Theoretical Research On Binocular Active Visual Monitoring Platform Of Parallel Mechanism

Machine vision is a comprehensive technology fusing vision sensor, image understanding, pattern recognition and computer control etc. Using machine vision to replace human eyes with measurement and judgment, It is advantageous to achieve system intelligence, automation and information. The application of machine vision system can greatly improve the level of intelligence and automation, and enhance efficiency, accuracy and reliability of equipments. To solve the problem that parallel robot is unable to perceive the changes in working conditions and environment, this paper puts forward a binocular active visual monitoring platform based on circular orbit adapt to the parallelism of parallel mechanism and the requirement of robot workpace monitoring. With the support of the National High Technology Research and Development Program(863), a prototype machine of binocular active visual monitoring platform of parallel mechanism is developed, and the problems including kinematic theory, vision measurement and others key technologies have been deeply studied. The main research contents are as follows:(1)A new design of binocular active visual monitoring platform of parallel Mechanism is proposed, and its motion model is also established, which breaks the traditional design that the baseline of the camera in monitoring platform must be fixed. The design that the two cameras freely move along circle orbit is presented for the first time, which can realize more flexible binocular vision such as baseline adjustable capacity, optical axis adjustable capacity, large-scale multi-angle observations and vision avoidance. Aiming at experimental prototype, the mechanism model of visual system is established, and the position, velocity, acceleration kinematics model (forward and inverse) of vision system is also given. The experimental results verify the correctness of the model. (2)Two levels calibration architecture of binocular active visual monitoring platform of parallel mechanism is established. A planar chess target is the first level calibration, and a non-linear calibration algorithm is proposed to solve intrinsic parameters and extrinsic parameters of cameras and realize system initialization. To solve the occlusion issue caused by the end effectors and machined body in the calibration process by a planar chess target, the second calibration target, which consist of six groups of 3D target distributing uniformly inboard circular orbit, is designed to satisfy the requirement of dynamic calibration for vision system. Then using this two level calibration architecture, it is implemented measuring structural parameters and control equivalent and machining accuracy of binocular active visual monitoring platform of parallel mechanism.(3)Binocular active visual monitoring platform of parallel mechanism can achieve the best observation for the object in the common view of two cameras though harmoniously adjusting its two chains. For this purpose, the binocular emmetropization mode is defined, and A single chain control strategy is improved to transfer a camera attentive focus to the object position, and the binocular cooperative kinematics model is developed to implement visual tracking in binocular emmetropization mode. The experimental results show the effectiveness and feasibility of the observation model and control strategy.(4)Considering some application questions of binocular active visual monitoring platform for parallel mechanism, visual navigation and motion detection are preliminarily explored. Firstly, based on guiding cutting tool of engraving parallel robot to expected positions, a simplified direct method is proposed to plan the path of the cutting tool using its extracted visual information from two cameras. Secondly, the pose detection method of the cutting tool base on a truncated cone-shapetarget and motion parameters analysis method of the cutting tool based on Extended Kalman Filter are successively developed. The experimental results show that the methods are effective and practicable.(5)The overall software design of binocular active visual system of parallel mechanism is given. The whole system is constituted by a foreground control system and a background visual service system front electrical control system. The foreground control system provides some functions of electric equipment control and image acquisition. The background visual service system provides some functions of Image analysis and control strategy generating. Information exchange is implemented through sharing the same format Text file between the foreground and background computers.