Importance

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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). At the same time the hydraulic cylinder (64, 68) which is connected to the support (32 or 34) for the first pinion wheel (56) is extended or retracted to raise or lower the work platform (10). At the same time the lock element (100) that is associated with the second pinion wheel (56) is retracted into an unlocked position, allowing its pinion wheel (56) to rotate along the rack (16) carried by the support column (12). The second cylinder (64, 68) is moved to a starting point so that at the end of the stroke of the first cylinder (64, 68) the second lock element (100) can be advanced to lock its pinion (26) in position and the first lock element (100) can be retracted to free its pinion wheel (26) for rotation along the rack (16), and the second cylinder (64, 68) can be operated to advance the work platform (10) and the first cylinder (64, 68) can be operated to return it to a start position.

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First Claim