Dual-ended X-ray tube electric motor

Abstract

An x-ray tube includes a housing filled with cooling oil and a vacuum envelope disposed within the housing, the housing including a solid envelope wall. The oil is disposed between the housing and the wall. An anode and a cathode are disposed within the vacuum environment and are surrounded by the wall. A rotor connected to the anode is disposed on a bearing within the vacuum environment. Additionally, a stator assembly disposed within the oil surrounds the rotor to define an oil-filled annular gap. The stator assembly includes a stator core, stator teeth spaced apart by intervening stator slots, and stator windings disposed within the stator slots. Each stator tooth includes a tooth tip adjacent to a boundary wall and spaced a distance from the stator winding, forming an in-slot cooling channel fluidly connected by the oil-filled annular gap such that the stator tooth, including the tooth tip, is immersed in the oil.

Description

[Background technology]

[0001] Vacuum tubes are used in a wide variety of applications to control the flow of electrical current between separate electrodes within a sealed vacuum chamber. X-ray tubes, in particular, are a specialized type of vacuum tube commonly used to generate and direct X-ray radiation for a variety of useful purposes, including medical imaging, radiology, diagnostics, radiography, tomography, nondestructive testing, materials analysis, security applications, and inspection. Traditional X-ray tubes operate by emitting a focused electron beam through an energized cathode. The emitted electron beam is then directed toward a target attached to an anode. In certain configurations, such as the high-energy dual-ended X-ray tube contemplated herein, the anode rotates via the action of an electric motor.

[0002] The emitted electrons gain energy and are accelerated by the large potential difference across the intervening space between the rotating anode and the stationary cathode. A portion of the accelerated electrons strike the target surface on the rotating anode, where a relatively small portion of the incident electron beam energy is converted into useful x-ray radiation. Most of the remaining energy becomes waste heat, which is dissipated from the x-ray tube via a cooling oil or other suitable cooling system. As a result, the thermal characteristics of the x-ray tube must be carefully regulated to protect the x-ray tube's electric motor and other heat-sensitive components.

[0003] The rotational force acting on the target anode disk in a high-energy dual-ended x-ray tube configuration is provided by the electric motor described above. In a typical configuration, the anode is driven by a small induction motor with a concentrically arranged rotor and stator. The rotor, located within the vacuum envelope, rotates on bearings. Liquid metal bearings (LMBs) are a new technology that offers numerous performance advantages over conventional metal bearings. The stator, for its part, is immersed in or surrounded by cooling oil outside the vacuum envelope, with the rotor and stator located on opposite sides of the solid envelope wall. However, tubes equipped with LMBs require higher levels of torque adequate to generate sufficient initial hydrodynamic lift while overcoming fluid friction at low speeds. Drag increases with rotor rotational speed. As a result of this relationship, high-speed operation of LMB-equipped tubes requires high levels of torque and excellent high-speed efficiency, both of which add significant thermal management challenges. Summary of the Invention

[0004] This disclosure relates to high-energy dual-ended X-ray tubes, where the stator is immersed in cooling oil and the opposing rotor is located in a vacuum and, as a result, is an insulator, presenting significant cooling challenges. In such X-ray tubes, the high anode potential necessitates a relatively large radial standoff distance between the rotor and the surrounding stator. For example, an exemplary radial gap of about 0.2 inches (5.08 mm) to about 0.6 inches (15.24 mm) may be used with the X-ray tubes described herein, an order of magnitude larger than typical radial gap sizes. Liquid metal bearing (LMB)-mounted dual-ended X-ray tubes such as those described above benefit from the integration of electric motors, which increases efficiency. One way to increase this efficiency is to reduce the large radial standoff distance. However, any reduction in stator-rotor gap can promote overheating. As a result, high-energy dual-ended X-ray tubes tend to be suboptimal in terms of their overall size and operating efficiency. Accordingly, various structural solutions presented herein attempt to reduce the standoff distance without adversely affecting operating efficiency. Such advantages are primarily provided by modifying the stator, as described in detail herein.

[0005] The term "standoff distance," as used herein and in the general art, includes (i) the thickness of the enclosure wall, (ii) the vacuum gap extending between the rotor and the inner side of the evacuated enclosure wall, and (iii) the oil-filled gap extending between the outer side of the evacuated enclosure wall and the surrounding stator. Cooling oil is circulated along the inner diameter (ID) of the stator assembly and through the oil-filled gap to prevent overheating of the stator and surrounding components of the X-ray tube. Reducing the standoff distance without further action can result in overheating of the X-ray tube, thereby raising thermal management concerns due to the need to extract excess heat from the cooling oil. Therefore, the following solutions also attempt to reduce the standoff distance without restricting the flow of cooling oil.

[0006] In particular, the solutions described below deviate from standard stator winding configurations by altering the flow path of circulating cooling oil and by modifying the spatial relationship between the stator slots and the windings disposed therein. As understood in the art, standard induction motors fill individual stator slots with conductive windings to provide a relatively large standoff distance. The modifications described herein result in a similar net cooling flow with a reduced standoff distance, thereby enabling increased output torque from the motor, improved overall performance, and improved operating efficiency. [Brief explanation of the drawings]

[0007] The drawings described herein are for illustration purposes only and are schematic in nature and are intended to be exemplary rather than limiting the scope of the present disclosure.

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

[0009] [Figure 1A] 2 is a partial cross-sectional view illustrating the stator assembly and rotor of the X-ray tube shown in FIG. 1, illustrating the radial stator-rotor gap.

[0010] [Figure 2] 2 is a typical performance curve illustrating a typical speed versus loss relationship for the X-ray tube depicted in FIG. 1.

[0011] [Figure 3] 2 is a top view of a stator assembly that can be used as part of the x-ray tube shown in FIG. 1; FIG.

[0012] [Figure 4] FIG. 4 is an explanatory view of a portion of the stator assembly shown in FIG. 3.

[0013] [Figure 5]FIG. 2 is a top view illustration of an exemplary stator tooth and slot arrangement according to one aspect of the present disclosure.

[0014] [Figure 6A] 5 is a schematic illustration of possible alternative slot geometries for constructing the stator assembly of FIGS. 3 and 4. FIG. [Figure 6B] 5 is a schematic illustration of possible alternative slot geometries for constructing the stator assembly of FIGS. 3 and 4. FIG.

[0015] [Figure 7] 2 is a plan view of another embodiment of a rotor assembly that can be used with the X-ray tube shown in FIG. 1. FIG. [Figure 8] 2 is a plan view of another embodiment of a rotor assembly that can be used with the X-ray tube shown in FIG. 1. FIG.

[0016] [Figure 9] 2 is an illustrative side view of a rotor assembly usable with the x-ray tube of FIG. 1;

[0017] [Figure 10] FIG. 10 is a plan view of an exemplary rotor tooth that can be used in the rotor assembly shown in FIG. 9.

[0018] [Figure 11] 1 is a top view of a representative stator tooth illustrating alternative methods for its manufacture or formation;

[0019] [Figure 12] FIG. 2 shows a plot of efficiency progression for a representative VFD control scheme usable with the x-ray tube of FIG. 1.

[0020] While the present disclosure is susceptible to modification and alternative forms, representative embodiments are shown by way of example in the drawings and are described in detail below. The inventive aspects of the present disclosure are not limited to the disclosed embodiments. Rather, the present disclosure is intended to cover alternatives that fall within the scope of the present disclosure as defined by the appended claims. DETAILED DESCRIPTION OF THE INVENTION

[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 to scale, and some features may be exaggerated or minimized to show particular details of interest. Therefore, specific structural and functional details disclosed herein should not be construed as limiting, but merely as a representative basis for teaching those skilled in the art how to employ the disclosed structures and methodologies in various ways.

[0022] Numbers in the flowcharts and process descriptions are intended to improve clarity and do not necessarily indicate a particular order or sequence. For purposes of this detailed description, approximation terms such as "about," "substantially," "generally," and "approximately" may each be used herein to mean "in, near, or approximately," or "within 0-5%," or "within acceptable manufacturing tolerances," or any logical combination thereof.

[0023] Referring now to the drawings, wherein like reference numerals refer to like components, an exemplary high-energy dual-ended x-ray tube 10 (hereinafter referred to as x-ray tube 10 for simplicity) is depicted in FIG. 1. The x-ray tube 10 contemplated herein is operable to generate and emit x-ray radiation 11 through a port 13 toward a subject to be imaged, such as a patient's chest or appendages (not shown). Such components include a solid enclosure wall 12 forming a vacuum enclosure, thus defining a vacuum chamber 14 ("VACUUM") as a void volume within which a positively charged anode assembly 16 and a negatively charged cathode assembly 18 are disposed. The solid enclosure wall 12, which in possible embodiments may be constructed of metal, ceramic, or glass, is enclosed within a housing 15 filled with cooling oil 19 ("OIL"). In a typical application, the cooling oil 19 may comprise a suitable transformer oil, i.e., dielectric oil, or other suitable dielectric liquid coolant. Thus, the solid enclosure wall 12 forms separate and isolated vacuum and fluid filled volumes, with the solid enclosure wall 12 also having a fluid side 12F and a vacuum side 12V.

[0024] In the two different operating environments of the x-ray tube 10 shown in FIG. 1 , the anode 16 and cathode 18 are disposed within the vacuum environment of the vacuum chamber 14. In various embodiments contemplated herein, the rotatable anode 16 is connected to an anode stem 160, which in turn is coupled to the rotor 20R of an electric motor 20 (including a rotor 20R and a stator 20S), e.g., an induction-type polyphase / four-pole squirrel-cage rotor, hereafter referred to as electric motor 20 for simplicity and brevity. Such electric motor 20, in some embodiments, can be controlled using speed control using a variable frequency drive (VFD) from a motor controller 50, whereby the motor controller 50 can adjust the frequency (f C ) and voltage (V C) to drive the electric motor 20. The rotor 20R, like the anode 16 and cathode 18 previously described, resides within the vacuum chamber 14, specifically within the axial neck 120 of the solid enclosure wall 12, and is mounted on bearings 25, e.g., mechanical roller bearings or liquid metal bearings (LMB) in different embodiments.

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

[0026] X-ray tube 10 is an example of a dual-ended x-ray tube having a high potential applied to anode 16. This high potential, as understood in the art, typically requires a large standoff distance (D), which as a result tends to be much larger than that typical of electric motors. A large standoff distance (D) hinders performance and efficiency. However, structural modifications made herein and described below with reference to FIGS. 2-12 allow the standoff distance (D) to be reduced, thereby providing significant performance improvements over the current state of the art.

[0027] Still referring to FIG. 1, the stator assembly 20S receives a voltage signal (V C), or via a corresponding current signal, the alternating forces of electromagnetic attraction and repulsion cause the rotor 20R to rotate about its longitudinal central axis 200. This in turn causes the anode 16, specifically the target disk 16D, constructed of, for example, tungsten, to rotate. The target disk 16D provides a physical target for interaction with the electrons emitted by the cathode 18, ultimately generating x-rays from such interaction. In a typical configuration, current flows through and heats the filament 21 of the cathode 18, causing electrons to be emitted via the process of thermionic emission, as will be understood by those skilled in the art.

[0028] Referring to Figure 2, a representative curve 22 illustrates the performance relationship between the rotational speed of the rotor 20R of Figure 1, listed in revolutions per minute (RPM) on the x-axis, and the bearing losses, listed in watts (W) on the y-axis. Figure 2 illustrates a particular challenge associated with the operation of the x-ray tube 10 of Figure 1 and similarly configured high-energy / double-ended vacuum tubes. The rotor 20R ultimately rotates at very high speeds, for example, from 5,000 RPM to 10,000 RPM or higher. However, as rotational speed increases, so do bearing losses.

[0029] In a possible embodiment of the present teachings, LMB technology can be retrofitted to an existing x-ray tube 10. However, the torque required from the electric motor 20 of FIG. 1 is higher in an LMB configuration than in a conventional ball-bearing-based tube to generate initial hydrodynamic lift and overcome fluid friction, as previously described herein. Curve 22 of FIG. 2 illustrates the significant increase in drag and resulting losses with increasing operating speed. Thus, while the present teachings are not limited to LMB tubes, such tubes would benefit from alternative configurations of the electric motor 20 of FIG. 1, specifically those with increased efficiency due to reduced standoff distance (D) and better overall cooling performance.

[0030] Referring now to FIG. 3 , stator assembly 20S is shown in plan view, i.e., viewed along central axis 200. The outer ring 30 of stator assembly 20S, which may alternatively be referred to as a stator core, forms a core support structure, with stator assembly 20S itself assembled from a stack of thin steel laminations, as understood in the art. Thus configured, stator assembly 20S has a cylindrical form with a plurality of radially extending stator teeth 32. Each of stator teeth 32 has a corresponding tooth tip 320 having a slightly arcuate shape such that stator teeth 32 are arranged end-to-end and spaced a short distance from one another by a tooth gap (e.g., 33). Such tooth gap 33 can be between about 0.5% and about 3.75% of the ID of the stator core, or in another embodiment, between about 1.5% and about 2%. Stator assembly 20S also includes electrically conductive stator windings 34 and phase leads 37, which are shown protruding from ring 30. As a result, stator windings 34, e.g., copper wire or cable, are wound around the stator teeth 32 to substantially fill the stator slots 35. However, unlike typical winding designs, cooling areas 36 are left open adjacent the stator teeth 32.

[0031] That is, this approach moves stator teeth 32 of stator assembly 20S closer to rotor 20R in Figure 1, thus placing oil flow in a path previously required. As a result, stator windings 34 are positioned further back in stator slots 35, thereby leaving tooth tips 320 open and surrounded by cooling oil in Figure 1. By directing flow to stator slots 35 through tooth gaps 33 located at the radially innermost surfaces of stator teeth 32, sufficient flow / equivalent head loss is provided with a reduced standoff distance (D) in Figure 1A.

[0032] The ratio of copper in the stator windings within the stator slots 35 to the total slot area is approximately 5% to 75% in a possible range, or approximately 30% to 35% in another embodiment. In a possible embodiment, the radial clearance between the rotor 20R and the stator assembly 20S can be approximately 1.8% to approximately 30% of the ID of the stator assembly 20S, or approximately 10% to approximately 12% in another configuration, where the ID is approximately 11 inches (approximately 279 mm) or less. The radial clearance can be between approximately 1.4% and approximately 20% of the outer diameter (OD) of the stator assembly 20S (e.g., the diameter of the ring 30 / stator core in FIG. 3 ), or its stator core, or approximately 5% to approximately 7% in another configuration, where the OD is approximately 14 inches (approximately 356 mm) or less in this example.

[0033] In the contemplated embodiment described below with reference to FIGS. 4-12, a substantial portion of the oil flow still passes between the inner diameter of the stator assembly 20S (e.g., the diameter extending between the opposing tooth tips 320 in FIG. 3) and the solid enclosure wall 12 in FIG. 1. However, the remaining oil flow passes through the cooling region 36, i.e., the unfilled portion of the stator slot 35 located near the tooth tips 320. This increases the surface area in contact with the cooling oil, and therefore increases the cooling of the stator assembly 20S. That is, without the disclosed enhancements, the high magnetic field at the tooth tips 320 would typically leave wasted heat and energy at this location. By introducing the cooling oil around the stator teeth 32 through this same cooling region 36, including the tooth tips 320, cooling efficiency is increased. Immersing the tooth tips 320 in the cooling oil 19 allows the tooth tips 320 to act as cooling fins, thereby promoting the cooling and efficiency benefits contemplated herein.

[0034] In the application contemplated herein, the rotor 20R resides in the insulating environment of the vacuum chamber 14, i.e., the rotor 20R resides in a vacuum environment. Accordingly, the rotor 20R cannot be efficiently cooled by circulating the cooling oil 19 of FIG. 1 . Thus, the x-ray tube 10 already generates significant heat during its operation and must manage additional heat from the rotor 20R. Inefficient cooling of the rotor 20R manifests itself as additional heat injection, thereby reducing the thermal overhead available for x-ray generation and increasing the time between exposures without the x-ray tube 10 or its bearings overheating. Particularly with LMB technology, the bearings 25 of FIG. 1 are susceptible to thermal seizure. This and other potential problems are mitigated through the use of a cooling zone (e.g., 36 shown in FIG. 3 ).

[0035] In terms of flow, at least 90% of the cooling oil 19 for cooling the stator assembly 20S should travel along the ID of the stator core and around the tips of the stator teeth 32. Thus, essentially none, or in this example less than 10%, of the cooling oil 19 travels across the OD of the stator core. Thus, the stator assembly is cooled by direct contact with the cooling oil 19 using a flow rate of approximately 0.5 gallons per minute (gpm) to 10 pgm, with associated geometries defined to maintain laminar flow even at such exemplary flow rates.

[0036] Referring now to FIG. 4, adjacent pairs of the stator teeth 32 of FIG. 3 are shown to further illustrate the cooling region 36. As noted above, the stator teeth 32 extend radially toward the solid enclosure wall 12, with the tooth tips 320 forming a generally T-shaped perimeter as viewed axially in FIG. 4. As envisioned herein, the cooling region 36 extends from the radially innermost surface 340 of the stator winding 34 to the solid enclosure wall 12. Thus, the stator teeth 32 and their tooth tips 320 are fully immersed in the cooling oil 19. In one exemplary configuration, the tooth tips 320 are spaced from the surface 340 by a distance (d1) of at least about 0.08 inches (2.032 mm).

[0037] An exemplary embodiment of a stator tooth 32 is shown in more detail in FIG. 5. A stator tooth 32, symmetrical about a centerline 32A, includes arcuate ends 40 (alternatively called tooth roots) and radial walls 42, whereby a stator slot 35 is defined as the space between the arcuate ends 40 and the radial walls 42. A tooth gap 33 separates the tooth tips 320. Dimensions d2, d3, d4, d5, d6, and d7 collectively describe the configuration of a stator tooth 32. A non-limiting exemplary set of such dimensions is [d2, d3, d4, d5, d6, d7] = [0.431, 0.078, 0.020, 0.010, 0.685, 0.970] inches ([10.9474, 1.9812, 0.508, 0.254, 17.399, 24.638] mm). Other embodiments with similar or different proportions are contemplated, and therefore the illustrated dimensions are intended to represent merely one possible configuration for use with the X-ray tube 10 of FIG. 1. In a possible configuration, the clearance (G2) between the solid enclosure wall 12 and the inner diameter (ID) of the stator core may be between about 0.3% and 3% of the ID dimension of the stator core, or in another embodiment, about 1% to 1.5%. Similarly, the radial clearance (G1) between the outer diameter (OD) of the rotor core (e.g., the outer diameter of the cores 133, 135 in FIGS. 7-8, or the outer diameter of the teeth extending from those cores 133, 135) and the solid enclosure wall 12 may be between about 1.5% and 50% of the outer diameter dimension of the rotor core, or in another embodiment, about 10% to 11%.

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

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

[0040] With brief reference to FIGS. 6A and 6B, the above-described shapes and dimensions of the stator teeth 32 may be varied within the scope of this disclosure to provide different levels of performance. For example, an alternative profile 145, as shown in FIG. 6A, may include polygonal walls 47 rather than the straight / single-walled approach of FIG. 5. Such an arrangement may be used to create a stator slot 135 having a generally hexagonal shape. Similarly, an alternative profile 245, as shown in FIG. 6B, may include curved surfaces 49 defining a stator slot 235 having a generally wedge-shaped or geometric shape, eliminating corners as opposed to FIGS. 5 and 6A, thereby providing possible advantages in shaping the desired magnetic flux concentration and resulting heating. Accordingly, the configuration of the stator teeth 32 described above may be varied within the scope of this disclosure without affecting the presence and benefits of the cooling region 36 surrounding the tooth tip 320.

[0041] Referring now to Figures 7 and 8, rotor 20R of Figure 1 can similarly vary in its configuration within the scope of the present disclosure. For example, Figure 7 contemplates rotor 120R having a plurality of generally circular rotor slots 129, while Figure 8 depicts alternative rotor 220R having rectangular rotor slots 131. Such a configuration can be configured for use with the three-phase / four-pole embodiment of electric motor 20 of Figure 1. Slots 29 and 129 in the completed structure would be filled with ferromagnetic rotor bars (e.g., 55 described in connection with Figure 9) of corresponding cross-sectional shape, as understood in the art. Relative performance may vary between the embodiments of Figures 7 and 8, or other possible embodiments. However, the higher speed capabilities of the LMB-based configuration of x-ray tube 10 contemplated herein would benefit from the design of Figure 8, particularly with regard to increased torque capability and efficiency at higher rotational speeds.

[0042] 9, a rotor 220R according to one aspect of the present disclosure includes a cylindrical end hub 51 having the aforementioned rotational axis 200. The illustrated structure includes end rings 53 and 54 between which extend a plurality of rotor bars 55. A rotor support 56 projects from end ring 54. Such a rotor 200R may include a plurality of rotor teeth 220T, one exemplary embodiment of which is shown in FIG. 10.

[0043] As shown in the exemplary embodiment of Figure 10, rotor teeth 220T are symmetrical about centerline 20A and include generally arcuate ends 40 and radial walls 52, whereby rotor slots 29 are defined as the spaces between ends 40 and radial walls 52. Rotor tooth gaps 58 separate rotor tooth tips 59, and rotor bars 55 of Figure 9 have been omitted from Figure 10 for ease of illustration. Dimensions d8, d9, d 10 , d 11 , d 12 , and d 13 collectively represent the configuration of rotor tine 220T in a non-limiting embodiment. If 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 setting of such dimensions is [d8, d9, d 10 , d 11 , d 12 , d 13 ]=[0.159, 0.265, 0.010, 0.060, 0.205, 0.080] inches ([4.0386, 6.731, 0.254, 1.524, 5.207, 2.032] mm). Other embodiments may be envisioned, with similar or different proportions, and thus the illustrated dimensions are intended to represent just one possible configuration for use with the x-ray tube 10 of FIG. 1.

[0044] The structure of the stator 20S of FIG. 1 according to the various embodiments described above is shown in FIG. 11. In a possible approach, a stop stick 60 or other suitable tool may be inserted into the stator slot 35 near the tooth tips 320. The stator slot 35 may be lined with an insulating slot liner material 62 appropriate for the application, and top and middle insulating layers 64 and 66 may be used within the stator slot 35 between different stator windings (not shown). After the stator assembly 20S is dipped and baked / thermoset, the stop stick 60 is removed, as understood in the art. The resulting space is then available to form a portion of the cooling region 60, as described in detail above.

[0045] Turning now to Figure 12, Figure 12 is an exemplary efficiency progression plot 70 for an exemplary VFD control scheme usable with the X-ray tube 10 of Figure 1. The overall control of the X-ray tube 10 can balance the VFD setting of the motor controller 50 and continuous operation at a particular speed where the efficiency of the electric motor 20 is maximized. In a possible implementation, a first setting can be used to ramp the speed of the electric motor 20 from zero to a predetermined maximum before switching to a high efficiency operating mode at the highest efficiency level, represented as operating point 72.

[0046] 1, the electric motor 20 is controlled via a VFD, where the motor controller 50 can switch between two or more mode-specific control settings. The settings may include one control mode that is active when starting the electric motor 20 from zero speed, and another setting that is used during a particular steady-state operating speed of the electric motor 20, where it is maintained during an x-ray exposure period when the x-ray tube 10 is used to image the target.

[0047] In another approach, if the X-ray tube 10 has been idle for some time, the VFD's operating mode can include a temporary "boost phase" during which the motor controller 50 increases the output power, for example, to at least 120% of the power level used to maintain steady-state driving operation. Boosting is expected to inject more heat into the electric motor 20, so its use should be limited. Other approaches, particularly LMB implementations of the X-ray tube 10, include maintaining steady-state rotation of the rotor 20R between X-ray exposures to prevent wear on the LMB and increase energy efficiency.

[0048] As will be appreciated by those skilled in the art in light of the foregoing disclosure, the inclusion of cooling regions in the overall structure of the stator assembly 20S ensures that the tips of the stator teeth remain submerged in cooling oil, thereby enabling increased torque levels at levels required for high-energy tubes, including commercially available LMB tubes. The cooling regions, integrated into the stator assembly as described herein, provide the advantage of reducing heat concentration within the rotor laminations, which reside in a vacuum environment. As noted above, the stator teeth protrude into the oil passages, forming an effective set of cooling fins while reducing the size of the gap between the stator teeth and the OD of the rotor 20R. Such an arrangement, due to the extended design of the stator teeth and their immersion in cooling oil, helps ensure cool operation of the motor 20. The resulting increased efficiency allows for the creation of a more efficient X-ray tube 10.

[0049] Although these systems and methods have been described with reference to exemplary embodiments, those skilled in the art will recognize that various modifications can be made, and equivalents substituted, to adapt these teachings to other problems, materials, and technologies without departing from the scope of the claims. Features, aspects, components, or operations of one embodiment may be combined with features, aspects, components, or operations of other embodiments described herein. Accordingly, the present invention is not limited to the particular examples disclosed, but rather includes all embodiments falling within the scope of the appended claims.

[0050] The claims that follow this disclosure document are expressly incorporated into this disclosure document, with each claim standing on its own as a separate embodiment. This disclosure includes all combinations of independent and dependent claims. Additionally, additional embodiments that can be derived from the following independent and dependent claims are also expressly incorporated herein. These additional embodiments are determined by replacing the dependency of a given dependent claim with the phrase "any of the claims beginning with claim [x] and ending with the claim immediately preceding this claim," where the parenthetical term "[x]" is replaced with the number of the most recently incorporated independent claim. For example, in the first set of claims beginning with independent claim 1, claim 3 can depend on either claim 1 or 2, resulting in two separate embodiments; claim 4 can depend on any one of claims 1, 2, or 3, resulting in three separate embodiments; claim 5 can depend on any one of claims 1, 2, 3, or 4, resulting in four separate embodiments; and so on.

[0051] One aspect of the present disclosure is a cooling oil cooling system comprising: a housing 15 containing cooling oil 19; a vacuum enclosure 12 disposed within the housing 15 and including a solid enclosure wall 12, wherein the cooling oil 19 is disposed between the housing 15 and the solid enclosure wall 12; an anode 16 and a cathode 18 disposed in a vacuum environment and surrounded by the solid enclosure 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 disposed within the cooling oil 19 and surrounding the rotor 20R to define an oil-filled annular gap 12F, wherein the stator Assembly 20S relates to an X-ray tube system 10 that includes a stator core 30; a plurality of stator teeth 32 extending from the stator core 30 and spaced apart from one another by intervening stator slots 35; and a stator winding 34 disposed within the stator slots 35, each one of the stator teeth 32 including a respective tooth tip 59 / 320 set a predetermined distance d1 from the stator winding 34, forming an in-slot cooling channel 36 fluidly connected by an oil-filled annular gap G2 such that the stator tooth 32, including each tooth tip 59 / 320, is fully immersed in cooling oil 19.

[0052] In some embodiments, bearings 25 include liquid metal bearings.

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

[0054] In some embodiments, the total slot volume is trapezoidal. In some embodiments, the total slot volume is defined by curved slot walls 49. In some embodiments, the radial distance between a tooth tip 59 / 320 and a corresponding tooth root 40 is less than 1 inch (25.4 mm).

[0055] In some embodiments, each tooth tip 59 / 320 is spaced apart from an adjacent pair of tooth tips 59 / 320 by a distance between 0.5% and 4% of the inner diameter (ID) dimension 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 (2.032 mm).

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

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

[0059] In some embodiments, the stator core 30 has an inside diameter (ID) dimension of less than about 11 inches (279.4 mm) and a length of less than about 2.5 inches (63.5 mm).

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

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

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

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

[0064] In some embodiments, the motor controller 50 is configured to use a ramp setting 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 relates 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 one another by intervening stator slots 35; and a stator winding 34 disposed within the stator slots 35, each one of the stator teeth 32 being positioned adjacent to a solid enclosure wall 12 and including a tooth tip 59 / 320 spaced a predetermined distance from the stator winding to form an in-slot cooling channel 36 fluidly connected by an annular gap G2 filled with oil 19, wherein the stator teeth 32 are immersed in the oil 19, and the stator assembly 20S is disposed within the oil 19 and configured to surround the rotor 20R / 120R / 220R to define the annular gap G2.

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

[0067] In some embodiments, the stator assembly 20S has a stator core 30 with an inner diameter dimension of less than about 11 inches (279.4 mm) and a longitudinal length dimension of less than about 2.5 inches (63.5 mm).

[0068] In some embodiments, the longitudinal length dimension of the stator core 30 is between approximately 35% and 40% of the inner diameter dimension of the stator core 30. In the claims, the recitation of the term "first" with respect to a feature or element does not necessarily imply the presence of a second or additional such feature or element. When an element is specifically recited in mean-plus-function format, it is intended to be construed to cover the corresponding structure, material, or acts described herein, and equivalents thereof, pursuant to 35 U.S.C. § 112(f). The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

Claims

1. Cooling oil-filled housing; A vacuum enclosure is disposed within the housing and includes the walls of a solid enclosure, wherein the cooling oil is located between the housing and the walls of the solid enclosure; Anode and cathode placed in a vacuum environment and surrounded by the walls of the solid enclosure; A rotor connected to the anode and positioned on a bearing in the vacuum environment; and The stator assembly is located in the cooling oil and surrounds the rotor so as to define an annular gap filled with oil, and the stator assembly is Stator core; A plurality of stator teeth extending from the stator core and spaced apart from each other by interposed stator rods; and The stator includes a stator winding arranged within the stator rod, and each stator tooth includes a tooth tip set to be separated from the stator winding at a predetermined distance, forming a fluid-connected cooling channel within the slot with an oil-filled annular gap, so that the stator tooth, including each tooth tip, is completely immersed in the cooling oil. X-ray tube system.

2. The X-ray tube system according to claim 1, wherein the bearing includes a liquid metal bearing.

3. The X-ray tube system according to claim 1, wherein each of the status lots has a corresponding tooth root, defining the total slot volume extending between the tooth tip and the corresponding tooth root, and the ratio of copper of the stator winding in the status lot to the total slot area of ​​the status lot is less than about 75%.

4. The X-ray tube system according to claim 3, wherein the total slot volume is trapezoidal.

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

6. The X-ray tube system according to claim 3, wherein the radial distance between the tooth tip and the corresponding tooth root is less than one inch (25.4 mm).

7. The X-ray tube system according to claim 1, wherein each tooth tip is spaced apart from an adjacent pair of tooth tips by a distance between 0.5% and 4% of the inner diameter dimension of the stator core.

8. The X-ray tube system according to claim 7, wherein the distance from the tooth tip to the stator winding is at least 0.08 inches (2.032 mm).

9. The X-ray tube system according to claim 1, wherein the rotor includes a plurality of rotor slots, each containing a ferromagnetic rotor bar.

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

11. The X-ray tube system according to claim 1, wherein the stator core has an inner diameter of less than 11 inches (279.4 mm) and a length of less than 2.5 inches (63.5 mm).

12. The X-ray tube system according to 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 according to claim 11, wherein the 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 according to claim 1, wherein the rotor includes a rotor core, and the radial clearance between the rotor core and the stator core is between approximately 1.5% and 30% of the inner diameter of the stator core.

15. The X-ray tube system according to any one of claims 1 to 14, further comprising a motor controller operable to switch between two or more mode-specific control settings, including a ramp setting which is activated when the rotation of the rotor starts from zero speed, and a steady-state setting which is maintained during the X-ray exposure period used to image a target.

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

17. A stator assembly comprising a stator core, a plurality of stator teeth connected to the stator core and spaced apart from each other by an interposed stator rod, and stator windings arranged within the stator rod; A rotatable anode connected to a rotor; and Equipped with solid outer walls, Each of the stator teeth includes a tooth tip positioned adjacent to the wall of the solid enclosure and set to a predetermined distance from the stator winding to form an in-slot cooling channel fluid-connected by an oil-filled annular gap, wherein the stator teeth are immersed in the oil, and the stator assembly is positioned in the oil and surrounding the rotor to define the annular gap. X-ray tube.

18. The X-ray tube according to claim 17, wherein each of the status lots has a corresponding tooth root, defining the total slot volume extending between the tooth tip and the corresponding tooth root, and the ratio of copper of the stator winding in the status lot to the total slot area of ​​the status lot is less than about 50%.

19. The stator assembly comprises a stator core having an inner diameter dimension of less than 11 inches (279.4 mm) and a longitudinal length dimension of less than 2.5 inches (63.5 mm), as described in claim 17 or 18.

20. The X-ray tube according to claim 19, wherein the longitudinal length dimension of the stator core is between approximately 35% and 40% of the inner diameter dimension of the stator core.

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