  Previous research has shown that the effective use of inertial motion (i.e.,
less or no torque input at the knee joint) plays an important role in achieving
a smooth gait of transfemoral prostheses in the swing phase. In our previous
research, a method for generating a timed knee trajectory close to able-bodied
individuals, which leads to sufficient clearance between the foot and the floor
and the knee extension, was proposed using the inertial motion. Limb motions
are known to correlate with each other during walking. This phenomenon is
called kinematic synergy. In the present study, we measure gaits in level
walking of able-bodied individuals with a wide range of walking velocities. We
show that this kinematic synergy also exists between the motions of the intact
limbs and those of the knee as determined by the inertial motion technique. We
then propose a new method for generating the motion of the knee joint using its
inertial motion close to the able-bodied individuals in mid-swing based on its
kinematic synergy, such that the method can adapt to the changes in the motion
velocity. The numerical simulation results show that the proposed method
achieves prosthetic walking similar to that of able-bodied individuals with a
wide range of constant walking velocities and termination of walking from
steady-state walking. Further investigations have found that a kinematic
synergy also exists at the start of walking. Overall, our method successfully
achieves knee motion generation from the initiation of walking through
steady-state walking with different velocities until termination of walking.
