Bi-directional, dual speed film transport gear drive apparatus with an

Abstract

A dual speed film drive apparatus to achieve high speed and low speed film drive employs a limited speed range stepper motor with pinion input drive gear, and an output driven gear connected to a film advance mechanism. High and low speed drive is achieved by use of a pivoted intermediate gear drive module having high speed and low speed gear set positions to interconnect the stepper motor input drive gear to the output driven gear. Shifting of the gear module between gear set positions is accomplished by a DC motor operated cam drive mechanism which pivots the gear module selectively between the high speed and low speed gear set positions. The cam drive mechanism includes a camming slot having dwell segments at each end of the slot. An open loop control gear mesh procedure includes is also described for meshing the high speed and low speed intermediate gear drives with the input drive gear and output driven gear. In this procedure, the cam drive mechanism initially drives the gears toward mesh and then reverses the cam drive by a limited amount. If the input drive gear properly meshed with the intermediate gear drive, the dwell segment prevents the gear from being unmeshed. If stubbing occurred, the cam drive is still in the drive segment of the cam and backs the intermediate gear drive away while the stepper is activated by a partial tooth pitch. The cam drive is then driven forward again to engage the intermediate gear with the input gear. The stepper motor is then driven forward and back by equal amounts to clear any stub condition that might still exist between the intermediate gear and output driven gear interface. The open loop control routine avoids the need for complex and costly active feedback mechanisms to detect and clear a gear stubbing condition during gear shifting.