US3755672A — Exposure compensating device for radiographic app…

Claim 1

Independent Claim 209 words

In a radiographic apparatus including a radiation source, an object plane for an object to be radiographed and an image plane for an image recording medium (5), a device for equalizing the average exposure of different portions of said image recording medium, comprising a compensating filter device disposed in the radiation path between said radiation Source and said object plane and including radiation absorbing means having a variable form such that the absorption values of said radiation absorbing means within different portions of the radiation beam from said radiation source can be varied substantially independently of other portions, control means (7) for varying the absorption values of said compensating filter device within different portions of the radiation beam by varying the form of said radiation absorbing means in response to control signals supplied to said control means, and radiation detecting means located beyond said object plane as seen from said radiation source for sensing the average intensity values of different portions of the radiation beam and generating output signals representing said average intensity values, the control signals for said control means determining the absorption values of said compensating filter device (6) within different portions of the radiation beam being derived from the output signals of said radiation detector means.

Claim 2

Dependent Claim 209 words

In a radiographic apparatus including a radiation source, an object plane for an object to be radiographed and an image plane for an image recording medium (5), a device for equalizing the average exposure of different portions of said image recording medium, comprising a compensating filter device disposed in the radiation path between said radiation Source and said object plane and including radiation absorbing means having a variable form such that the absorption values of said radiation absorbing means within different portions of the radiation beam from said radiation source can be varied substantially independently of other portions, control means (7) for varying the absorption values of said compensating filter device within different portions of the radiation beam by varying the form of said radiation absorbing means in response to control signals supplied to said control means, and radiation detecting means located beyond said object plane as seen from said radiation source for sensing the average intensity values of different portions of the radiation beam and generating output signals representing said average intensity values, the control signals for said control means determining the absorption values of said compensating filter device (6) within different portions of the radiation beam being derived from the output signals of said radiation detector means.

Claim 3

Dependent Claim 67 words

A device as claimed in claim 1, wherein said radiation absorbing means of said compensating filter device include a plurality of solid bodies of radiation absorbing material mounted so as to be movable relative to the radiation beam and each other in a plane substantially perpendicular to the direction of radiation, and said control means include servomotor means coupled to said absorption bodies for determining their positions.

Claim 4

Dependent Claim 61 words

A device as claimed in claim 1, wherein said radiation absorbing means of said compensating filter device include a layer of a formable radiation absorbing material disposed in a plane substantially perpendicular to the direction of radiation, and said control means include means for varying the thickness of said layer in the direction of radiation within different sections of the layer.

Claim 5

Dependent Claim 87 words

A device as claimed in claim 3, wherein said radiation absorbing means include a flat chamber arranged in a plane substantially perpendicular to the direction of radiation and filled with a radiation absorbing liquid, one of the major walls of said chamber consisting of a resiliently flexible diaphragm, and said control means being coupled to said diaphragm in a plurality of spaced points on the surface of the diaphragm for varying the distance of the diaphragm at said points from the opposite major wall of said chamber.

Claim 6

Dependent Claim 88 words

A device as claimed in claim 4, wherein said control means include a plurality of servomotors and associated Bowden cables, each of said Bowden cables having its one end coupled to the associated servomotor and its opposite end attached to said flexible diaphragm in one of said points thereon, whereby each servomotor can through its associated Bowden cable exert alternatively a pulling or a pushing force substantially parallel to the direction of radiation upon said diaphragm in the point of connection of the Bowden cable to the diaphragm.

Claim 7

Dependent Claim 27 words

A device as claimed in claim 4, wherein the points of connections of said control means to said diaphragm are arranged in a triangular grid pattern array.

Claim 8

Dependent Claim 47 words

A device as claimed in claim 4, wherein said flexible diaphragm has a smaller rigidity within portions of the diaphragm located along the junction lines between the connection points of said control means to the diaphragm than within portions of the diaphragm enclosed by said junction lines.

Claim 9

Dependent Claim 59 words

A device as claimed in claim 3, wherein said radiation absorbing means include a flat tray mounted in a plane substantially perpendicular to the direction of radiation and a moldable layer of a radiation absorbing material supported on said tray, and said control means include means for varying the thickness of said layer by molding the upper surface thereof.

Claim 10

Dependent Claim 104 words

A device as claimed in claim 8, wherein said means for molding the upper surface of said moldable layer of radiation absorbing material on said tray include an elongate resiliently flexible scraper means extending across said tray perpendicularly to the Direction of radiation and movable relative the tray in a direction perpendicular to the direction of radiation and the longitudinal direction of the scraper means, and said control means include a plurality of servomotors (40a-40e) coupled to said scraper means in spaced points along its length for varying the distance between the bottom of said tray and the scraping edge of said scraper means.

Claim 11

Dependent Claim 41 words

A device as claimed in claim 9, comprising dispensing means movable over said tray for dispensing said radiation absorbing material onto said tray through an elongate slot-shaped dispenser opening, said flexible scraping means forming the upper edge of said dispenser opening.

Claim 12

Dependent Claim 128 words

A device as claimed in claim 9, wherein said radiation absorbing material consists of an intrinsically loose and freely moving powder, said tray is provided with a foramenous bottom premeable to air but impervious to said powder, means are provided for producing a reduced air pressure underneath said bottom, whereby an air pressure gradient is established across the powder layer on said tray maintaining said powder layer in a substantially stable state, said scrapping means is adapted when moving over the tray to cut down into said powder layer (36) to a depth determined by the distance between said bottom of the tray and said scraping means, and means are provided for removing the portion of said powder layer located above the cutting edge of said scraping means.

Claim 13

Dependent Claim 33 words

A device as claimed in claim 11, wherein said means for removing said portion of said powder layer include an elongate suction nozzle extending along said scraping means above the cutting edge thereof.

Claim 14

Dependent Claim 111 words

A device as claimed in claim 9, wherein said radiation detecting means include elongate radiation detectors extending parallel to each other and to the direction of movement (38) of said scraping means (39), a diaphragm (43,44) provided with a slot-shaped aperture extending parallel to the longitudinal direction of said scraping means being movable relative to the radiation beam in the same direction as said scraping means and in synchronism therewith in such a manner that the portion of the radiation beam passing through said diaphragm aperture is identical with the portion of the radiation beam passing through said layer of radiation absorbing material on said tray close to said scraping means.

Claim 15

Dependent Claim 150 words

A device as claimed in claim 1, wherein said radiation absorbing means include a flat tray mounted in a plane substantially perpendicular to the direction of radiation for supporting a layer of an intrinsically loose and freely moving, radiation absorbing powder, said tray being provided with a foramenous bottom permeable to air but impervious to said powder, and means for producing a reduced air pressure underneath said bottom, whereby an air pressure gradient is established across said powder layer on said bottom maintaining said layer in a substantially stable state, and said control means include means responsive to said signals from said radiation detecting means for depositing said powder upon said bottom of said tray in a layer having a thickness within each portion of said tray determined by the radiation intensity beyond said object plane of the portion of the radiation beam passing through said portion of the tray.

Claim 16

Dependent Claim 44 words

A device as claimed in claim 14, wherein said powder depositing means include means for producing a narrow jet of said powder directed towards said tray and means for moving said powder jet over the bottom of the tray along a predetermined scanning pattern.

Claim 17

Dependent Claim 26 words

A device as claimed in claim 15, wherein said means (54) for moving said powder jet include means (62,63) for electrostatic deflection of the powder jet.

Claim 18

Dependent Claim 125 words

A device as claimed in claim 15, wherein said radiation detecting means include means for electronically scanning the radiation image of said object beyond said object plane along a predetermined scanning pattern and producing an electric video signal representing the intensity value of the portion of the radiation image being scanned at any moment, said means for moving said powder jet being controlled by said radiation image scanning means to move the powder jet along a scanning pattern over said tray corresponding to the scanning pattern for said radiation image, and said powder jet being controlled in response to said video signal so as to deposit an amount of powder upon said tray during its scanning motion determined by the amplitude of said video signal.

Claim 19

Dependent Claim 24 words

A device as claimed in claim 17, comprising means for varying the flow rate of said powder jet in response to said video signal.

Claim 20

Dependent Claim 33 words

A device as claimed in claim 1, wherein said control signals supplied to said control means are proportional to differences between the output signals of said radiation detecting means and a reference signal.

Claim 21

Dependent Claim 27 words

A device as claimed in claim 19, comprising a radiation detector located beyond said object plane as seen from said radiation source for generating said reference signal.

Claim 22

Dependent Claim 44 words

A device as claimed in claim 20, wherein said radiation detector generating said reference signal is disposed to be affected by a portion of the radiation beam having an intensity which is substantially independent of the varying absorption values of said compensating filter device.

Claim 23

Dependent Claim 57 words

A device as claimed in claim 1, wherein said control means are associated with signal generating means responsive to the operation of said control means for generating signals representing the absorption values of said radiation absorbing means determined by said control means, said signals being supplied as a negative feedback to the input of said control means.

Claim 24

Dependent Claim 13 words

A device as claimed in claim 22, wherein the feedback factor is variable.

Claim 25

Dependent Claim 76 words

A device as claimed in claim 1 for a radiographic apparatus including a variable pirmary diaphragm for restricting the radiation beam from said radiation source, comprising signal modifying means affected by the setting of said primary diaphragm for modifying said control signals supplied to said control means from said radiation detecting means in a manner making the adjustment of said compensating filter device by said control means substantially independent of the setting of said primary diaphragm.

Claim 26

Dependent Claim 24 words

A device as claimed in claim 1, wherein said radiation detecting means are located beyond said image plane as seen from said radiation source.

Claim 27

Dependent Claim 32 words

A device as claimed in claim 1, wherein said radiation detecting means are disposed between said object plane and said image plane and are removable from the path of the radiation beam.

Claim 28

Dependent Claim 29 words

A device as claimed in claim 1, in a radiographic apparatus including an automatic exposure control system operating in response to the output signals of said radiation detecting means.

Claim 29

Dependent Claim 37 words

A device as claimed in claim 1, wherein said radiation absorbing means comprises at least one element having a K absorption edge within the energy spectrum of the radiation used for the radiographic exposure of the object.

Claim 30

Dependent Claim 40 words

A device as claimed in claim 28, wherein the K absorption edge of said radiation absorbing element is located close to the energy value for the intensity maximum of the radiation being used for the radiographic exposure of the object.

Claim 31

Dependent Claim 56 words

A device as claimed in claim 28, wherein the K absorption edge of said radiation absorbing element corresponds to an energy which multiplied with a factor of 1.2 to 2.0, preferably a factor of about 1.4, corresponds to the voltage of an X-ray tube used as said radiation source for the radiographic exposure of the object.

Claim 32

Dependent Claim 17 words

A device as claimed in claim 28, wherein said radiation absorbing element is a rare earth metal.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1976-08-27	1977-02-26	1977-08-28	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	1980-08-27	1981-02-26	1981-08-28	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	1984-08-27	1985-02-26	1985-08-28	$7700.00	Window Closed / Lapsed

Exposure compensating device for radiographic apparatus

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