High quality impact printing requires that a sufficient supply of printer ink be presented to the print element for each character. It is also required that this supply of ink last for a reasonable length of time. To enable the IBM SELECTRIC Composer to meet the standards considered necessary under these criteria, it was necessary to increase the character yield per ribbon by a factor of two over that which was provided by the IBM SELECTRIC Typewriter. To do this a new constant ribbon tension control device had to be designed to eliminate the inertia and geometry effects associated with the larger composer ribbon spools. It was also necessary to eliminate ribbon feeding on no-print or spacebar operations and to provide various load controls.
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