Bundle adjustment (BA) refines the estimation of three-dimensional (3-D) structures and viewing parameters in multiview 3-D reconstruction. It is crucial to the accuracy of the reconstruction. Generic bundle adjustment (GBA) fails to make full use of a priori knowledge of the structure of the objects. We propose a new constrained BA algorithm for 3-D reconstruction of a cylinder surface. In this algorithm, 3-D point positions are parameterized as a combination of the parameters of the cylinder and their two-dimensional locations on the cylinder surface. A random-sample-consensus-based fitting step is used to initialize the parameters of the cylinder surface from more than nine points. Parameters of cameras, the cylinder, and 3-D point locations are then refined by solving the problem of minimizing the reprojection error. Experiments based on synthesized data and real images are performed. Experiment results with synthesized data show that the proposed algorithm achieved a 50% lower reconstruction error than the GBA. Experiment results with real images show that the proposed algorithm is more accurate than the GBA approach when the number of matched point pairs is limited.
In order to fulfill autonomous climbing and automatic weld seam tracking, a novel visual sensor has been developed for intelligent spherical tank welding robot. Composed of a high-resolution linear CCD, an optical system (including light source, filter, lenses and so on), and an all hardware photoelectrical signal processing circuit, the designed visual sensor could avoid the interference of the arc light during welding and provide the seam track signal precisely in real time. In this paper, the construction and working principle of the linear CCD based visual sensor have been illustrated, then principle of weld seam track detecting has been introduced thoroughly. Equipped with the visual sensor, the spherical tank welding robot could move along the weld seam autonomously, could align the welding torch with weld seam automatically. Therefore, the requirements of multi-layer, multi-pass welding process for spherical tank manufacturing have been met.
Due to the existing problem ofdata loss and time delay, Internet Multimedia applications always couldn't achieve good real-time performance. Real-time streaming of audiovisual content over Internet is emerging as an important technology area in multimedia communications. This paper presents a system for transporting real-time video stream over Internet. A MPEG-4 software CODEC is used to compress and decompress digital video data in this system for MPEG-4's built-in flexibility and error resilience capability. New transportation architecture is designed in this system to achieve minimum delay and high network resource utilization. Real Time Protocol (RTP in short) is adopted for the purpose of real-time transportation. Experimental results show that this delivery system obtains good perceptual picture quality and a very short delay under medium bit rate. The presented delivery system will be beneficial to applications that demand high real-time performance under medium bandwidth network environment.
This paper presents a time-varying feedback controller for stabilization of tracked mobile robot. Considering its nonholonomic property, we first transform the TMR kinematics into a advantageous model. Then the principle of exponential stabilization is discussed using a Lyapunov-type argument. The back-stepping technique is applied to obtain a global exponential regulator for the TMR model and simulation results are given.
At present, spherical tank manufacture is still staying at the level of manual welding or semi-automation. In order to improve quality of weld seam and guarantee safe operating of spherical tank, automatic welding equipment is needed urgently. A intelligent wheeled mobile robot equipped with CCD based visual sensor has been developed to acquire better weld quality in this research. Special mechanical structure has been proposed based a wheeled mobile robot body to realize reliably and flexibly absorbing and moving on the surface of spherical tank. A 3-DOF welding manipulator has been fixed on the robot to carry out welding tasks. A CCD sensor has been used to detect weld seam for the trajectory planing of both the mobile robot and the welding torch, control strategy for nonholonomic system with redundant DOF has been put forward to realize the accurate tracing of weld torch, an intelligent controller has been designed. In this paper, mechanical structure of robot, principle of CCD sensor, tracing model for robot and welding torch, and intelligent controller have been presented in details respectively. Experiments show that this robot can fulfill all-position welding tasks freely on the surface of tank with high weld torch tracing accuracy(up to +/- 0.5mm).
This paper addresses the tracking problem of tracked mobile robot. After the kinematic model of the nonholonomic system has been discussed, a robust motion controller based on backstepping technique is proposed for the TMR. Some singular perturbations, which maybe occur in practical situations, are also taken into account in order to ensure the tracking error of the closed-loop system to converge toward zero. Simulation results are provided to validate that the proposed controller ensure the TMR asymptotically track the desire trajectory.