Kensuke Harada

Biped walking pattern generation by using preview control of zero-moment point

We introduce a new method of a biped walking pattern generation by using a preview control of the zero-moment point (ZMP). First, the dynamics of a biped robot is modeled as a running cart on a table which gives a convenient representation to treat ZMP. After reviewing conventional methods of ZMP based pattern generation, we formalize the problem as the design of a ZMP tracking servo controller. It is shown that we can realize such controller by adopting the preview control theory that uses the future reference. It is also shown that a preview controller can be used to compensate the ZMP error caused by the difference between a simple model and the precise multibody model. The effectiveness of the proposed method is demonstrated by a simulation of walking on spiral stairs.

Resolved momentum control: humanoid motion planning based on the linear and angular momentum

We introduce a method to generate whole body motion of a humanoid robot such that the resulted total linear/angular momenta become specified values. First, we derive a linear equation, which gives to total momentum of a robot from its physical parameters, the base link speed and the joint speeds. Constraints between the legs and the environment are also considered. The whole body motion is calculated from a given momentum reference by using a pseudo-inverse of the inertia matrix. As examples, we generated the kicking and walking motions and tested on the actual humanoid robot HRP-2. This method, the resolved momentum control, gives us a unified framework to generate various maneuvers of humanoid robots.

Biped walking stabilization based on linear inverted pendulum tracking

A novel framework of biped walking stabilization control is introduced. The target robot is a 42 DOF humanoid robot HRP-4C which has a body dimensions close to the average Japanese female. We develop a body posture controller and foot force controllers on the joint position servo of the robot. By applying this posture/force control, we can regard the robot system as a simple linear inverted pendulum with ZMP delay. After a preliminary experiment to confirm the linear dynamics, we design a tracking controller for walking stabilization. It is evaluated in the experiments of HRP-4C walking and turning on a lab floor. The robot can also perform an outdoor walk on an uneven pavement.

Humanoid robot HRP-3

A development of humanoid robot HRP-2 is presented in this paper. HRP-2 is a humanoid robotics platform, which we developed in phase two of HRP. HRP was a humanoid robotics project, which had run by the Ministry of Economy, Trade and Industry (METI) of Japan from 1998FY to 2002FY for five years. The ability of the biped locomotion of HRP-2 is improved so that HRP-2 can cope with uneven surface, can walk at two third level of human speed, and can walk on a narrow path. The ability of whole body motion of HRP-2 is also improved so that HRP-2 can get up by a humanoid robots own self if HRP-2 tips over safely. In this paper, the appearance design, the mechanisms, the electrical systems, specifications, and features upgraded from its prototype are also introduced.

Biped Walking Pattern Generator allowing Auxiliary ZMP Control

A biped walking pattern generator which allows an additional ZMP control (auxiliary ZMP) is presented. An auxiliary ZMP is realized by an inverse system added to a pattern generator based on the ZMP preview control. To compensate the effect of the auxiliary ZMP, we apply virtual time shifting of the reference ZMP. As an application of the proposed method, a walking control on uneven terrain is simulated. The simulated robot can walk successfully by changing its walking speed as the side effect of the auxiliary ZMP control

An analytical method on real-time gait planning for a humanoid robot

This paper studies the real-time gait planning for a humanoid robot. By simultaneously planning the trajectories of the COG (center of gravity) and the ZMP (zero moment point), the fast and smooth change of gait, can be realized. The change of gait is also realized by connecting the newly calculated trajectories to the current ones. While we propose two methods for connecting two trajectories, i.e. the real-time method and the quasi-real-time one, we show that the stable change of gait can be realized by using the quasi-real-time method even if the change of the step position is significant. The effectiveness of the proposed methods is confirmed by simulation and experiment.

Motion Planning for Legged Robots on Varied Terrain

In this paper we study the quasi-static motion of large legged robots that have many degrees of freedom. While gaited walking may suffice on easy ground, rough and steep terrain requires unique sequences of footsteps and postural adjustments specifically adapted to the terrains local geometric and physical properties. In this paper we present a planner that computes these motions by combining graph searching to generate a sequence of candidate footfalls with probabilistic sample-based planning to generate continuous motions that reach these footfalls. To improve motion quality, the probabilistic planner derives its sampling strategy from a small set of motion primitives that have been generated offline. The viability of this approach is demonstrated in simulation for the six-legged Lunar vehicle ATHLETE and the humanoid HRP-2 on several example terrains, including one that requires both hand and foot contacts and another that requires rappelling.

Hybrid position/force control of flexible-macro/rigid-micro manipulator systems

Abstruct- In this paper, hybrid positiodforce control algorithms of combined flexible-macrokigid-micro manipulator systems are proposed. In the proposed system, the micro manipulator is attached at the tip of the flexible macro manipulator. The macro manipulator can move widely, but cannot realize fast and precise motion because of its flexibility. On the contrary, the micro manipulator cannot move widely, but can move fast and precisely. By taking advantage of the macrohicro system, both the end point position and the force exerted by its end effector can be easily controlled in spite of the flexibility in the macro part. This paper first discusses trajectory planning for the macrohicro system. Second, a quasi-static hybrid control algorithm and a dynamic hybrid control algorithm are developed. In our control algorithms, the macro part is controlled roughly to realize the desired trajectory, and suppress vibration. The micro part is controlled to compensate for the position and force errors due to the elasticity in the macro part. Finally, to verify the effectiveness of the proposed control algorithms, experimental results are shown.

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

Using Motion Primitives in Probabilistic Sample-Based Planning for Humanoid Robots

This paper presents a method of computing efficient and natural-looking motions for humanoid robots walking on varied terrain. It uses a small set of high-quality motion primitives (such as a fixed gait on flat ground) that have been generated offline. But rather than restrict motion to these primitives, it uses them to derive a sampling strategy for a probabilistic, sample-based planner. Results in simulation on several different terrains demonstrate a reduction in planning time and a marked increase in motion quality.