GB2148496A

GB2148496A - Measuring transmittance of a material

Info

Publication number: GB2148496A
Application number: GB08423647A
Authority: GB
Inventors: Bradley James Henry; Robert Charles Baugher
Original assignee: Steelastic Co LLC
Current assignee: Steelastic Co LLC
Priority date: 1983-10-21
Filing date: 1984-09-19
Publication date: 1985-05-30
Also published as: FR2575830A1; AU3344384A; JPS60133360A; DE3438672A1; GB8423647D0

Abstract

An apparatus and method for quantifying the transmittance of an object and further determining multiple attributes of the object therefrom include a radiation source which generates a radiation field which is exposed to the object through the top of the cabinet 11. A spot scanner 13 detects variations in the intensity of the radiation field and generates electrical signals proportional thereto, which are received by a computer console 15 which thence determines the transmittance of the object 90 and multiple product attributes. The source includes an X-ray tube 16 enclosed within container 12 and a cabinet 11 which holds the container 12 on a preselected axis and thereafter allows rotation of the container 12 through an angular displacement relative to the preselected axis. The spot scanner 13 includes a rotation element bearing radiation sensors in a plane intersected by the radiation field. <IMAGE>

Description

SPECIFICATION Spot scanner TECHNICAL FIELD The invention relates generally to a method and apparatus for quantifying the transmittance of a material and further quantifying the uniformity of the transmittance of a material.

As hereinafter used the Applicants refer to the term "transmittance" as a reference to that characteristic of a material which allows high energy waves or radiation to pass through the material. Under this definition, therefore, transmittance is a function of both the mass and density of the material. Moreover the invention relates to a utilization of the transmittance data to ascertain multiple product attributes such as, but not limited to, product dimensions, material uniformity, process uniformity and overall product acceptability. The results thus obtained can be compared to predetermined acceptance values and if substandard variations are detected the material can be rejected and changes made to the manufacturing process as required.By employing the present invention continuously to monitor the manufacturing process, trends can be determined while the product is still within the range of acceptability and corrections can be effected to curtail the trend so that substandard acceptance values can be obviated.

By way of example only, when rubber is extruded it is important for the manufacturer to be capable of accurately measuring the uniformity of the density of the extrudate so as to maintain control of the extrusion process. The quantified transmittance values can be compared to predetermined acceptance values and if variations are detected, the extrusion process can immediately be modified, within reason, to eliminate the variations, or if adequate changes cannot be timely effected, the substandard, variations can hopefully be rather quickly corrected to permit only the absolute minimal amount of defective extrudate which must be rejected. The quantitative transmittance values can also be used to determine the dimensional features of the extrudate as a further criteria of the extrudate acceptability.

BACKGROUND ART Analysis and evaluation of manufactured products and the respective manuf acturing processes requires accurate measurements of numerous product attributes such as, albeit not exclusively, product dimensions and material uniformity. Such dimensional measurements can be made with various instruments and gauges well known in the art or by comparing a sample of the product material with a visual standard such as a picture or drawing or transparent overlay. Material uniformity measurements require more complex analytical processes because a substantial amount of the needed data and information is not directly observable by the human senses.

These processes, for example, could be destructive physical analysis, chemical analysis or X-ray scanning analysis.

The aforementioned methods of measurement have several significant drawbacks.

First, these methods rely on human evaluation of the material physical characteristics. For example, X-ray scanning is a technique for analyzing attributes otherwise hidden from human view, but the human eye can normally discern only about 1 6 shades of grey in the range of black to white, a distinctively limiting factor when trying to ascertain subtle variations. Second, reliance on the human senses leads to unpredictable and uncontrollable inaccuracies because of the inherent variations in sensory perception from one human inspector to the next. Third, these methods entail a substantial dedication of time. Many inspections that require human evaluation use substantially more time than their automated equivalent.Not only does the actual evaluation use valuable time but often a production line must be slowed or stopped either until samples can be pulled or the evaluation completed on the in-process materials. Fourth, production labor and time are generally the primary costs incurred in a manufacturing facility.

By way of example only, in a rubber extrusion process extrudate material attributes must be measured. The uniformity of the extrudate density must be known in order to maintain control over the extrusion process. To maintain acceptable quality levels it is also desirable to measure dimensional features of the product.

The quantitative density value of a material can be in terms other than mass per unit volume because it is only the density variation from a predetermined norm that is needed for a correlated measurement of uniformity.

Therefore, quantitative density of a material can be ascertained by the use of X-ray scanning techniques. As X-rays diffuse through a material sample they are absorbed, generally, in proportion to the density and mass of the material. By detecting the relative levels of Xray penetration a quantitative transmittance value can be obtained.

Conventional X-ray scanning systems, such as those used in airport security systems, use a diode string array with a plurality of diodes as a detector and a separate amplification circuit is employed for each diode signal input. Such a system would be disadvantageous for density uniformity measurements because of the need to maintain accurate gain balancing of all the individual amplifiers and the fact that the resolution of the system is a fixed parameter, limited to the resolution of the diode array.

Conventional X-ray scanners used in the medical field for body imaging, such as is discussed in U.S. Patent 4,342,914, are undesirable in the commercial fields because of excessive capital, operating and maintenance costs.

Conventional X-ray scanners which utilize indirect viewing detection methods such as fluoroscopy are undesirable due to poorer resolution and noise problems as compared to direct view techniques.

It is, therefore, apparent that the state of the prior art is such that excessive loss of time, labor, cost and accuracy is necessary to achieve useful results from the available measurement systems. The need exists for a comprehensive method and apparatus which can, at low cost, minimal time and with a high degree of accuracy generate a useful data base of quantitative transmittance values and from this data base determine uniformity values, and dimensional attributes.

DISCLOSURE OF THE INVENTION It is, therefore, the primary object of the present invention to provide a new and improved method and apparatus for measuring the transmittance of a material and utilizing the transmittance data to ascertain multiple product attributes.

It is another object of the invention to provide an efficient, low cost apparatus which will generate a uniform intensity radiation beam pattern and detect variations in the pattern after a material or object has been interposed between the radiation source and the detector.

It is yet another object of the invention that the radiation source be accessible for maintenance without major teardown of the entire apparatus.

It is a further object of the invention that the radiation source be constructed so as to allow for simple maintenance.

It is still another object of the invention to provide a scanner which will detect direct radiation beam intensity patterns using a mini mal number of sensing elements, and provide variable resolution and size of the scanned area.

It is an even further object of the invention to provide a signal processing circuit to amplify the scanner sensing element signals and convert the analog signals to digital signals.

Another object of the invention is to provide computerized data reduction and analysis to ascertain multiple product attributes from the data base generated by the scanner and re lated circuitry.

It is yet a further object to provide a synchronizing circuit which synchronizes the scanning period of the sensing elements with the data sampling period of the data processing unit.

These and other objects are accomplished by the innovations comprising the present invention, a preferred embodiment of which is disclosed herein by way of example as comprising the best known mode of carrying out the invention. Various modifications and changes in details of construction are comprehended within the scope of the appended claims.

In general, the present invention relates to an apparatus for quantifying the transmittance of an object and further determininig multiple object attributes therefrom. Such apparatus includes a radiation source for generating a radiation field which is exposed to the object.

a scanner for detecting variations in the intensity of the radiation field and generating electrical signals proportional thereto, and an analyzer for receiving the electrical signals and determining from these signals multiple product attributes.

The radiation field is generated by a radiation source, such as an X-ray tube. A container encloses the radiation source, and a housing permits the container to be oriented with respect to a preselected axis. The container is movably supported within the housing such that it can slide out of the housing and be rotated through an angular displacement relative to the preselected axis.

A unique apparatus for scanning the radiation field and generating an electrical signal proportional thereto is also provided. This apparatus employs a radiation sensing element for generating an electrical signal in proportion to the intensity of the radiation field exposed thereto. Specifically, an element is provided for rotating the sensing element in a plane intersected by the radiation field. A coupling element conducts the electrical sig nals from the rotating sensing element to a non-rotating electrical contact element.

In order positionally to synchronize sequential scans a novel arrangement is provided for generating an electrical signal which indicates the rotational position of the scanner. The scanner is supported on a rotating shaft which includes an element for reflecting a beam of light incident thereon. The reflecting element presents sequential reflecting and non-reflecting surfaces such as walls with partially removed segments, the segments corresponding to rotational positions of the scanner. A light beam is projected toward the reflecting element and is eclipsed by the walls, but reflected back to a sensor by the partially removed segments. The reflected light impinging on the sensor generates an electrical signal which is employed to effect synchronization.

The present invention also relates to a method for quantifying the transmittance of an object and determining multiple object attributes there from. Such a method employs the steps of generating a uniform intensity radiation field, exposing the object to the radiation field, detecting variations in the intensity of the radiation field which penetrates the object and generating electrical signals proportional thereto which can then be analyzed to determine multiple product attributes.

One preferred, and three alternative embodiments of the novel and unique apparatus incorporating the concepts of the present invention and which are capable of performing the method thereof are shown by way of example in the accompanying drawings without attempting to disclose all of the various forms and modifications in which the invention might be embodied; the invention being measured by the appended claims and not by the details in the specification.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic Side elevation depicting an apparatus for quantifying the transmittance of an object and for further determining multiple attributes of that object; said apparatus incorporating a radiation generator which is depicted in its operative position and, in phantom, in a position to facilitate changing the radiation source tube.

Fig. 2 is an enlarged side elevation, partly broken away, of a scan head subassembly and the incorporated drive motor, synchronizing components, rotary electrical coupling and a sample workpiece as it might be oriented under the scan head assembly.

Fig. 3 is a sectional view taken substantially along line 3-3 of Fig. 2 and showing an example workpiece oriented under the scan head assembly.

Fig. 4 is an exploded perspective of the scan head subassembly depicted in the previous Figs.; Fig. 5 is a schematic circuit diagram of a video amplifier circuit employed herein; Fig. 6 is a further exploded perspective depicting the rotary coupling bracket assembly and the synchronizing device bracket assembly; Fig.7 is a schematic circuit diagram of an optical sensor circuit in conjunction with a schematic depiction of the optical interaction between the optical sensor and the reflective device in the synchronizing mechanism and contained on the same sheet of drawings as Fig. 5; Fig. 8 is a cross-sectional view of an exemplary radiation generator; Fig. 9 is an exploded perspective of a cabinet assembly to house a radiation generator; Fig. 10 is a schematic block diagram of a computer console system, as generally indicated in Fig. 1;; Fig. 11 is a perspective view of a typical sample which may be analyzed with the apparatus and methods disclosed herein.

Fig. 1 2 depicts a use of the apparatus of Fig. 1 in conjunction with a continuous feed system and an alternative lead shielding system.

PREFERRED EMBODIMENT OF THE INVEN TION Referring to Fig. 1 an apparatus embodying the concepts of the present invention is generally indicated by the numeral 10. A cabinet 11 houses a radiation source 1 2 and supports a spot scanner 1 3. An electrical cable 1 4 is comprised of a plurality of wires and provides means for transmitting electrical control signals from computer console 1 5 to spot scanner 1 3 and radiation source 1 2 and for transmitting electrical output signals from spot scanner 1 3 to computer console 1 5.

An operational overview follows. Each major subassembly of the apparatus will then be described under separate and distinct headings.

Referring primarily to Fig. 1 and Fig. 10, radiation source 1 2 is energized with electrical power from computer console 1 5 to high voltage transformers (not shown in Fig. 1) well known to one skilled in the art. Radiation source 1 2 may use a conventional constant potential X-ray tube 1 6 (partially shown in Fig. 1) which operates at about 60 kilovolts and 5 milliamperes but is rated about 1 20 kilovolts and 10 milliamperes. The lower operating power reduces turn-on power surge problems, lowers operating cost and prolongs the useful life of the X-ray tube. Lead shield 1 7 contains the X-ray exposure to spot scanner 1 3 and provides an X-ray shield from the environment.It is to be understood that radiation source 1 2 in the preferred embodiment is described as an X-ray source, however, the invention is not to be construed as limited to X-ray analysis, but rather, the apparatus and method herein described could be used with other radiation sources such as infrared light and an appropriate sensor device in spot scanner 13.

As material passes under spot scanner 1 3 the material is exposed to the X-rays emitting from radiation source 1 2 and localized by lead shield 1 7. Spot scanner 1 3 detects variations in the X-ray intensity after the X-rays have passed through the material and into a slot in the base of the spot scanner. Spot scanner 1 3 generates electrical signals with amplitudes that vary according to the relative X-ray intensity detected. These signals are transmitted to flash converter 1 8 (Fig. 10) along cable 14.

Flash converter 1 8 is a standard analog to ditial converter adapted to interface with the particular data analyzer 1 9 chosen by methods well known to one of ordinary skill in the art. The digital output of flash converter 1 8 is then received by a data analyzer generally indicated by the numeral 1 9 (Fig. 10). In the preferred embodiment an 8-bit flash converter 1 8 has been found to provide sufficient resolution but converters of more than 8 bits could be used if greater resolution was desired or less than 8 bits if less data analyzer 1 9 memory was available.

Data analyzer 1 9 may be any conventional digital computer with sufficient memory capacity and software capabilities to perform the data analysis and system control functions herein described. Data analyzer 1 9 is programmed by methods well known to one of ordinary skill in the art. Data analyzer 1 9 is programmed to store an initial data reading from flash converter 1 8 and to compare all subsequent data readings from the flash converter with the stored initial reading. This comparison is a calculated percent deviation between the two readings being compared.

The data analyzer then outputs the percent deviation between readings to a conventional digital readout display 20. The data analyzer is also programmed to output the data readings to a conventional chart recorder 21 or other graphic display device which graphically plots the separate data readings. Data analyzer 1 9 also is programmed to detect unacceptable variations between data readings and provide an output signal indicating product rejection.

Synchronizing device 22 provides a synchronizing electrical signal to data analyzer 1 9 which indicates when data analyzer 1 9 should record data readings. The synchronizing signal corresponds to that period during which spot scanner 1 3 is sensing X-ray intensity variations.

Data analyzer 1 9 is also programmed to provide control signals to spot scanner 1 3 for start-up, shutdown, speed control and also to provide control signals for energizing radiation source 1 2. Thus, data analyzer 1 9 is also the controller for apparatus 10.

Spot Scanner Referring to Fig. 2 the spot scanner is generally indicated by the numeral 1 3. There are two main subassemblies, specifically, the scan head subassembly generally indicated by the numeral 23 and the synchronizing device generally indicated by the numeral 22.

Fig. 2 is a partial cross-sectional view of the scan head subassembly 23 and a direct view of a drive motor 24. Scan head subassembly 23 includes a generally cylindrical housing 25 which encloses the scanning mechanism and related circuitry generally indicated by 26.

Housing 25 includes a lead ring 27 circumferentially located along the inside perimeter of housing 25 to provide a radiation shield to the surrounding environment. Affixed to the bottom of housing 25, by any suitable means such as screws 28, is the base plate 29.

Referring to Fig. 3, an arcuate slot 30 is made in base plate 29 near the perimeter of base plate 29 as in Fig. 3. Slot 30 subtends or extends across on angle of approximately ninety degrees.

Referring to Fig. 4, interposed between base plate 29 and housing 25 is a bottom lead plate 31. Bottom lead plate 31 provides an environmental radiation shield and reduces radiation scatter. Bottom lead plate 31 also includes an arcuate slot 32 similar to arcuate slot 30 in base plate 29 and is located and aligned with arcuate slot 30 in base plate 29.

Arcuate slot 32 in bottom lead plate 31 may be flanged as in Fig. 4 such that when arcuate slot 30 is aligned with arcuate slot 32 and plates 29 and 31 are bolted together as in Fig. 2, the flanged edges of arcuate slot 32 insert into arcuate slot 30 forming a lead ring around the periphery of arcuate slot 30.

As shown in Fig. 4 affixed to the top of housing 25 by any suitable means such as bolts 33 is a cover plate 34 which is both a cover for scan head subassembly 23 and a mounting plate for drive motor 24. Interposed between cover plate 34 and housing 25 is a top lead plate 35 which is used primarily to shield the environment from radiation exposure. Cover plate 34 and top lead plate 35 have concentric, generally circular cutouts 36 and 37, respectively, which provide an opening through which the drive shaft 38 of drive motor 24 extends into housing 25.

Drive motor 24 may be a low inertia DC motor and is affixed to cover plate 34 by any suitable means such as screws 39. Drive shaft 38 extends into housing 25 and terminates at a scanner hub 40.

Scanner hub 40 is a generally cylindrical structure and is concentrically disposed within housing 25. Scanner hub 40 has a back plate 41 to which drive shaft 38 is affixed. A mounting collar 42 is affixed to back plate 41 by any suitable means such as screws 43.

Mounting collar 42 includes a center tapped hole of sufficient diameter to allow insertion of drive shaft 38. An arcuate, half-moon shaped clamp 44 is cut out of mounting collar 42 and provides a clamp assembly by which securely to hold drive shaft 38. After drive shaft 38 has been fully inserted into collar 42, clamp 44 is affixed to collar 42 by screws 45. As such, drive shaft 38 is securely mounted to hub 40 such that as drive motor 24 rotates drive shaft 38, scanner hub 40 will likewise rotate. On the bottom side of back plate 41 is affixed an electrical connector 46 by any suitable means such as screws 47 and spacers 48.

Affixed by any suitable means such as screws to the front of scanner hub 40 is a scan disk printed circuit board 49. Fig. 5 shows an electrical schematic diagram of the video amplifier circuit 50 located on scan disk 49. Video amplifier 50 is a conventional circuit known to one of ordinary skill in the art. IC1 provides linear current to voltage conversion and IC2 provides non-inverting gain amplification. The function of video amplifier 50 in the preferred embodiment will be elaborated on further below. Scan disk 49 may be made of standard circuit board material well known to one of ordinary skill in the art. Both sides of the board are copper plated, and the plating may be electrically grounded to provide not only a ground plane but also improved noise immunity.The copper is etched as required to provide electrical isolation for mounting of the video amplifier 50 electronic components by methods well known in the art. As is shown in Fig. 3 the circuit components are intentionally mounted so as to assure that scan disk 49 is mechanically balanced around the center axis. Balance is important to minimize induced vibration during high speed rotation of scan disk 49.

Located diametrically at the outer periphery of scan disk 49 are the sensing elements 51.

These elements may be conventional silicon photodiodes. The diodes provide a linear current response to varying intensity of radiation exposure when used in a short circuit mode as in video amplifier 50.

Referring again to Fig. 4, connector 52 is affixed to scan disk 49 by any suitable means such as screws. Connectors 46 and 52 form a conventional pin and socket electrical connector assembly known to one of ordinary skill in the art (Fig. 2). Obviously, connector 46 must be affixed to back plate 41 in alignment with connector 52 such that when scan disk 49 is attached to scanner hub 40, connector 46 and connector 52 mate as in Fig. 2.

Scanner hub 40 also may have dowel pins 53 (Fig. 4) which provide an alignment guide when installing scan disk 49.

As stated previously, sensing elements 51 are photodiodes and are diametrically located near the periphery of scan disk 49 such that as scan disk 49 rotates, the diodes pass across arcuate slot 30 in base plate 29 as in Fig. 3. Arcuate slot 30, as shown, is just wide enough to allow exposure of sensing elements 51 to a radiation beam pattern.

Referring to Fig. 6, the rotary electrical coupling 54 may be a standard mercury contact slip ring of the type manufactured by Meridian Laboratories. Coupling 54 has a 1/4 inch rotatable shaft 55. Shaft 55 is drilled out to accommodate four wires 56. Shaft 55 inserts into motor drive shaft 38 and the two shafts are mechanically bonded using a standard bonding adhesive such as Room Temperature Vulcanizing Rubber sold under the registered trademark RTV 84 by General Electric -a family of silicone rubber compounds having good physical properties and electrical properties similar to silicone rubber.

Drive shaft 38 is center tapped to allow electrical wires 56 to pass through from rotary electrical coupling 54 to connector 46 (as in Fig. 2). These wires carry electrical power to video amplifier 50 (Fig. 2) and the video amplifier 50 output signal.

As shown in Fig. 6, a coupling bracket 57 is affixed to the top of drive motor 24 with any suitable means such as screws 58 and spacers 59. Bracket 57 provides a clamp design to accommodate coupling 54. Bracket 57 includes a through hole 60 of sufficient diameter for installing coupling 54. A notch 61 allows slight expansion or contraction of through hole 60 as clamping screw 62 is turned counterclockwise or clockwise, respectively. Coupling 54 is inserted into bracket 57 and, as previously described, coupling shaft 55 inserts into motor drive shaft 38. Coupling wires 56 are run down drive shaft 38 and terminate at connector 46 as previously described. When coupling shaft 55 and motor shaft 38 are secured together, clamping screw 62 is then turned clockwise until bracket 57 securely clamps and supports coupling 54.

Four stationary contacts 63 are the access points for inputting power to video amplifier 50 circuitry and for picking up the video amplifier 50 output. Contacts 63 correspond to wires 56 that traverse down coupling shaft 55 and motor drive shaft 38 to connector 46 on hub back plate 41. It will be appreciated by one of ordinary skill in the art that coupling 54 provides electrical coupling between stationary contacts 63 and wires 56 in coupling shaft 55 which wires necessarily rotate as the drive motor shaft 38 rotates. A mercury contact slip ring as used in rotary coupling 54 was preferred over a more conventional coupling method of brushes due to the need to have an electrically noiseless coupling. A pair of contacts 64 (Fig. 2) provide power input contacts for drive motor 24.Fig. 2 depicts a side elevation of rotary coupling 54 as it appears assembled to drive motor 24 and supported by bracket 57.

This concludes the structural description of scan head subassembly 23. The other major subassembly of spot scanner 1 3 is the synchronizing device generally indicated by the numeral 22 in Fig. 2. Synchronizing device 22 provides an electrical signal to computer console 1 5 (Fig. 1) which indicates the time period during which sensing elements 51 are traversing across arcuate slot 30 (Fig. 3).

Referring to Fig. 6, tachometer sensor hub 65 is essentially a sleeve which fits over motor drive shaft 38 and is affixed to shaft 38 by a set screw 66. The tach ring 67 is a generally cylindrical ring with walls that are partially cut away. The walls are cut away in such manner as to form two diametrically opposed essentially 90 degree arcs. Tach ring 67 slides over hub 65 and is affixed thereto by a set screw 68. Thus, tach ring 67 rotates with motor drive shaft 38. Tach ring 67 and hub 65 are disposed along drive shaft 38 between the top of drive motor 24 and bracket 57, but not in contact with bracket 57 (see assembled side view in Fig. 2).

The quadrant sync detector 69 is an elec tronic circuit which senses the position of tach ring 67 as drive motor 24 rotates. Detector 69 is comprised of a standard printed circuit board 70 with numerous electronic components mounted thereon (not shown in Fig. 6).

Fig. 7 is a schematic diagram of the detector 69 circuit, and also diagramatically shows how detector 69 operates as a function of the rotational position of tach ring 67. The optical sensor 71 is a light reflection sensor with a focal distance of 0.2 inches (5.1 mm). Sensor 71 emits an infrared light beam 72. If a reflective object, such as sensor hub 65, is at the focal distance the light is reflected back to optical sensor 71 which in turn outputs a discrete positive voltage of about 5 Vdc. If an object, such as the walls of tach ring 67, interrupts the light beam at less than the focal distance then the light beam is eclipsed and insufficient light re flects back to sensor 71 and sensor 71 outputs zero voltage. Thus, optical sensor 71 is positioned relative to sensor hub 65 at the distance of 0.2 inches (5.1 mm).The wall of tach ring 67 there fore nearly touches sensor 71 as in Fig. 2. As tach ring 67 rotates due to drive motor shaft 38 rotation, so long as the wall of tach ring 67 is in front of sensor 71, the output of sensor 71 is about 0 Vdc. But, as was described previously, tach ring 67 is cut away at diametrically opposed approximately 90 degree quadrants (Fig. 6). As tach ring 67 rotates past 1/4 of a turn, optical sensor 71 will be at 0.2 inches (5.1 mm) from sensor hub 65 and thus sensor 71 will output about + 5 Vdc. Thus, as tach ring 67 rotates, every other missing wall quadrant causes optical sensor 71 to output about + 5 Vdc. The output of sensor 71 will approximate a square wave signal, as drive shaft 38 rotates at a constant speed, whose logic high duration will be a function of both the rotational speed of tach ring 67 and the reflective wall widths.For a given rotational speed, a + 5 Vdc signal from optical sensor 71 indicates that the reflective wall of sensor hub 65 is at 0.2inches (5.1 mum).

The remaining circuitry of quadrant sync detector 69 (Fig. 7) requires minimal elaboration to one of ordinary skill in the art. A transistor, Q1, inverting gate Cl and assoc iated passive components provide a double inversion and waveshaping of the output of optical sensor 71 which is in essence a digital signal; that is, the output of optical sensor 71 is either about 0 Vdc or about + 5 Vdc at any point in time. The double inversion serves to buffer the output of optical sensor 71 and also provide more output drive as the output of quadrant sync detector 69 must be coupled with computer console 1 5 through cable 14 (Fig. 1).

Referring again to Fig. 6, optical sensor 71 is mounted on circuit board 70 with the optically sensitive area at one edge of board 70. A tach sensing bracket 73 is affixed to the top of drive motor 24 with any suitable means such as screws 74 and spacers 75. As shown, sensing bracket 73 has an arcuate notch 76 at the forward end to allow close positioning of bracket 73 to tach ring 67.

Slightly behind notch 76 is an arcuate slot 77. Circuit board 70 is affixed to bracket 73 in such a manner as to enable slight angular adjustments of optical sensor 71 with respect to tach ring 67. A board holder 78, bracket 73, a spacer bar 79 and circuit board 70 are mated together with screws 80. Screws 80 specifically pass through slot 77 so as to permit pivotal movement of circuit board 70 along slot 77. Spacers 81 act much like bearings so that the threads of screws 80 do not grate against bracket 73. Board holder 78 is generally a metallic bar with a slot cutout 82. Holes are located in the walls which partly comprise slot 82 and accommodate a threaded axis 83. Bracket 73 includes a hole 84 which accommodates an adjustment pivot axis 85. Pivot axis 85 is held in place by a snap ring 86. A spring 87 is disposed between pivot axis 85 and threaded axis 83.A knurled hand screw 88 is inserted through a hole 89 in adjustment pivot axis 85, on through spring 87 and through threaded axis 83. As screw 88 is turned, board holder 78 will travel in a direction along the thread axis of screw 88 due to threaded axis 83. The movement of board holder 78 is further constrained to the path of slot 77 because of screws 80. Spring 87 provides an axial restraining force to minimize screw 88 rotation after adjustment. Because circuit board 70 is affixed to board holder 78, as board holder 78 travels along arcuate slot 77 so too does circuit board 70. Thus, precise alignment of optical sensor 71 with tach ring 67 is achieved. Spacer bar 79 is used to dispose circuit board 70 and optical sensor 71 approximately at the mid area of tach ring 67 as in Fig. 2.

The purpose of synchronizing device 22 is to provide an electrical indicating signal to computer console 1 5 to begin data sampling.

Data sampling need only occur during that period when sensing elements 51 are traversing arcuate slot 30. In order to accomplish this function the following alignment procedure may be performed. Scan disk 49 is manually rotated in like manner as drive motor 24 would rotate disk 49 until either one of the two sensing elements 51 is at the leading edge of arcuate slot 30. Disk 49 is held at this position and the trailing edge of either wall of tach ring 67 is adjusted so as to just give a 5 Vdc output from quadrant sync detector 69. Fine tune alignment can be obtained by adjustment of knob 88 as previously described. Alignment of only one of sensing elements 51 is required as the second element is diametrically opposed from the aligned element and with respect to tach ring 67 the reflective wall quadrants are also diametrically opposed as described earlier.Thus, both sensing elements 51 are aligned at the same time that either one of them is aligned.

After alignment, as drive motor 24 rotates scan disk 49, tach ring 67 likewise rotates.

just as one of sensing elements 51 reaches the leading edge of arcuate slot 30, the leading edge of the corresponding reflective wall of tach sensor hub 65 intercepts and reflects back the light from optical sensor 71.

Quadrant sync detector 69 thus outputs a + 5 Vdc indicator signal to computer console 1 5. So long as one of the sensing elements 51 remains within the arc defined by arcuate slot 30, quadrant sync detector 69 continuously outputs + 5 Vdc. Since arcuate slot 30 and the walls of tach ring 67 both subtend or extend across one quadrant or about 90 degrees, when a sensing element 51 reaches the trailing edge of arcuate slot 30, the leading edge of the corresponding wall of tach ring 67 likewise reaches and moves in front of optical sensor 71. Since the wall of tach ring 67 eclipses the light beam from optical sensor 71, quadrant sync detector 69 outputs zero volts.It is thus apparent that for every 360 degrees rotation of shaft 38 each sensing element 51 passes across arcuate slot 30 once and quadrant sync detector 69 outputs a corresponding pulse for the duration of the time each sensing element 51 is traversing arcuate slot 30. As will be discussed further, only one of the two sensing elements 51 is needed to operate spot scanner 1 3. By programming data analyzer 1 9 to ignore every other pulse generated by quadrant sync detector 69, data is only collected on one of the sensing elements 51. Furthermore, the pulse width is a direct indication of the duration time that sensing elements 51 are traversing arcuate slot 30 independent of the rotational speed of drive motor 38.Synchronizing device 22 described above is a highly accurate and reliable method for determining the rotational position of sensing elements 51 with respect to time with minimal circuitry requirements.

Referring principally to Figs. 2 and 4, operation of spot scanner 1 3 as an assembled unit can now be described. First, optical sensor 71 alignment is performed as outlined above. The radiation beam pattern to be scanned is exposed to arcuate slot 30. Fig. 2 shows, by way of example only, how spot scanner 1 3 may be exposed to a radiation beam which has passed through a sample to be tested.

Sample 90 rests on collimating plate 91 within outer support 92 (Fig. 1). A slot 93 exposes a radiation beam pattern a (shown below plate 91 in Fig. 2) to sample 90. The radiation penetrates sample 90 as a function of the sample 90 geometry and material characteristics, and is thereafter exposed to sensing elements 51 via slot 30. Power is applied to drive motor 24 via contacts 64 thus causing motor drive shaft 38 to rotate. The amplitude of the applied motor voltage determines the motor 24 rotational speed. Because scanner hub 40 is affixed to drive shaft 38, scanner hub 40 likewise rotates as does scan disk 49 which is affixed to scanner hub 40.

As scan disk 49 spins, sensing elements 51 alternately pass over arcuate slot 30 once for each 360 degree rotation of scan disk 49.

Thus, for each full turn of scan disk 49, sensing elements 51 are once each exposed to the radiation pattern, for 1/4 of each full turn of disk 49. Exposure of sensing elements 51 to radiation such as X-rays, causes sensing elements 51 to generate small currents linearly proportional to the radiation intensity much the same way that a phototransistor responds to light exposure. The small currents generated by sensing elements 51 are converted to amplified voltage signals by video amplifier 50. Though in the preferred embodiment the video amplifier 50 converts the sensing elements 51 current signals to amplified voltage signals, it is contemplated that other signal processing circuits could be used which provide a signal suitable for analog to ditial conversion.Power for video amplifier 50 is supplied via contacts 63 on rotary electrical coupling 54 which electrically couples the contacts 63 to wires 56. Wires 56 run from rotary electrical coupling 54 to mated connectors 46 and 52. Wires 56 also carry the output of video amplifier 50 from scan disk 49, via mated connectors 46 and 52, to rotary electrical coupling 54 and this output is thereby coupled to one of external stationary contacts 63. The amplified video signal is then cabled to computer console 1 5 (Fig. 1) via cable 14 for further signal processing as will be elaborated on further below.

As described earlier, synchronizing device 22 generates a pulsed digital output, where the pulses precisely corresponding to the time during which sensing elements 51 are traversing arcuate slot 30. Prior to actual use of spot scanner 1 3 for product assessment the alignment of optical sensor 71 with tach ring 67 would be performed as previously described to ensure that the output of quadrant sync detector 69 exactly corresponds to the exposure period of sensing elements 51.

Radiation Source and Cabinet Assembly Referring to Fig. 1 a radiation source is indicated by the numeral 1 2. Source 1 2 is generally contained within cabinet 11 and is mounted on a set of slide rails 94 to allow access for maintenance. Radiation source 1 2 provides a constant intensity X-ray pattern contained by lead shield 1 7 and passed through the top of cabinet 11 to spot scanner 1 3. Again, the preferred embodiment herein disclosed is not to be construed as limiting the scope of the present invention to X-ray analy sis. For example, infrared light analysis may also be used with the invention.

Fig. 8 shows a cross-sectioned view of generator 12. Generator 1 2 is a generally cubic outer tank comprised of four outer side walls 95, a bottom wall 96 and a cover 97.

All wall joints are welded using conventional weld techniques to insure that tank 12 is gas and oil tight. Within tank 1 2 is an inner frame 98 which is also generally cubic in shape. The insulative material for inner frame 98 may be paper filled phenolic. Use of inner frame 98 provides electrical and thermal isolation from the outside tank 1 2 walls. Inner frame 98 is completely filled with oil which is used primarily as an insulator. Though not shown in Fig.

7, water filled cooling tubes run throughout the oil to dissipate heat generated when X-ray tube 1 6 is operating, a cooling method known to one of ordinary skill in the art.

Mounted to the inner side of the back wall of inner frame 98 is an X-ray tube socket generally indicated by the numeral 99. Socket 99 is comprised of a phenolic tube 100 and a pair of spring contacts 101. Tube contacts 102 are half-moon shaped contacts and are rotatable around the X-ray tube axis by use of a set screw, a design provided by the tube manufacturer. Contacts 101 are electrically connected to wires 103 which are routed to a high voltage transformer 104. A pair of input power wires 105 carry the control voltage power, supplied through connector 106, needed to energize X-ray tube 16 via transformer 104. Phenolic tube 100 is of just sufficient diameter to allow insertion of X-ray tube 16. The open end of tube 100 may be tapered to simplify X-ray tube 1 6 insertion.

Front side wall 95 includes a wide opening 107 for insertion of X-ray tube 1 6. As shown in Fig. 8, X-ray tube 1 6 includes a stepped-up flange 108 to provide a support frame for mounting tube 1 6 in X-ray tank 1 2. Outer mounting ring 109 has a stepped inner diameter which accepts the stepped-up flange 108. An O-ring 110 is placed around the outer perimeter of the small diameter flange 111 such that when X-ray tube 1 6 is inserted into ring 109, O-ring 110 is compressed between the mounting ring 109 and the Xray tube large diameter flange 108. O-ring 110 thus provides a seal against oil leakage. A clamping ring 11 2 acts as a backing plate for ring 109.Clamping ring 11 2 is affixed to ring 109 by any conventional means such as bolts 11 3. X-ray tube 16, outer mounting ring 109, O-ring 110 and clamping ring 112 are assembled together as a unit prior to installing X-ray tube 1 6 into X-ray tank 1 2. Flange 108 includes a blind hole 114 and clamping ring 11 2 includes a guide pin 11 5 such that for clamping ring 112 to be affixed to outer mounting ring 109, pin 11 5 must insert into hole 114.

After outer mounting ring 109 and clamping ring 11 2 are installed on X-ray tube 16, X-ray tube 16 is inserted into tank 1 2. To insure that the X-ray tube aperture 11 6 is aligned in a vertical orientation when inserted into shield 17, outer mounting ring 109 and clamping ring 112 each have a hole which must be aligned with dowel pin 11 7 located in front wall 95. The tube assembly comprised of tube 16, ring 109 and ring 112 is then affixed to front wall 95 by any appropriate means such as bolts 11 3. A gasket 118 is disposed between front wall 95 and outer mounting ring 109 to provide an oil seal.Xray tube 1 6 is inserted such that when tank 1 2 is horizontal, as in Fig. 8, the X-ray beam is directed vertically upward. It will be appreciated that the X-ray emitting source aperture 11 6 at the end of tube 1 6 opposite contacts 102 is not inserted within tank 12. As will be described shortly, the surrounding environment is protected from X-ray beam scattering by means of lead shield 1 7.

Two large eye nuts 11 9 are affixed to cover 97, disposed on opposite sides of cover 97 near front wall 95. Eye nuts 11 9 mate to support rods 1 20 which are affixed to inner frame 98 by any suitable means such as bolts and which provide mechanical support to inner frame 98. Eye nuts 119 can be used as handles when rotating or moving tank 1 2.

It will be appreciated that the tank design described above has the very important advantage of simple X-ray tube maintenance. By orienting tank 1 2 such that tube 1 6 is vertical with front side wall 95 on top, by removing a few bolts 113, tube 1 6 can be removed and replaced. Vertical orientation of tube 1 6 is necessary, of course, to prevent oil loss through opening 107 when tube 1 6 is removed. As will be described shortly, cabinet 11 is constructed in such a way as to allow a 90 degree rotation of tank 1 2.

Fig. 9 shows an exploded perspective of cabinet 11. Cabinet 11 provides a housing for radiation source 1 2 and provides mechanical support for spot scanner 1 3 (Fig. 1). Cabinet 11 is shown generally as a cubic structure comprised of a pedestal frame 121, side panels 122, front panel 1 23 and a top panel 1 24. For clarity in Fig. 9, side panels 122 and front panel 1 23 are shown partially cut away and the rear panel is not shown. Affixed to frame 121 along both side panels 122 are slide rails 94. Rails 94 are mounted to frame 1 21 by any suitable means such as bolts 1 25. Rails 94 are comprised of a track bar 126 and a rail bar 127, the rail bar 127 being so disposed as to slide along track bar 126. A tank basket 1 28 provides a support frame for radiation tank 1 2. Tank 1 2 is placed into basket 128 and bolts 1 29 affix tank 1 2 to basket 1 28. Tank basket 1 28 is then disposed between slide rails 94 and affixed by bolts 1 30. Rail bars 1 27 are affixed to the sides of basket 128 such that when rail bars 1 27 are fully extended, basket 1 28 and tank 1 2 contained therein are disposed outside of cabinet 11 and when rail bars 1 27 are fully contracted, basket 128 and tank 1 2 are disposed wholly within cabinet 11. In Fig. 1 radiation source 12 is shown in position A which would be the position for performing a material analysis. X-ray tube 1 6 is horizontal with the X-ray beam directed vertically upward through lead shield 1 7. Position B shows the tank 1 2 outside of cabinet 11 by fully extending slide rails 94, and then rotating tank 1 2 ninety degrees clockwise whereby tube 16 is vertically oriented enabling simple and quick maintenance.Rotation of tank 1 2 is accomplished by means further described below.

As described earlier, X-ray tube 1 6 is inserted into tank 1 2 such that the X-ray emitting source is located external to tank 12, directed vertically upwards when tube 1 6 is horizontal. As shown in Fig. 9, affixed to front side wall 95 of tank 1 2 is the bottom funnel half 131 of lead shield 17. That portion of Xray tube 1 6 which extends out of tank 1 2 is fully enclosed by bottom half 131 which is essentially a square tapered funnel and made of lead to provide a radiation shield to the environment.

Top panel 1 24 has a square opening cutout which allows insertion of the top funnel half 1 32. Top funnel 1 32 extends down into cabinet 11 and is disposed such that when radiation tank 1 2 is wholly enclosed within cabinet 11, top funnel 132 and bottom funnel 131 mesh together and comprise lead shield 1 7 (Fig. 1). A mounting plate 133 is provided to securely affix top funnel 1 32 to cabinet top 1 24 and to assure adequate radiation shielding.

As described previously, radiation tank 1 2 is mounted in basket 1 28 which is affixed to slide rails 94. In addition to allowing tank 1 2 to be easily pulled from cabinet 11, slide rails 94 also have pivot axes 1 34 which, when unlocked, allow a 90 degree clockwise rotation of tank basket 1 28 when rails 94 are fully extended. This rotation causes X-ray tube 1 6 to now be oriented in a vertical position and easily accessible for replacement. Thus, the cabinet design herein described allows for quick, efficient maintenance of X-ray tube 16.

When using spot scanner 13, top funnel 1 32 is covered with collimating plate 91.

Plate 91 includes arcuate slot 93 similar to slot 30 in spot scanner base plate 29 (Fig. 4).

Spot scanner 1 3 is placed over collimating plate 91 such that slot 93 and slot 30 (Fig. 4) are aligned. In this manner the X-rays emitting from top funnel 1 32 are collimated into a beam whose shape is defined by the geometry of arcuate slot 93. Interposed between spot scanner 13 and plate 91 is outer support 92 which is part of cabinet top 1 24 and separates scanner 13 from collimating plate 91 with enough room for passing the material to be X-rayed. Support 92 also provides radiation shielding and may be hinged to allow easy placement of the material being analyzed.

Computer Console Referring to Fig. 1, a computer console is generally indicated by the numeral 1 5. Fig.

10 shows a functional block diagram of the primary elements of console 1 5. The primary elements are flash converter 18, data analyzer 19, power console 1 37, display unit 20 and a motor speed servo 1 38.

Flash converter 18 is a standard 256 bit MATV analog to digital converter well known to one of ordinary skill in the art and which may continuously receive the video amplifier 50 analog output and virtually instantaneously convert it to a digital signal capable of being processed by data analyzer 1 9. It will be understood by one skilled in the art that adjustment of flas converter 18 is such that with sensing elements 51 exposed to zero radiation intensity the output from video amplifier 50 will likewise be about zero volts, and flash converter 1 8 outputs the digital equivalent to the integer 0.When elements 51 are exposed to the full radiation beam intensity a maximum output voltage is received by flash converter 1 8 from video amplifier 50 and flash converter outputs the digital equivalent of the integer 255. For all output signals from video amplifier 50 between 0 volts and the maximum voltage, flash converter 1 8 outputs the digital equivalent of an integer between 0 and 255, inclusive, linearly proportional to the signal received from video amplifier 50. Thus, the data values generated by flash converter 18 are digitized integers whose values are determined by the relative intensity of the radiation beam detected by sensing elements 51 at the position across arcuate slot 30 determined by the location of elements 51 at the time the data is generated.Furthermore, because flash converter 1 8 has 256 bit resolution, the present invention can distinguish 256 discrete levels of X-ray intensity which is a substantial and significant improvement over the prior art which, for example with human sight, was limited to a resolution of about 1 6 shades of X-ray intensity (that is, 1 6 shades of grey on, for example, an X-ray exposure plate). As previously stated, even greater resolution could be achieved with a flash converter which uses more than 8 bits providing computer console 1 5 has sufficient memory capacity.

Data analyzer 19 is programmed by methods known to one of ordinary skill in the art and, when so programmed, controls the functional operation of console 1 5. The digitized output from flash converter 1 8 is loaded by analyzer 1 9 into a computer memory 1 39 from an accumulator buffer 1 40. This data is stored only during that time indicated by the output of quadrant sync detector 69 that sensing elements 51 are traversing arcuate slot 30 in scan head subassembly 23 as previously described. Flash converter 18 data is sequentially transferred to memory 1 39 such that a finite set of data values is stored for each sweep of sensing elements 51 across arcuate slot 30 in scan head 23.As described, each data value will be the digital equivalent of an integer from 0 to 255 indicative of the relative intensity level of the X-ray pattern detected by sensing elements 51 at the corresponding position within arcuate slot 30 when flash converter 18 is sampled and stored. In the preferred embodiment the output of flash converter 1 8 is sampled and stored 5000 times during each sweep period when sensing elements 51 are traversing arcuate slot 30. Thus, each data set transferred from flash converter 1 8 to analyzer 1 9 during a sweep of elements 51 across slot 30 contains 5000 values. The 5000 samples per sweep rate is determined by a clock signal programmed Into the analyzer 1 9 software.

The selection of 5000 samples per sweep is a function of the rotary speed selected for drive motor 24, the memory capacity of computer console 15, the desired degree of image resolution of the signature image and the desired size of the scan area across slot 30. As motor 24 speed increases, more samples from flash converter 1 8 are needed to maintain the same degree of image resolution across a desired scan area. Likewise more memory capacity is needed if more samples are taken to increase image resolution.The tradeoff between scan area size, image resolution and memory capacity occurs in that the slower that motor 24 rotates the resultant scan area sensed by elements 51 across arcuate slot 30 is reduced since the sample rate by analyzer 1 9 of flash converter 1 8 is determined by the analyzer 1 9 programmed clock and is independant of motor 24 speed. For example only, if a motor 24 speed of 3000 rpm and a sample rate of 5000 samples per sweep results in a scan area of 3 inches (7.62 cm) across slot 30, then when the motor speed is reduced to 1 500 rpm the scan area across slot 30 will only be about 1.5 inches (38.1 mm) but image resolution is doubled.It should be realized that this variable resolution and variable scan area size relates to the video resolution of the signature image produced by spot scanner 13 and that the resolution of 256 discrete levels of X-ray intensity is a different parameter which is a function of the particular flash converter 1 8 selected. Thus, a significant accomplishment of the present invention is in providing a scanner that has a variable video resolution capability and a variable scan area capability with the use of only a single sensing element. Depending on the particular application the 5000 sample rate can also be changed to meet different video resolution requirements.

It will be understood by one of ordinary skill in the art that because the data samples are timed by a sample rate programmed into the data analyzer 1 9 software, the sampled scan area of arcuate slot 30 being traversed by sensing elements 51 will vary with the rotational speed of scan disk 49. Thus, precise rotational speed control of scan disk 49 is important. Constant drive motor 24 speed is achieved using servo drive circuit 1 38. This is a standard servo drive control circuit well known to one of ordinary skill in the art which utilizes a tachometer signal from motor 24 as the feedback input to circuit 1 38 to adjust the drive voltage applied to motor 24.

Accumulator buffer 140 provides a noise filter function, the filter sensitivity level being an optional control of the operator. As previously stated, during each scan by sensing elements 51 across arcuate slot 30, data values from flash converter 1 8 are sampled and correspond to the relative intensity level sensed by elements 51 as they traverse arcuate slot 56. To reduce spurious noise effects the data values for successive sweeps may be added together and then divided by a filter factor to obtain an average reading for each of the data values. In the preferred embodiment the filter factors can be selected from any integer a power of two between 1 and 256 but higher filter factors could be selected.For example, if a filter factor of 1 6 is selected the data set from the first scan (5000 data values in. the preferred embodiment) is sequentially loaded into accumulator buff er 140. When the second scan is performed each data value of the second set is added to the corresponding data value already stored in accumulator 140 and so forth for 1 6 scans. After the 16th set of data values is added into accumulator 140, accumulator 140 contains 5000 distinct data values of which each value is the summation of 1 6 readings sampled at the same position across slot 30.Each data value is then numerically divided by 1 6 and the results transferred to memory 1 39. Consequently, 5000 data values will be put into memory 139, each data value being the average of 1 6 successive readings. By using average readings, spurious noise variations only are reduced but the fixed product image is not affected. For maximum filtering, 256 scans would be performed before the average data set could be determined and loaded into memory 139. Filtering can be deleted by simply selecting a filter factor of 1, in which case each data set is directly loaded into memory 139. On the other hand, greater filtering can be achieved using more than 256 scans if the particular application so requires high filtering.

It is necessary at this time to describe, by way of example only, the relationships be tween a material being analyzed, spot scanner 1 3 and the stored data sets. A material under analysis may be any material suitable for radiation analysis. The example used herein will be a sample piece of extruded rubber exposed to X-rays but the method and apparatus embodying the concepts of the present invention should not be construed to be limited to X-ray analysis or radiation analysis of extrudates. Fig. 11 shows a perspective of a typical piece of extruded material 90 such as rubber.

A piece of the extrudate is placed under spot scanner 1 3 (Fig. 1) on top of collimating plate 91 (Fig. 9), thereby exposing sample 90 to the uniform intensity X-rays from radiation source 1 2 as previously described. Alternatively, extrudate material could be continuously passed under spot scanner 1 3 as it comes from an extrusion machine along a conveyor as in Fig. 1 2 which will be elaborated on further below. In either method the material is oriented such that it is radially positioned over the center of arcuate slot 93 in collimating plate 91. Thus, the uniform intensity X-ray beam intersects a cross-sectional "slice" of the extrudate.Figs. 2 and 3 depict how a typical alignment of the sample 90 would be relative to scanner 1 3. The beam then passes on through arcuate slot 30 into spot scanner 1 3. The X-ray beam intensity pattern that is transmitted through the material will vary across the width of the "slice" in relation to the density and the dimensional geometry of the extrudate. Sensing elements 51 detect this variation as they traverse or scan across arcuate slot 30 in base plate 29 as previously described. The output of video amplifier 50 is an analog voltage proportiona! to the variations detected by sensing elements 51. This voltage is digitized by flash converter 18 whose output may then be sampled 5000 times during each scan as previously described.As a result, the 5000 data values of each data set stored in memory 1 39 or accumulated in the accumulator buffer 1 40 described earlier are numerical representations of the transmittance of the extrudate as measured across a cross-sectional slice of the material. Thus spot scanner 1 3 provides a signature of the sample under analysis. Because the sample rate is fixed during any given test, it will be understood by one of ordinary skill in the art that the rotational speed of sensing elements 51 must be set so that as elements 51 scan across arcuate slot 30 the 5000 data points will be recorded during the period sensing elements 51 are passing across sample 90 located near the center of slot 30. The rotational speed of elements 51 may also be such that the entire sample 90 is within the scan area.Such considerations, in addition to the desired resolution, determine the appropriate motor 24 speed for any particular application as previously described.

With the sample material stationary it will be noted that each scan will be across the same cross-sectional slice of the material.

With a noiseless system each of the distinct 5000 data values measured during each scan should be equal in value to its corresponding data point in the next scan. Such will not usually be the situation however due to noise caused by radiation scattering, electrical noise induced at video amplifier 50, or even slight lateral movement of the sample itself. To minimize the effects of any spurious readings in the separate data values, the digital filtering method described previously may be used.

A calibrate memory 141 is used to store an initial data set, filtered or unfiltered, taken from a sample of extrudate known to have the requisite dimensional and density uniformity characteristics. That is, the initial data set numerically represents a predetermined acceptable signature of the sample being analyzed. Memory 141 stores this data for further processing. It will be understood that the filtering capability previously described would be useful when determining the data set to be stored in memory 141 because this data set will represent the predetermined acceptance values against which all successive scan data sets will be compared. Therefore, it is desirable that the calibrate data set be as noise free as possible.It is also to be understood that in piace of actually scanning a "known good" sample to obtain the predetermined acceptance values the predetermined values could be otherwise calculated and then entered into memory 141. For example and not limited hereto, if it were desirable to measure a dimensional tolerance the dimensions of interest could be taken from an engineering drawing of the sample and loaded into memory 141 to be used as the predetermined acceptance values. The actual samples can then be scanned, the data sets interpreted to produce the dimensional measurement of interest and then the comparison made with the data set stored in memory 141. This will be elaborated on further below.

Data analyzer 1 9 is programmed to perform not less than two major data manipulations.

First, it can take either a stored or current data set and calculate a transmittance value for the entire corresponding cross-sectional slice of material according to a predetermined formula. This transmittance calculation is repeated for the data set stored in calibrate memory 141. The two transmittance values are then compared and a percent deviation is calculated. Data analyzer 1 9 is programmed to exhibit on display unit 20 the percent deviation of the current transmittance value from the transmittance value calculated from the calibrate memory 141 data set. Display unit 20 may be a conventional CRT.Thus, visually displayed on unit 20 is the percent deviation of the current slice under analysis from a predetermined acceptance value or in other words the deviation between a known good signature reading and a signature reading whose accuracy is being determined. If the operator observes a deviation in excess of a predetermined limit he can interrupt the operation to remove the defective material.

Data analyzer 1 9 is also programmed to accept a deviation limit input from the operator and then automatically check for deviations in excess of the defined limit. If such is detected, analyzer 1 9 is programmed to output a control signal alarm to alert the operator that a defect has been detected. This control signal may be an illuminated red lamp, a warning bell sound or could even be a control voltage for triggering a blade to automatically cutoff the defective slice.

A second operating mode of data analyzer 1 9 is to output the values of any data set to recorder 21 by conventional graphics methods. A data set stored in calibrate memory 141, for example, could be sequentially plotted in green ink and simultaneously a data set in memory 1 30 could be sequentially plotted in red ink. Any deviation in the two data sets would be immediately apparent visually as a separation in the two graphs.It will be understood by one of ordinary skill in the art that a graphical plot of the data points of a given data set in the same sequence as the data values were stored into memory 1 39 or memory 141 will result in a point by point graphic representation of the transmittance characteristic of the corresponding "slice" of material from which the data values were measured during the scan operation. Since dimensional variations in the material under analysis affect the transmittance value it should be clear that such a graphic representation can be used to verify dimensional tolerances or product uniformity.

Computer console 21 also includes power console 1 37 which regulates electrical power distribution throughout apparatus 10 such as drive motor 24 power, video amplifier 50 power, high voltage power to X-ray tube 16, and data analyzer 19 power. Such power distribution is done by methods well known to one of ordinary skill in the art.

System Operation and Alternative Embodiments Referring primarily to Fig. 1 a detailed description of operation will now follow. The example given is for explanatory purposes only and should not be construed as limiting in any manner. A sample piece of material such as extruded rubber is placed on collimating plate 91 within outer support 92 (Fig. 9) such that the material radially intersects arcuate slot 93 in collimating plate 91. Spot scanner 13 is placed over the extrudate, on top of outer support ring 93 such that arcuate slot 30 in base plate 29 of spot scanner 1 3 is aligned with slot 93 in collimating plate 91 as shown in Fig. 2.

Radiation source 1 2 is energized by high voltage power and emits uniform intensity Xrays vertically upward within lead shield 1 7.

Lead shield 1 7 prevents X-ray scattering and provides an X-ray shield to the environment.

The X-rays pass only through slot 93 in collimating plate 91 resulting in a narrow, well defined uniform intensity Xray beam.

Because the material has been approximately centered and radially positioned over the slot in collimating plate 91, the X-ray beam intersects the material substantially cross-sectionally as previously described in detail, in effect transmitting through a cross-sectional slice of the material. The transmittance of the beam through the material will be a function of the density of the material as well as the crosssectional geometry of the material.For example, referring to Fig. 11, at point A very little material will intersect the X-ray beam so that near full intensity of the beam will be transmitted whereas at point B where the cross-sectional slice is thicker the Xrays will not penetrate fully resulting in a loss of intensity to be detected by spot scanner 1 3. By detecting the beam intensity across the crosssectional slice, it is now clear that this technique could be used to not only verify overall product uniformity and dimensional tolerances but also the presence of voids, contaminants which have a density different from that of the material or defects in the dimensional geometry of the material.By utilizing a predetermined acceptable signature stored in calibrate memory 141, all subsequent scans can be compared to this standard to verify acceptability of the various product attributes, as previously described.

Spot scanner 1 3 is used to detect the variant intensities of the X-ray beam across the slice of material. Base plate 29 of scanner 1 3 has arcuate slot 30 which allows the X-ray beam to be exposed to either one of the two sensing elements 51. Sensing elements 51 are diodes which produce a small electric current when exposed to radiation. The current generated is linearly proportional to the intensity of the radiation to which it is exposed. Sensing elements 51 are mounted on an essentially circular printed circuit board scan disk 49 which is rotated at high velocity by drive motor 24 (Fig. 2). Sensing elements 51 are diametrically disposed near the outer perimeter of scan disk 49 such that as disk 49 rotates elements 51 alternately traverse over arcuate slot 30.Thus, elements 51 are exposed to the X-ray beam which has transmitted through a cross-sectional slice of the material and each time the diodes pass over slot 30 they detect the varying intensity of the X-ray beam across the "slice" of material. Only one diode is needed to detect this beam pattern. Two diodes were used in order to maintain dynamic geometric balance of scan disk 49 and also provide easier maintenance in that if one of the diodes fails to function the other diode may be used thus saving repair time until both diodes wear out.

Which diode is used is a simple matter of selecting the appropriate corresponding sync pulse from quadrant sync detector 69.

Both diodes (D1 and D2 in Fig. 5) are electrically connected in parallel across the differential input of video amplifier 50 (Fig.

5). Video amplifier 50 is of a design well known to one of ordinary skill in the art and amplifies the small currents produced by sensing elements 51 as they are exposed to the Xray beam pattern. The output of video amplifier 50 is an analog voltage which is linearly proportional to the current signal generated by sensing elements 51. The output of video amplifier 50 is transmitted along one of the four wires 56 which run from conector 46, down drive motor shaft 38 to a standard electrical rotary coupling 54 (Fig. 2). Rotary coupling 54 uses noiseless mercury contact slip rings to couple the electrical signals from the four spinning wires in drive shaft 38 to the four stationary contacts 63 on the outside case of rotary coupling 54. As stated, one of the four wires carries the output of video amplifier 50. The other three wires carry the power input signals to video amplifier 50.

Some wire in cable 14 connects video amplifier 50 output signal from rotary coupling 54 to flash converter 1 8. Flash converter 1 8 is a standard circuit used to convert analog signals to digital signals. At every instant in time a given analog amplitude from video amplifier 50 will be converted to a binary representation of a number from 0 to 255, a digitizing process well known to one skilled in the art. Thus, the output of the flash converter 1 8 is a digital signal which numerically represents the relative X-ray beam intensity, as previously described, detected by sensing elements 51 scanning the X-ray beam. By storing this digital data at the appropriate time when elements 51 pass over sample 90 the variation in X-ray beam intensity transmitted through the material can be measured and stored.

Synchronizing device 22 provides a pulse to flash converter 1 8 every time either one of the two sensing elements 51 is traversing arcuate slot 30. The pulse is of a duration equal to the time that it takes each diode to scan the X-ray beam passing through slot 30.

By selecting only every other pulse from the synchronizing device, data is only collected for one of the two sensing elements 51. The selection of every other pulse is controlled by the software of data analyzer 1 9. Data analyzer 1 9 stores data from flash converter 1 8 5000 times during the time period indicated by the synchronizing device when sensing elements 51 are crossing arcuate plot 30. The scan area will be a function of the sample rate and the rotational speed of the elements 51 as previously described. The data set stored is a digital representation, therefore, of the varying X-ray intensity through a cross-sectional slice of the material, or in other words, a signature of the slice of material.

Data analyzer 1 9 is programmed to calculate the percent deviation between a current data set and one stored in calibrate memory 141 (Fig. 10) or to plot out graphically each sequential data point in a data set. Because the data points numerically represent the transmittance of the X-rays at a particular location in the material the graphical plots represent the density distribution through a cross-sectional slice of the material. First, a data set obtained from a scan of a piece of material predetermined to be acceptable is stored in calibrate memory 141. Then the material in question, such as normal production stock, is scanned and the results are compared with the data stored in calibrate memory 141 to determine product acceptability.Data analyzer 1 9 is programmed to calculate for each data set a complex equation which provides a general density reading for the cross-sectional slice and to compare it to the density computation for the data set in calibrate memory 141, calculate percent deviation, calculate whether the deviation exceeds a predeermined limit and provide a warning signal if it does so exceed the limit. Data analyzer 1 9 is also programmed to simply provide a graphic chart of all 5000 data points in any data set for visual determination of product acceptability by the operator.

In another embodiment of the invention, shown in Fig.12, instead of a stationary sample 90 of material being placed under spot scanner 13, the material may be continously fed along a conveyor lide 142 under scanner 1 3. For example, as extruded material exits from an extrusion machine (not shown in Fig.12) it could be transferred along conveyor 142 and under spot scanner 1 3 for continuous scanning of the material and early detection of defects in the extrusion process.

Also, instead of using a predetermined sample of material for the calibrate memory 141 data set, the calibrate data set could be the beginning piece of the continously fed material. By comparing this data set forth the data collected from scans on the continously moving material, material uniformity can be continuously ascertained. Thus the present invention may be used as an offline inspection device or an online monitoring device. The conveyor line 142 must be separated as at opening 1 43 to allow the radiation beam 94 to be exposed to sample 90 without interference from the conveyor belt.

In yet another embodiment of the invention partly shown in Fig. 12, spot scanner 1 3 and collimating plate 91 can be removed and phosphor viewing plates placed in the path of the transmitted beam to allow visual or optical observation of the X-ray scan. Though in the preferred embodiment the described spot scanner 1 3 uses direct view of the X-rays by sensing elements 51 it will be appreciated that the viewing plate may be a phosphor screen to allow indirect optical view or sensing. Viewing port 144 allows human optical view of the phosphor screen. Cover 145 protects apparatus 10 from dust, damage and other deleterious occurrences.

In yet another embodiment, lead shield 1 7 is removed and the entire inside perimeter of cabinet 11 is lead lined as generally indicated by the numeral 146 in Fig. 1 2. X-ray tube 1 6 directs the cone shaped X-ray beam 94 vertically upward toward spot scanner 1 3. The lead lined cabinet 11 walls provide the X-ray shield from the environment.

Inasmuch as the present invention is subject to many variations, modifications and changes in detail, a number of which have been expressly stated herein, it is intended that all matter described throughout this entire specification or shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense. It should thus be evident that an apparatus constructed according to and method embodied within the concept of the present invention, and reasonably equivalent thereto, will accomplish the objects of the present invention and otherwise substantially improve the art of measurement and utilization of material transmittance characteristics.

Claims

1. An apparatus for quantifying the transmittance of an object comprising: means for generating a radiation field and exposing an object to said radiation field; scanner means for detecting variations in the intensity of said radiation field and for producing electrical signals proportional to said variations; and analyzer means for receiving said electrical signals and quantifying the transmittance of said object from said electrical signals.

2. The apparatus of claim 1 wherein said radiation means includes, in combination: a radiation source means for producing a uniform intensity radiation field; container means for enclosing said radiation source means; and housing means for holding said container means in a preselected axis including means for sliding said container means out of said housing means and thereafter rotating said container means through an angular displacement relative to said preselected axis.

3. The apparatus of claim 2 wherein said container means includes plug-in socket means for receiving said radiation source means, said socket means having electrical contact means for supplying electrical power to said radiation source means.

4. The apparatus of claim 3, wherein said contact means further includes means for providing contact force between said electrical contact means and said radiation source means and wherein said container means includes means for clamping said radiation source means in said container means such that said contact force is maintained and said clamping means is externally affixed to said container.

5. The apparatus of claim 4 wherein said radiation source means is a uniform intensity X-ray tube.

6. The apparatus of claim 1 wherein said scanner means includes radiation sensor means for generating an electrical signal proportional to the intensity of the radiation field exposed thereto and means for rotating said sensor means in a plane intersected by said radiation field.

7. The apparatus of claim 6 wherein said rotation means is a disc concentrically mounted to the shaft of a motor which rotationally frirthers said disc, said radiation sensor means being mounted to said disc.

8. The apparatus of claim 7 wherein said disc further includes amplifier means for amplifying at least one parameter of said electrical signal to generate a second electrical signal.

9. The apparatus of claim 7 wherein said scanner means further includes electrical coupling means for sending said electrical signals from said rotation means to said analyzer means.

10. The apparatus of claim 1 wherein said analyzer means includes converter means for converting said electrical signals into representative digital signals.

11. The apparatus of claim 10 wherein said analyzer means further includes data storage means for storing said representative digital signals and processor means for computing one or more attributes of said object from said representative digital signals.

1 2. The apparatus of claim 11 wherein said analyzer means is a digital computer.

1 3. A method for quantifying the transmittance of an object using a radiation source and a radiation sensing device rotatably mounted to a shaft comprising the steps of: generating a uniform intensity radiation field with said radiation source; exposing the object to said radiation field; detecting variations in the intensity of said radiation field using said radiation sensing device; generating electrical signals proportional thereto; and anaylzing said electrical signals to quantify the transmittance of said object.

14. The method according to claim 1 3 including the further step of rotating said sensing device in a plane intersected by said radiation field.

1 5. The method according to claim 14 including the further steps of converting said electrical signals to digital representations thereof and storing said digital representations in a memory device.

1 6. The method according to claim 1 5 including the further step of calculating one or more attributes of said object from one or more of said digital representations.

1 7. The method according to claim 1 3 including the further step of comparing said transmittance quantities and comparing said one or more attributes with predetermined acceptance values.

1 8. The method according to claim 1 7 further including the steps of: calculating deviations from said predetermined acceptance values of said transmittance quantities and said attributes; detemining from said deviations whether said object is to be rejected; and when so rejectable sending a control signal which indicates a reject condition.

1 9. A device for generating an electrical signal which signal indicates the time period when an object mounted to a rotatable shaft is traversing a predetermined arcuate length comprising: circumferentially spaced reflector means mounted on the rotatable shaft for reflecting a beam of light incident thereon; and sensor means fixedly located radially of said reflector means, the sensor means emitting a beam of light towards said reflector means and thereafter the sensor means generating an electrical signal when said light beam is reflected back to said sensor means.

20. The device of claim 1 9 wherein said reflector means is a collar with partially removed walls, said collar surrounding said rotatable shaft and affixed thereto with the partially removed walls providing a reflective surface to said light beam at predetermined arcuate intervals.

21. An apparatus for generating a radiation field comprising: radiation source means for producing a radiation field; container means for enclosing the radiation source means; and, housing means for holding said container means on a preselected axis including means for sliding the container means out of the housing means and thereafter rotating said container means through an angular displacement relative to said preselected axis.

22. The apparatus of claim 21 wherein said container means includes plug-in socket means for receiving said radiation source means and includes electrical contact means for supplying electrical power to said radiation source means.

23. The apparatus of claim 22 wherein said contact means further includes means for providing contact force between said electrical contact means and said radiation source means and wherein said container means further includes means for clamping said radiation source means in said container means such that said contact force is maintained and said clamping means is affixed externally to said container means.

24. The apparatus of claim 23 wherein said radiation source means is an X-ray tube.

25. An apparatus for scanning a radiation field and generating an electrical signal proportional thereto comprising: radiation sensor means for generating an electrical signal proportional to the intensity of the radiation field exposed thereto; rotation means for rotating said sensor means in a plane intersected by said radiation field; and, coupling means for sending said electrical signal from said radiation means to a receiver located specifically apart from said rotation means.

26. The apparatus of claim 25 wherein said rotation means is a disc concentrically mounted to the shaft of a motor to rotationally further said disc, said radiation sensor means being mounted to said disc.

27. The apparatus of claim 26 wherein said disc further includes electronic amplifier means for amplifying at least one parameter of said electrical signal to generate a second electrical signal.

28. A method for scanning a radiation field comprising the steps of: constraining a radiation field within a predetermined detection area; and rotating a radiation sensing device on a rotating element in a plane intersected by said radiation field where said radiation sensitive device produces an electrical signal which is proportional to the intensity of the radiation field exposed thereto.

29. The method as in claim 28 further including the step of amplifying said electrical signal and coupling said amplified signal from said rotating element to an analyzer for further processing.

30. Any of the apparatuses for scanning a radiation field substantially as herein described with reference to the accompanying drawings.

31. Any of the methods of scanning a radiation field substantially as herein described with reference to the accompanying drawings.