Showing papers by "Yili Fu published in 2017"

3D stable biped walking control and implementation on real robot

Abstract: A combination of walking control methods was proposed and implemented on a biped robot. The LIPM-based model predictive control (MPC) was adopted to generate a basic stable walking pattern. The stability of pitch and yaw rotation was improved through pitch and yaw momentum control as a supplementation of MPC. It is found that biped robot walking tends to deviate from the planned walking direction if not considering the rotation friction torque in yaw axis under the support foot. There are basically two methods to control yaw momentum, waist and swing arms rotation control. However, the upper body is often needed to accomplish other tasks. Therefore, a yaw momentum control method based on swing leg dynamics was proposed. This idea does not depend on upper body’s motion and is highlighted in this paper. Through experiments, the feasibility of the combination of the control methods proved to be practical in keeping biped robot walking stable both in linear and rotation motion. The pros and cons of th...

Pose optimization and port placement for robot-assisted minimally invasive surgery in cholecystectomy

Abstract: Background Pose optimization and port placement are critical issues for preoperative preparation in robot-assisted minimally invasive surgery (RMIS), and affect the robot performance and surgery quality. Methods This paper proposes a method for pose optimization and port placement for RMIS in cholecystectomy that considers both the robot and surgery requirements. The robot pose optimization was divided into optimization of the positioning joint configuration and optimization of the end effector configuration. To determine the optimal location for the trocar port placement, the operational workspace was defined as the evaluation index. The port area was divided into many sub-areas, and that with the maximum operational workspace was selected as the location for the port placement. Results Considering the left robotic arm as an example, the location for the port placement and joints angles for robotic arm configuration were discussed and simulated using the proposed method. Conclusion This research can provide guidelines for surgeons in preoperative preparation.

Research on impedance control based on force servo for single leg of hydraulic legged robot

Abstract: A force servo based impedance controller that allows compliant behaviours of the leg of a hydraulic legged robot has been presented in this paper. A novel velocity compensation algorithm which makes for elimination of the redundant forces is also included. Their performance is assessed on a 2-DOF hydraulic leg whose kinematics and transfer functions have been modeled. A double hydraulic cylinders experiment platform is designed for performance testing of the force tracking of the hydraulic actuators. Experimental results have shown a good performance of the impedance controller which allows arbitrary virtual stiffness and damping of the leg.

Adaptive neural network visual servoing of dual-arm robot for cyclic motion

Abstract: Purpose The purpose of this paper is to develop a vision-based dual-arm cyclic motion method, focusing on solving the problems of an uncertain grasp position of the object and the dual-arm joint-angle-drift phenomenon. Design/methodology/approach A novel cascade control structure is proposed which associates an adaptive neural network with kinematics redundancy optimization. A radial basis function (RBF) neural network in conjunction with a conventional proportional–integral (PI) controller is applied to compensate for the uncertainty of the image Jacobian matrix which includes the estimated grasp position. To avoid the joint-angle-drift phenomenon, a dual neural network (DNN) solver in conjunction with a PI controller and dual-arm-coordinated constraints is applied to optimize the closed-chain kinematics redundancy. Findings The proposed method was implemented on an industrial robotic MOTOMAN with two 7-degrees of freedom robotic arms. Two experiments of carrying a tray repeatedly and turning a steering wheel were carried out, and the results indicate that the closed-trajectories tracking is achieved successfully both in the image plane and the joint spaces with the uncertain grasp position, which validates the accuracy and realizability of the proposed PI-RBF-DNN control strategy. Originality/value The adaptive neural network visual servoing method is applied to the dual-arm cyclic motion with the uncertain grasp position of the object. The proposed method enhances the environmental adaptability of a dual-arm robot in a practical manipulation task.

Smooth transition of the CPG-based controller for snake-like robots

Abstract: Nature snakes vary their gaits flexibly according to different terrains, so it is significant for snake-like robots to incorporate more available locomotion patterns and switch gaits smoothly for good adaptability. In this paper, a bionic joint mechanism with parallel links and active orthogonal omni-wheel is designed, and a novel central pattern generator (CPG) architecture is proposed. A sine approach is used in the modulation of CPG parameters to avoid stiff impulses. Moreover, the method also can be applied in the beginning stage to improve the motion effectiveness and save energy. Simulation results are presented to illustrate the effectiveness of the proposed smooth transition method.

Design of a novel robotic system for minimally invasive surgery

Abstract: Robot-assisted system for minimally invasive surgery (MIS) has been attracting more and more attentions. Compared with a traditional MIS, the robot-assisted system for MIS is able to overcome or reduce defects, such as poor hand-eye coordination, heavy labour intensity and limited motion of the instrument. The purpose of this paper is to design a novel robotic system for MIS applications.,A robotic system with three separate slave arms for MIS has been designed. In the proposed robot, a new mechanism was designed as the remote centre motion (RCM) mechanism to restrain the movement of instrument or laparoscope around the incision. Moreover, an improved instrument without coupling motion between wrist and grippers was developed to enhance its manipulability. A control system architecture was also developed, and an intuitive control method was applied to realize hand-eye coordination of the operator.,For the RCM mechanism, the workspace was analyzed and the positioning accuracy of the remote centre point was tested. The results show that the RCM mechanism can be applied to MIS. Furthermore, the master-slave trajectory tracking experiments reveal that slave robots are able to follow the movement of the master manipulators well. Finally, the feasibility of the robot-assisted system for MIS is proved by performing animal experiments successfully.,This paper offers a novel robotic system for MIS. It can accomplish the anticipated results.

How do the compliant legs affect walking stability

Abstract: The dynamics of walking can be achieved by using the compliant legs. Understanding the compliant mechanisms during walking would improve the design of assistive devices for humans. We studied how and the extent to which the compliant legs would affect the passive stability of walking. From the biomechanics of human walking, we built three 2D models with compliant legs of different leg structures. The three models had the same performance during constant-average-speed walking. We then perturbed these models by changing the elevation of the ground. We found that the compliant legs from different structures provided passive stability to resist perturbation from the ground. The SLIP model can maintain stability in a broader range of perturbation magnitude than the SSEG or STSM. By splicing legs from pure models with two identical legs to create hybrid models, we found the passive stability of hybrid models can be inherited from the pure models. The mechanical properties of the leg properties hence determine the passive stability. Understanding the passive stability from the compliant mechanism of legged locomotion helps to improve the design and control of powered prostheses and legged robots.