Advancing mechanism and system utilizing same for raising and lowering a work platform

A work platform, comprising:

• a platform member;
• a plurality of support columns for the platform member;
• and a mechanism for raising and lowering the platform member, comprising:
• at least one rack extending along a side of at least one support column;
• a movable member guided for movement along said support column;
• a pair of spaced apart pinion wheel supports, each carrying a pinion wheel which engages the rack, and each pinion wheel support including an extendible-retractable lock element having an end portion which when the lock element is extended is in locking engagement with tooth portions of the pinion gear, and when retracted is out of engagement with tooth portions of the pinion gear;
• and
• a separate extendible-retractible hydraulic cylinder innerconnected between each pinion wheel support and the movable member,
• whereby the lock element associated with a first one of the pinion wheel supports may be extended into locking engagement with tooth portions of its pinion, to in that manner prevent rotation of such pinion and hold it in position relative to the support column, while at the same time the hydraulic cylinder which is connected to the first pinion wheel support is extended or retracted to move the movable member in position relative to the first pinion wheel support and the support column and at the same time the lock element associated with the pinion wheel carried by the second pinion wheel support is retracted into an unlocked position, allowing its pinion wheel to rotate along the rack carried by the support columm, and the second cylinder is moved to the same starting position as the first cylinder, so that at the end of the stroke of the first cylinder the second lock element can be advanced to lock its pinion in position relative to the support column, the first lock element can be retracted to free its pinion from rotation along the rack carried by the support column, the second cylinder can be operated to advance the movable member and the first cylinder can be operated to return it to a start position.