成果報告書詳細
管理番号20160000000057
タイトル*平成26年度中間年報 環境・医療分野の国際研究開発・実証プロジェクト ロボット分野の国際研究開発・実証事業 Choreonoidフレームワークを用いた災害対応ロボットシュレータの研究開発 
公開日2016/3/23
報告書年度2015 - 2015
委託先名国立大学法人大阪大学
プロジェクト番号P12001
部署名ロボット・機械システム部
和文要約
英文要約Summary of Research Achievements for the Fiscal Year 2014.
Tomomichi Sugihara, Associate Professor, Osaka University

Osaka university group aims at an improvement of the accuracy of forward dynamics computation in the dynamics simulator and enhances a software library which the group has been developing. The group has tackled the following three missions this year.

1-1. Improvement of speed and robustness of contact computation between objects
Complex contacts between hundreds of objects have to be modelled in order to simulate robot behaviors in a disaster site. The group proposed a fast and stable algorithm to compute contact forces, which is favorable from the viewpoints of both numerics and physics. It only dealt with point-vs-face contacts so that it was required to handle volume-vs-volume. The intersection between objects, which in reality corresponds to the deformation of them, potentially implies the information of directions and magnitude of contact forces. The computation of intersection between a volume and another requires a geometric computation with a high cost, which is the bottleneck of the simulation. The developed technique consists of:
(1) collision check with Axis-aligned bounding box
(2) collision check with Oriented bounding box
(3) collision check and penetration computation by Gilbert-Johnson-Kheerti method
(4) intersection computation by Muller-Preparata method or B-rep
The robustness of (3) was improved so as to correctly detect collisions in most possible situations. The computation speed of (3) and (4) was also improved through the profiling by reducing the number of points that the coordinate transformation is conducted. As the result, the computation times of both Muller-preparata method and B-pre were less than halved.

1-2. complex simulation of motors, gears and links with collisions and contacts
A robot manipulator is modeled as rigid bodies, and its behavior is determined by the gravity, the internal forces acting at the interconnecting points with adjacent links) and the external forces acting at contact points with the environment. While the computation of the external forces has been broadly studied, that of the internal forces has not been so much discussed. The internal forces include actuation forces, bearing constraint forces and friction forces in transmissions. In many simulations, the actuation forces are given and the friction forces in transmissions are ignored. However, in reality, the friction is influencial to motions of robots with gears at high-reduction ratio, and the actuation forces are determined by the impedance of motor circuits. The coulomb friction forces in particular are mathematically indistinguishable from the external forces in principle so that it is difficult to compute them. Though it is possible to formally unify the computation of them, it lacks the physical interpretation since the linear and angular forces are mixed. Moreover, the computation complexity becomes cube of the sum of the number of joints and contact points.
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