On the Emulation of Stiff Walls and Static Friction With a Magnetically Levitated Input/Output Device

This technical brief addresses issues of mechanical emulation of stiff walls and stick-slip friction with a 6-DOF magnetically levitated joystick. In the case of stiff wall emulation, it is shown that the PD control implementation commonly used severely limits achievable wall damping and stiffness. It is also shown that the perceived surface stiffness can be increased without loss of stability by applying a braking force pulse when crossing into the wall. For stick-slip friction, Karnopp’s model was implemented using a PD controller within the stick friction threshold. Even though the PD controller allows some motion during the stick phase, the haptic feedback provided is remarkably similar to stick-slip friction.