Electric motor for double-ended x-ray tube

Abstract

An x-ray tube includes a housing containing cooling oil and a vacuum enclosure disposed within the housing and including a solid enclosure wall. Oil is disposed between the housing and the wall. The anode and cathode are arranged in a vacuum environment and surrounded by walls. A rotor connected to the anode is disposed on a bearing within the vacuum environment. Further, a stator assembly positioned within the oil surrounds the rotor to define an annular gap filled with oil. The stator assembly includes stator teeth spaced apart by intermediate stator slots, and stator windings disposed within the stator slots. Each stator tooth includes a tooth crest positioned adjacent the boundary wall and configured to be spaced apart from the stator winding by a distance to form an in-slot cooling channel in fluid communication with the oil-filled annular gap such that the stator tooth including its tooth crest is immersed in the oil.

Description

Background Art

[0001] Vacuum tubes are widely used to control the flow of electric current between separated electrodes in a sealed vacuum chamber. In particular, an x-ray tube is a special type of vacuum tube that is commonly used to generate and direct x-ray radiation for a variety of beneficial purposes, such as medical imaging, radiology, diagnostics, radiography, tomography, non-destructive testing, material analysis, security applications, and inspection. Conventional x-ray tubes operate by emitting a concentrated electron beam via an excited cathode. The emitted electron beam is then directed toward a target mounted on an anode. In some configurations, the anode is rotated via the operation of an electric motor, such as the high-energy double-ended x-ray tube contemplated herein.

[0002] The emitted electrons gain energy and are accelerated based on the large potential difference in the intermediate space between the rotating anode and the fixed cathode. Some of the accelerated electrons collide with the target surface on the rotating anode, and a relatively small portion of the incident electron beam energy is converted into useful x-ray radiation. Most of the remaining energy forms waste heat, which is dissipated from the x-ray tube via cooling oil or other suitable cooling systems. Therefore, the thermal properties of the x-ray tube must be carefully adjusted to protect the electric motor and other heat-sensitive components of the x-ray tube.

[0003] The rotational force acting on the target anode disk in a high energy double-ended x-ray tube configuration is applied by the electric motor described above. In a typical configuration, the anode is powered by a small induction motor having a concentrically positioned rotor and stator. The rotor is positioned within a vacuum housing and rotates on bearings, and liquid metal bearings (LMB) are an emerging technology that have numerous performance advantages over traditional metal bearings. The stator itself is immersed in or surrounded by cooling oil outside the vacuum housing so that the rotor and stator are located on opposite sides of the solid housing wall. However, pipes equipped with LMBs require higher levels of torque to generate sufficient initial hydrodynamic lift and overcome fluid friction at low speeds. Drag increases with increasing rotor speed. Due to this relationship, operation of tubes equipped with LMBs at high speeds requires high levels of torque and good high-speed efficiency, both of which have significant additional thermal management issues. Summary of the invention

[0004] The present disclosure relates to high energy double-ended x-ray tubes in which the stator is immersed in cooling oil and the opposing rotor is positioned in a vacuum, which in turn is an insulator and presents significant challenges for cooling. In such x-ray tubes, the high potential of the anode requires a relatively large radial separation distance between the rotor and the surrounding stator. For example, an exemplary radial gap of about 0.2 inches to about 0.6 inches can be used for the x-ray tubes described herein, which is an order of magnitude larger than the typical radial gap size. Double-ended x-ray tubes equipped with liquid metal bearings (LMBs) as described above will benefit from the integration of electric motors with improved efficiency. One way to improve this efficiency is to reduce the large radial separation distance. However, any reduction in the stator-rotor gap can cause overheating. Therefore, high energy double-ended x-ray tubes are often suboptimal in terms of overall size and operating efficiency. Therefore, various structural solutions proposed herein seek to reduce the separation distance without adversely affecting operating efficiency. These benefits are primarily provided by improvements to the stator, which will be discussed in detail below.

[0005] The term "gap distance" as used herein and in the general art includes (i) the thickness of the housing wall, (ii) the vacuum gap extending between the rotor and the inside of the housing wall of the above-mentioned vacuum housing, and (iii) the oil-filled gap extending between the outside of the housing wall of the vacuum housing and the surrounding stator. Cooling oil circulates through the oil-filled gap along the inner diameter (ID) of the stator assembly to prevent overheating of the stator and components surrounding the x-ray tube. If no further measures are taken, reducing the standoff distance can cause overheating of the x-ray tube, thereby causing thermal management problems due to the need to extract excess heat from the cooling oil. Therefore, the following solution also seeks to reduce the standoff distance without restricting the flow of cooling oil.

[0006] In particular, the solution set forth below deviates from the standard stator winding configuration by changing the spatial relationship between the stator slots and the windings disposed therein, and modifying the flow path of the circulating cooling oil. As understood in the art, standard induction motors fill each stator slot with conductive windings and provide a relatively large spacing distance. The changes described herein result in similar net cooling flow with reduced spacing distances, thereby enabling increased output torque from the motor, improved overall performance, and increased operating efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The drawings described herein are for illustrative purposes only, are illustrative in nature, and are intended to be exemplary and not to limit the scope of the present disclosure.

[0008] Figure 1 is an illustration of an exemplary high energy double ended x-ray tube constructed in accordance with the present disclosure.

[0009] Figure 1A is the radial stator-rotor clearance Figure 1 A partial cross-sectional illustration of the stator assembly and rotor of an x-ray tube is shown.

[0010] Figure 2 Is a description Figure 1 Representative performance curves of representative speed versus loss for x-ray tubes depicted.

[0011] Figure 3 Can be used as Figure 1 A plan view illustration of a portion of a stator assembly of an x-ray tube is shown.

[0012] Figure 4 yes Figure 3 An illustration of a portion of a stator assembly is shown.

[0013] Figure 5 is a plan view illustration of a representative stator tooth and slot arrangement according to an aspect of the present disclosure.

[0014] Fig. 6A and Figure 6B It is used to construct Figure 3 and Figure 4 Schematic illustration of possible alternative slot shapes for a stator assembly of FIG.

[0015] Figure 7 and Figure 8 It is available for Figure 1 Plan view illustrations of various embodiments of rotor assemblies for x-ray tubes are shown.

[0016] Fig. 9 It is available for Figure 1 Illustration of a side view of the rotor assembly of an x-ray tube.

[0017] Fig.10 It is available for Fig. 9 A plan view illustration of representative rotor teeth of a rotor assembly is shown.

[0018] Fig.11 is a plan view illustration of a representative stator tooth describing an optional method for manufacturing or forming the stator tooth.

[0019] Fig.12 It is available for Figure 1 A graph of the efficiency progression of a representative VFD control scheme for an X-ray tube.

[0020] The present disclosure is susceptible to modification and alternative forms, wherein representative embodiments are shown by way of example in the accompanying drawings and are described in detail below. The inventive aspects of the present disclosure are not limited to the disclosed embodiments. On the contrary, the present disclosure is intended to cover alternatives within the scope of the disclosure defined by the appended claims. DETAILED DESCRIPTION

[0021] Embodiments of the present disclosure are described herein. The disclosed embodiments are provided as examples and illustrations of various solutions. The drawings are not necessarily drawn to scale, and some features may be enlarged or reduced to show specific details of interest. Therefore, the specific structural and functional details disclosed herein should not be interpreted as limiting, but merely as a representative basis for teaching those skilled in the art to adopt the disclosed structures and methods in different ways.

[0022] The numbers provided in the flow charts and process descriptions are intended to improve clarity and do not necessarily represent a particular order or sequence. For the purpose of this detailed description, approximate words, such as "about", "substantially", "generally", "approximately", etc., may each be used in this article in the sense of "at, close to or nearly at", "within 0-5%", or "within an acceptable manufacturing tolerance", or any logical combination thereof.

[0023] Referring now to the drawings, wherein like reference numerals refer to like parts, Figure 1 An exemplary high energy double ended x-ray tube 10, hereinafter referred to simply as x-ray tube 10, is depicted in FIG. As contemplated herein, x-ray tube 10 is operable to generate x-ray radiation 11 and to emit x-ray radiation 11 through port 13 toward an object to be imaged, such as a chest or limb of a patient (not shown). Such components include a solid housing wall 12 forming a vacuum enclosure, thereby defining a vacuum chamber 14 (“VACUUM”) as a void volume, in which a positively charged anode assembly 16 and a negatively charged cathode assembly 18 are located. In a possible embodiment, solid housing wall 12, which may be composed of metal, ceramic, or glass, is enclosed within a housing 15 filled with cooling oil 19 (“OIL”). In a typical application, cooling oil 19 may be composed of a suitable transformer oil, i.e., dielectric oil or another suitable dielectric liquid coolant. Thus, solid housing wall 12 forms separate isolated vacuum and fluid filled volumes, wherein solid housing wall 12 also has a fluid side 12F and a vacuum side 12V.

[0024] exist Figure 1 In the two different operating environments of the x-ray tube 10 shown, the anode 16 and the cathode 18 are disposed in the vacuum environment of the vacuum chamber 14. The rotatable anode 16 in various embodiments contemplated herein is connected to an anode rod 160, wherein the anode rod 160 is in turn coupled to a rotor 20R of an electric motor 20 (including a rotor 20R and a stator 20S), such as an induction type multi-phase / 4-pole squirrel cage rotor, hereinafter referred to as the electric motor 20 for simplicity. In some embodiments, such an electric motor 20 can be controlled using speed control using a variable frequency drive (VFD) from a motor controller 50, such that the motor controller 50 controls the speed of the electric motor 20 by varying the frequency (fC ) and voltage (V C ) to drive the electric motor 20. As with the anode 16 and cathode 18 described above, the rotor 20R is located within the vacuum chamber 14, specifically within the axial neck 120 of the solid housing wall 12, and is disposed on bearings 25, such as mechanical roller bearings or liquid metal bearings (LMB) in different embodiments.

[0025] Figure 1 The rotor 20R and the neck 120 shown are surrounded by the stator assembly 20S of the electric motor 20, which in turn is immersed in the cooling oil 19. Therefore, the rotor 20R is mechanically and thermally isolated from the stator assembly 20S. Therefore, the rotor 20R operating in the vacuum environment of the vacuum chamber 14 is extremely well insulated, so that heat losses occurring in the rotor 20R must be dissipated via conduction to the bearings 25 or via radiation to the solid housing wall 12, or more precisely the neck 120 thereof. Therefore, a separation distance (D) is defined between the stator assembly 20S and the rotor 20R, and includes: (i) a vacuum gap (G1) extending between the rotor 20R and the vacuum side 12V of the solid housing wall 12, and (ii) an oil-filled gap (G2) extending between the fluid side 12F of the solid housing wall 12 and the surrounding stator assembly 20S, as shown in FIG. Figure 1A shown.

[0026] X-ray tube 10 is an example of a double-ended x-ray tube having a high potential applied to anode 16. As is understood in the art, such a high potential generally requires a large standoff distance (D), which in turn is often much greater than the typical standoff distance of an electric motor. The large standoff distance (D) impedes performance and efficiency. However, the methods described herein and referred to below are Figures 2 to 12 The structural modifications described allow the separation distance (D) to be reduced, thereby providing significant performance improvements over the prior art.

[0027] Still refer to Figure 1 When the stator assembly 20S is energized by a voltage signal (VC) from the motor controller 50 or via a corresponding current signal, the alternating forces of electromagnetic attraction and repulsion cause the rotor 20R to rotate about its longitudinal center axis 200. This in turn causes the anode 16, and in particular the target disk 16D composed of, for example, tungsten, to rotate. The target disk 16D provides a physical target that interacts with the electrons emitted by the cathode 18, wherein x-rays are ultimately generated by such interactions. In a typical configuration, the current flowing through and heating the filament (s) 21 of the cathode 18 causes electron emission through a thermionic emission process, as will be understood by those of ordinary skill in the art.

[0028] refer to Figure 2 , representative curve 22 shows Figure 1Performance relationship between the rotational speed of the middle rotor 20R, expressed in revolutions per minute (RPM) arranged on the x-axis, and the bearing losses, expressed in watts (W), arranged on the y-axis. Figure 2 The diagram shows Figure 1 The operation of the x-ray tube 10 and similarly constructed high energy / double ended vacuum tubes presents special challenges. The rotor 20R ultimately rotates at very high speeds, such as 5000 RPM to 10000 RPM or more. However, as the rotational speed increases, the bearing losses also increase.

[0029] In a possible implementation of the present teachings, LMB technology can be retrofitted onto an existing x-ray tube 10. However, Figure 1 The torque required of the electric motor 20 is higher in the LMB configuration than in a conventional ball bearing based tube in order to generate the initial hydrodynamic lift and overcome fluid friction, as described above. Figure 2 Curve 22 shows that as the operating speed increases, the drag and resultant losses increase significantly. Therefore, although the present teachings are not limited to LMB tubes, such tubes will benefit from Figure 1 An alternative configuration of the electric motor 20 is provided, particularly one having increased efficiency and better overall cooling performance due to a reduction in the separation distance (D).

[0030] Reference now Figure 3 , the stator assembly 20S is shown in a plan view, i.e., viewed along a central axis 200. The outer ring 30 (which may also be referred to as the stator core) of the stator assembly 20S forms a core support structure, and the stator assembly 20S itself is assembled from a stack of thin steel sheets, as is known in the art. When constructed in this manner, the stator assembly 20S has a cylindrical shape with a plurality of radially extending stator teeth 32. Each stator tooth 32 has a corresponding slightly arcuate tooth top 320, so that the stator teeth 32 are arranged end to end and are separated from each other by a short distance by a tooth gap (e.g., 33). Such tooth gaps 33 can be between about 0.5% and 3.75% of the inner diameter of the stator core, or between about 1.5% and about 2% in another embodiment. The stator assembly 20S also includes conductive stator windings 34 and phase leads 37, which extend from the ring 30. Stator windings 34, such as copper wire or cable, are in turn wound around the stator teeth 32 to substantially fill the stator slots 35. However, unlike typical winding configurations, the cooling regions 36 are open near the stator teeth 32.

[0031] That is, the present method brings the stator teeth 32 of the stator assembly 20S closer to the Figure 1 The rotor 20R is moved to enter the path required by the previous oil flow. The stator winding 34 is then positioned further back in the stator slot 35 so that the tooth top 320 is open and is Figure 1As the airflow is introduced into the stator slot 35 through the tooth gap 33 provided at the radial innermost surface of the stator tooth 32, Figure 1A The reduction in spacing distance (D) provides sufficient flow / equivalent pressure head loss.

[0032] The ratio of copper of the stator windings to the total slot area in the stator slots 35 may be in a possible range of about 5% to 75%, or about 30% to 35% in another embodiment. In one possible embodiment, the radial clearance between the rotor 20R and the stator assembly 20S may be about 1.8% to about 30% of the ID of the stator assembly 20S, or about 10% to about 12% in another configuration, in which case the radial clearance is about ID=11 inches (about 279 mm) or less. The radial clearance may be about 1.8% to about 30% of the ID of the stator assembly 20S (e.g., about 1.0% to about 1.5%) of the stator assembly 20S. Figure 3 The diameter of the ring 30 / stator core in the embodiment is between about 1.4% and 20% of the outer diameter (OD) of the stator core or the stator core, or in another construction is about 5% to about 7%, in which example the OD is about 14 inches (about 356 mm) or less.

[0033] Reference below Figures 4 to 12 In the contemplated embodiment described, the majority of the oil flow remains within the inner diameter of the stator assembly 20S (eg, Figure 3 The diameter extending between the opposite tooth tops 320) and Figure 1 The stator assembly 20S is constructed of solid, non-metallic materials, and is preferably disposed between the stator teeth 32 and the solid housing wall 12. However, the remaining oil flow passes through the cooling area 36, ​​which is the unfilled portion of the stator slot 35 located near the tooth top 320. Doing so increases the surface area in contact with the cooling oil, thereby increasing the cooling of the stator assembly 20S. That is, without the disclosed improvements, the high magnetic field at the tooth top 320 would typically leave wasted heat and energy at that location. The cooling oil is introduced around the stator teeth 32 at this same location (including the tooth top 320) through the cooling area 36, ​​thereby increasing the cooling efficiency. Therefore, immersing the tooth top 320 in the cooling oil 19 enables the tooth top 320 to act as a cooling fin, thereby promoting the cooling and efficiency benefits contemplated herein.

[0034] In the application contemplated herein, the rotor 20R is in the thermally insulating environment of the vacuum chamber 14, i.e., the rotor 20R is located in a vacuum environment. Therefore, the rotor 20R cannot be effectively Figure 1 The x-ray tube 10, which already generates a large amount of heat during its operation, therefore needs to manage the additional heat from the rotor 20R. Inefficiencies in cooling the rotor 20R manifest themselves in the injection of additional heat, thereby reducing the thermal overhead available for x-ray generation and increasing the time between exposures without overheating the x-ray tube 10 or its bearings. In particular, using LMB technology, Figure 1The bearing 25 is susceptible to seizure due to heat. This and other potential problems are addressed by cooling areas (e.g. Figure 3 36) shown in was alleviated.

[0035] In terms of flow rate, at least 90% of the cooling oil 19 used to cool the stator assembly 20S should flow along the inner diameter of the stator core and the tops of the stator teeth 32. Thus, substantially no cooling oil 19 passes through the outer diameter of the stator core, or in this case less than 10%. Thus, the stator assembly is cooled by direct contact with the cooling oil 19 using a flow rate of about 0.5 gallons per minute (gpm) to 10 gpm, with the associated geometry being defined so that the flow remains laminar at such example flow rates.

[0036] Reference now Figure 4 , Figure 3 A pair of adjacent stator teeth 32 in the embodiment also describes a cooling region 36. As described above, the stator teeth 32 extend radially toward the solid housing wall 12, wherein the tooth tops 320 are located at the bottom of the stator teeth 32. Figure 4 The stator winding 34 is formed into a generally T-shaped perimeter in an axial view of the embodiment of the present invention. As contemplated herein, the cooling region 36 extends from the radially innermost surface 340 of the stator winding 34 to the solid housing wall 12. Thus, the stator teeth 32 and their tooth tops 320 are completely immersed in the cooling oil 19. In a possible exemplary configuration, the tooth tops 320 are spaced apart from the surface 340 by a distance (d1) of at least about 0.08 inches.

[0037] Figure 5 A representative embodiment of a stator tooth 32 is shown in more detail. The stator tooth 32, which is symmetrical about a centerline 32A, includes an arcuate end 40 (alternatively referred to as a tooth root) and a radial wall 42, such that a stator slot 35 is defined by the space between the arcuate end 40 and the radial wall 42. A tooth gap 33 separates the tooth tops 320. The dimensions d2, d3, d4, d5, d6, and d7 collectively represent the configuration of the stator tooth 32. In a non-limiting set of exemplary dimensions, [d2, d3, d4, d5, d6, d7] = [0.431, 0.078, 0.020, 0.010, 0.685, and 0.970] inches. Other embodiments of similar or different scales are contemplated, and thus the dimensions shown are representative only for illustration purposes. Figure 1 In one possible configuration, the gap (G2) between the solid housing wall 12 and the inner diameter (ID) of the stator core can be between about 0.3% and 3% of the ID size of the stator core, or about 1% to 1.5% in another embodiment. Similarly, the outer diameter (OD) of the rotor core (e.g., Figures 7 and 8The radial clearance (G1) between the outer diameter of the cores 133, 135 or the teeth extending from these cores 133, 135 and the solid housing wall 12 can be between about 1.5% and 50% of the outer diameter size of the rotor core, where in another embodiment a range of about 10% to 11% is possible.

[0038] With respect to the stator assembly 20S itself, representative embodiments within the scope of the present disclosure include embodiments having an inner diameter of approximately 2 inches to 11 inches (50.8 mm to 279.4 mm). The stator assembly 20S may have a stator core length dimension between 0.70 inches and 2.5 inches (17.8 mm to 63.5 mm) (e.g., between 1.25 and 1.65 mm). Figure 1 In another embodiment, the stator assembly 20S extends parallel to the axis 200 between the left and right ends thereof, or about 1.25 inches and 1.50 inches (31.75 mm and 38.1 mm) in another embodiment. In another aspect of the present disclosure, Figure 1 The electric motor 20 may have a stator core length dimension of between 13% and 76% of the stator core inner diameter, or about 35% to 40% in a possible embodiment. With respect to the rotor 20R, in a possible configuration, the rotor length dimension (e.g., Figure 1 The length between the left and right ends of the middle rotor 20R extending parallel to the axis 200 is about 0.90 inches to 3 inches (22.9 mm to 76.2 mm), with a rotor length of about 1.5 inches to 2 inches (38.1 mm to 50.8 mm) used in other embodiments. Relative to the above inner diameter of the stator core, the rotor length can be about 14.7% and 82.0% of the inner diameter of the stator core, or about 35% to 45% in another embodiment. Relative to the depth of the stator slot 35 (e.g., d7), the tooth top (e.g., 320) can extend beyond the stator winding (e.g., along dimension d1) by more than 7%, such as 7% to 9%.

[0039] In yet other embodiments, the inner diameter of the stator core is about 2 inches to 11 inches (50.8 mm to 279.4 mm) and the length dimension is about 0.70 inches and 2.5 inches (17.8 mm to 63.5 mm). Here, for stator inner diameters less than 11 inches (63.5 mm), the radial clearance between the outermost surface of the rotor 20R and the innermost surface of the stator 20S (e.g., Figure 1A D) may be between about 0.20 inches and 0.60 inches (5.1 mm to 15.2 mm). The radial clearance may be between 1.8% and 30.0% of the inner diameter size of the stator core, with a clearance relationship of about 10% to 12% being beneficial in certain configurations.

[0040] Brief reference Fig. 6A and Figure 6BThe geometry and size of the stator teeth 32 described above may be varied within the scope of the present disclosure to provide different levels of performance. Fig. 6A The alternative profile 145 shown may include multi-angle walls 47 instead of Figure 5 This type of device can be used to produce stator slots 135 having a generally hexagonal geometry. Similarly, Figure 6B The alternative profile 245 includes a curvilinear surface 49 defining a stator slot 235 having a generally wedge-shaped or geometric shape, with Figure 5 and Fig. 6A In contrast, the elimination of the corners provides possible advantages in terms of creating the desired flux concentration and resulting heating. Thus, the configuration of the stator teeth 32 described above may vary within the scope of the present disclosure without affecting the presence and benefits of the cooling region 36 surrounding the tooth tip 320.

[0041] Reference now Figure 7 and Figure 8 , Figure 1 The rotor 20R in the embodiment may also have its structure changed within the scope of the present disclosure. For example, Figure 7 A rotor 120R having a plurality of generally circular rotor slots 129 is contemplated, and Figure 8 An alternative rotor 220R is depicted having rectangular rotor slots 131. Such a configuration may be configured with Figure 1 As is understood in the art, slots 29 and 129 in a complete configuration will be filled with ferromagnetic rotor bars of corresponding cross-sectional shape (e.g., in combination with Fig. 9 55) of the discussion. Relative performance can be found in Figure 7 and Figure 8 However, the higher speed performance of the LMB-based configuration of the x-ray tube 10 contemplated herein will benefit from Figure 8 design, especially in terms of increased torque performance and efficiency at higher rotational speeds.

[0042] refer to Fig. 9 The rotor 220R according to one aspect of the present disclosure includes a cylindrical end hub 51 having the above-mentioned rotation axis 200. The illustrated configuration includes an end ring 53 and an end ring 54, and a plurality of rotor bars 55 extend between the end ring 53 and the end ring 54. A rotor support 56 extends from the end ring 54. This type of rotor 200R may be equipped with a plurality of rotor teeth 220T, Fig.10 An exemplary embodiment of one of the rotor teeth is shown in FIG.

[0043] like Fig.10As shown in the representative embodiment of FIG. 2 , the rotor tooth 220T is symmetrical about the centerline 20A and includes a generally arcuate end 40 and a radial wall 52, so that the rotor slot 29 is defined as the space between the end 40 and the radial wall 52. The rotor tooth gap 58 separates the rotor tooth top 59, and for simplicity of description, Fig. 9 The rotor rod 55 from Fig.10 In a non-limiting embodiment, dimensions d8, d9, d 10 d 11 d 12 and d 13 When the rotor slots are trapezoidal, the depth-to-width ratio of each slot may be approximately 1.29:1, or within ±30% of such ratio. An exemplary set of such dimensions, [d8, d9, d 10 d 11 d 12 d 13 ] = [0.159, 0.265, 0.010, 0.060, 0.205, 0.080] inches. Other embodiments of similar or different scales are contemplated, and the dimensions shown are representative only for Figure 1 A possible configuration of the x-ray tube 10 is shown.

[0044] Fig.11 The various embodiments described above are shown in Figure 1 In one possible approach, a retaining bar 60 or other suitable tool may be inserted near the tooth top 320 within the stator slot 35. The stator slot 35 is lined with a suitable insulating slot liner material 62, with possible top and middle insulation layers 64 and 66 used within the stator slot 35 between different stator windings (not shown). After the stator assembly 20S is impregnated and baked / heat cured, the retaining bar 60 is removed, as is known in the art. The resulting space may be used to form a portion of the cooling zone 60 described in detail above.

[0045] Now turn to Fig.12 , Fig.12 It is available for Figure 1 Graph 70 of a representative efficiency progression for a representative VFD control scheme for an x-ray tube 10. In the overall control of the x-ray tube 10, one may seek to balance the VFD settings of the motor controller 50 and continuous operation at a particular speed at which the electric motor 20 is at its peak efficiency. In a possible implementation, a first setting may be used to ramp the speed of the electric motor 20 from zero to a predetermined maximum value, represented as an operating point 72, before switching to a high efficiency operating mode at the highest efficiency level.

[0046] Therefore, in possible control implementation, use Figure 1A motor controller 50 controls the electric motor 20 via the VFD, wherein the motor controller 50 is capable of switching between two or more specific mode control settings. These settings may include one control mode activated when the electric motor 20 is started from zero speed, another setting used during a specific steady-state operating speed of the electric motor 20, and one setting maintained during an x-ray exposure cycle in which the x-ray tube 10 is used to image a target.

[0047] In another approach, when the x-ray tube 10 has been idle for a period of time, the VFD operating mode may include a temporary "boost phase" during which the motor controller 50 increases the output power, such as to at least 120% of the power level used to maintain steady-state running operation. Because boosting is expected to inject more heat into the electric motor 20, its use should be limited. Other approaches, particularly for LMB embodiments of the x-ray tube 10, include maintaining steady-state rotation of the rotor 20R between x-ray exposures to prevent wear of the LMB and improve energy efficiency.

[0048] In view of the above disclosure, it should be understood by those skilled in the art that the inclusion of cooling regions in the overall structure of the stator assembly 20S ensures that the tips of the stator teeth remain immersed in cooling oil, which in turn improves the torque levels required for high energy tubes (including commercially available LMB tubes). As described herein, the cooling regions are integrated into the stator assembly, providing the benefit of reducing heat concentration in the rotor laminations present in a vacuum environment. As described above, the stator teeth protrude into the oil path to create a set of effective heat sinks and also reduce the gap size between the stator teeth and the OD of the rotor 20R. Due to the extended design of the stator teeth and the immersion in cooling oil, this type of positioning helps to ensure that the motor 20 runs cooler. The increase in efficiency, in turn, allows for the production of a more efficient x-ray tube 10.

[0049] Although these systems and methods have been described with reference to exemplary embodiments, it will be appreciated by those skilled in the art that various changes and equivalent substitutions may be made to adapt these teachings to other problems, materials, and techniques without departing from the scope of the claims. Features, aspects, components, or actions of one embodiment may be combined with features, aspects, components, or actions of other embodiments described herein. Therefore, the present invention is not limited to the specific examples disclosed, but includes all embodiments falling within the scope of the appended claims.

[0050] The claims following this written disclosure are hereby expressly incorporated into this written disclosure, with each claim standing on its own as a separate embodiment. This disclosure includes all permutations of independent claims and their dependent claims. In addition, additional embodiments that can be derived from subsequent independent and dependent claims are also expressly incorporated into this written description. These additional embodiments are identified by replacing the dependencies of a given dependent claim with the phrase "any claim starting with claim [x] and ending with the claim immediately preceding that claim", where the term "[x]" in parentheses is replaced with the number of the most recently cited independent claim. For example, for a first claim set starting with independent claim 1, claim 3 may be dependent on any of claims 1 and 2, where these independent dependencies yield two different embodiments; claim 4 may be dependent on any of claims 1, 2, or 3, where these independent dependencies yield three different embodiments; claim 5 may be dependent on any of claims 1, 2, 3, or 4, where these independent dependencies yield four different embodiments; and so on.

[0051] One aspect of the present disclosure relates to an x-ray tube system 10, comprising: a housing 15 containing cooling oil 19; a vacuum housing 12 disposed within the housing 15 and including a solid housing wall 12, wherein the cooling oil 19 is disposed between the housing 15 and the solid housing wall 12; an anode 16 and a cathode 18 disposed in a vacuum environment and surrounded by the solid housing wall 12; a rotor 20R connected to the anode 16 and disposed on a bearing 25 within the vacuum environment; and a stator assembly 20S positioned within the cooling oil 19 and surrounding the rotor 20R to define a filler There is an annular gap 12F filled with oil, and the stator assembly 20S includes: a stator core 30; a plurality of stator teeth 32, which extend from the stator core 30 and are separated from each other by a stator slot 35 in the middle; and a stator winding 34, which is arranged in the stator slot 35, wherein each corresponding stator tooth in the stator teeth 32 includes a corresponding tooth top 59 / 320, which is set to be separated from the stator winding 34 by a predetermined distance d1 to form an in-slot cooling channel 36 fluidly connected to the annular gap G2 filled with oil, so that the stator teeth 32 including the corresponding tooth top 59 / 320 are completely immersed in the cooling oil 19.

[0052] In some embodiments, bearing 25 comprises a liquid metal bearing.

[0053] In some embodiments, each respective one of the stator slots 35 has a respective tooth root 40 and defines a total slot volume extending between the tooth tip 59 / 320 and the respective tooth root 40 , wherein a ratio of copper of the stator winding in the stator slot to a total slot area of ​​the stator slot 35 is less than approximately 75%.

[0054] In some embodiments, the total slot volume is trapezoidal. In some embodiments, the total slot volume is defined by the curved slot wall 49. In some embodiments, the radial distance between the tooth top 59 / 320 and the corresponding tooth root 40 is less than 1 inch.

[0055] In some embodiments, the spacing between each tooth top 59 / 320 and a pair of adjacent tooth tops 59 / 320 is 0.5% to 4% of the inner diameter (ID) size of the stator core 30 .

[0056] In some embodiments, the distance from the tooth tip 59 / 320 to the stator winding 34 is at least 0.08 inches.

[0057] In some embodiments, the rotor 20R / 120R / 220R includes a plurality of rotor slots 29 / 129 / 131 each containing a corresponding ferromagnetic rotor bar 55 therein.

[0058] In some embodiments, the plurality of rotor slots 29 / 129 / 131 have a rectangular or trapezoidal cross-sectional shape.

[0059] In some embodiments, the inner diameter dimension of the stator core 30 is less than about 11 inches, and the length of the stator core is less than about 2.5 inches.

[0060] In some embodiments, the length of stator core 30 is between 13% and 76% of the inner diameter of stator core 30 .

[0061] In some embodiments, the longitudinal length dimension of the stator core 30 is between 35% and 40% of the inner diameter dimension of the stator core 30 .

[0062] In some embodiments, the rotor 120R / 220R includes a rotor core 133 / 135 , and a radial gap size between the rotor core 133 / 135 and the stator core 30 is between about 1.5% and 30% of an inner diameter size of the stator core 30 .

[0063] In some embodiments, the system may further include a motor controller 50 operable to switch between two or more mode-specific control settings, including a ramp setting activated when the rotor 20R / 120R / 220R begins rotating from zero speed, and a steady-state setting maintained during an x-ray exposure cycle in which the x-ray tube system 10 is used to image a target.

[0064] In some embodiments, using the ramp setting, the motor controller 50 is configured to temporarily increase the output power to at least 120% of the power level used to maintain the steady state setting.

[0065] Another aspect of the present disclosure is directed to a stator assembly 20S for use with an x-ray tube 10 having a rotatable anode 16 coupled to a rotor 20R, the stator assembly comprising: a stator core 30; a plurality of stator teeth 32 connected to the stator core 30 and spaced apart from each other by intermediate stator slots 35; and a stator winding 34 disposed within the stator slots 35, wherein each respective one of the stator teeth 32 includes a tooth top 59 / 320 positioned adjacent to the solid housing wall 12 and spaced apart from the stator winding a predetermined distance to form an in-slot cooling channel 36 in fluid communication with an annular gap G2 filled with oil 19, wherein the stator teeth 32 are immersed in the oil 19, and wherein the stator assembly 20S is configured to be positioned within the oil 19 and around the rotor 20R / 120R / 220R to define the annular gap G2.

[0066] In some embodiments, each respective one of the stator slots 35 has a respective tooth root 40 and defines a total slot volume extending between the tooth tip 59 / 320 and the respective tooth root 40 , wherein a ratio of copper of the stator winding in the stator slot to a total slot area of ​​the stator slot is less than about 50%.

[0067] In some embodiments, the stator assembly 20S includes a stator core 30 having an inner diameter dimension less than approximately 11 inches and a longitudinal length dimension less than approximately 2.5 inches.

[0068] In some embodiments, the longitudinal length dimension of the stator core 30 is between about 35% and 40% of the inner diameter dimension of the stator core 30. The recitation of the term "first" with respect to a feature or element in the claims does not necessarily imply the presence of a second or additional such feature or element. Pursuant to 35 U.S.C. §112(f), elements specifically recited in means-plus-function form, if any, are intended to be interpreted to cover the corresponding structures, materials, or acts described herein and their equivalents. Embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows.

Claims

1. An x-ray tube system, comprising: a housing containing cooling oil; a vacuum housing disposed within the shell and comprising a solid housing wall, wherein the cooling oil is disposed between the shell and the solid housing wall; an anode and a cathode, the anode and the cathode being arranged in a vacuum environment and surrounded by the solid housing wall; a rotor connected to the anode and disposed on a bearing within the vacuum environment; as well as a stator assembly positioned within the cooling oil and surrounding the rotor to define an annular gap filled with oil, the stator assembly comprising: stator core; a plurality of stator teeth extending from the stator core and spaced apart from one another by intermediate stator slots; and A stator winding is arranged in the stator slot, wherein each corresponding stator tooth in the stator teeth includes a corresponding tooth top, and the tooth top is set to be spaced apart from the stator winding by a predetermined distance to form an in-slot cooling channel connected to the annular gap fluid filled with oil, so that the stator tooth including the corresponding tooth top is completely immersed in the cooling oil.

2. The x-ray tube system of claim 1, wherein the bearing comprises a liquid metal bearing.

3. The x-ray tube system of claim 1 , wherein each respective one of the stator slots has a respective tooth root and defines a total slot volume extending between the tooth tip and the respective tooth root, and wherein a ratio of copper of the stator winding in the stator slot to a total slot area of ​​the stator slot is less than about 75%.

4. The x-ray tube system of claim 3, wherein the total slot volume is trapezoidal.

5. The x-ray tube system of claim 3, wherein the total slot volume is defined by curved slot walls.

6. The x-ray tube system of claim 3, wherein a radial distance between the tooth tops and corresponding the tooth roots is less than 1 inch.

7. The x-ray tube system of claim 1, wherein each respective tooth top is spaced apart from a pair of adjacent tooth tops by a distance between 0.5% and 4% of an inner diameter dimension of the stator core.

8. The x-ray tube system of claim 7, wherein a distance from the tooth tip to the stator winding is at least 0.08 inches.

9. The x-ray tube system of claim 1, wherein the rotor comprises a plurality of rotor slots, each of the plurality of rotor slots containing a corresponding ferromagnetic rotor bar therein.

10. The x-ray tube system of claim 9, wherein the plurality of rotor slots have a rectangular or trapezoidal cross-sectional shape.

11. The x-ray tube system of claim 1, wherein the stator core has an inner diameter dimension of less than approximately 11 inches and a length of the stator core of less than approximately 2.5 inches.

12. The x-ray tube system of claim 11, wherein the length of the stator core is between 13% and 76% of the inner diameter dimension of the stator core.

13. The x-ray tube system of claim 11, wherein a longitudinal length dimension of the stator core is between 35% and 40% of the inner diameter dimension of the stator core.

14. The x-ray tube system of claim 1, wherein the rotor comprises a rotor core, and wherein a radial gap size between the rotor core and the stator core is between about 1.5% and 30% of an inner diameter size of the stator core.

15. The x-ray tube system of claim 1 further comprising a motor controller operable to switch between two or more specific mode control settings, the two or more specific mode control settings comprising a ramp setting activated when the rotor begins rotating from zero speed, and a steady-state setting maintained during an x-ray exposure cycle in which the x-ray tube system is used to image a target.

16. The x-ray tube system of claim 15, wherein using the ramp setting, the motor controller is configured to temporarily increase output power to at least 120% of a power level used to maintain the steady state setting.

17. A stator assembly for use with an x-ray tube having a rotatable anode coupled to a rotor, the stator assembly comprising: stator core; a plurality of stator teeth connected to the stator core and spaced apart from each other by intermediate stator slots; as well as a stator winding disposed in the stator slots, wherein each respective one of the stator teeth includes a tooth tip positioned adjacent to a solid housing wall and spaced a predetermined distance from the stator winding to form an in-slot cooling passage in fluid communication with an annular gap filled with oil, wherein the stator teeth are immersed in the oil, and wherein the stator assembly is configured to be positioned within the oil and surround the rotor to define the annular gap.

18. The stator assembly of claim 17, wherein each respective one of the stator slots has a corresponding tooth root and defines a total slot volume extending between the tooth tip and the corresponding tooth root, and wherein a ratio of copper of the stator winding in the stator slot to a total slot area of ​​the stator slot is less than about 50%.

19. The stator assembly of claim 17, wherein the stator assembly comprises a stator core having an inner diameter dimension of less than about 11 inches and a longitudinal length dimension of less than about 2.5 inches.

20. The stator assembly of claim 19, wherein the longitudinal length dimension of the stator core is between about 35% and 40% of the inner diameter dimension of the stator core.

Images