WO2009147577A1

WO2009147577A1 - Transformer for a computer tomography gantry for transfering contactlessly electrical energy

Info

Publication number: WO2009147577A1
Application number: PCT/IB2009/052221
Authority: WO
Inventors: Christoph Loef; Christian W. Vollertsen
Original assignee: Philips Intellectual Property & Standards Gmbh; Koninklijke Philips Electronics N. V.
Priority date: 2008-06-02
Filing date: 2009-05-27
Publication date: 2009-12-10

Abstract

The invention provides a transformer for a computer tomography gantry (91) for transfering contactlessly electrical energy from a stationary part of the gantry (92) to a rotary part of the gantry (93), wherein the transformer comprises a set of primary windings, a set of secondary windings, wherein the set of primary windings being adapted to be mounted on the stationary part of the gantry (92), wherein the set of secondary windings being adapted to be mounted on the rotary part of the gantry (93), wherein a winding (504, 604) out of the group consisting of the set of primary windings and the set of secondary windings has a rotation of approximately 180 degrees around the center line (503, 606) of the winding (504, 604) or approximately an integer multiple of 180 degrees.

Description

TRANSFORMER FOR A COMPUTER TOMOGRAPHY GANTRY FOR TRANSFERING CONTACTLESSLY ELECTRICAL ENERGY

FIELD OF THE INVENTION

The present invention relates to a transformer for a computer tomography gantry for transfering contactlessly electrical energy from a stationary part of the gantry to a rotary part of the gantry. BACKGROUND OF THE INVENTION

For high power computer tomography applications the electrical power for the X-ray tube must be transferred to the rotating part of the gantry. Actually, this is achieved with the help of mechanical slip-rings. The embodiment with slip-rings can not be used for high power applications and high frequency applications as well as high rotation speeds of the gantry. Therefore, a power transformer with a stationary primary winding and a secondary winding, which is arranged at the rotary part of the gantry, will be used for energy transfer from the stationary part of the gantry to the rotary part of the gantry. Usually, the power transformer has a circular outline, wherein the inner diameter is determined by the inner bore of the computer tomography system. In order to achieve a compact arrangement of the transformer high frequency of the power transmission is used. In order to achieve a high frequency operation efficiently a topology with a resonant circuit is used. When a power transformer is used to transmit the electrical power to the rotating part of a computer tomography gantry, the use of high frequency resonant system is suitable. By using a high frequency resonant system the component size and weight can be reduced. For high frequency operation a wire with several strands can be prefered, which enables to avoid proximity losses. However, due to the magnetic field the current distribution in the single strands of the wire is not equal. Thereore, an application of high frequency concerning the power transmission leads to high proximity losses in the windings. SUMMARY OF THE INVENTION

It would be desireable to provide an improved device, which provides equal currents in the windings in order to avoid high proximity losses.

The invention provides a transformer for a computer tomography gantry for transfering contactlessly electrical energy from a stationary part of the gantry to a rotary part of the gantry, wherein the transformer comprises a set of primary windings, a set of secondary windings, wherein the set of primary windings being adapted to be mounted on the stationary part of the gantry, wherein the set of secondary windings being adapted to be mounted on the rotary part of the gantry, wherein a winding out of the group consisting of the set of primary windings and the set of secondary windings has a rotation of approximately 180 degrees around the center line of the winding or approximately an integer multiple of 180 degrees. The invention provides the solution to the problem of different currents inside different strands. The different current distribution in the winding strands is caused by the external magnetic field. Since the current distribution in the strands will differ, additional losses occur.

The solution will be provided by a rotation of the single strands around the center line of the winding, wherein the winding comprises a bundle of strands. It has also to be mentioned that usually the strands are isolated with respect to neighboured strands.

The above-mentioned term winding can also be interpreted by a single strand. Therefore, it is possible, that the winding comprises only one single strand. Further embodiments are incorporated in the dependent claims.

According to the present invention a transformer is provided, wherein the winding comprises at least two strands.

In this embodiment the single strands are twisted around their common center line. According to an exemplary embodiment a transformer is provided, wherein the rotation is arranged at or adjacent to a turning-point of the winding. This embodiment is advantageously because the rotated strands/windings need an increased space, which can be offered in the neigbourhood of the turning point of the winding.

According to the present invention a transformer is provided, wherein the rotation is approximately 180 degrees around the center line of the winding or approximately an odd multiple of 180 degrees.

In case of a rotation at or adjacent to the turning point of the winding, it is necessary to rotate the winding not 360 degrees e.g. . A rotation of 360 degrees would lead to different magnetic relevant areas of the single strands. According to an exemplary embodiment a transformer is provided, wherein the rotation is not arranged at or adjacent to a turning-point of the winding.

According to an exemplary embodiment a transformer is provided, wherein the rotation is approximately 360 degrees around the center line of the winding or approximately a multiple of 360 degrees. In case of a rotation of the strands along the elongated part of the gantry it is necessary that the rotation is 360 degrees or a multiple thereof. Only in this case the magnetic relevant areas of the single strands can be regarded as approximately equal.

According to another exemplary embodiment a transformer is provided,wherein the power transformer comprises a first core, wherein the set of primary windings is adapted to induce a magnetic flux into the first core,a second core, wherein the set of secondary windings is adapted to induce a magnetic flux into the second core.

According to another exemplary embodiment a transformer is provided, wherein the first core is E-shaped, wherein the second core is E-shaped. It may be seen as a gist of the present invention to provide an arrangement of windings/ strands of windings of a power transformer, wherein the currents of the different windings/strands of windings are equal. This aim is achieved by twisting the single windings/ strands of windings around the centerline of the winding.

It should be noted that the above features may also be combined. The combination of the above features may also lead to synergetic effects, even if not explicitly described in detail. These and other aspects of the present invention will become apparent from and elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present invention will be described in the following with reference to the following drawings.

Fig. 1 shows a part of a power transformer,

Fig. 2 shows a winding of a power transformer, Fig. 3 shows a winding of a power transformer,

Fig. 4 shows magnetic relevant areas of two strands,

Fig. 5 shows a part of a winding,

Fig. 6 shows a part of a winding, Fig. 7 shows a computer tomography gantry.

DETAILED DESCRIPTION OF EMBODIMENTS

The system described herein focuses on a contactless energy transmission system, which provides energy transfer to a rotating dish. i.e. to the rotating part of a computer tomography gantry.

Typically the use of E-cores is appreciated for power transformers, in order to avoid external leakage flux. Thus, a long winding path clockwise and counterclockwise return the circumflex will cause high values of inductances. The operating with high frequencies requires less resulting leakage inductance of the power transformer in order to transmit the required power. When high power transmissions are required, a plurality of primary windings at the contactless power transformer and inverter blocks can be used. In this case, each of the inverter modules generates an equal fraction of the total required output power.

With respect to manufacturing tolerances and temperature influences the value of the components will change and thus the resulting flux of each branch will change the resonance character and thus different power levels will be transferred in each the branches.

Fig. 1 shows a part of the power transformer 105 with a winding 103 and a further winding 104. Further, there is depicted a part of the core 102. It is shown a cross-section 106 of the winding 103, whereas the cross-section 106 shows different strands 101. Exemplarily, the cross-section 106 depicts 16 strands.

Due to the fact that the system is operated with high frequencies strands 101 (litz wires) are used to delimit proximity losses in the windings 103, 104. The windings 103, 104 consist of packages of strands 101 (litzwires, e.g. 100x0.01, other numbers of parallel strands of litzwire and diameter are thinkable and also depend of the frequency applied to the transformer). The cross-section 106 is of a square outline, however other types of cross-sections (especially rectangular, but also round) are applicable.

Fig. 2 shows a winding 203 of the power transformer. Further, it is depicted four single strands 201 as a part of the winding 203. There is no twist along the strands. In one schematically diagram it is shown a cross-section 202 and several strands 201. Furthermore, there is shown the center line 205 of the winding 203.

Fig. 3 shows a winding 305 of the power transformer with a schematically diagram of two strands 301, 302 of this winding 305. There is also depicted the cross-section 303 of the winding 305.

It is shown that the strand 301 has a longer path with respect to the strand 302 of the same winding 305. Thus, the area covered by the strand 301 is greater than the area covered by the strand 302. Therefore, the products dAxB are different. Thus, the induced voltage from the magnetic field is different, which results in different currents in the strand 301 and the strand 302 of the winding 305.

Fig. 4 shows a winding 404 of a power transformer 405. Further, the areas which are included by the two different strands 406, 407 are shown. The strand 406 includes the area 402. The second strand 407 includes the area 401. There is also depicted the cross-section 403 of the winding 404. Fig. 5 shows a winding 504 of a power transformer 505. There is also depicted a schematically diagram of the winding 504 with a cross-section 501. It is shown a strand 502, which has a rotation of approximately 360° around the center line 503. The strand 506 has also a rotation of approximately 360 degrees around the center line of the winding 504.

The part of strand 502 has a rotation of 360 degrees around the center line 503 along one part of the winding 504. The part of strand 506 also has a rotation of 360 degrees around the center line of the winding. The result thereof is that the currents in the different strands are identical. The same effect can be achieved, if the part of strands 502, 506 are rotated a multiple of 360 degrees around the centerline 503 of the winding 504. The description above focused on only two single strands of the winding.

For achieving the goal it is of course necessary to process all strands of the winding 504 as explained with the help of the strands 502 and 506.

Fig. 6 shows a further embodiment of the invention 605. It is depicted two strands 601, 602, whereas the strands 601 and 602 have a rotation around the center line 606 of the winding of about 180° at the turning point of the winding 604.

The strands 601 and 602 are twisted at the turning point of the winding 604. As a result thereof the magnetic relevant areas, which are comprised by the strands 601 and 602 are identical. This embodiment of the invention is advantageously because the twist of the strands 601, 602 requires an increased space. This required space can be offered at the turning point of the winding 604. It is more difficult to offer the increased required space at other positions of the winding 604.

Another embodiment of the invention is realized by a change of the vertical position of the strands 601, 602 at the turning point of the winding 604. The above was described with the help of two single strands. It is obvious that all strands have to be treated as above-mentioned to achieve a very good result.

A major advantage of the present invention is the fact that no additional component is necessary to achieve a current symmetry in the strands 502, 506, 601, 602. The inventive arrangement of the strands 502, 506, 601, 602 can be applied at the primary and/or the secondary winding of the power transformer for a computer tomography gantry. Fig. 7 shows an exemplary embodiment of a computer tomography gantry 91 arrangement. The gantry 91 comprises a stationary part 92 connected to a high frequency power source 98 and a rotary part 93 adapted to rotate relative to the stationary part 92. An X-ray source 94 and an X-ray detector 95 are attached to the rotary part 93 at opposing locations such as to be rotatable around a patient positioned on a table 97. The X-ray detector 95 and the X-ray source 94 are connected to a control and analysing unit 99 adapted to control the X-ray detector 95 and the X-ray source and to evaluate the detection results of the X-ray detector 95.

It should be noted that the term 'comprising' does not exclude other elements or steps and the 'a' or 'an' does not exclude a plurality. Also elements described in association with the different embodiments may be combined.

It should be noted that the reference signs in the claims shall not be construed as limiting the scope of the claims.

LIST OF REFERENCE SIGNS

91 Computer tomography gantry,

92 Stationary part of the gantry,

93 Rotary part of the gantry, 94 X-ray source,

95 X-ray detector,

97 Table,

98 High frequency power source,

99 Control and analysing unit, 101 Strand

102 Core

103 Winding

104 Winding

105 Part of a power transformer 106 Cross-section of a winding

201 Strand

202 Cross-section

203 Winding

204 Part of a power transformer 301 Strand

302 Strand

303 Cross-section

304 Part of a power transformer 401 Area 402 Area

403 Cross-section

404 Winding

405 Part of a power transformer 501 Cross-section 502 Strand

503 Center line 504 Winding

505 Part of a power transformer

601 Strand

602 Strand

603 Cross-section

604 Winding

605 Part of a power transformer

606 Center line

607 elongated part of the winding

Claims

CLAIMS:

1. A transformer for a computer tomography gantry (91) for transfering contactlessly electrical energy from a stationary part of the gantry (92) to a rotary part of the gantry (93), wherein the transformer comprises

- a set of primary windings,

- a set of secondary windings, wherein the set of primary windings being adapted to be mounted on the stationary part of the gantry (92), wherein the set of secondary windings being adapted to be mounted on the rotary part of the gantry (93), wherein

- a winding (504, 604) out of the group consisting of the set of primary windings and the set of secondary windings has a rotation of approximately 180 degrees around the center line (503, 606) of the winding (504, 604) or approximately an integer multiple of 180 degrees.

2. The transformer according to claim 1, wherein the winding (504, 604) comprises at least two strands (601, 602).

3. The transformer according to one of the claims 1 or 2, wherein the rotation is arranged at or adjacent to a turning-point of the winding (604).

4. The transformer according to claim 3, wherein the rotation is approximately 180 degrees around the center line (503, 606) of the winding (504, 604) or approximately an odd multiple of 180 degrees.

5. The transformer according to one of the claims 1 or 2, wherein the rotation is not arranged at or adjacent to a turning-point of the winding (504).

6. The transformer according to claim 5, wherein the rotation is approximately 360 degrees around the center line (503) of the winding (504) or approximately a multiple of 360 degrees.

7. The transformer according to one of the preceding claims, wherein the power transformer comprises

- a first core, wherein the set of primary windings is adapted to induce a magnetic flux into the first core,

- a second core, wherein the set of secondary windings is adapted to induce a magnetic flux into the second core.

8. The transformer according to claim 7, wherein the first core is E-shaped, wherein the second core is E-shaped.