Study On The Key Problems Of Solid Rocket Engines Inner-wall Insulation Grinding Robot

Solid rocket motor is the most important space power equipment. The insulation pasted in the combustion chamber (namely, the engine shell) inner-wall plays an important role in thermal insulation and avoiding washing to shell by combustion products. Presently, the domestic production is still by manual method. This manufacturing not only is inefficient, labor-intensie, extremely poor working conditions, but also is not able to ensure uniformity of grinding. The thickness of grinding too much or too little will lead to scrap the insulation as well as the whole engine. So this manufacturing has not meet today’s aerospace industry and future development needs.Development of advanced automatic grinding equipment insulation is the development trend of the space industry and also one practical co-operation projects between my research department and a factory of China Aerospace Science and Industry Group. Consequently, in this dissertation, the key technical issues of rocket engines inner-wall grinding robot have been made a detailed analysis and discussion. Moreover, according with the key problems, the effective solutions and their theoretical basis and technical support are given. The main research content and results are as follows:(1) The manufacturing of advanced automatic rocket engines inner-wall grinding equipment involves in military, aerospace and other sensitive areas, so there are few relevant reports international. And the automation level of domestic production is backward. Consequently, there is no precedent for reference. Moreover, due to the specificity requirements of grinding and the structure of insulation, they all limit the shape and size of robot mechanical structure and the movement patterns in grinding process. Hence, the manufacturing of advanced automatic grinding is different from the traditional outer surface. Hence, reference the design of grinding automation applied to other areas, the overall function and structure of grinding robot is designed from the aspects of the polished manner, functional modules and performance indicators.(2) Based on the characters of integrated optimal design of grinding robot mechanical structure, the improved encoding method and involing competition in small scope in GA is applied to optimize. Because the optimization model has six variables and all of them are positive integers, combination of ten numbers is used as chromosome table to encode genes. Consequently, the genetic manipulation of genes is essentially the genetic manipulation of optimal variables. This method not only uses the optimization mechanism of genetic algorithm, but also accords with the conventional optimization design idea. Moreover, combination encoding also reduces the numbers of chromosome so that it can also improve the efficiency of optimization search. Moreover, the competition in small scope is able to avoidng the individuals generated by the same parental type great carrid on genetic manipulation.(3) Traditional robot collision avoidance method applied to free operation space is carried out by adding robot DOF(Degree of Freedom). However, this method isn’t suitable to limited operation space such as a kind of slightness solid-propellant rocket engines inner-wall. Hence, this dissertation presents a new robot method with non-redundant DOF for limited operation space collision avoidance. Without adding robot DOF, this method judges collision situation in grinding trajectory by mathematical model, then adjusts dynamically the grinding interface of the robot end-effector. So robot bodies’poses are transformed to avoid collisions between the different robot bodies or between robot bodies and inner-wall. Moreover, kinematics optimization and simulation were carried on by setting the smoothness of joints’velocity variety as optimization objective and discriminant of collision as constraints. On the premises of minimum changing of original, this method use the optimal control way to collision avoidance.(4) Referring to the pre-interpolation S-shape acceleration/deceleration and smooth transfer in CNC, the grinding robot trajectory planning is carried on. The trajectory planning is able to avoid impact, overshoot and oscillation in the start and stop processes of robot basic. And through the analysis of parametric relationship, the constraints of S-shape acceleration/deceleration is presented to simplify the solution. Moreover, the heads of solid-propellant rocket engines body are ellipsoid thin-wall structure so the ellipse trajectory curve is not approximated by general linear or circular interpolation method. Otherwise, it will create a big bow high error. In view of the defects of above methods of interpolation, based on the contrast of three different ellipse interpolation algorithm, the equal arc length time-sharing interpolation algorithm is used to transform the displacement planned by S-shape acceleration/deceleration. The simulation results prove the inner-wall grinding robot’s trajectory planning and interpolation algorithm with high precision, speed and smoothness. All of these provide the necessary precondition for accuracy grinding of missile inner-wall grinding.(5) Because the insulation exist some local convex and cupped, this dissertation presents a impedance control system with multilayer perception NN-based predicting reference trajectory to compensate the ideal trajectory and control. Through formula deduction, the feasibility of NN-based predicting trajectory is proved with the NN sample inputs set as the actual contact trajectory points and contact forces, and the NN sample outputs set as the environment predictive trajectory points, stiffness and tangential angle.In addition, the actual force Pm and expected force Pd by the predictive trajectory based on neural network impedance reference control system are difficult to be directly access. Hence, Pm is substituted by the acquisition of the servo motor torque, which can be converted to the contact force of the end effector. And an experimental method has been designed to get Pd. In order to meet the requirements the method predict the expected grinding force referred to the grinding force that be indirectly measured and the thickness that be polished, and adjust grinding force slightly based on neural network reference trajectory of the impedance control system. Experimental data show that the thickness of griding can meet the requirements and ensure the quality and safety of grinding.(6) In the grinding process, the grinding robot mechanical structure is almost in the rocket engines, so it is necessary to build the three dimensions graph monitoring system on-line of grinding robot’s movement. In this dissertation, Solid Edge software and its secondary development technology are used to establish the parameters three dimensions model of grinding robot. Then, through five command functions provided openly by Solid Edge software, the grinding robot’s monitoring system online are build simply.