Vacuum lifter

1. A vacuum lifter apparatus for lifting sheet material articles, comprising an upper chassis, a modular lower suction plate supported beneath the chassis, a controller and a source of vacuum air pressure, the suction plate comprising a suction lifting surface for providing vacuum lifting pressure to said articles, wherein:

the modular suction plate has a plurality of side-by-side modules, each module abutting at least one adjacent module, the modules being fitted together to provide the lower suction plate, each module providing a different portion of the suction lifting surface and having one or more air outlets, said outlets of one module being separate from said outlets of other modules and being in fluid communication with the corresponding portion of the suction lifting surface and not with different portions of the suction lifting surface;

the chassis comprises at least one air outlet connected to said source of vacuum air pressure for conveying said vacuum air pressure to the suction lifting surface of the suction plate, and a plurality of separate air flow channels through the chassis, each of said channels leading from said outlets of one of said modules to at least one of said at least one air outlet of the chassis; and

said apparatus further comprises for each air flow channel an associated air flow valve and a valve actuator, the controller being operatively connected to said valves, and the controller being configured, in use, to open and close said valves to separately control the vacuum air pressure transmitted along said channels to each one of said modules whereby the vacuum air pressure conveyed to each one of said different portions of the suction lifting surface is individually controllable by the controller.

2. The vacuum lifter apparatus of claim 1 , in which said portions of the suction lifting surface are arranged in an array, the controller is configured to sequence opening of said valves to convey said vacuum air pressure to said portions at different times such that vacuum air pressure appears at a first one of said portions first and a second one of said portions last, said first and second portions being on opposite sides of said array.

3. The vacuum lifter apparatus of claim 2 , in which there is at least one intervening portion of the suction lifting surface between said first and second portions, and the controller is configured to sequence the opening of said valves to convey said vacuum air pressure to said at least one intervening portion sequentially in time such that said conveyed vacuum air pressure appears as a wave spreading across the suction lifting surface starting at said first portion and ending at said second portion.

4. The vacuum lifter apparatus of claim 1 , in which the chassis is separated at intervals from a suction plate upper side to provide a plurality of air chambers between the chassis and suction plate, each air flow channel extending through one of said chambers.

5. The vacuum lifter apparatus of claim 1 , in which each suction module comprises a housing, the housing comprising opposite top and bottom walls, said bottom walls together providing a lower side of the suction plate and said top walls each providing said outlets of said modules.

6. The vacuum lifter apparatus of claim 5 , in which said bottom walls are each perforated to provide orifices through which, in use, air is drawn along air flow paths through said top wall outlets and into said channels towards at least one of said at least one air outlet of the chassis to provide said suction lifting pressure.

7. The vacuum lifter apparatus of claim 2 , in which the chassis is separated at intervals from a suction plate upper side to provide a plurality of air chambers between the chassis and suction plate, each air flow channel extending through one of said chambers.

8. The vacuum lifter apparatus of claim 3 , in which the chassis is separated at intervals from a suction plate upper side to provide a plurality of air chambers between the chassis and the suction plate, each air flow channel extending through one of said chambers.