Research On Technology Of Wheel Polishing Based On Industrial Robot

Large aperture telescopes play an irreplaceable role in aerospace,deep space exploration,resource exploration and other fields,which is the embodiment of a country’s comprehensive strength.With the development of astronomical optics and space optics,the demand of large aperture aspheric optics is increasing.For the optical system,the large aperture optical element has the characteristics of high spatial angular resolution and strong energy collection ability.Aspherical optical elements can increase the degree of freedom of optical design,and have excellent performance in improving the image quality,improving the optical performance,reducing the size and weight of the optical system.However,due to the non-uniformity of curvature,non-rotation symmetry,complexity of structural parameters,gravity deformation and other factors,the manufacturing of large aperture aspheric optical components is more difficult and the manufacturing cycle is longer.Especially,in recent years,higher and higher requirements have been put forward for large aperture aspheric optical components,such as surface accuracy approaching nanometer level and surface quality approaching atomic level,which poses higher challenges to researchers in the field of optical manufacturing.In this paper,based on the existing computer controlled optical surfacing technology,the wheel polishing technology based on industrial robot is studied deeply.Industrial robots have the advantages of low cost,flexible movement and large working space.Wheel polishing has the advantages of flexible contact,good fit and high processing efficiency.In this paper,wheel polishing technology is carried out on industrial robots to achieve high efficiency,high precision and low cost ultra-precision optical manufacturing.The main research work is as follows:(1)Robot kinematic modeling is the basis of this paper.Firstly,based on the D-H parameter method,the physical model of the robot is transformed into a mathematical model,the rotation transformation matrix of each joint coordinate system is studied,and then the forward kinematics model of the robot is established.When the angles of each joint are known,the forward kinematics model can be used to conveniently calculate the position and attitude of the end coordinates relative to the base object.Secondly,based on the forward kinematics model and the coordinate system transformation matrix of each joint,the solution formula of each joint Angle was derived,and the inverse motion model of the robot was established.When the position and attitude of the end coordinates relative to the base object are known,the Angle value of each joint can be obtained one by one through the inverse kinematics operation of the robot.Finally,based on the robot kinematics model,Leica laser tracker is used to measure and calibrate the robot motion accuracy,which improves the motion accuracy by 3 times,which is beneficial to improve the certainty and pertinency of NC polishing,and is conducive to the rapid convergence of surface shape errors.(2)The research of polishing tool and tool influence function is the core of this thesis.Firstly,a rotating wheel polishing tool is designed based on the structure of planetary conical teeth.A motor is used to realize the rotation and rotation of the polishing wheel,which makes the structure compact,the moment of inertia small and the operation stable.A pneumatic floating structure is used to compensate the Z motion error of the robot to realize the stable control of polishing pressure.Secondly,based on Preston equation,the influences of polishing wheel speed,polishing pressure and polishing time on the removal function were studied,as well as the stability of the removal function.The nonlinear mechanism between the process parameters and the removal function was revealed,which provided a theoretical basis for the selection of polishing process parameters.It lays a solid foundation for accurately controlling material removal and realizing high precision optical machining.(3)The research of deterministic optical machining algorithm is the key of this paper.Firstly,aiming at the problem of edge effect existing in the dwell time algorithm,a method of zero correction and convolution of closed-loop feedback for the dwell time beyond the range of processing path was proposed,and iterative optimization of the calculated edge effect was carried out.The simulation results show that the edge effect is improved effectively by optimizing the algorithm,and the accuracy of surface shape is increased by 51.2%.Then,to meet the rapid manufacturing requirements of largediameter optical components,a multi-robot collaborative polishing strategy based on dwell speed was proposed.The material removal amount was controlled by the rotation speed of polishing wheel,so that multiple spiral traversal machining tracks could be realized,joint effect could be avoided,and intermediate frequency errors could be suppressed.A nonlinear model between the speed of polishing wheel and the amount of removal was established by sampling experiments,and a dwell speed solving algorithm was developed based on the model.The simulation results show that the residual of simulation machining based on dwell speed algorithm is very close to that based on dwell time algorithm,which proves the accuracy and feasibility of the dwell speed algorithm and lays a foundation for the verification of variable speed machining.(4)The experiment of optical machining is the verification of the research work in this paper.In this paper,the processing experiments of optical components are carried out based on dwell time strategy and dwell speed strategy respectively.Firstly,the inline or off-axis microcrystalline,quartz and silicon modified materials were processed by the robot wheel processing technology based on the stay time,and the surface accuracy was up to RMS-0.011λ,RMS-0.006λ and RMS-0.015λ,respectively,proving that the wheel polishing technology based on industrial robots has high processing efficiency and precision.Then,using the processing strategy based on dwell speed,the quartz plane is processed with grid and spiral path respectively,and the surface shape accuracy reaches RMS-0.015λ and RMS-0.014λ respectively,which proves that the wheel polishing technology based on dwell speed is feasible,and lays a solid foundation for the multi-robot collaborative machining technology based on dwell speed strategy.This technology will be applied in the machining of 2m large aperture optical components.