referring in more detail to fig1 and 3 , the palletizer - depalletizer 100 is shown . the machine has a frame 102 , shown formed of square tubes . the frame 102 is formed with a center beam portion 104 , a loading - unloading bay 106 and a storage bay 108 . for convenience the palletizer - depalletizer 100 will be referred to as a depalletizer , but it will be appreciated that it can perform both functions . the loading - unloading bay 106 will be for convenience called the unloading bay , but it will be appreciated that it can also perform both of those functions . the depalletizer 100 has a scaffold 110 mounted on one side of the machine at the top . the scaffold can be reached by stairs 112 . scaffold 110 and stairs 112 may be welded on the machine , but they can also be attached by bolts so that they can conveniently be placed on either side of the depalletizer 100 as the layout of the particular plant requires . the scaffold 110 and stairs 112 may even be changed , if the depalletizer 100 is moved to a different location or the process flow around it is changed . in the unloading bay 106 is a twin blade cantilevered elevator 114 and in the storage bay 108 is a similar twin blade cantilevered elevator 116 . the elevators are raised and lowered by parallel double lift sets 118 and 120 . one chain lift from each of sets 118 and 120 is shown in fig6 . the chain lift sets 118 and 120 are housed in the center beam portion 104 of the depalletizer 100 . the blades of cantilevered elevators 114 and 116 extend through the slots of the center beam portion 104 into the unloading bay 106 and the storage bay 108 , as shown in fig1 . it will be appreciated that other elevator means , such as hydraulic driven lifts or center hydraulic pistons , may be used instead of the cantilevered chain lifted elevators as shown . the chain sets 118 and 120 are driven by motors 122 and 124 acting through suitable chain driven gear sets 126 and 128 and provided with suitable safety covering 130 and 132 , as shown . chain and gear sets 126 and 128 drive rotating shafts 134 and 136 which extend into the center beam portion and have paired gear sets 138 and 140 which drive elevator chain sets 118 and 120 . the paired elevator chains 118 and 120 extend downwardly in the center of the depalletizer 100 and pass around idler gear sets 142 and 144 . gear sets 142 and 144 are attached to rotating shafts 146 and 148 which are journaled at the bottom in the center of the depalletizer 100 , as shown in fig4 . the parallel chain sets 118 are fastened to the back of elevator 114 at bosses 150 . see fig9 and 11 . the parallel chain sets 120 are fastened to the back of elevator 116 by similar bosses 152 . see fig6 and 10 . the outer edges of elevator 114 are provided with support rollers 154 and the outer edges of elevator 116 are provided with similar rollers 156 . rollers 154 and 156 ride against elements of the frame center beam portions 104 , as shown , to guide and support the elevators 114 and 116 as they are raised and lowered by motors 122 and 124 . unloading bin 106 has a input conveyor 158 which is driven by motor 160 and chain and gear set 162 . storage bay 108 similarly has an outlet conveyor 164 driven by motor 166 and chain and gear set 168 . associated with unloading bay 106 is an input conveyor 170 which may be of the driven or gravity feed type . storage bay 108 similarly has a conveyor 172 which may be driven or gravity operated . both conveyors 172 and 170 may be of the accumulating type having space for one or more pallets or stacks of pallets . above storage bay 108 is a sub - frame 174 in which is mounted a transversely extending cylinder and piston 176 and a longitudinally extending cylinder and piston 178 . these pistons may be either pneumatically or hydraulically operated by suitable valving , not shown . transversely extending cylinder and piston 176 operates plow 180 reciprocally across the top of the storage bay 180 , as shown , cylinder and piston 178 operates plow 182 reciprocally and longitudinally across the top of storage bay 108 , also as shown . plows 180 and 182 position ejected pallets 184 for stacking on elevator 116 . when plow 182 is retracted to the extreme position , shown to the far right in fig6 it is folded about a hinge 183 , to the position shown in fig7 by stationary pins 186 which impinge on the bottom of plow 182 , see fig8 . plows 182 and 180 are operated by their respective cylinders and pistons on sliding guides 188 and 190 , as shown . at the top of depalletizer 100 are two longitudinally operating carriage plates 192 , as shown each having a rack 194 , as shown in fig1 . each rack 194 meshes with pinion gears 196 which are mounted on a shaft 198 which extends transversely in the center beam portion 104 at the top of the depalletizer 100 . shaft 198 is rotated by gear and chain set 200 which is driven by motor 202 mounted in the center beam portion 104 of the depalletizer 100 . shaft 198 also carries a pair of rotating supports 204 which serve as bearing surfaces on which carriage 192 can rest as it reciprocates longitudinally in the depalletizer 100 when driven by motor 202 . depalletizer 100 has a control box and panel 206 at the top of sub - frame 174 and accessible to an operator on scaffold 110 . control panel 206 contains the switches by which the various operations of the machine , described herein , may be controlled manually . the operations may also be controlled semi - automatically by conventional relay and switching logic or by integrated circuitry . a master control panel , not shown , may contain all of the logic and a second set of activating switches . the master panel is positioned anywhere convenient on the machine or separately from the machine . the depalletizer 100 also has an associated conveyor 208 at the top of the device for conveying away for further use of the materials which are unloaded from the pallets 184 . when operated as a depalletizer , for example to unload pallets of cardboard boxes 210 containing goods such as new beverage bottles , input conveyor 170 may be a powered accumulating conveyor which is sized to accumulate two or more pallet loads upstream of the unloading bay 106 . when elevator 114 is in its lowermost position , it activates a micro - switch , not shown , to energize input conveyor 170 and unloading bay conveyor 158 to load a pallet 184 fully into the unloading bay 106 . when a pallet 184 is fully loaded into the input bay 106 above elevator 114 it activates a micro - switch or photocell , not shown , to stop conveyors 158 and 170 and to activate motor 122 which drives chain and gear set 126 , rotates shaft 134 and lifts elevator 114 through the operation of rotating gears 138 and chain lifts 118 . elevator 114 is indexed upwardly by motor 122 until the top layer or tier of boxes 210 is slightly above , approximately 1 centimeter the top edge of the depalletizer 100 and above the upper surface of the output conveyor 208 . in fig2 pallets 184 are shown as having single layers of boxes 210 , but it will be appreciated that usually each pallet 184 will contain multiple tiers of boxes 210 rather than single tiers as shown . with the pallet 184 in the raised position and the boxes 210 spaced slightly above the top of the depalletizer 100 and conveyor 208 , the boxes 210 can be removed and placed on the output conveyor 208 and taken to subsequent processing in the plant . when the last box 210 has been removed from the top tier on pallet 184 its absence is detected by a photosensor set 214 , 216 . as shown , the last carton on the pallet 210 will normally be in the corner of the unloading bay 106 nearest sensor 216 . the sensor 216 energizes motor 122 which indexes the next tier or layer into position for removal . sensor set 214 , 216 stops the elevator 114 at the proper location by sensing the presence of the next tier . this process is continued until the last tier or layer on the elevator 114 is reached . at this point a micro - switch , not shown , which responds to the travel of the elevator indexes the elevator upwardly an additional increment , 3 centimeters so that the pallet 184 is spaced above the location in unloading bay 106 which is occupied by carriage 192 when it is placed above the unloading bay 106 . this switch , with a suitable time delay , energizes motor 202 driving carriage 192 longitudinally across the top of depalletizer 100 into position above loading bay 106 and below the pallet 184 . when carriage 192 reaches the limit of its travel into unloading bay 106 a micro - switch , not shown , activates motor 122 which lowers elevator 114 allowing pallet 184 to rest on transverse carriage 192 . elevator 114 continues to be lowered to the bottom limit of its travel and a second pallet load of material is indexed into the machine from conveyors 170 by conveyor 158 as previously described . when the second pallet is in position above elevator 114 the previously described micro - switch activates motor 122 which raises that pallet upwardly to a ready position just beneath the pallet which is resting on transverse carriage 192 . normally this would be about 8 centimeters below the position of carriage 192 in bay 106 . when the last box 210 has been removed from the pallet 184 which is resting on carriage 192 , the photocell sensors set 214 and 216 and the micro - switch associated with carriage 192 energize motor 202 to move carriage 192 and to transport the pallet 184 from unloading bay 106 to the storage bay 108 . when carriage 192 clears unloading bay 106 the motor 122 is again energized to raise elevator 114 and position the top tier of the new pallet load of material in position for unloading . the unloading sequence then is repeated as previously explained . as the transverse carriage 192 moves into storage bay 108 the pallet 184 carried thereon moves beneath plow 182 which is in position pivoted about hinge pin 183 . when the carriage 192 reaches the limit of its travel into bay 108 it activates a micro - switch , not shown , which stops motor 202 and activates a suitable valve , not shown , for pneumatic or hydraulic valving of longitudinal cylinder and piston 178 , which moves plow 182 longitudinally into engagement with pallet 184 and pushes the pallet 184 to a position contacting the frame 102 at the extreme edge of the depalletizer 100 as shown in fig6 . when pallet 184 reaches the extreme edge , it stops cylinder and piston 178 and activates transverse cylinder and piston 176 which moves plow 180 transversely across depalletizer 100 to engage the edge of the pallet 184 and index it against the frame 102 of depalletizer 100 nearest the scaffold , as shown in fig1 . elevator 116 has previously been indexed upwardly to a position slightly below the position of carriage 192 . normally this position would be approximately three cm . below the pallet itself . when the last tier of the second pallet to be unloaded is reached , the elevator 114 again indexes that pallet above the position of carriage 192 in bay 106 . carriage 192 is then activated , as previously described , and is driven by motor 202 longitudinally in depalletizer 100 and into position in bay 106 below the pallet 184 . as the carriage 192 leaves bay 108 it drops the first pallet onto elevator 116 in bay 108 . elevator 116 is then indexed downwardly by suitable switching means , not shown , so that the pallet on the elevator 116 is below the position of the carriage 192 in bay 108 and , preferably , is then indexed upwardly in response to suitably placed switch means , not shown , so that the stacked pallet is in a ready position with the top of the pallet being approximately three centimeters below the position of carriage 192 in bay 108 . the stacked pallet is then ready to receive the next unloaded pallet . when elevator 116 has accumulated sufficient pallets , suitable switch means , not shown , associated with elevator 116 activates motor 124 to index the elevator down an additional distance and rest the pallet load on output conveyor 164 . switching means , not shown , then activates the motor 166 which ejects the pallet load to output conveyor 172 . the above description has shown the input and output to the depalletizer in a longitudinal mode . it will be appreciated , particularly from viewing fig2 that pallets could also be introduced and removed from the depalletizer transversely by changing the directions of conveyors 162 and 164 , 170 and 172 . fork lift trucks can be used from any direction . the particular mode will depend upon the design and layout of the particular process and plant served by the depalletizer 100 . it will also be appreciated that safety plates and screens are not shown on the device , they would normally be used to cover the areas of the machine which were not being used to transport materials through the device . it will also be appreciated that the arrangement of conveyor 208 can be changed as the layout of the plant dictates and can be located at either side of the machine or at the end . by using the process described above lag time is reduced to a minimum . the loading and unloading process is continuous and keeps subsequent pallet loads at the ready position . there is very little time lost in indexing spent pallets out of the machine or introducing new loads into the machine . the transverse carriage 192 , the elevators 114 , 116 are free , when the last tier of the pallet is reached to move down and pick up subsequent pallets for unloading or loading , as is not possible with bottom ejecting machines . the same convenience is found when the machine is operated in the palletizing mode by reversing the operation of the device . in the palletizing mode a load of pallets 184 is introduced to the storage bay 108 and indexed sequentially upwardly as the pallets are required . plows 180 and 182 properly index the pallets , a feature which allows a variety of pallets to be used without resetting the machine , in both the palletizing and depalletizing modes . the pallets are fed to the loading bay 106 by operation of the transverse carriage 192 where they are positioned on elevator 114 . as the pallets are loaded the elevator is indexed down until the load has been completed and the pallet is ejected by the operation of conveyors 158 and 170 . when the pallet has been positioned on elevator 114 transverse carriage 192 returns to the storage bay 108 and engages a second pallet which has been readied by the operation of elevator 116 indexing upward and has been indexed by plows 180 and 182 which position the pallet for subsequent transportation into the loading bay 106 . loading of the second pallet can commence before expulsion of the first loaded pallet is completed . it will be appreciated that this also eliminates the dead time necessary for the elevator 114 to eject a loaded pallet , load an empty pallet and cycle upwardly to the loading position . while the operation has been described here as semi - automatic , the operation of motors 122 and 124 and 202 , which sequence the elevators 114 and 116 and carriage 192 and conveyor motors 160 , 166 could be controlled manually by an operator on the scaffold 110 switching the motor controls through use of control panel 206 . in the foregoing specification i set forth the embodiments described herein for the purpose of illustration , but it is to be understood that such details may be varied widely by those skilled in the art without departing from the spirit and scope of the invention .