US2786949A - Controlled voltage system for X-ray tube units - Google Patents

Description

CONTROLLED VOLTAGE SYSTEM FOR X-RAY TUBE UNITS Cormack E. Boucher, Seattle, Wash. Application December 14, 1953, Serial No. 398,032 9 (Ilaims. (Cl. 250-103) This invention relates to a system for supplying a controlled voltage to the primary of the voltage step-up transformer for an X-ray tube. For convenience in description, the transformer and X-ray tube will be referred to as an X-ray tube unit.

A main object of the present invention is to provide a voltage sup ly system operable automatically when set into operation to supply to an X-ray tube unit, connected to the system, a voltage controlled to rise gradually from zero to a selected predetermined operating value, thus properly to warm up the tube, to remain at such operating value for a selected predetermined period of time to properly X-ray the material being inspected, and then to return to zero.

A more specific object of the present invention is to provide a system of the type described above, wherein means are provided for preventing the restoration, during a cycle of operation of the system in which a power interruption occurs, of a high voltage on the X-ray tube unit, when power is restored to the system following the interruption.

A further object of the present invention is to provide for an X-ray tube unit, a voltage supply system having a reversible motor controlled to drive a variable voltage output device connected to the X-ray tube unit, from a zero position to a selected predetermined operating value position, to be stalled to maintain the latter position for a selected predetermined time, and then reversed to cause the voltage output of the device to return to zero.

Another object of the present invention is to provide in a voltage supply system for an X-ray tube unit a variable voltage supply device connected to and energized from a source of electrical power, and connected to the X-ray tube unit through the contacts of a relay means, means operable to energize the relay means only at the commencement of a cycle of operation of the system and then to be inactivated, and relay holding means energized from the source through the contacts of the relay means and operable to energize the relay means from the source after the relay means is initially energized, whereby when a power interruption occurs during a cycle of operation of the system, the relay means is deenergized and its contacts opened to break the circuit of the holding means and the circuit of the X-ray tube unit, and the relay means and thus the X-ray tube unit will remain deenergized until the commencement of another cycle of operation despite the restoration of power to the system from the power source.

Various other objects of the present invention will be apparent from the following description taken in connection with the accompanying drawings wherein:

Fig. 1 shows a schematic wiring diagram of a voltage supply system embodying the concepts of the present invention; and

Fig. 2 is a graph illustrating how voltage is normally applied to the X-ray tube unit by the system of the present invention.

The voltage supply system of the present invention is designed to supply a controlled voltage to an X-ray tube unit, indicated at 3, the unit including a voltage stepup transformer 5, the secondary winding 7 of which is connected by conductors 9 and 11 to the anode 13 and cathode 15 of an X-ray tube 17. The system is supplied rates Patent with electrical power from power source conductors 19 and 21, which are connected to a source of electrical power through switches 23 and 25, respectively.

The autotransformer winding 27 of the variable voltage output device, indicated generally at 33, is connected across the conductors 19 and 21 by conductors 29 and 31. The device 33 is provided for supplying a variable voltage to the tube unit 3 and includes a movable contact 35. The primary 37 of step-up transformer 5 is connected by a conductor 39 to power source conductor 19, and by a conductor 41 to one contact of a pair of contacts 43 of relay 45. The other contact of said pair is connected to autotransformer contact 35 by a conductor 47.

Reversible motor 49 has its main field winding 51 directly connected between the conductors 19 and 21 by conductors 53 and 55. The rotor 57 of the motor directly drives contact 35 of the autotransformer as indicated by the dotted line 59, which may represent a shaft driven by the rotor. Motor 49 is provided with two pairs of shading poles 61 and 63, the former each including a simple copper band, and the latter each including a winding. The two windings of poles 63 are connected in series by a conductor 65, and are connected through conductors 67 and 69 to the opposite contacts of a switch 71, which when closed provides a closed circuit including both windmgs.

The ampere turns of the windings on the shading poles 63 is sufiicient that, when the switch 71 is closed, the rotational torque created by the shading poles 61 will be overcome and the motor will reverse direction. Motor 49 is of conventional construction and of the type shown in the patent to Crise et al. 2,134,685.

Switch 71 is controlled by an exposure time mechanism including a synchronous motor 73 connected by conductors 75 and 77 directly across conductors 19 and 21. Motor 73 drives a switch actuating cam 79, associated with switch 71, through a speed reduction unit 81 and an adjustable friction drive device 83, both being of conventional construction. The drive device includes a pair of constantlyengaged discs 85 and 87, one of the discs carrying a friction facing, disc 87 being spring biased into engagement with disc 85 as shown. Cam 79 is adapted to be selectively angularly spaced from switch 71 by turning a hand 89 mounted on the cam shaft, movement of the hand causing slippage between discs 85 and 87. A scale graduated in terms of exposure time is provided, as shown, adjacent hand 89 and across which the hand moves when it is adjusted. The setting of cam 79 determines the time of exposure of the system in a manner which will be presently apparent.

Provided in the path of travel of autotransformer contact 35 is a stop 91 carried by a hand 93, which is mounted for adjustable pivotal movement about shaft 59, and adapted when adjusted to move across the face of a scale, as shown, graduated in terms of thickness of the object to be radiographed. Several or more series of thickness graduations may be provided to account for diiferent classes of materials. Upon energization of motor 49, following closure of switches 23 and 25, contact 35 will be advanced, and after a selected predetermined period of time, determined by the speed of motor 49 and the spacing of stop 91 from the initial position of contact 35, will engage the stop, causing the motor to stall. This will not harm the motor as it is designed to permit this action without being damaged.

Relay 45, previously mentioned, has its winding connected by a conductor 95 to power source conductor 19,

' mounted on shaft 59, as indicated, in a position to-be in Patented Mar. 26, 1951 it 3 contact with fixed Contact '101 when movable autotransformer contact 35 is in its Zero position, the position shown in Fig. I. It follows from the just described circuit that when autotransformer contact 35 is moved away from its Zero position, switch 99 will be opened, both being operated by common shaft 59.

The winding of relay 45 is also connected across power source conductors 19 and 21 through a holding circuit arranged in parallel with switch 9?, the holding circuit including conductor 95, previously mentioned, second contacts 105 of relay 45, and a conductor it)? which is connected to power source conductor 21. Connected by a conductor 10? in parallel with the winding of the relay is an indicating lamp 111, which when energized informs the operator that the relay is energized and thus the X-ray tube unit is connected to the autotransformer through relay contacts 43.

A second indicating lamp 113 is connected by conductors 115 and 117 across the power source conductors 19 and 21 through a switch which includes a fixed arcuatc contact 119 and movable contact arm 103, previously mentioned. Thus, this switch will be open when autotransforme'r contact 35 is in its zero position, but will be closed shortly after motor 49 is energized because of contact arm 103 being brought into engagement with arcuate contact 119. Lamp 113 indicates that the system, apart from relay 45 and X-ray tube unit 3, is in operation.

The operation of the system is as follows. The desired operating voltage and exposure time are determined by taking into account the thickness and kind of material to be X-rayed. Hand 93 of the variable voltage device is adjusted to dispose stop 91 to stop contact 35 at a position on the autotransformer winding to achieve the selected operating voltage, and hand 89, of the timer, is adjusted to angularly space the lobe of cam 79 a distance tromswitch 71 to achieve the selected exposure time.

Then, switches 23 and 25 are closed and electrical power is immediately furnished to autotransformer winding 27, motor 49, motor 73, and to the winding of relay 45 and lamp 111 through closed contacts 161 and 103 of switch 9. Thus, simultaneously, motor 49 drives contact 35 away from its Zero position, motor 73 drives cam 79 toward a closing position with switch 71, and the contacts 43 and 105 of relay 45 are closed to connect the autotransformer winding to the X-ray tube unit and to close the relay holding circuit. The relay now being energized through the holding circuit is not afiiected by the opening of contacts 1&1 and 193 of switch 9%, which action occurs just as contact 35 leaves its zero position. Just after contact arm 103 leaves contact 101, will engage arcuate contact 115 and energize lamp 113 to show that the system is in operation.

As contact 35 moves toward stop 91, the voltage applied to the X-ray tube-unit increases gradually properly to warm up the tube. When contact 35 reaches stop 91,

motor 4-5 stalls and the voltage applied to the X.-ray

tube unit remains constant at its operating value. This supply of a constant value operating voltage continues for the selected predetermined time as determined by the setting of hand 89. At the end of such time, the material being X-rayed has been properly exposed, and the lobe on cam 75 engages and closes switch 71. Closing of said switch shortcircuits motor windings 63 and causes motor 43 to rotate in the opposite direction and thuscontact 35 is driven back along the autotransformer winding to its zero position, bringing the applied voltage to the X-ray tube back to zero. Just before contact 35 reaches its zero position, switch arm 103 leaves arcuate' contact 119 and lamp 113 is deenergized, informing the operator that the power switches 23 and 25 should be opened. The cycle of operation is now completed, and the setting of hands 93 and 89 may be left undisturbed if other similar pieces of material are to be X-rayed, or the settings may be changed ,for properly X-raying pieces of material of dif ferent thicknesses or classes.

Now, should a power interruption occur during a cycle of operation, the voltage on the X-ray tube unit will drop to zero, and were it not for the unique construction of the present system, a high voltage would be suddenly restored to the X-ray tube when power is restored to the system following the interruption. The sudden application of a high voltage to the tube would be detrimental and would considerably shorten its life, or in some cases immediately permanently damage the tube. However, with the system of the present invention, no detrimental efiects are produced by power interruptions, because when a power interruption occurs, the relay 45 is deenergized and its contacts'open to break the holding circuit. Since switch 99 is open with respect to contact 101 any time after the initial period of operation of the system, a restoration of power to the system cannot restore power to the X-ray tube unit because both circuits for energizing relay 45 are open, and thus contacts 43 in the X-ray tube unit voltage supply circuit will remain open. The restoration of power will, however, reenergize motors 49 and 73 and the cycle of operation of the system is completed and the system restored to the initial or zero condition without any power being supplied to the Y-ray unit. At the end of the cycle, a new cycle may be commenced and the material being tested may now be properly X-rayed.

By the present invention there has been provided a voltage supply system for an X-ray tube unit operable automatically when set into operation to supply gradually an increasing warm up voltage to the unit until a selected predetermined operating voltage is reached, maintain such operating voltage for a selected predetermined period of time, and then terminate the supply of voltage. The system is adjustable to permit varying the value of the operating voltage and the length of exposure time, and thus different thicknesses and classes of materials may be readily properly X-rayed. An important advantage of the present invention is that the system is operable to prevent the application of a high voltage to the X-ray tube when power is restored to the system following a power interruption.

Having described the invention in what is considered to be the preferred embodiment thereof, it is desired that it be understood that the specific details shown are merely illustrative and that the invention may be carried out in other ways.

I claim:

1. A system for supplying a controlled voltage to an X-ray tube unit, comprising a source of electrical energy, a variable voltage output device connected to said source, means for connecting the output of said device to the tube unit, a reversible motor mechanically connected to said device to vary the output of the same, and timer means for controlling the motor so as to elevate the output from a low value to a selected predetermined higher valueand then reversing operation of the motor after a predetermined period of time to bring the source back to a low value.

2. A system for supplying a controlled voltage to an X-ray tube unit, comprising a source of electric power, means energized from said source for furnishing a varying voltage to said tube unit, relay means connecting the lastnamed means to said tube unit, means energized from said source operable for momentarily furnishing electric current to said relay means, when said power source commences to furnish power to the system, only at the beginning of a cycle of operation of the system, and holding means energized from the source through contacts of the relay means for holding the relay means energized from the source after initial energization thereof, whereby, when a power interruption occurs in said source, said holding means is rendered inoperative to release said relay means, whereupon the relay means opens and remains open and said X-ray tube unit is deenergized for the remainder of the cycle of operation during which the power interruption occurs.

3. In a cyclic control circuit for an X-ray tube unit, including a source of electric power, means energized from said source for furnishing voltage to said tube unit, relay means for connecting the last-named means to said tube unit, a closed circuit connecting said relay means to said source, means connected to the source through contacts of said relay means for holding said relay means energized once the relay means is energized, and means energized from said source for opening said closed circuit after said relay means has been energized, and for maintaining said circuit open during the remainder of a cycle of operation irrespective of power interruptions and re-establishrrnents, whereby when a power interruption occurs in the source, said holding means is temporarily deenergized to release said relay means, which opens to break the circuits to the holding means and X-nay tube unit, so that the relay means and the X-ray tube unit remain deenergized during the remainder of said cycle during which the power interruption occurs, despite power restoration to the system.

4. A system for supplying a controlled voltage to an X-ray tube unit, comprising a variable voltage output device, means for connecting the device to the unit, a motor mechanically connected to the device operable when energized to operate said device so as to raise the output voltage thereof, said motor having normally inactive means responsive when activated to reverse the direction of rotation of the motor, and settable timing means operatively connected to the last-named means, responsive after the completion of a set interval of time to actuate the l-asnnamed means to cause the voltage of said device to decrease.

5. A system for supplying a controlled voltage to an X-ray tube unit, comprising a variable voltage output device, means for connecting the device to the unit, a motor mechanically connected to the device and operable when energized to operate said device so as to raise the output voltage thereof, said motor having normally inactive means responsive when activated to reverse the direction of rotation of t e motor, timing means responsive after the completion of an interval of time to actuate the last-named means to cause the voltage of said device to decrease, power source means for supplying electrical power to the said device, and relay means responsive to an interruption of power from said power source means to disconnect said device from. the X-ray tube unit.

6. A circuit comprising an X-ray tube unit, a variable voltage output device responsive when driven in one direction to supply an increasing voltage, and when driven in the opposite direction to supply a decreasing voltage, means operable to connect the device to the X-ray tube unit, reversible electric drive means operatively connected to said device and having normally inactive reversing means, and being operable when energized, when said reversible means is inactive, to drive said device in said one direction, means operatively associated with said device operable to limit driving movement in said one direction and thus cause the output voltage of said device, when said device is driven to said limit, to obtain a constant vmue, and means operatively connected to said electric drive means operable a selected predetermined period of time after said device is driven to said limit to activate said reversing means to cause the output voltage of said device to decrease.

7. A system for supplying :a controlled voltage to an X-ray tube unit, comprising a variable voltage output device adapted to be connected to a source of electric power and responsive when driven in one direction to supply an increasing voltage and when driven in the opposite direction to supply a decreasing voltage, means operable to connect the device to the X-ray tube unit, reversible electric drive means adapted to be electrically connected to said source of power, openatively connected to said variable voltage device and having normally inactive reversing means, and being operable when energized, when said reversing means is inactive, to drive said device in said one direction, means associated with said device operable to limit driving movement thereof in said one direction and thus cause the output voltage of the device, when said device is driven to said limit, to attain a generally constant value, electric timing means adapted to be connected to the source of power and operatively connected to said electric drive means, operable after passage of a predetermined period of time, after being energized, to activate said reversing means to cause the output voltage of the device to decrease, and switch means operatively connected to said variable voltage device, said electric drive means, and said timing means, operable to simultaneously connect said three means to said source of power.

8. A circuit comprising an X-ray tube unit, a source of power, a variable voltage output device, connected to said source and responsive when driven in one direction to supply an increasing voltage and when driven in the opposite direction to supply a decreasing voltage, means operable to connect said device to said X-ray tube unit, reversible electric drive means electrically connected to said source of power and mechanically connected to said variable voltage device and having normally inactive reversing means, and being operable when energized, when said reversing means is inactive, to drive said variable voltage device in said one direction, adjustable means operable to limit driving movement of said variable voltage device in said one direction and thus cause the output voltage of said variable voltage device, when said voltage device is driven to said limit, to attain a generally constant value, electric timing means connected to said source of power and operatively connected to said electric 'drive means operable after the passage of a predetermined period of time, after said timing means is energized, to activate said reversing means to cause the output voltage of said variable voltage device to decrease, switch means for substantially simultaneously connecting or disconnecting said variable voltage device, said reversible electric drive means, and said timing means to or from said source of power, and means responsive to a power interruption for disconnecting said Xray tube unit from said device for the remainder of the cycle of operation during which the interruption occurs.

9. A system for supplying potential for an X-ray tube, comprising a source of electrical potential, a variable transformer means connected between said source and said X-ray tube for varying the potential supplied to said tube, operating means for said variable transformer means connected to said source and adapted upon energization to effect actuation of said transformer means to increase gradually the potential applied to said tube from a low value to a predetermined higher value, and, after a predetermined period of time, gradually to decrease the potential from said higher value to a relatively low value, and means responsive to an interruption of power from said source for opening the circuit between said X-ray tube and said transformer means, said circuit opening means being operatively connected to said transformer means whereby said circuit opening meanscan be closed only after movement of said transformer means to the low potential position thereof whereby, in

. the advent of any power failure from said source during a cycle, the circuit to said X-ray tube will remain open even though power from said source should be restored.

References Cited in the file of this patent UNITED STATES PATENTS

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