Showing papers by "Oussama Khatib published in 2012"

A depth space approach to human-robot collision avoidance

Abstract: In this paper a real-time collision avoidance approach is presented for safe human-robot coexistence. The main contribution is a fast method to evaluate distances between the robot and possibly moving obstacles (including humans), based on the concept of depth space. The distances are used to generate repulsive vectors that are used to control the robot while executing a generic motion task. The repulsive vectors can also take advantage of an estimation of the obstacle velocity. In order to preserve the execution of a Cartesian task with a redundant manipulator, a simple collision avoidance algorithm has been implemented where different reaction behaviors are set up for the end-effector and for other control points along the robot structure. The complete collision avoidance framework, from perception of the environment to joint-level robot control, is presented for a 7-dof KUKA Light-Weight-Robot IV using the Microsoft Kinect sensor. Experimental results are reported for dynamic environments with obstacles and a human.

Motion control of redundant robots under joint constraints: Saturation in the Null Space

Abstract: We present a novel efficient method addressing the inverse differential kinematics problem for redundant manipulators in the presence of different hard bounds (joint range, velocity, and acceleration limits) on the joint space motion. The proposed SNS (Saturation in the Null Space) iterative algorithm proceeds by successively discarding the use of joints that would exceed their motion bounds when using the minimum norm solution and reintroducing them at a saturated level by means of a projection in a suitable null space. The method is first defined at the velocity level and then moved to the acceleration level, so as to avoid joint velocity discontinuities due to the switching of saturated joints. Moreover, the algorithm includes an optimal task scaling in case the desired task trajectory is unfeasible under the given joint bounds. We also propose the integration of obstacle avoidance in the Cartesian space by properly modifying on line the joint bounds. Simulation and experimental results reported for the 7-dof lightweight KUKA LWR IV robot illustrate the properties and computational efficiency of the method.

Prioritized multi-task motion control of redundant robots under hard joint constraints

Abstract: We present an efficient method for motion control of redundant robots performing multiple prioritized tasks in the presence of hard bounds on joint range, velocity, and acceleration/ torque. This is an extension of our recently proposed SNS (Saturation in the Null Space) algorithm developed for single tasks. The method is defined at the level of acceleration commands and proceeds by successively discarding one at a time the commands that would exceed their bounds for a task of given priority, and reintroducing them at their saturated levels by projection in the null space of a suitable Jacobian associated to the already considered tasks. When processing all tasks in their priority order, a correct preemptive strategy is realized in this way, i.e., a task of higher priority uses in the best way the feasible robot capabilities it needs, while lower priority tasks are accommodated with the residual capability and do not interfere with the execution of higher priority tasks. The algorithm automatically integrates a multi-task least possible scaling strategy, when some ordered set of original tasks is found to be unfeasible. Simulation and experimental results on a 7-dof lightweight KUKA LWR IV robot illustrate the good performance of the method.

Muscle force transmission to operational space accelerations during elite golf swings

Abstract: The paper investigates the dynamic characteristics that shape human skills using the task-space methods found in robotics research. It is driven by the hypothesis that each subject's physiology can be reflected to the task dynamics using the operational space acceleration characteristics and that elite performers achieve the optimum transmission from their available muscle induced torque capacity to the desired task in goal oriented dynamic skills. The methodology is presented along with the full body human musculoskeletal model used for the task-based analyzes. The robotics approach for human motion characterization is demonstrated in the biomechanical analysis of an elite golf swing. This approach allows us to trace the acceleration capacities in a given subject's task space. The results of the motion characterization show that humans in fact follow a path of trajectory in line with the maximum available operational space accelerations benefiting from their physiology shaped by the combination of the force generating capacities of the muscles as well as by the joint and limb mechanics.

Elastic strips: Implementation on a physical humanoid robot

Abstract: For robots to operate in human environments, they are required to react safely to unexpected changes in the work area. However, existing manipulation task planning methods take more than several seconds or minutes to update their solutions when environmental changes are recognized. Furthermore, the computation time exponentially increases in case of highly complex structures such as humanoid robots. Therefore, we propose a reactive system for high d.o.f. robots to perform interactive manipulation tasks under real-time conditions. The paper describes the implementation of the Elastic Strip Framework, a plan modification approach to update initial motion plans. To improve its real-time performance and reliability, the previous geometric approximation is replaced by an implicit method that constructs an elastic tunnel for collision checking. Additionally, in order to maintain a robust system even in exceptional situations, such as undetected obstacles, the force transformer module executes compliant motions, and the current elastic strip adapts the path tracking motion by monitoring tracking errors of the actual motion. The proposed system is applied to a Honda humanoid robot. Real-time performance is successfully demonstrated in real-world experiments.

Constraint-Consistent Analysis of Muscle Force Contributions to Human Gait

Abstract: The goal of this study is to apply a task-space approach to characterize muscle force contributions to the body center of mass during human gait taking into account the contacts with the environment and the constraints in the musculoskeletal system. Motion capture, electromyography and force plate data were taken from a male subject walking at free speed. The obtained data were used together with a full-body musculoskeletal model to generate and to analyze the simulation of one complete gait cycle. The contribution of the muscles spanning the lower body joints to the body center of mass acceleration were calculated using a task-space approach which was successfully applied to analyze human dynamic motions in our previous studies. The results showed that gluteus medius, vasti, biceps femoris long head and short head, tibialis anterior, medial gastrocnemius, rectus femoris and soleus were the primary contributors to gait at free speed. The study provides an approach for in depth motion analysis including the effects of contact forces and joint mechanics as well as physiological constraints, muscle dynamics and actuation.

Social Robotics: 4th International Conference, ICSR 2012, Chengdu, China, October 29-31, 2012, Proceedings

Abstract: This book constitutes the refereed proceedings of the 4th International Conference on Social Robotics, ICSR 2012, held in Chengdu, China, in October 2012. The 66 revised full papers were carefully reviewed and selected from numerous submissions. The papers are organized in topical sections on affective and cognitive sciences for socially interactive robots, situated interaction and embodiment, robots to assist the elderly and persons with disabilities, social acceptance of robots and their impact to the society, artificial empathy, HRI through non-verbal communication and control, social telepresence robots, embodiments and networks, interaction and collaboration among robots, humans and environment, human augmentation, rehabilitation, and medical robots I and II.