756,691. Conveyers. FOOD MACHINERY & CHEMICAL CORPORATION. Dec. 3, 1953 [Dec. 29, 1952], No. 33596/53. Class 78 (1). [Also in Group XVII] In a box stacking machine the boxes are fed in turn on to retractable supports which are retracted in response to the arrival of a box to drop the box on to a table adapted to move vertically, and to cause lowering of the table to allow another box to be deposited on top of the first box to form a stack, this procedure continuing until the first box engages an adjustably positioned stack limiting mechanism to cause the table to be lowered to a bottom position for removal of the stack. As shown, the table 30 is carried on a frame 29 at the upper end of piston-rod 28 of a cylinder 26, Fig. 12, embedded in the ground, and is guided by pairs of rollers 112a, 112b, 114a, 114b on a pair of guide rails 111a, 111b, Fig. 8. The table in its top portion is immediately below a pair of retractable supports formed by series of conical rollers 42a, 42b carried on respective horizontal bars 37a, 37b suspended by arms 39a, 39b from shafts 40a, 40b. The boxes are fed to the rollers 42a, 42b between guides 60a, 60b by a belt conveyer 56, Fig. 4, and are delivered against rubber stops 70a, 70b, but are prevented from bouncing back by spring- loaded catches 75a, 75b, Fig. 3, which engage behind the box. As a box arrives against the stops it engages a pair of levers 95a adapted to close a switch 328, Fig. 14, and open a switch 314. Assuming table 30 has just been raised to its top position a ramp 181 on the frame 29 engages a lever 225 to close a switch 320 and energize relay 322. The latter opens contacts 318 closing a valve 223 supplying fluid to cylinder 26 from a pressure chamber 218, and closes hold contacts 323 and contacts 325, 329 in the circuits of solenoids 327, 331. This completes a circuit to the solenoid 327 to operate a valve 94 supplying compressed air to the upper end of a cylinder 91, Fig. 4, the pistonrod 90 of which is thereby retracted to swing a pair of levers 87a, 87b, Fig. 3, to swing the shafts 40a, 40b and thereby retract the support rollers 42a, 42b and drop the box on to table 30. Solenoid 331 is not energized until a switch 332 is closed through a lever 105, Fig. 4, on shaft 40a, when the support rollers are fully retracted. Open energization, solenoid 331 operates a valve 238 supplying compressed air to raise piston 240 of a servo-cylinder 239, thus raising the piston of a valve 215, which normally causes fluid from a reservoir 212 to pass through pump 210 to the chamber 218, so that fluid is now pumped from the cylinder 26 into the reservoir 212 so as to lower table 30. While these operations proceed, a second box is prevented from reaching the support rollers 42a, 42b by the interposition of a clutch 65 and brake 309 in the drive to conveyer belt 56 from a continuously running motor M, so that, switch 314 being opened as described above, if a further box should arrive on belt 56 it strikes a lever 236, Fig. 4, opening a switch 340 so that supply to a relay 312 is cut off. Switches 308, 310 in the clutch and brake actuating circuits are thereby operated to declutch the drive and brake the belt 56. As table 30 descends, contacts 320 re-open, but relay 322 remains energized through the hold circuit. The table 30 descends until switch 328 is re-opened by the top of the box passing below levers 95a and thus below the level of support rollers 42a, 42b. This stops table 30 in position to receive a further box and re-closes switch 314 so that belt 56 is again driven to feed a further box which is delivered by a further cycle on top of the first box and the stack thus formed again lowered by the height of a box for the receipt of a further box. To limit the number of boxes in a stack, according to the heights of the boxes being stacked, a set of ramps 155-160, Fig. 9, is provided, each ramp being adjustably secured at a different angular position and height on a rod 131 carried at each end by a pair of cranks 137b and 150b respectively. One of the ramps is selected by lifting the rod against spring 169 lifting plate 132 off a pair of studs 168 so it can be rotated to a new position in which a selected ramp projects inwardly into the path of the descending boxes. A spring 144 holds the cranks 137b raised against a stop, cranks 150b also being held against a stop. When a stack of desired height has been formed, the bottom box of the stack engages the shoulder 161 of the selected ramp, forcing it down whereby the upper part 172a of a twopart lever 172, Fig. 11, effects closure of a switch 342 and opening of switch 343, the former switch maintaining solenoid 331 energized so that the table continues to drop to its bottom position below a pair of continuously driven chains 125a, Figs. 9 and 12, adapted to receive the stack, while the latter switch prevents energization of solenoid 327. In order to prevent further actuation of the retractable supports upon subsequent closing of switch 328, the ramp engaged by the stack is shaped such that after the bottom box has pushed its shoulder 161 aside, further movement down the ramp pushes the latter further to the side causing the lower part 172b of lever 172 to open a switch 346. Upon table 30 reaching the bottom position ramp 181 on frame 29 engages a lever 182 to open a switch 350 breaking the hold circuit of relay 322. This re-opens contacts 325, 329 de-energizing solenoid 331 so that descent of the table is stopped, and recloses contacts 318. Solenoid 316 is not, however, re-energized since the bottom box as it came to rest on chains 125a engaged springy bars 190a which through levers 194a opened a switch 317. As soon as the stack has been moved clear by the chains 125a switch 317 is re-closed and solenoid 316 re-energized to cause fluid again to be supplied to cylinder 26, whereupon table 30 rises again to start another cycle upon ramp 181 re-closing switch 320. To lessen shocks whenever descent of table 30 carrying a stack is suddenly stopped a dashpot 242 containing air is provided, its air chamber 245 being connected by a bleed tube 246 to a valve 248 connecting to the air supply to cylinder 239 and operable to restrict flow only in the direction away from the dashpot. By this means chamber 245 is refilled whenever cylinder 239 is actuated to lower the table.