| 摘要 |
<p>A workpiece support device comprises an array of rods (2) in columns and rows with free ends of the rods forming a support surface, in which support surface recesses can be created by selectively retracting individual ones of the rods (2). Each rod (2) is coupled to a respective piston (3) within a respective cylinder (1) and each cylinder (1) has an upper connection (4) for medium pressure, a lower connection (7) for high pressure and a middle connection (8) for low pressure. A trigger piston (5) is provided in a cylinder (6) below the piston (3). The rod (2) can be caused to extend from the cylinder (1) by applying low pressure to the connection (8) to press the trigger piston (5) downwardly to close the high pressure connection (7). Such low pressure passes around the lip of a lip seal (24) on the trigger piston (5) and through a connection (28) pressurises the underside of the piston (3) to raise the piston (3) and release it from pressing the trigger piston (5) downwardly. Subsequently pressurising the connections (4 and 7) causes the differential pressure to force the piston (3) upwardly. However by sequencing the application of pressure to the connections (4, 7 and 8) the rod (2) can be locked in the retracted position. Medium pressure applied to the connection (4) presses the piston (3) downwardly to abut the trigger piston (5) and hold it in a depressed condition in which it will remain even after pressure is restored to the high pressure connection (7).</p> |
