US Patent 5644329 (A),1997;European Patent EP0612184 (A2),1994;
European Patent EP0612184 (A3),1995;
European Patent EP0612184 (B1),1999;
German Patent DE69420437 (T2),1999.
US Patent 5689280, 1997;European Patent EP0618562 (A1),1994; European Patent EP0618562(B1), 1998; German Patent DE69410682 (T2),1999; Chinese Patent CN1110789(A), 1995.