Patent Application
20080111440
1. Field of the Invention
The present invention relates to a sliding contact assembly and, in particular, to a system for collecting particles of abraded matter formed by the movement of a brush contact member along a contact slide track.
Sliding contact assemblies are used in apparatus to maintain electrical contact between two mechanically separate parts that are adapted to move relative to each other, where leads cannot be employed. One of the parts is provided with an extended contact track and the other of the parts is provided with a sliding contact member adapted to move relative to the contact track whilst maintaining an electrical contact with the track. Parts connected by sliding contact assemblies may move linearly or rotate relative to each other.
Sliding contact assemblies are used as components of known slip-ring systems where an electrical contact is maintained between a rotatably supported circular or annular contact track and a brush contact member adapted to slide along the track. The systems may be used for transmission of electrical signals, or for mere transmission of electrical energy.
The term brush contact member is here used to denote any sliding brush-shaped, wire-shaped, rod-shaped, or pin-shaped contact member that may be made of metal, conducting plastic material, carbon material, or any other material known in prior art for this purpose. Mechanical movement between the contact slide track and the brush contact member causes friction and so-called brush wear owing to an abrasion of small particles of electrically conducting contact material. These particles form fine dust that is scattered into the surroundings and deposited on other components including any insulating material surrounding the contacts. This may cause an appreciable deterioration of insulating properties and in turn may lead to short circuits or an erosion and burning away of the insulating material. Damage may be prevented by regular maintenance of sliding contacts assemblies, involving a careful removal of deposited material from various components, but some particular applications necessitate long periods of operation before maintenance becomes possible.
2. Description of the Prior Art
A slip-ring system for computer tomographs is disclosed in JP 06005340. Transmission of electrical energy is effected by means of a brush running along a ring. A separately disposed dust-collecting device comprises a collector for dust and a tube through which the dust is removed by suction.
A slip ring system for computer tomographs, as described in DE 195 43 383 B4, comprises a slip-ring contact track, and a brush holder and a contact brush adapted to slide along the contact track to form a sliding contact. The system further comprises at least one collecting device for capturing abraded particles that are formed during the movement. The collecting device is adapted to be electrostatically charged, so that captured abraded particles are retained in the collecting device by electrostatic forces.
It is the object of the present invention to provide a sliding contact assembly comprising a contact slide track and a brush contact member with means for efficiently removing and collecting particles of matter abraded from the brush contact member, in order to reduce contamination of surrounding components by deposits of conducting material and thereby to reduce the frequency of necessary maintenance work on the sliding contact assembly.
In accordance with the present invention this object is achieved by a sliding contact assembly comprising: at least one contact slide track; a brush holder for holding at least one brush contact member and maintaining the at least one brush contact member in sliding contact with the at least one contact slide track during relative movement between the brush contact member and the contact slide track; and a collecting container disposed to collect particles of abraded material from the at least one brush contact member; wherein a cover is provided to surround substantially the brush holder and the at least one brush contact member, the cover having walls extending along a direction of the contact slide track laterally of the brush holder and the brush contact member and along a side of the brush holder remote from the contact slide track; the collecting container is disposed at a downstream end of the cover; and the cover is designed to channel a stream of air, generated within the cover by movement of the contact slide track, towards the collecting container.
The invention will be further illustrated with the aid of drawings which, although not to scale, schematically show non-limiting examples of embodiment.
In accordance with the present invention, a cover 5 or protective casing is placed around the sites of the sliding contact assembly in which abraded matter is produced and scattered. These sites are the surfaces of contact of the brush contact members 1 with the contact tracks 2, and the space on the downstream side of the surfaces of contact of the brush contact members 1 with the contact tracks 2. When a contact track 2 is moving relative to a brush contact member 1, the abraded matter is ejected into surrounding space mainly along the direction of arrows 7 as shown in
It is possible to increase the air stream through the cover 5 by creating an air-pressure in excess of atmospheric pressure inside the cover 5 on the upstream side of the brush contact members 1, for example by introducing pressurized air through a supply pipe 8. The supply pipe 8 may be replaced by a fan or blower for generating a stream of air to pass through the cover 5. Alternatively, suction can be applied on an outlet side of the collecting container 4. This can result in a more effective removal of particles of abraded matter.
It is expedient to channel the air current in the direction of the collecting container 4 with the aid of suitably placed air-guiding plates 10, examples of which are shown in
The cover 5 may be made of sheet metal when a high electrical conductivity of the cover material can be tolerated. In this case it could also serve as an electrical shield or screen. Furthermore some a conductive surface helps reducing electrostatic charging. For this purpose preferably the surface Resistance is between 1 kOhm and 10 MegOhm. This prevents electrostatic attraction of dust to the cover surface before it reaches the filter. Alternatively, the cover could be formed from an insulating material such as plastic sheeting. Both features can be obtained by using an isolating material having a conductive surface coating. The brush holder 3 may be a part of the cover 5 or may be enclosed therein. The inside walls of the cover 5 and any air-guiding plates 10 should be designed to have no sharp edges and undercut portions where abraded dust can collect. The air-guiding plates 10 may be positioned to deflect air streams away from inside corners of the cover 5. Inside surfaces of the cover 5, air guiding plates 10, the collecting container 4 and the support of contact slide tracks may be provided with an anti-adhesive coating, like micro- and nano-particles resulting in a lotus-effect. Furthermore at least one edge may be provided within the cover to generate a turbulent air flow. Such turbulences can help to remove dust particles adhering at any surface of the contact track or its support or any brush contact member. A cover made of conductive material or with a conductive surface may also be used as electrical or electromagnetic shield.
The collecting container 4 is a dust filter mounted onto the downstream end of the cover 5 and permitting a passage of air through a filter medium. It may be designed to be an electrostatic dust filter or an electret filter or it may comprise any one of these filters. In another embodiment the collecting container 4 may comprise some material attracting dust like cloth or plush. Furthermore it may comprise a dust collection bag like a vacuum cleaner bag. The bag or the filter is preferably contained in an exchangeable cartridge. This cartridge can be conveniently exchanged and/or cleaned. In addition the collecting container 4 may be provided with an anti-adhesive coating, like micro- and nano-particles resulting in a lotus-effect or any of the materials and surfaces as described above for the cover. In another embodiment the collecting container comprises a deflector for deflecting the air stream inside the collecting container and improving disposal of dust or particles within the collecting container.
In a further embodiment of the invention hatches or vanes are provided for redirecting the air stream in accordance with the direction of rotation. Furthermore the air stream generated by the rotating member may be used for blowing air into the collecting container and for suction of air out of the collecting container. Preferably the bottom of the collecting container is covered by a porous material like Polyurethane foam to absorb particles.
Another embodiment of the invention comprises means for adapting the air flow actively or passively in dependence of the contact slide track rotational direction by actively or passively adapting vanes, vents, a fan direction or an additional filter. Therefore the air flow into or through the filter is maximized dependent of the rotational direction to obtain optimum particle removal characteristics.
In the sectional view of
The cover 5 is designed as an air-guiding channel to guide an air stream caused by movement of the contact track 2 and carrying particles of material abraded from the brush contact members 1 along the direction of arrows 7 into the collecting container 4.
