Film transport mechanism

摘要

A film transport mechanism for use in conjunction with a motion picture projector is a free standing unit carrying supply and takeup reels and associated drive motors. The arbors for the supply and takeup reels are generally parallel, and positioned therebetween is a free running sprocket assembly. Film direction rollers cause film from the supply reel to run over one side of the sprocket and additional rollers to direct the return film from a projector over the opposite side of the sprocket whereby the rate of film advance to the projector and return are equal. The transport mechanism transfers a major portion of the torque required to pull film off the supply reel from the projector to the transport thereby significantly reducing the tension on the film going to and from the projector. The entire assembly includes a support structure having a vertical column supporting the motors, arbors and the control electronics, and constitutes a conduit for virtually all electrical interconnections. Control circuitry controls the takeup motor as a function of film movement between the sprocket and the takeup reel and energizes both rewind and takeup motors during the rewind cycle. The speed on rewind is controlled by the control circuitry by controlling the current to the normal run takeup motor. Failsafe circuitry prevents unintended shutoff during restart situations, but turns off the transport mechanism after a few seconds in case of a film break or runout.