Construction of gait adaptation model in human splitbelt treadmill walking

Abstract

There are a huge number of studies that measure kinematics, dynamics, the oxygen uptake and so on in human walking on the treadmill. Especially in walking on the splitbelt treadmill where the speed of the right and left belt is different, remarkable differences in kinematics are seen between normal and cerebellar disease subjects. In order to construct the gait adaptation model of such human splitbelt treadmill walking, we proposed a simple control model and made a newly developed 2D biped robot walk on the splitbelt treadmill. We combined the conventional limit-cycle based control consisting of joint PD-control, cyclic motion trajectory planning and a stepping reflex with a newly proposed adjustment of P-gain at the hip joint of the stance leg. We showed that the data of robot (normal subject model and cerebellum disease subject model) experiments had high similarities with the data of normal subjects and cerebellum disease subjects experiments carried out by Reisman et al. (2005) and Morton and Bastian (2006) in ratios and patterns. We also showed that P-gain at the hip joint of the stance leg was the control parameter of adaptation for symmetric gaits in splitbelt walking and P-gain adjustment corresponded to muscle stiffness adjustment by the cerebellum. Consequently, we successfully proposed the gait adaptation model in human splitbelt treadmill walking and confirmed the validity of our hypotheses and the proposed model using the biped robot.

Keywords:

• biped robot
• model of human walking
• splitbelt treadmill
• gait adaptation
• stepping reflex
• P-gain adjustment

Acknowledgements

This work has been partially supported by a Grant-in-Aid for Scientific Research on Priority Areas ‘Emergence of Adaptive Motor Function through Interaction among Body, Brain and Environment’ from the Japanese Ministry of Education, Culture, Sports, Science and Technology.

Notes

¹We have not yet understood the reason.

²The value of the slow leg became much larger. This meant an asymmetric gait.

³The value of the fast leg became much larger. This meant another asymmetric gait.

⁴The ability for mutual entrainments (Orlovsky et al. 1999; Rossignol et al. 2006) would be employed in future.

⁵We did not use the output of the rate gyro sensor as vestibule but the ankle joint angular velocity for the stepping reflex, since the output of the rate gyro is a little noisy and the joint angular velocity is more reliable.

⁶If a flexor reflex is employed, Tetsuro can avoid falling down by stumbling of the swing leg.

⁷The knee joint of the swing leg in the single leg stance phase is free and this PD control is not used.

⁸An inappropriate value of k _sr (for example, 0.28) made Tetsuro fall down easily under disturbances.

⁹The differences of the stride length and the step length between human and robot experiments are due to the difference of the leg length between human and Tetsuro.

¹⁰If we employ a CPG of which phase is reset by PEP (post-exterior position) information of the stance leg (Aoi and Tsuchiya 2005; Morimoto et al. 2008), the duty ratio can be adjusted reactively as being suggested by Reisman et al. (2005) and Morton and Bastian (2006)

¹¹In the sense that P-gain adjustment needs _off calculated in the baseline stage, it could be goal-directed (Ilg et al. 2007).

¹²We assume the inelastic collision at foot contact and the law of conservation of angular momentum.