Development of a Multidirectional Controlled Small-Scale Spherical MR Actuator for Haptic Applications

In robotics and haptics, actuators that move at multiple degrees of freedom (DOFs) without the intermediate transmission mechanisms and have high force/torque output with compact size are widely expected to improve the stability and transparency of interactions. For this reason, utilizing the characteristics that the rheological properties of magnetorheological (MR) fluid can be continuously and reversibly changed by an external magnetic field within a few milliseconds, a multidirectional controlled three-DOF spherical MR actuator is proposed in this paper. Through the special design of the stator part, the actuator can implement force feedback control in multiple directions. Then, based on the calculated torque model and analysis of the magnetic circuit, finite-element analysis is used to optimize the geometry and internal magnetic field distribution of the actuator. In order to achieve precise control and positioning of multi-DOF motion, a small inertial measurement unit is integrated in the upper part of the joystick. We built a prototype of this actuator and tested its performance under various control conditions. The results show that the actuator can provide force feedback with reasonable magnitude and direction to users according to the change of interaction conditions, thus overcoming the disadvantage of the existing spherical MR actuators that limit the movement of the user in all directions after being activated.