Shizuko Hattori

A universal stability criterion of the foot contact of legged robots - adios ZMP

This paper proposes a universal stability criterion of the foot contact of legged robots. The proposed method checks if the sum of the gravity and the inertia wrench applied to the COG of the robot, which is proposed to be the stability criterion, is inside the polyhedral convex cone of the contact wrench between the feet of a robot and its environment. The criterion can be used to determine the strong stability of the foot contact when a robot walks on an arbitrary terrain and/or when the hands of the robot are in contact with it under the sufficient friction assumption. The determination is equivalent to check if the ZMP is inside the support polygon of the feet when the robot walks on a horizontal plane with sufficient friction. The criterion can also be used to determine if the foot contact is sufficiently weakly stable when the friction follows a physical law. Therefore, the proposed criterion can be used to judge what the ZMP can, and it can be used in more universal cases

Constraint-based dynamics simulator for humanoid robots with shock absorbing mechanisms

We propose a simulation system that achieves realistic and efficient simulations of humanoid robots. This paper focuses on a constraint-based contact force solver and virtual spring-damper joints from among the components of the system. The contact force solver can accurately simulate contacts between rigid bodies including articulated rigid bodies. LCP-like formulation of constraint conditions is solved by an iterative calculation method that extends the Gauss-Seidel method. This paper clarifies how to integrate existing methods to implement a robust and efficient solver. Virtual spring-damper joints are proposed to simulate a shock absorbing mechanism that many biped humanoid robots have in their feet to increase the stability of walking motion. The combination of the rigid contact model and the elastic virtual joints can improve the accuracy of the simulation. The simulation system was verified by experiments using humanoid robot HRP-2, and the results shows the validity of the system.

Power-assisted walking support system for elderly

This system is to support elderly people who need some help in standing up from the bed, walking around, sitting down to the toilet or bed for rehabilitation. In the design of this system, the use of the left function of the user was strongly considered. The experimental mechanism of the walking support system is developed. The basic features are: (1) electrically power-assisted in both motions of standing-up/sitting-down and walking; (2) a sensor system for easier motion instruction for the elderly. Future research includes field test and evaluation of the system functions. The force sensitive motion control method with compensation of gravity on the slope is also discussed.

A Pattern Generator of Humanoid Robots Walking on a Rough Terrain

This paper presents a biped humanoid robot that is able to walk on a rough terrain while touching a handrail. The contact wrench sum (CWS for short) is used as the criterion to judge if the contact between the robot and the environment is strongly stable under the sufficient friction assumption, where the contact points are not coplanar and the normal vectors at the points are not identical. It is confirmed that the proposed pattern generator can make the robot walk as desired in dynamics simulations and experiments, and the motions can be improved by a hand position control and using waist joints.

Two-Stage Time-Parametrized Gait Planning for Humanoid Robots

In this paper, we propose a framework on planning collision-free walking motion for biped humanoid robots. Our proposed planner is composed of two phases. In the first phase, the constraint condition is generated as a function of time by using the walking pattern generator. In the second phase, the collision-free walking motion is planned. To generate the collision-free motion, we add a time parameter to each milestone of the single-query, bidirectional, lazy collision checking planner in order to explicitly consider the time-parametrized constraint conditions. Further, we smoothen the generated path by using B-spline interpolation. Through experimental results, we show that our planner is effective in realizing collision-free walking motion by real humanoid robots.

Power-assisted walking support system with imbalance compensation control for hemiplegics

Walking ability is essential for the elderly if they are to live a self-supported daily life. Conventional walkers have been used by people with weak lower limbs, but manipulating these walkers for desired direction is difficult for hemiplegic patients. This paper describes a power-assisted walking support system that allows these patients better control of their walk by compensating for the force input bias caused by their imbalanced gait. Experimental use by hemiplegics improved the stability and speed of their walk.

A pattern generator of humanoid robots walking on a rough terrain using a handrail

This paper presents a motion pattern generator of humanoid robots that walks on a flat plane, steps and a rough terrain. It is guaranteed rigorously that the desired contact between a humanoid robot and terrain should be maintained by keeping the contact wrench sum between them inside the contact wrench cone under the sufficient friction assumption. A walking pattern is generated by solving the contact wrench equations and by applying the resolved momentum control.

Motion planning for walking pattern generation of humanoid

In this paper, we plan the collision free motion for walking pattern generation of a humanoid robot. Our motion planner can take into account several features of the walking pattern generator. We first run the walking pattern generator by considering the contact wrench applied to the robot and monitor the collision among the links and the environments. Then, we plan the collision free motion for the period of time causing the collision. In our motion planner, we can consider the constraint condition which are the functions of time. Also, for keeping balance of the robot, we plan the motion with keeping the horizontal position of the COG as well as the position/orientation of the feet/hand. The effectiveness of the proposed method is confirmed by simulation and experiment.

System design and field-testing of the walk training system

The ability to walk enhances overall ability of daily life (ADL) of the elderly. Technically aiding the ability to walk is a basic solution for elderly society. A walk training system for the elderly is now under development. It has two parts: a training environment and a patient support element. The training environment comprises a treadmill and a display. The user stands on the treadmill and begins to walk. The endless belts of the treadmill are driven by active impedance control. The user is supported by a two degree-of-freedom manipulator. The force on the support is determined by the displacement of the user from the reference point, so as to maintain the attitude of the user or to support the users weight. The walk training system was tested on 30 persons. Its basic function was rated highly.