US3118665A

US3118665A - Apparatus for checking and sorting sheet material

Info

Publication number: US3118665A
Application number: US126933A
Authority: US
Inventors: Thompson Jack Evans; Simmons Michael Carol Atlee
Original assignee: Individual
Current assignee: Individual
Priority date: 1961-07-26
Filing date: 1961-07-26
Publication date: 1964-01-21
Anticipated expiration: 1981-01-21

Description

APPARATUS FOR CHECKING AND SORTING SHEET MATERIAL Filed July 26, 1961 1954 J. E. THOMPSON ETAL 3 Sheets-Sheet l 1954 J. E. THOMPSON ETAL 3,113,655

APPAfiATUS FOR CHECKING AND SQRTING SHEET MATERIAL 3 Sheets-Sheet 2 Filed July 26. 1961 1954 J. E. THOMPSON ETAL 3,118,6fi5

APPARATUS FOR CHECKING AND SORTING SHEET MATERIAL Filed July 26, 1961 3 Sheets-Sheet 5 3,118,665 APPARATUS FOR CHECKING AND SORTENG SHEET MATERIAL Jack Evans Thompson, Sungates, West Drive, Chearn,

England, and Michael Carol Atlee Simmons, The rehard, Montreal Road, Riverhead, England Filed July 26, 1961, Ser. No. 126,933 7 Claims. (Cl. 271-89) This invention relates to a method of and apparatus for checking and sorting sheet material.

In the manufacture of fine paper, it is difiicult to obtain sheets of consistent quality, and the individual sheets have to be checked for flaws and sorted into sheets which are acceptable and sheets which are rejected. The flaws which occur in such fine papers are generally in the form of holes, marks, dirt or foreign matter, or creases, tears or turned-in corners, or lumps of partially digested paper pulp, and it is an object of the present invention to provide a method of and an apparatus for detecting such flaws in fine paper. It is, however, to be appreciated that similar flaws occur in other papers, and in other sheet material in general, and it is also an object of the present invention to provide a method of and an apparatus for detecting such fiaws or similar flaws in sheet material in general.

According to the present invention there is provided a method of checking and sorting sheets of material, wherein the sheets are passed over a surface and beneath a photoelectric scanning unit which scans the sheets under reflected light as they pass over the surface, the surface being of a colour which the photoelectric scanning unit can distinguish from the sheet material, and wherein a signal generated in the scanning unit by a flaw in the sheet material is employed to operate means for rejecting the sheet containing such flaw.

In applying this method to white paper, the paper may be fed over a black surface so that small holes in the paper will show as black spots, and will have the same effect on the photoelectric scanning unit as a piece of foreign matter.

It is also highly desirable to scan the paper by means of transmitted light to detect creases and variations in the thickness thereof, the latter being of particular importance in the case of coated papers where localised concentrations of the coating material have to be avoided since they are liable to cause damage to a printing machine in a subsequent printing operation.

According to another aspect of the present invention there is provided apparatus for checking and sorting sheets of material, wherein means is provided for passing the sheet material between a photoelectric scanning unit and a surface the colour of which the photoelectric scanning unit can distinguish from the sheet of material, and wherein means operable by the photoelectric scanning unit are provided for rejecting sheets which the photoelectric scanning unit has detected as being unsuitable.

In order to enable the invention to be more readily understood, reference will now be made to the accompanying drawings which illustrate diagrammatically and by way of example some embodiments thereof, and in which:

FIG. 1 is a diagrammatic elevation of apparatus for checking and sorting sheets of paper,

FIG. 2 shows on a larger scale, a detail of the apparagus shown in FIG. 1,

FIG. 3 shows, on a larger scale, a detail of the apparatus shown in FIG. 1, and

FIG. 4 is part view, similar to FIG. 1, showing a modification of the apparatus.

Referring now to FIG. 1 of the drawings, there is shown apparatus for checking and sorting sheets of paper, the

3,ll8,6h5 Patented Jan. 21, 1964 ice apparatus being shown diagrammatically and many parts being omitted for the sake of clarity and explanation. The apparatus essentially comprises two endless chains 1 running round two pairs of chain wheels 2 (of which only one is shown in the drawing) on horizontal shafts 3 at each end of the apparatus. Extending transversely between the chains 1 are gripper bars 4 arranged to grip the leading edges of sheets of paper 5 fed from an automatic paper feeding machine 6 which will not be described in further detail. The gripper bars 4 are attached to the chains 1 which are spaced apart from one another a distance equal to the length of the gripper bars, and the gripper bars are slightly longer than the width of the sheets of paper 5. The gripper bars 4 are spaced equidistantly throughout the length of the endless chains 1, and are spaced apart from one another a distance slightly greater than the length of the longest sheets of paper which the apparatus is to check and sort.

A sheet of expanded metal 7 is provided between the two pairs of chain wheels 2 so as to form the upper strand of the apparatus, and the grippers are arranged to move just above the sheet of expanded metal in the direction of the arrow 12.

The first pair of the chain wheels 2 are mounted adjacent to the automatic paper feeding machine 6, and are driven by a motor 8, the driven chain wheels serving to drive, by means of the chains ll, the second pair of chain wheels (not shown) and their associated shaft 3 on which is mounted a drum 9 disposed between the chain wheels. To maintain an even tension in the top and bottom chain tracks, the shafts 3 are mechanically connected through gear boxes and a lay shaft which are not shown.

The whole apparatus is supported in a skeletal arrangement of girders, but these have been omitted from FIG. 1 for the sake of clarity.

A sucker mechanism is provided for feeding the sheets of paper 5 from the automatic paper feeding machine 6 into the gripper bars 4. The sucker mechanism comprises two or more suckers it} which are linked to an arm 11 which is capable of describing an are as shown in FIG. 1, the arrangement being such that the suckers 1t} reciprocate horizontally above the first chain wheel shaft 3.

The drum 9 is formed with a longitudinal recess 14 and is covered with a sleeve 15 of rubber, synthetic plastic material, such as polyvinyl chloride, or felt, which is of a colour distinguishable from that of the sheets of paper 5. The sleeve is held together by a slide fastener which is positioned in the recess 14, and a shaft 16 extends across the drum and is held above the sleeve 15, but within the recess l4 by means of springs 17 so as to maintain the covering tightly around the drum. The width of the recess 14 is such that it can accommodate a gripper bar 4.

Three photoelectric scanning units are provided for scann ng the sheets of paper and for detecting faults in the sheets, so that faulty sheets will be deposited in a reject hopper 18 while acceptable sheets will be deposited in one or other of two accept

hoppers

19 and 20, the

hoppers

13, 19 and 20 being disposed below the apparatus.

The first photoelectric scanning unit 22 is mounted above the upper strand of the apparatus and comprises a light source 23 arranged to project a beam of light on to the sheets of paper 5 as they pass over the upper strand of the apparatus, and a photoelectric cell unit 24 arranged to scan the sheets under the influence of the light from the source 23 which is reflected off the sheets. The photoelectric cell unit 24 is connected to a comparator unit 25. Mounted above the light source 23 and photoelectric cell unit 24 is a drum 25 on which is mounted a sheet 27 of paper of acceptable and desired quality, the sheet 27 beiru of the same size as the sheets being fed in the apparatus. Mounted above the drum Z6 is a further light source 23 and a further photoelectric cell unit 21, the photoelectric cell unit 25 being arranged to scan the sheet 27 in exactly the same manner as the photoelectric cell unit 24 scans the sheets as they pass therebeneath. The photoelectric cell unit 29 is also connected to the comparator 25 which in turn is connected with a memory storage unit 369 arranged to actuate a gripper bar release mechanism for eleasing rejected sheets so that they fall into the reject hopper 13, as will be described in greater detail here nafter. The memory storage unit essentially comprises a series of solenoid switches and is associated with the lay shaft of the apparatus.

A second scanning unit 32 is provided after, in the direction of travel of the sheets 5, the scanning unit 22, and comprises a light source 33 mounted below the upper strand of the apparatus and arranged to transmit light through the sheets of paper 5 as they pass thereover into a photoelectric cell unit 3 mounted above the upper strand of the apparatus. The photoelectric cell unit 34 is also connected to the memory storage unit 38.

The third scanning unit 35 is mounted to scan the sheets of paper 5 as they pass over the drum and comprises a light source 36 and a rotary scanning drum 3'! arranged to scan the sheets under the influence of light reflected off the sheets from the light source 36. The third scanning unit 35 is also connected to the memory storage unit 39.

The construction of the hoppers l8, l9 and 2 will now be described in greater detail with reference to FIGS. 1 and 2 of the drawings. it is to be noted that the term hopper as employed in the specific description herein is intended to mean not so much a bin or closed sided container, but rather a station at which the sheets of paper are deposited.

Each hopper includes a main base plate 46 which is suspended by four chains 41 passing over chain wheels 42 located at the top of the hopper. In FIG. 1, the chain wheels are shown as lying in the plane of the paper, but in actual fact they are mounted on shafts which have their axes lying in the plane of the paper. The shafts of the chain wheels 42 are driven by motors, one for each hopper, and each motor is controlled by a pile height control device to be described hereinafter. Located on each base plate it is a stihage or pallet 43 for receiving the sheets of paper, the stillage having legs 44 so as to define a space between the base of the stillage and the base plate 4% so that a pile of papers may be removed, together with the stillage, from the base plate 49 by for example means of a fork lift truck.

Sheets of expanded metal 44 extend between the drum 9 and the hopper 1S, between hopper l8 and the hopper l9, and between the hopper l3 and the hopper 29, only the latter being shown in FIG. 1.

The rear edge of each hopper is defined by a rakeshaped member 45, having downwardly projecting teeth against which the sheets of paper can abut. The rakeshaped member 4-5 carries an air blast pipe 4-6 arranged to direct air in the direction of arrow 47 for a purpose to be specified hereinafter.

The upper sides of each hopper are defined by jogger bars 43 reciprocable by means of the lay shaft 49 of the apparatus. The lay shaft carries an eccentric 59 which bears against a follower bar 51 connected to a carriage 52. The carriage 52 has at each end brackets 53 extending between which is a lead-screw shaft 54 on which one of the jogger bars 43 is carried. At its end, the lead screw shaft 54 carries a pinion 55 meshing with a pinion 5-6 carried on a telescopic shaft 57. At its other end, the telescopic shaft 5'7 carries a pinion 53 meshing with a pinion 59 carried at the end of another lead-screw shaft 69 on which the other jogger bar is mounted. The lead-screw shaft of is carried between -rackets 61 on a second carriage 62 to which is connct fit a follower bar 51A bearing against another eccentric 59A mounted on the lay shaft 49. The eccentric 56A is, for simplicity, shown on the right hand side of the apparatus in F1". 2, but is actually positioned adjacent to the eccentric on the lay shaft 49. The positions of the jogger bars 48 may be adjusted by turning the lead-screw shaft by means not shown so as to move the jogger bars 48 nearer together or further apart so as to accommodate different widths of paper.

The carriages 52 and 62 are slidable on slideways (not shown) on a horizontal framework member of the skeletal structure of the apparatus connected between two vertical members parts of which are indicated at 63.

Two brackets 64, mounted on the aforesaid horizontal framework member carry a shaft 65 on which are mounted two suction rollers 66 which are apertured and connected to a source of suction. The shaft 65 also carries metal rollers 67. A reciprocable shaft 63 is mounted above the shaft 65 and carries two arms 69 at the ends of which rubber rollers 7%) are mounted so as to be freely rotatable, the rubber rollers being capable of en gaging the metal rollers 67.

Although FIG. 2 is a view on the line IIII of FIG. 1 and thus shows the front edge of the hopper 19, it is to be appreciated that the construction of the front edge of each of the

hoppers

18 and 20 is identical with that shown in FIG. 2.

An automatic pile height control device is provided for each of the hoppers, but is shown only in conjunction with the hopper 29 in FIG. 1. This pile height c0ntrol device comprises a light source arranged to reflect a beam of light off the front edges of a pile '71 of sheets of paper in the hopper on to a photoelectric cell unit 7e connected to a switch 77 arranged to actuate the motor (not shown) for turning the shaft on which the chain wheels 42 are mounted.

An air brush arrangement is provided above each of the hoppers l? and 20, but is shown associated only with the hopper 2%? in FIG. 1. The air brush arrangement may also be associated with reject hopper 18 if a large member of rejected sheets are expected, but this is, in general, unnecessary.

The air brush arrangement comprises four chain wheels 89 mounted above the hopper two at each end thereof and spaced apart from one another. Each pair of chain wheels 89 is connected by a chain 81 which carries two hollow bars 82 whichare apertured to blow air downwardly into the hopper. The bars 32 of each air brush arrangement are associated with two respective ring manifolds located one at each side of the hopper, and connected to a source of compressed air.

In front of the hopper 19 a photoelectric sensing unit is provided and comprises a light source 83 mounted above the lower strand of the apparatus which is constituted by the lower strand of the chain 1 and arranged to reflect light off a sheet passing therebeneath into a photoelectric cell unit 84 arranged to actuate a memory storage unit 85 which serves to operate gripper bar release mechanisms associated with the hoppers l9 and 2%) in such a manner as to control the numbers of sheets of paper fed into such hoppers. The light source 33 and the photoelectric cell unit may be arranged to scan the sheets under transmitted light, but it is preferred to scan under reiiected light to obviate the effect of sunlight shining through the roof, or strong overhead lights which might otherwise actuate the photoelectric cell unit 84.

The memory storage unit 35 is also arranged to opcrate the air brush arrangement in a manner to be described hereinafter, and may be arranged to actuate mechanisms for inserting tabs into the piles 71 after a desired number of sheets have been deposited in the hopper. Devices for inserting tabs into piles of sheets are known, and the devices will not therefore be described.

Also associated with each hopper is a hollow bar 8-6 which is connectable to a source of compressed air when the machine is running at slow speeds, the bar being arranged to direct air in the direction of the arrow 87 for a purpose that will be explained hereinafter.

Referring now to FIG. 5 f the drawings, there is shown the gripper release mechanism associated with any one of the hoppers. Two slideways 83 extend for substantially the length of the lower strand of the apparatus and a slide plate 89 is mounted on the slideways 88. A solenoid 949 is mounted on the plate 89 and is connected through an arm 91 with one arm 92 of a toggle

mechanism comprising arms

92 and 93. The arm 93 of the toggle mechanism is connected to a cam arm 94 which is pivotally mounted on the plate 39 and 95. A spring 96 is connected to the arm 92 of the toggle mechanism and urges the latter to occupy the position indicated in broken lines. As shown in FIG. 3, the gripper bar 4 comprises a bar proper 97 on which is pivoted a gripping arm 93 which is spring loaded to engage against the bar 97 to hold a sheet of paper therebetween. Also pivoted on the bar 97 is an arm 99 carrying at its end a roller 1% engageable against the cam arm 94 when the latter is in the full line position shown in the drawing but not when the cam arm is in the broken line position.

The slide plates 39, associated with the hoppers, are movable lengthwise of the machine together with the rake-shaped members 45 to accommodate different lengths of paper. The rake-shaped members, as shown in FIG. 1, have tapes 1% attached to their rear ends, the tapes passing over pulleys 1'92 and being attached to weights 1%. The tapes 191 serve to bridge the gap between the rake-shaped members 45 and the expanded metal sheets 44 in the case where the members 45 have been adjusted to accommodate sheets of paper which are shorter than the full length of the hopper.

Cams associated with the automatic paper feeding machine serve for controlling the apparatus, including the speed of rotation of the chains and thus the speed of the gripper bars and their associated release mechanisms, and for controlling the reciprocating suckers for feeding the sheets into the gripper bars. Such cams are adjustable so that variation of the speed of the apparatus is possible, but have been omitted from the drawings for the salts of clarity.

In the operation of the apparatus just described, the sheets of paper 5 are fed from a pile by the automatic paper feeding machine 6 which feeds the sheets upwardly from the pile in such a manner that they overlap one another, the overlap being conveniently about four fifths in this particular case. As the sheets are fed upvardly, the leading edge of each sheet is caught by the suckers 10 which reciprocate horizontally above the first chain wheel shaft 3. The suckers feed the leading edge of each sheet into a respective gripper bar 4 which is opened by a stationary cam (not shown) to receive the leading edge of the sheet, and which is then closed as soon as the leading edge of the sheet is within the gripper bar, so as to hold the sheet firmly. The gripper bar 4 then moves in the direction or" the arrow 12 drawing the sheet of paper over the sheet of expanded metal 7, and it is found that the sheet of paper runs in a taut condition.

The sheet of paper then passes beneath the first scanning unit 22 where it is scanned by reflected light, the scanning unit 22 serving to check that the gloss of the paper is correct, by comparing it with that of the sheet 27 which is also scanned under reflected light by the photoelectric cell unit 29. So long as the gloss of the sheet passing beneath the photoelectric cell unit 24 is acceptable, no signal is generated in the comparator unit 25. However, should the sheet 5 be unacceptable as regards its gloss, then a signal will be generated in the comparator unit 25, and will be fed to the memory storage unit 30 which will then ensure that the gripper bar holding the unacceptable sheet is opened above the hopper 18 to deposit the rejected sheet therein.

After passing beneath the scanning unit 22, the sheet passes beneath the scanning unit 32 where it is scanned by transmitted light to detect creases and variation in thickness of the paper. This is of particular importance where the paper is a coated paper since local agglomerations of the coating material may cause considerable damage to a printing machine in a subsequent printing operation. The photoelectric cell unit 34 of the second scanning unit 32 is also arranged to pass a signal to the memory storage unit 3% should the sheet passing beneath the photoelectric cell unit 34- be unacceptable.

The gripper bar of the sheet under consideration then enters the recess 14 of the drum 9, so that the sheet of paper will lie tangential to the drum. The diameter of the drum, the distance between the gripper bars, and the speed of the apparatus being such that after the drum has completed one revolution it will be ready to receive in its recess 14 a subsequent gripper bar 4.

The sleeve of the drum 9 over which the sheets pass as they are being scanned may be rubber, synthetic plastic material, such as polyvinyl chloride, or felt, and is of a colour which the photoelectric scanning unit 35 can distinguish from the paper. Thus, when checking white paper the sleeve is conveniently of a black or other dark colour, whereas when scanning black paper the sleeve is conveniently of a white or other light colour.

As the drum rotates, the sheet passes beneath the third scanning unit 35 where it is again scanned under reflected light. If a flaw occurs in the sheet, then the flaw will be registered by the scanning unit which will pass a signal to the memory storage unit 3!). Due to the fact that the sleeve 15 is of a colour which the scanning unit can distinguish from the paper (e.g. the sleeve is black when the paper is white) a hole in the sheet will have the same effect on the scanning unit as any of the previously mentioned flaws.

Assuming that the scanning unit 35 has detected a flaw in a sheet, then the scanning unit will pass a signal to the memory storage unit 34 which will operate the gripper release mechanism associated with the hopper 1%, so that the gripper bar will open as it nears the end of the hopper 18 and the rejected sheet will drop into the reject hopper 18, in a manner to be described more fully hereinafter.

Any fault detected by the scanning unit 35 is stored in the scanning unit which generates a signfl and passes it to the memory storage unit 30. As a subsequent gripper bar passes beneath the scanning unit 35 it clears the scanning unit so that it is ready to register faults in the subsequent sheet. The memory storage unit thus has to ensure release of a rejected sheet while a subsequent sheet is passing beneath the scanning unit. The memory storage unit is actually associated with the lay shaft of the apparatus, and after it has passed a signal to operate the gripper, release mechanism associated with the hopper 18 will be reset by the lay shaft which is in pitch with the apparatus and the gripper bars. The memory storage unit 34 is actuated in a similar manner by the other scanning units 22 and 32 and will be reset in a similar manner.

The gripper bar release mechanism associated with any hopper is arranged to open the gripper bar as it nears the end of the hopper, i.e. before it passes over the rakeshaped member 45. A signal generated by the memory storage unit operates the solenoid 9% which pulls the

toggle mechanisms

92, 93 against the action of the spring 96 into the full line position shown in FIG. 3, whereupon the roller 1% will engage against the cam arm 94 and depress the arm 99 to open the gripping arm 98 so that the latter occupies the broken line position shown in FIG. 3. As soon as the gripping bar 98 opens to release its sheet, the shaft 68 is reciprocated to turn the arms 69 downwardly so that the rubber rollers 70 engage the sheets and hold them against the metal roller 67. Suction, which is continuously applied to the suction rollers 66, retards the sheets. The rollers 67 and 66 are rotated and feed the rear edge of the sheet forwardly into the hopper, the

7 front edge moving forward under its own momentum. After the sheet has entered the hopper, the shaft 63 is again reciprocated to lift the arms 69 and their rollers 7% so as to allow passage of a subsequent gripper bar between the rollers 74 and 67.

As the lay shaft 49 rotates, it rotates the eccentrics 50 and 56A and causes the follower bars 51 and 51A to reciprocate the carriages 52 and 62 thereby moving the jogger bars 48 together or apart in a direction transverse to the length of the paper so as to assist in positioning each sheet of paper on the pile 71 in the hopper.

The light source 75 is arranged to reflect light off the leading edges of the sheets in the hopper into the photoelectric cell unit 7 6. When the hopper is empty, no light can be reflected into the photoelectric cell 76, so that it will remain inactivated. As the pile of sheets rises in the hopper, more and more light will be reflected off the edges of the sheets into the photoelectric cell 76 until such time as a point is reached when the cell will be operated. At this point, the cell will pass a signal to the switch 77 and operate the motor for rotating the chain wheels 42 to lower the base plate 43. As the base plate '43 is lowered, the amount of light reflected oif the edges of the paper will decrease and the photoelectric cell unit 7 6 will thus become inactivated again, whereby the motors will cease.

The apparatus of the present invention is designed to run at high speeds, for example at speeds such as to scan 10,090 sheets of fine paper of about 70" in length per hour, and it is for this reason that two hoppers for acceptable sheets of paper are provided. The apparatus may be arranged to feed the acceptable sheets alternately into the hoppers 1? and so as to allow the sheets to settle in the hoppers before additional sheets are placed therein, or may be arranged to feed a number of sheets first to one hopper and then to the other, the air brush arrangement coming into operation after the required number of sheets have been fed to the appropriate hopper. In this connection, it is preferred to feed about 10 sheets to each hopper in succession, with a possible maximum of 100 sheets for fine paper. The sides of the hoppers may have hollow bars (not shown) through which air can be sucked out from between the sheets of paper if so desired.

The sensing unit comprising the light source 83 and photoelectric cell unit 84 is arranged to actuate the gripper release mechanisms of the hoppers 19 and Ztlyin such a manner that, for example, ten sheets will be fed into the hopper 19, and then ten sheets will be fed into the hopper 2th whereupon ten sheets will again be fed into the hopper 19; The reason for this is to allow the ten sheets fed into any one hopper to settle down before feeding in a further ten sheets. The photoelectric cell unit 84- is also arranged to operate through the memory storage unit 85 the air brush arrangement. The operation is such that ten sheets are fed into the hopper l9, and then ten sheets are fed into the hopper 26. After five of these ten sheets have been fed into the hopper 29, the air brush arrangement associated with the hopper 19 is operated to blow air downwardly into the first hopper, the air acting as a brush to smooth the pile of sheets in the hopper and to remove trapped air from between the sheets. After the second of the five sheets have been deposited in the hopper 2%, the air brush arrangement associated with the hopper 19 is stopped and ten further sheets are deposited in the hopper 19. After the first five of these sheets have been deposited in the hopper "19, the air brush arrangement associated with the hopper 2% is now brought into operation. a

As indicated above, the memory storage unit 85 may also be arranged to actuate a tab inserting device for inserting a tab into a pile of sheets in the hopper after a desired number, e.g. 500 sheets have been deposited in the hopper.

When the apparatus is in operation, air is blown through the pi e 46 in the direction of the arrow 47, so

that as a gripper bar with its associated sheet passes over the rear edge of one hopper (e.g. the hopper 19, in the case where the gripper bar is intended to deposit its sheet in the hopper 2&5), the sheet of paper will be blown away from the edge of the rake-shaped member so as to prevent damage of the sheet should it catch against the rake-shaped member 45.

If for any reason the apparatus should be stopped, there is the possibility that it will be stopped with a sheet or paper, in a position where it has been released from the gripper bar but is still held between the rollers and 67. In this case, the'leading edge of the sheet of paper may not be abutting against the rake-shaped member 45, so that when the apparatus is started up again rotation of the rollers at will feed the trailing edge of the paper forward but may have no effect on the leading edge, thus casuing the paper to crease. To prevent this, air is supplied to the pipes 86 when the apparatus is started up or is running at very slow speed, and this air serves to blow the sheet out so that the leading edge thereof will be carried to abut against the rake-shaped member 45, thus preventing such creasing.

It may also be desirable to ensure that the sheets of paper make good contact with the sleeve 15 on the drum 9 as they pass therearound. To assist in this, a horizontal pipe 1% is provided above the axis of the drum and is arranged to discharge air downwardly so as to ensure that the sheets make contact with the drum. It may also be desirable to assist in holding the sheets against the drum by providing another horizontal pipe 96 arranged to blow air against the lower part of the drum.

Referring now to FIG. 4 of the drawings, there is shown a modification of the apparatus shown in FIG. 1. In this modification, a'further drum H99 is associated with the lower strand of the apparatus, after the drum 9 in the direction of travel of the gripper bars. The drum m9 is identical with the drum 9. Mounted above the drum 199 is a further scanning unit 11% which is identical with the scanning unit 35. The scanning unit being also connected to the memory storage unit 39. With this arrangement, it is possible to scan both sides of a sheet of paper or other material, and in all other respects the apparatus may be identical with that shown in FIG. 1. If desired, the sheets after leaving the drum 9 may be scanned by transmitted light by another scanning unit comprising a light source and a photoelectric cell unit 116 also connected to the memory storage unit 3% FIG. 4 also shows an alternative arrangement for ensuring that the sheets make good contact with the drum 5", this arrangement comprising three

shafts carrying pulleys

111, 112 and 113 located to one side of and below the drum 9 and a tape 114 running around the pulleys and in contact with the drum. Three such tapes 114 and associated pulleys are provided and spaced apart from one another so that the tapes contact the edges and centre of a sheet on the drum.

It will be appreciated that many modifications of the apparatus are possible, and instead of the sheet of expanded metal 7, it is possible to form the upper strand of the apparatus by a series of divergent, driven tapes running over pulleys. It is possible to make the gripper bars hollow and to associate them with a ring manifold supplied with compressed air, and to arrange that the gripper bars themselves replace the air brush arrangement for smoothing the piles of sheets in the hoppers. Alternatively, a roller or brush or apertured hollow bar similar to the bar 82 may be reciprocated across the pile of sheets in the hopper to smooth the sheets. A further modification of the air brush arrangement comprises a number, e.g. six, tubular devices mounted longitudinally above each hopper. Each tubular device comprises a stationary bar with a keyway milled in its lower edge, to which keyway compressed air is applied in accordance with signals from the memory storage unit 85. A hollow tube surrounds the bar and has a series of apertures heiically arranged therein and having a pitch equal to the length of the tube. The tube is rotated around the bar so that each aperture is supplied with compressed trom the keyway whereby a series of jets of air are blown on to the sheets in the hopper.

Furthermore, it may be possible to dispense with the suction rollers 66 and to form the leading edge of each of the hoppers by a member containing a slot to which suction is applied, so that as the gripper passes over the hopper the sheet of paper is retarded by the suction applied to the slot, thereby keeping the paper taut and smooth during its passage over the hopper.

Each of the photoelectric scanning units employed in the apparatus may be arranged to detect a flaw and register it as a blip on an oscilloscope screen in conjunction with which an adjustable hairline is provided. The hairline may be adjusted so that small blips will not feed a signal to the memory storage unit 38 and will thus have no effect on the gripper release mechanism associated with the reject hopper 3'8, so that, if desired, only sheets with large flaws of a predetermined size will cause operation of the gripper release mechanism for the reject hopper so that only such sheets will be rejected.

If there are a number of small imperfections each of which is of insuflicient size to warrant rejection of a sheet, but which cumulatively make the sheet rejectable, it is possible to provide an electronic counter which will count these small imperfections and will reject a sheet when any predetermined count is exceeded. The electronic counter may be associated with all the scanning units so that a cumulative count of different flaws may be obtained, or an electronic counter may be associated with each scanning unit so that a cumulative count of the particular flaws which the scanning unit is intended to detect may be obtained.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. In apparatus for checking sheets of material, such as paper, and of the type including gripper means for gripping the sheets and moving them along a path, and scanning means along the path operable to detect variations in surface finish, variations in thickness and other flaws and defects, and including at least one reject station and at least one accept station along the path, and means operable by the scanning means to divert defective sheets to a reject station and acceptable sheets to an accept station: the improvement comprising each of said stations including a base member; a member defining the rear of the stations; side members; means operable to reciprocate said side members in a direction substantially perpendicular to their length; and means at the leading edge of each station operable, when a sheet has been diverted from the gripper means to the station, to engage and retard the trailing edge of such sheet.

2. In apparatus for checking sheets of material, the improvement claimed in claim 1, including at least two accept stations; gripper release mechanism at each station; means operable to operate the gripper release mechanism at one accept station to divert sheets thereto until a predetermined number of sheets has been diverted thereto;

and means operable, responsive to the diversion of said predetermined number of sheets to said one station, to activate the gripper release mechanism at another accept station during a period sufiicient to divert to said other accept station said same predetermined number of sheets.

3. in apparatus for checking sheets of material, the improvement defined in claim 1, in which the means for retarding the trailing edge of a sheet comprises reciprocably mounted rollers arranged to be moved into engagement with the trailing edge of a sheet; and rotatably mounted suction rollers arranged to maintain the trailing edge of a sheet under suction.

4. in apparatus for checking sheets of material, the improvement claimed in claim 1, wherein said means for retarding the trailing edge of a sheet of material comprises a member mounted at the leading edge of the station and formed with a slot extending therealong; and means for applying suction to said slot.

5. In apparatus for checking sheets of material, the in provement claimed in claim 1, including a hollow apertured bar operatively associated with the member defining the rear edge of the station; a source of compressed air connected to said bar; the apertures in said bar being oriented to direct air in a direction to inhibit a sheet of material engaging said member defining the rear of the station as such sheet passes over said member definin the rear of the station.

6. In apparatus for checking sheets of material, the improvement as claimed in claim 1, including means operable to lower the base member of each station to maintain the upper sheets thereon at substantially a constant level; and a photoelectric cell unit included in said lowering means and operable by light reflected from the edges of the sheets at the station to actuate the said lowering means.

7. In apparatus for checking sheets of material, the improvement claimed in claim 1, including an apertured pipe extending across the leading edge of each station; and means operative, when the apparatus is running at speeds substantially below normal, to connect said apertured pipe to a source of compressed air to direct air against the sheet to carry the sheet so that the leading edge of the latter will abut against the rear member of the station to prevent creasing of the sheet.

References Cited in the file of this patent UNITED STATES PATENTS