weed eater - automatic line feed

This is a public disclosure of a patentable process for the automatic feeding of the cutting string from weed eaters. This disclosure does not grant or imply permission to copy the idea or concept. Involving me in the process of the developing the design would be the right thing to do.
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Presently, there is a cumbersome and inconvenient way to lengthen the string. You have to find a hard patch of earth and pound the machine to release the string brake. Sometimes too much string is released and constant attention must be paid as to when the string is getting shorter. (As the string shortens, the machine revs higher and this is one indication of when to pound the machine.)
The solution is to have an automatic sensor which gauges the string length and releases the brake. There are at least 4 different mechanical and instrument systems I can think of that would gauge when the string gets shorter. Upon release of the string the same, chosen, system would detect the lengthening and engage the brake again.
The operator could mow away with attention to string feed. it would all be automatic.
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There is a string feed system which complements this system. I will not reveal that here.