Fig: MR force feedback joystick (MRFFJ)
This system provides the user with tactile information in a two-degree-of-freedom environment. The end-effector for this system is a probe that can sense deflections in two planar directions. This probe is connected to a five bar linkage that is able to move in the horizontal plane. The motion of the five bar linkage is controlled by an innovative MR force feedback joystick (MRFFJ). Three single rotary dampers are designed for this system: the smaller Y-axis dampers are energized when the probe hits a barrier in the x direction and similarly the larger X-axis damper on works when the probe hits a barrier in y-direction. A 24 gauge copper coil with 1400 and 900 coil turns is used for the small and large dampers respectively. There are two encoders on the x and y shafts to send the handle movement signal to the 5-link bar system. The small and large dampers are designed to generate resistance torques of 2.5 and 5 N.m. respectively.
Fig: 2-DOF system setup
Fig: Profile tracking path
The 2DOF system is designed to trace a two dimensional curved path. As the user moves the MRFFJ handle the x and y axis digital encoders sense the position of the joystick. The encoders signals are sent to a data acquisition system that, in turn, sends voltage to the five-bar linkage actuators. When the probe comes into contact with boundaries of a curved path, the probe pivots and the angular changes are sensed by a second set of encoders which are directly connected to rotary springs. This coupling allows one to infer the force that the probe experiences. This calibrated signal is then sent to data acquisition board and the corresponding control commands are sent to a DC power supply and as a result the current sent to MRFFJ dampers is increased. This activates the MR fluid within the dampers and the user feels the boundaries of the curved path.
Fig: Force feedback results for 2DOF system