Kinematic comparison of single degree-of-freedom robotic gait trainers

Single degree-of-freedom mechanized gait trainers employing linkage mechanisms
can imitate the gait trajectory of the human user at a potentially lower cost than current
commercial solutions. Our goal was to evaluate recently introduced four-, six- and
eight-bar designs from the standpoint of kinematics, that is, the ability to follow a
natural gait pattern. Based on gait database of 113 healthy individuals, we synthesized
mechanisms allowing two link length adjustments and compared trajectory and path

accuracy of the ankle across mechanisms. We used cross-validation to obtain data-
independent accuracy. We used gait trajectories from a large human database and

predicted additional trajectories to represent effects of varying heights and speeds. We
found that trajectory error was significantly lower in the eight-bar mechanism (3.77 ±
0.17 cm, mean ± SD) than the four- (6.84 ± 0.37 cm) and six-bar (7.15 ± 0.48 cm)

configurations (p<0.0001). However, we did not observe differences in time-
independent path error between configurations, or in mechanical advantage (p>0.05).

We conclude that the eight-bar configuration is best when the mechanism is tied to a
constant velocity actuator, whereas the four-bar mechanism performs as well if the
actuator is well-controlled.