Spoolless film takeup chamber with improved spooling spring

摘要

A spoolless film takeup chamber with a pair of expandable film coiling springs. The springs are flat springs coiled generally in a spiral configuration. The thickness of the springs varies from the point at which the springs are attached to the inner takeup chamber out to the free, distal ends of the springs such that the thickness at the distal end is less than the thickness at end attached to chamber. Preferably the thickness decreases continuously from the attached ends to the distal ends of the spring. The effect is to reduce the spring rate at the outer ends of the springs thereby maintaining a relatively constant spring force on the film as the diameter of the film coil grows as compared to springs with a constant spring rate along the length of the springs. Additionally, the radius of curvature of a segment of each spring at the distal end is longer than the radius of curvature at an intermediate segment of the spring to better conform the spring to the outer circumference of the film coil thereby avoiding interference between the ends of the springs and features on the film such as perforations.