a plurality of wires, some of the wires are sliding relative to a first side of the center of the track, while others are sliding on the other side of the center of the track. Due to the convex form, there are forces pulling the wires sideward and downwards of the track. As these forces apply to both sides of the center of the track, these compensate and keep the brush as a whole in stable position.

In a further embodiment, there is at least one groove at one side of the convex-shaped sliding track. Preferably, there are two grooves on both sides of the convex-shaped sliding track. These grooves may limit the movement of brush wires. This may further be improved by having at least one side wing and/or elevated side. In a further embodiment, there may be a contact surface, which has at least two convex shape cross-sectioned segments. There may be a plurality of brushes in parallel to each other, each on its own cross-sectioned segment.

The sliding track preferably has a circular shape, which may also be described as an arc segment. The center of the convex sliding track defines a center plane. Preferably, at least one brush is held in the center plane. It is preferred, if the brush is at least essentially parallel to the center plane.

A further embodiment provides a slip ring module comprising at least one sliding track as described herein. Another embodiment provides a slip ring comprising at least one slipring module and at least one multi-wire brush as described herein. Furthermore, it is preferred, if the at least one multi-wire brush includes at least two brush wires and a brush holder for holding the at least two brush wires. Preferably, the at least one multi-wire brush is mounted within a center plane defined by the center of a circular contact surface.

Due to the convex sliding track, there is a better distribution of the brush wires on the sliding track. Tests have shown that more than 90% of the brush wires are in immediate contact with the sliding track. Therefore, by using a sliding track according to the previous embodiments, the number of brush wires staying in sliding contact with the sliding track can be increased without increasing the total number of sliding wires. This leads to an increased current capacity, lower contact resistance and lower contact noise. Furthermore, heat is dissipated over a larger surface and better distributed over the wires and the track surface, which further increases current capacity and lifetime by decreasing wear. Due to the increased current capacity, sliprings may be built smaller. Especially, if there is a high number of sliding wires in an embodiment as known from prior art having a concave sliding track, the wires may shift their location relative to the other wires. This causes additional contact noise. Such a contact noise is prevented by the embodiments described herein.

The sliding tracks and the brush wires mentioned herein most preferably include at least one metal, preferably a noble metal. Such a noble metal may be gold, silver, or an alloy thereof. The sliding track and/or at least one brush wire may have a surface of one of such metals or may be solid of such metals. It is preferred, if the sliding track has a metal body, which may be copper or any copper alloy, or a similar conductive metal material with a surface comprising at least one noble metal. At least one brush may have an inner body of a conductive material, such as steel, brass, or copper, which is coated by a material comprising at least one noble metal. Generally, a brush as mentioned herein includes a plurality of brush wires.

DETAILED DESCRIPTION

InFIG. 1, a sectional view of a convex sliding track according to a first embodiment is shown. The sliding track has a sliding track body14. The sliding track body14is held by or embedded into slip ring body16. To allow a good electric contact with the brushes, there is a sliding track coating15at the surface of sliding track body14. A plurality of brush wires50are sliding at the sliding track coating. The sliding track basically has a convex shaped cross-section19with a center section41defining the center plane49. Besides this center section, preferably there are side wings42and43, which preferably are also coated as previously described. During normal operation, the wires50are sliding on the convex-shaped sliding track portion and do not slide on the side wings. These may provide some safety margin for the case the wires50leave their normal position. This may be caused by misalignment, shock, or vibration. The convex sliding track may have a cross-section of a segment of a sphere, an ellipse, a sinus or any other form resulting in a convex shape. In this and the following figures, only a single sliding track is shown. There may also be a plurality of such tracks mounted side by side at a slipring module. The tracks may be connected electrically or may be insulated from each other.

InFIG. 2, a sectional view of a second embodiment of a sliding track is shown. Here, side grooves44and45are configured to catch any brush wires sliding away from the convex-shaped sliding track. Furthermore, elevated sides46and47may be configured to provide an additional safety margin.

InFIG. 3, forces at sliding wires are shown in a sectional view of a sliding track. In this example, only two sliding wires are shown for simplicity. Basically, the same forces apply, if there is a larger number of sliding wires. A first brush wire51is shown at the left side of center plane49, while a second brush wire52is shown at the right side of the center plane49. The forces, which apply to the brushes51and52, are symmetrical to the center plane49. At the first brush51, a first tangential force61pulls the brush outwards to the left side. This force has two components. A first component62pulls the brush at a right angle to the center plane away from the center plane, while a second force63presses the brush51parallel to the center plane to the sliding track surface. The second force63is generated by the elasticity of the brush wire, pressing the brush wires of a brush in the direction of a rotational axis of the slip ring and parallel to the center plane49. The same applies to the second brush52with the tangential force65, the first force66, and the second force67, basically pressing the second brush to the right side. If this arrangement is symmetrical, the first force62at brush51and the first force66at the second brush52have the same size and opposite direction. Therefore, these forces compensate each other and allow for a stable positioning of the both brush wires51and52on the surface of the convex sliding track. To allow for such a compensation of forces, the brushes51and52preferably are tightly attached and held together in a brush holder.

InFIG. 4, a plurality of brushes50held by a brush holder53are shown in a side view. At least a part of the brush holder53may be a sleeve, holding all the wires tightly together. Preferably, the brush holder53is arranged within the center plane49and may be held by the printed circuit board20(as shown inFIG. 7) or any other brush holding assembly.

InFIG. 5, a sliding track as known from the prior art is shown. On a slip ring body30, there is a sliding track coating31, forming a V-shaped groove33. Basically, this is a concave form. There is a plurality of brush wires32sliding in this groove. It can be seen, that only some of the brush wires32are in electrical contact with the groove, while the other brush wires are located on top of the sliding brush wires.

InFIG. 6, a sliding track as known from the prior art is shown. On a slip ring body30, there is a sliding track coating31, forming a flat sliding track. There is a plurality of brush wires32sliding on this track. It can be seen, that only some of the brush wires32are in electrical contact with the track, while the other brush wires are located on top of the sliding brush wires.

InFIG. 7, a schematic view of a slip ring is shown in a sectional view. The slip ring has a slip ring module10, which may be rotatable around a rotation axis11in rotation direction12. It may also be rotated in the opposite direction. The slip ring module has a slip ring body16, which preferably includes an isolating material, most preferably ceramic, plastic, polymer, or epoxy. There is at least one sliding track13held by and/or embedded into the slip ring body16. A first wire brush21and/or a second wire brush22may slide on the sliding track13and contact the sliding track in the vicinity of a first contact point23and a second contact point24. Preferably, both wire brushes may be held by a printed circuit board20or any other kind of brush holding assembly. Instead of the printed circuit board, any other means like a metal plate may be used.

LIST OF REFERENCE NUMERALS