Patent ID: 6957683

Claim:
A cover system, comprising: a base; an extendible cover mounted to the base and having a free end depending from the base; a rail mounted proximate the free end of the extendible cover; pulley means mounted proximate the base for rotation; and lift cord means wound around the pulley means and attached to the rail; a spring drive system, comprising: a spring drive comprising first spool means, second spool means, and a flat spiral spring mounted on and wound between the first and second spool means; a cord transmission comprising first and second rotatable transmission shafts and a cord or band wrapped around the first and second transmission shafts for rotating the second transmission shaft at a rate that varies selectively relative to the rate of rotation of the first transmission shaft; the first transmission shaft being operatively connected to the second spool means; and the cord transmission thereby selectively varying the rotating speed of the second transmission shaft thereof relative to the rotating speed of the second spool means; a gear transmission comprising a plurality of intermeshed gears, the gear transmission having a given ratio between two of the gears thereof; a first of the two gears being operatively connected to the second transmission shaft and the second of the two gears being operatively connected to the pulley means, thereby applying the given ratio of the gear transmission between the cord transmission and the pulley means for altering the speed of the second gear and of the pulley means relative to the speed of the first gear and of the second transmission shaft; the extendible cover thereby being supported by the spring drive system via the lift cord means and being oriented such that moving the rail back and forth retracts and extends the extendible cover along a path between open and closed positions, and whereby the associated supported weight of the extendible cover varies along said path; the force of the spring drive, the ratio of the variable ratio cord transmission and the ratio of the gear transmission being selected for counterbalancing the varying supported weight of the extendible cover along said path; and the spring drive system maintaining the extendible cover at rest along said path.