A method and apparatus for use with a computer for tracking the position of a user manipulatable object and for providing forces to lock the apparatus. The manipulatable object is coupled to a mechanical linkage which is supportable on a fixed surface and is tracked by sensors for sensing the location...http://www.google.co.uk/patents/US6046727?utm_source=gb-gplus-sharePatent US6046727 - Three dimensional position sensing interface with force output
