US3887889A

US3887889A - High power variable autotransformer

Info

Publication number: US3887889A
Application number: US419694A
Authority: US
Inventors: Frank J Karlov; Leonidas Sidorewicz; Charles L Redfield; Robert Evans
Original assignee: Litton Medical Products Inc
Current assignee: ELSCINT IMAGING Inc; Elscint Ltd; Litton Medical Products Inc; Elscint Inc
Priority date: 1973-11-28
Filing date: 1973-11-28
Publication date: 1975-06-03
Anticipated expiration: 1992-06-03

Abstract

An autotransformer is disclosed for a power supply system for an x-ray generating apparatus. The autotransformer includes at least two interconnectable windings with at least one inner winding mounted within an outer winding. On three phase equipment, three such pair are provided on each transformer core. Taps at fixed intervals along the windings are brought out from the windings for external electrical connections. The inner windings are interconnected, with respect to the outer winding, in a lowvoltage input connection, where the tap connections are mostly in parallel, to a high-voltage input connection, where the tap connections are mostly in series. The outer winding is wound on a tube at a constant pitch and is made accessible for receiving a contact mechanism at any point along the entire length of winding. The contact mechanism has a metal contact movably mounted to contact the winding only at the time the power is being used. A solenoid and rod are utilized to actuate the metal contact. The entire contact mechanism is mounted on a carriage driven by a motor-driven lead screw having the same pitch as the outer winding of the autotransformer. The drive system functions to position the metal contact approximately over the proper turn of the outer winding for providing the desired output voltage. An indexing mechanism is provided to center the metal contact exactly over the selected turn. The indexing mechanism comprises a left-hand/right-hand 180* helical barrel cam mounted on the lead screw. A cam follower is provided to engage either the lefthand or right-hand helix to rotate the cam and lead screw to the 180* or absolute locking position. Since the lead screw has the same pitch as the outer winding, the center or locked position of the lead screw corresponds to the center position of the outer winding.

Description

United States Patent 11 1 Karlov et al.

[ June 3, 1975 1 HIGH POWER VARIABLE AUTOTRANSFORMER [75] Inventors: Frank J. Karlov, Park Ridge;

Leonidas Sidorewicz, Chicago; Charles L. Rediield, Woodridge; Robert Evans, Evanston, all of 111.

[73] Assignee: Litton Medical Products, Inc., Elk

Grove, 111.

221 Filed: Nov. 28, 1973 [21] Appl.No.:4l9,694

[56] References Cited UNITED STATES PATENTS 1,187,228 6/1916 Asch 338/181 1,652,017 12/1927 Krauss 338/181 X 1,821,927 9/1931 Caruso 338/178 1,955,906 4/1934 Crouse 338/180 X 2,091,371 8/1937 MCMaster 338/181 2,214,864 9/1940 Stonehill 336/148 X 2,440,540 4/1948 Farr 336/146 2,859,421 11/1958 Hoppermann... 336/148 3,215,963 1 1/1965 Frcdrickson 336/148 3,268,842 8/1966 Gibson et a1 336/148 X [57] ABSTRACT An autotransformer is disclosed for a power supply system for an x-ray generating apparatus. The autotransformer includes at least two interconnectable windings with at least one inner winding mounted within an outer winding. On three phase equipment, three such pair are provided on each transformer core. Taps at fixed intervals along the windings are brought out from the windings for external electrical connections. The inner windings are interconnected, with respect to the outer winding, in a low-voltage input connection, where the tap connections are mostly in parallel, to a high-voltage input connection, where the tap connections are mostly in series. The outer winding is wound on a tube at a constant pitch and is made accessible for receiving a contact mechanism at any point along the entire length of winding. The contact mechanism has a metal contact movably mounted to contact the winding only at the time the power is being used. A solenoid and rod are utilized to actuate the metal contact. The entire contact mechanism is mounted on a carriage driven by a motordriven lead screw having the same pitch as the outer winding of the autotransformer. The drive system functions to position the metal contact approximately over the proper turn of the outer winding for providing the desired output voltage. An indexing mechanism is provided to center the metal contact exactly over the selected turn. The indexing mechanism comprises a left-hand/right-hand 180 helical barrel cam mounted on the lead screw. A cam follower is provided to engage either the left-hand or right-hand helix to rotate the cam and lead screw to the 180 or absolute locking position. Since the lead screw has the same pitch as the outer winding, the center or locked position of the lead screw corresponds to the center position of the outer winding.

13 Claims, 11 Drawing Figures PATENTEU M3 ms SHEET 207. 0mm FDA-T; W72

HIGH POWER VARIABLE AUTOTRANSFORMER BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to power supply systems for x-ray generating devices and, more particularly, to autotransformers utilized in such systems.

2. Description of the Prior Art A typical x-ray generator, or power supply system, for an x-ray generating device, requires a highpower variable voltage primary source which may be an autotransformer.

There are basically two types of autotransformers utilized in x-ray generators. They are the carbon brush" autotransformer and the tapped autotransformer. The carbon brush autotransformer is designed to provide a continuously variable output, while the tapped autotransformer, with its power switches, is adapted to operate in coarse and fine steps.

Autotransformers also provide correction for known variable load losses. For the tapped autotransformer, this is accomplished by means of additional taps on the autotransformer and power switch. For the carbon brush autotransformer this is accomplished by providing means to drive the carbon brushes to different positions determined by the load.

Although the above-mentioned types of autotransformers have been used successfully in x-ray generators, both types suffer various shortcomings in their construction, which makes their assembly cumbersome and costly.

A serious shortcoming with the tapped autotransformer is that it is relatively expensive because it requires a multitude of taps being brought out during the winding operation. Moreover, such autotransforrners require power tap switches to accommodate the variable output and to correct the input utility main power deviations. As a result, a considerable amount of labor is required during assembly to interconnect the taps to the switches.

Another serious shortcoming with tapped autotransformers is that because of the multitude of tap switch contacts in the circuit, the autotransformer has up to 5 percent voltage drop across the contact. Moreover, one design and winding cannot serve all three nominal line inputs; namely, 240-volt, 380-volt and 480-volt lines. Each line input requires a different design in terms of wire size and amount of turns.

A serious shortcoming with the carbon brush autotransformer is that the brush can short out one or more turns, thereby creating circulating current in the turn or turns of wire, resulting in unnecessary heating. Because of this short-circuiting characteristic, the brush itself must have sufficient resistance to limit the circulating current to levels that will not burn out the wire. This resistance in turn is very objectionable when high current is being drawn therethrough because the voltage drop across the brush is high.

Another problem is that the carbon brush autotransformer has relatively low volts per turn to further limit the circulating current. As a result, more wire is required.

For the reasons stated above, the carbon brush autotransformer is relatively inefficient and has limits as to the current that can be carried. Furthermore, carbon brush autotransformers, because of the negative temperature resistance coefficient of carbon are subject to catastrophic failures when overloaded.

As with the tapped autotransformer, one design of the carbon brush autotransformer cannot cover the three most common nominal line voltages.

SUMMARY OF THE INVENTION The present invention obviates the above-mentioned shortcomings by providing an autotransformer that is simple in construction, relatively inexpensive to manufacture and efficient in operation.

In its broadest aspect, the invention pertains to an autotransformer having an outer winding for receiving a metal contact at any point along the entire length of winding. The metal contact is mounted on a carriage driven by a lead screw to enable the contact to be positioned approximately over the proper turn of the outer winding. An indexing mechanism is provided for centering the metal contact exactly over the selected turn.

The primary advantage of the present invention is that the indexing mechanism prevents the metal contact from being positioned over two adjoining turns thereby preventing arcing and short circuiting between the turns.

Another important advantage of the present invention is that, unlike the carbon brush, the metal contact has a very low voltage drop across it, thereby being capable of carrying high momentary currents, which is typical of an x-ray generating system.

The autotransformer also has at least one inner winding mounted within the outer winding, with taps being brought out therefrom for external electrical interconnections between the windings. The inner winding has easily chargeable taps for shifting from a low voltage connection, with the tap interconnections being mostly in parallel, to a high-voltage connection, with the tap interconnections being mostly in series.

A primary advantage of this construction is that at the low-voltage connections, the parallel interconnections increase the wire size, thereby increasing the current carrying ability. Conversely for a given power output, the size of the copper wire decreases as the voltage is increasing, thereby always maintaining optimum current-carrying capabilities of the wire.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The present invention, both as to its organization and manner of operation, together with the further advantages thereof, may best be understood by reference to the following description, taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an isometric view of an autotransformer in accordance with the present invention;

FIGS. 20, b, c and d are schematic views of the telescoping windings showing the low input voltage position in FIG. 2a and increasing to the high input voltage position in FIG. 2d;

FIG. 3 is a fragmentary view of the contact mechanism;

FIG. 4 is a fragmentary view of the contact and indexing mechanisms;

FIG. 5 is a fragmentary perspective view of the contact and indexing mechanisms;

FIG. 6 is a fragmentary view of the indexing mechanism;

FIG. 7 is a sectional view of the indexing mechanism taken along line 7-7 of FIG. 6; and

FIG. 8 is a fragmentary view of the indexing mechanism rotated 90 with respect to that shown in FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, FIG. 1 illustrates an autotransforrner generally indicated by arrow 20 comprising three sets of windings which are interconnected to form a three-phase x-ray generator. Although a three-phase x-ray generator is illustrated in FIG. 1, the novel construction of the present invention can also be utilized in a single-phase x-ray generator where only one set of windings is required. Each of the three sets includes an outer winding 21 having a pair of

windings

22 and 23 mounted within the winding 21. The reason that the

windings

22 and 23 can be mounted within the outer winding is because in a typical x-ray generator system, it is not necessary to operate at an output potential of less than 26 pKv. Thus, the portion of the winding from O to 26 pKv (the winding 22) does not need to be contacted. Similarly, the winding 23, which is used to accommodate different line voltage inputs, also does not need to be contacted. It should be noted that if the

windings

22 and 23 were not wound under the winding 21, the whole assembly shown in FIG. 1 would be twice as long and weigh approximately 30 percent more.

For each set of windings, a plurality of taps at fixed intervals are brought out for external electrical connections dictated by the input line voltage. In the preferred embodiment, the construction of the three windings allows any line input between 189 and 567 volts by the simple reconnection of the taps. For sake of clarity, these taps and interconnections are shown schematically only in FIGS. 2a, 2b, 2c and 2d. However, a partial set of representative taps 4, 5 and 6 are shown on the uppermost winding 21 of the apparatus 20 in FIG. 1.

In FIG. 2a, the winding 22 has two

taps

1 and 2, with the tap 1 connected to the nominal 240 v line input and the tap 2 connected to a tap 3 of the winding 21. The winding 21 also has a plurality of

taps

4, 5, 6 and 7 brought out at various points along the winding. The winding 23 has a plurality of taps 8 through 13 brought out at various points along the winding. The taps 11 and 12 are utilized to be interconnected with the line input. The

taps

8, 9, l0 and 13 are utilized to be interconnected with various of the taps 3 through 7 of the winding 21.

The type of interconnection depends on the line input voltage. In FIG. 2a, the low voltage input connection, the tap interconnections are 8-3, 9-4, -5 and 13-6. As can be seen, these interconnections are mostly in parallel to allow for greater wire size in order to have greater current carrying capabilities. In FIG. 2a, the line input is 240v. In FIG. 2b, for a 380v input, the tap interconnections are 8-4, 9-5, 10-6 and 13-7. In FIG. 2c, the 480v input, the tap interconnections are 8-6 and 9-7. Finally in FIG. 2d, the tap connection is 8 to 7. In this position, the winding interconnections are now entirely in series to accommodate the 550v input. It should be noted that in this position the wire size has been halved as compared to that shown in FIG. 20.

Referring again to FIG. 1, the windings 21 are wound on tubes (not shown) at a constant pitch and are supported by a pair of

columns

24 and 25. The

columns

24 and 25 are reinforced by a pair of cross beams 26 and 27 interconnecting the two.

The

columns

24 and 25 also function to support a contact mechansim 30 and an indexing mechanism 40. The contact mechanism 30 comprises three metal contacts 31 pivotally mounted on a movable support bar 32. This structure, in turn, is supported on a carriage 33 slidably mounted on a cylindrical rod 34. The carriage 33 also includes an apertured flange 35 for receiving a lead screw 36 to be axially driven thereby. In accordance with the present invention, the lead screw 36 is made to have the same pitch as the transformer coils in the windings 21. The lead screw 36 is rotatively driven by a motor 37 connected to the one end thereof. This drive system functions to move the contact mechanism 30 along the length of the windings 21 to enable the contacts 31 to contact any desired turn. The contacts 31, in turn, are electrically connected to the x-ray load which typically may include an additional power supply circuitry, i.e., a step-up transformer, and the x-ray tube.

As shown in FIGS. 1, 3 and 4, the metal contacts 31 are pivotally movable by means of a reciprocating drive rod 38 driven by a solenoid 39. The metal contacts 31 are movable to a first position to contact a respective turn on the windings 21 when the power is being used and to a second position to move out of engagement when the power is not being used.

An electronic logic system, not shown, is utilized to integrate the input information (KVP, mA load compensation, and line voltage input condition) into a signal that will indicate the specific turn on the transformer coil to be contacted to achieve the output selected. Also a feedback potentiometer (not shown) is utilized to indicate that the carriage 33 and the contacts 31 are positioned over the selected turn along the coil length. Whenever a KVp selector of mA selector (mA load compensator) is changed, a new set of logic factors is fed into the logic system which in turn generates a signal to the drive motor 37 to seek a new and correct position on the winding 21. Potentiometer feedback balances this signal when the lead screw 36 has positioned the contacts 31 approximately over the proper turn and turns off the drive motor 37 and disengages it from the lead screw 36.

The indexing mechanism 40 is then engaged to center the contacts exactly over the selected turns.

As more clearly shown in FIGS. 5 through 8, the indexing mechanism 40 comprises a left-hand/right-hand 180 helical barrel cam 41 mounted on the one end of the lead screw 36. The indexing mechanism also includes a linearly actuated index pin 42 mounted on a carriage 43. The carriage 43 is threadedly mounted on a second lead screw 44 which, in turn, is rotatively driven by a second drive motor 45.

In operation, after the indexing mechanism has been actuated, the index pin 42 traverses the length of the cam 41 until it engages either the left-hand or the righthand helix. Further travel of the index pin 42 causes the cam 41 and lead screw 36 to rotate until the cam follower reaches the l or absolute locking position, denoted by letter A.

Since the lead screw 36 and the transformer coils 21 have the same pitch, every full turn of the lead screw 36 will cause the contacts 31 to traverse a one turn distance over the one length of the autotransformer coils 23. Moreover, the locked position A of the cam 41 and lead screw 36, for each turn of the lead screw, has been calibrated to correspond with the center position of each turn of each winding 21. As a result, in any locked position A, the contacts 31 are assured of being centered over the center of a particular turn.

When the index pin 42 is in the locked position A, a switch (not shown) is energized which, in turn, closes the circuit to actuate the solenoid 39 to move the contacts 31 into engagement with the desired turns of the windings 21.

As can be seen, a new and improved autotransformer has been described that can easily accommodate various line inputs, and that ensures proper and centered contact engagement with the windings.

It should be noted that various modifications can be made to the assembly while still remaining within the purview of the following claims.

What is claimed is:

l. A transformer comprising:

a first continuous winding forming a plurality of turns;

means for contacting individual turns of said Winding, said means comprising a metal contact movably mounted on a carriage, said contact having a bearing surface for engaging said turns;

means for axially moving said metal contact along the length of said winding and positioning said metal contact approximately over any desired turn of said winding; and

indexing means for automatically centering said metal contact exactly over the midpoint of any selected turn, said indexing means including means for sensing the position of said metal contact with said selected turn and moving said metal contact, in response to the sensed information, to the midpoint of said selected turn.

2. The combination of claim 1 further including means for actuating said metal contact in and out of engagement with said turns.

3. The combination of claim 2 wherein said actuating means includes a solenoid connected through a connecting rod to said metal contact.

4. The combination of claim 1 wherein said moving and positioning means comprises a lead screw drivingly engaging the carriage of said metal contact.

5. The combination of claim 4 wherein the threads of said lead screw are of the same pitch as the turns of said winding.

6. The combination of claim 5 wherein said indexing means comprises:

a cam for rotating said lead screw, said cam having a predetermined angular position corresponding to each revolution of the lead screw, said predeter mined angular position also being calibrated to correspond to the center position of the metal contact with respect to each turn; and

a cam follower for engaging said cam and rotating said cam until it reaches said predetermined angular position.

7. The combination of claim 6 wherein said cam includes a pair of cam surfaces, said first surface being a left-hand surface corresponding to one of the angular position of said lead screw for each revolution, said second surface being a righthand surface corresponding to the other 180 of the angular position of said lead screw for each revolution.

8. The combination of claim 7 wherein said cam surfaces face each other and converge at a point corresponding to said predetermined angular position.

9. The combination of claim 1 wherein said first continuous winding has a plurality of taps at fixed intervals along the length of said winding brought out for external electrical connections.

10. The combination of claim 9 further including:

a second continuous winding having a plurality of taps at fixed intervals along the length of said winding brought out for external electrical connections; and

means for interconnecting one or more of the taps of said first winding with one or more of the taps of said second winding.

11. A transformer comprising:

a first continuous winding forming a plurality of turns;

means for axially moving said metal contact along the length of said winding and positioning said metal contact approximately over any desired turn of said winding, said moving and positioning means comprising a lead screw drivingly engaging the carriage of said metal contact, the threads of said lead screw being of the same pitch as the turns of said winding; and

indexing means for centering said metal contact exactly over the midpoint of any selected turn, said indexing means comprising a cam for rotating said lead screw, said cam having a predetermined an gular position corresponding to each revolution of the lead screw, said predetermined angular position also being calibrated to correspond to the center position of the metal contact with respect to each turn, and a cam follower for engaging said cam and rotating said cam until it reaches said predetermined angular position.

12. The combination of claim 11 wherein said cam includes a pair of cam surfaces, said first surface being a left-hand surface corresponding to one 180 of the angular position of said lead screw for each revolution, said second surface being a right-hand surface corresponding to the other 180 of the angular position of said lead screw for each revolution.

13. The combination of claim 12 wherein said cam surfaces face each other and converge at a point corresponding to said predetermined angular position.

Claims

1. A transformer comprising: a first continuous winding forming a plurality of turns; means for contacting individual turns of said winding, said means comprising a metal contact movably mounted on a carriage, said contact having a bearing surface for engaging said turns; means for axially moving said metal contact along the length of said winding and positioning said metal contact approximately over any desired turn of said winding; and indexing means for automatically centering said metal contact exactly over the midpoint of any selected turn, said indexing means including means for sensing the position of said metal contact with said selected turn and moving said metal contact, in response to the sensed information, to the midpoint of said selected turn.

6. The combination of claim 5 wherein said indexing means comprises: a cam for rotating said lead screw, said cam having a predetermined angular position corresponding to each revolution of the lead screw, said predetermined angular position also being calibrated to correspond to the center position of the metal contact with respect to each turn; and a cam follower for engaging said cam and rotating said cam until it reaches said predetermined angular position.

7. The combination of claim 6 wherein said cam includes a pair of cam surfaces, said first surface being a left-hand surface corresponding to one 180* of the angular position of said lead screw for each revolution, said second surface being a right-hand surface corresponding to the other 180* of the angular position of said lead screw for each revolution.

10. The combination of claim 9 further including: a second continuous winding having a plurality of taps at fixed intervals along the length of said winding brought out for external electrical connections; and means for inTerconnecting one or more of the taps of said first winding with one or more of the taps of said second winding.

11. A transformer comprising: a first continuous winding forming a plurality of turns; means for contacting individual turns of said winding, said means comprising a metal contact movably mounted on a carriage, said contact having a bearing surface for engaging said turns; means for axially moving said metal contact along the length of said winding and positioning said metal contact approximately over any desired turn of said winding, said moving and positioning means comprising a lead screw drivingly engaging the carriage of said metal contact, the threads of said lead screw being of the same pitch as the turns of said winding; and indexing means for centering said metal contact exactly over the midpoint of any selected turn, said indexing means comprising a cam for rotating said lead screw, said cam having a predetermined angular position corresponding to each revolution of the lead screw, said predetermined angular position also being calibrated to correspond to the center position of the metal contact with respect to each turn, and a cam follower for engaging said cam and rotating said cam until it reaches said predetermined angular position.

12. The combination of claim 11 wherein said cam includes a pair of cam surfaces, said first surface being a left-hand surface corresponding to one 180* of the angular position of said lead screw for each revolution, said second surface being a right-hand surface corresponding to the other 180* of the angular position of said lead screw for each revolution.