This paper describes a motion generation method for dynamic lifting by a humanoid robot. The proposed technique suggests the possibility of taking advantage of the whole body motion in order to facilitate the lifting movement. In particular, the idea is to perform a preliminary motion in order to generate a momentum which is instantaneously transferred to the object as an impulsive force. This allows the humanoid to lift up an object that could not be lifted up only by continuous force. However an impulsive force may make the humanoid unstable. Then, we propose to set the center of percussion (CoPn) of the whole system at the center of the support polygon of the humanoid when it lifts up the object. We also propose a design method of a preliminary motion of the humanoid that generates a sufficient momentum to lift up an object without any slip, tumble and hop of the whole system. The effectiveness of the proposed method is confirmed by simulation and experiment.
There are many kinds of large, heavy objects, or objects with geometrical constraints in our daily life, but non-fixed robots such as humanoid robots are still not able to manipulate them sufficiently well. In this paper we focus on a swing door as a heavy object with geometrical constraints, and present a method for the humanoid robots to open it by using impulsive forces. We first discuss on momentum transfer from the robot to the door. Then we propose a method of generating a whole body motion to impact on the door. We analyze the dynamic model of the door, and we confirm the validity of our method through simulation. At last, we realize a motion of the robot opening a swing door quickly by the method in experiment with the HRP-2 robot hardware.
Abstract-Humanoid robots are getting increasingly attention in the robotics community, not only for the scientific challenge of the complex multibody system issues and mechatronic designs, but also due to their high mobility and versatility. Humanoid robots have the potential to navigate through complex environments such as the standard living surrounding of humans. This is mainly due to the bipedal legged nature of the robotic system, which allows higher mobility than its wheeled counterpart. One of the advantages is that it can negotiate obstacles by stepping over them, which is the topic of the work presented in this paper. The main focus of this research is to investigate stepping over large obstacles. Previous work has reported on algorithms using quasi-static balancing, which resulted in somehow unnatural slow motions. This work however is focussing on stepping over larger obstacles in a fluent dynamic motion, using stability criteria on zero moment point instead of center of gravity. All the work is formulated in function of the elaborate HRP-2 humanoid research platform. In this paper a preliminary 2D study on stepping over leg trajectories and their dynamic implications on the overall stability are investigated. The paper discusses the implementation of the stepping over procedure in the overall dynamic motion generator, the implications on the kinematics and dynamics and finally the actual stepping over foot trajectory planner.
Abstract-A motion control method of lifting a heavy object up to a higher position with humanoid robots is developed. The key issue of lifting motion is how to reduce the load on humanoid arms in which low-power actuators are implemented. The use of singular postures of arms is well-known to avoid actuator saturation of the arms. By combining two different kinds of humanoid motions such as accelerating an object upward and sliding the body into under the object, we propose a method that enables to transit one singular posture of arms to another while lifting the object. Simulation results show the effectiveness of the proposed method for reducing the load on the arms. We realize a motion of lifting a heavy object dynamically with the humanoid robot HRP-2 through experiment.
We have developed a casting manipulator that includes a flexible light string in the link mechanism to enlarge the workspace of the manipulator. In the casting manipulation, an endeffector is launched to its target by releasing the string connected to it, and its trajectory is controlled by the tension of the string. In this paper, we present the midair control of the end-effector. As a simple way, we propose the braking technique to apply impulsive force to the end-effector by braking the movement of the string. Examining dynamic characteristics of the string when an impulsive force applies to it, we show that the midair motion of the end-effector can be controlled by the braking technique. Then, we apply the braking technique to the multiple braking control of the trajectory. We confirm the effectiveness of the proposed method through simulations and experiments using casting manipulator hardware.
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