Abstract: A work platform (10) is guided for up and down movement along support columns (12). Advance/retract cylinders (50, 52) are interconnected between a portion (26) of the platform (10) and a first support (28). Advance/retract cylinders (64, 66) are interconnected between the platform (10) and a second support (30). Each support is in the nature of a clamping mechanism. Each includes a pair of clamp members (32, 34) and (54, 56) which are pivotally connected together. Hydraulic cylinders (46, 48) and (60, 62) move the members (32, 34) and (54, 56) together and apart. When these members (32, 34) and (54, 46) are moved apart, they move grip pads (44, 58) into gripping contact with the support column (12). When they are moved together, they move the gripping pads (44, 58) out of contact with the support column (12). In use, one support (28, 30) is clamped to the support column (12) while the other is unclamped.

Abstract: A rack (16) extends along a support column (12) for a work platform (10) which is guided for up and down movement along the support column (12). A pair of independently movable supports (32, 34) are provided. A separate extendible/retractable hydraulic cylinder (64, 68) is interconnected between each support (32, 34) and a frame portion (30, 88, 90) of the work platform (10). Each support (32, 34) includes an extendible/retractable lock element (100) having an end portion which when the lock element (100) is extended is in locking engagement with either tooth portions of a pinion wheel (56) carried by the support (32, 34), or with the rack (16). In use, the lock element (100) is extended to lock the support in position relative to the support column (12). At the same time, the hydraulic cylinder (64, 68) which is connected to the support (32 or 34) is extended or retracted to raise or lower the work platform ( 10).

Abstract: A rack (16) extends along a support column (12) for a work platform (10) which is guided for up and down movement along the support column (12). A pair of vertically spaced apart pinion wheels (56) engage the rack (16). Each pinion wheel (56) is mounted on its own pinion wheel support (32, 34). A separate extensible-retractable hydraulic cylinder (64, 68) is interconnected between each pinion wheel support (32, 34) and a frame portion (30, 88, 90) of the work platform (10). Each pinion wheel support (32, 34) includes an extendable-retractable lock element (100) having an end portion which when the lock element (100) is extended is in locking engagement with two portions of the pinion wheel (56). In use, the lock element (100) associated with one of the pinion wheels (56) is extending into locking engagement with tooth portions of its pinion wheel (56), to in that manner prevent rotation of the pinion wheel (56) and hold it in position relative to the guide member (12).