Adaptive reel-to-reel tape control system

An adaptive reel-to-reel tape transport apparatus for maintaining tape motion control as the amount of tape on each reel changes with time, comprising:

• a storage for storing digital values which correspond to predetermined increments of reel radius;
• at least one reel tachometer for measuring reel angular displacement;
• a tape tachometer for measuring the amount of tape linearly displaced during each successive preselected amount of reel angular displacement;
• counter logic responsive to the measurements by said tape and reel tachometers for calculating the instantaneous radius of tape on at least one of said reels, to provide digital reel radius numbers;
• and
• means connecting said storage with said logic for causing said storage in response to said reel radius numbers to select the inertial value corresponding to the instantaneous reel radius.

A reel-to-reel magnetic tape transport comprising:

• a supply reel and motor for driving said supply reel;
• a take-up reel and motor for driving said take-up reel;
• means adapted to allow a length of unbuffered tape to extend between said reels and to be wound thereupon;
• a tape tachometer circuit adapted to coact with the tape for providing a signal indicative of actual tape displacement;
• a supply reel tachometer circuit connected to coact with said supply reel for providing a signal indicative of the actual radius of tape wound upon said supply reel;
• a take-up reel tachometer circuit connected to coact with said take up reel for providing a signal indicative of the actual radius of tape material wound upon said take-up reel;
• a storage storing inertial values corresponding to different predetermined reel radii, for generating signals representing inertial values corresponding to actual reel radius signals applied to said storage;
• and
• control means connected to said motors and responsive to said tachometer circuits and said storage for calculating motor currents in accordance with a predetermined servo algorithm to thereby generate motor currents of a magnitude sufficient to drive said reels in an appropriate direction and by such an amount so as to reduce to zero tape displacement difference from a nominal position.

Apparatus for transporting an unbuffered length of web between two reels, comprising:

• a pair of motors, one for driving each of said reels;
• reel tachometer circuit means for measuring angular displacement of at least one of said reels;
• tape tachometer circuit means for measuring the varying amount of tape actually displaced during each successive preselected degree of reel rotation;
• storage means storing inertial values corresponding to different predetermined reel radii;
• and
• control means connected to said motors and including means responsive to the amount of tape actually displaced during such preselected degree of reel rotation for deriving instantaneous values of reel radii and, using inertial values corresponding to said radii as stored in said storage means, calculating motor currents in accordance with a predetermined servo algorithm thereby to generate motor currents of a magnitude sufficient to drive said reels in an appropriate direction and by such an amount as to maintain web speed and tension at substantially constant values as preselected by said algorithm.

Apparatus for transporting an unbuffered length of web along a fixed path between two reels, comprising:

• means for generating for each reel a respective signal whenever such reel is rotated through a predetermined angle as the web is advanced along the path;
• means for measuring the lineal tape displacement during the time interval between successive ones of said signals;
• means responsive to the magnitude of said lineal tape displacement during said time interval to derive instantaneous values of radius of such reel following each such signal;
• means for storing inertial values corresponding to predetermined values of reel radius;
• means responsive to said inertial values to provide acceleration motor currents of corresponding magnitude according to a predetermined servo algorithm for controlling reel rotation;
• and
• means responsive to each such signal to actuate the last-introduced means to provide continuing changes in acceleration current as reel radius changes.

A method of measuring the changing inertia of a reel of tape during winding and unwinding of the tape on the reel, comprising the steps of:

• storing in a storage unit inertial values corresponding to predetermined different values of tape reel radius;
• measuring the amount of tape displaced around the reel during successive time intervals, each terminating when the reel is rotated through a predetermined angle;
• using the tape displacement as measured and said predetermined angle to derive the instantaneous radius of the reel;
• and
• using the radius as derived for looking up the corresponding inertial value in the storage unit.

A reel-to-reel tape transport apparatus wherein an unbuffered length of tape follows a fixed-length path from a supply reel past a read/write head and guide to a take-up reel, and one motor drives the take-up reel and another motor drives the supply reel to maintain appropriate tension and tape motion at the read/write head, characterized by

• a control mechanism which is continually adaptive to dynamic changes as the tape is moved from the supply reel to the take-up reel comprising:
• means for measuring the variable amount of tape displaced each time one of said reels is rotated through a preselected angle;
• motion control logic means responsive to said measuring means, including means for deriving reel radii and tape inertial values corresponding thereto, and including means for calculating tape velocity error;
• and
• arithmetic logic means responsive to said measuring means for calculating from said tape velocity error and said inertial values the appropriate torque for each reel to drive said velocity error to zero along a predetermined profile with negligible tape tension disturbances.

A reel-to-reel tape transport apparatus wherein an unbuffered length of tape follows a fixed-length path from a supply reel past a read/write head and guide to a take-up reel, and one motor drives the take-up reel and another motor drives the supply reel to maintain appropriate tension and tape motion at the read/write head, characterized by

• a control mechanism which is continually adaptive to dynamic changes as the tape is moved from the supply reel to the take-up reel comprising:
• means for measuring the variable amount of tape displaced each time one of said reels is rotated through a preselected angle;
• motion control logic means responsive to said measuring means, including means for deriving reel radii and tape inertial values corresponding thereto, and
• arithmetic logic means responsive to said measuring means for calculating from said reel radii values and inertial values the appropriate torque for each reel to maintain tape tension substantially constant.