US3828192A

US3828192A - Spherical segment electrode imaging chamber

Info

Publication number: US3828192A
Application number: US00393419A
Authority: US
Inventors: A Morsell
Original assignee: Xonics Inc
Current assignee: ELSCINT IMAGING Inc; Elscint Ltd; Elscint Inc
Priority date: 1973-08-31
Filing date: 1973-08-31
Publication date: 1974-08-06
Anticipated expiration: 1991-08-06
Also published as: FR2242700A1; CA1035828A; IT1018976B; NL7410164A; GB1428942A; FR2242700B1; DE2434557A1; BE817995A; JPS5055287A

Abstract

An imaging chamber for an electron radiography system, including spaced spherical electrodes defining a gas gap therebetween. An arrangement for clamping the receptor sheet and stretching it to a spherical configuration against one of the electrodes. A plurality of clamp strips disposed about one electrode and spring loaded toward the other electrode, with the other electrode being moveable toward the first electrode to clamp the receptor sheet at the clamp strips and then move the clamp strips against the spring load to stretch the clamped receptor sheet.

Description

United States Patent 1191- Morsell Aug. 6, 1974 SPHERICAL SEGMENT ELECTRODE IMAGING CHAMBER Primary Examiner-William F. Lindquist [75] .Inventor: Arthur Lee Morsell, Tarzana, Calif. $32 25 Agent or Flrm Hams Kern wane & [73] Assignee: Xonics, Inc., Van Nuys, Calif. 22 Filed: Aug. 31, 1973 h be d, h

Imaging c am r or an e ec ron ra tograp y sys- [211 Appl' 3932419 tem, including spaced spherical electrodes defining a gas gap therebetween. An arrangement for clamping 52 us. Cl. 250/315, 250/379, 313/100 the reoeptorsheetand Stretching itto aspherieal [511 1m. C1. .I.1T..i1i....'..;"..;.III603517726 figuration, against one of the eleotrodes- A plurality of [58] Field of Search 250/315, 315 A, 374, 379, clamp Stops dlsposed about one eleotrooe and sp g 250 332; 313 100 loaded toward the other electrode, with the other electrode being moveable toward the first electrode to [55] R f n Cit d clamp the receptor sheet at the clamp strips and then UNITED STATES PATENTS move the clamp strips against the spring load to stretch the clamped receptor sheet. 3,766,385 l0/l973 Morsell et a] 250/315 3,774,029 l1/l973 Muntz et al 250/315 8 Claims, 7 Drawing Figures 6/7.: SUPPL 5 pa W52 SHPPL 5 PATENTEI] 5 74 saw 2 ur 3 1 SPHERICAL SEGMENT ELECTRODE IMAGING CHAMBER This invention relates to electron radiography and in particular, to a new and improved imaging chamber. In electron radiography or ionography, an x-ray opaque gas is utilized between two electrodes in an imaging resolution loss in the images produced by conventional electronradiographic devices results from the fact that the x-rays entering the planar imaging chamber are parallel to the electric field in the gas gap only at one point (the center of the image if the x-ray source is positioned directly over the center of the imaging chamber). The angle between the incoming x-ray and the electric field can be appreciable at the edges of the image, with the result that electrons or ions formed in the gas gap along a well defined ray will spread out as they travel to the receptor surface along the electric field lines. This problem is discussed in detail in copending application Ser. No. 3l9,999, filed Jan. 2, 1973, entitled lonography Imaging Chamber and assigned to the assignee as the present application. Reference may be made to said copending application for a further dis cussion of the problem and a description of one solution utilizing complex electrode construction which produces a spherical electric field in a planar gas gap. Also, it is recognized that the severity of the resolution loss can be reduced by decreasing the gap thickness, but there is an accompanying loss in quantum efficiency in system operation which ordinarily is undesirable.

The conventional imaging chamber has utilized flat or cylindrical electrodes because the receptor sheet must be mounted on one of the electrodes during exposure. The present invention provides spherical electrodes in the imaging chamber and an arrangement for mounting the normally flat receptor sheet on one electrode. The spherical electrode system will eliminate the loss of resolution encountered in the planar electrode system, while permitting the use of larger gas gaps with their higher quantum efficiency. There are also certain mechanical advantages to the system of the invention. A concave spherical shape is convenient and practical for the top of the imaging chamber through which the x-rays pass. For the preferred embodiment of the table model cassette imaging chamber, the top of the chamber can have a radius of curvature equal to the imageto-source distance (typically 40 inches) and the inside surface of this top can be used as one of the spherical electrodes.

, Accordingly, it is an object of the present invention drawings merely show and the description merely describes a preferred embodiment of the present invention which is given by way of illustration or example. In the drawings:

FIG. 1 is a diagrammatic view of an electron radiographic system incorporating the presently preferred embodiment of the imaging chamber;

FIG. 2 is a plan view of the imaging chamber of FIG.

FIG. 3 is an enlarged sectional view taken along the line 3-3 of FIG. 2;

FIG. 4 is an enlarged sectional view taken along the line 4-4 of FIG. 2 showing the imaging chamber in the open position;

FIG. 5 is a view similar to that of FIG. 4 showing the imaging chamber in the closed position;

FIG. 6 is an enlarged sectional view taken along the line 6-6 of FIG. 2; and

FIG. 7 is a sectional view taken along the line 77 of FIG. 6.

The system of FIG. 1 includes an x-ray source 10 and an imaging chamber or cassette 11, with an object 12 to be x-rayed positioned above the imaging chamber. The imaging chamber includes an upper housing member 14 carrying an electrode 15, and a lower housing member 16 carrying another electrode 17 with an insulation sheet 18 therebetween. The dielectric receptor sheet 20 is mounted against the electrode 15. An electric field is established in the gap 21 between the electrodes by means of a power supply 22 connected via line 23 to the electrode 15 and via line 24 and feed through insulator 25 to the electrode 17. A supply of gas under pressure is provided to the gap 21 through line 26.

The system of FIG. 1 is operated in the usual manner to produce the desired picture and the present invention is directed to the electrode configuration and means for holding the receptor sheet at an electrode.

The electrodes l5, 17 have uniformly spaced spherical surfaces at the gap 21, with center coinciding with the x-ray source at 10. With this configuration, the electric field in the gap is everywhere directed toward the x-ray source, and the ions and electrons formed in the gas gap move along paths coinciding with rays from the x-ray source.

The imaging chamber 11 may be mounted in a table 30, with the rim of the upper housing member 14 resting on a lip 31 of the table.

The imaging chamber includes means for moving the lower housing member 16 toward and away from the upper housing member 14 between opened and closed positions. When in the open position, an exposed receptor sheet may be removed and the new receptor sheet inserted. When in the closed position, the imaging chamber is ready for an x-ray exposure. A preferred arrangement for opening and closing the chamber is illustrated in detail in FIGS. 3-7.

Four screws 35 are threaded into the upper housing member 14 and locked in place with keys 36. A nut 37 is threaded onto each of the screws 35, with a thrust bearing 38 positioned about the screw between the nut and the lower housing member 16. A sprocket 39 is affixed to each nut.

Four shafts 42 are carried in the lower housing member 16 on bearings 43 held in place by collars 44, with thrust bearings 45 between the shafts 42 and the lower housing member 16. Each shaft 42 has 51 threaded upper portion 47 which engages a mating opening 48 in the upper housing member 14. A felt pad oiler 49 may be mounted on the upper housing member 14 about each of the threaded portions 47. A sprocket 50 is carried on the lower end of each of the shafts 42.

A drive sprocket 53 is mounted on a shaft 54 carried in the lower housing member 16. A drive chain engages the

sprockets

39, 50, the drive sprocket'53, and additional idler sprockets as desired. A drive motor 56 is mounted on the lower housing member 16 and isconnected to the shaft 54 through a belt 57, pulley 58, slip clutch 59 and ratchet mechanism 60. The imaging chamber is driven from the open position of FIGS. 3 and 4 to the closed position of FIGS. -7 by energizing the motor 56 which drives the chain 55. The nuts 42 are rotated on the screws 47, raising the lower housing member 16. As the member 16 moves upward to an intermediate position, the rotating screws 47 enter the threaded openings 48. The lowermember l6 continues its upward movement until the chamber is closed with the eight screws providing a tight clamping force around the periphery of the chamber. When the chamber is closed, the clutch 59 slips and prevents damage to the mechanism until the drive motor is shut off. The ratchet mechanism 60 provides a lock up for maintaining the chamber closed after the drive motor is shut off. The chamber is opened by releasing the ratchet mechanism and running the motor 56 in the opposite direction.

The imaging chamber of the invention includes means for clamping or gripping the receptor sheet and holding it against one of the electrodes, here the electrode 15, as the chamber is closed. In the preferred embodiment illustrated, a frame is provided about the electrode 17, typically in the form of an upstanding ridge 63 on the lower housing member 16. The ridge 63 has the contour of the edge of the other electrode 15,

and a seal gasket 64 is'carried in a groove in the upper surface of the ridge.

Another frame is provided around the electrode and in the preferred embodiment illustrated comprises four

clamp strips

66, 67, 68, 69 along the four sides of the rectangular electrode. Each clamp strip has a lip 72 which tapers to a point and conforms to the contour of the corresponding edge of the electrode 15. Each clamp strip is carried on a plurality of spring mechanisms 74. Each of the spring mechanisms 74 includes a screw 75 mounted in the upper housing member 14, a'sleeve 76 positioned about the screw, and a spring 77 positioned about the sleeve in an opening in the upper member 14. The spring 77 engages a flange 78 of the clamp strip and urges the clamp strip downward against the head of the screw 75, to the position shown in FIG. 4.

A receptor sheet 80, typically an initially flat sheet of a dielectric plastic such as Mylar or Lexan is placed in the open imaging chamber resting on the ridge 63. The motor 56 is then energized to drive the lower housing member 16 upward into engagement with the upper housing member 14. As the lower member moves upward, the seal 64 initially engages the lower side of the lips 72 of the clamp .strips, with the receptor sheet therebetween. As the lower member continues to move upward, the receptor sheet is clamped or gripped between the clamp strips and the ridge. As the lower member continues upward, the springs 77 are compressed permitting a corresponding upward movement of the clamp strips bringing the upper surfaces of the lips 72 into engagement with the electrode 50, and the receptor sheet 80 is progressively stretched as it comes into contact with the convex surface of the electrode 15. When the chamber is closed, the receptor sheet is clamped in place and stretched into a spherical shape against the electrode 15 as shown in FIG. 5. Gas is introduced into the gap between the electrodes by the line 26 and passage 82 in housing member 16, the electric power supply is connected to the electrodes, and the x-ray exposure is made. The power supply is disconnected, the chamber pressure is reduced, and the chamber is opened, permitting removal of the receptor sheet for subsequent development. A typical imaging chamber may be in the order of 14 inches by 17 inches and when used with an x-ray source positioned at 40 inches from the gap, the receptor sheet is stretched less than 1 percent in being conformed to the spherical configuration. The receptor materials presently available, such as those mentioned above, are sufficiently strong and elastic to withstand such stretching without tearing or assuming a permanent set. When the receptor sheet is .positioned in the open chamber, it conforms quite well to the curved shape of the ridge 64 due to the force of gravity, although being stiff enough to clear the lower electrode. At this time the sheet is still flat in the middle and is circularly cylindrical for some distance inward from each corner. This sheet maintains this shape until the clamp strips are engaged and the center of the sheet contacts the upper electrode 15.

I claim:

1. In an imaging chamber for an x-ray system, the combination of:

first and second electrodes having the shape of spherical segments;

means for mounting said electrodes in spaced relation defining a gap therebetween so that an x-ray source will be located at the spherical center of said electrodes;

means for holding a charged particle receptor sheet in said gap at one of said electrodes; and

means for maintaining a gas under pressure in the gap.

2. An imaging chamber as defined in claim I wherein said means for mounting includes means for moving said first electrode toward and away from said second electrode, and said means for holding includes a first frame positioned about said first electrode,

a second frame positioned about and moveable toward and away from said second electrode, and

spring means urging said second frame away from said second electrode,

with said first and second frames clamping said receptor sheet therebetween as said first electrode is moved towards said second electrode, and stretching said receptor sheet into the shape of a spherical segment against said second electrode as said second frame is moved towards said second electrode against the urging of said spring means.

3. An imaging chamber as defined in claim 2 wherein said means for moving includes a plurality of threaded members, a drive motor, and means coupling said motor to said threaded members.

4. An imaging chamber as defined in claim 2 wherein said means for moving includes a plurality of screws mounted with one of said electrodes, at corresponding plurality of mating nuts mounted with the other of said electrodes for rotation on a screw, a drive motor, and

- ried in said ridge and engageable with said receptor having lips conforming to edges of said second electrode, with one surface of a lip engageable with said second electrode and with the opposite surface of the lip engageable with said receptor sheet.

7. An imaging chamber as defined in claim 6 wherein said first frame comprises a projecting ridge conforming to edges of said second electrode and fixed with respect to said first electrode.

8. An imaging chamber as defined in claim 7 wherein said means for maintaining includes a seal gasket carsheet at said lips.

Claims

1. In an imaging chamber for an x-ray system, the combination of: first and second electrodes having the shape of spherical segments; means for mounting said electrodes in spaced relation defining a gap therebetween so that an x-ray source will be located at the spherical center of said electrodes; means for holding a charged particle receptor sheet in said gap at one of said electrodes; and means for maintaining a gas under pressure in the gap.

2. An imaging chamber as defined in claim 1 wherein said means for mounting includes means for moving said first electrode toward and away from said second electrode, and said means for holding includes a first frame positioned about said first electrode, a second frame positioned about and moveable toward and away from said second electrode, and spring means urging said second frame away from said second electrode, with said first and second frames clamping said receptor sheet therebetween as said first electrode is moved towards said second electrode, and stretching said receptor sheet into the shape of a spherical segment against said second electrode as said second frame is moved towards said second electrode against the urging of said spring means.

4. An imaging chamber as defined in claim 2 wherein said means for moving includes a plurality of screws mounted with one of said electrodes, a corresponding plurality of mating nuts mounted with the other of said electrodes for rotation on a screw, a drive motor, and means coupling said drive motor to said nuts.

5. An imaging chamber as defined in claim 4 including means mounted with one of said electrodes defining a plurality of threaded openings, a corresponding plurality of second screws mounted in the other of said electrodes for rotation in said openings as said first electrode is moved toward said second electrode, and means coupling said motor to said second screws.

6. An imaging chamber as defined in claim 2 wherein said second frame comprises a plurality of clamp strips having lips conforming to edges of said second electrode, with one surface of a lip engageable with said second electrode and with the opposite surface of the lip engageable with said receptor sheet.

8. An imaging chamber as defined in claim 7 wherein said means for maintaining includes a seal gasket carried in said ridge and engageable with said receptor sheet at said lips.