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Research On Optoelectronic Vision-based Robot Control Theory And Its Application

Posted on:2016-03-18Degree:DoctorType:Dissertation
Country:ChinaCandidate:S YeFull Text:PDF
GTID:1108330473452455Subject:Optical Engineering
Abstract/Summary:PDF Full Text Request
The closed loop control for vision-based robot control system is realized by using machine vision to acquire the target information. Compared with the traditional robot control, it has higher production flexibility and intelligent level. This system is an important research direction in the field of robotics that applied to the high-speed and high-precision industrial tasks, and has important socio-economic and theoretical research value. Several key technical problems associated with system efficiency and control accuracy are investigated in this dissertation, the main contents and achievements are listed as follows:(1) The perspective matching algorithm is modified using Phong model to enhance the algorithm efficiencyThe edge-based perspective shape matching algorithm is modified using Phong’s bidirectional reflectance distribution function(BRDF) model to decrease the time consumption of algorithm and the overall work efficiency of auto stiffener bonder(ASB) system is enhanced;The purpose of this dissertation is to solve the issue of inclined target positioning in ASB systems for flexible printed circuits(FPC). The proposed approach uses Phong’s BRDF model to simulate the reflection of light off a target in ASB systems in order to predict the current pose of the target based on image brightness, update the template, decrease the initial errors in the template, and narrow down the search range. The experimental results indicate that the proposed approach can predict the inclination angle of the target with precision, presenting angle prediction errors of less than 3 degrees. Furthermore, with larger inclined angles, the overall matching errors were less than 1.5 pixels. Comparisons with the unmodified matching algorithm revealed that the proposed approach results in 65% less calculation time for the algorithm and 14% higher overall work efficiency in the ASB system;(2) The calibration model is modified from two-dimension to three-dimension in order to improve the calculation accuracy of hand-eye calibrationThe proposed three-dimensional calibration model is capable to effectively improve the accuracy of hand-eye calibration with the finite degree of freedom system, and has no additional constraints such as camera installation;To eliminate the error of hand-eye calibration caused by installation error associated with the verticality of the camera’s optic axis in the automatic stiffness bonder, the conventional two-dimensional calibration model is modified in this dissertation. The external parameters of camera obtained with the calibration boards, is combined with the conventional two-dimensional calibration model, thereby extending the dimensions of the model to three, which includes the whole information associated with the camera pose, in order to calculate the homogeneous coordinate transformation between the camera frame and the robot base frame. The experimental results indicate that the error of the calibration with the three-dimensional model is less than 0.1 μm, which is decreased by an order of magnitude compared with the two-dimensional model. Using the thin films to modify the value in Z direction in coordinate transformation, the system has high location precision and the error of the calibration is less than 0.015 mm. For FPC products with specification limit(SL) of 0.12 mm, the process capability index(CPK) of system after modification is increased from 0.838 to 5.389, the error mean is reduced effectively, and the performance of system is significantly improved;(3) A novel error compensation method is proposed to eliminate placement error of the FPCASB systemThe proposed compensation method is aimed at eliminating placement error caused by hand-eye calibration and pick-and-place tool motions in FPCASB system. This method is rapid and practical, without the need of detecting and calculating the calibration error item by item;Using the transformation of homogeneous coordinates to develop an error model of the system describing the coupling of errors among various coordinate systems, and the least squares method is used to calculate the unknown model parameters for the development of error model. Experiment results demonstrate that this error compensation method reduced placement error by an order of magnitude, compensation aimed at pick-and-place tool motions reduced the magnitude of error by an additional 28%. The mounting precision throughout the entire work area was ±0.046 mm@3sigma, and for FPC products with SL of 0.1 mm, the CPK of ASB in this dissertation was 2.19. This represents the system is capable of fully satisfying the precision requirements of FPC stiffener bonding;(4) The proposed visual servoing control without using the filter structure is capable to reduce the system complexityThe proposed adaptive controller is removed the filter structure which is used to predict the image velocity, the method makes the controller structure is more simple and reliable, reduces the difficulty of project implementation and tuning parameters;To avoid performance decaying caused by measurement errors of the image velocity, an adaptive controller for visual servoing systems is proposed to allow the tracking of a two-dimensional desired trajectory without using image velocity measurements when the kinematics and dynamics parameters are uncertain. The designed sliding-mode vector first derivative is not affected by actual image speed parameters, the image position parameter estimation method is proposed to replace the image speed parameter estimation. The asymptotic stability of the system is proved by using the Lyapunov’s method. Simulation results show that the end-effector of SCARA robot is able to converge to a desired trajectory;(5) The proposed ASB system is applicable to a variety of stiffeners and has higher production flexibilityCompared with the traditional FPCASB equipment, the proposed ASB system is applicable to a variety of stiffeners, which enhances production flexibility. Several technical issues of the ASB system are improved and solved, the proposed system architecture and related technical solutions have not been reported in the domestic.
Keywords/Search Tags:vision-based robot control, perspective matching, hand-eye calibration, error compensation, uncalibrated visual servoing, auto stiffener bonder
PDF Full Text Request
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