CA2759587C

CA2759587C - Slip ring unit

Info

Publication number: CA2759587C
Application number: CA2759587A
Authority: CA
Inventors: Ludwig Angerpointner
Original assignee: LTN Servotechnik GmbH
Current assignee: LTN Servotechnik GmbH
Priority date: 2010-11-29
Filing date: 2011-11-22
Publication date: 2016-02-23
Anticipated expiration: 2031-11-22
Also published as: EP2458693A3; DE102010052645A1; EP2458693A2; CA2759587A1; EP2458693B1

Abstract

The invention relates to a slip ring unit comprising a first and a second component group (1, 2), wherein the first component group (1) comprises a holder (1.1) on which a brush element (1.2, 1.2') is secured at two bearing positions (Y, Z). The second component group (2) has a closed peripheral slip ring (2.2). The holder (1.1) is arranged at an axial distance (a) from the slip ring (2.2), and the slip ring (2.2) is contacted by the brush element (1.2; 1.2') at a contact point (X). The slip ring unit is configured so that the contact point (X) is arranged between the bearing positions (Y, Z) along the course of the brush element (1.2; 1.2') and the contact point (X) is arranged at a radial offset (d) from a line (Y, Z) connecting the bearing positions (yz).

Description

Slip Ring Unit The invention relates to a slip ring unit for transmitting electric currents between two component groups that are rotatable in relation to one another as described herein.
Slip ring units usually consist of two component groups, namely a stator and a rotor.
The stator usually comprises brush elements but the rotor usually has a plurality of concentric slip rings. In operation, the brush elements are in sliding contact with the rotating slip rings. The design in which the component groups that are rotatable in relation to one another are arranged at an axial distance from one another is often referred to a disk slip ring design. Such slip ring units are used in many technical fields for transmitting electric signals or electric power from a stationary unit to a rotating electric unit.
For example, corresponding slip ring units are used in robots, where control signals and electric drive power must be transmitted between modules rotating in relation to one another.
German Utility Model DE 94 01 715 describes a slip ring unit for transmitting signals and electric power. In this context, pairs of cantilevered spring contacts are used,

2 arranged tangentially opposite one another and establishing a sliding contact with contact rings.
The object of the present invention is to create a slip ring unit which operates reliably, takes up a comparatively small amount of space and is simple to manufacture.
This object is achieved according to the invention by the features as described herein.
Accordingly, the slip ring unit comprises a first component and a second component, which are arranged rotatably about an axis in relation to one another, such that the slip ring unit is suitable for transmitting electric currents or signals between the two component groups over several revolutions. The first component group comprises a holder on which at least one brush element is secured at two bearing positions. The second component group has at least one closed peripheral slip ring. The holder is arranged at an axial distance from the slip ring, and the slip ring is in sliding contact with the brush element at a contact point. The slip ring unit is configured, so that the contact point is arranged between the bearing positions along the course of the brush element and the contact point is radially offset from a line which connects the bearing positions.
Bearing positions are understood to be the locations where the brush element is supported on the holder in the sense of a bearing support according to the principles of industrial mechanics. Accordingly, reactive forces and/or reactive torques in response to the forces applied to the brush element are supported on the bearing positions. The bearing positions may be reduced to a geometric point for the sake of idealization. If the contact location is not a point, then the midpoint or the center of the area of the contact location may be used for these considerations.
Electric currents are understood below to be currents which are necessary for transmission of electric power but this also includes currents which are in the form of signals and serve only to transfer information. The brush elements of the slip ring unit

- 3 -according to the invention are advantageously suitable and are intended for signal transmission.
The slip ring unit advantageously has several brush elements each with the identical geometry.
The slip ring unit may be configured so that the fixation of or the means for securing the brush element at the bearing positions is designed so that a reactive torque about the line connecting the bearing positions can be transmitted through this fixation. A
corresponding bearing at this bearing position may be understood to be a binary bearing, in particular when the fixation at the bearing positions is designed so that reactive forces oriented radially and tangentially through them can be transferred to the holder.
In addition, the fixation at one of the bearing positions may be designed so that the brush element is rigidly secured at the respective bearing position in relation to the holder. In this context, it is possible to speak of rigid clamping of the brush element on the holder at the respective bearing position, i.e., a ternary bearing. The slip ring unit may also be designed so that the fixation at both bearing positions is designed to be rigid.
In another embodiment of the invention, the fixation in at least one of the bearing positions may be designed so that the brush element is secured at the respective bearing position so that it is axially displaceable in relation to the holder.
The angle between a connecting line connecting the contact point to the one bearing position and a connecting line which connects the contact point to the other bearing position advantageously amounts to less than 1800, in particular less than , advantageously less than 1000 .
It is advantageous if at least one of the bearing positions comes to lie closer to the axis than the contact point, based on a brush element, i.e., with regard to one and the same

- 4 -brush element within the slip ring unit. In addition, the slip ring unit may be constructed so that it has multiple brush elements, in which case then the contact points of the brush elements are arranged along a line, in particular a line that is oriented radially and/or the bearing positions of the brush elements are arranged along a line, in particular one that is oriented tangentially.
Furthermore, the brush element may have a round cross section. In particular, the brush element may be manufactured from round material, such as a wire, so that the brush element can also be referred to as a wire strap. If such a brush element has a cross section deviating from the round cross section only in a locally limited area, it is nevertheless possible to speak of a brush element having a round cross section.
In another embodiment of the invention, in particular for optimizing its spring properties, the brush element may have a taper. The taper then advantageously has a course along a line, such that the line is oriented with a directional component parallel to a line connecting the bearing positions. Accordingly, the bending resistance can thus be reduced in comparison with bending moments introduced into the contact location by axial forces. A corresponding taper may be established, for example, by shaping without cutting, e.g., by pressing and/or by plastic deformation at one location of the brush, so that the material of the brush element is displaced, and the absolute size of the cross-sectional area, which is measured in mm2, for example, is not changed or reduced per se. This is advantageous in particular because the current to be transmitted is limited under some circumstances by the absolute size of the cross-sectional area. The taper also advantageously has a course oriented orthogonally to the axis.
Advantageous embodiments of the invention can be derived from the dependent claims.
Additional details and advantages of the slip ring unit according to the invention are derived from the following description of two exemplary embodiments with reference to the accompanying figures.
They show:

- 5 -Figure 1 a a top view of the slip rings with the respective brush elements of a slip ring unit according to view B-B, Figure lb a side view of the slip ring unit according to view C-C, Figure 1 c a side view of the slip ring unit according to view D-D, Figure 2 a detailed view of a brush element, Figure 3a a detailed view of a brush element according to a second exemplary embodiment, Figure 3b another detailed view of a brush element according to a second exemplary embodiment.
According to Figures 1 a, 1 b, 1 c, the slip ring unit according to the invention comprises a first component group 1, which may serve as a stator, for example, and a second component group 2, which may function as a rotor, for example. The slip ring unit serves to transmit electric currents between the first component group 1 and the second component group 2, wherein the component groups 1, 2 are arranged to be rotatable about an axis A in relation to one another. Electric currents are understood to be currents which are necessary for transmission of electric power but also currents in the form of signals which serve only to transmit information.
The second component group 2 comprises a ring disk 2.1, which in the present example is embodied as a circuit board having a circular outer contour. Multiple slip rings 2.2, 2.3, which are arranged concentrically with the axis A and are designed to run in a closed circle over 3600, are applied to one side of the ring disk 2.1, so that a transmission of electric currents can be achieved with the slip ring unit with an unlimited angle of rotation, i.e., over any number of revolutions. In order to achieve a long lifetime, the slip rings 2.2, 2.3 are each made of a noble metal layer, which is applied to an electrically conductive intermediate layer or directly to the circuit board

- 6 -material of the ring disk 2.1. The slip rings 2.2, which are positioned further on the outside radially in Figures 1 a-1 c and have a smaller ring width and/or form a narrower track, serve to transmit electric signals, i.e., to transmit currents at a much lower amperage. However, the slip rings 2.3 with a larger ring width are intended for transmission of higher amperages between 1 A and 16 A, for example. The slip rings 2.2 having the smaller ring width in particular are designed so that they have an electric resistance of less than 10 11/m, in particular less than 1 fl/mdue to the choice of materials and the dimensions of the cross section.
For the sake of simplicity, the figures do not show the electric lines which are provided on the side of the ring disk 2.1 opposite the slip rings 2.2, 2.3 and are electrically connected to the slip rings 2.2, 2.3 by means of through-contacts.
The first component group 1 has a holder 1.1, which is also designed as a circuit board.
The holder 1.1 is arranged at an axial distance "a" from the slip rings 2.2, 2.3. Such slip ring units are often referred to as disk slip rings or pancake slip rings.
Both the holder 1.1 and the ring disk 2.1 are attached to machine parts that can rotate relative to one another, their relative arrangement defining the distance "a". Such machine parts may of course assume varying directions of rotation during operation and may vibrate or cause impacts in the slip ring unit. The axial distance "a" may therefore be subject to changes over time due to the vibrations or impacts, although they are only minor.
Brush elements 1.2, 1.3, which are to be assigned to the first component group 1 and are in elastic contact with the slip rings 2.2, 2.3, are attached to the holder 1.1. The four brush elements 1.3 on the inside radially are made of a flat material with the help of a punch and bending operation and serve to transmit electric power.
However, the other brush elements 1.2 are made of a wire that is bent, and in the exemplary embodiment presented here, it has a copper core and is coated with noble metal, such that the coating is applied selectively only in the area of the contact point X
or over the entire length of the brush element 1.2. These brush elements 1.2 are intended

- 7 -for signal transmission and are each designed to be the same within one slip ring unit, so that they each have an identical geometry.
The ends of the brush elements 1.2 for signal transmission are inserted into boreholes provided in the holder 1.1 for this purpose. These connecting points consequently form bearing positions Y, Z, at each of which a brush element 1.2 is secured on the holder 1.1. According to Figure 2, a solder point 1.11 is also placed at the bearing position Z, so that the respective brush element 1.2 is rigidly secured at the bearing position Z in relation to the holder 1.1 and is secured with respect to all six degrees of freedom. In the exemplary embodiment presented here, no other fastening measure is taken at the other bearing position Y, so that the respective brush element 1.2 there is secured in an axially displaceable manner in relation to the holder 1.1. Due to the rigid connection of the brush element 1.2 at the bearing position Z, and on the other hand due to the curvature connected to the end area of the brush element 1.2, the axial mobility of the brush element 1.2 within the borehole at the bearing position Y in the holder 1.1 is limited.
The brush elements 1.2 are electrically connected to conductors on the side opposite the brush elements 1.2, 1.3 for transmitting electric power. The corresponding cables are not shown in the figures. With respect to the brush element 1.2 for signal transmission, the electric connection to the rear conductor at the bearing position Z is ensured by solder point 1.11 in combination with a through-contact. No electric contacting is provided at bearing position Y. Alternatively, an axially movable electric connection may be provided at the bearing position Y, so that the arrangement is optimized with respect to criteria of electromagnetic compatibility, for example.
From a purely geometric standpoint, as shown in Figure 2, the bearing positions Y, Z
may be connected by a line yz. For example, in the area of bearing positions Y, Z, the midpoints of the round cross section of the brush element 1.2 and/or the midpoints of the boreholes through the holder 1.1 may be used as geometric connecting points. The brush elements are then designed and arranged in the slip ring unit so that the contacting

- 8 -point X is arranged with a radial offset d from the line yz. The offset d is a partial segment of the connection between the contact point X and the axis A.
Accordingly, a plane E may be spanned between the contact point X and the two bearings points Y, Z according to Figure lb, this plane coming to lie in space so that it is intersected by the axis A.
The fixation of the respective brush element 1.2 at both bearing positions Y, Z is designed so that a reactive torque may be transmitted through them about the line Y, Z
connecting the bearing positions Y, Z. This is achieved in particular by the fact that the ends of the brush element 1.2 are inserted with an accurate fit into corresponding axial boreholes in the holder 1.1. Because of this design, the fixation of the respective brush element 1.2 at the bearing positions Y, Z is also equipped so that radially and tangentially oriented reactive forces can be transmitted from the brush element 1.2 to the holder 1.1. Finally, the fixation of the respective brush element 1.2 at the bearing position Z is embodied so that a reactive force can be transmitted in the axial direction through this bearing position.
The brush element 1.2 comes in contact with the respective slip ring 2.2 at a contact point X, which is arranged along the course of the brush element 1.2 between the two bearing positions Y, Z. In other words, starting from the first bearing position Y, the contact point X is reached first, following the course of the brush element 1.2, and then the second bearing position Z is reached.
The connecting line xy connects the contact point X to the bearing position Y, while the connecting line xz connects the contact point X to the other bearing position Z. The brush elements 1.2 are curved, so that in the exemplary embodiment presented here, an angle a of approximately 1150 is enclosed between the geometrically assumed connecting lines xy, xz.
During operation of the slip ring unit, the second component group 2 rotates in relation to the first component group 1. Consequently, there is sliding contact between the brush

- 9 -elements 1.2, 1.3 and the corresponding slip rings 2.2, 2.3. Due to the fact that the brush elements 1.2, which transmit electric signals, are secured on the holder 1.1at the bearing positions Y, Z at both sides of the contact point X, slip-stick effects in particular are suppressed. Accordingly, this ensures that the brush elements 1.2 will contact the respective slip rings 2.2 without interruption, which is extremely important for reliable signal transmission. In addition, due to the design, a temporary lifting of the brush elements 1.2 away from the slip rings 2.2 is effectively prevented, even when there are tremors or vibrations. The radial offset d acts as a lever arm for initiating a bending moment about the connecting line yz, so that an elastic prestress of the brush elements 1.2 can be generated. Consequently, a suitable contact force against the slip rings 2.2 is achieved by means of a comparatively wide axially oriented vibration-induced change in the distance "a" over time. Accordingly, the new slip ring unit operates reliably when exposed to these vibrations. At the same time, the new design allows a very space-saving arrangement. It is possible in particular to achieve the result through this new design that the bearing positions Y, Z of al brush elements 1.2 are a smaller distance from the axis A for signal transmission than the outside diameter of the ring disk 2.1.
Therefore a compact design of the slip ring unit can be achieved.
The second exemplary embodiment according to Figures 3a, 3b differs from the preceding in that the brush element 1.2' has a taper 1.21'. This taper 1.21' was created by a pressing operation in which a pressing tool was applied, so that the taper 1.21' runs along a line yz' which is oriented parallel to the line yz in the installed state of the brush element 1.2'. The course of the taper 1.21' is thus oriented according to the course of the thinnest location within the taper 1.21' of the brush element 1.2'.
The taper 1.21' serves essentially to reduce the bending resistance of the brush element 1.2', which is definitive for operation of the slip ring unit in that the moment of inertia of the area is reduced in the area of the taper 1.21'. At the same time, however, in the exemplary embodiment presented here the absolute cross-sectional area in mm2 has not been reduced so that there are practically no losses with regard to the size of the current that can be transmitted.

Claims

1. A slip ring unit comprising a first and a second component group (1, 2), where the two component groups (1, 2) are arranged rotatably about an axis (A) in relation to one another and the slip ring unit is suitable for transmitting electric currents or signals between the two component groups (1, 2) over several revolutions, wherein - the first component group (1) comprises a holder (1.1) on which a brush element (1.2, 1.2') is secured at two bearing positions (Y, Z) and - the second component group (2) has a closed peripheral slip ring (2.2), wherein the holder (1.1) is arranged at an axial distance (a) from the slip ring (2.2), and the slip ring (2.2) is contacted by the brush element (1.2; 1.2') at a contact point (X), characterized in that the slip ring unit is configured, so that the contact point (X) is arranged between the bearing positions (Y, Z) along the course of the brush element (1.2; 1.2'), and the contact point (X) is arranged at a radial offset (d) from a line (Y, Z) connecting the bearing positions (yz).

2. The slip ring unit according to claim 1, characterized in that the slip ring unit has several brush elements (1.2; 1.2') each having an identical geometry.

3. The slip ring unit according to claim 1 or 2, characterized in that the fixation at the bearing positions (Y, Z) is designed so that by means of this fixation, a reactive torque can be transmitted about the line (yz) connecting the bearing positions (Y, Z).

4. The slip ring unit according to any one of claims 1 to 3, characterized in that the fixation at the bearing positions (Y, Z) is designed so that reactive forces oriented radially and tangentially can be transmitted to the holder (1.1).

5. The slip ring unit according to any one of claims 1 to 4, characterized in that the fixation at the bearing positions (Y, Z) is designed so that the brush element (1.2;
1.2') is rigidly secured at the respective bearing position (Y, Z) in relation to the holder (1.1).

6. The slip ring unit according to any one of claims 1 to 5, characterized in that the fixation at the bearing positions (Y, Z) is designed, so that the brush element (1.2;
1.2') is axially displaceably secured at the respective bearing position (Y, Z) in relation to the holder (1.1).

7. The slip ring unit according to any one of claims 1 to 6, characterized in that an angle (.alpha.) between a connecting line (xy) which connects the contact point (X) to the one bearing position (Y) and a connecting line (xz) which connects the contact point (X) to the other bearing position (Z) amounts to less than 150°.

8. The slip ring unit according to any one of claims 1 to 7, characterized in that based on a brush element (1.2; 1.2'), at least one of the bearing positions (Y, Z) is closer to the axis (A) than the contact point (X).

9. The slip ring unit according to any one of claims 1 to 8, characterized in that the brush element (1.2; 1.2') has a round cross section.

10. The slip ring unit according to any one of claims 1 to 9, characterized in that the brush element (1.2') has a taper (1.21').

11. The slip ring unit according to claim 10, characterized in that the taper (1.21') has a course along a line (yz') such that the line (yz') connects a directional component parallel to the line (yz) which connects the bearing positions (Y, Z).