US2185826A

US2185826A - Rotatable anode x-ray tube

Info

Publication number: US2185826A
Application number: US212268A
Authority: US
Inventors: Zed J Atlee
Original assignee: General Electric X Ray Corp
Current assignee: General Electric X Ray Corp
Priority date: 1938-06-07
Filing date: 1938-06-07
Publication date: 1940-01-02
Anticipated expiration: 1957-01-02

Description

Jan. 2, 1940. 2. J. ATLEE 2,185,825

ROTATABLE ANODE X-RAY TUBE Filed June 7, 1938 Inventor: Zed J. Atlee 0 SPEED SYNCHRONOUS by W 7 SPEED Hi8 Attorney I Patented Jan. 2, 1940 PATENT OFFICE ROTATABLE ANODE X-RAY TUBE Zed J. Atlee, Chicago, Ill., assignor to General Electric X-Ray Corporation, a. corporation of New York Application June 7, 1938, Serial No. 212,268

4 Claims.

The present invention relates in improvements in X-ray apparatus of the type which includes an X-ray tube having a stationary electrode and a relatively rotatable electrode.

It is an advantage of X-ray tubes of this character that they are able to operate with very high discharge currents. However, the safe use of such currents depends upon the maintenance of a definite speed of rotation of the relatively movable electrode. To employ the full operating current with the movable electrode stationary or rotating at reduced speed may result in serious damage to the X-ray target.

It is an object of my present invention to provide means for automatically preventing the supply of normal discharge current to a rotating element X-ray tube unless and until the said element is revolving at its intended speed.

The features of novelty which I desire to protect herein are pointed out with particularity in the appended claims. The invention itself together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the drawing in which Fig. 1 illustrates diagrammatically an X-ray apparatus suitably embodying the invention and Fig. 2 is a graphical representation useful in explaining the invention.

Referring particularly to Fig. 1, I have shown an Xray tube of the type described in application Serial No. 78,996, filed May 11, 1936, in the names of Malvern J. Gross and Zed J. Atlee. This comprises a sealed evacuated envelope Ill enclosing a separately heated cathode, shown in outline at It, and a rotatable anode I2 having thereon an inclined peripheral target face 3. The anode it is intended to be rotated during normal operation and is mechanically connected to a driving means comprising an induction rotor 54. The rotor may comprise a squirrel cage construction such as is described and claimed in the application Serial No. 78,996 above referred to. In order to supply driving force to the rotor it there provided an electromagnetic stator which is outside the discharge envelope and which is indicated diagrammatically in dotted outline at E5. The stator is provided with polyphase windings l6 and ll (shown separately of the stator for clarity) whose character and mode of energization will be set forth more fully hereinafter.

The energizing means for the various instrumentalities is shown as comprising a common power source I8 which is connected to an autotransformer I9 through a manually operable switch 2i. 'The auto-transformer is provided with a plurality of terminals which make it possible to derive a number of different potentials from the same voltage source.

One set of these terminals, namely,

terminals

23 and 24, are used for supplying heating current to the cathode I! through the intermediation of a transformer 25. Regulation of the heating current is accomplished by means of a variable resistor 26 connected in series with the transformer primary.

The main discharge current for the X-ray tube is provided by means of a transformer 21 which has its primary connected between

terminals

23 and 28 of the auto-transf0rmer 19. The energizing cir uit thus provided is controlled jointly by a manually operable switch 29 and by a sole-- noid operated relay 30, the operation of which will be more fully explained hereinafter.

Referring again to the windings I6 and I! of the stator I5, it should be pointed out that these are of such character as to provide a rotating magnetic field when supplied with polyphase currents. In order to obtain such currents from the single phase source 3, a phase-splitting device is employed in the form of a condenser 32. In operation, the potential which exists between

terminals

23 and 35 of the auto-transformer i9 is applied directly to the stator winding I6 by means of conductors 36 and 31. It is applied indirectly to the winding ll through these same conductors connected in series with the condenser 32. The action of this condenser is to produce a phase difference between the currents flowing in the two windings so as to obtain the effect of polyphase excitation of the stator. By this means a rotating magnetic field is produced which is effective to exert a strong torque on the rotor I 4 and to rotate it and the connected anode'l2.

Rotation of the anode I2 during use causes the heating efiect of the discharge current passing between it and the cathode II to be distributed over the entire target surface I3 and obviates the danger of localised burning. The amount or" discharge current which can be safely handled is a function of the speed of rotation and may be very high under proper conditions. However, the use of extremely high currents involves the danger that a decrease in speed below the intended value may result in destructive hearings on which the rotating parts are supported.

In accordance with my present invention, means is provided for assuring that the discharge circuit shall be fully energized only when the rotor I4 is turning at its normal speed or at a speed not materially below normal. To this end there is provided in connection with the stator energizing circuit, means effective to control the operation of the relay 30 in such a manner as to accomplish the desired result. This means comprises a device which is responsive to an electrical condition of the stator energizing circuit, specifically a solenoid operated relay 39 which is controlled by variations in voltage across the stator winding IT. The particular control arrangement shown includes a condenser 4| and a pair of resistors 42 and 43 connected in series across the stator winding I1. coil .of the relay 39 is connected across the condenser so that the relay is maintained in its closed position when and as long as the voltage of the condenser 4| is in excess of a predeter- -mined minimum value.

It will be observed that actuation of the relay opens the upper contacts 48, 49 of the relay and places the resistor 42 in circuit with the winding H. This'makes the relay more sensitive to a slight drop in voltage. The condenser 4i has the eiTect of preventing chattering action of the relay.

The action of the control circuit just described may be understood by referring to Fig. 2 which shows the relationship which exists between the time, the speed of the rotor again drops, say, tov

the point B, the relay 39 will reopen.

Closure of the relay 39'serves to complete the energizing circuit for the relay 30--at least insofar as this circuit depends upon the existence of a connection between relay terminals 46 and 4?. (The re1ay30 is under the joint control of the relay 3i) and of an exposure-timing device 50). The complete relay circuit may be traced from terminal 5! of the auto-transformer I9 through the coil of relay 30, timer 50, conductor 52, relay contacts 46 and 41, and conductor 53 back to terminal 23 of the auto-transformer.

Assuming that the timer 5!! is in its closed position, closure of the relay 39 will permit the supply of discharge current to the X-ray tube. Furthermore, subject to the operation of the timer 50, such discharge current may be continued as long as the speed of the rotor l4 remains above the predetermined minimum. If, for any reason this speed drops below such minimum, the relay 39 will open so as to prevent further flow of discharge current and consequent damage to the Xray target. The operation of the relay 39 may be adjusted to provide for its closure at different speeds of the rotor. [4 or its use at difierent voltages by varying thefvalues of the resistors 42 and 43. It will be understood that as the value of the resistors is decreased the proportion of the total voltage'which appears across the condenser The energizing- 4| will increase. Consequently the relay will remain closed for lower speeds than would be the case with higher resistor values.

It is not necessary that the relay 39 operate to interrupt the supply of discharge current completely. It would be a sufiicient protection, for example, if its operation were to introduce into the discharge circuit an impedance of such magnitude as to reduce the current flow to a safe value.

It will further be understood that the particular circuit which I have illustrated is in no Way essential to the purposes of the invention. Various changes may be made by those skilled in the art and I aim in the app-ended claims to cover all such equivalent modifications as fall within the true spirit of the foregoing disclosure.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In an apparatus of the type which includes a discharge tube having a stationary'electrode, a rotatable electrode and electromagnetic means for driving the rotatable electrode, the combination which comprises a first electrical circuit for supplying operating current to the said tube, a second electrical circuit for energizing the said electrode driving means, the electrical conditions of said second circuit being variable in accordance with variations in the speed of rotation of said electrode, and means associated with said second circuit and responsive to an electrical condition thereof for preventing the supply of normal operating current to the tube except upon the attainment of a desired speed of rotation of the said rotatable electrode.

2.-In an apparatus of the type which includes an 'X ray tube having a stationary cathode, a rotatable anode, an electromagnetic rotor mechanically connected to the anode and an electromagnetic stator for supplying driving force to'the rotor, the combination which comprises a first electrical circuit for supplying discharge current to the tube, a second electrical circuit for supplying energizing current to the stator, the electrical conditions of said second circuit being variable in accordance with variations in the speed of rotation of said rotor, and means associated with said second circuit and responsive to an electrical condition thereof for preventing the completion of the said discharge current circuit except upon the attainment of I a desired speed of rotation of the rotor.

3. In an apparatus of the type which includes an X-ray tube having a cathode, a rotatable anode, an electromagnetic rotor mechanically connected to the anode, and an electromagnetic stator for supplying driving force to the rotor, the combination which comprises a first electrical circuit for supplying discharge current to the tube, a second electrical circuit including energizing windings for the stator, at least certain of said windings being of such character that the voltage drop therethrough varies materially in response to variations in the speed of rotation of the rotor and means responsive to such variations in voltage drop for preventing completion of the said first circuit except upon the existence of a predetermined speed of rotation of the rotor.

4. An X-ray apparatus including an X-ray tube having a stationary cathode and a rotatable anode, an electrical circuit for supplying discharge current to the tube, an induction rotor connected with the anode for driving the same, an electromagnetic stator having a pair of polyphase windings "for supplying driving force to the rotor, a 75 source of single phase potential adapted to be connected directly to one of said windings and indirectly to the second winding through a phase shifting device, a relay for controlling the said discharge current circuit, and means responsive to the potential drop across the said second stator winding for controlling the operation of the relay, whereby the supply of normal discharge current to the tube is made dependent on the attainment of a desired operating condition of the rotor.

ZED J. ATLEE.