Hengyu Li

Design and Control of 3-DoF Spherical Parallel Mechanism Robot Eyes Inspired by the Binocular Vestibule-ocular Reflex

With the wide application of robot in unstructured environment, cognizing and understanding environmental information accurately is the key for robots to complete the task. Thus, visual stability problems in these robot control systems have become important design issues. In this paper, to solve the problem of vision instability caused by attitude variation of the robot working under bumpy environment, a bionic eyes system of active compensation for robot visual error is proposed inspired by the binocular VOR. The bionic vision system is developed based on features of oculomotor behaviors and bionic control algorithm of the binocular VOR. According to the behaviors features of eye movement, the bionic eye mechanism is designed by using a 3-DoF spherical parallel mechanism(SPM). Meanwhile, to improve the performance, the mechanism parameters of SPM are optimized by utilizing the worst-case performance index as the optimizing target in required workspace. An adaptive control model of the binocular VOR is established on neural control mechanisms of eye movement, and the model is used as the bionic control algorithm to drive and control the eye mechanism. The results indicate that the model can actively compensate the visual errors from postural changes of robot. Physical robot experiments also show that the system is robust even with bumpy environment.

Autonomous obstacle avoidance of an unmanned surface vehicle based on cooperative manoeuvring

Autonomous obstacle avoidance is important in unmanned surface vehicle (USV) navigation. Although the result of obstacle detection is often inaccurate because of the inherent errors of LIDAR, conventional methods typically emphasize on a single obstacle-avoidance algorithm and neglect the limitation of sensors and safety in a local region. Conventional methods also fail in seamlessly integrating local and global obstacle avoidance algorithms. This paper aims to present a cooperative manoeuvring approach including both local and global obstacle avoidance.,The global algorithm used in our USV is the Artificial Potential Field-Ant Colony Optimization (APF-ACO) obstacle-avoidance algorithm, which plans a relative optimal path on the specified electronic map before the cruise of USV. The local algorithm is a multi-layer obstacle-avoidance framework based on a single LIDAR to present an efficient solution to USV path planning in the case of sensor errors and collision risks. When obstacles are within a layer, the USV uses a corresponding obstacle-avoidance algorithm. Then the USV moves towards the global direction according to fuzzy rules in the fuzzy layer.,The presented method offers a solution for obstacle avoidance in a complex environment. The USV follows the global trajectory planed by the APF-ACO algorithm. While, the USV can bypass current obstacle in the local region based on the multi-layer method effectively. This fact was validated by simulations and field trials.,The method presented in this paper takes advantage of algorithm integration that remedies errors of obstacle detection. Simulation and experiments were also conducted for performance evaluation.

Dynamic analysis and control system of spherical robot for polar region scientific research

To figure out the limitation of enough power resource or energy supplied in Antarctic expedition, this paper presented a large-size spherical robot which can drive by internal power and wind. It consists of a 2-DOF pendulum inside the shell, rotating with transverse and longitudinal axis. Due to the non-holonomic restraint of motion, for smooth and steady control, the spherical robot is designed to finish its movement by turning and linear motion independently, and simpler through decouple method. Base on this, a dynamic model of spherical robot is developed using Lagrange, and analyzed the dynamic characteristic. Further, the hardware implementations and software system are introduced. The test result showed that rolling angular velocity and pendulum angle approach to stability with smart steering, fast rolling, and accomplish common detection mission.

The Disturbing Effect of the Stray Magnetic Fields on Magnetoimpedance Sensors

The disturbing effect of the stray magnetic fields of Fe-based amorphous ribbons on the giant magnetoimpedance (GMI) sensor has been investigated systematically in this paper. Two simple methods were used for examining the disturbing effect of the stray magnetic fields of ribbons on the GMI sensor. In order to study the influence of the stray magnetic fields on the GMI effect, the square-shaped amorphous ribbons were tested in front, at the back, on the left and on the top of a meander-line GMI sensor made up of soft ferromagnetic films, respectively. Experimental results show that the presence of ribbons in front or at the back of GMI sensor shifts the GMI curve to a lower external magnetic field. On the contrary, the presence of ribbons on the left or on the top of the GMI sensor shifts the GMI curve to a higher external magnetic field, which is related to the coupling effect of the external magnetic field and the stray magnetic fields. The influence of the area and angle of ribbons on GMI was also studied in this work. The GMI sensor exhibits high linearity for detection of the stray magnetic fields, which has made it feasible to construct a sensitive magnetometer for detecting the typical stray magnetic fields of general soft ferromagnetic materials.

People detection and tracking using RGB-D cameras for mobile robots:

People detection and tracking is an essential capability for mobile robots in order to achieve natural human–robot interaction. In this article, a human detection and tracking system is designed and validated for mobile robots using color data with depth information RGB-depth (RGB-D) cameras. The whole framework is composed of human detection, tracking and re-identification. Firstly, ground points and ceiling planes are removed to reduce computation effort. A prior-knowledge guided random sample consensus fitting algorithm is used to detect the ground plane and ceiling points. All left points are projected onto the ground plane and subclusters are segmented for candidate detection. Meanshift clustering with an Epanechnikov kernel is conducted to partition different points into subclusters. We propose the new idea of spatial region of interest plan view maps which are employed to identify human candidates from point cloud subclusters. Here, a depth-weighted histogram is extracted online to feature a human candidate. Then, a particle filter algorithm is adopted to track the human’s motion. The integration of the depth-weighted histogram and particle filter provides a precise tool to track the motion of human objects. Finally, data association is set up to re-identify humans who are tracked. Extensive experiments are conducted to demonstrate the effectiveness and robustness of our human detection and tracking system.

A sonar image mosaicing algorithm based on improved SIFT for USV

As the USV (Unmanned Surface Vehicles) works in offshore waters whose operating environment is complex, sonar images obtained are low-resolution, noisy and narrow overlap region, and ultimately led to the sonar image cannot be stitched or get a serious distortion after image mosaicing. In response to these problems, this paper proposes a sonar image mosaicing algorithm based on improved SIFT for USV. For sonar image registration, we applies RANSAC (RANdom Sample Consensus) algorithm to check feature points to improve the accuracy of image registration. For the problem that the distribution of original image brightness is different, this paper conducts brightness normalization algorithms for brightness adjustment. To avoid empty points in stitched image and the problem that mapping coordinates may not be an integer, this paper respectively take inverse mapping method and image interpolation algorithm to solve the problem. In order to improve the sonar image borders and edge fusion effect, this paper proposes a weighted fusion algorithm based on threshold and edge. Finally, the experiments show that the algorithm has a certain practicality.

Wind-driven land-yacht robot mathematical modeling and verification

Purpose – The purpose of this paper was to solve the shortage of carrying energy in probing robot and make full use of wind resources in the Antarctic expedition by designing a four-wheel land-yacht. Land-yacht is a new kind of mobile robot powered by the wind using a sail. The mathematical model and trajectory of the land-yacht are presented in this paper. Design/methodology/approach – The mechanism analysis method and experimental modeling method are used to establish a dual-input and dual-output mathematical model for the motion of land-yacht. First, the land-yacht’s model structure is obtained by using mechanism analysis. Then, the models of steering gear, servomotors and force of wing sail are analyzed and validated. Finally, the motion of land-yacht is simulated according to the mathematical model. Findings – The mathematical model is used to analyze linear motion and steering motion. Compared with the simulation results and the actual experimental tests, the feasibility and reliability of the propo...

Seeker optimization algorithm for optimal control of manipulator

Purpose This paper aims to improve the adaptability and control performance of the controller, a proposed seeker optimization algorithm (SOA) is introduced to optimize the controller parameters of a robot manipulator. Design/methodology/approach In this paper, a traditional proportional integral derivative (PID) controller and a fuzzy logic controller are integrated to form a fuzzy PID (FPID) controller. The SOA, as a novel algorithm, is used for optimizing the controller parameters offline. There is a performance comparison in terms of FPID optimization about the SOA, the genetic algorithm (GA), particle swarm optimization (PSO) and ant colony optimization (ACO). The DC motor model and the experimental platform are used to test the performance of the optimized controller. Findings Compared with GA, PSO and ACO, this novel optimization algorithm can enhance the control accuracy of the system. The optimized parameters ensure a system with faster response speed and better robustness. Originality/value A simplified FPID controller structure is constructed and a novel SOA method for FPID controller is presented. In this paper, the SOA is applied on the controller of 5-DOF manipulator, and the validation of controllers is tested by experiments.

Accuracy model, analysis, and adjustment in the context of multi-closed-loop planar deployable mechanisms

The links of the multi-closed-loop deployable mechanism are generally adjusted when being assembled, for the purpose of making the whole mechanism satisfy the requirements in fully deployed, folded, or the other key configurations. In order to calculate the appropriate adjustment amount, the complex adjustment amount of the whole mechanism is first defined by root mean square. And then, the adjustment model for planar mechanism involving different constraints is constructed according to the different situations. Through linearization of this model, it can be applied to calculate the adjustment sensitivity of this type of mechanisms. Second, with the factor of the practical adjustment in engineering, the three computation modes of adjustment (bidirectional adjustment, invariant adjustment, and unidirectional adjustment) have been developed. Furthermore, the multi-configuration adjustment approach has been proposed to make the assembled mechanism satisfy the requirements in different configurations. At last, all the above approaches in this article have been implemented in the scissor-like element mechanism and two-loop deployable mechanism. The achievement of this research provides a significant reference for assembling the multi-closed-loop mechanisms.

Real-time RGB-D image stitching using multiple Kinects for improved field of view

This article concerns the problems of a defective depth map and limited field of view of Kinect-style RGB-D sensors. An anisotropic diffusion based hole-filling method is proposed to recover invalid depth data in the depth map. The field of view of the Kinect-style RGB-D sensor is extended by stitching depth and color images from several RGB-D sensors. By aligning the depth map with the color image, the registration data calculated by registering color images can be used to stitch depth and color images into a depth and color panoramic image concurrently in real time. Experiments show that the proposed stitching method can generate a RGB-D panorama with no invalid depth data and little distortion in real time and can be extended to incorporate more RGB-D sensors to construct even a 360° field of view panoramic RGB-D image.