脚負荷情報に基づく脚相調整を用いた四脚動歩行の生成と安定化

摘要

Regarding the issue of legged locomotion stabilization, it can be pointed out that, atlow speeds, since gravity is dominant, posture control using sensory information suchas ground reaction force or vestibular information is predominant. On the other hand,at high speeds, since the influence of the inertial forces is dominant, rhythmic motioncontrol to construct a limit cycle becomes primordial. Consequently, legged locomotioncontrollers should integrate both posture control and rhythmic motion control to be ableto cover the whole range of locomotion speeds.This thesis considers the use of sensory information related to leg loading (i.e. theload supported by the leg) in a CPG type controller to generate stable quadrupedaldynamic walk. Leg loading information is used at the individual leg level to regulate thetransitions between the stance and the swing phases. Accordingly, the CPG activity isadjusted of via phase modulations, i.e. modulations of the relative durations of the stanceand swing phases of the stepping motion in each leg. This study concentrates on therole of the regulation of stance-to-swing transition using leg loading information. Usingdynamics simulations, it investigates the contribution of this mechanism to rhythmicmotion control and posture control, in the range from low- to medium-speed walking.This issue is investigated in the case of two-dimensional stepping motions and threedimensionalquadrupedal dynamic walk. In both cases, a sensor-dependent CPG isused, where phase transitions in each leg controller is controlled using leg loading information.Swing-to-stance and stance-to-swing transitions are respectively triggeredwhen the touchdown event is detected and when leg loading becomes smaller than agiven threshold.Generation of two-dimensional stepping motions is achieved with musculoskeletal modelsfaithful to the cat anatomy. For the hind legs, a preexistent model is used, whilean original model of the forelegs is developed. A neural leg controller architecture, ableto induce stepping motions of a leg at various speeds, is proposed. Using a pair ofleg controllers, stepping patterns at constant speed are generated with the hind legsmodel and the forelegs model separately, by replacing the not-actuated pair of legs bya wheeled support. As a result of the phase modulations based on leg loading information,stable alternate stepping coordination of the legs emerges, even when the two legcontrollers are independent. Next, the issue of speed modulation is considered with thehind legs model. The leg coordination maintains in the whole range of speeds considered and adaptations of walking patterns according to the speed are characterized. Strikingsimilarities with the adaptations taking place during real cat locomotion are found, reinforcingthe hypothesis that, in animals, stance-to-swing transition is mainly regulatedusing sensory signals related to leg unloading.In order to facilitate the study of the action of the phase modulations in the threedimensionalcase, a traditional robotic approach, combining trajectory generation andlocal PD control, is used instead of a muscular model to generate the motor patterns.Using four independent controllers, stable quadrupedal dynamic walk is generated in abroad range of cyclic periods and speeds. Phase modulations using leg loading informationcontribute to the emergence of left-right alternate stepping coordination of the legs.The phase difference between ipsilateral legs is adjusted by setting appropriately twocategories of the leg controllers parameters: the vertical coordinate of nominal touchdownposition of the feet and the PD control gains of the ankle and knee joints. Thestability of the walking patterns is assessed by subjecting the model to lateral perturbations.In most of the application timings, the phase modulations adjust the rhythmicmotion of the legs to stabilize the body rolling motion against the disturbance. However,when the perturbation results in a sufficient decrease of the rolling motion amplitude onone side, the foreleg on the other side cannot swing and the leg coordination is severelydisturbed. Hence, a leg coordination mechanism, promoting stance-to-swing transitionin the foreleg when the ipsilateral hind leg is swinging, is added to the previous architectureto improve the performances. With the additional coordination mechanism,the control system realizes good performances against the lateral perturbations for allthe timings of applications. Moreover, it is able to tackle terrain irregularities (such assteps and slopes) while stabilizing the posture. Hence, basic integration of posture controland rhythmic motion control is demonstrated with a simple and distributed controlarchitecture grounded on phase modulations using leg loading information.