A method and apparatus for providing low-cost, realistic force feedback
including an improved actuator. The invention provides force sensations
to a user and includes an interface device coupled to a host computer and
allowing a user to interact with a host application program. A user
object, such as a joystick, is moveable by a user in at least one rotary
degree of freedom. A sensor reports a locative signal to the host
computer to indicate a position of the user object. An actuator outputs
forces on the user object in response to signals from the host computer
and program. The actuator includes a housing, a set of grounded magnets
provided on opposing surfaces of the housing and creating a magnetic
field, and a rotor coupled to the user object positioned between the
magnets. The rotor rotates about an axis of rotation and includes a shaft
and teeth spaced around the shaft. An electric current flows through one
or more coils on the teeth to cause the rotor to rotate. The teeth and
the magnets are provided in a skewed, helical arrangement relative to
each other so that, as the rotor rotates, a first tooth gradually exits
the magnetic field as the next consecutive tooth gradually enters the
magnetic field, thereby significantly reducing a cogging effect of the
rotor when the user object is moved by the user and increasing the
fidelity of forces experienced by the user.