us patent 4647924 (1987) https://patentimages.storage.googleapis.com/a5/dc/27/34d036c71365dc/US4647924.pdf https://patentimages.storage.googleapis.com/a5/dc/27

us patent 4647924 (1987) https://patentimages.storage.googleapis.com/a5/dc/27/34d036c71365dc/US4647924.pdf https://patentimages.storage.googleapis.com/a5/dc/27/34d036c...