Patent ID: 6076415
Filing Date: 2000-06-20
Classification: F16H,Y10T

Abstract:
A method of operating a dual speed film transport gear drive apparatus of the type having:film drive stepper motor having an input drive gear;an output driven gear;a movable gear module having first and second intermediate gear drives adapted for movement between first and second drive positions in which one of said first and second intermediate gear drives is selectively meshed with said input drive and output driven gears, the gear module having a cam follower;a gear shift unit including a cam drive motor and a cam having a cam slot engaged with said gear module cam follower, the cam slot having extended dwell zones at each end of travel of the cam separated by a gear shift drive zone; anda controller operative, using open loop control, to cause movement of said gear module between said first and second positions meshing a selected one of said intermediate gear drives with said input drive gear and said output driven gear by performing the following steps comprising:(a) driving said cam drive motor forward for a first predetermined amount of time sufficient to drive said gear module normally to the selected one of said positions with said cam follower in a dwell segment corresponding to said selected position;(b) driving said cam drive motor in reverse to move said cam through a length of travel equivalent to a predetermined portion of said dwell segment;(c) driving said stepper motor through a fraction of a tooth pitch on said input drive gear; and(d) driving said cam drive forward for a second predetermined amount of time sufficient normally to drive said gear module to said selected one of said positions;whereby any stubbing between said input drive gear and intermediate gear drive is cleared by steps (a)-(d) and, if no stubbing of said gears has occurred, said dwell segment of said cam drive prevents unmeshing of said input drive gear and intermediate gear drive during step (b).