In Situ Sphericity Error Detection And Compensation In Large Spherical Grinding

Three-coordinate measuring machine is mainly adopted as a traditional sphericity measuring method to measure sphericity of spherical parts off-line,but it can only measure the upper half of the sphere at one time.To measure the complete sphere,sphere rotation is needed,which will introduce repetitive position errors.Moreover,the use of off-line sphericity measurement need to tear down the workpiece,which will reduce the manufacturing efficiency and introduce repetitive position errors again due to secondary-clamping.On the contrary,online detection and compensation of sphericity can improve manufacturing efficiency and reduce reject rate at the same time.Therefore,online detection and evaluation of sphericity has important implication for in situ compensation of sphericity error while grinding.In this dissertation,in situ sphericity error detection and compensation method of large sphere were studied.Mathematical model and analysis of geometric deviation were carried out based on spherical grinder to study its influence on sphericity.Grain trajectory considering geometric deviation was studied and the mathematic model was built.Sphericity and geometric deviation were calculated based on machine vision technology.Finally,a sphericity compensation device was designed and the relevant compensation method was proposed.The research contents include:First,the influence of geometric deviation on sphericity was analyzed.Based on the principle of large spherical grinder,the mathematical model of geometric deviation was set up.Single-grain trajectory model considering geometric deviation was built and simulated.The influence of several factors on grain trajectory was analyzed.Second,the characteristics of surface grinding marks were studied.Cross ratio of grinding marks has been defined as a statistic feature to evaluate the geometric deviation and sphericity error.Mathematical formula of cross ratio according to the critical position conditions was derived.Furthermore,the influence of several factors to the cross ratio was analyzed.The inner relationship among the cross ratio,geometric deviation and sphericity was revealed.Next,the key technologies of image processing were studied.Edge extraction,image blocking,area sifting as well as template matching were studied to calculate the cross ratio.Image was blocked according to its self-characteristics,and a novel area searching method was proposed to improve template matching efficiency.Template database of different grinding marks was set up and the sphericity detecting method was evaluated.Finally,a sphericity error compensation device based on the micro-displacement actuator was designed and the relevant compensation method was proposed.Proper micro-displacement actuator was chosen based on the maximum load and maximum displacement required.The advantages and disadvantages of the compensation method were analyzed.