US3410421A - Sheet stacker - Google Patents

Description

v A. F. GROLL SHEET STACKER 8 Sheets-Sheet 1 Filed April 1, 1966 I I l D M I I I I I I I I I I I I I I I g I HI... I II m- IIIIIIPIIII I. H I 4 I h h I H| I 2 mt I IMWWWI I 1 IIIIIIIIIIIIIIIIII IIIIIIII INVENTOR. ALVIN F GROLL Wilson 6:9

.A. F. GROLL Nov. 12, 1968 SHEET STACKER Filed April 1, 1966 mL 8 Na- 0 m w w m II M N If] s w 8 A NOV. 12, 1968 GROLL 3,410,421

SHEET STACKER Filed April l, 1966 B Sheets-Sheet 4 A. F. GROLL SHEET STACKER Filed April 1, 1966 III 203 FCR \202 FCR III W 204 MAN: /AUTO2 256[ LS9 ICR SHEET FEED, E m POSITION I i MANUAL 20 IM f-2cR F 2I4 2|3 SHEET CONVEYOR ELM BACK END 244 2s8- Ef' k l 3CR CLOSE END GATES STOP STACK CONVEYOR t246 247: 20R if 4CR 8CR 30R ILS I R OPEN 2L8 TfiR F O 2CR 1 a24sb IC' |248 c l STACK CONVEYOR REV.

8 Sheets-Sheet 5 -307, IM,308,38I,38I,38|

-323, GCR, 374,374

1 INVENTOR. 204 208 ALVIN F. GROLL NOV. 12, 1968 GROLL 3,410,421

SHEET STACKER Filed April 1, 1966 8 Sheets-Sheet 8 LEAD ON MAGNET BANK INVENTOR. ALVIN E GROLL mvaizmmgymw MAGNET BANK l afl 's.

United States Patent M 3,410,421 SHEET STACKER Alvin F. Groll, P.0. Box 391, Napoleon, Ohio 43545 Filed Apr. 1, 1966, Ser. No. 539,403 11 Claims. (Cl. 214-6) ABSTRACT OF THE DISCLOSURE A stacker including a sheet delivery conveyor extending to a stacking station, a stack conveyor extending from the stacking station and a stacking path from the sheet conveyor to a stack receiver at the stacking station. Corner gates define the stacking path and are retractable to permit movement of the stack. Sheet catchers are extendable into the stacking path to permit continued feed of sheets to the stacking station while a stack is being removed therefrom. Automatically sequenced controls sense the accumulation of a desired stack, extend the sheet catchers, open the corner gates, move the stack from the stacking station, close the gates when cleared by the stack and retract the catchers to release the sheets in the stacking path to a stack receiver in the stacking station. The system is arranged for automatically or manually loading a plurality of stacks on a single stack receiver.

This invention relates to the handling of sheet material and more particularly to the stacking of sheets in a rapid and continuous fashion.

While the following detailed description is directed to the handling of sheets of ferromagnetic material, it is to be appreciated that certain aspects of the invention are applicable to other materials in sheet form.

It is known to assemble sheets of ferromagnetic material which have been sheared from strip stock advancing at a high rate of speed by magnetically picking up the sheared sheets as they issue from a shear, maintain the suspended sheets against non-magnetic endless belts, advance the belts to a stacking station with the sustained sheets in contact therewith, and release the sheets at the stacking station. United States Patent 2,374,174 which issued Apr. 24, 1945 to Buccicone illustrates a piling apparatus of this type. Adjuncts to this type of apparatus have been developed in an effort to increase the rate at which it accommodates sheets, to reduce the damage to the edges and faces of sheets, to eliminate delays due to interruptions in the stacking process required to transfer completed stacks from the stacking station, and to accommodate several forms of sheet as by accumulating one form in a first stack and an alternately produced form in a second stack.

An object of the present invention is to improve apparatus and systems for stacking sheet material.

A second object is to increase the flexibility of apparatus and systems for stacking sheet material whereby a wide range of sheet sizes and gauges can be accommodated.

A third object is to minimize the interruptions in the accommodation of sheets delivered from a source capable of supplying them at a high rate.

A fourth object is to facilitate the introduction of pallets to and removal of pallets from a stacking station.

A further object is to assemble a plurality of stacks of sheets on a single pallet.

A sixth object is to guide sheets precisely from a conveyor to a stack receiver and to avoid interference by the guiding means with the transfer of the stacks.

An additional object is to automatically program the stacking of sheets into a plurality of stacks and, when necessary, upon a succession of stack receivers such as pallets.

In accordance with these objects, one feature of this invention resides in a conveying and stacking apparatus having means for adjusting the width and length of the conveying path and stacking station whereby sheets can be oriented over a wide range of positions in a stacking station.

A second feature involves removable gates forming the sides of a chute along which sheets are dropped from a sheet conveyor to a stack receiver. The gates are arranged to accurately position the sheet stack. They are readily shifted in order to permit the transfer of the stack from the stacking station without interference and to return to a chute defining position when a clear stack receiving surface is oriented in the stacking station.

A third feature comprises a program control which avoids interference between cooperating elements of the system.

A fourth feature includes automatic sequencing controls coupled with sensing means to ascertain the stack height, the stack position, the position of the gates and the position and state of the several conveyors in a continuous stacking system. This control automatically replaces a stack receiving surface which is loaded with sheets to a predetermined height with a clear stack receiving surface upon which a second stack is accumulated.

Another feature resides in means for transporting sheet stack receiving pallets in a precisely controlled manner to a stacking station and means for precisely positioning the pallets with respect to the location within the stacking station at which a stack is deposited. This feature is realized by means of a pallet conveyor system integrated with the sheet conveyor and stacker. In one example sheets of a size which permits several stacks to be accommodated on a pallet are carried to one extreme of the stacking station and an initial stack deposited upon one side of a pallet. Upon completion of the initial stack the stacker accumulates succeeding sheets in a reservoir while the partially loaded pallet is advanced sufiiciently to position a vacant region in registry with the area of the stacking station in which the accumulated sheets and succeeding sheets are deposited.

The reservoir then releases it sheets to the pallet and stacking continues until the second stack is completed. If sufiicient pallet surface is available to accommodate additional stacks, the pallet can be repositioned repetitively to bring a vacant region into the area in which the stacker deposits the accumulated sheets and succeeding sheets.

A further feature comprises a transfer path for pallets including a first empty pallet station, a conveyor for advancing an empty pallet from the first station to the stacking station along a path transverse of the sheet conveyor path, and a conveyor for advancing a loaded pallet from the stacking station along a path parallel to the sheet conveyor path.

Additional features reside in the controls for programming the stacking system to introduce and remove pallets from the stacking station in synchronization with the positioning of stacking guides and the operation of sheet catchers whereby the stacking guides clear the stacks as they are displaced and sheets are accumulated for deposit on a clear pallet surface following pallet transfer.

Another feature includes sheet catchers for catching the sheets brought to a stacking station and supporting the sheets intermediate the transverse limits of the station whereby the tendency of light gage stock to sag is overcome. In the illustrative embodiment catchers are mounted on the sheet stop extending transverse of the sheet conveyor path and on the backup plate similarly oriented. These catchers cooperate with catchers extended from the 3 sides of the sheet path to provide supports on four sides of the sheet.

A further feature comprises a backup plate which is shiftable longitudinally of the sheet conveyor path so that it can be oriented closely adjacent the trailing edge of stacked sheets. This adjustable plate enables the accommodation of any size sheet within the capacity of the stacking station. It further orients a sheet catcher to catch the trailing edge of the sheets intermediate the sheet sides paralleling the sheet feeding path.

The above and additional objects and features of this invention will be more fully appreciated from the following detailed description when read with reference to the accompanying drawings in which:

FIG. 1 is a side elevation with portions thereof broken away to illustrate certain aspects of the stacking system of this invention and with the pallet loading conveyor for feeding pallets to the stacking station removed and only a portion of the end conveyor for carrying loaded pallets from the stacking station shown;

FIG. 2 is an enlarged detail of an end view of the side catchers for sheets as viewed along the line 22 of FIG. l;

FIG. 3 is an end elevation of the stacking system of FIG. 1 with the pallet loading conveyor broken longitudinally;

FIG. 4 is a plan view of the upper portion of the system showing portions of the stacker and the sheet feed of FIGS. 1 and 3 with the pallet conveyors removed and some portions broken away or shifted from their true position to reveal details;

FIG. 5 is a plan of the lower portion of the system of FIG. 1 showing the pallet conveyor system with portions broken away for illustrative purposes; and

FIGS. 6 through 10 are across the line diagrams of the electrical control circuits for the system of this invention.

General operation Before proceeding with a detailed description of the apparatus, it will be helpful to consider its organization and operation. As shown in FIG. 1 the system is intended for use with apparatus capable of producing sheets at a high rate such as a shear 11 including a shear frame 12 and a shear face 13 at which sheets are severed from strip stock (not shown). The stock is advanced from right to left as viewed in FIG. 1 from the shear face and extends as a cantilever therefrom until sheared to sheet form. In the region from which the stock issues it is sustained by a bridge 16 of a magnetic conveyor 17 including a plurality of endless belts 18 of non-magnetic material such as neoprene impregnated duck belting trained around rolls 19, 20 and 21 in a path extending above a stacking station 22. Electromagnets 10 within the loop of belts 18 hold the ferromagnetic sheets against the lower face of the belts as they are driven clockwise to transport the sheets to the left as viewed in FIG. 1 to a position above the stacking station 22. While electromagnets are utilized as the means to sustain the sheets against the lower face of the belts 18, it is to be appreciated that other sustaining means are known. For example non-magnetic sheets can be sustained by developing a vacuum between the lower face of the belts or corresponding continuous convey'or elements and the upper face of the sheets.

Once the sheet has been conveyed to an appropriate position in the stacking station, the force sustaining it is released as by deenergizing the magnets and it is permitted to fall under the influence of gravity along a path defined by guides forming a chute 14 to a pallet 23 or other suitable receiving surface. The sheet guides forming chute 14 include a bumper 24 at the end of the sheet travel, a backup plate 25 adjustably positioned along the path of sheet travel to be in proximity to the trailing edge of the sheet, side plates 26 adjustably positioned transverse of the path of sheet travel; and end gates 27 defining the corners of the leading edge of the sheet. These plates and gates define a vertical chute 14 in which the sheet falls while maintaining its major face generally horizontal.

The sheet-s are stacked on pallets 23 positioned beneath the guiding plates and gates. Pallets are brought into the stacking station 22 by a cross conveyor 28, FIGS. 3 and 5. Once they are loaded by a stack of sheets of suitable height, as determined by suitable means such as an inductively responsive proximity switch PS1 which is adjustable to the height of the desired sheet stack, the pallets are advanced out of the stacking station along a path paralleling the path of sheet travel of means of a conveyor 30 which passes them to an end conveyor 31 from which they can be removed as by a forklift (not shown).

Controls are provided to correlate the operation of the several elements of the system. When the pallet in the stacking station is moved, sheets can be permitted to continue to issue from the shear 11 and can be permitted to fall only a short distance from the magnetic conveyor 17 while being maintained clear of any stack on the pallet 23. Catchers 32, 33 and 34 are extended from the lower portion of bumper 24, from backup plate 25 and from side plates 26 to engage the edges of sheets and sustain them until a pallet is in sheet receiving position within the stacking station. When the pallet has been properly positioned the controls cause the catchers to release the accumulated sheets to their stacking position on the pallet. Where sheets are of such size that several stacks can be accommodated on a pallet, the control sequence involves positioning the pallet to receive a first stack on its leading edge. When the first stack is completed the catchers are actuated, the end gates 27 are opened, the pallet is advanced toward end conveyor 31 sutficiently to position a clear pallet surface below the stacking chute 14 and to permit the reclosing of end gates 27 without interfering with the first stack, the end gates are closed, the catchers are released and a new stack accumulated. When a pallet is completely loaded, the cycle involves extending the catchers, opening the end gates, advancing the pallet to the end conveyor, operating the cross conveyor 28 to position an empty pallet in the stacking station, closing the end gates and withdrawing the catchers.

As will be evident from the following details, once the system is set up it will operate automatically to issue sheets stacked on pallets without interruption of the strip stock fed to the shear. Suitable adjustments are available to enable it to be set up to stack a wide range of sheet sizes. Automatic protective controls are available to avoid malfunctions which might damage the sheets or the apparatus.

Sheet conveyor Conveyor 17 as best seen in FIGS. 1, 3 and 4 is supported above the pallet manipulating equipment on legs 35 and shear frame 12 supporting a frame of channels 36 which also supports the plates and gates forming the chute through which the sheets drop. It comprises end rolls 19 and 20 and a hinge roll 21 each supporting a plurality of belts 18. End roll 20 is driven by motor 41 through a suitable chain 42 coupled to drive sprocket 43 and driven sprocket 44 on the stub shaft 45 from roll 20. Roll 20 is journaled for rotation in pillow blocks 46 receiving stub shafts 45 protruding therefrom. Pillow blocks 46 provide tensioning means for belts 18 since they are movable longitudinally of the frame 36 by means of lead screws 37 mounted in nuts 38 fixed to the frame.

Hinge roll 21, as best seen in FIG. 4, is journaled on stub shafts 47 secured to frame 36. Also journaled in shafts 47 is a hinged frame 48 forming a bridge 16 between shear 11 and conveyor 17. The end roll 19 is journaled on stub shafts 49. Thus the bridge 16 can be moved away from the shear 11 by pivoting it around shafts 47 without altering the length of the path for belts 18 provided the belts are maintained tangent to the upper portion of hinge roll 21. Tensioning roll 54 is positioned between rolls 20 and 21 in parallelism therewith as shown in FIG. 1, and with its lowermost face below the plane defined by the uppermost faces of rolls 20 and 21 to maintain the belts 18 in tension while the bridge 16 is pivoted to its open position. In FIG. 4 the tension roll 50, side plate adjusting screw 86 and its handwheel 87 have been shifted longitudinally of their true positions as shown in FIG. 1 in order to illustrate the details of their mounting.

Magnetic attraction sustains the sheets against the lower face of the belts 18. Controlled magnetic attraction is provided by banks of electromagnets which extend transverse of the belts in rows of 6 magnets in a conveyor accommodating widths up to 72 inches as a lead on bank 56 of two rows of magnets 10 within the bridge frame and between end roll 19 and hinge roll 21 and six banks 52 to 57 disposed in sequence along the length of the frame between end roll and binge roll 21. The electromagnets 10 are of conventional form and are not shown in detail here. They are centered between the belts 18 which are maintained in a proper transverse position on the conveyor by suitable crowns 58 on the end rolls 19 and 20 such that they protrude sufiiciently above the magnet faces to prevent contact of the sheets with the faces. When the belts 18 are driven clockwise as viewed in FIG. 1 and the magnets are energized, sheets are attracted against the belt crowns by the energized lead on magnets of bank 51 and are carried to the left as viewed in FIG. 1 with the belts until released by deenergization of the electromagnets.

A limit switch SLS having its sensing element responds when a sheet on the conveyor is a short distance from the bumper 24 actuates a magnet deenergizing means to permit the sheet to fall from the conveyor, as will be described with reference to the details of the controls.

Sheet chute A sheet is released from its horizontal conveying position by demagnetizing the banks of conveyor magnets 52 to 57 extending the length of the sheet from the bumper 24. It is therefore cushioned in its drop to the underlying pallet 23 by the windage of the broad surface it presents since it is confined in its fall to a predetermined path defined by the walls of its chute 14.

In the upper portion of the sheet path the chute 14 is defined at its front face by bumper 24 which is mounted for limited adjustment along the path of travel of the sheet by screws 60. The bumper is cushioned to relieve the impact of sheets by means of springs 61 fitted over the ends of screws 60 and seated on studs in axial alignment with the screws and secured to the back of the bumper. The springs 61 are held in compression between the back face of bumper 24 and a washer seated against an enlarged diameter on the screw. Screws 60 are carried in tapped bores in a wall 62 secured to a beam 63 which extends between legs 35. The front catcher 32 is also suspended from the beam 63 and an extension plate 64 suspended by the beam projects below the catcher to a position somewhat above the end gates 27 and the maximum height of the sheet stacks accommodated by the stacker.

The back end guide is adjustable longitudinally of the sheet path over nearly the entire length of the stacker. It extends across about twenty four inches of the center of the stacker, where sheets of at least that width are to be accommodaed, and it extends between the side plates 26. Back end guide 25 has an upper inclined portion 65 which guides sheets which are dropped short of the bumper 24 into a position wherein they are closely confined by the bumper 24 and end gates 27 at their leading edge and by the remainder of the back end guide 25 at their trailing edge.

A pair of lead screws 66 extending longitudinally of and beside the conveyor path are journaled in suitable bosses 67 and 68 on the inner faces of the webs of channels 36. Apertures in bosses 69 and 70 secured to a cross channel 71 are threaded to receive the lead screws 66 such that the simultaneous rotation of the screws causes movement of backup plate 25 along the conveyor path. As best seen in FIG. 4, the lead screws are coupled for rotation by a chain 72 trained over sprockets 73 and are driven by motor 74 through a gear train 75 to a sprocket 76 driving a chain 77 engaging a sprocket 78 keyed to an extension of lead screw 66.

Back end guide 25 also supports a pneumatically extended and retracted catcher 33 to sustain the middle portion of sheets caught by the side catchers 34.

The sides of the drop chute 14 for the sheets is defined by transversely adjustable side plates 26. Plates 26 extend over a substantial portion of the length of the stacking station 22 and, as in the case of the back end guide, extend downward to a position wherein their lower limit is closely adjacent but clear of a pallet 23 on the conveyor 30. As shown in FIG. 3, the upper portions of side plates 26 have outwardly inclined surfaces '80 for gradually bringing the sides of sheets into alignment with their ultimate position on the pallet 23. Side plates 26 have stilfening frames made up of I beam 81 and ribs 82. They are supported by end bosses 83 and 84 having apertures with axes extending transverse of the conveyor path and threaded internal walls mounted on lead screws 85 and 86 extending transverse and across the entire conveyor path.

Adjustment of the separation of the side plates 26, is accomplished by rotating screws 85 and 86. A hand wheel 87 is keyed to a. stub shaft on the end of screw 86 for rotating that shaft in its bearings 88 and 89 (FIG. 4) mounted in pillow-blocks 91 depending from the underside of the channels 36. A stub shaft on the opposite end of screw 86 supports a sprocket 92 for rotational coupling to a sprocket 93 on shaft 85 through chain 94 trained thereover. Shaft 85 is mounted in bearings 95 secured to legs 35.

The side plates 26 carry side catchers 34 (FIG. 1), to be discussed, and end gates 27 (FIGS. 1 and 3). End gates 27 have vertical walls 96 and 97 at right angles to each other and defining the corners for the leading edge of the stacked sheets such that wall 97 has its face adjacent the stacking station in vertical registry with the bumper 24 and the wall 96 lies in the same plane as the major face of side plate 26 adjacent the stacking station. End gates 27 are hinged for rotation around a vertical axis by pintle 98 passing through gudgeons 99 on the outer face of wall 96 and on the outer face of side plate 26. A pair of vertically spaced, outward projecting lugs 102 provide a crank arm for gate 27 to which is coupled the piston rod 103 of a pneumatic cylinder 1104 as by the pivot pin 105. The cylinder is pivotally mounted on the side plate 26 as by pin 106 by lugs on the cylinder straddling a lug on the plate. As will be described the end gates are opened to permit movement of the stacked sheets to the left as viewed in FIG. 1. This control of the gates is afforded by a solenoid actuated valve (not shown) controlling the flow of air through flexible conduit (not shown) from a suitable high pressure reservoir (not shown).

Catchers In order to avoid interruption of the sheet feed to the conveyor following completion of a stack of sheets on a pallet 23, sheets are permitted to fall only a limited distance in the stacking chute during the period a pallet is being oriented in sheet receiving position. Catchers are provided on all four sides of the sheets so that the tendency of a sheet to sag transversely of the conveyor is reduced and the catchers are effective on relatively light gauge sheets of substantial xtent. In the present embodiment two side catcher arms 34 are extended from each side plate 26 and a single centered catcher arm 32 and 33 is extended from below the bumper 24 and the back end guide 25 respectively.

The side catchers 34 are best seen in FIGS. 1 and 2. Each comprises a pair of arms spaced longitudinally of the side plate 26 and fitting within suitable apertures 114 in the side plate when in the sheet releasing position. The arms are each supported on horizontal shaft 115. The shaft 115 is journaled in gudgeons 116 horizontally spaced on and secured to side plate 26. Rotation of shaft 115 through 90 extends th arms 34 as horizontal shelves extending from side plates 26 in the same plane as the upper surfaces of catcher arms 32 and 33. Shaft 115 is rotated by pneumatic cylinder 118 pivoted at 119 to the side plate 26 and coupled through piston rod 121 to bifurcated crank 122 by pin 123. Crank 122 is keyed to shaft 115. The arms 34 are retracted into the apertures 114 so they are even with or below the inner face of plate 26 when the piston rod 121 is extended its full stroke.

As in the case of the end gates, air at a high pressure is supplied to and carried from the side catcher cylinders 118 through flexible conduits under control of solenoid actuated four way valves (not shown).

End catcher arms 32 and 33 are of the reciprocating type. Such arms in some applications may tend to mar the under surface of the lowermost sheet when they are withdrawn since they slide across that surface. Where such marring is to be avoided horizontally pivoted catcher arms of a construction similar to arms 34 can be utilized whereby the outer limits of the arm are moved away from the sheet in a direction generally normal thereto. This eliminates the gradual increas in pressure developed as the reciprocating arms are withdrawn and avoids any abrading of the surface, particularly where the pivoted arms are withdrawn at a speed exceeding the acceleration of gravity.

In the case of the reciprocating catcher arms a relatively simple slide mounting is provided for the arm and a fixed hydraulic cylinder extends and retracts the arm along the guide formed by the slide. In FIGS. 1, 2 and 3 the catchers are all extended to their sheet engaging position. Thus arm of backup catcher 33 is extended along slide 125 by a piston rod extending from cylinder 127 secured on backup plate 25. Similarly, the arm of bumper catcher 32 is extended along slide 128 by the full extension of the piston in cylinder 131 as coupled thereto by a piston rod. The catcher assembly is secured on the I beam 63 extending between legs 35. Fixed conduit can be employed to carry high pressure air to and from cylinder 131 while a flexible conduit is necessary to cylinder 127 to accommodate the motion of backup plate 25. Four way solenoid actuated valves (not shown) also control the flow of high pressure air to and from cylinders 127 and 131.

Pallet conveyors Empty pallets 23 are fed to the stacking station beneath the stacking chute 14 by cross conveyor 28 comprising a pair of inner rails 133 and a pair of outer rails 134 on the upper surface of a box base 135 of suflicient depth to orient the upper surface in alignment with the upper face of conveyor 33. Pallets positioned on the rails are advanced into the stacking station by a reciprocating ram 136 driven by chains 137 trained over inner sprockets 138 and outer sprockets 139.

Ram 136 is shown in FIGS. 3 and as a fabricated element which rides upon the upper surface of inner rails 133. Lugs 142 depend from plate 141 for coupling to the drive chains adjacent each of rails 133. Push face 143 engages the sides of pallets positioned on the conveyor rails.

Drive chains 137 are supported by shafts 146 and 147 mounted in suitable pillow blocks 148 and 149 on the ends of base 135. Shaft 147 is keyed to outer sprockets 139 and is driven through a chain 151 trained over sprocket 152 keyed thereto and a sprocket 153 on the output shaft of a gear train 154 secured to the base 135. The reducer 154 is driven by a hydraulic motor 155 supplied through conduits (not shown) from solenoid actuated, four way valve 158 on the side of base 135.

The motor 155 drives the ram inward to position the pallets on the conveyor 30 in the stacking station and retracts the ram to the position shown in FIGS. 3 and 5 according to a program in part controlled by a proximity switch PS2 on back end gate 25 sensing the presence of a pallet on conveyor 30 and the position of the ram 136 at its limits of travel sensed by LS6 at th maximum inward stroke and LS7 for full retraction. While limit switches can be positioned in any convenient position the pallet loading conveyor switches are shown with LS6 oriented below the plane of tracks 133 and 134 in a position to respond to the full advance of drive lug 143 of the ram and LS7 positioned at the rear of ram 136 to engage its back side when fully retracted. Inductively actuated proximity switch PS2 on gate 25 responds to steel pallets. When wooden pallets are employed they are provided with a metal strip forming a switch actuating means. Orientation of pallets on conveyor 30 in a position to clear stacker leg 35 and to advance into a proper stock receiving position is facilitated by a pallet guide 159 (FIG. 3) positioned longitudinally of the conveyor and made up of a face plate 161 mounted on a plurality of stanchions 162 extending from a base 163.

The pallet conveyor 36 in the stacking station comprises a series of steel slats 164 secured to the links of side chains 165 and center chain 166. These slats are transverse of the conveyor advance and thus are parallel to the pallet loading direction from conveyor 28 whereby they provide slides for the advance of the pallet into the stacker. Chains 165 and 166 are of the roller type wherein rollers protrude beyond the side links. The conveyor base is made up of three longitudinal beams 167 having flanges forming rails to provide bearing surfaces for the rollers of chains 165 and 166.

Chains 165 and 166 are driven from shaft 169 to which side sprockets 171 and center sprocket 172 are keyed. Shaft 169 is supported for rotation in suitable bearings 173 secured to the end cross beam 174 of the conveyor frame. Sprockets 175 and 176 carry the chains 165 and 166 at the opposite end of the conveyor by means of shaft 177 mounted in bearings 178 which are supported for longitudinal adjustment of the position of the shaft. Adjusting screws 179 establish the position of bearings 178.

Shaft 169 is driven by chain 181 which is trained over sprocket 182 keyed thereto and over sprocket 183 on the output shaft of reducer 184. Hydraulic motor 185 drives reducer 184 under the control of a four way solenoid actuated valve 186 supplying fluid to the motor through conduits (not shown). The programming controls to be discussed are responsive to conditions sensed to operate the valve 186.

The lead out conveyor 31 is made up of a plurality of rollers 188 mounted with their axes normal to the direction of advance of a pallet from the stacker and with their upper limits in the horizontal plane of the upper face of the slats 164 and the rails 133 and 134 of the side conveyor 28. Rollers 188 are mounted for free rotation about their axes by a frame made up of channel members 189. The drive of the slat conveyor 30 is utilized to advance loaded pallets on conveyor 31 from which they are removed as by a forklift truck.

Hydraulic fluid is supplied from a tank (not shown) located within the frame of conveyor 30. Pressure is developed in the fluid by pump 192 driven by electric motor 193 having an intake in the tank and an output manifold (not shown) distributing fluid under pressure to the several hydraulically operated elements of the system.

Pr gram controls The program controls for this system are set forth in FIGS. 6 through in across the line diagram form wherein the contacts controlling the actuation of relay coils, electric motors, solenoids and magnets are in general horizontal alignment therewith and the relay contacts controlled by the relay coils are related to those coils by a marginal key. In this key each line or horizontal band across the circuit is assigned a number between 301 and 386 as shown in the index column to the right of the drawings. Where a relay coil appears in a line, its reference character is set forth to the right of the line index number. Each contact controlled by a relay coil is identified by its location designated by the index number of the line in which it appears. In order to distinguish front contacts, those which are normally open and which close when the relay armature is pulled in, from back contacts, those which are normally closed and are opened when the relay armature pulls in, the index numbers of the back contacts are underlined in the marginal key.

The system is arranged for either manual or automatic control according to the setting of ganged slector switch 201 having contacts at lines 303 and 305 which can be set to an off condition in which all contacts are opened, a manual condition in which the contact at 305 is closed and an automatic condition in which the contact at 303 is closed. Power is supplied from a suitable alternating current source to the primary of transformer 202, the secondary of which feeds leads 204, 205, 206 and 207 through the power on relay contacts FCR of the sheet feeding device (the shear 11 of the example) and suitable fuses 203. Thus the sheet feeding device must be activated and have its power on relay energized to close contacts FCR as a prerequisite to any operation of this system since it is only with these contacts closed that leads 204, 205, 206 and 207 are energized.

If switch 201 is set for manual operation, relay 2CR is energized at 305 to close contacts at 308 energizing lead 208 and contacts at 317 and 32.2 in control circuits for relays 4CR and 6CR. With leads 204 and 205 energized, the circuits are enabled for the hydraulic pump motor control relay 1M at 307 and its indicator lamp 209 at 306, the sheet conveyor motor control relay 2M at 309 and its magnet control relay 26CR at 310, and the back end guide motor forward control relay 3MF and reverse control relay 3MR at 311 and 312. The pump motor controls are manually started by push button switch 211 around which a seal is developed by a contact of 1M at 308 when relay 1M is energized. Thereafter, the pump motor is stopped by normally closed stop push button switch 212. Sheet conveyor motor relay 2M is manually started by switch 213, sealed by contact 2M at 310 and stopped by switch 214. Back end gate positioning motor 74 is controlled by the interlocked ganged push button switches 215 to energize relay 3MF for lengthening the chute 14 by backing plate from bumper 24 and deenergize relay 3MR or by switches 216 to energize relay 3MR to shorten the chute by advancing plate 25 toward bumper 24. The safety cutouts for motors 93, 41 and 74 are shown as normally closed contacts in series with their control relays at 307, 309 and 311 respectively.

' Before proceeding to the details of operation of the system consideration will be given to the controls for the electromagnets 50 of the sheet conveyor. As shown in FIG. 6 at line 310, upon starting the sheet conveyor magnet control relay 26CR is energized to close its contacts in FIG. 10 at lines 382, thereby energizing leads 217 and 218 tothe magnet banks, only two of which are shown. Any time the system is activated and power is applied between leads 204 and 205, the relays 13CR through 25CR at lines 340 to 361 of FIGS. 7 and 8 can be energized. Relays 13CR through 18CR are selectively controlled to in turn control relays 19CR through 25CR 10 which control the banks of electromagnets 51 through 57 exemplified in FIG. 10'.

A three phase alternating current supply is connected in FIG. 10 to leads 219 220 and 221 through the fused disconnect 222. These leads supply electric motors 93, 41 and 74 through their respective control relay contacts 1M, 2M and 3MF and 3MR at line 3811. Leads 219 and 221 also supply the primary of transformer 223, the secondary of which is connected through fuses 224- to leads 217 and 218. Each bank of electromagnets 50 is normally connected across leads 217 and 218 through a continuously variable autotransformer 225 the output tap of which is connected through a fuse 2.26 to a full wave rectifier bridge 227 across which back to back rectifiers 228 are connected for surge suppression. The output of the bridge 227 is connected through a fuse 229 to the individual coils of the electromagnets 50. In FIG. 10" only the lead on bank 51 of twelve electromagnets fitted into the bridge section 16 of the sheet conveyor and a single typical bank 52 of six electromagnets providing the magnetic attraction over the initial twelve inches of the total seventy-two inches of length of conveyor 17, bank No. 1, are illustrated. It is to be appreciated that five additional banks, Nos. 2 to 6, each including an additional twelve inch increment of length of conveyor 17 toward its bumper 24 are similarly individually controlled.

In practice a sheet is held against the sheet conveyor 17 until the magnets attracting it are deenergized. Only a length of the conveyor corresponding to the length of the sheet being stacked and extending for that length from the bumper 24 is deenergized to drop the sheets into the stacking chute 14.

The magnet control relays 19CR to 25CR each have two back contacts in the supply leads to the magnets of the respective lead on on Nos. 1 to 6 banks. Accordingly, these relays are energized to demagnetize their respective zones of the conveyor. Normally each of the magnet control relay toggle switches as lead on switch 231 and switches 232 through 237 are in the open state as illustrated at lines 346 through 361. Magnet relays 19CR to 25CR are then controlled by the setting of selector switch 238 at 342 and the actuation of limit switch 81.8, as shown in FIG. 1, having a sheet sensing element in the path of sheet travel toward bumper 24 so that a sheet actuates switch 8LS as it advances to within about six inches of the bumper.

Selector switch 238 is calibrated in sheet lengths as six, twelve inch increments from twelve inches to seventytwo inches. Thus a twelve inch sheet will be released to the stacker chute 14 if only the final bank of magnets effective in the twelve inches immediately adjacent the bumper are demagnetized. With switch set at 12 inches relay 18CR at 345 is energized to close its contact at 363 thereby coupling relay 25CR of the No. 6 magnet bank control to leads 204 and 205 through lead 230. Thus the sixth bank 57 adjacent the bumper is deenergized and as the sheet is advanced toward the bumper it is released. Had the switch 238 been set at forty-eight inches the advance of the leading edge of the sheet would have caused energization of relay 15CR at 342. This would close contacts at lines 353, 356, 359 and 362 completing circuits from leads 204, to 230 to 239 to the coils of relays 22CR, 23CR and 250R. Magnet banks Nos. 3 to 6, 54 to 57 of FIG. 1, would be deenergized in this manner to reduce the magnetic attraction over the forty-eight inches of conveyor length adjacent the bumper 24. In a like fashion any of the other four increments of sheet length can be selected for demagnetization by switch 238.

On manual programming of the system, the positioning of the catchers 32, 33 and 34, of the end gates 27, of the pallet conveyor 30, and of the pallet loading conveyor 28 are all controlled manually. Lead 208 is energized and lead 240 is deenergized on the manual program.

Catchers are extended into sheet catching position by energizing relay 3CR at 314 through the closure of push button switch 241 at 315. Relay 3CR establishes a seal at contacts 3CR line 316 to bypass switch 241 and closes a contact 3CR at 319 with no effect on manual programming. It also actuates the catcher valve solenoids 242 and 243 at 370 and 371 of FIG. 9 by closing contacts 3CR at 370 between leads 206 and 207 and the solenoids. Once a pallet is positioned below the stacking chute to receive stacks the catchers can be retracted by operating normally closed push button switch 244 at 315 to deenergize relay 3CR and valve control solenoids 242 and 243.

On the manual program contact 2CR at line 317 enables manual control of the end gates 27 through control of the valve control solenoid 245 at 372 by means of relay 4CR at 319. The end gates are opened by energizing relay 4CR and solenoid 245 through closure of push button switch 246 at 317. A seal for relay 4CR around switch 246 is provided by contacts 4CR at 318. Relay 4CR is deenergized to deenergize solenoid 245 and close end gates 2 7by operating normally closed push button switch 247 at 317.

Manual control of the stack conveyor 30 is afforded through ganged push button switches 248 and 249' having contacts 248a and 2490s at 321, 248b at 322, and 248c and 2490 at 323. Depressing of switch 249 closes contact 249:: at 321 to energize relay SCR and opens contact 2490 at 323 to lock out relay 6CR. Relay SCR opens back contact SCR at 333 with no effect under manual control. It closes contacts SCR at 373 between the stack conveyor forward valve control solenoid 250 and leads 206 and 207 to cause hydraulic motor 185 to move in a direction to advance loads thereon from right to left as viewed in FIG. 1. Reversal of motor 185 is accomplished by deenergizing solenoid 250 and energizing stack conveyor reverse control solenoid 251 at 374 by closing contacts 6CR. Relay SCR is locked out and relay 6CR energized by operating reverse push button switch 248 to open contact 248a at 321 and close contact 248b at 322. Contact 248a has no effect on manual control. Both switches 248 and 249 are biased to their illustrated condition. Motion of the conveyor under manual control continues only so long as one of the push buttons is depressed and the other is released.

Manual control of pallet loading conveyor 28 is accomplished by operation of push button switch 252 at 335 to complete a circuit through back contact 12CR to pallet loading conveyor in control relay 11CR at 333. On the manual program this energizes solenoid 253 at 375 of FIG. 9. When the conveyor 28 advances its full stroke, it closes limit switch 6L5 at 336 indicating that it has advanced to a position which will properly orient a pallet. This energizes pallet loading conveyor out control relay 12CR at 336. This closes contact 12CR at 337 to seal the relay until loading conveyor end of stroke out limit switch 7LS at 337 is displaced from its normally closed to an open condition by the retreat of ram 136 to the position shown in FIGS. 3 and 5. Contacts 12CR at 376 connect the valve control solenoid 254 for controlling the fiow of hydraulic fluid to motor 155 of conveyor 28 in a manner to cause the withdrawal of ram 136.

On manual programming a pallet is positioned below the chute of the stacking station by pressing button 252. Button 247 is pressed to close the end gates and the catchers are retracted by pressing button 244. Any accumulated sheets are dropped to the pallet. When the desired stack has been accumulated, button 241 is depressed to extend the sheet catchers. Then the end gates are opened by pressing button 246 and the pallet with the stack is moved from beneath the chute by pressing button 249. The pallet in the stacker station is replaced after the stack conveyor is stopped by pressing button 252 to operate the pallet loading conveyor. If for any reason the pallet loading conveyor is extended and relay 12CR is deenergized, that relay can be manually energized to retract the conveyor by closing push button switch 255 at 338.

The automatic programming of the system is instituted by setting switch 201 to enable the circuits for relay 1CR at 303. Once the equipment is properly set up, the automatic cycle is instituted by closing the start cycle push button switch 256 at 303. If the bridge 16 of the sheet lead in conveyor is lowered to the sheet delivery station of shear 11, limit switch LS9 is closed, FIG. 1, and closure of switch 256 energizes automatic cycle relay 1CR. If bridge 16 is raised, limit switch LS9 is open to prevent automatic operation. Relay 1CR seals itself at 304 around switch 256 and is thereafter maintained until stop cycle push button switch 257 is opened at 303 or switch 201 is transferred from the automatic setting.

Automatic control relay 1CR conditions the control for automatic programming wherein the pallets are positioned in the stacking station automatically and the stacks are made up continuously and automatically. It closes contact 1CR at 306 to activate lead 240, primary supply to the automatic controls. It closes contact 1CR at 31 4 to enable the catcher control relay 3CR, contact 1CR at 319 to enable the end gate control relay 4CR, contacts 1CR at 320 and 323 to enable the stack conveyor advance and retract relays SCR and 6CR, contact 1CR at 325 to enable second time delay 2TD and relay 7CR controlling the closure of the end gates 27 and stopping of stack conveyor 30, contact 1CR at 326 to relay SCR which controls retraction of the catchers, and contact 1CR at 333 enabling pallet loading conveyor advance relay 11CR.

It will be assumed that the shear is issuing sheets of a size for which the stacker is set, that the end gates 27 are closed, that a pallet 23 has been properly positioned in the stacking station, and that the catchers are retracted so that sheets are being stacked upon the pallet. Inductively actuated proximity switches are utilizedto sense the stack and pallet positions It the automatic program. Proximity switch PS1 is mounted on one of side plates 26 adjacent the end gates 27 .and at the height of the sheet stack to be accumulated in order to sense the stack height in the stacking station. A suitable arrangement is to mount switch PS1 so that it is adjustable in height in accordance with the stack heights described. A second proximity switch PS2 is mounted on the back end gate 25 out of the path of the path of the sheets being stacked and responsive to the presence of a pallet which is available for stacking. A third proximity switch PS3 is located along the stack conveyor 30 and beyond the stacking station a distance less than the minimum length of sheet to be accommodated by the system from the longitudinal position of switch PS1. Thus if the system is arranged to handle sheets no shorter than twelve inches and if PS1 is located to respond to sheets within seven inches of the end gates 27 then PS3 is located no more than five inches down stream on conveyor 30 from the end gates, i.e. within twelve inches along the conveying direction of PS1.

In the stacking operation sheets fall past the proximity switch PS1. The momentary response of switch PS1 to those falling sheets is rendered ineffective on the system by applying its control through a time delay 3TD at 339 which is of the slow so operate variety and therefore does not respond to the brief passage of the sheets. When the stack builds to the height of switch PS1, the continued proximity holds contact PS1 at 339 closed to operate 3TD and close its contacts at 313 and 314 to operate lTD and 3CR respectively.

Time delay 1TD is a fast to operate, slow to release type having a normally closed contact at 325. Its contact opens at 325 to prevent operation of 2TD, 7CR and SCR. Prior to this time, these relays had been operated by the presence of the pallet in the stacking station to operate proximity switch PS2 and open its back contact at 331 so that both relays 9CR and 10CR are deenergized and their back contacts at 325 and 326 are closed.

Relay 3CR is energized through contacts 3TD and ICR to extend the catchers 32, 33 and 34 into the chute and prevent the addition of further sheets to the stack. Relay 3CRC closes a contact at 316 with no eitect on the automatic program. It closes a contact at 319 to provide a holding circuit around contact 3TD. It closes contacts at 370 to energize solenoids 242 and 243 and extend the catchers.

Extension of the catchers closes limit switch 1LS located on l-beam. 81 of side plate 26 to sense the position of the catchers and having a contact at 319 to complete a circuit for relay 4CR from lead 240 through contacts 3TD or 8CR and 3CR to lead 258, then contacts 1LS, 2TD and 1CR to coil 4CR. Contact 4CR at 318 closes with no effect on the automatic program. Contacts 4CR at 372 energize solenoid 245 to open the end gates 27.

When the end gates reach the full open position, limit switch 2LS on side plate 26 of FIG. 1 is actuated to close its contact at 320 to energize relay SCR. Contact SCR is opened at 333 with no effect at this time and contacts SCR at 373 are closed to energize solenoid 250. This advances the stack conveyor to move the stack through end gates 27 and out of the range of influence of switch PS1 so that contact PS1 at 339 opens when the trailing edge of the sheet stack is carried past it.

Opening of PS1 drops 3TD to immediately open contacts 3TD at 313 and 314. Opening of contact 3TD at 314 is Without effect at this time. Contact 3TD at 313 upon opening initiates the release of time delay for lTD at the end of which contact 1TD at 325 closes.

At this juncture two modes of operation are available. If the pallet is so loaded that the trailing edge of the stack is adjacent the trailing edge of the pallet as it is advanced on conveyor 30, the pallet is completely removed from the stacking station .and a new pallet must be loaded into the station to receive the sheets being accumulated by the catchers. If the trailing edge of the stack is substantially ahead of the trailing edge of the pallet, the advance of the stack can be terminated once it is removed from the stacking station and an additional stack can be accumulated on the vacant portion of the pallet remaining in the stacking station. In either event the time delay 1TD is of sufficient length to permit the stack conveyor to carry the trailing edge of the stack beyond the end gates 27 before contact lTD at 325 closes.

A fully loaded pallet will be considered first. When the stack and pallet trailing edges pass proximity switch PS1 and then end gates 27, contact 1TD is closed. At this time no pallet is available for stacking, hence another pallet should be loaded from conveyor 28 to conveyor 30. The absence of a pallet in the stacking station permits proximity switch PS2 to close its contact at 331 prior to the complete removal of the stack and the closure of contact 1TD at 325. Presence of the stack on the loaded pallet in the range of influence of proximity switch PS3, just beyond the end gates 27, opens back contact PS3 at 332. Thus relay 9CR is energized and relay IOCR is deenergized. Relay 9CR opens its back contact at 325 to hold relays ZTD, 7CR and SCR deenergized until the trailing edge of the pallet passes beyond the end gates and proximity switch PS3. When the pallet :passes beyond PS3, back contact PS3 at 332 closes to energize relay CR. At this time no pallet is in the stacking station and the catchers should be maintained extended.

Relay 10CR, when energized, opens back contact 10CR at 331 to drop relay 9CR and opens back contact 100R at 326 so that the closure of back contact 9CR at 325 permits energization of ZTD and 7CR While SCR is held deenergized. Time delay 2TD is of the slow to operatequick to release type and delays the opening of back contact 2TD at 319 upon the opening of the end gates. At this time it closes its back contacts rapidly to energize relay 4CR and close the end gates 27. Relay 7CR is ener- *gized to open its back contact at 320 and drop relay SCR, thereby terminating the advance of the stack conveyor 30.

Contact IGCR at .333 closes so that with the stack conveyor 30 stopped and the end gates 27 closed or closing the pallet loading conveyor 28 is activated by energizing relay llCR. This is accomplished from lead 240 through back contact SCR, closed whenv the stack conveyor was stopped, and contacts ltlCR, lCR and 12CR all at 333. Solenoid 253 of the advance control valve of the pallet loading conveyor is energized by closed contacts 11CR at 375. Relay 11CR seals itself at 334.

When the pallet on the loading conveyor has been pushed onto the stack conveyor 30 and beneath the stacking chute 14, limit switch 6-LS is closed to energize relay 12CR and proximity switch PS2 opens its contact at 331. Relay 12CR seals itself at contact 12CR line 337 until the conveyor is fully retracted to open limit switch 7LS at 337. It also drops relay 11CR and the pallet loading conveyor advance solenoid 253 by opening back contact 12CR at 333 and energizes pallet loading conveyor retract solenoid 254 by closing contacts at 376. As the ram 136 retreats limit switch 6LS at 336 opens and at the fully withdrawn position normally closed limit switch 7LS at 337 opens to drop relay 12CR. At this time the opening of cont-act PS2 at 331 has deene-rgized relay IOCR and opened the circuit for relay 9CR. Back contact 10CR at 325 closes on the drop of relay 10CR. Since the end gates are closed at this time limit switch 3LS is closed at 326 and relay 8CR is energized through contacts 1TD, 9CR, 10CR, 3LS and ICR.

Relay SCR opens the seal circuit for relay 3CR by opening back contact SCR at 319. The drop of 3CR opens its contacts at 370 to deenergize solenoids 242 and 243 thereby permitting the catchers to retract and drop the sheets they have accumulated during the pallet transfer onto the newly introduced pallet.

When the sheets being stacked have their trailing edges substantially in advance of the trailing edge of the pallet, the advance of the stack is terminated by the timing out of lTD to close its contact at 325 While a portion of the pallet is still available in the stacking station so that proximity switch contact PS2 at 331 is held open. Relays 9CR and IOCR therefore remain deenergized so that the closing of contact lTD energizes 2TD and 7CR and enables a circuit for relay SCR. Relay 7CR stops the advance of the stack conveyor by opening its back contact at 320 to drop relay SCR and stack conveyor advance solenoid 250 while the pallet remains in the stacking station. Time delay 2TD opens its back contact at 319 to deenergize relay 4CR and ends gates open solenoid 245. Thus the pallet is stopped with an unloaded surface in the stacking station below the chute and the end gates are closed to define the chute.

Full closure of the end gates closes limit switch 3LS at 326 to energize relay SCR and open its back contact at 319. This drops relay 3CR to deener'gize catcher control solenoids 242 and 243 and Withdraw the catchers. The accumulated sheets are dropped on the pallet and succeeding sheets accumulated until proximity switch PS1 is again actuated to institute another stack advance cycle. Such a cycle can either advance the stack out of the stacking station and locate another vacant portion of the pallet in the station for reception of a third stack on the pallet or if the insuflicient pallet area remains in the stacking station and proximity switch contact PS2 at 331 is closed the pallet is carried completely from the station and a new pallet inserted in the manner of the cycle first described.

Thus the present system includes an integrated sheet conveyor stacker and a pallet conveyor which has automatic controls for placing stacks of sheet metal on pallets to' the capacity of the pallets; The stacks are precisely located by a chute which encompasses the path of the sheets to within a very short distance of the pallet surfaces yet is manipulated to avoid inference with the movement of the stacks and introduction of new stack receiving surfaces.

In transferring stacks no interruption in the delivery of sheets is required since sheets are accumulated until the system is conditioned for the development of a new stack. Sheets of a wide range of sizes and gauges can be handled in the system since the dimensions of the chute can be altered and even light gauge sheets of substantial extent can be supported by the catcher arrangement including catchers intermediate the sheet sides at the leading and trailing edges.

It is to be appreciated that the invention lends itself to modification and that certain of its elements can be adopted advantageously to less refined systems or even individual elements of prior art systems. Accordingly, it is to be understood that the present disclosure is presented as illustrative of the invention and its several features and is not to be read in a limiting sense.

Having described the invention, I claim:

1. A system for stacking sheets upon a stack receiving means comprising, a first conveyor for a stack receiving means, a sheet receiving station at a location spaced from said first conveyor, a stacking station above said first conveyor, a sheet conveyor extending from said sheet receiving station to said stacking station, means to sustain sheets on said sheet conveyor, means to advance said sheet conveyor and sheets sustained thereon between said sheet receiving station and said stacking station, means to release sheets from said sheet conveyor at said stacking station and to permit said sheets to fall along a predetermined path and upon said stack receiving means on said first conveyor, sheet catchers mounted on opposite sides of said predetermined path, catcher drive means for extending said catchers into said path to catch and sustain sheets above said stack receiving means and for withdrawing said catchers from said predetermined path, first sensing means responsive to a predetermined magnitude of sheets stacked in said stacking station, means responsive to said magnitude responsive means for actuating said catcher drive means to extend said catchers, stack advancing means for said first conveyor to move said sheet stack from said stacking station, means actuating said stack advancing means in response to the extension of said catchers, means responsive to the sensing of the removal of said stack from said stacking station and the presence of a portion of a stack receiving means in said stacking station for terminating operation of said stack advancing means and for actuating said catcher drive means to withdraw said catchers from said predetermined path.

2. A combination according to claim 1 including second sensing means for sensing the presence of said stack receiving means in said stacking station, said control means being responsive to said second sensing means to actuate said catcher drive means to withdraw said catchers only in response to the presence of a stack receiving means in said stacking station.

'3. A combination according to claim 2 wherein said first sensing means senses the advance of the trailing side of said stack relative to said first conveyor path of advance to a position closely adjacent but removed from said stacking station, said stack receiving means being of greater lateral extent than said sheets whereby upon advance of a first stack from said stacking station by said first conveyor advance a portion of said stack receiving means remains in said stacking station for reception of a second stack.

4. A combination according to claim 1 including a second conveyor for a stack receiving means positioned adjacent said first conveyor and arranged to convey stack receiving means to said first conveyor, drive means for said second conveyor, second sensing means for sensing the presence of a stack receiving means in said stacking station, and third control means for said second conveyor drive means, said third control means being responsive to said second sensing means when no stack receiving means is in said stacking station for actuating 16 said drive means to transfer a stack receiving means to said first conveyor.

5. A combination according to claim 4 wherein said second conveyor includes a reciprocating ram drive for said stack receiving means, means to sense the displacement of said ram to a position of interference with said first conveyor, and control means to prevent the operation of said stack advancing means while said ram displacement sensing means indicates an interfering relationship between said ram and said first conveyor.

6. A combination according to claim 1 including a pair of opposed plates having major surfaces which are generally vertical and extend parallel to the path of advance of said sheets on said sheet conveyor and bound a portion of said predetermined path between said sheet conveyor and said stack receiving means, a gate on each of said plates, mounted for extension therefrom to guide the leading edge of said sheets along a portion of said predetermined path, and means to retract said gates away from each other and out of a projection of the major surface of said respective plates.

7. A combination according to claim 6 including means to sense the retraction of said gates, and control means to prevent the advance of said stack advancing means While said gates are displaced from their retracted position.

8. A combination according to claim 6 including means for adjustably positioning said opposed plates transversely of the path of advance of said sheets on said sheet conveyor.

9. A combination according to claim 1 including a pair of gates mounted for extension transversely of the path of advance of said first conveyor and having generally vertical surfaces to guide an edge of said sheets released from said sheet conveyor along a portion of said predetermined path, means to retract said gates away from each other and clear of the path of advance of the sides of a stack of sheets advanced by said first conveyor, said first sensing means sensing the removal of a stack to a position clear of and closely adjacent the path of retraction of said gates, and means to extend said gates in response to said first sensing means.

10. A combination according to claim 1 including a pair of gates mounted for extension transversely of the path of advance of said first conveyor and having generally vertical surfaces to guide an edge of said sheets released from said sheet conveyor along a portion of said predetermined path, means to retract said gates away from each other and clear of the path of advance of the sides of a stack of sheets advanced by said first conveyor, said first sensing means sensing the removal of a stack to a position clear of and closely adjacent the path of retraction of said gates, means to extend said gates in response to said first sensing means, and second sensing means for sensing the presence of said stack receiving means in said stacking station, said control means actuating said catcher drive to retract said catchers only in response to the coincidence of the presence of a stack receiving means in said stacking station and the extension of said gates.

11. A system for stacking sheets upon a stack receiving means, comprising a stacking station to accommodate at its lower limit a stack receiving means, a sheet receiving station, a sheet conveyor etxending from said sheet receiving station to a position above said stacking station means to release sheets from said sheet conveyor at said stacking station and to permit said sheets to fall along a predetermined path and upon said stack receiving means, a support frame for said sheet conveyor, a pair of gates supported from said support frame at the forward end thereof and having generally vertical first surfaces parallel to a vertical projection of an edge of sheets carried by said sheet conveyor and defining a longitudinal portion of said predetermined path, said first surfaces being located adjacent a vertical projection of opposed forward corners of said edge of sheets, a second generally vertical surface on each gate fixed with respect to said respective first surfaces at the angle of the vertical projection of opposed corners of said edge of sheets whereby each of said respective first and second surfaces define a projection of the corner of said sheets to precisely orient the forward end of said sheets, a pivotal mounting for each of said first surfaces of said gates having a pivot axis generally vertical and outward of said path and said second surface whereby the pivoting of said gates retracts said second surface from said path, and drive means to retract said gatesharound said pivot axes and away from each other and clear of a horizontal projection of the edge of the stack of said sheets accumulated on said stack receiving means.

References Cited UNITED STATES PATENTS Daves et a1. 2146 Otfutt et a1. 21441 X Stevenson 214-6 Buccicone 214-6 Hudak 271-74X Buccicone 271-88X ROBERT G. SHERIDAN, Primary Examiner.

R. J. SPAR, Assistant Examiner.

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