60 tie bars 90 and crossrails 46 47 48 77 79 can be made from any material suitable for such structural members for example extruded aluminum beams and associated fasteners commercially available from mb kit systems ltd of akron ohio the outer and inner frames are assembled by tapping a center through hole in the ends of the siderails and crossrails drilling clearance holes through the sides of the vertical posts at the appropriate locations and using a threaded fastener to connect the rails together the conveyor siderails can be made from any stock material that provides sufficient strength for example an extruded aluminum right angle bar stock or angle iron the roller assemblies comprising the conveyors 30 32 are commercially available from interroll corporation of wilmington n c and the cylinders 34 are commercially available from smc pneumatics of indianapolis ind referring to fig3 the elevator conveyor 20 includes an elevator controller 100 which provides output signals on lines 102 104 to operate the upper and lower roller motors 66 72 respectively in addition at the appropriate times the elevator controller 100 provides command signals on an output 106 to a solenoid valve 107 that appropriately ports pressurized air to the cylinders 34 thereby causing the cylinders 34 to either extend or retract their respective cylinder rods 86 the presence and absence of a pallet or tote on the conveyors 30 32 is detected by respective proximity sensors 108 110 referring to fig1 in this example the proximity sensor 108 is mounted on the inner upper side rail 58 at the opposite end 38 of the conveyor 30 and the proximity sensor 110 is mounted on the inner upper side rail 58 at the one end 36 of the conveyor 32 the proximity sensors 108.