Study On Some Key Techniques For Spray-Painting Robot

Spray-painting robot is a fruit from two kinds of technologies of robotics and surface spray-painting. It is a special kind of industrial robots and mostly is used for surface spray-painting. Compared with others, there are some special requirements for this kind of robot: Firstly, its end-effector is required to move on a trace with higher and well-proportioned speed when it is working. Secondly, because of the highly combustible and explosive work environment, the robot is demanded to be exploding defended. Thirdly, the material sprayed to surface of the workpiece by robot is semiliquid, so the pipelines used to transfer lacquer and compressed air are not allowed to be disposed out of the arm of the robot in order not to destroy the painted surface. According to the special requirements of enterprise and application activities of numerical controlled painting robot in china, some practical problems in development of spray-painting robot are studied in this paper.(1) The structure scheme of the painting robot is introduced firstly according to the requirement of spray-painting techniques. Then, its kinematics equations such as displacement equation, velocity equation and acceleration equation are all established, and inverse solutions of these equations are discussed too. Analytic expressions of the inverse displacement solution, matrix element expressions of the jacobian matrix and the second order coefficient matrix are deduced. A new approach is introduced for solving inverse speed problems. This method employs mixed gene algorithm to solve the problem and used recursive speed formula of robot links to establish a function for evaluating the genic unit. The velocity jacobian matrix does not need to be constructed and the inverse jacobian matrix is also unnecessary with this method. Obviously, this method is simpler than traditional ones, which can be used to solve speed inverse problems for less than 6 DOFs(degrees of freedom) robot or 6 DOFs robot. function for kinematical parameter optimization of the robot. According to the demand that the relative displacement between robot and workpiece and the shortcoming of present index for evaluating integral manipulability, a new index system is presented, which takes the average manipulability -ηand the poorest manipulability -D_min as combined evaluation index to evaluate the manipulability of task space for spray-painting robot.(3) To meet the requirement of robot design, an approach based on dynamics for designing robot mechanism is discussed. This approach requires the designer to know the dynamics contributing of a link that just fulfills the design, to analyze in time and to modify if necessary. Compared with the traditional method which carries out dynamics analysis after the robot design work finishes and the modification work will be done behind that, the new method reduces repeat times of the design. Also an optimal method for robot arm design based on dynamics is also presented in this paper.(4) As the air spray-painting techniques are widely employed in engineering and the existing spray gun model is not compatible with the air spray-painting gun, the spray shape of air spray gun is not a cone and an elliptical paint area adhered to a planar surface is formed, so the distributing rule of paint-film thickness which is formed in painting process is investigated based on a painting experiment with an unmovable spray gun. A new analytical paint film thickness distribution function named as ellipse dual-βmodel is proposed by comparing the fitted paint-film profile on some different sections in x and y directions. This model is a new practical spray gun model for off-line robotic spray-painting programming. Based on the new model and aimed at spray gun moving path when a robot paints a typical hexahedron surface, an optimal approach for spray gun trajectory parameters is discussed. Spray gun's trajectory parameters are optimized by employing GA. two schemes are presented by the difference of painting-gun movement, then the robot dynamic model is utilized to deal with this case taking the minimization of the sum of all joints moment maximum as a goal. The best painting-gun path is selected from the above two methods, by which, the spray-paint quality can be ensured and the robot joint motor can work with lower load. The optimized result can be reference for off-line programming or on line teaching programming for spray-painting robot.(5) Aimed at a mobile spray-painting robot composed of a two-wheel differentially driven AGV(Automatic guided vehicle) and a manipulator with 6-DOFs, the dynamics models of the manipulator and the AGV are all established respectively using Newton-Euler method. Then two models are combined to analyze the interplay of the AGV's movement and the manipulator joint movement in moving manipulation and in the AGV's or manipulator's independently working process. Some important rules are introduced for making the mobile robot working harmoniously. These rules provide a foundation for designing and controlling this kind of mobile spray-painting robot.(6) Aimed at calibration of kinematics parameters of spray-painting robot, considering the modified D-H model and distance error model, the feasibility of identifying kinematics parameter errors by different robot end-effector pose(position and orientation) distance information is studied. A new method is presented in which kinematics parameter errors are identified according to portion end-effector pose distance information, equations about errors are directly established with interrelated element in kinematics equation and least mean square solution of those equations obtained by employing mix-genetic algorithm. The feasibility and validity are proved by simulation results and experiment results.