Design and control of an assistive exoskeleton with passive toe joint

Abstract

Several exoskeletons with various configurations and degrees-of-freedoms (DOFs) have been introduced in the literature, but not many have addressed the optimal selection of the mechanism's DOFs. In the proposed system a semi-passive toe joint is introduced to achieve several advantages. The performance of the proposed novel passive toe joint is evaluated experimentally. In addition, the semi-passive abduction/adduction DOFs in the hip joint and eversion/inversion DOFs in ankle joint is proposed to facilitate turning while providing more comfort during normal walking. The effect of passive DoFs existence on the user comfortability is studied with the aid of three kinematic indices. In the proposed mechanism, a set of compact, low-backlash rotary series elastic actuators are designed and incorporated to actuate the joints. A novel torque control is also introduced and evaluated experimentally. Results show good performance of the robot in zero-force control and impedance control during swing phase of motion.