Research On Key Technology Of Ultra-precision Robot-finishing Complex Surface

Optical element is the core component of optical system.Large-aperture optical elements have the advantages of high spatial Angle resolution and strong light collection ability and so on.Aspheric optical elements can greatly simplify the structure and reduce the weight of the optical system.With the increasing requirements for optical systems,large aperture aspheric optical elements are widely used in the field of optics as an important part of optical system.Bonnet Polishing,Computer Controlled Polishing of Small Grinding Head,Stressed Lap Polishing,Magnetorheological Finishing,etc.are all important methods of optical element processing.These techniques have some limitations in polishing optical elements with large diameter and complex surface.Polishing pressure is one of the important parameters in optical element processing.How to control the constant pressure between the grinding head and the workpiece is an important problem to ensure the polishing quality.In this paper,a robot polishing system is established and its key technologies are studied.For large aperture optical elements,a spherical male rotation polishing tool for the end is designed.The end polishing tool and force sensor are installed at the end of the 6-DOF industrial robot.According to the real-time polishing pressure and intelligent control strategy,the robot pose is adjusted to ensure the constant polishing pressure.This paper mainly includes the following aspects:(1)Based on Preston empirical equation and Hertz contact theory,the mathematical model of polishing optical element of spherical grinding head is established.By analyzing the shape,size,pressure distribution and velocity distribution of the contact area,the removal function model of the spherical grinding head is established.The shape of the removal function under different velocity ratio is simulated and compared.By analyzing the simulation results,the influence of revolution and rotation of the spherical grinding head on the polishing results is obtained.(2)According to the design requirements of the end polishing tool,a new type of spherical common rotation end polishing tool is designed.Due to the addition of an internal mesh drive and a planetary drive into the end polishing tool,the position of the spherical head moves upwards.The new end polishing tool solves the problem that the curvature of the workpiece and speed ratio are limited.The application range and machining efficiency of end polishing tools have been improved.(3)The whole system of robot polishing system is established,including industrial robot,end polishing tool,computer,workpiece and workbench.The coordinate system of the robot is established based on the XZ transformation of d-H model.The transformation matrix of the robot end relative to the coordinate system of the base is deduced.The inverse solution of the robot is calculated based on the inverse kinematics of the robot.The gravity compensation strategy is applied to the detection data of the gravity sensor.(4)The control framework of force-displacement control strategy in robot polishing system is designed.Through Simulink toolbox,conventional PID controller,fuzzy PID controller and fuzzy neural network PID controller are designed.Take the step signal as the system input,three kinds of controllers are simulated respectively.The simulation results of step responses of different controllers are compared and analyzed.