Changle Li

Stereo Matching Algorithm Based on 2D Delaunay Triangulation

To fulfill the applications on robot vision, the commonly used stereo matching method for depth estimation is supposed to be efficient in terms of running speed and disparity accuracy. Based on this requirement, Delaunay-based stereo matching method is proposed to achieve the aforementioned standards in this paper. First, a Canny edge operator is used to detect the edge points of an image as supporting points. Those points are then processed using a Delaunay triangulation algorithm to divide the whole image into a series of linked triangular facets. A proposed module composed of these facets performs a rude estimation of image disparity. According to the triangular property of shared vertices, the estimated disparity is then refined to generate the disparity map. The method is tested on Middlebury stereo pairs. The running time of the proposed method is about 1 s and the matching accuracy is 93%. Experimental results show that the proposed method improves both running speed and disparity accuracy, which forms a steady foundation and good application prospect for a robot’s path planning system with stereo camera devices.

The apposite way path planning algorithm based on local message

According to the problems of autonomous robotic navigation in complex environments, an opposite way path planning algorithm and a novel robot controller based on inertial property is proposed. Firstly, the opposite way path planning algorithm getting the local obstacle message through robot, according to the known obstacles a optimal path calculated which can carries the robot to get to the ultimate target. Secondly, a robot controller based on attractive force function and repulsive force function is designed. The controller can keep the robot away from the obstacle, and escape from the local minima when the robot is blocked by obstacle. The simulation results show that this method has a better optimization result than other common methods such as bug and artificial potential field.

A Force-Sensing System on Legs for Biomimetic Hexapod Robots Interacting with Unstructured Terrain

The tiger beetle can maintain its stability by controlling the interaction force between its legs and an unstructured terrain while it runs. The biomimetic hexapod robot mimics a tiger beetle, and a comprehensive force sensing system combined with certain algorithms can provide force information that can help the robot understand the unstructured terrain that it interacts with. This study introduces a complicated leg force sensing system for a hexapod robot that is the same for all six legs. First, the layout and configuration of sensing system are designed according to the structure and sizes of legs. Second, the joint toque sensors, 3-DOF foot-end force sensor and force information processing module are designed, and the force sensor performance parameters are tested by simulations and experiments. Moreover, a force sensing system is implemented within the robot control architecture. Finally, the experimental evaluation of the leg force sensor system on the hexapod robot is discussed and the performance of the leg force sensor system is verified.

Automatic space calibration of a medical robot system

In order to build an uniform coordinate system for a medical robot and its vision system in surgery, an automatic space calibration method is proposed based on the rotational and translational movements of the robot. With this method, both the robot and the NDI vision system can be calibrated to the patients bones contour, which matches the virtual model built from the CT images. Thus surgical operation can be carried out by the robot following the preoperative design based on the virtual model. The calibration accuracy directly determines the precision of surgical operation. Experiments were carried out to evaluate the effectiveness of this calibration method, and the result showed that the position and posture error can meet the operation requirements. Also the calibration can be executed automatically to decrease the human effect and increase the reliability and stability.

Design and application of parallel stereo matching algorithm based on CUDA

To accurately construct the topographic information of a six-legged walking robot in real time, this study proposes a stereo matching algorithm that can conduct disparity estimation on each pixel by using the Bayesian posterior probability model based on GPU-accelerated parallel processing. In the proposed algorithm, supporting points construct a disparity space to obtain the prior distribution probability density of each pixel and then substitute it into the Bayesian posterior probability model to establish the energy function of the disparity. The estimated disparity value of the unknown pixel can be obtained by minimizing the energy function. By performing a consistency check on the left and right sides of an image, the mismatching pixel can be eliminated. According to the disparity value of the supporting point, the disparity filling of the mismatching area can be achieved by applying the adaptive weight method on the basis of cross extending to obtain the accurate density of the disparity map. Parallel computing in each stage of the proposed algorithm is performed by using the compute unified device architecture to reduce the running time. Experimental results show that the proposed algorithm has good robustness for different illuminations and texture curved surface reconstruction. The algorithm can also adapt to the fast matching of images in different sizes and reconstruct the disparity map of scenes in real time under the resolution ratio of 640 480. The stereoscopic vision test board is employed to construct the disparity map of real scenes and verify the practical application effect of the algorithm. Good experiment effect is achieved.

Space calibration of the cranial and maxillofacial robotic system in surgery

Abstract Space registration in cranial and maxillofacial surgery is intended to map the image space to the robot space. This requires calibration of multiple coordinate systems. In this process, the calibration accuracy between the robot coordinate system and the NDI vision coordinate system directly determines the precision of the surgical navigation system, which is the key to success. In this paper, the relationship between robot space and visual space is studied according to the requirements of surgery, and with reference to the characteristics of the vision system itself. Based on this analysis and traditional methods, a new linear rotation calibration method is presented. Calibration can be automated to decrease human error and increase the reliability and stability. Finally, an experiment is conducted in order to evaluate the effectiveness of the calibration algorithm. The results show that the minimum position error was less than 0.87 mm and the minimum posture deviation was about 0.83 degrees, indicating that the calibration precision can meet the operation requirements. There are good prospects for this method using in surgical calibration application.

SIFT algorithm-based 3D pose estimation of femur

To address the lack of 3D space information in the digital radiography of a patient femur, a pose estimation method based on 2D-3D rigid registration is proposed in this study. The method uses two digital radiography images to realize the preoperative 3D visualization of a fractured femur. Compared with the pure Digital Radiography or Computed Tomography imaging diagnostic methods, the proposed method has the advantages of low cost, high precision, and minimal harmful radiation. First, stable matching point pairs in the frontal and lateral images of the patient femur and the universal femur are obtained by using the Scale Invariant Feature Transform method. Then, the 3D pose estimation registration parameters of the femur are calculated by using the Iterative Closest Point (ICP) algorithm. Finally, based on the deviation between the six degrees freedom parameter calculated by the proposed method, preset posture parameters are calculated to evaluate registration accuracy. After registration, the rotation error is less than l.5°, and the translation error is less than 1.2 mm, which indicate that the proposed method has high precision and robustness. The proposed method provides 3D image information for effective preoperative orthopedic diagnosis and surgery planning.

ADAPTIVE MOTION PLANNING FOR HITCR-II HEXAPOD ROBOT

Multi-legged robots have the ability to traverse rugged terrain and can surmount the obstacles, which are impossible for being overcome by wheeled robots. In this regard, six-legged (hexapod) robots are considered to provide the best combination of adequate adaptability and control complexity. Their motion planning envisages calculating sequences of footsteps and body posture, accounting for the influence of terrain shape, in order to produce the appropriate foot-end trajectory and ensure stable and flexible motion of hexapod robots on the rugged terrain. In this study, a high-order polynomial is used to describe the trajectory model, and a new motion planning theory is proposed, which is aimed at the adaptation of hexapod robots to more complex terrains. An attempt is made to elaborate the adaptive motion planning and perform its experimental verification for a novel hexapod robot HITCR-II, demonstrating its applicability for walking on the unstructured terrain.

Surface Defect Edge Detection Based on Contourlet Transformation

In order to preferably capture the surface defect edge information of strip steel, and provide more accurate data for subsequent defect analysis, this paper researches on the principle and implementation method of Contourlet transformation, analyzes the multi-directional and anisotropic characteristics, and proposes the image edge detection algorithm based on Contourlet transformation. This paper uses Laplacian Pyramid filter and directional filter for combination to realize Contourlet filter bank, and extracts the image edge information by the way of detecting the method of modulus maximum of Contourlet sub-band coefficient. The comparative experiments of the edge detection algorithm based on wavelet transformation and Sobel algorithm prove that the defect edge extracted by this algorithm is closer to the true edge of surface defect.

Adaptive Impedance Control for Docking of Space Robotic Arm Based on Its End Force/Torque Sensor

Aiming at space transposition using Space Robotic Arm (SRA), flexible docking between SRA’s end effecter (EE) and grapple fixture (GF) is the most important for space tasks. To avoid position errors leading to large contact force between EE and GF in the docking process, an adaptive impedance control method is proposed in this paper. PID feedforward with adaptive parameters is added into the impedance controller, and the force error function is used to deduce the adaptive parameters according to Lyapunov stability theory, which makes the force error decrease automatically during the connection process. Simulation proves that the adaptive impedance strategy gets better force control effect than the traditional impedance algorithm. Finally the SRA EE/GF connection experiments were conducted respectively based on traditional and adaptive impedance control strategy. The results showed that the adaptive impedance control strategy can achieve better control effect than the traditional strategy.