Qingxuan Jia

Repetitive Motion Planning of Free-Floating Space Manipulators

Abstract In this paper, a repetitive motion-planning scheme of free-floating space manipulators is presented. Repetitive motion means when one task ends, the end-effector pose, the joint angles and the base pose should reset (return to their initial value), which will facilitate the subsequent tasks. First, due to the lack of DOF, an order of priority to the given tasks is introduced. Second, the joint reset optimization operator, the base attitude reset optimization operator and the end-effector attitude reset optimization operator are designed. Then, the repetitive motion scheme is proposed by combining the three optimization operators above in a creative way. Finally, to make the optimization of repetitive motion obvious, the base attitude maintenance is also considered. Simulation results verify the correctness and the validity of the repetitive motion planning method of space manipulator.

3D augmented reality teleoperated robot system based on dual vision

Abstract A 3D augmented reality navigation system using stereoscopic images is developed for teleoperated robot systems. The accurate matching between the simulated model and the video image of the actual robot can be realized, which helps the operator to accomplish the remote control task correctly and reliably. The system introduces the disparity map translation transformation method to take parallax images for stereoscopic displays, providing the operator an immersive 3D experience. Meanwhile, a fast and accurate registration method of dynamic stereo video is proposed, and effective integration of a virtual robot and the real stereo scene can be achieved. Preliminary experiments show that operation error of the system is maintained at less than 2.2 mm and the average error is 0.854 7, 0.909 3 and 0.697 2 mm at x, y, z direction respectively. Lots of experiments such as pressing the button, pulling the drawer and so on are also conducted to evaluate the performance of the system. The feasibility studies show that the depth information of structure can be rapidly and recognized in remote environment site. The augmented reality of the image overlay system could increase the operating accuracy and reduce the procedure time as a result of intuitive 3D viewing.

Study on the perception mechanism and method of virtual and real objects in augmented reality assembly environment

Augmented reality assembly, is a promising application of virtual reality in design and manufacturing and has drawn much more and more attentions from industries and research institutes. The foucs of this study are as follows. (1) using the agent-oriented modeling for subassembly object and the behavior reasoning based on petri net model of environment, to build the system model of augmented reality assembly environment and construct the percepting mechanism of the virtual and real objects; (2) based on above percepting mechanism, to solve the epipolar geometry constraint by least robustness square estimation model, and to sense the depth of the occluded virtual objects or real objects in the environment through assembly scene recognizing, background eliminating and geometrical features restructuring of product contour; (3) combining awareness process of object features matching, constrained motion and features fitting with image based visual hull generating and volume querying, to detect the collision of virtual and real objects, including the dynamic deformable objects. The reseach results is of very important academic and applicative interest in the field of digital design, assembly and maintenace. It would be helpful to promote the application research of augemented reality and virtual reality technology.

Dynamic Obstacle Avoidance Algorithm for Redundant Robots with Pre-selected Minimum Distance Index

A pre-selected minimum distance index is presented considering the real-time performance of dynamic obstacle avoidance for redundant robots.The OBB(oriented bounding box) is applied to modeling robot,and safe links are removed by intersection test before calculating real-time distance.The real-time minimum distance is calculated by local mapping based distance calculation method according to the coordinates of objective points.Based on that,avoidance factor and escaping velocity related to minimum distance are built and then mapping matrix in zero space of redundant robots is utilized to accomplish obstacle avoidance path planning.Finally,the validity and efficiency of pre-selected minimum distance index for dynamic obstacle avoidance are manifested by simulation.Compared with traditional path planning methods,the overall planning time is reduced by 15.5%.

Calibration Method and Experiments of Robot Kinematics Parameters Based on Error Model

A method of robot kinematics parameters calibration based on error model is proposed,which separates positional parameters and angle parameters in calibration process.Robot kinematics equations are built using MCPC(modified complete and parametrically continuous) method,while kinematics error model relative to inertial coordinate system is derived.On the basis,the separated kinematics parameters calibration method is put forward.In order to solve the problems caused by joint angle error during calibration process,experimental methods for robot kinematics calibration based on joint angle correction are designed systematically.The effectiveness of the mentioned methods is verified by experiment results.

The Design of the Spherical Robot Autonomous GPS-Based Positioning and Navigation System

This paper presents a design for the autonomous navigation system of spherical robot based on GPS (Global Positioning System). Firstly, the mechanical structure and control system of the spherical robot are given particularly. The process of the system includes four main steps to realize the function. In the process, due to the large position information error provided by the GPS positioning system, Kalman filter algorithm is adopted to improve the accuracy of the position data. Two schemes are compared, and the better program of algorithm is chosen to apply in the design. Finally, experimental results in the spherical robot show feasibility of the design for the autonomous GPS-based positioning and navigation system.

Building recognition from aerial images combining segmentation and shadow

We propose a novel building detection algorithm for processing high-resolution aerial images. Our algorithm exploits the building-shadow geometric relationship according to lighting models, making it suitable to detect buildings in a more general setting, possibly with irregular shapes. We use image segmentation to provide spatial support for both building and shadow detections. A novel confidence method is developed to label building and shadow segments by jointly reasoning: 1) the likelihood of shadows; 2) building-shadow configuration, and 3) building-building similarity. Our method is tested on a wide range of aerial images. Qualitative and quantitative results demonstrate its effectiveness on detecting and extracting buildings from background clutter.

Simultaneous positioning and non-minimum phase vibration suppression of slewing flexible-link manipulator using only joint actuator

This paper presents a new global terminal sliding mode control (GTSMC) methodology for the simultaneous positioning and vibration suppression of slewing a flexible-link manipulator. The proposed control scheme is realized using only a joint actuator without an extra actuator (for example, the widely used piezoelectric zirconate titanate), and the non-minimum phase vibration control problem is solved. Firstly, based on the differential geometry method, the initial dynamic system is decomposed into two subsystems, namely an input-output subsystem and a zero-dynamics subsystem. Secondly, a continuous GTSMC strategy without chattering phenomenon is designed for the input-output subsystem, and the limited convergence time is deduced. Moreover, the eigenvalues of the zero-dynamics subsystem can be pointed by setting proper controller parameters for Lyapunov asymptotical stability. Finally, simulation and experimental results demonstrated the efficacy and feasibility of the proposed control methodology.

Design and implementation of the teleoperation platform based on augmented reality

Predictive display based on virtual environment models is an effective method of solving the problem of time delay in teleoperation. However, this method will not work well without the precise virtual environment model. Thus, it is of great significance that augmented reality with video feedback is introduced into teleoperation, instead of the virtual environment models. A teleoperation system platform based on augmented reality was developed to improve system stability and enhance system telepresence, facilitating the operators observation and operation. The improved algorithm ARToolkit-based made the system adaptable to many types of lighting environments. This paper introduces system structure and the realization of key modules. Lots of experiments such as pressing the button, pulling the drawer and so on are also conducted to evaluate the system performance. The simulation results indicate that the proposed system can compensate the defect of prediction and improve teleoperation system reliability.

Study of rapid collision detection algorithm for manipulator

Bounding box algorithm is generally used to detect whether a manipulator is in collision with environment or itself. In this paper, we propose a rapid collision detection algorithm for manipulator based on the vector relation of basic geometrical elements. Firstly, we analyze the precision and efficiency of three commonly used algorithm - sphere, AABB (Axis-Aligned Bounding Box) and OBB(Oriented Bounding Box). Secondly, we extract the concept of “center distance” and “geometric dimension” by simplifying a manipulator and its environment to the combination of some geometry for detecting collision rapidly. Then, we simplify the collision of manipulator to 4 kinds of collision - sphere-cylinder, sphere-cuboid, cylinder-cylinder and cuboid-cuboid. Finally, the validity of this collision detection algorithm is verified by developing a simulation system based on OSG(OpenSceneGraph) for a 8-DOF manipulator.