| dc.description.abstract | Knee exoskeletons have been developed to assist, stabilize, or improve human movement or recovery over a range of locomotion tasks. However, exoskeleton designers must implement transparency (i.e., get out of the way) modes during the swing phase of locomotor tasks to avoid impeding or interfering with desired movement. Transparency mode is commonly achieved using clutches, adjustable-parameter springs, modulating cable slack, or by using active control methods to minimize impedance. However, transparency mode is not perfect in practice, as residual forces from springs, friction, cable tension, or imperfect controller timing still exist during swing phase. The problem is that it is not understood how sensitive people are to small knee torques or what level of knee stiffness or damping is acceptable (sufficiently transparent) during swing phase.
In this dissertation, we (i) characterized the biomechanical consequences of knee stiffness and damping during swing phase, and (ii) leveraged user perceptions of being impeded and minimum toe clearance to define transparency thresholds. Below the defined transparency thresholds, the participants were sufficiently unimpeded. We conducted a series of human subject experiments that involved walking and stair ascent/descent while wearing a modified knee brace with four different adjustable stiffness and damping values. We measured changes to lower limb kinematics, knee flexor muscle activity, and participants' perception of being impeded during swing phase. We consequently used this data to determine transparency thresholds based on minimum toe clearance and perceived impedance data. These values may provide useful benchmark values for defining quantitative design requirements for knee exoskeletons intended for locomotor activities. | |
