Patents linked:

http://www.google.com/patents/US5978594 http://www.google.com/patents/US6816898 http://www.google.com/patents/US6895586 http://www.google.com/patents/US7062683 http://www.google.com/patents/US7617073 http://www.google.com/patents/US8646093 http://www.google.com/patents/US8674992