Xuechao Chen

Design and Development of the Humanoid Robot BHR-5:

This paper presents the mechanical and control system design of the latest humanoid robot platform, BHR-5, from Beijing Institute of Technology. The robot was developed as a comprehensive platform to investigate the planning and control for the fast responsive motion under unforeseen circumstances, for example, playing table-tennis. It has improvement on mechanical structure, stiffness, and reliability. An open control architecture based on concurrent multichannel communication mode of CAN bus is proposed to upgrade the real-time communication performance and the expansibility of the control system. Experiments on walking and playing table-tennis validate the effectiveness of the design.

Design and similarity evaluation on humanoid motion based on human motion capture

This paper explores the design of humanoid complicated dynamic motion based on human motion capture. Captured human data must be adapted for the humanoid robot because its kinematics and dynamics mechanisms differ from those of the human actor. It is expected that humanoid movements are highly similar to those of the human actor. First, the kinematics constraints, including ground contact conditions, are formulated. Second, the similarity evaluation on the humanoid motion based on both the spatial and temporal factors compared with the human motion is proposed. Third, the method to obtain humanoid motion with high similarity is presented. Finally, the effectiveness of the proposed method is confirmed by simulations and experiments of our developed humanoid robot “sword” motion performance.

Distributed Control System for a Humanoid Robot

A humanoid robot generally has more than thirty DOFs to be controlled in real-time and needs to deal with information of multiple sensors such as encoders, force, gyro, acceleration and vision sensors. Therefore an effective control system is crucial for the humanoid robot. In this paper, we propose a distributed control architecture for humanoid robots based on the combination of Memolink and CAN bus. This architecture consists of a vision and hearing processing sub-system for vision information processing, a tele-operation sub-system and a realtime motion control sub-system. The operating systems of this architecture are composed of Windows and RT-Linux. The Windows OS is used as the operating system of the former two subsystems to process multimedia and tele-operation information tractably. Linux and real-time RT-Linux OS are used as the operating system of motion control sub-system to achieve the realtime control capability. The biped walk experiments show that this control architecture is effective, reliable and tractable.

Computer control system and walking pattern control for a humanoid robot

A humanoid robot generally has more than thirty DOFs to be controlled in real-time and needs to deal with information of multiple sensors such as encoders, force and moment sensors, inertial attitude sensors and vision sensors. Therefore an effective control system is crucial for the humanoid robot. In this paper, we propose a distributed computer system consisting of the online planning sub-system and the real-time motion control sub-system based on CAN bus and Ethernet for humanoid robots. CAN bus is used for distributed real-time motion control and Ethernet is used for non-real-time and large data quantities communication between the online planning and motion control sub-systems. The Windows and RT-Linux are used as operating systems for the online planning and motion control sub-systems respectively. The walking pattern control modifies the planned walking pattern based on sensory information when there are unexpected sudden events. The effectiveness of our proposed computer system and walking pattern control method was confirmed by walking experiments on our newly-built humanoid robot.

Robust push recovery by whole-body dynamics control with extremal accelerations

This paper presents a whole-body dynamics con- troller for robust push recovery on a force-controlled bipedal robot. Using Featherstones spatial vector method, we reveal a relationship between the accelerations of the floating base and the desired external forces needed for those accelerations. Introducing constraints on the desired external forces causes corresponding constraints on the accelerations. Quadratic pro- gramming is applied to find the extremal accelerations, which recover the robot from pushes as best as it can. Using the proposed robustness criterion, our method is robuster than presented methods. The effectiveness of the proposed method is demonstrated by recovering from pushes in simulation.

An improved ZMP trajectory design for the biped robot BHR

An improved ZMP (Zero Moment Point) trajectory for a biped robot is designed in this paper, which imitates a humans actual ZMP trajectory in the walking process. A new method of walking pattern generation based on forward moving ZMP in SSP (Single Support Phase) is also provided. It can keep the ZMP moving forward instead of staying in the center of supporting region during SSP, which is helpful for increasing the walking speed. We have been developing BHR, which has 38 DOFs (degree of freedom). The effectiveness of the method is conducted by simulation and walking experiment on BHR.

Gait Planning of Omnidirectional Walk on Inclined Ground for Biped Robots

When a biped robot moves about in a physical environment, it may encounter inclined ground. Biped walking on inclined ground still remains challenging for biped robots. Previous studies have discussed biped walking on inclined ground along specific directions. However, omnidirectional walk on inclined ground has rarely been investigated. In this paper, we propose a gait pattern generation method for omnidirectional biped walking on inclined ground. First, a model that describes the motion of biped walking on inclined ground uniformly with two angle parameters is proposed. A mathematical relationship between motions in the sagittal and coronal planes of the biped robot are presented. Then, based on nonorthogonal motion decoupling, a method that generates gait patterns for omnidirectional walking with a double support phase for biped robots is proposed. The trajectories of each foot are designated by the walking speed, step length, and walking direction. The motion trajectory of the center of mass (CoM) of the robot is planned using a linear inverted pendulum model in the sagittal and coronal planes. The motion of CoM in the sagittal and coronal planes is constrained in parallel to the gradient vector of the inclined ground and the horizontal plane, respectively. Finally, the effectiveness of the proposed gait planning method for biped walking on is validated by simulations and experiments with an actual biped robot.

Hand-eye servo and impedance control for manipulator arm to capture target satellite safely

A crucial problem is the risk that a manipulator arm would be damaged by twisting or bending during and after contacting a target satellite. This paper presents a solution to minimize the risk of damage to the arm and thereby enhance contact performance. First, a hand-eye servo controller is proposed as a method for accurately tracking and capturing a target satellite. Next, a motion planning strategy is employed to obtain the best-fit contacting moments. Also, an impedance control law is implemented to increase protection during operation and to ensure more accurate compliance. Finally, to overcome the challenge of verifying algorithms for a space manipulator while on the ground, a novel experimental system with a 6-DOF (degree of freedom) manipulator on a chaser field robot is presented and implemented to capture a target field robot; the proposed methods are then validated using the experimental platform.

Design of a Redundant Manipulator for Playing Table Tennis towards Human-Like Stroke Patterns

This study investigates the design of a 7-DOF humanoid manipulator capable of playing table tennis with human-like stroke patterns. The manipulator system includes a redundant arm, real-time stereo vision system, and a distributed motion control system. First, the size, weight, workspace, and motion capability of the designed arm are similar to those of a humans arm. The forward and inverse kinematics, and the Jacobian matrix of the redundant manipulator are formulated. Next, a distributed motion control system is designed. The ball trajectory prediction method is proposed. Then, a human-inspired optimization method based on Jacobian pseudoinverse and the comfort of the arm posture for stroke pattern trajectory is proposed to achieve human-like stroke patterns and decrease the counterforce exerted on the manipulator. Finally, the validity of the proposed system and methods is demonstrated via human-like stroke pattern experiments.

Design of a humanoid ping-pong player robot with redundant joints

This study investigates the design of a humanoid ping-pong robot system with a 7-DOFs redundant arm. The design of the arm mechanism, real-time binocular vision system, and a distributed control structure was presented. The methods for ball trajectory prediction and motion planning for the ping-pong racket were proposed. A Jacobian pseudoinverse method considering joint limits and manipulability optimization terms is employed to solve inverse kinematics in order to decrease the counterforce exerting on the humanoid robot. The proposed system is validated by a series of rally experiments between the robot and a human.