US2967947A

US2967947A - Sheet inspection method and apparatus

Info

Publication number: US2967947A
Application number: US613926A
Authority: US
Inventors: Jr William M Flook
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1956-10-04
Filing date: 1956-10-04
Publication date: 1961-01-10
Anticipated expiration: 1978-01-10

Description

Jan. 10, 1961 w. M. FLOOK, JR 2,967,947

SHEET INSPECTION METHOD AND APPARATUS Filed Oct. 4, 1956 3 Sheets-Sheet '1 Ifig,.1

PREFERRED L00 FOR 5 {INSPECTION DE 7 9 EFERRED TION FOR 7 INVENTOR 38 WILLIAM M. FLOOK, JR.

BY m

ATTORNEY Jan. 10, 1961 w. M. FLOOK, JR

SHEET INSPECTION METHOD AND APPARATUS 3 Sheets-Sheet 2 Filed 0ct. 4, 1956 INVENTOR WILLIAM M. FLOOK, JR.

ATTORNEY Jan. 10, 1961 w. M. FLOOK, JR

I SHEET INSPECTION METHOD AND APPARATUS 3 Sheets-Sheet 3 Filed 001;. 4, 1956 INVENTOR WILL/AM M. FLOOK, JR.

ATTORNEY list m Pew SHEET INSPECTION METHODAND APPARATUS William M. Flook, Jr., 'Greenville, Del., assignor to L du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed Oct. 4, 1956, Ser. No. 613,926 r 9 Claims. (Cl. 250-219) This invention relates to amethod and apparatus for the inspection of a running sheet such as a textile yarn \varp'sheet, woven textile fabric, paper or the like, and particularly to a method and apparatus for the continuous inspection of a warp sheet of heavy denieryarn made up of textile tire cord yarn or similar strands;

Textile tire cord is typically made up from twisted filaments of yarn of about 840 denier. It is convenient to beam the yarn on a large common spool which often contains a multiplicity, typically 160, of ends wound adjacent one another, so that each end can be againunwound without interference from other ends by the purchaser who utilizes the yarn in the fabrication of tire cord. A number of small packages of'yarn are commonly wound on the beam for each yarn end, the yarn from one package being spliced to that of a succeeding package with weavers knots, which is an acceptable procedure not affecting the quality of the product. An average of 300 passable knots may occur in-the processing of 160 individual yarn ends in thecourse of an hour of normal production, therefore, any inspection procedure must discriminate successfully in favor of passage of the knots as non-objectionable phenomena over true defects. Another anomaly which exists, but which is not presently classified in the trade as a cause for rejection, is the existence of loops, which may result from one or more monofilarnents being longer than the'rest and projecting from the yarn.

A more serious defect is the so-called flufi ball, which usually consists of a small twisted mass in the yarn resulting from a break in one or more monofilaments at one point, or the collection of substantial lengths of such broken monofilaments at one point in the yarn. This defect is objectionable because it usually is accompanied by a loss of strength, if caused by the breakage of one or more filaments, and by difficulties in subsequent handling due'to interference occasioned by the existence of the fluff ball in the product. Accordingly, it is the present practice to subject the running yarn to visual inspection, stopping the yarn in its travel whenever an objectionable number of fluff balls is determined to exist, cutting out the objectionable area, retying the severed ends and passing the product on to the beam. Visual inspection is tedious, vulnerable to human failure, and reduces production output, since the yarn could normally be wound at relatively high speeds if it were not for the necessity for slow speeds imposed by the inspection pro cedure. The following description is particularly directed to the inspection of yarn warp sheets; however, it will beunderstood that inspection of other sheet-like materials is equally feasible by the use of this invention and the term sheet as utilized herein is intended to comprehend opaque and transparent webs, such as paper, plastic, woven textile fabric and the like, as well as a multiplicity of running yarn ends disposed in generally inspection procedure for running sheets traveling at very high speeds. Other objects of this invention are the provision of an electro-optical inspection method and apparatus for a warp sheet of running yarns which is capable of discriminating between passable and nonpa'ssa'bleanomalies in the yarn to effect evaluation on the proper basis, and which can operate rapidly enough to detect defects at substantially greater operating speeds thanare now possible. Further objects of this invention are-the provision of a very stable sheet inspection apparatus which is capable of counting defects and giving a warning signal whenever a rejectable defect is encountered, together with automatic stopping of windup, if-desired, which are achieved as brought out in the detailed "description and the drawings, in which:

Fig; lis a partially schematic side elevation of a multiple-end yarn beaming installation,

Fig. 2'is a top plan view of the installation of Fig. 1,

Fig.3 is a schematic representation in sectional plan of a preferred embodiment of the optical arrangement of the inspection apparatus of this invention,

Fig. '4"is' a section taken transverse the sighting paths on line 4-4of Fig. 3,

Fig. 5 is a schematic representation of an electrical circuit adapted for use in conjunction with the optical arrangement of Figs. 3 and 4,

Fig. 6 is a schematic representation transverse the sighting paths of a split path embodiment of this invention, and

Fig. 7 is a schematic representation in sectional plan of an optical arrangement of inspection apparatus according to this invention wherein light beams are employed to scan the running yarn warp sheet.

Generally, this invention consists of a method and apparatus for sensing a defect in a running sheet ina pair of discrete regions spaced lengthwise of the sheet a suflicient distance apart so that rejectable defects solely are sensed coincidentally for both of the regions, and obtaining an indication of any defects responsive to coincidental sensing in the two regions.

A great variety of transducers are adapted to sense the existence of individual defects in a selected region of a running sheet, typical examples being a defiectible wire stretched across the sheet closely adjacent thereto and connected in circuit with a pulsing microphone, con ventional capacitometers of various types, and other devices; however, it is preferred to utilize electro-optical means for conducting inspection'according to this invention. In the following detailed description relating to electro-optical inspection systems particularly, the

' plied from a multiplicity of packages mounted in a creel indicated generally at 5', which deliver a plurality of yarn" ends 6 for windup on a beam 10 driven by a conventional beaming machine 11. consisting of approximately separate strands, is formed as a fiat sheet of individual yams-trends disposed closely adjacent one another by convergence guide 8,

which receives ends 6 from the creel; In a typical case, warp 7 may be 54" wide and convergence guide '8' 'is spaced away from idler roll 9 on beaming machine 11 a distance far enough to permit stopping the yarn windup process, if desired, upon detection of a defect within a short enough time interval to remedy matters before the yarn is wound up on beam 10.

unitary discrete regions of defect sensing is shown; in

The yarn warp sheet 7,'

Figs. 3 and 4. All of the optical components are preferably mounted within a common light-tight housing 15 which is provided with an opening 16 oriented transverse warp 7. Opening 16 is sufficiently wide to accommodate two

sighting paths

17 and 18 normal to warp 7, path 17 (refer Fig. 4) preferably being disposed on the opposite side of the yarn from path 18, although this is not essential. Paths 17 and 1S terminate in light trap 19, which is simply a box closed at all points except for apertures in line with the sighting paths and painted on the inside with light absorptive black paint to provide a constant reference for operation of the apparatus and, at the same time, reduce the ambient light normally incident on

photomultiplier detectors

27 and 34 hereinafter described.

Sighting path 17 is spaced from sighting path 18 a suificient distance along the direction of yarn travel so that only rejectable defects will lie across both channels simultaneously and, thereby, give a coincidence signal, as hereinafter described, representative of anomalies which constitute a basis for rejection. That is, the spacing between

sighting paths

17 and 18 in the direction of yarn travel is equal to the minimum length of defect it is desired to base rejection upon. Normally, a spacing of A" is satisfactory to achieve the necessary discrimination. The ends of the sighting paths within housing 15 terminate at silvered reflective 90 prism 23, one face of which is disposed transverse sighting path 17 and the other face of which is disposed transverse sighting path 18. Reflected light from path 17 is passed through collimating lens 25, which is mounted behind light mask 24, the light from lens 25 being thereby focused through the aperture of mask 26, disposed at the focal point of lens 25, on the light-sensitive cathode of photomultiplier cell 27. The aperture of mask 26 in a typical case was 0.010" wide, the lens 25 used therewith having a focal length of 8". A completely symmetrical optical counterpatr consisting of light mask 31, collimating lens 32, mask 33, and photomultiplier cell 34 is provided for the sighting path 18.

Referring to Fig. 4, the light for the system is provided by a fluorescent tube bulb 38, which may be a General Electric'type 90/Tl7 operated on direct current with periodic reversal of polarity as hereinafter described, mounted in housing 39 open at 41 along the side adjacent yarn warp 7. Although light source 38 is mounted beneath the yarn warp, it serves to also illuminate the region above the warp as well as the region below the warp, because light passes freely through the spaces between the running yarn strands. Smooth, wear-resistant steady rests 40 are preferably provided in abutment with the yarn warp at the opening of housing 39 to prevent cyclic vibrations or fluttering of the warp sheet, such as might occur from windage or the like. Where the distance between the inspection apparatus and guide 8 is relatively great, steady rests 40 are preferably supplemented by passing yarn warp 7 in an S-wrap about a pair freely rotating rollers before the yarn passes to rests One conventional circuit which has performed satisfactorily in conjunction with the inspection apparatus of this invention is detailed schematically in Fig. 5. As shown, light reflected from prism 23 is impressed on the cathode elements of

photomultiplier tubes

27 and 34 individually, the output of photomultiplier 27 being representative of conditions existing along sighting path 17, whereas the output signal of photomultiplier 34 is representative of conditions existing along sighting path 18.

The power supply for

photomultipler tubes

27 and 34, indicated generally at 45, may deliver a thousand v. D.-C. filtered output, as does a Powellhigh voltage unit, which is utilized in association with a suitable auxiliary, such as a Model 28 Lambda power supply. The power input to supply 45 is derived from power supply line 55 through lead 43, 44 being'an electrical ground, and the output is delivered through lead 46 and the tap of resistor 47, to the cathodes of

tubes

27 and 34 in conventional manner. The amplified electrical output signals representative of the light amounts impressed on the respective cathodes are passed through

leads

50 and 51 connected to the anode elements of the photomultiplier tubes to A.-C. adjustable gain voltage amplifiers 52 and 53 (operative in the 20 1000 c. range approximately), respectively. A.-C. amplifiers are utilized because the signals processed by the apparatus are electrical pulses and, accordingly, steady state D.-C. conditions have no effect on operations. Operating power is supplied to amplifier 52 by direct con nection with B+ 190 v. power supply line 55, while amplifier 53 is powered from the same source by connection through lead 56. The circuit past the amplifiers is also powered from line 55, the electrical circuit being completed through common ground 54.

The output of amplifier 52 is impressed on grid 60 of the first section of double triode section coincidence circuit tube 61 (which may be a l2AX7 type) through tapped resistor 62 (typically 5 megohms) connected in series with fixed resistor 63 (which may be 22 megohrns) to power lead 55. Similarly, the output of amplifier 53 is impressed on grid 65 of the other triode section of tube 61 through tapped resistor 66 in series with fixed resistor 67, also connected to lead 55. The cathode elements of both of the triode sections of tube 61 are grounded at 68, while the plate elements of both of the triode sections are connected together to line 55 through fixed resistor 69, which may have a magnitude of about 270K. The output signal of tube 61 is derived through coupling capacitor 70 (typically 0.01 rnfd.) and impressed on the control grid 72 of thyratron tube 71 (which may be a type 21321) through series resistor 73 (which may be a 100K resistor). Grid resistor '74 (of about 220K value) is connected to ground 54. Thyratron cathode resistor 75 and resistor together constitute a voltage divider to provide the appropriate cathode bias. The suppressor grid 79 is connected to the cathode element of tube 71 as is conventional practice.

The output signal from thyratron 71 is drawn from the plate element thereof through lead 81 connected to one contact of normally closed pushbutton switch 82, the other contact of which is connected in series with normally closed relay contacts C operated by relay C, hereinafter described. The circuit to power supply line 55 is completed through normally closed relay contacts E; of relay E, which are connected in series with the relay coil and fixed resistor 83. Relay E may be a three contact type of 15 ma. size provided with a holding capacitor 78 of approximately 8 mfd. capacitance.

Two auxiliary circuits are provided to: (1) obtain a count of rejectable defects as these occur from time to time and (2) halt windup of the yarn by beaming machine 11, at the operators option, so as to permit cutting fluff balls or other defects from the ends and retying them prior to winding product on beam 10.

The counter circuit, indicated generally at 84, consists of a counter actuation coil 85 connected in series through normally open relay contacts E of relay E with 115 v. A.-C. power lines 86 and 87. An operative condition verifying fiash lamp S8 is preferably connected in shunt with coil 85, and an R-C arc suppressor network 89 is connected in shunt with relay contacts E A practical control circuit for beaming machine 11 utilizes a manually operated double pole, double throw switch 8,, the left-hand side of which is effective, when closed on the upper pair of switch contacts, to shunt the output signal from thyratron 71 around relay contacts E The right-hand side in upper switch closure position is simultaneously effective to complete the circuit through control leads 94 and 95 in the power supply circuit (not further shown) of beaming machine 11. An interlock is provided through normally open relay contacts E of relay E, which are connected in series with leads 94 and ass-7,94?

95. The lower pair ofcontacts of switch S -are open circuited.

The circuit includes relay C, which is connected in series with resistor 96 from power supply line 55 to ground 54 through normally open switch contacts D Contacts D are closed periodically at predetermined intervals of an hour, or somewhat longer, by a conventional timing cam, indicated generally at 100, through the driving connection shown in broken line representation. Re lay C is provided with additional contacts, not further detailed herein, which operate in the power supply 1691 of fluorescent tube bulb 38 to thereby reverse the polarity thereon, as hereinbefore mentioned. This polarity reversal avoids localized accelerated deterioration of the phosphor lining of 38 with accompanying objectionable uneven illumination of the yarn.

In operation, it will be understood that a fluff ball or otherrejectable defect in the running yarn will obtrude beyond the plane of yarn warp 7 either above or below the yarn, where it reflects light incident on it from fluorescent tube bulb 38 along the sighting paths. To constitute a registered defect, as hereinbefore brought out, light must be reflected simultaneously along both

sighting paths

17 and 18, so as to produce a signal of appropriate potential by actuation of coincidence circuit tube 61. Tube 61 is operated so that each of its triode sections are normally conducting to saturation. Under these circumstances, the negative signal derived at the grid responsive to light impinging on a photo-multiplier tube, such as 27 as an example, immediately cuts off current flow through the associated triode section and raises the potential at point A in the plate circuit a finite amount. 1n the typical circuit described, the parameters are chosen so'that cutoff of the left triode section results in a rise of potential at point A from an ambient level of about 40 v. to about 60 v., a rise of20 v., whereas cutoif of both sections raises the potential of point A to the level of the B+ supply, or approximately 190 v.

Thyratron 71 in this instance was adjusted to fire on a sudden voltage rise of about 30 v., so that the thyratron will fire only when there is coincidental cutoif of both of the triode sections of tube 61. Since cutoff of both sections occurs only in the presence of a rejectable defect, it will be understood that discrimination is thereby achieved against all anomalies except those which are known to be of rejectable nature. If this criterion is met, grid 72 of thyratron tube 71 has impressed thereon a positive signal, which causes the thyratron to conduct with deliveryof an output pulse to relay E.

Assuming that switch S is in open position as shown in Fig. 5, the output pulse from thyratron 71 causes relay E to close contacts E in the counter circuit, which permits current to flow temporaily through coil 85, thus giving asingle count. Relay E at the same time acts to open relay contacts E and to hold them open for a finite interval by the time delay action of capacitor 78. This time interval is proportioned to permit sufficient time for-counter 84 to make a count while, at the same time, restoring the circuit to detection condition as rapidly as practicable to safeguard against registration of a plurality of defects as only a single defect. 'Opening of relay contacts E terminates conduction through thyratron 71, whereupon the tube is restored to inspecting condition.

With the foregoing operation, inspection islimited solely to the counting of rejectable defects. Where it is desired that beaming. halt upon the occurrence ofa defeet, the operator closes switch S on the upper set of contacts. Switch S then shunts contacts E while, at the same time completing theelectrical circuit through control leads 94 and 95, except for relay contacts E If the apparatus now detects a defect, contacts E close and an appropriate signal passes through leads Hand 95, halting windup by beaming machine 11 until the operator can remove the defect from warp 7, or other- Wise. take corrective action. Opening of relay contacts E does not, with this operation, halt conduction through thyratron 71 and the operator must open switch 82 manually to clear the circuit for further inspection service, thus insuring that attention has been given to matters before resumption of beaming. The counter circuit is, of course, actuated through one count corresponding to each individual defect regardless of the setting of switch S Periodic reversal of polarity of fluorescent tube bulb 38 under control of timing cam 100 will give a spurious rejection signal unless positive safeguards are provided, because some light is always passed to the photomultiplier tubes due to stray light effects, which light drops to zero level when bulb 38 goes off during polarity reversal. Relay C averts the possibility of spurious signals-by opening relay contacts C upon closure of switch contacts D a slight interval in advance of polarity reversal. With contacts C open relay E remains unenergized and there is no defect registration by the apparatus for the brief interval contacts D remain closed. Since polarity reveral requires only a few milliseconds time, and occurs but once during an hour or more of operation, this is no serious disadvantage.

The gains of

amplifiers

52 and 53 are adjustable, as hereinbefore described, which permits adjustment of the sensitivity of the inspection apparatus with respect to density of defects encountered.

In some instances improved defect discrimination is obtained by the use of a pair of'split path regions of defect sensing, such as the sighting paths represented in Fig. 6. Here each sighting path is divided into two separate portions, the leading path consisting of 17a, above warp 7, and 17b, below the warp. Similarly, path 18 is divided into an upper part 18a and a lower part 18b, each disposed along the line of warp travel with a spacing of about M4 from their counterparts in path 17, as hereinbefore described for the embodiment of Figs. 3 and 4. The cross sectional areas of 17a and 17b may each be about equal to that of 17 previously described, 18a and 181) each then equalling 18. The optical system for the arrangement of Fig. 6 is identical with Fig. 3,- it being understood that radiation received along the two split portions of each sighting path now passes to'a common detector for each path and that operation is otherwise identical with that hereinbefore described. The increased reliability of the scanning arrangement of Fig. 6 is probably due to the fact that each sighting path now views areas both aboveand below the warp. Un symmetrical defects which may project, for example, more above the warp than below it are less likely to fail to yield coincidence signals.

While it is preferred to conduct the inspection with defect sensing based on light reflected from individual defects, it is also practicable to employ selective interruption of light transmission in the sensing, a preferred optical arrangement for which is detailed in Fig. 7. Here the detection side of the system is identical with that shown in Fig. 3; however, the opposite side corresponding to what was formerly light trap 19 is now housing 106 for the light source, which may be two independent 50 watt

incandescent light bulbs

107 and 108, each disposed back of

individual masks

109 and 110, respectively, in line with collimating lenses 111 and 112, respectively. The two light beams are deflected along

sighting paths

17 and 18 by silvered reflective prism 113 and con stitute the defect sensing means by virtue of selective interruption of light transmitted therealong responsive to the presence of rejectable defects. It will be understood that the same electrical circuit as shown inFig. 5 can be employed in conjunction with the embodiment of Fig. 7, except that it is now necessary to adjust the gain control suitably to accommodate for the changed ambient lightlevel. When the arrangement of Fig. 7 is utilized, =fluo= rescent tube bulb 38 is dispensed with.

The split sighting path arrangement of Fig. 6 may, if

desired, be employed with defect sensing by the apparatus of Fig. 7, conventional light dividers being then employed to define the separate light beams which are directed along

paths

17a, 17b, 18a, and 18b.

It will be understood that the several embodiments hereinbefore described for the inspection of Warp sheets are equally applicable to the inspection of sheet materials generally, such as paper, plastic, textile fabrics and the like, except that it is, of course, then necessary to use an individual light source on opposite sides of the sheets wherever the sheets are light-opaque.

From the foregoing it will be understood that my invention provides a method and apparatus capable of inspecting running sheet material which is adapted to distinguish between rejectable defects and non-rejectable anomalies rapidly and dependably, and that numerous alterations can be made therein without departure from the essential spirit, wherefor it is intended to be limited only by the following claims.

What is claimed is:

1. An apparatus for the inspection of a running sheet for defects protruding along a normal to said sheet comprising in combination a pair of sighting paths disposed transverse said sheet closely adjacent thereto in planes substantially coparallel to the plane including said running sheet and spaced apart in the direction of sheet travel a distance equal to the minimum length of defect it is desired to base rejection upon, a light source directed at said sheet in the vicinity of said sighting paths, and electro-optical means responsive to light reflected along said sighting paths from said defects consisting of a pair of individual photomultiplier tubes each responsive to light from one of said sighting paths solely, a voltage amplifier in electrical circuit with the output of each of said photomultiplier tubes individually, a coincidence circuit including a vacuum tube having two triode sections, the grid of one of which triode sections is in electrical circuit with the amplified voltage output of one said photomultiplier tube while the grid of the other of said triode sections is in electrical circuit with the amplified voltage output of the, other of said photomultiplier tubes, 2. thyratron tube having its control grid in electrical circuit with the combined output of both of said triode sections of said vacuum tube in said coincidence circuit, and means responsive to the output of said thyratron tube indicating the existence of individual ones of said defects.

2. An apparatus for the inspection of a running sheet according to claim 1 wherein said light source consists of a fluorescent tube operated on direct current having means periodically reversing the polarity of said direct current across the terminals of said fluorescent tube and a switch momentarily rendering said electro-optical means indicating the existence of defects in said sheet inoperative during the time interval in which said polarity is in course of reversal.

3. An apparatus for the inspection of a running sheet for defects protruding along a normal to said sheet comprising in combination a pair of sighting paths disposed closely adjacent to and transverse said sheet in planes substantially coparallel to the plane including said running sheet, each of said sighting paths being split into a portion disposed above said sheet and another portion disposed below said sheet, the corresponding portions of each sighting path being spaced apart in the direction of sheet travel a distance equal to the minimum length of a detect it is desired to base rejection upon, a light source directed at said sheet in the vicinity of said sighting paths, and electro-optical means responsive to light reflected along said sighting paths from said defects indicating the existence of individual ones of said defects which obtrude coincidentally in said pair of sighting paths.v

4. An apparatus for the inspection or a running sheet for defects protruding along a normal to said sheet comprising in combination a pair of sighting paths disposed transverse said sheet directed toward the region closely adjacent to said running sheet in planes substantially coparallel to the plane including said running sheet, and spaced apart in the direction of sheet travel a distance equal to the minimum length of defect it is desired to base rejection upon, a light source directed down each of said sighting paths, and electro-optical means responsive to changes in the amount of light transmitted down each of said sighting paths due to the presence of a defect in said paths indicating the existence of individual ones of said defects which obtrude coincidentally in said pair of sighting paths.

5. A method for the inspection of a running sheet for defects protruding along a normal to said sheet, comprising scanning the space closely adjacent to said running sheet in planes substantially coparallel to the plane including said running sheet, detecting the presence of a defect in each of a pair of discrete regions spaced apart lengthwise of said sheet a distance equal to the minimum length of a defect it is desired to base rejection upon, and obtaining an indication of any defects responsive to coincidental detecting in said pair of discrete regions.

6. A method for the inspection of a running sheet ac cording to claim 5 wherein detecting of said defects in said discrete regions is conducted on opposite sides of said sheet.

7. An apparatus for the inspection of a running sheet for defects protruding along a normal to said sheet, comprising in combination means scanning the space closely adjacent to said running sheet in planes substantially coparallel to the plane including said running sheet, means detecting a defect in said sheet in a pair of discrete regions spaced apart lengthwise of said sheet a distance equal to the minimum length of a defect it is desired to base rejection upon, and means responsive to said means detecting said defect indicating the existence of any defects which are detected coincidentally in said pair of discrete regions.

8. An apparatus for the inspection of a running sheet according to claim 7 wherein said means detecting a defect in said sheet in said pair of discrete regions spaced lengthwise of said sheet are adapted to detect said defects on opposite sides of said sheet.

9. An apparatus for the inspection of a running sheet for defects protruding along a normal to said sheet, comprising in combination a pair of sighting paths disposed transverse said sheet closely adjacent thereto in planes substantially coparallel to the plane including said running sheet, and spaced apart in the direction of sheet travel a distance equal to the minimum length of defect it is desired to base rejection upon, a light source directed at said sheet in the vicinity of said sighting paths, and electro-optical means responsive to light reflected along said sighting paths from said defects indicating the existence of individual ones of said defects which obtrude coincidentally in said pair of sighting paths.

References Cited in the file of this patent UNITED STATES PATENTS 2,233,483 Metcalf Mar. 4, 1941 2,246,501 Bradner et al. June 24, 1941 2,295,327 Bendz Sept. 8, 1942 2,429,331 Sachtleben Oct. 21, 1947 2,640,152. Hartwig May 26, 1953 2,721,942 Friel et al. Oct. 25, 1955 2,753,464 Stone July 3, 1956 2,791,931 Summerhayes May 14, 1957 2,806,401 Demuth et a1 Sept. 17, 1957 UNITED STATES PATENT OFFICE Certificate of Correction January 10, 1961 Patent No. 2,967,947

William M. Flook, J r. certified that error appears in the above numbered patent requiring as corrected below.

g Fig. 5, should appear as shown below instead It is hereby correction and th at the said Letters Patent should read In the drawings, Sheet 2, containin of as in the patent:

Jan. 10, 1961 w. M. FLOOK, JR

SHEET INSPECTION METHOD AND APPARAT S 3 Sheets-Sheet 2 Filed Oct. 4, 1956 INVENTOR WILLIAM M FLOOK, JR.

ATTORNEY column 3, line 38, for patr read part; column 5, line 53, for temporaily read ternporari1y.

[SEAL] Attest:

ERNEST WV. SWIDER,

Attesting Oficeo".

DAVID L. LADD,

U0vmniwioney of Patents.