Positioning apparatus for an electron beam

Abstract

A positioning apparatus is provided for an electron beam of an electron tube, the apparatus including a first DC voltage circuit having a high potential difference and a second DC voltage circuit having a smaller potential difference, having in each case a first potential level and a second potential level, and a deflection module, which has two inputs and at least one deflection coil, wherein the at least one deflection coil is connected between the two inputs of the deflection module.

Claims

1. A positioning apparatus for an electron beam of an electron tube, the positioning apparatus comprising: a first DC voltage circuit comprising a high potential difference, a first potential level, and a second potential level; a second DC voltage circuit comprising a smaller potential difference, a first potential level, and a second potential level, wherein a ratio of a voltage drop across the second DC voltage circuit contributes to a voltage drop across the first DC voltage circuit by up to 1:4; and a deflection module comprising two inputs and at least one deflection coil, the at least one deflection coil connected between the two inputs, wherein the first potential level of the first DC voltage circuit is connected switchably to one of the two inputs of the deflection module to provide a first switching path, and the second potential level of the first DC voltage circuit is connected to a second of the two inputs of the deflection module, and wherein the first potential level of the second DC voltage circuit is connected switchably to one of the two inputs of the deflection module to provide a second switching path, which is switchable separately from the first switching path, and the second potential level of the second DC voltage circuit is connected to a second of the two inputs of the deflection module.

2. The positioning apparatus as claimed in claim 1, wherein the deflection module comprises a full bridge comprising a first input terminal, a second input terminal, a first output terminal, and a second output terminal, wherein both the first input terminal and the second input terminal are connected to one of the two inputs of the deflection module, and wherein the at least one deflection coil is connected between the first output terminal and the second output terminal.

3. The positioning apparatus as claimed in claim 2, wherein the first switching path and the second switching path end are at a same input of the deflection module.

4. The positioning apparatus as claimed in claim 3, wherein the first switching path comprises a first semiconductor switch, and the second switching path comprises a second semiconductor switch.

5. The positioning apparatus as claimed in claim 4, wherein a first diode is connected back-to-back in parallel with the first switch, a second diode is connected in parallel with the second switch, or the first diode is connected back-to-back in parallel with the first switch and the second diode is connected in parallel with the second switch.

6. The positioning apparatus as claimed in claim 5, wherein a coil and a diode connected back-to-back in parallel are connected in the first switching path.

7. The positioning apparatus as claimed in claim 1, wherein the first switching path and the second switching path end are at a same input of the deflection module.

8. The positioning apparatus as claimed in claim 1, wherein the first switching path comprises a first semiconductor switch, and the second switching path comprises a second semiconductor switch.

9. The positioning apparatus as claimed in claim 8, wherein a first diode is connected back-to-back in parallel with the first switch, a second diode is connected in parallel with the second switch, or the first diode is connected back-to-back in parallel with the first switch and the second diode is connected in parallel with the second switch.

10. The positioning apparatus as claimed in claim 1, wherein a coil and a diode connected back-to-back in parallel are connected in the first switching path.

11. The positioning apparatus as claimed in claim 1, wherein a current measuring device is connected on an input side, an output side, or the input side and the output side of the at least one deflection coil.

12. A method for actuating, by pulse width modulation, a positioning apparatus for an electron beam in an electron tube, the positioning apparatus comprising (1) a first DC voltage circuit comprising a high potential difference, a first potential level, and a second potential level, (2) a second DC voltage circuit comprising a smaller potential difference, a first potential level, and a second potential level, and (3) a deflection module comprising two inputs and at least one deflection coil, the at least one deflection coil connected between the two inputs, the method comprising: connecting, in a first cycle, the first potential level of the first DC voltage circuit to the at least one deflection coil by switching until a first threshold value for the current is exceeded in the deflection coil; connecting, in a plurality of further cycles, the first potential level of the second DC voltage circuit by switching to the at least one deflection coil until a second threshold value for the current is exceeded in the deflection coil; and determining a respective duty factor of a switching time for exceeding the first threshold value in the first cycle and for exceeding the second threshold value in the plurality of further cycles using a number of characteristic parameters of the at least one deflection coil.

13. The method as claimed in claim 12, further comprising measuring a current flowing through the at least one deflection coil with a current measuring device connected on an input side, an output side, or the input side and the output side of the at least one deflection coil; comparing the measured current with the first threshold value in the first cycle and with the second threshold value in a plurality of further cycles; and determining the respective duty factor of the switching time using the compared measured current.

14. An X-ray tube comprising: an electron source for generating an electron beam, a positioning apparatus focusing the electron beam, the positioning apparatus comprising: (1) a first DC voltage circuit comprising a high potential difference, a first potential level, and a second potential level; (2) a second DC voltage circuit comprising a smaller potential difference, a first potential level, and a second potential level, wherein a ratio of a voltage drop across the second DC voltage circuit contributes to a voltage drop across the first DC voltage circuit by up to 1:4; and (3) a deflection module comprising two inputs and at least one deflection coil, the at least one deflection coil connected between the two inputs; and a control apparatus configured to: (1) connect, in a first cycle, the first potential level of the first DC voltage circuit to the at least one deflection coil by switching until a first threshold value for the current is exceeded in the deflection coil; and (2) connect, in a plurality of further cycles, the first potential level of the second DC voltage circuit by switching to the at least one deflection coil until a second threshold value for the current is exceeded in the deflection coil.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 depicts an example of a positioning apparatus for an electron beam of an X-ray tube.

(2) FIG. 2 depicts an example of a current profile generated by a method for actuating, by pulse width modulation, a positioning apparatus as depicted in FIG. 1.

(3) Mutually corresponding parts and variables have each been provided with the same reference symbols in all of the figures.

DETAILED DESCRIPTION

(4) FIG. 1 depicts schematically a positioning apparatus 1. An X-ray tube 2 has an electron source 4, which generates an electron beam 6. The electron beam 6 is accelerated onto the anode 8, wherein the focal spot position is regulated via the positioning apparatus 1 by a method yet to be illustrated in more detail, which is controlled by the control apparatus 10.

(5) The positioning apparatus 1 has a first DC voltage circuit 12 including a first potential level 14 and a second potential level 16 and a second DC voltage circuit 18 including a first potential level 20 and a second potential level 22. Furthermore, the positioning apparatus 1 has a deflection module 24, which is formed substantially by a full bridge 26 and a deflection coil 28. In this case, the deflection coil 28 is connected in series with a current measuring device 33 between the first output terminal 30 and the second output terminal 32 of the full bridge 26. A first switching path 34 leads from the first potential level 14 of the first DC voltage circuit 12 to the first input terminal 36 of the full bridge 26. A second switching path 38 leads from the first potential level 20 of the second DC voltage circuit 18 to that input 37 of the deflection module formed by the first input terminal 36 of the full bridge 26.

(6) In this case, the first switching path 34 has a first switch 40 and a diode 42 connected back-to-back in parallel therewith. The second switching path 38 has a second switch 44 and a diode 46 connected in parallel therewith. The second potential level 16 of the first DC voltage circuit 12 and the second potential level 22 of the second DC voltage circuit 18 are connected jointly to that input 49 of the deflection module 24 formed by the second input terminal 48 of the full bridge 26. Furthermore, the first switching path 34 includes a coil 50 and a diode 51, which is connected back-to-back in parallel therewith and with which a resistor 52 is connected in series.

(7) In order to generate a current with as steep edges as possible by PWM in the deflection coil 28 of the deflection module 24, the first switch 40 in the first switching part 34 may be closed and the second switch 44 in the second switching path 38 may be opened. As a result, the entire deflection module 24 is present at the first DC voltage circuit 12, and the fine adjustment for the duty factor may be performed, for example, by corresponding switching of the full bridge 26. In order to keep the current in the deflection coil 28 stable with as few fluctuations as possible by PWM, the second switch 44 may be closed and the first switch 40 opened, correspondingly. As a result, the deflection module 24 is only present at the second DC voltage circuit 18, and is disconnected from the first DC voltage circuit 12. The fine adjustment of the respective duty factor may likewise be performed by switching in the full bridge 28.

(8) FIG. 2 depicts a current profile I.sub.L generated by a method 60 for actuating, by pulse width modulation, a positioning apparatus as depicted in FIG. 1. The method 60 envisages applying the deflection coil 28 to the first DC voltage circuit 12 in a manner not illustrated in any more detail in a first cycle Z.sub.1. This may take place, for example, by virtue of the fact that the first switch in the first switching path is closed, and therefore both inputs of the deflection module are initially applied to the first DC voltage circuit 12. Then, by corresponding switching within the full bridge, the voltage present at the inputs of the deflection module may also be applied to the deflection coil.

(9) In the first cycle Z.sub.1, the voltage U.sub.1 of the first DC voltage circuit 12 is present at the deflection coil 28, as a result of which the current in the deflection coil 28 increases until it reaches a first threshold value S.sub.1. The voltage U.sub.1 is clamped again by the deflection coil 28, and the deflection coil 28 is short-circuited via two switches of the full bridge. The duty factor T.sub.1, namely the length for which the voltage U.sub.1 is to be applied, may be calculated in this case, for example, from the inductance and the ohmic resistance of the deflection coil 28, or the current I.sub.L may be measured explicitly for this. After clamping of the voltage U.sub.1 and short-circuiting of the deflection coil 28, the current I.sub.L in the deflection coil 28 decreases. At the beginning of the next cycle Z.sub.2, the deflection coil 28 is applied to the second DC voltage circuit 18, so that the voltage drop U.sub.2 there may again increase the current I.sub.L in the deflection coil 28 until, after a duty factor T.sub.2, a second threshold value S.sub.2 is reached. Then, the deflection coil 28 is clamped by the voltage U.sub.2 up to the end of the cycle Z.sub.2 and the deflection coil 28 is short-circuited, so that the current I.sub.L decreases again, and at the beginning of the third cycle Z.sub.3 is again applied to U.sub.2 until the current I.sub.L again reaches the second threshold value S.sub.2. This procedure may be continued schematically in a comparable manner in further cycles Z.sub.4, . . . , et al.

(10) While the current I.sub.L has a comparatively steep edge F during rise in the first cycle Z.sub.1 as a result of the high applied voltage U.sub.1, in the further cycles Z.sub.2, Z.sub.3, Z.sub.4, the profile of the current I.sub.L is characterized by a plateau P with relatively small fluctuations. The stable profile in the plateau P may be attributed to the low voltage U.sub.2 present for comparatively long duty factors T.sub.2, T.sub.3, T.sub.4 in the corresponding cycles Z.sub.2, Z.sub.3, Z.sub.4. If the current I.sub.L in the deflection coil 28 is intended to be set to a radically different value, this may take place again by virtue of the deflection coil 28 again being applied to the first DC voltage circuit 12 with a corresponding duty factor. The subsequent stabilization of the current I.sub.L in the case of the new value then again takes place in the above-described way by the voltage U.sub.2 of the second DC voltage circuit 18.

(11) It is to be understood that the elements and features recited in the appended claims may be combined in different ways to produce new claims that likewise fall within the scope of the present invention. Thus, whereas the dependent claims appended below depend from only a single independent or dependent claim, it is to be understood that these dependent claims may, alternatively, be made to depend in the alternative from any preceding or following claim, whether independent or dependent, and that such new combinations are to be understood as forming a part of the present specification.

(12) While the present invention has been described above by reference to various embodiments, it may be understood that many changes and modifications may be made to the described embodiments. It is therefore intended that the foregoing description be regarded as illustrative rather than limiting, and that it be understood that all equivalents and/or combinations of embodiments are intended to be included in this description.