A force feedback interface having isotonic and isometric control capability coupled to a host computer that displays a graphical environment such as a GUI. The interface includes a user manipulatable physical object movable in
physical space, such as a mouse or puck. A sensor detects the object's movement and an
actuator applies output force on the physical object. A mode selector selects isotonic and isometric control
modes of the interface from an
input device such as a physical button or from an interaction between graphical objects. Isotonic mode provides input to the host
computer based on a position of the physical object and updates a position of a cursor, and force sensations can be applied to the physical
object based on movement of the cursor. Isometric mode provides input to the host
computer based on an input force applied by the user to the physical object, where the input force is determined from a sensed deviation of the physical object in space. The input force opposes an output force applied by the
actuator and is used to control a function of an application program, such as
scrolling a document or panning or zooming a displayed view. An
overlay force, such as a jolt or vibration, can be added to the output force in isometric mode to indicate an event or condition in the graphical environment.