Google turns up these: https://www.google.com/patents/US5628016 https://www.google.com/patents/US5628016 https://www.google.com/patents/US6247169 https://www.

Google turns up these: https://www.google.com/patents/US5628016 https://www.google.com/patents/US5628016 https://www.google.com/patents/US6247169 https://www.google.com/patents/US6247169 https://patents.google.com/patent/US20070016894A1 https://patents.google.com/patent/US20070016894A1 I'm not sure about the last one since it's an apparently abandoned application rather than a granted patent... Interestingly, US6247169 reports "lapsed" on the google page due to non-payment of fees... I'm really not sure what to make of US5628016 - it's filing date is in 1994, but there's a report of a 2015 "Assignment" legal event. (edit - fixed links)