Fumihiko Asano

Biped gait generation and control based on a unified property of passive dynamic walking

Principal mechanisms of passive dynamic walking are studied from the mechanical energy point of view, and novel gait generation and control methods based on passive dynamic walking are proposed. First, a unified property of passive dynamic walking is derived, which shows that the walking systems mechanical energy increases proportionally with respect to the position of the systems center of mass. This yields an interesting indeterminate equation that determines the relation between the systems control torques and its center of mass. By solving this indeterminate equation for the control torque, active dynamic walking on a level can then be realized. In addition, the applications to the robust energy referenced control are discussed. The effectiveness and control performances of the proposed methods have been investigated through numerical simulations.

Energy-Efficient and High-Speed Dynamic Biped Locomotion Based on Principle of Parametric Excitation

We clarified that the common necessary condition for generating a dynamic gait results from the requirement to restore mechanical energy through studies on passive dynamic walking mechanisms. This paper proposes a novel method of generating a dynamic gait that can be found in the mechanism of a swing inspired by the principle of parametric excitation using telescopic leg actuation. We first introduce a simple underactuated biped model with telescopic legs and semicircular feet and propose a law to control the telescopic leg motion. We found that a high-speed dynamic bipedal gait can easily be generated by only pumping the swing leg mass. We then conducted parametric studies by adjusting the control and physical parameters and determined how well the basic gait performed by introducing some performance indexes. Improvements in energy efficiency by using an elastic-element effect were also numerically investigated. Further, we theoretically proved that semicircular feet have a mechanism that decreases the energy dissipated by heel-strike collisions. We provide insights throughout this paper into how zero-moment-point-free robots can generate a novel biped gait.

A novel gait generation for biped walking robots based on mechanical energy constraint

This paper proposes novel energy-based gait generation and control methods for biped robots based on an analysis of passive dynamic walking. First, we discuss the essence of dynamic walking using a passive walker on a gentle slope from the mechanical energy point of view. Second, we propose a simple and effective gait-generation method, which imitates the energy behavior in every walking cycle considering the zero-moment point condition and other factors of the active walker. The control strategy is formed by taking into account the features of mechanical energy dissipation and restoration. Following the proposed method, the robot can exhibit a natural and reasonable walk on a level ground without any gait planning and design in advance. The effectiveness of the method is examined through numerical simulations and experiments.This paper proposes a novel energy-based control law for biped robots based on an analysis of passive dynamic walking. Firstly we discuss the essence of dynamic walking using a passive walker on a gentle slope. In the second, we propose a simple and effective control law which imitates the energy behavior in every cycle considering the ZMP condition and other factors of the active walker. The control strategy is formed by the feature of mechanical energy dissipation and restoration. By the effect of the proposed method, the robot can exhibit natural and reasonable walk on a level ground without any gait design in advance. The validity of the proposed method is examined by numerical simulations and experiments.

The Effect of Semicircular Feet on Energy Dissipation by Heel-strike in Dynamic Biped Locomotion

This paper investigates the effect of semicircular feet on dynamic bipedal walking. It has been clarified by Asano and Luo (2006) that underactuated virtual passive dynamic walking can be realized by using the rolling effect, which acts as the ankle-joint torque virtually. It has been also shown that, throughout parameter studies, the rolling effect dramatically increases the stable domain of limit cycles. Now that the effect of semicircular feet during stance phase has been discussed, this paper then focuses the effect on mechanical energy dissipation by heel-strike. It is theoretically clarified that, through modeling and analysis of an inelastic collision, increasing walking speed is achieved not by the rolling effect during stance phase but by the effect of reducing mechanical energy dissipation by heel-strike.

On Energy-Efficient and High-Speed Dynamic Biped Locomotion with Semicircular Feet

This paper investigates effectiveness of semicircular feet on dynamic biped locomotion. We first introduce the simplest biped model with semicircular feet and show its level walking by hip-joint actuation. In the second, parameter study is performed by adjusting the physical and control parameters. Throughout numerical analysis, it is shown that the semicircular feet dramatically increases the walking speed and the stable domain. By the effect of the rolling, energy-efficient and high-speed dynamic biped locomotion on a level can be realized easily without ankle-joint actuation nor concerning the zero moment point condition

Asymptotically stable biped gait generation based on stability principle of rimless wheel

We investigated and identified the conditions necessary for stable dynamic gait generation in biped robots from the mechanical energy balance point of view. The equilibrium point at impact in a dynamic gait is uniquely determined by two conditions; keeping the restored mechanical energy constant and settling the relative hip-joint angle to the desired value before impact. The generated gait then becomes asymptotically stable around the equilibrium point determined by these conditions. This is shown by a simple recurrence formula of the kinetic energy immediately before impact. We verified this stability theorem using numerical simulation of virtual passive dynamic walking. The results were compared with those for a rimless wheel and an inherent stability principle was derived. Finally, we derived a robust control law using a reference mechanical energy trajectory and demonstrated its effectiveness numerically.

Extended passive velocity field control with variable velocity fields for a kneed biped

In this paper, two aspects for task specification and control of biped walking robot, i.e. (i) realization of safe control against human beings and the outside environment by utilizing a passive velocity field controller (PVFC), and (ii) energy-effective gait design based on virtual passive dynamic walking, are studied and a new control method is derived based on them. In our previous work, we have given a method which satisfied the required properties and examined the validity by numerical simulations. In the method a single trajectory is realized; however, the walking behavior should be modified and adapted by its energy level and initial conditions. Based on the observations, we introduce multi-pattern walking using the virtual passive gait to realize more natural walking motion. The virtual passive gait is shown to require less control input than other methods which can generate a limit cycle automatically without any gait design, and we combine the virtual passive walk with PVFC to change its walking speed easily and effectively.

Parametric Excitation Mechanisms for Dynamic Bipedal Walking

It is already clarified throughout studies of passive dynamic walking mechanisms that the common nec essary condition for dynamic gait generation comes from the requirement on mechanical energy restoration. Until now we have treated only rotational joints of the robot, whereas in this paper we consider a novel dynamic gait generation method based on mechanical energy restoration by parametric excitation using telescopic leg actuation. We first introduce a simple walking model and a control law for the telescopic leg motion, and show the typical walking pattern by numerical simulations. We then analyze the gait performance by adjusting some control and physical parameters. In addition, some extensions of the mechanism and control applications are investigated.

Passive velocity field control of biped walking robot

The study of bipedal walking in the framework of humanoid robot is a recent active research area. In this paper, we apply passive velocity field control to the control of a biped walking robot which walks on the level ground by actuators. Using this method, we can change the walking speed easily by modifying a virtual energy. The validity of the proposed method is demonstrated by numerical simulations.

Dynamic Analyses of Underactuated Virtual Passive Dynamic Walking

Realization of an energy-efficient and high-speed dynamic walking has come to be one of the main subjects in the research area of robotic biped locomotion, and passive dynamic walking has been widely attracted as a clue to solve the problem. It has been empirically known that the effect of convex curve shape of foot, which characterizes passive-dynamic walkers, is important to increase walking speed. This paper then investigates the driving mechanism of compasslike biped robots and the rolling effect of semicircular feet are mainly investigated. We first analyze the mechanism of a planar fully-actuated compass-like biped model to clarify the importance of ankle-joint torque introducing generalized virtual gravity concept. In the second, a planar underactuated biped model with semicircular feet is introduced and we show that virtual passive dynamic walking by hip-joint torque only can be realized based on the rolling effect. We then compare with a flat feet model through linear approximation, and show that the rolling effect is equivalent to its virtual ankle-joint torque. Throughout this paper, we provide novel insights into how ZMP-free robots can generate a dynamic bipedal gait.