Field of the invention The invention relates to contactless rotary joints specifically for transfer of high levels of electrical power, also called rotating power transformers. Such contactless rotary joints may be used in CT scanners.

Description of the related art A contactless rotary joint comprising an inductive power coupler is disclosed in the US patent US 7,197,113 Bl. Such a rotary joint is able to transfer power of more than hundred kilowatts from a stationary to a rotating part. Such rotary joints have heavy iron or ferrite cores for guiding the magnetic fields. For example in CT scanners a free bore diameter of more than one meter is required. Ac- cordingly the inner diameter of such a rotary joint may be more than 1 meter requiring large and massive mechanical support structures.

The European patent publication EP 1 481 407 Bl discloses a rotating transformer with a winding form made of a plurality of shaped parts held within a U - shaped ring. Summary of the invention

The problem to be solved by the invention is to improve rotating power transformers by simplifying the mechanical design, increasing robustness, the ability to withstand large centrifugal forces and reliability while decreasing weight. Solutions of the problem are described in the independent claims. The dependent claims relate to further improvements of the invention.

The rotating power transformer has a stationary and a rotating part. Herein the basic structure and function of such parts are shown. Generally it is preferred, when the rotating transformer is symmetrical, having basically identical statio- nary and rotating parts. Of course these parts may differ to meet specific needs of the stationary or rotating parts like in the means for fixation to a machine. At least one of the stationary and rotating parts, preferably both are based on a body which preferably is ring shaped. It may have the shape of a disk or a drum. The main function of the body is to give a stable support to the electric and mag- netic components of the rotating power transformer. The body may be further supported by parts of a machine, like a CT scanner, into which the power transformer is integrated. The body may be made of metal, like aluminum or of plastic material which preferably is further reinforced. It is preferred, to make the body from electrically isolating and non-magnetic material. The body preferably has circular shape. It may also have different shapes adapted to the machine.

According to a first embodiment a plurality of transformer segments of metal or a plastic material are provided. Each segment has at least one rectangular shaped soft magnetic cores comprising ferrite or iron materials. Preferably the soft magnetic cores are standard ferrite cores used for power transformers hav- ing a rectangular cross-section. The cores may be E- or U- cores. E- cores are preferred, as they provide a better magnetic coupling and lower magnetic stray field. Each segment provides further means for holding at least one turn of at least one winding. Preferably the transformer segments have means for holding the soft magnetic cores at predetermined positions. These transformer segments allow for simple assembly of the rotating transformer. First the soft magnetic cores may be inserted into the transformer segments. Optionally the position of the soft magnetic cores may be adjusted within the transformer segments. Then the transformer segments may be either attached to a body or a plurality of transformer segments are connected together to form the body. For the latter case the transformer segments must have some minimum stability which is required for the body. In the following step the windings may be inserted into the transformer segments. After assembly of the winding the transformer segment may be casted to increase mechanical stability and electrical isolation. The transformer may comprise one or several windings each comprising one or several turns. In a preferred embodiment a cover is provided, holding the windings in place. For terminating the windings and specifically for deflecting the direction of the windings out of the magnetic cores a termination segment may be provided. It is preferred, if the soft magnetic cores are secured by glue or epoxy or a similar material within the segments. It is further preferred, if the segments hold at least two sets of soft magnetic cores and windings for dual power transmission, e.g. simultaneous transmission at two power channels. Even a higher number of channels may be realized. According to further modification of this embodiment the transformer segments comprise at least two parts. The first part holds the soft magnetic cores, while the second part holds the windings. Both parts are assembled together to obtain the transformer segment.

In another embodiment the body has a circular groove for holding the magnetic and electrical components of the transformer. Within the groove there are soft magnetic cores having a rectangular shape comprising ferrite or iron materials. Preferably the soft magnetic cores are standard ferrite cores used for power transformers having a rectangular cross-section. The cores may be E- or U- cores. E- cores are preferred, as they provide a better magnetic coupling and lower magnetic stray field. To adapt the rectangular soft magnetic cores to the circular shape of the groove, wedge-shaped spacers are provided. Between every two soft magnetic cores preferably one spacer is inserted. In this embodiment the segments may comprise one soft magnetic core and a spacer. The spacers may also be formed or machined out of the material of the body.

At least one winding is provided in or on the soft magnetic cores, generating magnetic fields for coupling between stationary and rotating parts. Generally a winding may comprise of a plurality of wires, preferably litz wires. The winding is generally arranged within the circular groove and surrounded by the soft mag- netic cores.

For terminating and electrically connecting the at least one winding, a termination module is provided. This termination module may provide electrical contacts to the windings or to the individual wires of the windings. It may furthermore deflect the windings or the wires thereof from their first direction parallel to the circular groove to an external connector. The termination module may also have means for interconnecting windings.

In general it is preferred, if the winding does not fill the whole space within the soft magnetic core. The windings shall be kept distant from the outer surfaces of the bars as magnetic stray fields which preferably occur in air gaps between the soft magnetic cores might penetrate the windings and cause losses therein.

The soft magnetic cores may have at least one hole or groove, preferably under the center bar to fix the soft magnetic cores to the body. This hole or groove may be used to insert a screw or bolt from below or a bar at the body.

It is further preferred, when at least one of the spaces between a soft magnetic core, neighboured soft magnetic cores, spacers, windings and the circular grove of the body are casted. This will improve mechanical stability and electrical isolation significantly.

A preferred method of manufacturing a rotating transformer comprises the steps of providing a body with a circular groove, inserting soft magnetic cores with a rectangular cross-section and wedge shaped spacers between the soft magnetic cores into the groove, and casting or glueing of the soft magnetic cores and spacers into the groove of the body. Tools may be provided to hold the magnetic cores in predetermined positions until curing has finished. Such tools may be rings which may have further indentations or protrusions for fixing the soft mag- netic cores. The tools may also have the inverted shape of the soft magnetic cores fitting therein. Preferably the tools are designed to interact with the center bar of an E-shaped core as this usually has the smallest mechanical tolerances. Furthermore the winding is inserted before or after the step of casting or glueing. In a final step the surface, preferably the surface of the soft magnetic cores may be machined to maintain a planar surface.

Another preferred method of manufacturing a rotating transformer comprises the steps of providing a casting mold, inserting soft magnetic cores with a rectangular cross-section and wedge shaped spacers between the soft magnetic cores into the groove, and casting the soft magnetic cores and spacers. Further- more the winding is inserted before or after the step of casting or glueing. In a final step the surface, preferably the surface of the soft magnetic cores may be machined to maintain a planar surface. This mold may then be inserted into a groove of a body or fixed to the surface of a body.

Description of Drawings In the following the invention will be described by way of example, without limitation of the general inventive concept, on examples of embodiment with reference to the drawings.

Figure 1 shows a part of two parts of the rotating transformer. Figure 2 shows a section of the transformer in detail. Figure 3 shows a first sectional view through a soft magnetic core. Figure 4 shows a second sectional view.

Figure 5 shows a preferred embodiment of the transformer segment. Figure 6 shows a preferred embodiment of a segment cover.

Figure 7 shows a rotating transformer in general.

Figure 8 shows a general part of two parts of the transformer.

Figure 9 shows the termination module.

Figure 10 shows a sectional view of a transformer part. Figure 11 shows a further spacer.

Figure 12 shows a spacer with fins for holding soft magnetic corer.

Figure 13 shows a different embodiment of a spacer.

Figure 14 shows a modified soft magnetic core.

Figure 15 shows a modified soft magnetic core with a groove. Figure 16 shows a soft magnetic core with a clamp. Figure 17 shows a soft magnetic core with a clamp in a side view.

Figure 18 shows windings held by clamps.

Figure 19 shows the usable space for windings.

Figure 20 shows the usable space for windings in detail.

In figure 1 a preferred embodiment of the invention is shown. It shows one of the two parts of the transformer. In general a rotating transformer has two similar parts 100, one on the stationary side and the other on the rotating side. For simplicity only one of these parts is described in detail. A plurality of transformer segments 150a ... 150n are provided. These transformer segments may comprise of metal or plastic material. Due to its isolation characteristics a plastic material, preferably a fiber reinforced plastic material is preferred.

In figure 2 a section of the rotating transformer is shown in detail. Transformer segment 150a holds five soft magnetic cores 160a ... 160e. Windings are located within the soft magnetic cores. The soft magnetic cores may be standard ferrite cores used for power transformers having a rectangular cross-section. The cores may be E- or U- cores. There may also be two U- cores combined to one E-core.

In figure 3 a sectional view according to line A - A of figure 2 through a soft magnetic core is shown. The soft magnetic core 160 is held within transformer seg- ment 150. Turns 141 and 142 of a first winding and turns 143 and 144 of the second winding are located within the soft magnetic core. A cover 170 holds the windings in place within the soft magnetic core.

In figure 4 another sectional view according to line B - B through the body of transformer segment 150 is shown. Here Turns 141 and 142 of a first winding and turns 143 and 144 of the second winding are located within and held by the body of transformer segment 150. Each transformer segment has a bar 151 similar to the center bar of a flat E-shaped ferrite core.

In figure 5 a preferred embodiment of a transformer segment is shown. For clarity only the mechanical support structure, this transformer segment body 150 without soft magnetic cores is shown. This transformer segment is a dual transformer segment for the dual power transformer holding E- shaped flat ferrite cores with a rectangular cross-section. The soft magnetic cores of the first power transformer are located at an inner circle and held within first main openings 152. The soft magnetic cores of the second power transformer are located at an output circle and are held within second main openings 153. Preferably there are small bars 151 for separating the windings. There are further openings 154, 155 for the side bars of the ferrite cores. Furthermore in this embodiment elastic elements 156, 157 preferably made of rubber are provided to hold the ferrite cores in place. Due to the friction caused by the elastic elements the ferrite cores are held within the transformer segment and cannot for all out during assembly. Furthermore they allow the ferrite cores small movements which may be caused by magnetic fields align themselves with opposing ferrite cores. This allows simple alignment during manufacturing. After the segments have been assembled current may be fed through the magnetic cores causing them to align with op- posing cores. Alignment may further be supported by rotation of two transformer parts against each other. Then they may be fixed to the position by means of glue or epoxy or a similar material.

In figure 6 an embodiment of a cover 170 is shown. This cover is fixed on the top of the transformer segment as shown in the previous figure. It has first openings 172 for first soft magnetic cores and second openings 173 for second magnetic cores. There are bars 171 preferably located between the soft magnetic cores for holding the windings in place. Screw holes 178 are provided for fixing the cover 170 to the transformer segment body 150 by means of screws. In figure 7 a rotating transformer is shown in general. It has a first transformer part 100a on the stationary side and a second transformer part 100b on the rotating side, rotating around rotation axis 103. Both transformer parts may be very similar or identical. Each transformer part has a body 101a, 101b and soft magnetic cores 110 with windings 141, 143 therein. Coupling between rotating and stationary side is achieved by coupling of magnetic fields of the windings.

In figure 8 another embodiment according to the invention is shown. It shows one of the two parts of the transformer. Generally the transformer uses two similar parts 100. The transformer part has a body 101 holding a plurality of soft magnetic cores 110a ... 110η. There are wedge shaped spacers 111a ... lllo, between the individual magnetic cores. A termination module 112 is provided for terminating the windings.

In figure 9 the termination module 112 and the section of the power transformer surrounding it is shown. The termination module preferably has a similar rectangular shape as the soft magnetic cores 110a ... 110η. There may be also wedge shaped spacers llln and lllo between the termination module and the neighboring soft magnetic cores 110a and 110η. In an alternative embodiment the termination module may have a shape combining the neighboring wedges llln and lllo into one piece. In this embodiment the termination module has a terminating contact 124, preferably fixed by screw 125, to terminate and connect a second end 121 of a first winding and a second end 123 of a second winding. Furthermore the termination module is provided for deviating the first end 120 of the first winding and the first end 122 of the second winding from that standard into a direction through the body 101 to the bottom of the body. The termination module increases electrical isolation and further limits the bending radii of the windings or the wires. In figure 10 a sectional view of a transformer part is shown. The body 101 has a groove 102 holding a soft magnetic cores and spacers 111. This sectional view is made through a soft magnetic core 110. The soft magnetic core has a base 130, a center bar 131 and a first and a second sidebar 132 and 133. Between the first sidebar 132 and the center bar 131 is first winding 134, comprising of individual turns 141 and 142. While second winding 135 is between center bar 131 and second sidebar 133 comprising of individual turns 143 and 144.

In figure 11 a cross-section of a different spacer 111 is shown. In this embodiment the spacer 111 encloses the individual turns of the windings to keep them in place. For this purpose a locking bar is provided above the windings. This bar may be removed and for easy insertion of the windings during assembly. Furthermore protrusions 136 and 137 are shown to improve fixing of the spacer within body 101, preferably by holes provided within the body. Although it is preferred, it is not necessary to provide protrusions or other means for improve fixing, when the spacer is made to enclose the windings.

In figure 12 a further modification of a spacer 111 is shown in top view. This spacer has fins 138a ... 138d to hold neighboring soft magnetic cores at their places. In general a spacer may have means for holding neighboring soft magnetic cores into a predetermined position relative to the spacer. In figure 13 a different embodiment of the spacer is shown. It has an extended base at corners 139a and 139b which may be used to hold the spacer within an undercut section of the grove 102. Preferably the soft magnetic core is glued or cemented into the groove.

In figure 14 a modified soft magnetic core is shown. The magnetic core has a hole 140 for fixing it by a screw or bolt to the base 130, which preferably comprises a flexible or at least vibration absorbing material. A spacer 111 may also have such a hole for fixing it by a screw or bolt to the base 130. In figure 15 a modified soft magnetic core is shown. The magnetic core has a groove 145 for fixing it by a screw or bolt to the base 130, which preferably comprises a flexible or at least vibration absorbing material. The groove may be aligned by a bar or protrusion of the base. A spacer 111 may also have such a groove for fixing it by a screw or bolt to the base 130.

In figure 16 a soft magnetic core is shown in a side view. It is held by a clamp 148 which preferably encircles its center bar to a base plate 149. The base plate may be a plate attached to body 101. Alternatively the clamp may be fixed to base 101. The clamp may have a latch. The soft magnetic core shown herein is a typi- cal E-shaped core with rectangular cross-section as it may be used herein.

In figure 17 the soft magnetic core of the previous figure is shown in a top view.

Figure 18 shows the individual turns 141, 143 of windings held by clamps 147 to a base plate 149. The base plate may be a plate attached to body 101. Alternatively the clamp may be fixed to base 101. The clamp may have a latch. Further- more the clamp may be glued, cemented or pressed into the base plate or body. The clamp may also be crafted together with the winding. Furthermore it is preferred, if the clamp does not have sharp edges to prevent damage of the insulation of the windings.

Figure 19 shows the usable space for windings. A first soft magnetic core 110a which may be of the stationary part is opposed a second soft magnetic core 110b which may be of the rotating part. Due to mechanical tolerances the is an airgap 113 between the soft magnetic cores. Around the airgap there is a magnetic stray field which may penetrate into the windings. Such that magnetic field within the winding may cause additional losses decreasing overall efficiency and pos- sibly causing local overheating of the windings. To prevent penetrating of magnetic stray fields into the windings there should be some distance between the windings and the air gaps. Preferably the space available for windings 114a and 114b is chamfered to keep a minimum distance from the magnetic stray field.

Figure 20 shows the usable space for windings in more detail. It is preferred, when the winding 114a is distant at a radius 115 from the edge 116 of any bar of soft magnetic core 110a. Preferably this radius is greater or equal than the air gap 113.lt is obvious that this applies to all other soft magnetic cores.

List of reference numerals

100 transformer part

101 body

102 circular groove

103 rotational axis

110 soft magnetic core

111 spacer

112 termination module

113 air gap

114 space available for winding

115 radius

116 edge of bar

120 first end the first winding

121 second end of first winding

122 first end of the second winding

123 second end of second winding

124 terminating contact

125 screw

130 base

131 center bar

132 first sidebar

133 second sidebar

134 first winding

135 second winding

136, 137 protrusions

138 fins of spacer

139 cores of base 140 hole

141-144 turns of windings

145 groove

147, 148 clamps

149 base plate

150 transformer segment body

151 winding separation bar

152 first opening for first soft magnetic cores

153 second opening for second soft magnetic cores 154, 155 opening for sidebar

156, 157 elastic elements

160 soft magnetic core

170 cover

172 first opening

173 second opening