US3043957A - Protection device for rotating anode x-ray tube - Google Patents

Description

July 10, 1962 E. B. GRAVES 3,043,957 PROTECTION DEVICE FOR ROTATING ANODE X-RAY TUBE Filed Jan. 4, 1960 37-"T/MER INVENTOR.

EDWARD B. GRAVES United States Patent 3,043,957 PROTECTION DEVICE FOR ROTATING ANODE X-RAY TUBE Edward B. Graves, South Euclid, Ohio, assignor to Picker X-Ray Corporation, Waite Manufacturing Division, Inc., Cleveland, Ohio, a corporation of Ohio Filed Jan. 4, 1960, Ser. No. 270 16 Claims, (Cl. 250-103) This invention pertains to X-ray devices and more specifically to mechanisms which employ a rotating anode type X-ray tube.

When an X-ray exposure is made, the anode of an X-ray tube is bombarded with a high energy beam of electrons emitted by the cathode of the tube. In the usual X-ray tube the cathode and anode are positioned in a vacuum chamber and a high tension exposure circuit is connected to them. When an exposure is made this circuit is closed and the bombarding of the anode occurs.

This bombarding of the anode is usually focused on a relatively small target area in order that the X-rays emitted as a result of the bombarding will be as concentrated and focused as possible. This focused bombarding causesthe target surface of the anode to become very hot. Holding the anode temperature within permissible limits is the principal factor limiting the capacity of X-ray tubes.

One well established technique for increasing the capacity of the tube while maintaining the anode tempera ture within permissible limits is to provide a rotatable anode which has an annular, usually frustoconical shaped target surface. To cause this anode rotation, a small induction motor is incorporated in and forms a part of the X-ray tube. The tube anode, or target as it is often known, is mounted on the rotor of the induction motor for rotation with the rotor.

When the tube is in use the rotation is initiated before an exposure is made. The beam is then focused against a segment of the annular target surface. Since the target surface is rotating the segment of the surface which is being bombarded is constantly changing as it moves around the annulus so that the segment of the target being bombarded is constantly changing. This allows ample time for the target surface to cool and permits extremely high energy and long duration exposures, relatively speaking, as compared with other tubes.

One long-standing problem which is inherent in these rotating anode type X-ray tubes is that if the anode is, for some reason, either not rotating at an adequate speed or perhaps not rotating at all when an exposure is made, the tube in all probability will be destroyed. The tube will be destroyed because the electron bombardment is concentrated on one segment of the target surface. This concentration will cause that segment of the target surface to overheat and be burned or melted away. The problem is that since the X-ray tube must be carefully shielded within a suitable housing to protect the operator from exposure to X-rays, it is very diflicult to know whether or not the anode is actually rotating before an exposure is made.

A large number of proposals have been made in attempts to provide some means of determining whether or not an anode is actually rotating. All such proposals have had serious shortcomings. One very common arrangement which is used for this purpose is a simple timedelay arrangement. The theory is that given a suitable delay the anode will be up to a tolerable minimum speed. These time-delay arrangements presuppose a proper functioning of the circuits which excite the windings of the X-ray tube induction motor, and presuppose that there are no other faults in the mechanism which would cause improper or non-existent anode rotation. Other proposals have often failed because if the condition testing arrangement fails the exposure can nonetheless be made. Still other proposals have failed because of complexity and cost, while others have failed because they were sensitive to a limited range of anode speeds far less than the actual'operative range. Some proposals, such as temperature responsive mechanisms, are not sufiiciently responsive to protect against a complete and sudden failure.

The present invention provides a simple, fool-proof sensing arrangement which automatically initiates an exposure after an exposure button is pushed. This mechanism can only automatically initiate the exposure if the anode and the novel condition responsive mechanism are operating properly.

With this invention the windings of the X-ray tube induction motor are energized. Subsequently, the winding energizing circuit is broken and a condition responsive circuit is closed. If the anode is rotating the induction motor will operate as an induction generator. A back electromotive force is generated in the windings when the anode is rotating. When the energizing circuit is broken the only current flowing through the deenergized winding will be the current caused by the generated back The condition responsive circuit includes some sensing element which can be energized by the back This condition responsive element in turn 'will cause an exposure timer to start operating and an X-ray exposure of a predetermined duration will be made.

In the preferred arrangement the condition sensing element is one which is responsive to the back generated in the winding by a minimum acceptable rotation of the anode. Thus, if with a given X-ray tube the minimum acceptable speed is 2,000 rpm. and a back of say 12 volts is generated at that speed, the condition responsive element will be one which requires at least 12 volts to operate.

The usual rotating anode type X-ray tube has a pair of parallel connected windings. In the preferred arrangement the circuit energizing only one of those windings is broken. The other of the windings will maintain the anodes speed at a satisfactory level substantially indefinitely, and at least for a period which is far longer than any normal X-ray exposure period.

Accordingly, one of the principal objects of the invention is to provide a novel and improved mechanism in which an X-ray exposure can be taken with a rotating anode tube only if the anode is rotating at a suitable speed.

Another object of the invention is to provide a novel and improved mechanism in which, once the operator tion and claims, taken in conjunction with the accompanying drawing, in which:

FIGURE 1 is a wiring diagram showing the one form of the novel and improved anode protection.

The usual rotating anode type X-ray tube includes a small induction motor which causes the anode to rotate. The stator of this motorincludes windings represented by windings 10, '11 in the drawings.

The winding 10 is connected through conductors 12,

13 to a source of electricity designated by L-l. A phase shifting capacitor 14 is connected in series with the winding 11 through conductor 15. The winding 11 and the phase shifting capacitor 14 are connected to the conductors 12, 13 to place them in parallel with the winding and connect them to the source of electricity L-l. A squelch capacitor 17 is connected in parallel with the Winding 11.

A number of condition responsive circuits are suitable for the accomplishment of the present invention. In any such condition responsive circuit some means must be provided to break the circuit energizing at least one of the motor windings. A means responsive to back generated in the winding is provided to initiate the exposure when a generated of a predetermined magnitude exists. In the succeeding discussion one preferred mode of accomplishing the invention is disclosed.

In light of the preceding discussion any skilled mechanic will recognize that any number of alternate arrangements and sophistications may be utilized. At the same time, the suitability of this embodiment particularly because of its adaptibility to existing equipment will also be recognized.

The drawing shows a single pole, double throw switch 18 which normally connects the phase shifting capacitor 14 and the conductor 15 to the winding 11. The switch 18 is controlled by a solenoid 19. The solenoid 1% is actuated after the windings 10, 11 have been energized sufliciently long enough to permit the anode to be rotating at the desired speed. Usually about one second is an adequate time delay to permit the anode to reach its speed of operation. The preferred and disclosed time delay is a trigger tube 20 time delay which is in series with the solenoid 19. The solenoid and- tube 19, 20 are connected to the source of electricity L-l through conductors 21, 22 which are connected to the conductors 12, 13 respectively.

When the solenoid 19 is energized the switch 18 connects the motor winding 11 to a normally closed switch 24. The normally closed switch 24 is in turn connected to a rectifier 25 by a conductor 26. To complete the rectifier circuit, the rectifier 25 is connected to the conductor 13 by a conductor 27.

A relay is connected in parallel with the motor winding 11 through conductors 31, 3 2. The conductor 32 is connected at 33 to the conductor 13. The relay 30 is what is known as a protector or anti-sneaker. If there is a break in the conductor 13 between the motor windings 10, 11 and the connection 33, for example, the coil 30 will be energized by energy passing through the windings 10, 11. This will hold the switch 24 open to prevent the passage of line current through the condition sensing circuit. At the same time the impedance of the relay 30 is high enough that back generated in the winding 11 when the rectifier 25 is connected to the winding 11 by the switch 18 will not cause the solenoid 30 to open the switch 24.

In addition to the winding 11, the rectifier 25 and the switch 18, the condition sensing or condition responsive circuit includes a sensing solenoid 35. The solenoid is connected to the rectifier 25 and actuated by the rectified back of the winding 11. The sensing solenoid 35 controls a normally open switch 36. The switch 36 is connected to an X-ray tube exposure control timer 37. The timer 37 in turn controls the high tension circuit which energizes the X-ray tube shown schematically at 38.

In the usual timer, a tube is fired when the switch 36 is closed. Firing of this tube energizes an exposure control solenoid 40. The solenoid 40 closes a high tension exposure switch 41 to connect high tension transformer 42 to a high tension source L-2.

Operation When an operator wishes to take an X-ray exposure, he

closes an exposure control switch 45. Closing of the switch 45 connects the induction motor windings 10, 11 to the source of electricity L1. If all of the elements of the system are in proper operating condition, this will cause the anode of the X-ray tube to begin to rotate and come to full speed very quickly. The normal operating speed of these rotating anodes is about 3,200 revolutions per minute.

Once the anode has reached operating speed, the circuit connecting the winding 11 to the source of electric potential may be broken and the combination of inertia and the magnetism induced by the winding 10 will maintain the speed of anode rotation at a very satisfactory level. With the present system 2,000 rpm. is a speed which is quite adequate to protect the anode. Preferably the speed will not drop below this level, and in normal operation of the device exposures will be made with the speed of anode rotation of around 2,100 to 2,400 revolutions per minute.

After a sufficient time interval has elapsed, the solenoid 19 is energized to actuate the switch 18 and connect the winding 11 to the rectifier 25. In the disclosed arrangement this time delay is provided automatically by the trigger tube 20 which fires to energize the solenoid 19 after about one second delay. Assuming there are no breaks in the line, or other defects which permit current to sneak from the winding 10 through the winding 11 and thence back through the solenoid 30 to the conductor 13, the switch 24 will be closed. When the switch 18 connects the winding 11 to the rectifier 25, the circuit energizing the winding 11 is broken. If the anode is rotating a back will be generated in the winding 11. This back will be in the order of about 10 to 15 volts in the operating ranges under consideration. If this back E.M.F. is generated, the sensing relay 35, or other suitable current sensing device, will energize the timer. Energizing the timer will start an exposure period and actuate the relay 40 to cause high tension current to be imposed across the X-ray tube for a predetermined and selectable time interval.

While the invention has been described with a great deal of particularity and detail, it will be seen that it essentially comprises a means for connecting a winding of a rotating anode type X-ray tube to a back sensing mechanism, which sensing mechanism actuates an X-ray tube exposure timer.

Although the invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and the scope of the invention as hereinafter claimed.

What is claimed is:

1. In an X-ray device having an X-ray tube including a cathode and a rotatable anode and windings to induce a magnetic field to drive the anode and a high tension circuit connected to the tube, the combination of a winding energizing circuit, exposure control means connected to the high tension circuit to maintain the circuit normally open, a condition responsive means responsive to a back generated in the windings, other means in said energizing circuit to open at least a part of the energizing circuit and to connect the condition responsive means to at least one of the windings when at least such part of the circuit is open, and said condition responsive means when so connected to the exposure control means and to each such winding disconnected from the energizing circuit causing the exposure control means to close the high tension circuit when a back is generated in one such disconnected winding.

2. The device of claim 1 in which the condition rcsponsive means causes the exposure control means to close the'high tension circuit only when predetermined mini- 'mum back is present.

3(The device of claim 1 wherein the condition responsive means is a relay.

4. The device of claim 1 wherein the other means comprises a solenoid actuated switch and a time delay means connected to the winding energizing circuit to energize the solenoid after the windings have been energized a predetermined length of time.

5. In combination a rotating anode X-ray tube, a high tension exposure circuit connected to the tube, an exposure control timer operatively connected in the exposure circuit, said tube including first and second windings for inducing a magnetic field, a winding energizing circuit connecting the windings in parallel to a source of electric energy, a condition sensing circuit, switch means in series with the first winding and selectively connecting the first winding to the energizing circuit and to the sensing circuit one at a time, and said sensing circuit including means responsive to a back generated in said first winding to actuate said timer when a back E.M.F. of a predetermined magnitude is generated in such first winding.

6. The device of claim 5 wherein said means responsive to the back is a solenoid.

7. The device of claim 5 wherein the switch means comprises a series connected solenoid and time delay means connected in parallel with the windings.

8. The device of claim 7 wherein the time delay means is a trigger tube.

9. The device of claim 5 wherein a phase shifting capacitor is in series with said one winding.

10. In combination, an X-ray tube including a cathode and a rotatable anode, a high tension transformer including a secondary winding connected to the anode and to the cathode, first and second parallel connected windings for inducing a magnetic field to cause said anode to rotate, a winding energizing circuit including an exposure control switch connected to said windings, a single pole double throw solenoid actuated switch in series with one of said windings, a time delay trigger tube series connected to the switch solenoid and connected in parallel with the windings, a rectifier in series with said single pole double throw switch and said one winding, said rectifier being energized when said switch solenoid is energized and the anode is rotating, a sensing solenoid connected to the rectifier, an exposure control timer, a sensing solenoid control switch connected to the timer, and a high tension control switch connected to the timer to close the high tension circuit and energize said transformer when the sensing solenoid control switch is closed to energize the timer.

11. In combination, an X-ray tube of the rotating anode type, said tube including a plurality of windings, a winding energizing circuit parallel connecting the windings, a high tension exposure circuit connected to the X-ray tube and including a normally open switch means, a sensing circuit including switch control means to close the normally open switch means when the sensing circuit is energized, and control means connected to said energizing circuit and said sensing circuit to selectively disconnect one of the windings from the energizing circuit and connect said one winding to the sensing circuit and thereby energize the sensing circuit only with induced current flowing in the one winding.

12. The device of claim 11 wherein the control means includes a time-delay means energized by the energizing circuit and a selection switch actuated by the time-delay means a predetermined time interval after the energizing circuit has been closed, and wherein the selection switch disconnects said one winding and connects said one winding to the sensing circuit after such interval.

13. In combination, an X-ray tube including a cathode and a rotatable anode, a high tension transformer includ- 6 ing a secondary winding connected to the anode and to the cathode, a plurality of parallel connected windings for inducing a magnetic field to cause said anode to rotate, a winding energizing circuit including an exposure control switch connected to said windings, a solenoidactuated switch means in series with one of said wind- I ings, a time-delay trigger tube series connected to the switch means solenoid and connected in parallel with the windings, a rectifier in series with said switch means and said one winding, said rectifier being energized when said switch solenoid is energized and the anode is rotating, a sensing solenoid connected to the rectifier, a timer, a sensing solenoid-controlled switch connected to the timer, and a high tension control switch connected to the timer and other high tension circuit to close the high tension circuit and energize said transformer when the sensing solenoid-controlled switch is closed to energize the timer.

14. In combination, an X-ray tube including a cathode and a rotatable anode, a high tension transformer including a winding connected to the anode and to the cathode, a plurality of windings for inducing a magnetic field to cause said anode to rotate, a winding energizing circuit including an exposure control switch connected to said windings, a solenoid-actuated switch means in series with one of said windings, a time delay means series connected to the switch means solenoid and connected to the energizing circuit, a sensing solenoid connected to said switch means, said sensing solenoid being energized when said switch solenoid is energized and the anode is rotating, a timer, a sensing solenoid-controlled switch connected to the timer, and a high tension control switch connected to the timer and to the high tension circuit to close the high tension circuit and energize said transformer when the sensing solenoid-controlled switch is closed to energize the timer.

15. In combination, an X-ray tube including a cathode and a rotatable anode, a high tension transformer including a winding connected to the anode and to the cathode, a plurality of parallel connected windings for inducing a magnetic field to cause said anode to rotate, a winding energizing circuit including an exposure con trol switch connected to said windings, switch means in series with one of said windings for disconnecting said one winding from said energizing circuit when the switch means is actuated, a time delay means connected to the switch means and connected to said winding energizing circuit for actuating the switch means a predetermined time interval after the exposure control switch has been closed, a sensing means connected to said one winding when said switch means is actuated, said sensing means being energized by the induced current flowing in said one Winding when the anode is rotating, a high tension control means connected to the high tension control circuit to close the high tension circuit and energize said transformer, said high tension control means being actuatable by the sensing means when the induced current exceeds a predetermined minimum value and the sensing means is connected to said one winding.

16. In combination, an X-ray tube including a cathode and a rotatable anode, a high tension transformer including a winding connected to the anode and to the cathode, a plurality of parallel connected windings for inducing a magnetic field to cause said anode to rotate, a Winding energizing circuit including an exposure control switch connected to said windings, switch means in series with one of said windings for disconnecting said one winding from said energizing circuit when the switch means is actuated, a time delay means connected to the switch means and connected to said winding energizing circuit for actuating the switch means a predetermined time interval after the exposure control switch has been closed, a sensing means connected to said one winding when said switch means is actuated, said sensing means being energized by the induced current flowing in said one winding when the anode is rotating, a timer, a sensing means controlled switch connected to the timer and actuatable by the sensing means when the induced current exceeds a predetermined minimum value and the sensing means is connected to the one winding, and a high tension control switch connected to the timer and to the high tension control circuit to close the high tension circuit and energize said transformer when the sensing means controlled switch is closed to energize the timer.

References Cited in the file of this patent UNITED STATES PATENTS

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