Kinematic and Kinetic Assessment of a Novel Polycentric Knee Joint for Powered Walking Assist Exoskeletons

Loss of mobility and independence directly affects the quality of life of many vulnerable individuals. In order to address this, researchers have been developing wearable walking assist exoskeletons to aid users with their daily activities. While this technology has advanced tremendously in the past decade, current exoskeletons are yet to be ergonomic, causing discomfort and injuries to the user, leading to early device rejection. This research intends to assess the kinematic and kinetic compatibility of a novel knee joint suitable for exoskeletons. The proposed knee design can be adapted to accommodate a kinematic offset and optimize force delivery. This is achieved by ensuring that the mechanical and biological joint rotation axes are aligned and that the moment arm can be varied to mimic the mechanical characteristics of a biological knee. Model simulations and mechanical testing of fabricated prototypes were achieved to analyze and validate the design. Results confirmed the compatibility of the design, which demonstrated kinematic absolute error values of 1.68 and 0.32 mm for the offset and aligned joints, respectively. It was shown that the moment arm can be varied throughout flexion, allowing future iterations to achieve optimal and effective moment transfer.