Patent Description:
PTL <NUM> discloses an X-ray generating tube including an insulating tube, a cathode, an anode, and an inner anode layer. The insulating tube, the cathode, and the anode constitute an envelope that defines an inner space, and the inner anode layer extends from the anode along the inner surface of the insulating tube. The inner anode layer is electrically connected to the anode and suppresses charge of the insulating tube.

PTL <NUM>: <CIT> further cited prior art document is <CIT> showing a radiation generating tube, radiation generating unit, and radiation image taking system, as well as document <CIT> showing an x-ray tube.

It is desired to thin the insulating tube in order to lighten the X-ray generating tube. However, the thin insulating tube may weaken the insulating tube or the X-ray generating tube. Further, the thin insulating tube may decrease the withstand voltage of the insulating tube. At the distal end (end on the cathode side) of the inner anode layer where the field strength readily increases, discharge may occur in a direction passing through the insulating tube to cause leakage via a through hole formed by the discharge.

The present invention has as its object to provide a technique advantageous for lightening an X-ray generating tube while suppressing discharge passing through an insulating tube and ensuring the strength of the insulating tube.

According to the present invention, there is provided an X-ray generating tube comprising an insulating tube having a first open end and a second open end, a cathode including an electron emission source and arranged to close the first open end of the insulating tube, an anode including a target that generates an X-ray upon collision with an electron from the electron emission source and arranged to close the second open end of the insulating tube, and a tubular electrical conductive member extending from the anode in an inner space of the insulating tube, wherein the insulating tube includes a tubular rib at a position spaced apart from the first open end and spaced apart from the second open end, the tubular rib is arranged in a radial direction when viewed from an end of the tubular electrical conductive member on a side of the cathode, the end of the tubular electrical conductive member on the side of the cathode is positioned between a first virtual plane including an end face of the tubular rib on the side of the cathode and a second virtual plane including an end face of the tubular rib on a side of the anode, an end face of the tubular electrical conductive member on the side of the cathode is spaced apart from the first virtual plane, the end face of the tubular electrical conductive member on the side of the cathode is spaced apart from the second virtual plane; a thickness of a portion of the insulating tube where the tubular rib is arranged is larger than a thickness of a remaining portion of the insulating tube where the tubular rib is not arranged such that the tubular rib increases a strength of the insulating tube, and the insulating tube and the tubular rib are made of an insulator.

The present invention provides a technique advantageous for lightening an X-ray generating tube while suppressing discharge passing through an insulating tube and ensuring the strength of the insulating tube.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the claims of the present invention, and not all combinations of features set forth in the embodiments are essential to the present invention. Two or more of features set forth in the embodiments may be combined arbitrarily. The same reference numerals denote the same or similar parts and a repetitive description thereof will be omitted.

<FIG> schematically shows the arrangement of an X-ray generating tube <NUM> according to a first embodiment of the present invention. The X-ray generating tube <NUM> according to the first embodiment can include an insulating tube <NUM>, a cathode <NUM>, an anode <NUM>, and a tubular electrical conductive member <NUM>. The insulating tube <NUM> has a first open end OP1 and a second open end OP2. The insulating tube <NUM> is made of an insulating material (for example, ceramic or glass) and has a tubular shape extending in an axial direction AD. The tubular shape is a shape that forms a closed figure on a section perpendicular to the axial direction AD and is, for example, a cylindrical shape. The concept of the tubular shape can include a shape having different sectional areas at different positions in the axial direction AD.

The cathode <NUM> is arranged to close the first open end OP1 of the insulating tube <NUM>. The cathode <NUM> includes an electron emission source <NUM> configured to emit electrons. The electron emission source <NUM> can include, for example, a filament, a converging electrode configured to cause electrons emitted from the filament to converge, and the like. For example, a potential of -<NUM> kV with reference to the anode <NUM> can be applied to the cathode <NUM>.

The anode <NUM> is arranged to close the second open end OP2 of the insulating tube <NUM>. The anode <NUM> can include a target <NUM>, a target holding plate <NUM> that holds the target <NUM>, and an electrode <NUM> that holds the target holding plate <NUM>. The electrode <NUM> is electrically connected to the target <NUM> and applies a potential to the target <NUM>. Electrons from the electron emission source <NUM> collide with the target <NUM> and the target <NUM> generates an X-ray. The generated X-ray passes through the target holding plate <NUM> and is radiated outside the X-ray generating tube <NUM>. The anode <NUM> can be maintained at, for example, the ground potential but may be maintained at another potential. The target <NUM> can be formed from a material of high melting point and high X-ray generation efficiency such as tungsten, tantalum, or molybdenum. The target holding plate <NUM> can be formed from, for example, a material that transmits an X-ray, such as beryllium or diamond.

The tubular electrical conductive member <NUM> is arranged to extend from the anode <NUM> in the inner space of the insulating tube <NUM>. The tubular electrical conductive member <NUM> has a tubular shape extending in the axial direction AD. The tubular electrical conductive member <NUM> is electrically connected to the anode <NUM>. The tubular electrical conductive member <NUM> is spaced apart from the cathode <NUM>. The tubular electrical conductive member <NUM> can be arranged to surround at least part of the orbit (path between the electron emission source <NUM> and the target <NUM>) of electrons emitted from the electron emission source <NUM>. The tubular electrical conductive member <NUM> can function to reduce the influence of charge of the insulating tube <NUM> on the orbit of electrons emitted from the electron emission source <NUM>. The tubular electrical conductive member <NUM> can be arranged to, for example, contact the inner side surface of the insulating tube <NUM>, but may be arranged apart from the inner side surface of the insulating tube <NUM>. The tubular electrical conductive member <NUM> may be constituted integrally with the anode <NUM>, but may be constituted separately from the anode <NUM> and coupled or fixed to the anode <NUM>. The tubular electrical conductive member <NUM> can be, for example, a film formed on the inner side surface of the insulating tube <NUM> by vapor deposition such as CVD (Chemical Vapor Deposition) or PVD (Physical Vapor Deposition), plating, coating, or the like. Alternatively, the tubular electrical conductive member <NUM> may be inserted into the insulating tube <NUM> after formed separately from the insulating tube <NUM>.

The insulating tube <NUM> can include a tubular rib <NUM> at a position spaced apart from the first open end OP1 and spaced apart from the second open end OP2. The thickness of a portion of the insulating tube <NUM> where the tubular rib <NUM> is arranged is larger than that of the remaining portion of the insulating tube <NUM>. The tubular rib <NUM> increases the strength of the insulating tube <NUM>. Hence, the tubular rib <NUM> is provided advantageously to decrease the thickness of a portion of the insulating tube <NUM> except the portion where the tubular rib <NUM> is arranged. This can contribute to lightening of the X-ray generating tube <NUM>. The tubular rib <NUM> can be arranged to face the inner space of the insulating tube <NUM>.

The tubular rib <NUM> can be arranged in a radiation direction RD when viewed from an end <NUM> of the tubular electrical conductive member <NUM> on the cathode <NUM> side. The end <NUM> of the tubular electrical conductive member <NUM> is a portion where the field strength readily increases. Thus, to suppress discharge in a direction passing through the insulating tube <NUM>, it is effective to provide the tubular rib <NUM> in the radiation direction RD of the end <NUM>. That is, the tubular rib <NUM> is advantageous for achieving both suppression of discharge passing through the insulating tube <NUM> and ensuring of the strength of the insulating tube <NUM>. For example, the end <NUM> of the tubular electrical conductive member <NUM> on the cathode <NUM> side can be positioned between a first virtual plane VPL1 including an end face of the tubular rib <NUM> on the cathode <NUM> side and a second virtual plane VPL2 including an end face of the tubular rib <NUM> on the anode <NUM> side. As will be described later, the first virtual plane VPL1 and an end face <NUM> of the tubular electrical conductive member <NUM> on the cathode <NUM> side are preferably spaced apart from each other in terms of improvement of the withstand voltage.

<FIG> shows a simulation result representing a potential in the X-ray generating tube. The field strength is high at a portion where the interval between equipotential lines is small. As indicated by a symbol A, the field strength at the end of the tubular electrical conductive member <NUM> is high and discharge passing through the insulating tube <NUM> readily occurs at this portion. To suppress the discharge, it is effective to provide the tubular rib <NUM> at this portion and thicken the insulating tube <NUM>.

<FIG> schematically shows the arrangement of an X-ray generating tube <NUM> according to a second embodiment of the present invention. Matters not mentioned in the second embodiment can comply with the first embodiment. The X-ray generating tube <NUM> according to the second embodiment is different from the X-ray generating tube <NUM> according to the first embodiment in that it includes a covering member <NUM> which is arranged to cover the outside of an insulating tube <NUM> and receives a potential. The covering member <NUM> can be arranged to be electrically connected to a cathode <NUM> and an anode <NUM>. The covering member <NUM> can cover the cathode <NUM>, the insulating tube <NUM>, and the anode <NUM> so as to, for example, contact the cathode <NUM> and the anode <NUM>. The sheet resistance value of the covering member <NUM> is smaller than that of the insulating tube <NUM>.

For example, assume that the specific resistance of the insulating tube <NUM> at <NUM> is equal to or higher than <NUM> × <NUM>Ωm and equal to or lower than <NUM> × <NUM><NUM> Ωm, the sheet resistance value of the insulating tube <NUM> at <NUM> is Rs<NUM>, and the sheet resistance value of the covering member <NUM> at <NUM> is Rs<NUM>. In this case, Rs<NUM>/Rs<NUM> is preferably equal to or higher than <NUM> × <NUM>-<NUM> and equal to or lower than <NUM> × <NUM>-<NUM>. The covering member <NUM> can be formed from, for example, a glassy material such as Kovar glass, glaze, or frit glass, or a metal oxide film.

The covering member <NUM> covers the insulating tube <NUM> advantageously to, for example, form a smooth surface on the outside of the insulating tube <NUM> and suppress entrance of dirt between particles constituting the insulating tube <NUM>. This can improve a creepage withstand voltage on the outer surface of the insulating tube <NUM>. The covering member <NUM> has low conductivity, and even if charge occurs on the outer surface of the insulating tube <NUM>, charges can be moved before generating a large potential difference. Generation of discharge that may damage the insulating tube <NUM> can be prevented.

However, the covering of the insulating tube <NUM> with the covering member <NUM> may increase the field strength at the end of a tubular electrical conductive member <NUM>, as shown in <FIG> shows a simulation result representing a potential in the X-ray generating tube in which the insulating tube <NUM> is covered with the covering member <NUM>. The field strength (interval between equipotential lines) on the surface of the covering member <NUM> is uniformed by providing the covering member <NUM>. However, this further increases the field strength at the end of the tubular electrical conductive member <NUM> near the end of the tubular electrical conductive member <NUM>, as indicated by a symbol A.

To suppress discharge in a direction passing through the insulating tube <NUM>, it is highly effective to provide the tubular rib <NUM> in a radiation direction RD of an end <NUM> in the arrangement in which the covering member <NUM> is provided.

<FIG> schematically shows the arrangement of an X-ray generating tube <NUM> according to a third embodiment of the present invention. Matters not mentioned in the third embodiment can comply with the first or second embodiment. Although a covering member <NUM> covering an insulating tube <NUM> is provided in all the following embodiments, the covering member <NUM> is not an essential constituent in the present invention. In the third embodiment, the covering member <NUM> is arranged to be electrically connected to a cathode <NUM> and an anode <NUM>, but is arranged not to cover the side surfaces of the cathode <NUM> and anode <NUM>.

<FIG> schematically shows the arrangement of an X-ray generating tube <NUM> according to a fourth embodiment of the present invention. Matters not mentioned in the fourth embodiment can comply with the first or second embodiment. In the fourth embodiment, a covering member <NUM> is arranged to be electrically connected to a cathode <NUM> and an anode <NUM>, but is arranged not to cover the side surfaces of the cathode <NUM> and anode <NUM>. The cathode <NUM> has a portion covering part of the side surface of the covering member <NUM>, and/or the anode <NUM> has a portion covering part of the side surface of the covering member <NUM>.

<FIG> schematically shows the arrangement of an X-ray generating tube <NUM> according to a fifth embodiment of the present invention. Matters not mentioned in the fifth embodiment can comply with the first to fourth embodiments. In the fifth embodiment, a tubular electrical conductive member <NUM> is arranged to surround an end of an electron emission source <NUM> on an anode <NUM> side. <FIG> shows an example in which the arrangement in which the tubular electrical conductive member <NUM> is arranged to surround the end of the electron emission source <NUM> on the anode <NUM> side is applied to the X-ray generating tube <NUM> according to the second embodiment. This arrangement is applicable to even the X-ray generating tubes <NUM> according to the first, third, and fourth embodiments.

<FIG> schematically shows the arrangement of an X-ray generating tube <NUM> according to a sixth embodiment not covered by the present invention. Matters not mentioned in the sixth embodiment can comply with the first to fifth embodiments. In the sixth embodiment, a tubular electrical conductive member <NUM> is arranged to form a space between the outer surface of the tubular electrical conductive member <NUM> and the inner surface of an insulating tube <NUM>. This arrangement is applicable to even the X-ray generating tubes <NUM> according to the first to fifth embodiments.

<FIG> schematically shows the arrangement of an X-ray generating tube <NUM> according to a seventh embodiment that is not covered by the present invention. Matters not mentioned in the seventh embodiment can comply with the first to sixth embodiments. In the seventh embodiment, an end face <NUM> of a tubular electrical conductive member <NUM> on a cathode <NUM> side belongs to a first virtual plane VPL1 including an end face of a tubular rib <NUM> on the cathode <NUM> side. This arrangement is applicable to even the X-ray generating tubes <NUM> according to the first and third to fifth embodiments.

<FIG> schematically shows the arrangement of an X-ray generating tube <NUM> according to an eighth embodiment of the present invention. Matters not mentioned in the eighth embodiment can comply with the first to seventh embodiments. In the eighth embodiment, a tubular rib <NUM> is arranged to project toward the outer space of an insulating tube <NUM>. This arrangement is applicable to even the X-ray generating tubes <NUM> according to the first and third to seventh embodiments.

<FIG> schematically shows the arrangement of an X-ray generating tube <NUM> according to a ninth embodiment of the present invention. Matters not mentioned in the ninth embodiment can comply with the first to seventh embodiments. In the ninth embodiment, a tubular rib <NUM> includes an inner tubular rib <NUM> arranged to face the inner space of an insulating tube <NUM> and an outer tubular rib <NUM> arranged to project toward the outer space of the insulating tube <NUM>. This arrangement is applicable to even the X-ray generating tubes <NUM> according to the first and third to seventh embodiments.

A design method for the tubular rib <NUM> and the tubular electrical conductive member <NUM> will be exemplarily described with reference to <FIG> and <FIG>. T is the thickness of a portion of the insulating tube <NUM> that does not have the tubular rib <NUM>, H is the thickness of the tubular rib <NUM>, and TT is the thickness of a portion of the insulating tube <NUM> that has the tubular rib <NUM>. L is the distance between the first virtual plane VPL1 and the end face <NUM> of the tubular electrical conductive member <NUM> on the cathode <NUM> side.

In general, the creepage withstand voltage of an insulator is lower than the bulk withstand voltage, and the creepage withstand voltage is experimentally known to be <NUM>/<NUM> to <NUM>/<NUM> times. E1 (kV/mm) is the bulk withstand voltage of an insulator forming the insulating tube <NUM>, and E2 (kV/mm) is the creepage withstand voltage of the insulator. A withstand voltage (withstand voltage on a path PH1) in the direction of thickness of the portion of the insulating tube <NUM> that has the tubular rib <NUM> is E1 × TT (kV). In the example of <FIG>, a withstand voltage (withstand voltage on a path PH2) via the creepage surface of the tubular rib <NUM> is E2 × (L + H) + E1 × T. In the example of <FIG>, the withstand voltage (withstand voltage on the path PH2) via the creepage surface of the tubular rib <NUM> is E2 × H + E1 × T. The arrangement in <FIG> is superior in the withstand voltage via the creepage surface to the arrangement in <FIG>.

The arrangement in <FIG> will be explained below. To avoid discharge via the creepage surface, E2 × (L + H) + E1 × T ≥ E1 × TT is preferable. Since TT = T + H, L ≥ (E1 - E2)/E2 × H. When the creepage withstand voltage is <NUM>/<NUM> times the bulk withstand voltage (E1 = <NUM> × E2), L ≥ <NUM> is preferable. When the creepage withstand voltage is <NUM>/<NUM> times the bulk withstand voltage (E1 = <NUM> × E2), L ≥ <NUM> is preferable. When TT is set to be <NUM> in terms of lightening of the X-ray generating tube <NUM>, L ≥ <NUM> is preferable and L ≥ <NUM> is more preferable.

<FIG> schematically shows the arrangement of an X-ray generating tube <NUM> according to a 10th embodiment not covered by the present invention. Matters not mentioned in the 10th embodiment can comply with the first to ninth embodiments. In the 10th embodiment, an insulating tube <NUM> includes a tubular rib <NUM> arranged in the radial direction when viewed from an end of a tubular electrical conductive member <NUM> on a cathode <NUM> side. An end <NUM> of the tubular electrical conductive member <NUM> on the cathode <NUM> side can be positioned between a first virtual plane VPL1 including an end face of the tubular rib <NUM> on the cathode <NUM> side and a second virtual plane VPL2 including an end face of the tubular rib <NUM> on an anode <NUM> side. The second virtual plane VPL2 can form an end face of the insulating tube <NUM> on the anode <NUM> side. In other words, the end face of the tubular rib <NUM> on the anode <NUM> side can belong to the same plane as that of the end face of the insulating tube <NUM> on the anode <NUM> side. From another viewpoint, the tubular rib <NUM> can be arranged in contact with the anode <NUM>.

The X-ray generating tube <NUM> according to the 10th embodiment can include a covering member <NUM> that is arranged to cover the outside of the insulating tube <NUM> and receives a potential. The covering member <NUM> can be arranged to be electrically connected to the cathode <NUM> and the anode <NUM>. The covering member <NUM> can cover the cathode <NUM>, the insulating tube <NUM>, and the anode <NUM> so as to, for example, contact the cathode <NUM> and the anode <NUM>. The sheet resistance value of the covering member <NUM> is smaller than that of the insulating tube <NUM>.

<FIG> shows the arrangement of an X-ray generating apparatus <NUM>. The X-ray generating apparatus <NUM> can include an X-ray generating tube <NUM> and a driving circuit <NUM> that drives the X-ray generating tube <NUM>. The X-ray generating apparatus <NUM> can further include a booster circuit <NUM> that applies a boosted voltage to the driving circuit <NUM>. The X-ray generating apparatus <NUM> can further include a container <NUM> that contains the X-ray generating tube <NUM>, the driving circuit <NUM>, and the booster circuit <NUM>. The container <NUM> can be filled with insulating oil.

<FIG> shows the arrangement of an X-ray imaging apparatus <NUM>. The X-ray imaging apparatus <NUM> can include an X-ray generating apparatus <NUM>, and an X-ray detecting apparatus <NUM> that detects an X-ray <NUM> having passed through an object <NUM> after radiated from the X-ray generating apparatus <NUM>. The X-ray imaging apparatus <NUM> may further include a control apparatus <NUM> and a display apparatus <NUM>. The X-ray detecting apparatus <NUM> can include an X-ray detector <NUM> and a signal processor <NUM>. The control apparatus <NUM> can control the X-ray generating apparatus <NUM> and the X-ray detecting apparatus <NUM>. The X-ray detector <NUM> detects or images the X-ray <NUM> having passed through the object <NUM> after radiated from the X-ray generating apparatus <NUM>. The signal processor <NUM> can process a signal output from the X-ray detector <NUM> and supply the processed signal to the control apparatus <NUM>. The control apparatus <NUM> causes the display apparatus <NUM> to display an image based on the signal supplied from the signal processor <NUM>.

Claim 1:
An X-ray generating tube comprising:
an insulating tube (<NUM>) having a first open end (OP1) and a second open end (OP2);
a cathode (<NUM>) including an electron emission source (<NUM>) and arranged to close the first open end (OP1) of the insulating tube (<NUM>);
an anode (<NUM>) including a target that generates an X-ray upon collision with an electron from the electron emission source (<NUM>) and arranged to close the second open end (OP2) of the insulating tube (<NUM>); and
a tubular electrical conductive member (<NUM>) extending from the anode (<NUM>) in an inner space of the insulating tube (<NUM>),
wherein the insulating tube (<NUM>) includes a tubular rib (<NUM>) at a position spaced apart from the first open end (OP1) and spaced apart from the second open end (OP2),
the tubular rib (<NUM>) is arranged in a radial direction when viewed from an end (<NUM>) of the tubular electrical conductive member (<NUM>) on a side of the cathode,
the end of the tubular electrical conductive member on the side of the cathode is positioned between a first virtual plane (VPL1) including an end face of the tubular rib on the side of the cathode and a second virtual plane (VPL2) including an end face of the tubular rib on a side of the anode;
an end face (<NUM>) of the tubular electrical conductive member on the side of the cathode is spaced apart from the first virtual plane;
the end face of the tubular electrical conductive member on the side of the cathode is spaced apart from the second virtual plane;
a thickness of a portion of the insulating tube where the tubular rib is arranged is larger than a thickness of a remaining portion of the insulating tube where the tubular rib is not arranged such that the tubular rib increases a strength of the insulating tube, and characterized in that
the insulating tube (<NUM>) and the tubular rib (<NUM>) are made of an insulator.