Air Cooled Metal Ceramic X-Ray Tube Construction

This invention relates to x-ray tubes and more particularly to air cooled metal ceramic x-ray tubes.

Typically in conventional x-ray tubes both the anode and the cathode are vacuum sealed in a glass envelope Electrons released by the hot cathode filament are accelerated toward the anode by a high voltage. These high energy electrons generate x-rays upon impact on the solid anode and at the same time generate copious amounts of heat. The tube is mounted in a housing to protect the environment from unwanted x-rays. The housing typically of a rotating anode x-ray tube is filled with oil to provide electrical insulation and also to absorb heat generated by the anode. Such conventional x-ray tubes have numerous disadvantages including high cost and relatively short lifetimes. The oil cooling utilized greatly increases the cost of insulation and also inhibits repair of the same. There is therefore a need for a new and improved x-ray tube construction which overcomes these disadvantages.

In general it is the object of the present invention to provide an x-ray tube construction which utilizes metal and ceramic in its construction rather than a glass envelope.

Another object of the invention is to provide a construction of the above character which can be manufactured to high precision allowing the incorporation of double-ended bearings.

Another object of the invention is to provide an x-ray tube construction of the above character in which a precise focal spot alignment can be obtained.

Another object of the invention is to provide an x-ray tube construction of the above character in which arcing created by filament evaporation onto glass is eliminated.

Another object of the invention is to provide an x-ray tube construction of the above character in which the back scattered electrons are absorbed by surrounding metal resulting in less off focus radiation and improved image contrast.

Another object of the invention is to provide an x-ray tube construction of the above character in which the bearings are protected from heat dissipated from the anode.

Another object of the invention is to provide an x-ray tube construction of the above character in which the feedthroughs and in particular the cathode feedthrough is protected from the anode heat.

Another object of the invention is to provide an x-ray tube construction of the above character which can withstand higher temperatures than can be accommodated with glass tubes.

Another object of the invention is to provide an x-ray tube construction of the above character in which greatly improved heat dissipating qualities have been incorporated into the tube.

Another object of the invention is to provide an x-ray tube construction of the above character having an improved x-ray window construction.

Another object of the invention is to provide an x-ray tube construction of the above character which includes improved cable terminations.

Another object of the invention is to provide an x-ray tube construction of the above character in which the high voltage receptacles provided can accommodate various types of federal standard terminals.

Another object of the invention is to provide an x-ray tube construction of the above character in which different types of high temperature shafts can be accommodated.

Another object of the invention is to provide an x-ray tube construction of the above character having high temperature shafts which carry heat emissive coatings thereon to facilitate the emission of heat from the shaft.

Another object of the invention is to provide an x-ray tube construction of the above character which eliminates the need for an insulating oil bath and which can operate with and without forced air cooling.

Another object of the invention is to provide an x-ray tube construction of the above character which is of reduced size and weight.

Another object of the invention is to provide an x-ray tube construction of the above character in which the bearing life is improved dramatically.

Another object of the invention is to provide an x-ray tube construction of the above character which makes possible the use of heavier anodes with resulting higher heat storage capacity.

Another object of the invention is to provide an x-ray tube construction of the above character in which a heat cage is provided which is thermally extended to the rear end of the tube to provide an efficient heat exchange with forced air cooling.

Another object of the invention is to provide an x-ray tube construction of the above character in which forced air cooling is utilized.

Another object of the invention is to provide an x-ray tube construction of the above character in which heat dissipated from the anode is diverted to the exterior before reaching the extremities of the shaft.

Another object of the invention is to provide an x-ray tube construction of the above character in which the shielding is in intimate contact with the aluminum housing and the stainless steel envelope to provide excellent heat transfer characteristics.

Another object of the invention is to provide an x-ray tube construction of the above character in which replacement of the tube in the field can be readily accomplished.

Another object of the invention is to provide an x-ray tube construction of the above character in which a ceramic coupling is provided between the shaft and the rotor permitting the rotor to operate at the same ground potential as the stator.

Another object of the invention is to provide an x-ray tube construction of the above character in which intimate electromagnetic coupling is achieved between the rotor and the stator.

Another object of the invention is to provide an x-ray tube construction of the above character in which the anode can be rapidly accelerated and decelerated.

Another object of the invention is to provide an x-ray tube construction of the above character which can lend itself to compact lightweight applications such as for mobile systems, C-ARM and mammography.

Another object of the invention is to provide an x-ray tube construction of the above character in which microfocus x-ray spots can be obtained.

Another object of the invention is to provide an x-ray tube construction of the above character which permits a higher anode speed making possible reduced anode diameter without losing power capability and the requirements needed for mammography and other similar applications.

Additional objects and features of the invention will appear from the following description in which the preferred embodiments are set forth in the accompanying drawings.

FIG. 1 is a side elevational view with certain portions broken away of a air cooled metal ceramic x-ray tube construction incorporating the present invention.

FIG. 2 is an end view looking along the line 2--2 of FIG. 1.

FIG. 3 is an end view looking along the line 3--3 of FIG. 1.

FIG. 4 is a cross sectional view taken along the line 4--4 of FIG. 1.

FIG. 5 is an enlarged partial cross-sectional view showing the rear bearing construction utilized in the construction shown in FIG. 4.

FIG. 6 is an enlarged cross-sectional view of the central portion of the drive shaft and showing the anode plate mounted thereon.

FIG. 7 is an enlarged cross-sectional view showing the construction of the x-ray tube in the vicinity of the x-ray window.

FIG. 8 is an enlarged cross-sectional view of the anode feedthrough and the front bearing construction.

FIG. 9 is a cross-sectional view showing the cathode feedthrough and the cathode assembly.

FIG. 10 is a cross-sectional view showing the cathode feedthrough and cathode assembly rotated by 90.degree. from that shown in FIG. 9 but omitting the male banana type plugs and the spring metal clamps.

FIG. 11 is a cross-sectional view of another embodiment of a shaft for the tube construction shown in FIG. 1.

FIG. 12 is a partial cross-sectional view taken along the line 12--12 of FIG. 11.

FIGS. 13A, 13B, 13C and 13D are plan views of four different inserts used to accommodate four different federal terminations in the high voltage receptacles in the x-ray tube construction.

FIG. 14 is a cross-sectional view similar to that shown in FIG. 3 showing another embodiment of an x-ray tube construction incorporating the present invention and taken along the line 14--14 of FIG. 17.

FIG. 15 is a top plan view of the anode plate shown in FIG. 14.

FIG. 16 is an isometric view of the coupling for mounting the anode plate on the shaft as shown in FIG. 13.

FIG. 17 is a top plan view of the end cap shown in FIG. 14.

FIG. 18 is a cross-sectional view taken along the line 18--18 of FIG. 17.

FIG. 19 is a cross-sectional view of a syringe showing the same used for making a cable terminal.

FIG. 20 is a cross-sectional view of a cable terminal made with the syringe shown in FIG. 19.

In general, the x-ray tube construction of the present invention is comprised of a housing with a metal tube envelope therein and a shaft. An anode plate is carried by the shaft. Bearings are disposed on opposite sides of the anode plate and rotatably mount the shaft in the envelope. A motor drive is coupled to the shaft for rotating the shaft and the anode plate carried thereby. A cathode is provided for supplying electrons which are accelerated by a high voltage to the anode plate for creating x-rays upon impingement with the anode plate. A heat cage is disposed in the housing and the envelope and surrounds the anode plate. X-ray shielding means is disposed within the housing between the envelope and the housing. Windows are provided in the shielding means, the metal envelope and in the heat cage to permit x-rays to pass therethrough. Particularly novel means is provided for dissipating the heat generated in the anode and for dissipating the same exterior of the housing prior to the heat passing to the opposite extremities of the shaft. Shaft constructions have been utilized which inhibit the travel of heat to the opposite ends of the shafts and thereby serving to protect the bearings rotatably supporting the shaft.

As shown more particularly in FIGS. 1-13 of the drawings, the air cooled metal ceramic x-ray tube construction 21 consists of a cylindrical housing 22 formed of a suitable material such as aluminum. The cylindrical housing 22 can be formed as an investment casting. The housing 22 is closed at one end and open at the other end to provide a cylindrical interior recess 23 which is coated to facilitate the adherence of lead thereto. For this purpose an electroless nickel plating is provided. The exterior of the cylindrical housing 22 is provided with a flat 24 on one side thereof which serves as a collimator support base. It is provided with a plurality of threaded holes 26 provided in two spaced parallel rows extending longitudinally of the housing and four additional threaded holes 27 disposed at the corners of an imaginary rectangle surrounding an opening 28 which can accommodate multipurpose windows to permit the x-ray tube 21 to be utilized for CT as well as conventional x-ray imaging. As can be seen the opening 28 is basically in the form of a rectangle which can be utilized for conventional x-ray imaging. It is also provided with sidewardly extending slots 29 disposed on two sides of the rectangular opening 28 to facilitate use with a 60.degree. fan beam for CT scanning.

The exterior surface of the cylindrical housing with the exception of the flat 24 is provided with longitudinally and radially extending fins 31 which are spaced circumferentially exterior of the cylindrical housing 22. The fins 31 serve as heat radiating fins. By way of example, 36 of such fins can be provided around the outer circumference of the housing 22. The housing 22 on its extremities is provided with trunnion interfaces 32 and 33 which as is well known to those skilled in the art are utilized for mounting the x-ray tube in the apparatus in which the tube is to be utilized. The closed end portion 22a of the cylindrical housing is provided with a centrally disposed hole 34 extending through the same. The portions 31a of the fins 31 extending longitudinally beyond the closed end portion 22a have slots 36 extending therethrough through which air can pass as hereinafter described. The housing is also provided with a pair of diametrically disposed cylindrical recesses 37 (see FIG. 2) which extend into and between two fins 31 and are adjusted to receive connectors of a conventional harness (not shown) to provide power for a purpose hereinafter described.

A cylindrical vacuum envelope 41 is mounted within the cylindrical recess 23 of the cylindrical housing 22. The vacuum envelope is open at one end. The vacuum envelope 41 is provided with a circular base 42 which has a thin walled cylindrical sleeve 43 secured thereto by suitable means such as welding or brazing. The base 42 can be formed of a suitable material such as copper of the type hereinafter described. The sleeve 43 can be formed of a suitable material such as stainless steel. The sleeve 43 is provided with thinned wall portion 43a which serves as a window through which x-rays can pass as hereinafter described. The thinned wall portion can be provided by machining a rectangular recess on the exterior surface of the sleeve 43 to provide a thinned wall portion 43a of a suitable thickness such as approximately 0.005 inches. The base 42 closes the other end and is provided with a hole 44 which is in registration with the hole 34 in the housing 22. A lead liner 46 is provided between the vacuum envelope 41 and the interior of the cylindrical housing 22. This lead envelope can be formed in a suitable manner such as by pouring molten lead into the space between the vacuum envelope 41 and the interior of the cylindrical housing 22. Since the interior wall of the cylindrical housing 22 has been coated with electroless nickel, the introduction of the lead into the cylindrical recess 23 causes a solder-like bond to be formed between the lead and the cylindrical housing 32 and the sleeve 43 of the tube envelope 41. The lead liner 46 serves two purposes, first as a massive heat sink for the x-ray tube construction and second as a shield against stray radiation which may attempt to pass from within the tube. Because of the excellent bond formed between the lead liner and the aluminum housing 22, there is good heat transfer from the lead to the housing and the fins 31 carried by the housing. A window 47 is provided in the lead liner 46 which is in registration with the opening 28.

A cylindrical heat cage 48 is provided within the interior of the vacuum envelope 41. This heat cage has one end seated in an annular recess 49 provided in the base 42 of the vacuum envelope 41 and is bonded therein by suitable means such as soldering or brazing. The lower extremity of the heat cage 48 is provided with a plurality of holes or openings 51 which are spaced circumferentially around the heat cage 48 and are provided to permit the escape of any cleaning agent which may be used during assembly and becomes entrapped between the cage 48 and the sleeve 43.

The heat cage 48 is formed of a suitable material such as a chromium copper in which the chromium content is approximately 1% by weight. The copper is provided with a chromium content so that it is possible to cause an oxide of chromium to be formed on the exterior surface of the same during heating of the same in an atmosphere of wet hydrogen. It has been found that this oxidation process provides a greening of the exterior surface caused by the formation of a chromium oxide coating on the exterior surface of the heat cage. This coating provides an excellent heat emission surface which substantially enhances the heat dissipating capabilities of the heat cage 48.

The heat cage 48 can be formed in a suitable manner such as by casting. Alternatively it can be formed from machined copper and chromium plated to provide a chromium oxide emissive coating. The heat cage 48 is provided with a window 53 which is in registration with the opening 28 provided in the cylindrical housing 22 through which the x-rays which are generated within the tube 21 can pass as hereinafter described.

A curved plate 56 (see FIG. 7) which is curved in one direction is formed of a suitable material such as beryllium. Beryllium is desirable because it has a low absorption coefficient for x-rays but provides protection for the stainless steel window portion 43a from damage by secondary electrons being emitted from within the tube 21.

The plate 56 which serves as an x-ray window is held in place over the openings 28 and 53 by suitable means such as brazing it to the heat cage 48. Alternatively the plate can be loosely held in a frame (not shown) secured between the sleeve 43 and the heat cage 48. By way of example the beryllium window can have a thickness of approximately 40 mils to protect a stainless steel wall 5 mils thick.

A shaft assembly 61 is rotatably mounted within the cylindrical housing 22 and the envelope 41 and extends through the holes 44 and 34. The shaft assembly 61 consists of a shaft 62 formed of a suitable material which is capable of withstanding high temperatures. For example a material called Hastelloy or also identified as Haynes No. 230 can be used.

The shaft 62 is hollow as shown and can be formed in a suitable manner such as by machining. It is provided with a thickened portion 62a which is intermediate the ends of the shaft. The thickened portion is provided with an annular seat 63 which abuts a shoulder 64. The shaft 62 is provided with relatively long thin-walled portions 62b and 62c on opposite ends of the thicker portion 62a. The portions 62b and 62c can have a suitable wall thickness as for example 0.020 to 0.025 inches. These thin-walled portions are provided to inhibit the travel of heat towards both extremities of the shaft.

The Hastelloy material from which the shaft 62 is formed has a high percentage of chromium in it as for example in the range of approximately 32% by weight. The shaft is heated up to a suitable temperature as for example approximately 1,100.degree. C. in a wet hydrogen atmosphere to cause a chrome oxide coating to form on the shaft which has the greenish appearance. This oxide coating on the exterior of the shaft 62 provides excellent heat emission from the shaft.

A solid ceramic coupling 66 is mounted on one end of the shaft 62. It is provided with metal Kovar collars 67 and 68 on opposite ends thereof. The metal collar 67 is secured to one end of the Hastelloy shaft 62 by suitable means such as brazing. The coupling 66 has a skirt portion 66a to enhance the voltage insulating capabilities of the part. The metal collar 68 at the other end of the coupling 66 is also secured by suitable means such as brazing to a cylindrical sleeve 71 of a suitable material such as stainless steel.

The sleeve 71 (see FIG. 5) serves as a rotor support and has a cylindrical squirrel cage rotor 72 mounted thereon and held in place by a circular plate or washer 73 formed of suitable material such as stainless steel. The plate 73 is secured to the rotor support sleeve 71 by suitable means such as screws 74. A drive pin 76 is carried by the outer extremity of the plate 73 and extends upwardly into the squirrel cage rotor 72. The squirrel cage rotor 72 is formed in a conventional manner as for example of alternating strips of copper and magnetic steel. The washer 73 can be utilized for balancing purposes for balancing one end of the shaft 62. This can be accomplished by removing the plate or washer 73 and shaving material from the same in appropriate locations to achieve the desired balance for the shaft assembly 61.

Means is provided within the envelope 41 for mounting the shaft assembly 61 for rotatable movement within the envelope in a direction in which the axis of rotation extends longitudinally of the envelope 41. Such means is provided for mounting one end of the shaft carrying the rotor 72 and consists of a rear ball bearing assembly 81 (see FIG. 5) having an outer race 82 which is mounted within and secured to the rotor support sleeve 71. The outer race 82 is adapted to rotate with the rotor support sleeve 71. The inner race 83 of the ball bearing assembly is held in a stationary position with respect to the envelope and is supported in such a manner so as to accommodate the expansion and contraction of the ball bearing assembly 8 assembly 81 during operation of the x-ray tube 21. A flanged bearing support member 84 extends into the inner race 83 and is secured to the inner race 83 by suitable means such as a collar 86 overlying a wave washer 87 engaging the inner race. The collar 86 is retained against the yieldable wave washer 87 by a pin 88 extending through the flanged bearing support member 84. The flanged bearing support member 84 is provided with a bore 91 which is adapted to receive a pin 92 that extends at right angles from a circular support plate 93. The pin 92 is provided with a flat 94 extending longitudinally of the same and disposed on one side of the pin 88. The flat 94 is adapted to engage the pin 88 extending substantially diametrically of the flanged bearing support member 84. This prevents rotation of the flanged bearing member 84 and the inner race 83 carried thereby while accommodating expansion and contraction of the shaft assembly 61 axially or longitudinally of the shaft assembly 61.

A rotor housing 96 is provided for enclosing the rotor 72 within a vacuum-tight enclosure and also for providing support for the support plate 93 to prevent rotation of the same. This rotor housing 96 consists of a rotor sleeve 97 which has one end bonded in the hole 44 of the plate 42 by a suitable means such as brazing. The other end of the rotor sleeve 97 is closed off by rotor end plate 98 that is secured to the rotor sleeve 97 by suitable means such as brazing. The rotor sleeve 97 is provided with a thin wall portion 97a intermediate the ends of the same as for example having a thickness of approximately 12 mils to provide good magnetic coupling between the rotor and the stator. The support plate 93 is mounted in a fixed position within the rotor housing 96 by a suitable means such as a C-ring 98 seated in an annular recess 99 provided on the interior surface of the rotor sleeve 97. From the foregoing construction it can be seen that the interior of the rotor sleeve is in communication with the interior of the vacuum envelope 41.

Front bearing support means 101 (see FIG. 8) is provided for mounting the other end of the shaft 62 and consists of a cylindrical cup-shaped front bearing housing 102 which is seated within the front extremity of the shaft 62. The outer race 103 of a front ball bearing assembly 104 is seated within the front bearing housing 102 for rotation therewith. The outer race 103 of the ball bearing assembly 104 is retained within the cup-shaped front bearing housing 102 by suitable means such as a C ring 106. Yieldable spring means is provided in the form of a helical coil spring 107 (see FIG. 4 and FIG. 8) formed of a suitable high temperature material such as stainless steel or Inconel which has one end engaging the front bearing housing 102 and has the other end engaging a washer 108. The washer 108 engages a push-rod pin 109 (see FIG. 8) which is mounted in a push-rod 111. The push-rod 111 is slidably mounted in the front bearing housing 102 and has its rear distal extremity adapted to engage a push disc 112 (see FIG. 6) slidably mounted within the shaft 62. The push disc 112 is provided with a dished recess 113 which is adapted to receive the rear end of the push-rod 111. The push disc 112 engages a clamping pin 116 which extends through elongated slots 117 provided in the shaft 62. The longer axes of the slots 117 extend in a direction axially of the shaft 62. The outer extremities of the clamping pin 116 are seated in slots 118 provided on the front surface of an anode washer 119. The anode washer 119 engages an anode plate 121 which is mounted on the annular seat 63 of the shaft 62 and is seated against the shoulder 64. The anode washer 119 is yieldably retained in engagement with the shoulder 64 by the pin 116 which is yieldably urged rearwardly by the spring 107. From the construction hereinbefore described it can be seen that the spring 107 serves to yieldably urge the anode plate 121 towards the shoulder 64 provided on the shaft 62.

The anode plate 121 is provided with a special surface 122 formed of rhenium tungsten material of a conventional type. It can be seen that the surface 122 is disposed at an angle and is positioned so that electrons striking the same will form x-rays that will pass through the opening 28. A large annular graphite block 126 is carried by the anode plate 121 and serves as a large heat sink as hereinafter described.

The front ball bearing assembly 104 is provided with an inner race 131 (see FIG. 8). A front bearing support member 132 is mounted in the inner race. A spacer 133 is mounted on the bearing support member 132 and engages the inner race 131. The bearing support member 132 also extends through a hole 134 provided in a bearing support bracket 136 and is retained in the hole 134 by a nut 137 threaded onto the front bearing support member 132 to retain the inner race of the ball bearing assembly in a stationary or non-rotatable position while retaining it in a fixed position within the tube envelope 41. The L-shaped bracket 136 is mounted upon a crossbar 139 formed of a suitable high temperature non-conducting insulating material such as silicon nitride. The bracket 136 is retained on the bar 139 by a spring clamp 141 secured to the bracket 136 by a suitable means such as a bolt 142. The bar 139 extends across the vacuum envelope 41 and is mounted upon a pair of support brackets (not shown) on opposite ends of the same which. support the same on a circular cross plate 146 (see FIG. 4). The brackets (not shown) which carry the bar 139 and the plate 146 are formed of a suitable metal such as stainless steel. The cross plate 146 overlies a cage cover plate 147 formed of the same copper material as the copper heat cage 48. The cover plate 147 overlies an annular flange 148 provided on the cage 48. Means is provided for establishing intimate contact between the cover plate 147 and the flange 148 of the cage 48 and includes a C-ring 151 seated in annular recess 152 in the cage 48. The C-ring 151 captures the outer circumferential surface of the cross plate 146. The cross plate 146 carries a plurality of screws 153 near its outer margin which are adapted to engage the cover plate 147. It can be seen by adjusting the screws 153 large forces can be provided on the cover plate 147 to form a n intimate contact with the flange 148 when the cross plate 146 is in engagement with the C-ring 151.

The cover plate 147 and the cross plate 146 are provided with aligned openings 154 and 156 through which the shaft assembly 61 extends and on which the anode plate 121 is mounted. A major amount of the heat given off by the anode plate 121 is absorbed by the cross plates 146 and 147 to protect the front bearing assembly 104 from high heat. The heat from the cross plates 146 and 147 enters the heat cage 48 which dissipates the heat through the lead liner 46 and the finned cylindrical housing 22.

A circular mounting ring 161 is mounted on the end of the sleeve 43 and is of greater thickness than sleeve 43. The mounting ring 161 is secured to the sleeve 43 by suitable means such as brazing. A circular terminal or top mounting plate 162 is mounted upon the mounting ring 161. The mounting ring 161 is formed of a suitable material such as stainless steel material hereinbefore described. The plate 162 is formed of a suitable material such as stainless steel also. To augment the seal which is provided between the mounting ring 161 and the plate 162, a strip 163 of a suitable material such as stainless steel is welded to the plate 162 and to the mounting ring 163. When it is desired to remove this seal, this stainless steel ring 163 can be removed by machining and then the top cover plate 162 can be removed to facilitate the repair of the tube when necessary.

A cup-shaped ceramic anode feedthrough 166 and a cup-shaped ceramic cathode feedthrough 167 are mounted in holes 168 and 169 provided in the cover plate 162. The feedthroughs 166 and 167 are of conventional construction and are provided with Kovar metal skirts 171 which are welded to the stainless steel cover plate 162 to provide vacuum-tight seals. The anode feedthrough 166 is provided with a single external female terminal 174 which receives an internal male banana-type plug 176 mounted within the feedthrough 166. The terminal 174 engages the metal spring clamp 141. The clamp 141 carries a coil spring 177 through which the terminal 174 extends. The spring 177 makes electrical contact with the plate 178 which is electrically connected to the terminal 174. The clamp 141 makes electrical contact to the anode shaft 62 through the bracket 196 and through the front ball bearing assembly 104.

The cathode feedthrough 167 is provided with five female terminals with one central grid terminal 181 and one common terminal 182 and three filament terminals 183 disposed around the central terminal 181. Corresponding male banana-type plugs 184 are mounted internally of the feedthrough 167 in the female terminals 181 182 and 183.

A conventional cathode assembly 186 is provided which has three filaments 187. One end of each of the filaments 187 is connected to one of the filament terminals 183 and the other end is connected to the common terminal 182. One of the filaments 187 is shown in FIG. 9. The cathode assembly 186 is carried by a pair of screws 188 (see FIG. 10) which are threaded into the cathode assembly 186. The screws 188 are carried by a quartz disc 191 which is provided as a subassembly 192 and is mounted upon the terminals 181, 182 and 183 of the cathode feedthrough 167. Lock nuts 189 are provided on the screws 188 and serve to clamp the cathode assembly 186 onto the screws. Lock nuts 190 are also provided on these screws and serve to secure the screws to the quartz disc 191. This subassembly 192 can be supported in a suitable manner. For example, as shown in particularly FIGS. 9 and 10, a second quartz disc 193 is provided which is also mounted upon the terminals 181, 182 and 183 and engages a metal washer 194 mounted on the terminals and disposed between the disc 193 and the lower extremity of the cathode feedthrough 167. Additional washers 196 are mounted on the same terminals and serve to space the quartz disc 191 from disc 193. Spring-like contact elements 197 in the form of metallic strips of a suitable material such as nickel are provided. These strips 197 are provided with U-shaped extremities 197a which are secured to the outer extremities of the terminals 181, 182 and 183 by C-rings 198. Coil springs 199 are also mounted on the terminals 181, 182 and 183 between the U-shaped extremities 197a. The springs 199 serve two functions, one to yieldably urge the quartz disc 191 in a direction toward the feedthrough terminal 167 and the other to ensure that the spring-like strips 197 make good electrical contact with the terminals. The other ends of the strips 197 are secured to posts 200 provided on the cathode assembly 186.

Additional means is provided for insulating the cathode assembly from heat and consists of an outer sleeve 202 of stainless steel surrounding a quartz tube 203. The upper extremity of the stainless steel sleeve 202 is secured to the cover plate 162 by bringing it to the lower extremity of the skirt 171 of the cathode feedthrough 167. The sleeve 202 can be of suitable thickness such as 0.005 inch. As be seen particularly in FIG. 4, the cathode assembly 186 extends through holes 206 and 207 provided in the plates 147 and 146. Electrons emitted from the filament 27 are directed onto the rhenium tungsten surface 132 to create x-rays which travel through the window 28. The cover plate 162 is provided with a pinch-off tube 211 which can be pinched off after the vacuum envelope 41 has been evacuated. A cover 212 is provided for covering the pinch-off tube 211. A viewing window (not shown) is also provided in the cover plate 212.

A termination is provided for the x-ray tube which conforms to present federal termination standards for x-ray tubes. Thus there has been provided an end cap 216 formed of a suitable material such as lead which seats over one extremity of the cylindrical housing 22. The end cap 216 is provided with a planar surface 217 in which two receptacles 218 and 219 are provided of a conventional type. The space within end cap 216 not required for the receptacles 218 and 219 and the space within the anode and cathode feedthroughs 166 and 167 can be filled with a suitable insulating material 221 such as an RTV silicon rubber. Cables 222 and 223 with appropriate terminations are mounted in the receptacles 218 and 219. The cables 222 and 223 are adapted to be connected to a suitable high voltage source.

Suitable means is provided for securing the end cap 216 (see FIG. 144) to the cylindrical housing 22 to ensure that there is no leakage of x-rays from within the tube. Such means consists of hook-like elements 226 formed of stainless steel having one hook-like portion 226a secured to the plate 162 and which extend outwardly between the interior of the lower extremity of the end cap 216 and the exterior of the cylindrical housing 22. The hook-like elements 226 also have hook-like portions 226b which are connected to hook-like portions 227a of yieldable means in the form of springs 227 which extend longitudinally of the cylindrical housing between the fins 31 (see FIG. 1). Hook-like elements 227b provided on the other ends of the springs 227 are secured to the other end of the housing 22 by connection to the trunnion interface 32.

A stator assembly 231 is provided as a part of the squirrel cage motor for the x-ray tube. It is of conventional construction and is provided with a laminated core 232 which carries windings 233. Means is provided for securing the stator assembly 231 to the cylindrical housing 22 and consists of threaded bushings 236 which are secured to the core by suitable means such as welding. Screws 237 are threaded into the threaded bushings 236 and extend inwardly to engage the bottom side of the housing 22. Springs 238 are provided on the screws between the bushings 236 and a triangular plate 239. Means is provided for securing the plate 239 to the housing 22 and consists of springs 241 which have one end of the same hooked to the corners of the triangular plate 239 and have the other end secured to pins 242 carried by the housing 22. A fan assembly 246 is mounted on the plate 239 and is provided with a centrally disposed motor 247 which drives a fan blade 248.

Suitable means is provided for enclosing the fan assembly 247 and the rear extremity of the finned housing 22 and includes a cylindrical grill 251 and an end cover grill 252. The cylindrical grill 251 and the end cover grill 252 can be spot welded to each other and secured to the housing 22 by suitable means such as springs (not shown).

Means is provided for supplying power to the stator assembly 231 of the squirrel cage motor and to the fan assembly 246 and consists of a terminal block 253 secured to the housing 22 (see FIG. 1) and connected to a cable 254 disposed longitudinally of the tube 21 between two of the finds 31 and connected to a connector 256 which is adapted to be connected to a suitable source of power such as 110 volts 60 cycle A.C.

Operation and use of the air-cooled metal ceramic x-ray tube construction hereinbefore described may now be briefly described as follows. Let it be assumed that the x-ray tube 22 has been mounted in an x-ray apparatus and connected to suitable power supplies. Thus the cables 222 and 223 would be connected into the high power supply to provide the desired high voltages to the x-ray tube 22. In addition, power is connected to the connector 256 connected to the fan motor 246 and to the alternating current squirrel cage motor comprised of the rotor 72 and the stator assembly 231.

Electrons generated by the selected heated filament 187 of the cathode assembly 186 are subjected to a high voltage placed between the cathode and the anode and are rapidly accelerated to travel in the evacuated envelope 41 toward the surface 122 of the rotating anode plate 121 as indicated by the rays 271. These electrons upon striking the inclined surface 122 generate x-rays indicated by the rays 272 which are propagated in a direction at substantially right angles to the beam 271 and pass through the opening 153 through the beryllium window 56 and through the thinned down stainless steel window portion 43a provided in the vacuum envelope 41. The x-rays then pass through window 47 provided in the lead liner 46 and through the opening 28 provided in the housing 22 as shown particularly in FIG. 7. The copious amounts of heat which are generated at the time the x-rays are generated are dissipated into the anode plate 121 which dissipates its heat into the large graphite heat sink 126. The heat which is radiated from the graphite heat sink 126 and the anode plate 121 is collected by the highly conductive relatively thick walls of the heat cage 48 which surrounds the anode plate 121. As hereinbefore explained, the heat cage 48 is thermally extended to the rear of the tube and is joined to the base 42 to provide for an efficient heat exchange with the forced air which is being directed from the rear of the tube between the fins 31a and upwardly towards the base 22a of the cylindrical housing 22 as indicated by the arrows 276. As explained previously, an excellent heat transfer interface is provided between the base 22a of the housing, the lead liner 46 and the base 42 of the vacuum envelope 41 and also forming the base for the copper heat cage 48. For this reason a major portion of the heat dissipated by the anode is dissipated from the tube before it can reach the thin walls of the tube, the ceramic connectors and the bearings provided for mounting the shaft. As hereinbefore explained, particular design features have been incorporated in the x-ray tube to inhibit the transfer of heat to the double-ended bearing construction. Thus as explained previously, the shaft 62 is provided with very thin walled portions on opposite sides of the location at which the anode plate 121 is mounted on the shaft 62 to substantially inhibit the transfer of heat along the shaft towards the bearings mounted on each end of the shaft. By utilizing a construction of this type, it is possible to provide an x-ray tube which can be air-cooled and which does not require the use of more sophisticated oil cooling techniques and the like.

From the foregoing description, it can be seen that the high voltage connectors which are utilized in the x-ray tube are fully integrated into the tube permitting the high voltage to be supplied directly to the tube. The shaft 62 is mounted upon two bearings which are located on opposite sides of the anode plate 121 at the remote ends of the tube facilitating shielding of the bearings from the anode heat radiation. The double-ended bearing construction utilized is facilitated by the metal ceramic design incorporated into the tube. The construction of the tube has made it possible to increase bearing life dramatically. The bearing construction makes possible the support of heavier anodes thereby making possible higher heat storage capabilities. The construction also makes possible higher anode heat dissipation capabilities because of the thermal protection provided for the bearings. The double-ended bearing support provided for the shaft reduces mechanical stresses on the shaft and reduces the likelihood of the bending of the shaft when it is subjected to the extreme heat encountered within the x-ray tube. Also because of the bearing construction provided it is possible to provide improved mechanical stability, and greatly reduced likelihood of vibrations developing during the tube life. Higher rotational speeds are permissible with the use of the shaft disclosed with its bearing supports making it possible the use of higher power or smaller focal spots where size is important to provide a reduction in anode size for mobile applications.

As hereinbefore described, the rear end of the shaft 62 is provided with high strength ceramic coupling 66 which provides high voltage insulation between the anode and the rotor and permits the rotor to be operated at the same ground potential as the stator. For that reason, short distances can be utilized to establish an intimate electromagnetic coupling between the rotor and the stator of the motor while still maintaining the rotor in a vacuum. This construction makes it possible to utilize a low cost, low power electrical supply.

The x-ray tube construction of the present invention is particularly adapted for use in newly manufactured x-ray equipment. However it is constructed in such a manner that it can be utilized to retrofit existing x-ray equipment. Because of the construction utilized in the x-ray tube, there is a sharply reduced service and replacement expense associated with the tube. The tube is plug compatible with the existing CT and conventional x-ray equipment. The construction of the tube utilizing a metal ceramic construction with air cooling makes it possible to eliminate the use of expensive oil cooling.

The x-ray tube construction of the present invention can have a weight ranging from approximately 30 to 45 pounds. It can have a length ranging from 10 to 15 inches with a diameter of approximately 6.5 inches. It can be operated at voltages up to 150 kilovolts. Rotor speeds of 12,000 rpm with 1 to 2 second acceleration and deceleration can be accomplished. The anode can be approximately 4.250 inches in diameter and has a heat storage capacity which can range from 400,000 to 2,000,000 heat units. The construction is capable of dissipating 2,000 to 3,000 watts of energy. The construction of the tube is such that the external temperature of the housing should not exceed 140.degree. Fahrenheit. Excellent protection against radiation is provided. The high voltage termination utilized meets the federal standards.

In FIGS. 11 and 12 there is shown a modified shaft 279 corresponding to the shaft 62 hereinbefore described. The shaft 279 differs from the shaft 62 in that it is provided with a plurality of rectangular slots 281 arranged in pairs or two spaced apart parallel rows with the slots in one row overlapping the slots in the other row. The major axis of each of the slots extends in a direction perpendicular to the longitudinal axis of the shaft 62a. One or more pairs of rows of slots can be provided on the shaft on opposite ends of the shaft 279 and spaced away from the thicker walled portion 279a. Thus there are provided two spaced apart pairs 282 and 283 on the front end of the shaft 279 and a single pair 284 on the rear end of the shaft 279. The slots 281 serve to inhibit heat transfer longitudinally of the shaft by providing less mass for the heat to travel through and also by providing a staggered circuitous path for heat to flow through the pairs of rows.

Means is provided in the receptacles 218 and 219 (see FIG. 3) to make it possible for the receptacles to accommodate various types of federal terminations. Thus there has been provided in each of the receptacles 218 and 219 circular plates 286 (see FIG. 4) of a suitable insulating material such as RTV silicon rubber in which there has been provided five male banana-type terminals 287-291. The terminal 287 is the grid terminal, the terminal 288 is the common terminal and the terminals 289, 290 and 291 are the three filament terminals, respectively, the small focus, medium focus and large focus respectively. A registration notch 292 is provided in each of the receptacles 218 and 219.

A plurality of inserts 293, 294, 295 and 296 (see FIGS. 13A-13D) are provided which are adapted to be placed within receptacles 218 and 219 and mate with the male type terminals 287-291 provided therein. The inserts 293-296 are formed of circular plates 297 of a suitable insulating material such as an RTV silicon rubber.

The inserts 293-296 are provided with a plurality of smaller holes 299, 300, 301, 302 and 303. All but one in each insert have metal female receptacles (not shown) therein and are adapted to mate with the male banana-type terminals 287-391. The receptacle 299 can be the grid receptacle, the receptacle 300 the common receptacle, and receptacles 301, 302 and 303 the small, medium and large filament receptacles respectively. Larger openings 304-308 are provided which also have metal female receptacles therein (not shown). The receptacle 304 serves as the grid receptacle, 305 as the common receptacle, and receptacles 306 and 307 as the filament receptacles. The electrical connections between the inserts provided in the receptacles 299-307 are shown in FIGS. 13A-13D. In this manner, the insert 293 serves to accommodate a three pole federal high voltage terminal which provides supply voltage for the large and the medium focus of the three foci in the x-ray tube, whereas the insert 294 serves to accommodate a four pole federal high voltage terminal which provides supply voltages for the grid, the large and the medium focus of the three foci in the x-ray tube. The insert 295 accommodates a three pole federal terminal to supply the large and the small filaments of the three filaments in the x-ray tube whereas the insert 296 accommodates a four pole federal high voltage terminal to supply voltage to the grid, the large and the small focal spots provided by the three filaments in the x-ray tube. In those terminals where no grid connection is provided, the grid receptacle is connected to the common receptacle by a conductor 308 embedded in the insulating material of the insert so that the common and grid receptacles are interconnected.

A central threaded bore 309 is provided for receiving a threaded service tool for removing and inserting the inserts 293-296.

In this way it can be seen that by utilizing the inserts 293-296 four different federal terminations can be utilized with the x-ray tube. This makes it possible for the user to establish which federal termination the user desires. It also makes it possible for a user to make a change in the field from one federal termination to another.

An observation window 406 (see FIG. 1) is provided in the end cap 351. It is formed of a rod 407 of lead glass to permit viewing during operation of the tube.

In addition a four pole terminal adapter can accommodate all three focal spots provided by the three filaments of the x-ray tube if no grid voltage supply is required.

Another embodiment of the air cooled metal ceramic x-ray tube construction incorporating the present invention is shown in FIGS. 14-20. The x-ray tube 310 therein shown consists of many parts which are identical or substantially identical to the x-ray tube 21 hereinbefore described and are given the appropriate corresponding numerals. One of the principal differences between the x-ray tube 310 and the x-ray tube 21 is the use of a columbium shaft assembly 311 in place of the Hastelloy shaft assembly 61. The shaft 311 consists of a hollow thin-walled shaft 312 formed of a suitable high temperature material such as columbium. Such a shaft should be able to withstand temperatures up to 1700.degree. C. whereas such a shaft formed of Hastelloy should be able to withstand a temperature of approximately 1100.degree. C. The shaft 312 can have a suitable wall thickness ranging from 0.020 to 0.040 inches and preferably a thickness of approximately or 0.030 inch. One end of the shaft 312 is brazed to a metal collar 313 formed of a suitable material such as columbium which is brazed to the shaft 312 and which is mounted on one end of the ceramic coupling 66.

A large cylindrical heat sink 316 is mounted on the front end of the shaft 312. The heat sink 316 is formed of a suitable material such as stainless steel having a chromium content so that an emissive coating of chromium oxide is formed on the same when heated in a wet hydrogen atmosphere as hereinbefore described. The heat sink 316 is provided with a large central bore 317 extending longitudinally the length thereof. The bore 317 is of a size which is substantially greater than the external diameter of the shaft 312 so that there is provided an annular space 318 between the shaft 312 and the heat sink 316. The heat sink 316 is provided with a well 319 in the front end thereof which is adapted to receive the outer race 103 of the ball bearing assembly 104. The heat sink 316 is retained on the shaft 312 by suitable means such as a pin 321 extending diametrically of the shaft 312. The cylindrical heat sink 316 is provided with three circumferentially spaced threaded bores 323 in which there are mounted set screws 324. The set screws 324 are adjustable within the bores and are used for balancing the heat sink 316 as well as the metal anode 326 formed of a suitable material such as molybdenum which carries an inclined annular surface 327 formed of rhenium and tungsten that serves as the target for the electron beam.

Means is provided for mounting the anode plate 326 on the shaft 312 and consists of a coupling 331. An isometric view of the coupling 331 is shown in FIG. 16. It can be formed from a cylindrical block of columbium in which there has been machined annular recesses 332 and 333. A pair of spaced parallel flats 334 are formed on the portion 331a between the annular recesses 332 and 333. Similarly spaced flats 336 are formed on the portion 331b on the other side of the recess 333. A bore 338 has been provided extending from the front side of the coupling 331 and opens into a larger bore 339 (see FIG. 14) extending through the other end of the coupling 331. The bore 339 as shown in FIG. 14 is of a size so that it is substantially larger than the shaft 312 so as to provide a substantial space between the shaft and the interior of the coupling 331.

The anode plate 326 is constructed in a manner so as to be able to receive the coupling 331. It is provided with a central bore 341. The bore 341 opens into four substantially semicircular lobes 342 which are spaced 90.degree. apart (see FIG. 16). These lobes 342 facilitate the insertion of the coupling into the anode plate. The coupling 331 is introduced through the rear side with the flats 334 and 336 in alignment with two of the diametrically opposed lobes 342 so that it extends through the anode plate. After the coupling 331 has been inserted through the anode plate, washers 346 and 347 are inserted.

The coupling 331 is held in place by suitable means such as a washer 346 which engages the anode plate 336 and a plate 347 which is rotated in position over the portion 331b of the coupling and so it underlies the portion 331b to lock the anode plate onto the coupling 331. The coupling 331 can be secured to the shaft 312 in a suitable manner such as welding.

The x-ray tube construction which is shown in FIG. 14 is a compact version and is for use when lower output requirements can be tolerated. In order to make it compact, the fan assembly 246 provided in the previous embodiment has been omitted so that the cooling relied upon for the tube occurs through the transfer of heat to ambient air without the necessity of forced air cooling. This type of tube is limited in output but can serve many high performance applications.

A special termination terminal has been provided for the tube 310 and consists of an end cap 351 formed of lead. The end cap 351 can be held in place in the same manner as the end cap 216 in the previous embodiment. The end cap 351 is provided with a pair of L-shaped integral protrusions 352 and 353 (see FIGS. 17 and 18) which are provided with openings 354 and 356 through which high voltage cables 357 and 358 extend. Collars 359 are mounted on the cables 357 and 358 adjacent the openings 354 and 356 in the protrusions 352 and 353. The cables 357 and 358 are provided with special termination terminals 361, one of which is shown in FIG. 20. The terminals are of a type which can be manufactured in the field when that necessity arises. The cable shown in FIG. 17 is of a conventional type and consists of conductors 364 formed of a suitable material such as copper which are enclosed within a sheath 366 of conducting rubber to minimize corona discharge. The sheath 366 is enclosed in EPR rubber 367 to provide the termination terminal 361. The cables are also enclosed with an additional braided sheath 368 covered by a vinyl sheath 369.

In preparation of a special terminal 361, the ends of the conductors 364 are stripped clean and thereafter female threaded fittings 371 are crimped onto the conductors. A syringe 372 of the type shown in FIG. 19 is then utilized to place vulcanized rubber around the fittings 371. The syringe 372 consists of a cylinder 373 formed of suitable material such as aluminum in which a piston 374 is slidably mounted. The piston is carried by a piston rod 376 which is threaded into a threaded portion 373a provided on the proximal extremity of the cylinder 373. A handle 377 is mounted in the piston rod and is provided for rotating the piston rod so that the piston 374 can be advanced and retracted. The syringe 372 is adapted to be utilized in connection with a cylindrical split mold 381 formed of a suitable material such as aluminum which is adapted to fit over the proximal extremity of the cable 358 and be secured thereto by a hose clamp 382. A conductive rubber sleeve 385 is placed in the mold 381 near the proximal extremity thereof. A circular plate 383 then is mounted on the other end of the member 381 and is secured to the fittings 371 by screws 384. The plate 383 is provided with additional holes 386 through which an insulating material such as an EPR silicon rubber can be extruded. The member 381 with the plate 383 secured thereto is adapted to be inserted into an annular recess 388 provided in the distal extremity of the cylinder 373 and is retained therein by bushings 389 extending through the cylinder 373 and extending through into the cylindrical member 381 to retain the member 381 connected to the cylinder 373. After the EPR silicon rubber has been introduced into the cylinder 373, the piston 374 can be actuated to force the silicon rubber into the member 381 to fill the space between the fittings with the silicon rubber. After this has been accomplished a heater 391 is placed around the mold formed by the split casing 381 and heat is applied to the mold to cure the EPR silicon rubber to vulcanize the same about the fittings 371 to provide a vulcanized rubber region 392 at the end of the cable 358.

After appropriate heat cured vulcanization, the bushings 389 are removed and the syringe 372 is separated from the casing or mold 381. The heater 391 is removed and thereafter the split casing 381. The screws 384 are then removed as is the plate 383. Thereafter, another plate 396 formed of an insulating material is provided and banana type terminals 397 are threaded into the fittings 371 to hold the plate 396 in place to complete the terminal 361 with the cable 358. The cable 357 can be provided with a similar terminal 399 (see FIG. 18). The terminal 399 can be inserted into the opening 354 in cap 351. The terminal 399 is bent through approximately 90.degree. by being pushed through a curved passage 401 which has previously been formed within the end cap 351 by RTV silicon rubber 402 therein. The curved passage makes it possible to direct the cable terminal 399 so that the banana plug fitting 397 carried thereby can be pushed into the female receptacle carried by the feedthrough 166.

In this way it can be seen that in the event of damage of a high voltage cable, the cable can be readily repaired by cutting off the damaged portion and building a new terminal on the same in the field and thereafter inserting the terminal into the end cap.

The operation and use of the x-ray tube shown in FIG. 14 is substantially identical to that hereinbefore described. However, the tube is more compact and lighter in weight than the x-ray tube hereinbefore previously described. It is able to withstand the high temperature encountered without forced air cooling.

It can be seen from the foregoing that there has been provided a metal ceramic x-ray tube construction which has many advantageous features. The need for an insulating oil bath has been eliminated while still making it possible to operate the tube with forced air cooling and in certain compact smaller size versions to operate the tube without forced air cooling. As can be seen particular attention has been paid to the manner in which heat is dissipated from the anode while at the same time protecting the bearings supporting the shaft from heat generated by the anode. A particular unique x-ray window has been provided as well as improved cable terminations. The x-ray tube is constructed in such a manner so that field repair can be accomplished. In addition the construction is such that when the tube is returned to the manufacturer many of the expensive parts thereof can be salvaged and used in remanufactured tubes. The construction of the tube is such that the anode and cathode feedthroughs are mounted to accommodate a long shaft so that one extremity of the shaft can extend therebetween.