Film web motion control system

In a film preparation workstation for advancing photographic film in a film transport path between a supply reel having a supply quantity of film wound thereon and a take-up reel having a take-up quantity of film wound thereon at a constant reference velocity in either a forward or rewind direction of advancement past one or more read and write magnetic head assemblies in intimate contact with a magnetic layer on the film and imposing drag thereon, the workstation further comprising:

• metering means responsive to a metering drive signal defining a forward or rewind direction of advancement for engaging the film in the film transport path and advancing the film between said supply reel and said take-up reel at a film velocity;
• a metering encoder for providing metering encoder signals representing incremental advancement of the film with respect to the metering means;
• a supply reel torque motor coupled to the supply reel and responsive to a supply motor torque signal for applying a supply reel torque thereto to impart a supply reel tension on the film extending between the supply reel and the metering means dependent on the magnitude of the supply reel motor torque signal and the supply quantity;
• a supply reel encoder for providing a supply interrupt signal at least once during each full rotation of the supply reel;
• a take-up reel torque motor coupled to the take-up reel and responsive to a take-up motor torque signal for applying a take-up reel torque thereto to impart a take-up reel tension on the film extending between the take-up reel and the metering means dependent on the magnitude of the take-up reel motor torque signal and the take-up quantity;
• and
• a take-up reel encoder for providing a take-up interrupt signal at least once during each full rotation of the take-up reel;
• a system for accelerating the film in a selected direction of forward or rewind advancement from a stopped state, wherein the film in the film transport path is stationary and the actual supply quantity and actual take-up quantity are unknown in the stopped state, to an at speed state in a velocity mode or a position mode, wherein the film speed is at the reference velocity and the supply quantity and take-up quantity are determined, comprising:
• means for disabling said metering means for allowing the film to be threaded in said film transport path;
• means operable after threading of the film in the film transport path for providing starting motor drive signals to said supply reel torque motor and said take-up reel torque motor to generate starting supply and take-up reel torques to said supply and take-up reels, respectively, to pre-tension said film sufficiently to take up slack in the film and for then incrementing the magnitudes of said starting motor drive signals to said supply reel torque motor and said take-up reel torque motor to default motor drive signals dependent on the selected direction of advancement, the default supply reel torque motor drive signal magnitude correlated to a default supply quantity and the default take-up reel torque motor drive signal correlated to a default take-up quantity;
• means for providing a metering drive signal to said metering means to counter the tendency of the film to move under the influence of the starting motor drive signals to thereby hold the metering means and film stopped;
• means operable upon incrementing of the starting motor drive signals to the default motor drive signals, for providing a metering drive signal that is effective to advance the film in a selected forward or rewind direction of advancement in the transport path at a predetermined rate of acceleration for accelerating the film to the reference velocity;
• means operable on achievement of the at speed state for calculating the actual supply and take-up quantities from the supply and take-up interrupt signals and the metering encoder signals;
• means for calculating supply and take-up motor torque signals correlated to the calculated actual supply and take-up quantities, respectively, for equalizing tension in the film through the film transport path and advancing the film in the selected direction of advancement at the reference velocity;
• and
• means for applying the calculated supply and take-up motor torque signals to the supply and take-up reel torque motors, respectively, in substitution for the default motor torque signals.