Patents.
4,893,003; 4,896,929; 4,907,847; 4,896,928; 4,913,533; 4,913,534; 4,900,134; 4,913,547; 4,914,287; 4,919,501; 4,919,516; 4,919,536; 4,925,261; 4,925,273; 4,925,279; 4,925,281; 4,927,036; 4,927,234; 4,915,463; 4,918,987; 4,920,268; 4,927,254.