US2950640A

US2950640A - Mechanism and method for classifying and assorting metal sheets

Info

Publication number: US2950640A
Application number: US258700A
Authority: US
Inventors: James B Camp
Original assignee: United States Steel Corp
Current assignee: United States Steel Corp
Priority date: 1951-11-28
Filing date: 1951-11-28
Publication date: 1960-08-30
Anticipated expiration: 1977-08-30
Also published as: LU33065A1; FR1112167A

Description

B. CAMP 2,950,640 on FOR CLASSIFYING AND a METAL SHEETS J. MECHANISM AND METH ASSORTIN Aug. 30, 1960 6 Sheets-Sheet 1 Filed Nov. 28, 1951 J. B. CAMP 2,950,640 MECHANISM MET FOR CLASSIFYING AND SORTI METAL SHEETS HOD NG Aug. 30, 1960 6 Sheets-Sheet 2 Filed Nov. 28, 1951 FIE-l4- Ioweniar: J4ME 5. (4M2 Aug. 30, 1960 J. B. CAMP MECHANISM AND METHOD FOR CLASSIF'YING AND ASSORTING METAL SHEETS 6 Sheets-Sheet 3 Filed Nov. 28, 1951 Aug, 30, 1-960 J. B. CAMP 2,950,640

MECHANISM AND METHOD FOR CLASSIFYING AND ASSORTING METAL SHEETS Filed Nov. 28, 1951 6 Sheets-Sheet 4 Aug, 30, 1960 J. B. CAMP MECHANISM AND METHOD FOR CLASSIFYING AND ASSORTING METAL SHEETS 6 Sheets-Sheet 5 Filed Nov. 28, 1951 J. B. CAMP MECHANISM AND METHOD FOR CLASSIFYING AND Aug. 3@, 1960 ASSORTING METAL SHEETS 6 Sheets-Sheet 6 Filed Nov. 28, 1951 E um & wm p w m v n 6 6 lhl PQQ. M M N C V q m A @L w, HF J u n L J QM g. m 3% fi a n w n fl EN 3L0 m n i Q mm QWN .v $5M. T r 5: L n w n wal WWW m @ww. IL mw m a \wm (13 lllll I]: WQRRPQ mmfigxgm QQW R\ 55% wmthmkv u MECHANISM AND lVIETHOD FOR CLASSIFYING AND ASSORTING lVIETAL SHEETS James B. Camp, Fair-field, Ala, assignor to United States Steel Corporation, a corporation of New Jersey Filed Nov. 28, 1951, Ser. No. 258,700

20 Claims. (CI. 83-29) This invention relates to an improved mechanism and method for classifying and assorting metal sheets in high speed shear lines.

Modern practice in shearing metal strip into sheets is to feed the strip from an uncoiler through a roller leveler and a rotary flying shear, which cuts the strip to sheets of appropriate length, and to a conveyor which carries the sheets to pilers. Such shear lines are equipped with mechanism which automatically classifies and assorts the sheets. This mechanism comprises essentially a means for detecting imperfections in the strip ahead of the shear, a deflector at the exit end of the conveyor, and a time delay means for operating the deflector at the proper interval after an imperfection has been detected. Normally the deflector allows prime sheets to pass to a prime sheet piler, but, when operated by the detecting and time delay means, it diverts imperfect sheets to a reject sheet piler. The detecting means commonly includes a light sensitive device for detecting pin holes and a gauge for detecting off-gauge thickness. Usually there is a marking device which embosses the strip opposite the pin holes to aid in subsequent identification of defective sheets. Such shear lines are used, for example, for shearing and assorting electrolytically tinned steel strip or black plate steel strip preliminary to hot dip tinning.

Previous classifying and assorting mechanisms with which I am familiar relay largely on mechanical devices, commonly embodying pin wheel timers, several relays and switches, and mechanical deflectors. They respond rather slowly and also require frequent maintenance and adjustment. In high speed lines, each time the deflector operates, it diverts to the reject piler at least three sheets and often more. Consequently several prime sheets go to the reject pile whenever the deflector operates to divert one or more imperfect sheets, and the sheets in the reject pile subsequently must be hand-inspected to salvage primes. Cobbles in the line are frequent due to operation of the mechanical deflector while a sheet is passing it. Timing of the marker is not sufliciently precise to insure always marking the right sheet, particularly for imperfections near a shear cut. The deflector must operate ahead of the leading edge of the imperfect sheet, yet the reference point from which timing begins is either the defect itself or else the cutting of the trailing edge of a defective sheet by the shear, an arrangement which can induce a further inaccuracy.

An object of the present invention is to provide an improved classifying and assorting mechanism which responds quickly enough to divert single sheets from a high speed shear line and thus diverts only sheets actually having imperfections unaccompanied by prime sheets.

A further object of the invention is to provide an improved classifying and asserting mechanism which largely eliminates mechanically moving parts, but instead embodies a magnetic memory device, a magnetic roll deflector, and an electronic circuit for recording imperfecnited States Patent tions in the memory device and subsequently operating the deflector therefiom.

A further object of the invention is to provide an improved classifying and asserting mechanism and method which transfer the reference point for timing deflector operation to the leading edge of each imperfect sheet.

A further object of the invention is to provide an improved classifying and assorting mechanism Which times operation of the marker very precisely from the same memory device that times operation of the deflector and thereby insures that the mark is applied opposite the imperfection.

A further object of the invention is to provide an improved classifying and assorting mechanism and method which insure with complete certainty that every sheet containing an imperfection and only those sheets are diverted to the reject pile.

In accomplishing these and other objects of the invention, I have provide improved details of structure, a preferred form of which is shown in the accompanying drawings, in which:

Figure 1 is a schematic side elevational view of a shear line which is equipped with a classifying and assorting mechanism embodying features of the present invention;

Figure 2 is a vertical sectional view of the magnetic roll embodied in the preferred deflector;

Figure 3 is a sectional view taken substantially on line I1l-III of Figure 2;

Figure 4 is a vertical sectional view of the preferred memory device;

Figures 5 and 6 are vertical sectional views on a larger scaleof recording heads or pickups embodied in the memory device; and

Figures 7, 7a, 7b and together are a wiring diagram of the electronic control.

Figure 1 shows schematically a shear line which comprises a roller leveler 1, a rotary flying shear 2, a conveyor 3, a prime sheet piler 4 and a reject sheet piler 5. These parts can be of any standard or desired construction and therefore are not shown in detail. Strip S enters from the left from an uncoiler, not shown, and passes through the roller leveler and the shear. The latter cuts it into sheets :8 which are deposited on the conveyor and travel to the pilers. A deflector is interposed between the exit end of the conveyor and the pilers. Normally this deflector allows prime sheets to pass undisturbed to the prime piler, but it can be operated by the detecting means and time delay means hereinafter described to divert imperfect sheets to the reject piler.

The preferred deflector comprises a fixed blade 7 and a normally magnetized roll 8 driven at about the same circumferential speed as the linear speed of the conveyor 3. The blade is spaced from the exit end of the conveyor and directed theretoward. The roll is situated above the space between the conveyor 3 and the blade 7. As long as the roll is magnetized, it carries sheets discharging from the conveyor across the blade to the prime piler 4. When demagnetized, the roll allows sheets from the conveyor to pass underneath the blade to the reject piler 5.

Figures 2 and 3 show details of roll 8 and its mounting. The roll includes a body, a fixed shaft 9 on which the body is rotatably mounted on antifriction bearings 10, and a drive pulley 11 fixed to one end of the body. Shaft 9 is supported on brackets 12 fixed to the conveyor frame. The roll body is hollow and of a nonmagnetic metal, such as brass, stainless steel, or the nickel alloy sold under the trademark Inconel. Within the body the shaft carries electromagnets .13 which have downwardly directed poles. The roll is in effect magnetized whenever the magnets are energized and attracts sheets to its outer surface. 7

A deflector thus constructed is especially quick acting. The electromagnets 13 can be' deenergized and the roll demagnetized during the very brief interval after the trailing edge of a rapidly moving sheet has passed the roll and before the leading edge of the next sheet arrives. The electromagnets can be energized again and the roll magnetized during the next such interval. This quick action enables the deflector to divert only a single imperfect sheetto the reject piler, or as many in succession as are imperfect, without diverting any primes. Nevertheless the remainder of the classifying and assorting mechanism could be used with other deflectors, even though they might not act quickly enough to accomplish the object of diverting only imperfect sheets unaccompanied by primes. a

Thedetecting means includes a light sensitive pin hole detector 14 and a thickness gauge 15 both situated ahead of the roller leveler. Between the detector and gauge there is preferably a marker 16 for marking the margin of the strip opposite each pin hole to facilitate identification. The pin hole detector, marker and thickness gauge can be any standard or desired commercial devices suitable'for this purpose and therefore are not shown 1101 described in detail. Nevertheless, as a detector I .prefer to employ a General Electric Super Sensitive Pin Hole Detector, since it furnishes a fine straight line of high intensity light that can'detect extremely fine pin holes. The detecting means is connected to the deflector through time delay means which comprises essentially an electronic control, the circuits of which are shown only in block in Figure 1 but are hereinafter fully described, and a memory device. a

As shown in Figures '4, and 6, the memory device includes a nonmagnetic rotor 19, which preferably is a machined aluminum casting and carries around its circumference two

recording tracks

20 and 21 formed of a large number of turns of magnetic recording wire. The rotor is chain driven from the roller leveler 1 so that both recording tracks travel at a-rate directly proportional to the rate of striptravelr Track 20 has a pinhole recording'head 22, and off-gauge recording head 23, a marker pickup 24, a circuit cocking pickup'25 and a permanent magnet eraser 26 (Figure 1). Track 21 has a recording head 27, a pickup 28 and a permanent magnet eraser 29. These recording heads contain magnetizing coils which, when energized, magnet-ize'the adjacent portion of the

recording track

20 or 21. Subsequent rotationofthe recording track carries the'magnetized spot opposite one of the pickups, in which it induces an electric current. Any magnetized spots are removed as they pass the eraser 26 or 29. The memory device is shown somewhat schematically in the present application, but is shown in detail and claimed in my joint application with ColemanH. wats'on, Serial No. 258,699, filed November 28, l951,-now Patent No. 2,735,987, entitled Magnetic Memory Device.

The pin hole detector 14 is connected to the pin hole recording head-22 via a pulse shaping circuit 30 and an amplifier circuit31 of the electronic control. Simi larly the thickness gauge is connected to the off-gauge recording head 23 via an amplifier circuit 32. Whenever the pin hole detector ,or the thickness gaugedetects an imperfection in the strip, it energizes the magnetizing coil of the

corresponding recording head

22 or 23 through the electronic control and thus magnetizes a spot on the recording track 20. g The spacing between the recording head 22 and the marker pickup 24 is proportional to that between the pin hole detector 14 and the marker 16. The marker pickup .is connected to the marker via an amplifier circuit 33 of the electronic control; 'Whenever the pin hole recording head 22 (but not head 23) magnetizes aspot on the recording track 20, this spot subsequently energizes the marker pickup 24 and actuates the marker 16 as the pin hole passes the marker. The spacing between the recording head 22 and the circuit cocking pickup 25 is proportional to that between the pin hole detector and the rotary elements of the shear 2. Like, wise the spacing between the recording head 23 and the pickup 25 is proportional .tothat between the thickness gauge and the rotary elements of the shear. Consequently any spot magnetized on the recording track by either

recording head

22 or 23 reaches the pickup simultaneously with the arrival of the imperfection in the strip at the shear. The pickup 25 is connected to a first storage circuit 34 in the electronic control via an amplifier circuit 35. Energization of the pickup 25 cocks this storage circuit, so that now it is recorded in the control that the next sheet cut from the strip will contain an imperfection and should go to the reject piler.

A normally closed shear switch 36 is connected to the storage circuit 34 via an amplifier circuit 37. Once each revolution of the shear 2, as the shear cuts, this switch momentarily opens. If the storage circuit is cocked, opening of switch 36 triggers it; otherwise its opening has no effect. Triggering the storage circuit resets this circuit, cocks a second storage circuit 38 in the electronic control, and thus records that the sheet last cut contains an imperfection.

At this stage the reference point is of course the trailing edge of the sheet last cut. For greater accuracy the mechanism of the present invention transfers this reference point to the leading edge. The transferring means includes a photoelectric cell 39 below conveyor 3 and beyond shear 2 and a light source 40 above the conveyor in line with said cell. The spacing between the cell and the shear must exceed one sheet length, but must not be suflicient for two full sheets to be therebetween; that is, after the shear cuts a sheet from the strip, the next leading edge which passes the cell must be the leading edge of that sheet. The cell 39 is connected to a flipflop circuit 41, which in turn is connected to the second storage circuit 38 and to a third storage circuit 42 all in the electronic control. As fully explained hereinafter, the flip-flop 41 has two alternative current paths, one of which conducts current when cell 39 is exposed to the flight source 40, but not when it is darkened by a sheet between the cell and the light source, and the other of which does the reverse. With circuit 38 cocked, when the leading edge of a sheet passes between the light source and the cell and circuit 41 thus flips, the latter triggers circuit 38. Each such triggering changes the current path through a third storage circuit 42.

The storage circuit 42 is connected to an oscillator circuit 43, which in turn is connected to the recording 7 head 27 of the second recording track 21 of the memory device. I Whenever the storage circuit 38 is triggered (i.e., if circuit 38 was cocked when the leading edge of a sheet darkened the photoelectric cell 39), the circuit 42 keys the oscillator 43, which thereupon sends current to the recording head 27. The storage circuit 38 immediately resets, but the storage circuit 42 continues to key the oscillator as long as the photoelectric cell 39 is darkened -(i.e., until the trailing edge of the imperfect sheet passes this cell). Consequently the recording head 27 remains energized until the trailing edge of the imperfect sheet passes the photoelectric cell and again exposes this cell to the light source 40. Thus the recording head 27 magnetizes an arc of the recording track 21 proportional to the length of the imperfect sheet. Since circuit 38 resets immediately, it can be cocked again by detection of a second imperfect sheet anywhere following the first. even next to it.

The spacing between the recording head 27 and the pickup 28 is proportional to that between the photoelectriccell 39 and thedeflector roll 8. The electromagnets 13 of the latter normally. are energized via a grid controlled rectifier 44. The pickup/28 E connected to the grids of the rectifier 44 via an amplifier 45. When a magnetized lents are possible.

part of the track 21 energizes the pickup 28, the rectifier 44- ceases to pass current to the electromagnets. Consequently they are deenergized, and the sheet is diverted to the reject piler 5. The timing of course is accurately adjusted so that the electromagnets are deenergized an instant before the arrival of the imperfect sheet and again energized an instant after it clears roll 8.

Electronic control Figures 7, 7a, 7b and 7c together show a Wiring diagram of an exemplary arrangement of circuits in the electronic control, but it is obvious that many equiva- To facilitate describing these circuits the ensuing description indicates possible actual numerical values of some of the voltages and resistances, but it is to be understood these values are only exemplary and could be varied widely Without departing from the invention.

Referring first to Figure 7, the circuit includes a grounded line 50 of zero potential, a line 51 of relatively high positive D.C. potential, and a line 52 of relatively high negative D.C. potential energized by any suitable outside power source not shown. For example, the line 51 can be at 265 volts positive and the line 52 at 300 volts negative. A conductor 53 extends between

lines

51 and 50 and contains five resistances 54 to 58, which can be for example of 10,000 ohms, 5,000 ohms, 5,000 ohms, 300 ohms and 150 ohms respectively. Four conductors 59 to 62 are connected to conductor 53 between the various resistances and thus have successively diminishing positive potentials, which can be for example 132 volts, 68 volts, 6 volts and 2 volts respectively. Similarly a conductor 63 extends between

lines

52 and 50 and contains four resistances 64- to 67, which can be for example of 15,000 ohms, 12,500 ohms, 1500 ohms and 1500 ohms respectively. Three

conductors

68, 69 and '70 are connected to conductor 63 between the various resistances and thus have successively diminishing negative potentials, which can be for example 108 volts, 20 volts and volts respectively.

The pulse shaping circuit 30 of the control includes a dual Triode vacuum tube 71 (for example that designated in the trade as 6SN7) which receives impulses of any shape from the pin hole detector 1 and transmits a sharply peaked pulse, always of the same magnitude and shape, to be recorded on the track of the memory device. A conductor 72 containing a 220,000 ohm resistance 73 connects the left plate of this tube to line 51 (potential 265 volts positive) and a conductor 74 containing a 22,000 ohms resistance 75 connects the right plate also to line 51. A conductor 76 containing a resistance 77 connects both cathodes of this tube to the grounded line 50. A conductor 78, containing a condenser 79 and a 500,000 ohm resistance 80 in parallel, connects the right grid of this tube with line 51 via the conductor 72 and resistance 73. A conductor 81 con taining a one megohm resistance 82 connects the right grid to the line 52 (potential 300 volts negative) via the conductor 78. A conductor 83 containing a condenser 84 and a 100,000 ohm resistance 85 in series connects the pin hole detector 14 with conductor 70 (potential 10 volts negative). A conductor 510,000 ohm resistance 87 connects an intermediate point on resistance 85 with the left grid of the tube. Normally the right grid of tube 71 is positive with respect to the cathode, since it receives a positive potential of 15 /2 volts from line 51 via conductors 72 and 78, which potential overcomes the smaller negative potential from line 52 received through the megohm resistance 82. Normally the left grid of tube 71 is negative with respect to the cathode, since it reecives a negative potential from conductor 70 (potential 10 volts negative) via

conductors

83 and 86. Consequently current normally flows through the right side of this tube, but not through the left side.

Since resistance 75 is relatively small, this current is relav 86 containing a.

tively large and produces a relatively large voltage drop across resistance 77.

When a pin hole in the strip passes the pin hole detector 14, the latter transmits both a positive and a negative pulse through the condenser 84, the magntiude and shape of which vary with the size of pin hole. The negative pulse has no effect, but the positive pulse momentarily overcomes the negative charge on the left grid of tube 71 and thus momentarily allows current to flow through the left side of the tube. Since resistance 73 is much higher than resistance 75, the current through the left side is is much smaller than the normal current through the right side, but it causes a voltage drop across resistance 73 and overcomes the positive charge on the right grid, which thereupon receives a negative charge from line 52 via conductor 81. The smaller current through the left side of tube 71 produces only a negligible voltage drop across resistance 77, whereby a stoppage of current through the right side of this tube can be regarded as eliminating the voltage drop across this resistance. A critical point occurs when the left grid reaches a potential which switches conduction through the tube almost instantaneously from the right to the left side. This critical point and resultant switch occur because elimination of the voltage drop across the resistance 77 is equivalent to adding this voltage change to the pulse from detector 14 and in effect makes the left grid immediately more positive. A conductor 88 is connected between conductor 74- and conductor 69 and contains a condenser 39 and a resistance 90 in series. A sudden stoppage of current through the right side of the tube produces a sudden current surge through conductor 88 and condenser 89 and applies positive voltage to the grids of a tube 91 of the amplifier circuit 31, next described.

The tube 91 of amplifier circuit 31 is another dual Triode (for example that designated in the trade as 6N7) and it energizes the magnetizing coil of the pin hole recording head 22 in response to pulses in conductor 88. A conductor 92 connects both plates of this tube to one end of the primary coil of a transformer 93, the other end of which is connected to line 51. A conductor 95 connects both cathodes of tube 91 to the grounded line 50. A conductor 96 containing a damping rectifier 97 connects conductor 92 and line 51. Said rectifier prevents an oscillating potential from appearing from the plate of tube 91. Conductor 88 is connected to both grids of the tube via a resistance 99.

Normally both grids of tube 91 are negative with respect to the cathodes, since they receive a negative potential from conductor 69 (potential 20 volts negative) via conductor 88. Consequently no current flows through either side of this tube. A current surge through conductor 88 produces both a positive and a negative pulse. The negative pulse has no effect, but the positive pulse momentarily applies a positive charge to both grids of tube 91. Now for an instant an amplified current flows through both sides of this tube and energizes the primary coil of transformer 93. The current path is from the grounded line 50 via conductor 95, the cathodes and plates of the tube, conductor 92, and the primary coil of the transformer 93, to line 51. Conductors 100 connect the ends of the secondary transformer coil to the magnetizing coil of the recording head 22. Thus a momentary current is induced in the secondary coil of the transformer and it energizes the magnetizing coil and magnetizes a spot on the recording track 20. Energization of the magnetizing coil is only momentary, since the grids of tube 91 quickly resume their negative charge after the current surge through conductor 88 dissipates.

The coil of the marker pickup 24 is grounded at one end and connected at the other end via a conductor 101 to the primary coil of a transformer 102 of the amplifier circuit 33. This primary coil is connected to the grounded line 50 via a conductor 103. The amplifier circuit 33 includes a combined amplifier and rectifier tube 104 (for example that designated in the trade as ,6AQ7 The left or" amplifier side of tube 104 has a plate con.- nected to line 51 (potential 265 voltspositive) via a conductor. 105 containing

resistances

106 and 107 in series. The left side of tube 104 also has a cathode which is connected to the grounded line 50 Via conductor 1113 and a conductor containing a condenser 109 and a resistance 110 in. parallel. One end of the secondary coil of transformer 102 is connected to a grid in the left side of tube 104 via a conductor 111 and the other end. of the secondary cofl is connected to the grounded line 50 via

conductors

103 and 108. A resistance 112 is connected across the secondary coil. A

conductor 113 containing a condenser 114 is connected between conductor 105 intermediate its resistances 166 and 107 and grounded conductors 103and 108.

When a magnetized spot in the recording track induces a current in the marker pickup 24 and hence in the primary coil of transformer 102', the resulting current surge in the secondary coil of the transformer applies first a positive and then a negative charge to the left grid of tube 104. The positive charge causes an amplified current'surge to flow through the left side of the tube. The current path is from grounded line 50 via

conductors

103 and 108, the parallel condenser 109 and resistance 110, the left. cathode and plate of tube 104, and conductor 105 to line 51 (potential 265 volts P051: tive).

A conductor 115 containing a resistance 116 and a condenser 1 7 in series is connected between conductors 105 and 61 (potential 6 volts positive). The right or rectifier side of tube 104 has a cathode connected to conductor 115 and a pair of plates connected to a conductor 118. The amplifier circuit 33 also includes a dual Triode tube 119, which can be of the same type .as tube 71 (6SN7).. A conductor 120 containing a resistance 121 connects the left plate with line 51 (potential 265 volts positive). A conductor 122 containing a marker relay coil 123 connects the right plate also with line 51. A conductor 124 connects both cathodes of tube 119 with the grounded line 50. The aforementioned conductor 118 is connected between conductor 68 (potential 108 volts negative) and conductor 122' and contains a 330,000 ohm resistance 125. and a 500,000 ohm resistance 126 in series onopposite sides of its cormection to the right plates of tube 104. Conductor 118 also is connected to the left grid of tube 119. A conductor 127 containing a condenser .128, a 2 megohm variable resistance 129 and a 100,000 ohm resistance 130. all in series is connected to conductor 120 and to a conductor 131. The latter is connected to conductor 68 (potential 108 volts negative) via a 50,000 ohm resistance 132 and to the grounded line 50 via another 50,000 ohm resistance 133 and in the present example has a potential of 54 volts negative. Conductor 127 is connected to the right grid of tube 119 via a resistance 13 4. Normally the positive and negative chargeson the left grid of tube 119 balance each otherso that the grid is at zero potential. Normally the right grid has a 52 volt negative charge received via conductor 131 (potential 54 volts negative) and conductor 1127. Consequently current normally flows .throughthe left sideof the tube but not 7 through the right sicle.

The'amplified positive and negative pulses from the left side of tube'104 send a negative and a positive pulse through conductor 115 via its condenser 117. The rectifierside of tube 104 passes the negative pulse, which thus applies a negative charge to the left grid of tube 119. The resistance 116 dissipates the positive pulse. The negative pulse thusmomentarily stops the flow of current through the left side of tube 119. This current stoppageproduces both a positive. and a negative pulse through conductor 127 because ofthe actionof condenser 12S. The'positive pulse'prcduces a momentary; positive charge on the right grid of tube 119 and a current flow through the right side of the tube. The current path is from the grounded line 50 via conductor 124, the right cathode and plate, conductor 1 2 2, and relay coil. 123 to line 51. A diode tube 135 is connected to conductor 127 to dissipate the positive pulse from condenser 128.

Energization of coil 123 operates the marker 16 to mark the strip opposite the pin hole. The relay 123 preferably is the only mechanical relay in the entire circuit Its operation is accurately timed with movement of the strip, since it is controlled by the recording track 20 of the memory device driven at a speeed proportionalto the strip speed. a

. The amplifier circuit 32, through which the thickness gauge 15 energizes the magnetizing coil of its recording head 23 in response to elf-gauge thickness in the strip, includes essentially a transformer 136 and an oscillator tube 137 (for example that known in the trade as 6F6). The primary coil of transformer 136v is connected to an AC. line 138 and to the plate and one grid of tube 137 via a conductor 139. A conductor 140 connects the cathode of tube 137 with the grounded line 50. A conductor 141 containing a resistance 142 connects the other grid oftube 137 with conductor 131 (potential 54 volts negative) and thus normally applies a negative charge which prevents current flow. The gaugelS includes a normally open switch 143 which is in a conductor 144 that connects

conductors

140 and 141. Whenever the strip is off-gauge, switch 143 closes and thus grounds conductor 141 and removes the negative charge from the grid. Thereupon current flows through tube 137 and the primary coil of transformer 136. A resistance 145 and a condenser 146 in series are connected across switch 143. The secondary coil of transformer 136 is connected to the magnetizing. coil of the ofi-gauge recording head 23 via conductors 147 and 148, so that current flowing through the primary coil induces a current in the secondary coil which energizes the magnetizing coil and Inagnetizes a spot on the recording track 20.

When rotation of the recording track 20 moves a magnetized spot thereon (originating from either ,of the recording heads 22 or 23) alongside pickup 25, the magnetized spot induces a current in the pickup and cocks the first storage circuit 34 of the electronic control. Referring next to Figure 7a; the coil of this pickup is grounded at one end and connected at its other end via a conductor 149 to the primary coil of a transformer 150 of the amplifier circuit 35. A conductor 151connects the other end of this primary coil to the grounded line 50. The secondary coil of transformer 150 is connected to an amplifier tube 152 (such as that known in the trade as a 65]7) of the amplifier circuit 35. This latter circuit is well known and operates in the conventional Way; consequently it is not explained in detail, although Figure 7a contains a complete showing. The amplifier tube 152 transmits an amplified positive. and negative pulse through a conductor 153 which contains a condenser 154 and a resistance 155 in series and is connected to conductor 70 (potential 10 volts negative).

The amplifier circuit 35 next includes a combined amplifier and rectifier tube 156 of the same type as tube 104 of the amplifying circuit 33 already described. Normally its grid at the left has a negative charge, but whenever a positive pulse passes throughcond-uctor 153, the grid momentarily becomes positively charged. Tube 156 thereupon acts in the same fashion as already explained for tube 1134 and transmits a, negative pulse through a conductor 157, which is connected to its right plates and to conductor 63 (potential 108 volts negative). The operation of the tube and its circuit is not repeated in detail, since it is the same as for tube 104, although Figure 7a contains a complete showing. M

The first st rage circuit 34 includes a dual Triode. tube 170, preferably similar to tubes 71 and 119. A conductor 171 containing a 39,000 ohm resistance 172 connects the left plate to line 51 (potential 265 volts positive). A conductor 173 containing a 39,000 ohm resistance ii-l connects the right plate also to line 51. A conductor 175 connects both cathodes to the grounded line 50. A conductor 179 containing a condenser 180 and a resistance 181 in series (Figure 7b) connects conductor 171 with conductor 61 (potential 6 volts positive). A conductor 132 containing a 200,000 ohm resistance 183 and a condenser 184 in parallel connects the left grid with conductor 173. A conductor 185 containing a 220,000 ohm resistance 3.86 connects the right grid with conductor 68 (potential 108 volts negative). A conductor 137 containing a 200,000 ohm resistance 188 and a condenser 189 in parallel connects the right grid with conductor 171. A conductor 190 connects the left grid with conductor 157.

Normally the left grid of tube 170 is positive with respect to the cathode, since it receives a positive charge from line 51 via

conductors

173 and 182. Normally the right grid is negative since it receives a negative charge via conductors 68 and 1'35. Consequently current flows through the left side of the tube, but not the right side. However, when a rectified negative pulse appears in conductor 157, as already explained, it reaches the left grid via conductor 19%, overcomes the positive charge and charges this grid negative and thus stops flow of current through the left side of the tube. Now current flowing in conductor 171 can go only through

conductors

187 and 135, which are connected to the right grid. This current overcomes the negative charge on this grid and charges it positive. Current now flows through the right side of tube 170. With flow of current through tube 17% thus reversed from normal, the storage circuit 34 is cocked. Since the recording track 20 is synchronized to energize its pickup 25 when an imperfection is exactly between the rotary elements of the shear 2, the storage circuit become cocked virtually at this same instant.

Conductor 62. (potential 2 volts positive) is connected to the primary coil of a transformer 191 of the amplifier circuit 37. A conductor 192?. containing a resistance 193 connects the other end of this primary coil with the grounded line -9. Tire normally closed shear switch 36, hereinbefore referred to, is connected in parallel with resistance 193. The secondary coil of transformer 191 is connected to conductor -30 (potential 68 volts positive) and to the grid of a Triode amplifier tube 104 of the amplifier circuit 37.

As long as the shear switch 36 remains closed, direct current flows through the primary coil of transformer 191, but such current does not pulse the secondary coil. Once each revolution of the shear at the instant it cuts the strip S, the shear switch momentarily opens. Opening this switch instantly cuts off the current flowing through the primary coil and thus produces a negative pulse in the secondary coil and the grid of tube 194. This pulse causes the plate of said tube to become more positive and thereby produces a positive pulse which is transmitted to the left grid of tube 17% via a rectifier tube 1&5 of the amplifier circuit 37 and conductor 193. The operation of this portion of the circuit is not explained in detail, as it follows well known principles, but the circuit is fully shown in Figure 7a. If current is flowing normally through the left side of tube 170 (storage circuit not cocked), the positive pulse applied to the left grid has no effect since the grid already is positive. However, if the storage circuit has been cocked and current is flowing through the right side of tube 170, the positive pulse triggers the circuit. With the circuit cocked, the left grid is negative with respect to the cathode. The positive pulse overcomes the negative charge, causing current once more to flow through the left side of the tube. Resumption of this current takes current away from

conductors

187 and 185, and the right grid again becomes negatively charged. This current also produces a current pulse through conductor 179because of the action of condenser 180 (Figure 7b). Triggering of the first storage circuit resets it, since it returns to its normal state, where it can again be cocked by an impulse from the pickup 25.

Referring next to Figure 7b, triggering the first storage circuit 34 cocks the second storage circuit 38. The latter includes a dual Triode tube 201 which is of the same type as tube and similarly connected. Therefore the connection and immediately associated parts are not described in detail, although fully shown in Figure 7b. Like tube 170, the left grid of tube 201 normally is charged positively and the right grid negatively, so that current normally flows through the left side but not the right. The left grid is connected to conductor 179 through a rectifier 202 which passes only negative pulses. Thus pulses transmitted through conductor 179 apply a negative charge to the left grid of tube 201 and change the flow of current therethrough and cock the circuit 38 in the same fashion as pulses applied to the left grid of tube 3170 cock the circuit 34.

Assuming that an imperfection has been detected, at this stage the sheet containing the imperfection has just been cut from the strip and lies on conveyor 3 in the space between shear 2 and the photoelectric cell 39. The reference point of the imperfect sheet is of course its trailing edge, which has just been cut by the shear. Next the photoelectric cell acts to transfer this reference point to the leading edge of the sheet.

Referring back to Figure 7, the anode of the photoelectric cell 32 is connected to source of positive voltage (i.e., conductor 59) via a voltage divider comprised of resistances 203 and 2.05. The cathode is connected to a source of negative voltage, through a conductor 206 which contains a resistance 207 and leads to a voltage divider comprised of

resistances

208 and 210. The cell passes current when exposed to light (i.e., when no sheet is passing between it and the light source 4-0), but not when darkened (i.e., when a sheet is passing). The potential of conductor 206 is positive when current flows through the cell because the positive potential of conductor 59 (132 volts) overcomes the Weaker negative potential transmitted via

resistances

207 and 208. The potential of conductor 2436 becomes negative when the cell is darkened because the source of positive potential is cut off.

Referring again to Figure 7a, the flip-flop circuit 41 includes a dual Triode tube 211, which is connected similarly to the tube '71 and preferably is the same type. Therefore no detailed description is included, although the connection is fully shown in Figure 7a. A conductor 212 containing a resistance 213 conneots conductor 206 with the left grid of tube 211. When conductor 206 has a positive potential caused by exposure of cell 39 to light, this grid bears a positive charge and current flows through the left side of the tube, but not the right. When conductor 206 has a negative potential caused by darkening of cell 39, this grid bears a negative charge and current flows through the right side, but not the left.

A conductor 214 containing a condenser 215 and a rectifier 216 is connected between the current path through the right side of tube 211 and the right grid of tube 201 (Figure 712). When current commences to flow through the right side of tube 211, the condenser and rectifier transmit a negative pulse to the right grid of tube 201. If the second storage circuit 38 is in its normal uncooked state, the right grid already is negative and the negative pulse has no effect. This pulse merely marks the entry of the leading edge of a prime sheet opposite the cell 39. If this circuit is cocked, the negative pulse triggers it. This pulse marks the entry of the leading edge of an imperfect sheet opposite the cell. In the -cocked state the right grid of tube 201 is positive and the negative pulse changes it back to negative and thus changes the flow of current through the tube conductor'223 containing a' condenser 224.

back to the left side. A conductor 217 containing a condenser 218 and a resistance 219 in series is connected to the current path through the left side of tube 201. When flow of current resumes through the left side in response to triggering, the condenser causes a negative pulse through conductor 217. Conductor 217 is connected to a rectifier 220 which leads to the third storage circuit 42 and transmits only the negative pulse. Triggering of the storage circuit 38 also resets it.

Referring to Figure 7b, the third storage circuit 42 includes another dual Triode tube 221 of the same type and connected in the same fashion as tube 201, except that the rectifier 222 connected to its right grid (corresponds with rectifier 216) is connected also to the current path through the left side of tube 211 via a The left grid of tube 221 is connected to the current path through the left side of tube 201 via the rectifier 220. Normally the left grid of the tube 221 is positive and the right grid negative so that current flows through the left side of the tube, but not through the right side. A negative pulse transmittedto the left grid from conductor 217 and rectifier 224) reverses this current flow. In review such a negative pulse comes whenever the leading edge of a previously identified imperfect sheet darkens the photoelectric cell 39 and triggers the second storage circuit 38. w A conductor 230 containing a 510,000 ohm resistance 231 and a,1.5 megohm resistance 232 is' connected to the current path through the left side of tube 221 and to line 52 (potential 300 volts negative). An oscillator tube 233 of the oscillator 43 has its cathode connected to the grounded line 50 and its plate connected to line 51 (potential 265 volts positive) via the primary coil of a transformer 234. A condenser 234a is connected in parallel with this primary coil. The control grid is connected to conductor 230 intermediate its resistance 231 and 232. Normally this grid bears a negative charge derived from line 52 and no current flows through tube 233. When current ceases to flow through the left side of tube 221, the additional positive potential is applied to the grid of tube 233 via conductor 230 md resistance 231. This positive potential overcomes the normal 'negative potential and keys the oscillator, which puts out an AC. voltage. A conductor 235 connects the secondary coil of this transformer with the magnetizing coil of the recording head 27 on the recording track 21 of the memory device (Figure 7c). The other end of this magnetizing coil is grounded.

As long as tube 233 puts out.an A.C. voltage, transformer 234 does likewise and the magnetizing coil is energized and magnetizes an arc of therecording track 21. This coil remains energized as long as an imperfec sheet is passing the photoelectric cell 39 and darkening this cell. When the trailing edge of the imperfect sheet finally passes the cell and permits it again to conduct current, the left grid of tube 211 of the flip-flop circuit 41 again assumes its positive charge, and the left side of tube 211 commences to conduct current. A negative pulse appears'in conductor 223. The rectifier 222 transmits this pulse to the right grid of tube 221, which thereupon resumes its normal state in which its left side but not its right side conducts current. This action takes current from conductor 230 and the grid of oscillator 233 resumes its normal negative charge. Thus the magnetizing coil is deenergized. The length of arc magnetized on the recording track 21 is proportional to the. length of the imperfect sheet, since the speed at which this track moves is proportional to the sheet speed and the time the magnetizing coil is energized equals the time required for the sheet to pass a given point, i.e., the

V photoelectric cell 39.

' Referring to Figure 70, when rotation ofthe recording track 21 moves a magnetized portion thereon alongside the pickup 28 ('coincidentwith the arrival of the leading 12 edge of an imperfect sheet at the deflector), this portion of the track generates an AC. voltage in the pickup and continues to do so as long as it is passing. the pickup. The pickup coil is grounded at one end and connected at its other end via a conductor 236 to the primary coil of a transformer 237. A conductor 238 connects the other .end of said primary coil to the grounded line 50. An

amplifier tube 239 of the amplifier circuit 45. is connected between line 51 and grounded line 50. The secondary coil of transformer 237 is connected atone end to conductor 238 and thence to the grounded line 50 and at its 250, so that the grid normally is negative with respect 7 to. the cathode, and the tube does not conduct current. A conductor 251 containing a condenser 252'connects the grid of tube 245 to the current path through the amplifier tube 239.

A conductor 255 is connected between the plate of tube 245 and line 52 and contains resistances 256 and 257 in series. The grid controlled rectifier 44 includes two

Thyratron tubes

258 and 259, whose filaments are connected to the grounded conductor 50 and to the secondary coil of a transformer 260 in the fashion shown in Figure 7c. The primary coil of this transformer is connected to any suitable outside A.C. source for energizing these filaments. A conductor 261 connects the grids of both Thyratron tubes with conductor 255, having

resistances

262 and 263 interposed therebetween. Normally both grids receive a positive charge derived from line 51, since the combined resistances 248 and 256 are considerably less than the resistance 257. A conductor 264 connects the plates of both Thyratron tubes with one side of the magnets 13 of the magnetic roll 8 through the center tap of a power transformer 265, whose primary coil is connected to any suitable A.C. source. The other side of these magnets is connected to the grounded line 50. Thus normally (i.e., aslong as their grids are positive). the Thyratrons pass a rectified current to the magnets 13 and keep the magnetic roll energized.

When a current is induced in the pick-up 28, this current acts through the amplifier tube 239 to overcome the negative charge on the grid of tube 245. The latter tube now conducts current and takes away the positive potential of conductor 261. Thislatter conductor now receives a negative potential from line 52, which potential is applied to the grids of both

Thyratron tubes

258 and 259. These tubes cease to pass current to the magnets 13, thus deenergizing the magnetic roll 8 and defleeting an imperfect sheet beneath blade 7. A resistance 266 and condenser 267 preferably are connected across the magnets 13 to absorb the current surge produced by flux decay as the magnets are deenergized.

The magnets 13 remain deenergized until the magnetized Spot on track 21 passes beyond the pickup 28. When no more current is induced in this pickup, thegrid of tube 245 resumes its negative charge, which in turn allows

conductors

255 and 261 to resume their normal positive potential. Thus the grids of the Thyratronf tubes againybecome positive'and the tubes conduct current to the magnets 13 as before.

From the foregoing description it is seen that the magnetic roll 8 can be deenergized .or energized almost instantancously. The reference point which controls deenergization'is the leading edge of the sheet actually to be deflected. Consequently it is possible to deenergize the magnetic roll just ahead of any imperfect sheet and to reenergize this roll immediately after the trailing edge 13% of this sheet passes the roll. This very rapid and accurate action enables the mechanism to divert single imperfect sheets or any number of such sheets without diverting prime sheets. At the same time the mechanism virtually eliminates the need for mechanically moving parts.

While I have shown and described only a single embodiment of the invention, it is apparent that modifications may arise. Therefore, I do not wish to be limited to the disclosure set forth but only by the scope of the appended claims.

I claim:

1. In a shear line for metal strip, which includes a. shear and prime and reject sheet pilers, a mechanism for classifying and assorting sheets comprising a deflector normally allowing sheets to pass to said prime piler but operable to divert sheets to said reject piler, means for detecing imperfections in the strip ahead of said shear, means operatively connected to said detecting means and to said shear for recording that a sheet cut by said shear contains an imperfection, means situated beyond said shear responsive to the passing of the leading edge of a sheet thus recorded as imperfect for further recording that a sheet is imperfect, and time delay means operatively connected with said further recording means for operating said deflector, whereby the reference point for operating said deflector is the leading edge of an imperfect sheet. 7

2. In a shear line for metal strip, which includes a shear and prime and reject sheet pilers, a mechanism for classifying and assorting sheets comprising a deflector normally allowing sheets to pass to said prime piler but operable to divert imperfect sheets to said reject piler, means for detecting imperfections in the strip ahead of said shear, a storage circuit operatively connected to said detecting means and said shear and adapted to be cocked as said shear cuts from the strip a sheet containing an imperfection, means situated beyond said shear responsive to passing of the leading edge of a sheet for triggering said storage circuit, and time delay means responsive to triggering of said storage circuit for operating said deflector whereby the reference point for operating the latter is the leading edge of an imperfect sheet.

3. In a shear line for metal strip, which includes a shear and prime and reject sheet pilers, a mechanism for classifying and assorting sheets comprising a deflector normally allowing sheets to pass to said prime piler but operable to divert imperfect sheets to said reject piler, means for detecting imperfections in the strip ahead of said shear, means driven at a rate proportional to the strip speed for recording imperfections thus detected, a storage circuit operatively connected with said recording means to be cocked thereby when a recorded imperfection reaches said shear, a switch actuated by said shear when the latter cuts the strip and operatively connected with said storage circuit for triggering the latter when cocked, a second storage circuit connected with said first named storage circuit and adapted to be cocked by triggering thereof, means situated beyond said shear for triggering said second storage circuit when cooked on passing of the leading edge of the sheet, means driven at a rate proportional to the strip speed for recording triggering of said second storage circuit, and means operatively connecting said second named recording means and said deflector for operating the latter.

4. In a shear line for metal strip, which includes a shear and prime and reject sheet pilers, a mechanism for classifying and assorting sheets comprising a deflector normally allowing sheets to pass to said prime piler but operable to divert imperfect sheets to said reject piler, means for detecting imperfections in the strip ahead of said shear, a magnetizable recording track driven at a rate proportional to the strip speed a magnetizing coil and a pickup cooperable with said recording track and spaced proportionately to the spacing between said de- 14 tecting means and said shear, an electronic control, a circuit in said control connecting said detecting means and said coil, a storage circuit in said control connected to said pickup and said shear and adapted to be cocked by the former when an imperfection reaches said shear and triggered by the latter when cutting a sheet containing the imperfection, a second storage circuit in said control adapted to be cocked by triggering of said first storage circuit, means responsive to passing of a leading edge of a sheet for triggering said second storage circuit when cocked, a second magnetizable recording track driven at a rate proportional to the strip speed, a magnetizing coil and a pickup cooperable with said second recording track and spaced proportionately to the spacing between the triggering means for said second storage circuit and said deflector, a circuit in said control connecting said second storage circuit and said second named coil, and a circuit in said control connecting said second named pickup and said deflector.

5. In a shear line for metal strip, which includes a shear and prime and reject sheet pilers, a mechanism for classifying and assorting sheets comprising a magnetic roll deflector normally energized and allowing sheets to pass to said prime piler but when de-energized diverting sheets to said reject piler, means for detecting imperfections in the strip ahead of said shear, means driven at a rate proportional to the strip speed for recording imperfections thus detected, a storage circuit operatively connected with said recording means to be cocked thereby when a recorded imperfection reaches said shear, a switch actuated by said shear when the latter cuts and operatively connected with said storage circuit for triggering the latter when cocked, a second storage circuit connected with said first named storage circuit and adapted to be cocked by triggering thereof, a photoelectric cell beyond said shear and connected to said second storage circuit for triggering the latter when cocked on darkening of the cell by the leading edge of a sheet, means driven at a rate proportional to the strip speed for recording triggering of said second storage circuit, and a circuit operatively connecting said second named recording means and said deflector for de-energizing the latter.

6. In a shear line for metal strip, which includes a shear and prime and reject sheet pliers, a mechanism for classifying and assorting sheets comprising a magnetic roll deflector normally energized and allowing sheets to pass to said prime piler but when tie-energized diverting sheets to said reject piler, means for detecting imperfections in the strip ahead of said shear, a magnetizable recording track driven at a rate proportional to the strip speed, a magnetizing coil and a pickup cooperable with said track and spaced proportionately to the spacing between said detecting means and said shear, an electronic control, a circuit in said control connecting said detecting means and said coil, a storage circuit in said control connected to said pickup and adapted to be cooked thereby when an imperfection in the strip reaches said shear, a switch actuated by said shear as it cuts the strip and connected to said storage circuit for triggering it, a second storage circuit in said control adapted to be cocked by triggering of said first storage circuit, a photoelectric cell beyond said shear and connected to said second storage circuit for triggering the latter when cocked on darkening of the cell by the leading edge of a sheet, a second magnetizable recording track driven at a rate proportional to the strip speed, a magnetizing coil and a pickup cooperable with said second track and spaced proportionately to the spacing between said cell and said deflector, a circuit in said control connecting said second storage circuit and said second named coil, and a circuit in said control connecting said second named pickup and said deflector for tie-energizing the latter.

7. In a shear line for metal strip, which includes a shear and prime and reject sheet pilers, a mechanism for classifying and asserting sheets comprising a 'magnetic roll deflector, a grid controlled rectifier through which the magnets of said deflector normally are energized for allowing sheets to pass to said prime piler, but adapted when receiving a negative potential on its grids to de-energize the magnets for diverting sheets to said reject piler, means for detecting imperfections in the strip ahead of said shear, a magnetizable recording track driven at a rate proportional to the strip speed,

a magnetizing coil and a pickup cooperable with said track and spaced proportionately to the spacing between said detecting-means and said shear, a circuit connecting Said detecting means and said coil, a storage circuit connected to said pickup and adapted to be cocked thereby whenan imperfection in the strip reaches said shear, a switch actuated by said shear as it cuts the strip and connected to said'storage circuit for triggering it when cocked, a second storage circuit adapted'to be cocked by triggering of said first storage circuit, means beyond said shear connected to said second storage circuit for triggering it when cocked on passing of the leading edge of a sheet, a second magnetizable recording track driven at a rate proportional to the strip speed, a magnetizing coil and a pickup cooperable with said second track and spaced proportionately to the spacing between the triggering means for said second storage circuit and said magnetic roll, a circuit connecting said second storage circuit and said second named coil, and a circuit connecting said second named pickup and the grids of said rectifier for applying a negative potential thereto as a magnetized spot on said second track passes said second named pickup.

8. In a shear'line for metal strip, which includes a shear and'prirne and reject sheet pilers, a mechanism for classifying and asserting sheets comprising a magnetic roll deflector, a grid controlled rectifier through which the magnets of said deflector normally are energized for allowing sheets to pass to said prime piler, but adapted when receiving a negative potential on its grids to de-energize the magnets for diverting sheets to said reject piler, means for detecting imperfections in the strip ahead of said shear, a magnetizable recording track driven at a rate proportional to the strip speed, a magnetizing coil and a pickup cooperable with said track and spaced proportionately to the spacing between'said detecting means and said shear, a circuit connecting said detecting means and said coil, a storage circuit connected to said pickup and adapted to be cocked thereby when an imperfection in the strip reaches said shear, a switch actuated by said shear as it cuts the strip and connected to said storage circuit for triggering it when cocked, a second storage circuit adapted to be cocked by triggering of said first storage circuit, a photoelectric cell spaced beyond said shear by more than one sheet length and a maximum of two sheet lengths and connected to said second storage circuit for triggering the latter when cocked on darkening of the cell by the leading edge of a sheet, a second magnetizable recording track driven at a rate proportional to the strip speed, a magnetizing coil and a pickup cooperable with said second track and spaced proportionately to the spacing between said cell and said deflector, a circuit connecting said second storage circuit and said second named coil, and a circuit connecting said second named pickup and the grids of said rectifier for applying a negative potential thereto as a magnetized spot on said second track 7 passes said second named pickup.

9. In a shear line for metal strip, which includes a shear and prime and reject sheet pilers, a mechanism for classifying and asserting sheets comprising a magnetic roll deflectona grid controlled rectifier through which the magnets of said deflector normally are energized for al-' lowing'sheets to pass 'to said prime piler, but adapted when receiving a negative potential on its grids to deengize the magnets 'for diverting sheets to said reject piler, means for detecting imperfections, in the strip ahead of.

15 said shear, a magrietizable recording track driven at a rate proportional to the strip speed, a magnetizing coil and a pickup cooperable with said track and spaced proportionately to the spacing between said detecting means and said shear, an amplifier circuit and a pulse shaping circuit connecting said detecting means and said coil, a storage circuit connected to said pickup and adapted to be cocked thereby when an imperfection in the strip reaches said shear, a switch actuated by the shear, an amplifier circuit connecting said. switch and said storage circuit, actuation of said switch triggering said storage circuit when cocked, a second storage circuit connected to said first storage circuit and adapted to be cocked by triggering thereof, a photoelectric cell spaced beyond said shear by more than one sheet length and a maximum of two sheet lengths, a flip-flop circuit connected'to' said cell and adapted to pass current one Way whenthe cell is exposed to light and another Way when the cell is darkened by a passing sheet, said flip-flop circuit being connected to said second storage circuit and triggering it when cocked on darkening of said cell by the leading edgecf a sheet, a second magnetizab le recording track 'driven at a rate proportional to the strip speed, a magnetizing coil and a pickup cooperable with said second track and spaced proportionatly to the spacing betweensaid cell and said deflector, a third storage circuit and an oscillator connecting said second storage circuit and said second named coil, and an amplifier connecting said second named pickup and the grids of said rectifier for applying a negative potential thereto as a magnetized spot on said second track passes said second named pickup. r

10. in a shear line for metal strip, which includes a shear and prime and reject sheet pilers, a mechanism for classifying and assorting sheets and marking defective sheets comprising a deflector normally allowing sheets to pass to said prime piler but operable totdivert imperfect sheets to said reject piler, a pin hole detector ahead of said shear, a marker between said detector and said shear, a magnetizable recording track driven at a rate proportional to the strip speed, a magnetizing coil and a marker pickup and a circuit cocking pickup cooperable with said trackand spaced proportionately to the spacing between said detector and said marker and said shear respectively, an amplifier circuit and'a pulse shaping circuit connecting said detector and saidcoil, an amplifier circuit connecting said marker pickup and said marker, a, storage circuit connected to said circuit cocking pickup and adapted to be cocked thereby when an imperfection noted by said de tector reaches said shear, means connecting said shear with said storage circuit for triggering the latter when cocked as the shear cuts the strip, and time delay means for operating said deflector initi'ated'by triggering of said storage circuit. V t i 11. A shear line asdefined in claim 10in which the classifying and asserting mechanism includes means for transferring the reference point for operating said deflector to theleading edges of the sheets. 7

12. A shearrline as defined in claim 10 in which classifying and assortingrmechanisnr includes means for transferring the reference point for operating said deflector to the leading edges of the sheets and said time delay means includes a second magnetizable recording track, a magnetizing coil and a pickup cooperable therethe with andspaced proportionately to the spacing between said transferring means and 'said deflector, and circuits connecting said last named coil with said transferring means and said last named pickup with said deflector.

13. In a shear line for metal strip, which includes a shear and prime and reject sheet pilers, a mechanism for classifying and asserting sheets and marking defective sheets comprising a deflector normally allowing sheets to pass .to said prime piler but operable to divert imperfect sheets to said reject piler, a pin hole detector ahead of said shear, a marker between said detector and said shear, a magnetizable recording track driven at a rate proportional to the strip speed, a magnetizing coil and a marker pickup and a circuit cocking pickup cooperable with said track and spaced proportionately to the spacing between said detector and said marker and said shear respectively, an amplifier circuit and a pulse shaping circuit connecting said detector and said coil, an amplifier circuit connecting said marker pickup and said marker, a storage circuit connected to said circuit cocking pickup and adapted to be cocked thereby when an imperfection noted by said detector reaches said shear, a shear switch actuated by said shear as it cuts the strip and connected to said storage circuit for triggering it when cocked, a second magnetizable recording track driven at a rate proportional to the strip speed, a magnetizing coil and a pickup cooperable with said second track, transfer means connected to said storage circuit and said last named coil for energizing the latter on passing of the leading edge of a defective sheet, and means connecting said last named pickup and said deflector.

14. A sheet classifying line comprising a shear, means for conveying uncoiled continuous metal strip to said shear and sheets therefrom, prime and reject sheet pilers, a magnetic roll deflector between said conveying means and said pilers normally having magnetic characteristics to route sheets to said prime piler, means for detecting imperfections in the strip ahead of the shear, and means operatively connected to said detecting means and controlled by the leading edge of a sheet containing an imperfection for changing the magnetic characteristics of said deflector immediately ahead of the arrival of this sheet and by the trailing edge of this sheet for resetting said deflector immediately after departure thereof, said deflector routing sheets to said reject piler when its magnetic characteristics are thus changed.

15. A sheet classifying line comprising a shear, means for conveying uncoiled continuous metal strip to said shear and sheets therefrom, prime and reject sheet pilers, a magnetic roll deflector between said conveying means and said pilers normally having magnetic characteristics to route sheets to said prime piler, means for detecting imperfections in the strip ahead of the shear, and a memory device and electronic control connected with said detecting means and said shear for recording that an imperfection detected in the strip lies within a particular sheet cut by said shear said memory device and control also being connected with said deflector for changing its magnetic characteristics immediately ahead of the arrival of the leading edge of a sheet containing an imperfection to divert that sheet to said reject piler and for resetting said deflector immediately after the departure of the trailing edge of that sheet.

16. A sheet classifying line comprising a shear, means for conveying uncoiled continuous metal strip to said shear and sheets therefrom, prime and reject sheet pilers, a magnetic roll deflector between said conveying means and said pilers normally having magnetic characteristics to route sheets to said prime piler, means for detecting imperfections in the strip ahead of the shear, means operatively connected to said detecting means and said shear for registering that a particular sheet cut by the shear contains an imperfection, photoelectric means situated between said shear and said deflector and being operatively connected to said registering means, a recording track driven at a rate proportional to said conveying means, means operatively connected to said photoelectric means and associated with said track for recording on said track the movement past said photoelectric means of both the leading and trailing edges of a sheet containg an imperfection, and a circuit actuated by said recording track and connected to said deflector for changing its magnetic characteristics immediately ahead of the arrival of the leading edge of a sheet containing an imperfection to divert that sheet to said reject piler and for resetting said deflector immediately after the departure of the trailing edge of that sheet.

17. A sheet classifying line comprising a shear, means for conveying uncoiled continuous metal strip to said shear and sheets therefrom, prime and reject sheet pilers, a magnetic roll deflector between said conveying means and said pilers normally having magnetic characteristics to route sheets to said prime piler, means for detecting imperfections in the strip ahead of the shear, means operatively connected to said detecting means and said shear for registering that a particular sheet cut by the shear contains an imperfection, photoelectric means situated between said shear and said deflector and being operatively connected to said registering means, a magnetic recording track driven at a rate proportional to said conveying means, a recording head cooperable with said track and connected to said photoelectric means for magnetizing an arc on said track commencing when the leading edge of a sheet containing an imperfection passtfi said photoelectric means and terminating when the trailing edge of that sheet passes, and a pickup cooperable with said track and spaced from said recording head a distance proportional to the spacing between said photoelectric means and said deflector, said pickup being con nected to said deflector to change its magnetic characteristics when the beginning of a magnetized arc reaches the pickup to divert a sheet to said reject piler and to reset said deflector when the end of this are reaches the pickup.

18. In a shear line for metal strip, which includes a shear, prime and reject sheet pilers, and means for conveying sheets from said shear to said pilers, a mechanism for classifying and assorting sheets comprising a deflector normally allow ng sheets to pass to said prime piler but operable to divert sheets to said reject piler, means for detecting imperfections in the strip ahead of said shear, means operatively connected to said detecting means and said shear for initially establishing the trailing edges of sheets which have imperfections as reference points for subsequently operating said deflector, means for transferring the reference points for operating the deflector to the leading edges of the imperfect sheets and establishing the trailing edges of the imperfect sheets as reference points for resetting the deflector, and time delay means operatively connected to said deflector and to said transferring means for operating and resetting said deflector.

19. A method of classifying and assorting sheets comprising detecting imperfections in moving continuous strip, recording the imperfections, cutting said strip into individual sheets, identifying any sheet containing a recorded imperfection simultaneously with the cutting of this sheet from the strip, moving the sheets in a line away from the point of cutting, recording the passing of a given point in the line of the leading and trailing edges of sheets identifled as containing imperfections, diverting from the line at a subsequent point only those sheets of which passing of the leading and trailing edges has been recorded, resetting the line after a sheet is diverted, and timing the resetting to occur when the trailing edges of sheets containing imperfections pass said subsequent point to enable a sheet immediately following to continue in the line if free of imperfections.

20. A method of classifying and assorting sheets comprising detecting imperfections in moving continuous strip, recording the imperfections, cutting the strip into individual sheets, identifying any sheet containing a recorded imperfection simultaneously with the cutting of this sheet from the strip, moving the sheets in a line away from the point of cutting, recording the passing of a given point in the line of the leading edges of sheets identified as containing imperfections as reference points for deflecting such sheets, recording the passing of the same point of the trailing edges of sheets identified as containing imperfections as reference points for resetting, diverting from the line at a subsequent point only those sheets of which passing of the leading edge has been recorded, resetting the line after a sheet is diverted, and timing the resetting to occur when the trailing edges of sheets con