A Robotic Cadaveric Gait Simulator With Fuzzy Logic Vertical Ground Reaction Force Control

Lower limb dynamic cadaveric gait simulators are useful to investigate the biomechanics of the foot and ankle, but many systems have several common limitations, which include simplified tendon forces, nonphysiologic tibial kinematics, greatly reduced velocities, scaled body weight (BW), and, most importantly, trial-and-error vertical ground reaction force (vGRF) control. This paper presents the design, development, and validation of the robotic gait simulator (RGS), which addresses these limitations. A 6-degrees-of-freedom (6-DOF) parallel robot was utilized as part of the RGS to recreate the relative tibia to ground motion. A custom-designed nine-axis proportional-integral-derivative (PID) force-control tendon actuation system provided force to the extrinsic tendons of the cadaveric lower limb. A fuzzy logic vGRF controller was developed, which altered tendon forces in real time and iteratively adjusted the robotic trajectory in order to track a target vGRF. The RGS was able to accurately reproduce 6-DOF tibial kinematics, tendon forces, and vGRF with a cadaveric lower limb. The fuzzy logic vGRF controller was able to track the target in vivo vGRF with an average root-mean-square error of only 5.6% BW during a biomechanically realistic 3/4 BW, 2.7-s stance phase simulation.