Tape motion control for reel-to-reel drive

A method of controlling motion of an unbuffered length of tape as it is transferred from one reel to another reel, comprising the steps of:

• employing reels having hubs of identical diameter,
• using a radius constant, which is related to the maximum radius of tape on said one reel at completion of an initial wrap of the tape on said other reel, in conjunction with a manifestation indicative of the changing amount of tape transferred from said one reel to said other reel during successive revolutions of said one reel to repeatedly derive values related to the respective radii of both of said reels;
• and
• converting the values as derived into manifestations corresponding to appropriate reel-motor acceleration currents for each reel according to its then existing radius.

Method for controlling the size of an inter-block gap between blocks of data on a magnetic tape, comprising the steps of

• counting in a first counter, after the last byte of a block of data is written on the tape, a series of clock period pulses until a tachometer pulse is generated by rotation of a tape reel through a preselected small angle;
• upon occurrence of said tachometer pulse, storing the number of said clock period pulses in a register and simultaneously resetting a second counter to a reference count;
• counting tachometer pulses in said second counter, up or down relative to said reference count according to the direction of rotation of the reel, independently of reel radius;
• continually counting clock period pulses in said first counter;
• and
• initiating writing of a new block of data on the tape when the number of clock period pulses reaches a preselected number corresponding to the time required to traverse the inter-block gap at normal velocity, if a reinstruct command is received before the inter-block gap is traversed.