Patents.
4,963,017; 4,974,946; 4,984,855; 4,996,441; 5,002,347; 5,008,908; 5,009,486; 5,018,861; 5,020,905; 5,031,199; 5,031,993; 5,035,478; 5,044,750; 5,048,966; 5,049,753; 5,050,965; 5,050,966; 5,051,577; 5,056,895; 5,058,968; 5,061,027; 5,061,046; 5,062,694; 5,067,788.