Note: Descriptions are shown in the official language in which they were submitted.
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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,
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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
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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
1500
,
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
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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:
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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
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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
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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
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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
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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.
