US2647645A - Sheet stacking mechanism - Google Patents

Description

Aug. 4, 1953 Filgd June 6. @949 A. F. PIERCE SHEET STACKING MECHANISM 6 Sheets-Sheet 1 IT H f n 1| 74 /v 46 46 W 1 In 56 l 66 50 g l I INVENTOR. ALFRED FRANK PIE/ace- 70 V ATTORNEYS 1 72 REYNOLDS a BEACH BYM/CJM 4, 1953 A. F. PIERCE 2,647,645

SHEET STACKING MECHANISM Filed June 6, 1949 6 Sheets-Sheet 2 E JNVENTOR.

7 ALFRED FRANK PIERCE ATTORNEYS REYNOLDS 5 BEACH M/a): M

Aug. 4, 1953 A. F. PIERCE 2,647,645

SHEET STACKING MECHANISM Filed June 6, 1949 6 Sheets-Sheet 3 IN VEN TOR.

ALFRED F'KA NK PIERCE I ATTORNEYS H REYNOLDS & BEACH H BYW/MM 4, 1953 A. F. PIERCE 2,647,645

SHEET STACKING MECHANISM Filed June 6, 1949 e Sheets-Sheet 4 N q X l b o I N VEN TOR.

ALF/e51: FRANK PIERCE ATTORNEYS REYNOLDS a: BEACH BYW/QJE W Aug. 4, 1953 A. F. PIERCE SHEET STACKING MECHANISM 6 Sheets-Sheet 5 Filed June 6, 1949 INVENTOR ALFRED F'EANK PIERCE ATTORNEYS REYNOLDS & BEACH Aug. 4, 1953 A. F. PIERCE SHEET STACKING MECHANISM 6 Sheets-Sheet 6 Filed June 6, 1949 ///.fi/v// WNW //v/// @P ww iv 3 ow JNVENTOR. ALFRED F'RANK PIERCE ATTORNEYS REYNOLDS & BEACH BY WWW Patented Aug. 4, 1953 SHEET STACKING MECHANISM Alfred Frank Pierce, Tacoma, Wash., assignor to American Manufacturing Company,

Inc.,

Tacoma, Wash., a corporation of Washington Application June 6, 1949, Serial No. 97,411

11 Claims. (01. 214-6) In modern plywood factories presses of the multi-platen type, because of their large load capacity, are used almost universally for binding the plywood panels. In this type of press the panels bonded are not arranged in a solid column or stack but are separated, individually or in groups, by a series of press platens suppotring them, which can then apply heat directly to the individual panels for activating the bonding adhesive used. Preferably unloading of the press is accomplished by discharging the entire load of panels as a single group by sliding them edgewise off the press platens and into open shelves of a receiving rack stationed adjacent to the offbear side of the press. This unloading technique enables putting the press back to work immediately on a fresh load of panel stock, whereas the receiving rack can be unloaded and the panels stacked during the ensuing period while the press is in operation.

In the past the unloading and stacking of panels from the rack has been manual. However, as they were rather inconveniently disposed in the rack to be grasped and removed by hand, and are usually too large and heavy for one man alone to handle, this unloading and stacking operation required virtually the full time of two men working as a team.

My present invention relates to a method and to novel apparatus operating automatically in removing the panels from the receiving rack and stacking them in a desired location for removal by a lift truck or similar conveyance. The invention includes, among various features, the method, the automatic stacker, and the combination of such an automatic stacker and a re ceiving rack cooperating therewith, the whole occupying a minimum of floor space.

As a further object the stacking apparatus is compact, reliable in operation and comparatively inexpensive to manufacture and maintain. Moreover, it operates rapidly, so that there is no delay between readiness of the press todischarge a load of panels into the rack and completion of the operation of unloading the precedingbatch of panels. v

Still another and more specific object is to overcome the evident physical problem of withdrawing the expansive, heavy, yet flimsy, horizontally disposed panels from between the narrowly spaced shelves which they occupy in the raclgand transfer them to the top of a stack with minimum lost motion and delay. There are complications in doing this in that the stack grows progressively from zero to a selected height.

Moreover, the panels emerging successively from the rack shelves must do so at the different heightsof such shelves. It is obvious that if the emerging end of a panel or panel group were allowed, unsupported, to droop increasingly in process of emerging from a rack space, the trailing end of the panel or group would eventually spring upward against the rack shelf above it, halt the movement of the panel or group, and possibly cause damage. It is therefore evident that the panels cannot simply be ejected haphazardly from the rack shelves, and allowed to drop as they may. v

In light of these circumstances my invention comprises novel panel unloading and stacking apparatus having a-djus'tably elevated conveyor means cooperating with the receiving rack and operable to move the panels one after another edgewise from the rack shelves in successive order, preferably commencing with the lowermost and progressing to the uppermost panel on the rack, into position for deposit on top of the stack of panels being formed. Coacting with such conveyor means is a panel stacking plat form disposed adjacent to the rack and automatically adjusted in its elevation differentially in relation to the panel conveyor means, to maintain the top of the stack at all times just slightly below the changing elevation of the emerging panels. f

Preferably such elevated transfer conveyor means is of the continuous belt or similar type, and comprises a horizontal row of belt conveyors which extend lengthwise of the rack into its shelf spaces to engage the bottom faces of the panels, lift them off their respective shelves and transport them edgewise therefrom to the stack, successively. In. order to permit these conveyor elements to enter the rack spaces to engage and remove the panels in that manner, and to allow the conveyor elements to be elevated directly through the rack progressively from the level of one rack shelf to another, the rack shelves are constructed in special cantilever fashion.

A further feature of the invention resides in the provision of elevator means carrying both the ,conveyor means and the stack-supporting platform, the latter being carried by a jack which is preferably of the hydraulic type and valve-controlled automatically in response to operation of the conveyor means transferring successive panels from the rack to the stack being formed on such platform. In the illustrated and preferred case the valve-controlled loaded hydraulic jack is intermittently released to descend by 9 grawlty an incremental amount relative to the conveyor means, such amount corresponding approximately to the thickness of a panel or group of panels carried by one shelf of the loader, each time a panel or panel group is transferred to the stack on the platform. More particularly, the control valve which permits this incremental descent of the hydraulic jack is preferably controlled by mechanically actuated switch means set to open the hydraulic relief valve with the reception of each new panel or panel group on the top of the stack, and to close such valve auto matically after the stack has descended a distance approximately equal to the increased height of the stack.

These and other features, objects and advantages of the invention will be understood better by reference to the following more detailed description and the accompanying drawings.

Figure 1 is avertical sectional view of the combination stacking mechanism and receiving rack, taken transversely thereof on line :|-l in Figure 3, part of the rack, shown in broken lines, being broken away; Figure, 2 is a similar view showing the stacking mechanism in a different operating position. Figure 3 is a horizontal sectional view of the same taken on line 33 of Figure 1.

Figure 4 is a horizontal sectional View of the stacking mechanism taken on line l-fi in Figure 1, parts, such as of the panel conveyor elements, being broken away for convenience in illustration.

Figure 5 is an enlarged detail of a portion of the stacking mechanism and receiving rack as shown in Figure 2.

Figure 6 is an end elevation View of the stackingrnechanismfrom its side facing the receiving rack.

Figure 7 is a detail view of limit switch mechanism shown in Figure 6.

Figure 8 is a side elevation view of the receiving shown in Figure 8, are designated .P in other 7 figures. The invention itself resides broadly in the method of handling the panels after their discharge from the press into the receiving rack, andin the combination receiving rack and stacking mechanism implementing such method. However, the invention is not limited in its application to the handling of plywood panels or to thehandling of plywood panels received from a multiplaten bonding press, but extends to any similar type of situation involving the handling of panels or similar objects forstacking purposes generally.

The multiplaten plywood bonding press illustrated in Figure 8 is of conventional form, generally comprising a stationary head or upper press block I 6 supported by standards It, a lower reciprocable press block or ram 20, usually hydraulically actuated, and a plurality of work separating platens 22 arranged in series between the upper block [6 and ram 2!]. The press is loaded by inserting stock for one or more panels between each successive pair of platens 22 which are separated typically about three inches to receive the stock when the press is open. The hydraulic ram 26 is then raised to pick up the lowermost platen 22 carrying panel stock, then the next successive platen and the next, progressively, one platen resting on the other ith the plywood panel stock interposed therebetween, until the press platens 22 and panel stock form a solid column which is pressed to the desired degree by ram 29, forced against press block it for the requisite bonding period. At the same time, heat may be applied to the panels by the press blocks and individual platens to activate the bonding adhesive used.

When the press is opened by descent of the ram 26 to restore the original three-inch spacing between platens 22 the panels are discharged from the interplaten openings by suitable means (not shown) into the waitin' receiving r oi; l2 stationed adjacent to the The height of a twenty opening press when open, between block 55 and ram 2t, may be in the vicinity of ten for example. This means that the receiving rack it must be of corresponding height, as the individual rack shelves 2 5 must lie rohmately in horizontal registry with the individuai press platens 22 to which they correspond the panels are to be transferred from the press to the rack by simply moving them horizontally edgewise, which is the preferred method.

With a receiving rack in the vicinity of ten feet in height above floor level, and with plywood panels four feet by eight feet and larger, in groups perhaps as much as two inches thick, carried by the shelves of the rack to its full height, one may readily appreciate the difliculty of taking the panels out of the rack and stacking them when done manually. By the present invention the receiving rack is constructed specially and cooperates with novel mechanism which automatically unloads the rack and stacks the panels. All of this is done in the few minutes between the time the press closes on a succeeding batch of panels and later opens with those panels freshly bonded and ready to be discharged into the receiving rack.

While various details of the rack 12 are entirely optional in form, there are certain features about it which are important according to the practice of my invention. Of importance is the general construction of the rack shelves and the general manner in which they are supported from the rack framework. The rack framework itself is subject to considerable variation and consists in the present case of a base 2% and upright rec-- tangular side frames 28 braced by diagonal mem-- bers 3i! connected to the base. For considerations of convenience not here important the base 25 has wheels 3?. at its four corners which ride on supporting rails 3d, extending lengthwise between the press and the stacking mechanism I l.

One vertical side of each rectangular rack frame 28 is situated at the end of the rack nearest the press iii. The other and parallel side of each such frame is situated generally intermediately between that end and the opposite end of the receiving rack. Between these vertical side members of the rectangular frame 223 on opposite sides of the rack extend a plurality of structural members 36, such as angle iron or the like, arranged horizontally and at vertical intervals corresponding to the spacing between platens 22 of the press I0 when the press is open. If the press with which the receiving rack is to be used accommodates twenty plywood panels, then there will be at least twenty of these horizontal structural members 36 in each of the two vertical rows bridged between elements of the opposite frames. Thesehorizontal structural members 36 constitute supports for individual rack shelves or form a part thereof. Preferably such shelves are constructed in the manner herein illustrated (see Figures 8 and 3), comprising one or more longitudinal members 38 extending substantially the full length of the rack between its ends adjacent to the press and the stacking mechanism i4, respectively. The longitudinal members 38 in each shelf are spaced apart widthwise of the rack at suitable intervals for a purpose to be explained later herein.- They are each connected to the two horizontal structural members 36 of the rack for such shelf, and project cantilever fashion a substantial portion of their length from their intermediate point of support, namely, on the intermediately'located structural member 36, toward the end of the rack adjacent to the stacking mechanism l4. 1 v

As much as one-half or more of the total length of members 38 may project in this manner, their free ends not being connected in any manner to each other or to any other part of the rack, so that endwise of the rack, viz. from press I!) to stacking mechanism I4, the shelf spaces are completely open throughout, and heightwise the rack is similarly unobstructed in that portion of its length between the projecting ends of the cantilever shelf members 33 and their generally intermediate p-oints of support. Preferably the number of such longitudinal members included in each rack shelf is no greater than necessary, and they are distributed, to provide ample support to the freshly bonded plywood panels discharged from the press, without excessive sagging of the panels between supporting rack elements.

The panels moving from the press onto the rack shelves cannot move edgewise far out of line laterally because of the presence of the rectangular side frames 26 of the rack, which serve as retainer guides, although they will usually not be contacted by the panels. Each of the longitudinal shelf members 38 carries a plurality of rollers 46 to support the panels and minimize fric-- tion in sliding the panels on and off the rack shelves The shelvesare in the illustrated case of such proportions that the longitudinal dimension of the panels supported thereby extend widthwise of the rack, so that a long edge of the panel is its leading edge in moving through the rack from thepress toward the stacking mechanism l4.

The stacking mechanism includes a plurality of generally horizontal conveyors 42, preferably of the belt type, arranged substantially in horizontal registering and carried for bodily movement up and down through the open spaces between the cantilever elements 63 comprising the rack shelves. As shown in Figure 3, four of these conveyors are employed, located at intervals across the width of the receiving rack I2, Their function is to engage the underside of a panel P or a group of panels on a rack shelf and transfer the panel or panel group from such shelf to the top of a stack S of panels being formed by the stacking mechanism, as will be explained. Generally these conveyors 42 extend lengthwise of the rack far enough into the rack shelf spaces so that when they engage the underside of a panel and lift it from the rack the conveyor beltswill carry a sufficient'part of the total weight of the panel and'contact a sufficient surface area thereof to draw the panel from its remaining supporton the shelf and set it into motion on the -conveyor belts toward the stack. These conveyors 42 are mounted on the side of an elevator cage or frame 44 to project cantilever fashion into the rack shelf spaces, interdigitated with the cantilever shelf supports 38 (Figure 3), and to be moved up and down by such elevator.

The stacking mechanism also includes a panel stacking platform 46 carried by a jack 48 which in this case is preferably a hydraulic jack mounted directly in the base of the elevator frame 44, as shown (Figure 1). Initially the stacking platform 46 is positioned by the hydraulic jack 48 on the elevator frame slightly below the level of the belt conveyors 42. When the stacking operation is to be commenced, the belt conveyors, thus positionally related'to the platform, are disposed by'the elevator in their lowermost position, name- 1y, beneath the bottom panel or panel group P in the loaded rack. The conveyor belts are then started and the elevatorc-arrying the conveyors, the stackin platform and jack, gradually raised until the conveyor belts engage first the panel loaol in the bottom rack space, then that in the matically reversed and the entire elevated mechanism lowered until the conveyors have descended to their initial positions at the base of the rack ready for commencing the unloading of the next batch of panels therefrom.

.During the time the conveyors re ascending through the rack spaces successively to unload the panels the stacking platform 46 supported by the jack lfi is being lowered by increments on the elevatorframe in relation to the conveyors, so that as the growing stack of panels on the platform increases in height, the top of such stack will nevertheless be maintained at a level always slightly below that of the ascending conveyors.

Thus, the panels transferred by the conveyors do not have to drop or tilt downward appreciably in coming to rest onthe stack. Moreover, the top of the stack will never be so high as to obstruct such transfer. After the stack has grown to the desired size, perhaps comprising two or three press loads of panels, it may be removed from the stacking platform by a lift truck or similar conveyance and a new stack commenced. At that time the stacking platform is restaged in relation to the conveyors so that the platform will again be located only slightly below the level of the conveyors, preparedto receive the lowest panel in the receiving rack. I

Having in mind these general features of the apparatus certain other details of construction and operation of its illustrated form will now be explained. Because it isusually convenient to mount the press and to support the receiving rack at'fioor level, it is necessary to mount the elevatormechanism on. a sub-floor 56 (Figure l). The elevator frame consists of four corner posts 52 whichextend from the sub-floor 56 to a height somewhat above the top of the receiving rack and serve as guides for travel of the elevator frame 44 and stacking platform 46 movable differentially in relation to such frame. At its top the elevator framework is comp-leted by a suitable girder str1ict1ire54 which spans between the four posts to constitute a support for the elevator hoist -mechanism'.- 'I'he-- latterin'cludcs an, electric motor drive unit 56 (Figures land 6 connected by'a chain and sprocket transmission to a central drive shaft 58 which rotates two cable drums 60, one at each end. At the four corners of the top'of' the elevator framework are located cable guide sheaves 62, over which run the hoist cables E4 connected to the corners of the base of the elevator cage, as shown in Figures 1 and 6, for example. The hoisting mechanism as such is rather conventional and should require no further description.

The minimum height dimension of the elevator frame or cage 44 between its base 56 and the mounting'location thereon of the conveyors 42 is governed primarily by the desired maximum height of a stack of panelsto be accumulated on the stacking platform 45. The length of the barrel or cylinder 58 of the hydraulic jack 48 will be governed by substantially the same considerations. This hydraulic cylinder, mounted on the elevator projects downwardly therefrom and is accommodated in a sub-floor pit Ill in the lowered position. of the elevator 44. The cylinder is of the single-ended type, having a fluid conduit connection '52 (Figure 1) only at its bottom end and asolenoid actuated control valve I 30 in such fluid conduit to control actuation of the hydraulic piston 14 cooperating with such cylinder, whereby to establish the height of the stacking platform on the cage 44 and in relation to the conveyors 42.

The details of the stacking platform 46 and the elevator frame or cage 44 are not especially pertinent to an understanding of the invention. Suffice it to say that the elevator, the stacking platform, and the base of the elevator cage are suitably constructed to carry their respective loads, and are suitably guided for vertical travel on the corner guide posts 52. On its end remote from the receiving rack the stacking platform preferably carries two or more upright rods I6 which serve as stops for the panels sliding across the top of the stack being formed on the platform, carried by momentum from the belt conveyors 42 to their rest positions on the stack. At its end adjacent to the receiving rack the elevator cage embodies a vertical framework 18 (Figure 6) which supports the belt conveyors and certain other mechanism near its upper end, and which has suitable slide elements 80 (Figure 8) at each end by which it is guided from cornerposts 52 for vertical travel.

The upper end of this framework I8 carries projecting arms '82 which actuate slide rods 84 for movement up and down with the elevator. The upper ends of these slide rods telescope within cylindrical guide tubes 86 supported from the ceiling and braced laterally from the elevator framework, as shown (Figure 1). These rods serve as stops to prevent panels discharged from the press into the rack overtraveling the rack shelves by momentum in the direction of the stacking mechanism. They do not interfere with transfer of the panels from the rack to the panel stack by belt conveyors 42 because their lower ends are maintained a short constant distance above the tops of the conveyor belts to clear the panels thereon, and because the rod-supporting arms 82 are mounted on and move vertically with the conveyor-supporting framework 18.

As shown in Figure 6, this portion 18 of the elevator cage or frame 44 carries at its top an electric motor drive unit 88 connected by a transmission chain and sprocket, encased in a guard 99, to a countershaft 92 which extends th width of such elevator frame portion, and is journaled thereon. This countersliaft rotates belt conveyor drive pulicys 94 (Figure 5) in each of the respective belt conveyors 42. As shown best in this figure, each belt conveyor additionally includes a guide sheave 96 journaled at the outer end of a supporting arm 98 which is pivotally supported on the elevator cage framework 18 by pivot 99 for swinging about a horizontal axis defined thereby. This arm carries a second belt guide sheave I06 at an intermediate location between pulleys 94 and '96. The conveyor belt Hi2 passes around all three of these sheaves which locate its upper stretch appreciably above the top of the arm or any other puts carried-thereby which might tend to interfere with free movement of the panels carried by the belts. Belt tension is maintained oradjusted by providing the guide sheave with an adjustable journal support IM to establish its position lengthwise of the arm.

The arm fit is mounted pivotally on pivot 99 in the manner described as a protective or safety feature. In the absence of special. provision, should a panel being transferred from the rack to the stack on the elevator platform by the belt conveyors be interrupted for any reason and fail to move clear of the rack before the progressively ascending belt conveyors 42 raise the panel so far as to contact the rack shelf next above, there will bea complete blockage in operation of the stacking mechanism because the stopping of the panel in that intermediate position will check further ascent of the elevator. The special provision which circumvents any such possibility comprises yieldable supports for the pivoted belt conveyor arms which normally hold such arms generally level, but which can yield if necessary to allow for some additional ascent of the elevator cage even after a panel becomes caught between a rack shelf and the belt conveyor in the manner previously indicated, without damage to the mechanism as a whole. The yieldable support for a cantilever conveyor arm (Figure 5) comprises-a spring H16 reacting upwardly against the arm from a support bracket 03 to maintain the arm normally in horizontal position projecting its conveyor belt endwise into the receiving rack. The arms position may be varied by means of a support iii} adjustable for raising and lowering the base end of the spring as desired.

In addition, the precautionary support construction of the belt conveyors includes a safety switch H2 arranged to be actuated by excessive downward deflection of a conveyor arm in the event of a panel P being caught between the belt conveyor and the rack shelf next above the panel, as shown in Figure 5. This switch H2 is included in the energizing circuit (not shown) for the elevator hoist motor 55; preferably also in the energizing circuit for the belt conveyor motor 88. The motor-energizing circuits may be conventional and need no illustration herein.

The switch may include a control lever I M actuated by an arm H6 whose base end is pivoted on a-supporting bracket l I 8. This actuating arm is depressed by a rod or bolt iiill interconnecting the same with the conveyor arm 98 so that as the latter is forced to swing down by a predetermined amount relative to the elevator cage, the actuating arm I it releases the lever I l of switch H2, which is spring-pressed toward open position and deenergizes the electric motors operating the stacking mechanism. Preferably each of the four belt conveyors and sup-porting parts thereof have similar switch mechanism since it is possible that blockage of the ascent of only one of the belt conveyors may take place while the others are free to rise, and it will be just as desirable to stop the motors in that event as in the case where all are blocked. a I

A greater degree of positveness in the conveyance or transfer of panels from the rack to the stacking platform is obtained by provision of arm-supported driven hold-down rollers I32, shown in Figures 1 and 2, which press the panel or panel group down against the belt conveyors I82 and cooperate with such conveyors in moving it, after being moved far enough from the rack to pass beneath such rolls. These rollers are belt-driven from pulleys I46 on a countershaft I34 (Figure 6), driven by the same chain mechanism which drives countershaft 92 from drive unit 88. Such countershaft also serves as thesupport for arms I36 which carry the rollers I32. These arms are free to swing downward toward their respective belt conveyors I82, being journaled on shaft I34, but are limited in their downward displacement so that the rollers I32 cannot actually contact or wedge past the conveyor-belts beneaththem, although they can readily press against the top of a panel resting on such belts. Their lowermost positonis established by an adjustable stop I38 (Figure 2 The arms are swung downward aflirmatively and their rollers I32 forced against the panel, producing a firm grip on the panel when being trans ferred, by virtue of the torque applied to the arms as an inherent result of the turning of the belt drive pulleys I46 which drive the roller drive belts I42. Such rotation of the arms is resisted by a panel on the belt conveyors I62, or by the stop I38 when no panel is interposed between the conveyors 42 and the rollers I32.

The upper end of the elevator cage or frame 44 also carries a bracket I2I, shown in Figure 2, to which a control arm I22 is pivotally connected. This swingable arm extends laterally over the stacking platform 46 and carries a roller I24 at its swinging end, which is adapted to rest directly on top of the stack of panels being formed on the stacking platform. The supported end of the-arm is arranged to actuate a switch I 26 which operates the solenoid valve I 36 (Figure, 1). Thearm has a normal position in which such switch is open and the solenoid valve closed to prevent discharge of hydraulic fluid from the cylinder 68, and thereby maintain at a constant elevated position the jack and stackng platform relative to the elevator cage. However, if the armis raised slightly, namely,- by the thickness of a panel, from this normal position, it closes the switch I26 which opens the solenoid valve I30 to allow discharge of hydraulic fluid from the cylinder, enabling the platform to descend by its own weight on the jack.

As the platform descends the arm I22 resting on the stack of panels swings downward, and after its swinging end has descended an amount approximately equal to the increase in height of the panel stack the switch I26 is again opened and the discharge of fluid from the cylinder cut off. It will therefore be evident that each time a panel or panel group moves from the belt conveyor onto the stack and slides beneath the roller I24 it raises the swinging end of arm I22 to close the valve control switch I26, and initiates descent of the jack. By ths means the top of the stack of panels on the stacking platform 46 is always maintained slightly below the level of the belt conveyors, as desired.

The upper and lowerlimits of travel of the ele-' vator cage and belt conveyors carried thereby are established by means of limit switch mechanism illustrated in Figures 6 and '7. Such mechanism includes a switch control rod I44 extending generally the height of the elevator structure. The weight of this rod is carried at its upper end by support means including a switch box I46 having apertures through which the rod is guided for limited vertical displacement, and a spring I48 reacting against a fixed collar I50 at the upper end of the rod to urge such rod normally into anupwardly displaced position. Inside the switch box I46 the rod carries a cam sleeve I52 constituting a switch-actuating element. Two switches are arranged inside the switch box, an upper switch I54 arranged to be actuated by the sleeve I52 upon upward movement of the rod I44 to, reverse the electric motor operating thehoist mechanism, and a lower switch I56 arranged ,to be actuated by such sleeve I52 to stop the hoist motor by downward displacementof such rod. The straight portion of the rod depending from the switch box carries thereon two fixed collars, an upper collar I58 and a lower collar I68, spaced apart by the desired length of travel of the elevator. The base of the elevator cage has an element I62 whichprojects laterally therefrom to slide over the section of rod I44, between these collars, and raise and lower the rod by contacting the collars I58 and I60, respectively.

During ascent of the elevator cage, when the abutment element I62 strikes the upper fixed collar I 58 it thereby raises the control rod I44, which trips the switch I54 and reverses the electric motor driving the hoist mechanism, to cause the elevator to descend. When the elevator cage approaches the desired lowermost position this abutment strikes the fixed collar I66 and, against the force of spring I48, depresses the control rod I44 to actuate the switch I56 and stop the hoist drive motor. The drive motor can then be started again only by external means, such as bya separately controlled switch of thepush-button type which will be depressed momentarily by hand at a desired later time, bypassing the switch I56 in a suitable hoist motor energizing circuit, until the elevator cage has ascended again sufficiently to break the engagement of abutment I 62 with collar I60 which has been held depressed by the abutment to hold switch I56 open. It will be obvious that various other control arrangements, could be utilized to control stopping and starting of the elevator and to limitits vertica1 travel in either direction.

As an added precaution, or in lieu of limit switches I54 and I56, I may provide an additional limit switch I64 (Figure 4), the same to be driven by a chain I66 synchronously with the hoist drive shaft 58. The switch I64 amy be so constructed and arranged that after a predetermined number of rotations of hoist drive shaft 58 in one direction or the other to the desired extremepositions of corresponding travel of the elevator cage 44, the switch will operate to reverse or deenergize the hoist motor in unit 56,

as desired. I

In general, it will be evident that the invention is not confined to the particular embodiment herein illustrated or to the details of such embodiment, but may assume various forms. For example, any elevator or hoist mechanism which causes the stacking platform and the transfer conveyors to be elevated differentially in order to 7 maintain the top of the stack of panels on the stacking platform even with or a desired distance below the level of the transfer conveyors at all times may be employed. That is the important thing, although the preferred manner of implementing it is that illustratedin which the hydraulic jack or other means supporting the stacking platform is mounted directly on the elevator means which carries the transfer conveyors. Another and perhaps more obvious way of obtaining relative elevation of platform and transfer conveyors would be by use ofa jack mounted stationarily and coordinated with movement of the elevator carrying the conveyors. Likewise, other forms of transfer conveyors may be employed to remove the panels from the receiving rack and deposit them in a stack on the platform.

Moreover, in connection with the manner in which the conveyors and stacking platform are elevated, it will be evident further that the hoist mechanism raising the elevator cage 44, hence the transfer conveyor 42, need not be operated continuously, but may be caused to operate by progressive increments, so that the transfer conveyors 44 will be elevated in stages, stopping at each receiving rack shelf long enough to transfer the panel or panel group supported thereon to the stacking platform, and then moving up to the next shelf, etc. Likewise, the stacking platform supporting jack need not be lowered by increments each time a single panel or panel group is transferred to the stack, but may be lowered in larger steps initiated with the reception each time on the stack of an additional predetermined number of panels or layers. Alternatively, the stacking platform could be lowered relative to the transfer conveyors at a generally constant rate, whether the transfer conveyors were to be raised by increments or steadily. It is important, however, these two principal moving elements may be motivated, that the top of the stack of panels be kept always belowthe level of the transfer conveyors, but not so far below that level that the panels must drop excessively in moving from the transfer conveyors to the top of the stack. Otherwise they might be damaged or become caught and obstruct operation of the system.

As a matter of convenience in removing the stack of panels from the stacking platform, I prefer to lay a group of skids or spacers lSB (Figures 2 and 6) on top the stacking platform to serve as the support for the panels thereon. These skids are oriented parallel to the directionof movement of the panels onto the stack, so that a lift truck or similar conveyance can pick up the stack by inserting its lift fork beneath it.

I claim as my invention:

1. Panel stacking apparatus comprising a stacking platform, means operable to. deliver panels at depositing locations directly above said platform at various elevations for stacking on said platform, and platform support means operable to adjust automatically the elevation of said platform in relation to the height of the stack of panels on said platform and the elevation of the location for delivery of each particular panel by said delivery means, to dispose the top of the stack not more than a predetermined small distance below each such panel'delivery location irrespective of the elevation thereof.

2. Panel stacking apparatus defined in claim 1, wherein the panel delivery means comprises conveyor means operable to transfer panels edgewise in a generally horizontal direction to the di livery location, and conveyor elevator means carrying said conveyor means and guided for vertical movement to vary the operating height thereof.

3. Panel stacking apparatus defined in claim 2, wherein the platform support means is carried by the conveyor elevator means.

4. Panel stacking apparatus defined in claim 2, wherein the platform support means is carried by the conveyor elevator means and comprises a hydraulic jack, and means controlling said jack to effect descent of the platform by successive increments automatically in response to successive panel deliveries by the conveyor means to the top of the stack on the platform.

5. Panel stacking apparatus comprising a stacking platform, a panel-supporting rack disposed adjacent to said stack-ing platform and having a vertical series of panel-receiving shelf spaces opening edgewise toward the space above said platform, panel conveyor means operable to engage and transfer a panel in the lowermost shelf space to the platform for depositing the same thereon, said platform normally being disposde in elevation slightly below said lowermost shelf space, elevator means operable to elevate said conveyor means progressively so to engage and transfer, one after another, successively, panels supported in the higher shelf spaces of said rackto the stack of panels on said platform, means supporting said platform and operable to lower the same relative to said conveyor means, and control means, actuated automatically in response to operation of said conveyor means to transfer a panel to the platform stack, to operate said platform supporting means to lower said platform progressively relative to said conveyor means during successive transfer of panels to the platform stack, in such manner that the top of said stack is maintained within a predetermined maximum distance below the conveyor means during progressive elevation thereof to engage and transfer the panels.

6. Panel stacking apparatus comprising a stacking platform, a panel-supporting rack disposed adjacent to said stacking platform and having a vertical series of panel-receiving shelf spaces opening edgewise toward the space above said platform, panel conveyor means operable to engage and transfer a panel in the lowermost shelf space to the platform for depositing the same thereon, said platform normally being disposed in elevation slightly below said lowermost shelf space, elevator means operable to elevate said conveyor means progressively so to engage and transfer, one after another, successively, panels supported in the higher shelf spaces of said rack to the stack of panels on said platform, hydraulic jack means carried by said elevator means and supporting said platform, fluid actuating means for said jack, operable to lower said hydraulic jack and platform, and control means, actuated intermittently by operation of said conveyor means to transfer a panel to the platform stack, to operate momentarily said fluid actuating means and thereby to lower said platform progressively by increments during successive transfer of panels to the platform stack, in such manner that the top of said stack is maintained slightly below the conveyor means during progressive elevation thereof to engage and transfer the panels.

7. Panel stacking apparatus defined in claim 6, wherein the fluid actuating means comprises a control valve, and the control means comprises a valve-operating means and a control member cooperating with said valve-operating means, said control member being mounted on the elevator means'for movement between a. lowered position resting on the top panel on the platform stack, in which position said control member and valve-operating means controlled thereby operatively position said control valve to restrain lowering of the hydraulic jack relative to the elevator means, and a raised position effected by transfer thereunder of a succeeding panel to the top of the stack, to reposition said control valve for lowering of the hydraulic jack, the platform and the stack of panels thereon and said control member into the latters lowered position to position said valve again in its jack-restraining position, incremental lowering of the hydraulic jack occurring in such manner with each transfer of a panel to the stack.

8. Panel stacking apparatus defined in claim 6, wherein the fluid actuating means comprises a solenoid-controlled normally closed hydraulic relief valve, opening of which vents fluid from the loaded hydraulic jack to enable lowering of same by gravity, and closure of which halts such lowering, and the control means operating said valve comprises a switch and a switch-actuating member carried by the elevator means for movement thereon between opposite switch-actuating positions and engageable by the top panel on the platform stack, said member being movable into one switch-actuating position to open the valve by engagement of such member by a panel transferred to the stack, to initiate lowering of the hydraulic jack, and said member being movable oppositely to close said valve again after the jack, and thereby said panel engaged by said switchactuating member, has descended by substantially a panels thickness relative to the elevator means.

9. Panel stacking apparatus comprising a panel-supporting rack including a plurality of supportin shelves arranged in vertical series therein, said rack having an open discharge end for edgewise removal of the panels from the rack shelves, a stacking platform disposed adjacent to said racks discharge end, conveyor means cooperating with said rack, means operable to vary progressively the elevation of said conveyor means in relation to the rack to transfer the panels generally edgewise from the different rack shelves, in successive order, to depositing locations directly above said platform and for depositing thereon, and jack means operable to adjust automatically the elevation of said platform, and hence of the top of the stack thereon, relative to the elevation of the conveyor means, to locate the top of the 14 stack in panel-receiving position at all times slightly below said conveyor means elevation.

10. Stacking apparatus defined in claim 9, wherein the rack comprises an open-ended framework, and the plurality of rack; shelves are supported, vertically arranged, by said framework, said shelve individually comprising a longitudinal member spaced from and between the sides of said framework, transverse support members extending between the framework sides, a first one at a location generally between the ends of the rack, and another at a location spaced longitudinally therefrom, to support said longitudinal member projecting cantilever fashion from said first transverse member in the direction away from the other transverse member, the projecting cantilever portions of the longitudinal members of the plurality of shelves in the rack defining both longitudinal and vertical unobstructed opening therebetween, and further wherein the conveyor means comprises a plurality of belt conveyors movable in the rack spaces adjacent to and between said longitudinal members.

11. Panel stacking apparatus comprising rack means for initially supporting a serie of substantially horizontally disposed panels arranged in spaced superposed relationship, platform supporting means movable vertically incrementally distances corresponding to the vertical spacing between the panels of said series, a stacking platform disposed adjacent to said rack means, carried by said platform supporting means and operable to receive thereon a stack of panels discharged from said rack means, means operable to alter the vertical position of said stacking platform relative to said platform supporting means to dis ose the top of the panel stack on said platform slightly below a panel supported by said rack means in each incrementally adjusted position of said platform supporting means irrespective of the height of the panel stack on said platform, and means operable to transfer said panels individually edgewise from said rack means into stacked position on said platform.

ALFRED FRANK PIERCE.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,615,813 Romine Jan, 25, 1927 1,772,734 Romine Aug. 12, 1930 2,113,926 Pierce Apr. 12, 1938 2,181,357 Chipman Nov. 28, 1938 2,228,887 Peterson Jan. 14, 1941 2,376,176 Neja May 15, 1945

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