Conference Paper

A walking pattern generator for biped robots on uneven terrains

Dept. of Comput. Sci., Univ. of North Carolina at Chapel Hill, Chapel Hill, NC, USA
DOI: 10.1109/IROS.2010.5653079 Conference: Intelligent Robots and Systems (IROS), 2010 IEEE/RSJ International Conference on
Source: IEEE Xplore

ABSTRACT We present a new method to generate biped walking patterns for biped robots on uneven terrains. Our formulation uses a universal stability criterion that checks whether the resultant of the gravity wrench and the inertia wrench of a robot lies in the convex cone of the wrenches resulting from contacts between the robot and the environment. We present an algorithm to compute the feasible acceleration of the robot's CoM (center of mass) and use that algorithm to generate biped walking patterns. Our approach is more general and applicable to uneven terrains as compared with prior methods based on the ZMP (zero-moment point) criterion. We highlight its applications on some benchmarks.

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Available from: Ming Lin, Apr 17, 2014
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    • "The contact wrench naturally solves the redundancy issue, as its dimension is minimal (six). It was advocated as a generalization of ZMP in [2], along with a stability theorem, and applied to walking pattern generation on rough terrains [11] [12]. However, this theorem makes the same " sufficient friction " assumption as ZMP, which means the resulting criterion does not account for sliding and yaw rotations. "
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    ABSTRACT: Humanoid robots locomote by making and breaking contacts with their environment. A crucial problem is therefore to find precise criteria for a given contact to remain stable or to break. For rigid surface contacts, the most general criterion is the Contact Wrench Condition (CWC). To check whether a motion satisfies the CWC, existing approaches take into account a large number of individual contact forces (for instance, one at each vertex of the support polygon), which is computationally costly and prevents the use of efficient inverse-dynamics methods. Here we argue that the CWC can be explicitly computed without reference to individual contact forces, and give closed-form formulae in the case of rectangular surfaces -- which is of practical importance. It turns out that these formulae simply and naturally express three conditions: (i) Coulomb friction on the resultant force, (ii) ZMP inside the support area, and (iii) bounds on the yaw torque. Conditions (i) and (ii) are already known, but condition (iii) is, to the best of our knowledge, novel. It is also of particular interest for biped locomotion, where undesired foot yaw rotations are a known issue. We also show that our formulae yield simpler and faster computations than existing approaches for humanoid motions in single support, and demonstrate their consistency in the OpenHRP simulator.
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    ABSTRACT: This paper proposes 3-D command state (3-D CS)-based modifiable walking pattern generator (MWPG) on the uneven terrain with the different inclinations and heights for humanoid robots. In the previous researches on walking pattern generation on the uneven terrain, the humanoid robot was unable to modify a walking pattern on the uneven terrain without any additional footstep for adjusting the center of mass (COM) motion. Thus, a novel MWPG is developed to solve this problem. It is based on the conventional MWPG which allows the zero moment point (ZMP) variation in real-time by closed form functions. Initially, a 3-D CS is defined as a navigational command set which consists of the foot height and foot pitch and roll angles of the swing leg in addition to the single and double support times and sagittal and lateral step lengths of the swing leg, for walking on the uneven terrain. Next, the COM trajectories in the single and double support phases are generated to satisfy the 3-D CS. Also, the foot trajectory of the swing leg is generated according to the commanded sagittal and lateral step lengths, foot height, and foot pitch and roll angles to walk on the uneven terrain. The proposed algorithm is implemented on a simulation model of the small-sized humanoid robot, HanSaRam-IX (HSR-IX), developed at the Robot Intelligence Technology laboratory, KAIST and the effectiveness is demonstrated through the simulation.
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