US3735176A

US3735176A - Rotating anode balance and getter

Info

Publication number: US3735176A
Application number: US00252509A
Authority: US
Inventors: H Langer; W Fengler
Original assignee: Machlett Laboratories Inc
Current assignee: Varian Medical Systems Inc
Priority date: 1972-05-01
Filing date: 1972-05-01
Publication date: 1973-05-22
Anticipated expiration: 1990-05-22

Abstract

A rotating anode for X-ray tubes having a supporting rotatable shaft carrying fixed swing weights which may be initially positioned as necessary to achieve balance of the anode, and which simultaneously provide getter and heat shielding functions.

Description

United States Patent Langer et al.

ROTATING ANODE BALANCE AND GETTER Inventors: l-lelmut Langer, Springdale; William W. Fengler, Fairfield, both of Conn.

Assignee: The Machlett Laboratories, Incorporated, Springdale, Conn.

Filed: May 1, 1972 Appl. No.: 252,509

US. Cl. ..3l3/60, 74/573, 313/42,

313/174 1m. 01 ..i-l01 35/10 Field of Search ..3 13/60 51 May 22, 1973 [56] References Cited UNITED STATES PATENTS 3,081,413 3/1963 Cummings ..3l3/6O Primary Examiner-John Kominski Assistant ExaminerDarwin R. Hostetter Att0rney- Harold A. Murphy, Joseph D. Pannone, Edgar 0. Rest et al.

[ 5 7 ABSTRACT 8 Claims, 3 Drawing Figures ROTATING ANODE BALANCE AND GETTER BACKGROUND OF THE INVENTION sary to balance the rotatable target in order to meet the high speed requirements of the target-rotor systems which may operate at speeds in excess of 10,000 RPM. Such balancing of the target commonly involves a metal removal process such as by grinding or drilling the rear surface of the target in the outer areas thereof in order to eliminate uncompensated centrifugal forces and moments which could otherwise produce high dynamic bearing pressure and subsequent destruction of the bearing system which supports the target.

Although a target may be prebalancedto some degree before being attached to a rotor system, sufficient imbalance remains because of the combining of the target system with the rotor system, with its inherent dimensional tolerances, preprocessing and assembly effects. It will be apparent also that since targets are provided with metal coatings for various reasons, such coatings must be uniformly deposited in order to provide a properly balanced tube, and this is very difficult.

The present technique has several disadvantages which include, for example, contamination of the tube to degassing integrity; creation of particles by grinding or drilling, which particles may give rise to high voltage arcing, etc.; high costs resulting from precise manufacturing controls which are required, and time consumption expended during the balancing process, which time may be from to minutes.

Furthermore, adding to the overall cost of an X-ray tube of the described character is that which is incurred in making and mounting within the tube envelopes any of various types of getters and bearing heat shields.

SUMMARY OF THE INVENTION The foregoing and other disadvantages of prior art devices of the type described are overcome or eliminated by the present invention wherein a rotating anode is balanced by a novel swing weight technique which also provides a tube getter structure and a heat shield for protection of the anode bearings.

Balancing is actually achieved by a pair of weights which are located on the upper or lower surface of the target, preferably the lower, which weights are mounted for rotation individually about the targetsupporti'ng shaft during the balancing process and thereafter fixed to the shaft or the target by welding or by mechanical securement so as to retain the balanced conditions.

' The weights may be fabricated from a refractory metal and coated with a film having gas absorptive characteristics and low atomic member to achieve the additional advantages of getteringand reduced offfocus radiation when located on the upper target surface.

. Furthermore, the weights when mounted on the rear surface of the target may be properly configured to provide heat shielding of the rotor bearing system, which results in lower bearing temperatures, better rotational performance, and longer bearing life.

BRIEF DESCRIPTIONOF THE DRAWINGS The above and other advantages of the invention will become apparent from the following description taken in connection with the accompanying drawings, wherein:

FIG. 1 is an axial sectional view of a rotating anode X-ray tube embodying a preferred form of the invention;

FIG. 2 is a top plan view of a swing weight employed in the invention; and

FIG. 3 is a side elevational view of the swing weight shown in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT ment to which a suitable electrical potential is applied through leads 24 extending externally of the tube through cylinder 16.

The opposite end of the envelope 10 carries the anode 12 which includes a target 26 mounted on one end of a rotor shaft 28 which extends upwardly from a rotor which is located within a neck portion 30 of the envelope. The rotor carries a skirt 32 which is bolted thereto at its upper end, and the rotor is mounted in a conventional manner by ball bearings on a supporting cylinder (not shown) within skirt 32 and is adapted to rotate rapidly when the tube is provided with suitable inductive means surrounding the neck 30 when the inductive means is energized, as is well known.

The shaft 28 is provided with a nosepiece 34 in the form of a portion of enlarged diameter spaced from the extreme upper end of the shaft. The target disc 26 normally rests upon the ledge formed by the nosepiece and is held -thereupon by a nut 36 which is threaded onto the end of the shaft against the upper surface of the target 26.

In operation of the tube, electrons from the cathode fall upon a focal track area 38 of the target 26 which in response thereto generates X-rays which pass out of the tube through the envelope wall. The target may be tungsten or molybdenum and the focal track 38 thereon is preferably a coating of rhenium-tungsten alloy which is deposited in an annular path which re- I mains constantly inthe path of the electron beam as the target rotates. The target 26 will, of course, generate considerable amounts of heat during bombardment by the electrons.

It will be apparent that since the target 26, and also the rotor structure associated therewith, rotates at speeds which sometimes exceed 10,000 RPM, the structure must be balanced to eliminate uncompensated centrifugal forces and moments which could result in high dynamic bearing pressure and subsequent destruction of the bearing system.

Although the rotor system and target system may be individually prebalanced to some degree, it will be apparent that combination of the two systems will undoubtedly produce a residual imbalance which must be eliminated.

illustrated in FIG. 1, the weights are positioned upon shaft 28 between the target 26 and the nosepiece 34. At least one of the weights 40-40:: is slotted, as indicated at 44 in FIG. 2, at its apertured end and the material 46 at one side of the slot is bent to obtain a leafspring effect.

After the weights are positioned on the nosepiece 34 the target 26 is mounted in position and the assembly is completed by placing nut 36 on the shaft and tightening it securely. In a preferred structure the nosepiece 34 has an annular step 48 formed in its upper peripheral surface within which reside the portions of the weights around the apertures 42. The depth of step 48 is somewhat greater, about 0.010 inch for example, than the combined thicknesses of the two weights. Therefore, the weights are rotatable about the axis of the shaft 28. However, the leaf spring or lock washer effect achieved by the slot 44 and angled portion 46 tends to-restrict rotational movement of the weights to some extent.

The imbalance of the target or anode assembly may have been predetermined before the complete assembly of target and swing weights were mounted on the rotor, in which case the heavy point will be marked on the target. Alternatively, the actual heavy spot may be found with the swing weights in place, located to extend about 180 apart and moved in a clockwise direction until the least imbalance is found. At this point in the procedure the weights are located about 90 left and right respectivelyof the heavy spot. The Weights are now moved away from the heavy spot toward each other until optimum balance is established.

' The complete balancing process is done by mounting a target rotor assembly on a balancing machine and simply moving the swing weights manually or by means of an appropriate assembly tool. At the completion of the balancing process the target-rotor assembly is re- 'moved from the balancing machine and the two swing weights are fixed to the nosepiece 34 or to the target 26 by welding or mechanical securement.

The weights 40 -400 may be fabricated from a refractory metal such as tungsten, tantalum, rhenium, molybtarget from efficiently radiating down toward the bearing structure.

From the foregoing it will be apparent that all of the objectives of this-invention have been achieved by the described invention whereby an X-ray tube rotating anode may be efficiently and precisely balanced without requiring the reworking, as by grinding or thelike, of any part of the anode assembly. The balancing process is fast and precise, .is non-contaminant, and the resultant structure provides efficient and inexpensive gettering and heat shielding.

It is to be understood, however, that various modifications and changes in the structure shown and described may be made by those skilled in the art without departing from the spirit of the invention as expressed in the accompanying claims. Therefore, all matter shown and described is to be interpreted as illustrative and not in a limiting sense.

We claim:

1. An X-ray tube having a rotating anode structure including a shaft revolvable about its longitudinal axis, a target mounted on the shaft for rotation therewith and means for balancing the anode structure comprising weights fixed to the structure at strategic locations with respect to heavy and light areas of the target.

2. An X-ray tube as set forth in claim 1 wherein said weights are flat rigid members fixed to the anode shaft adjacent the target.

3. An X-ray tube as set forth in claim 1 wherein said weights have a gettering substance on at least one surface thereof.

4. An X-ray tube as set forth in claim 1 wherein said weights are flat rigid members fixed to a surface of the target. I i

5. An X-ray tube as set forth in claim 1 wherein said weights are flat, elongated, rigid members having an aperture at one end receiving the shaft and having its major portion extending radially of said shaft.

6. An X-ray tube as set forth in claim 1 wherein said weights are flat, elongated, rigid members each having one end portion provided with arcuate arms encircling respective opposite sides of the shaft, one of said arms being initially bent into a plane different from the plane of the other arm, said arms being positioned between adjacent portions of the target and shaft whereby said arms have a lock washer affect thereon.

7. An X-ray tube comprising an evacuated envelope, cathode and anode structures mounted in spaced relation within the envelope, means extending through the envelope and connected respectively to the cathode and anode structures for applying an electrical potential across the two structures for causing flow of electrons from the cathode electrode to the anode electrode, said anode electrode including a rotor structure, a shaftlocated within the rotor structure for rotation therewith, and a target fixed to the shaft for rotation therewith and positioned to receive electrons from the cathode structure, said target being of a material which generates considerable amounts of heat when bom barded by electrons, and combined heat shielding and balancing means for the anode structure, said means comprising weights which are fixed to the anode structure between the target and the rotor structure, said weights being positioned at strategic positions with respect to heavy and light areas of the anode structure and each-having a portion which is angled out of physical engagement with the target for reducing heat radiation from the target to the rotor structure.

8. An X-ray tube comprising an evacuated envelope, cathode and anode structures mounted in spaced relation within the envelope, said anode structure comprising a rotor structure, a shaft mounted in the rotor strucstructure at strategic locations with respect to heavy and light areas of the target, said weights having a gettering substance on at least one surface thereof.

Claims

4. An X-ray tube as set forth in claim 1 wherein said weights are flat rigid members fixed to a surface of the target.

7. An X-ray tube comprising an evacuated envelope, cathode and anode structures mounted in spaced relation within the envelope, means extending through the envelope and connected respectively to the cathode and anode structures for applying an electrical potential across the two structures for causing flow of electrons from the cathode electrode to the anode electrode, said anode electrode including a rotor structure, a shaft located within the rotor structure for rotation therewith, and a target fixed to the shaft for rotation therewith and positioned to receive electrons from the cathode structure, said target being of a material which generates considerable amounts of heat when bombarded by electrons, and combined heat shielding and balancing means for the anode structure, said means comprising weights which are fixed to the anode structure between the target and the rotor structure, said weights being positioned at strategic positions with respect to heavy and light areas of the anode structure and each having a portion which is angled out of physical engagement with the target for reducing heat radiation from the target to the rotor structure.

8. An X-ray tube comprising an evacuated envelope, cathode and anode structures mounted in spaced relation within the envelope, said anode structure comprising a rotor structure, a shaft mounted in the rotor structure for rotation therewith, and a target mounted on the shaft for rotation therewith, and combined means for balancing the anode structure and gettering occluded gases from parts of the tube within the envelope, said means comprising weights fixed to the anode structure at strategic locations with respect to heavy and light areas of the target, said weights having a gettering substance on at least one surface thereof.