| 1. IntroduceMore and more aspherical lens are used in these fields such as industry,medical treatment,national defence,communication etc. with the development of optoelectronic technology.Traditional ultra-precision polishing technology have their advantages in polishing the large aspherical parts,but they also have their shortcomings in polishing the micro aspherical parts . The technology of electrorheological polishing aspherical parts can make up for their shortcomings.The technology of electrorheological polishing aspherical parts is an up-to-date abrasive polishing process in our country,and there is no experiment platform which is used in electrorheological polishing aspherical parts,so it's necessary to design and establish a new experiment platform which is used in electrorheological polishing aspherical parts.2.Theory of electrorheological polishing aspherical parts1) Aspherical theoryThe aspherical parts are these optical parts which radiuses of surface shape are different.Axis-symmetrical asphere is used in traditional optical system,the simplest axis-symmetrical asphere is conicoid.Some conicoid equations which are often used and their aspherical degree are listed as follow:The equation of elliptic surface and its aspherical degreeThe equation of hyperboloid and its aspherical degree2) Theory of electrorheological polishingElectrorheological fluid(ER fluid)is a new functional fluid,which is made up of small particles dispersed in non-conducting liquid.The viscosity of ER fluid is altered when the external electric field is applied,and the state of ER fluid becomes solid state when the value of external electric field reaches to a certain value,the state of ER fluid becomes liquid state when the external electric field is canceled,this phenomenon is called ER effect.We can use ER fluid in polishing aspherical parts and can acquire good surface quality.The schematic diagram of ER polishing is showed as figure 1.As shown in figure 1,the larger particles are ER particles,and the smaller particles are abrasives.When an electric field is applied between the electrode and the workpiece,the electrostatic attraction force is generated around the surface of ER fluid particles and abrasives owing to the polarization of particles,and this force is dominant in all the forces which act on the particles.The shear friction of ER fluid increases with the value of the electric field strength because the attraction forces of ER particles resist the movement of particles.In addition,the abrasives are attached to ER particles because of the electrostatic attraction force,and theabrasives will move with ER particles when the electrode rotate,then the abrasives scrub the surface of workpiece and the material are removed.The equations related to the mechanism of ER polishing are listed as follow:The electrostatic attraction force between particlesThe moment of particle in the electric field3.Design of the experiment platformThe parameters of experiment platform is made based on the need of ER polishing aspheric parts.The experiment platform is composed of X table,Y table,Z table,deflexion setup and precision electric rotational table.The project of the experiment platform can be designed based on different drive system,transmission system and detector system, three projects have been designed and be discussed,we can choose a best project from them.The model of the best project is shown up as figure 2. 1-Z table;2- deflexion setup;3-platform base;4-Y table; 5-X table;6- precision electric rotational table Figure 2 The model of the experiment platformThe ball screws which are drived by AC servo-motors move along the straight rail in X,Y,Z orientation,the deflexion setup can make the electrode waver,the precision electric rotational table can make the workpiece rotate.High precision grating-rulers are installed in X,Y,Z orientation in order to ensure the precision of experiment platform.Finally,we can design and model the parts of experiment platform according to the best project.4.Finite element analysis of the experiment platformThe distortion of the shaft-coupling and the joint block can affect the precision of the experiment platform,so it's necessary to make the static analysis of their structures,and find out the max distortion.In addition,the vibration of the base of the table also can affect the precision of the experiment platform,so it's indispensable to make vibration analysis of their bases.1) Static analysisFirst,we can design and model the shaft-coupling and the joint block in Pro/E,then transfer the model to ANSYS and establish the finite element model,solve the model,at last,check out the result.The results of static analysis are shown up as figure 3. (a) The result of the shaft-coupling (b) The result of the joint block Figure 3 The results of static analysisAs we can see from figure 3,the distortion value of the shaft-coupling is 0.151×10 ?4mm,and the distortion value of the joint block is 0.170×10 ?4mm,their distortion value is smaller than the precision of the experiment platform,so we can make a conclusion that their design is right.2) Vibration analysisFirst,we can design and model the base of X table in Pro/E,then transfer the model to ANSYS and establish the finite element model,solve the model,at last,check out the result.The results of vibration analysis are shown up as figure 4. Figure 4 The results of vibration analysisThe vibration of X table is brought by the vibration of X AC servo-motor,according to the equation:The max vibration frequency of the X AC servo-motor is 50,it's far larger than the intrinsic frequency of the X table,so it's impossible to bring the resonance.5.Virtual Assembly of the experiment platformThe process of virtual assembly is the process of carrying the restriction.First, We can use the models to assemble in Pro/E,then check out whether there are some interferences in the assembly model of the experiment platform,if there are some interferences,and we will redesign the model till there isn't interference.The process of assembly is expatiated in this paper,the assembly model of X table is given as figure 5.Figure 5 The assembly model of X tableThe assembly model of X table is carried out the interference test,and there is one interference in the model,this phenomenon is not wrong after we analyse the structure of the experiment platform. 6.ConclusionThe technology of electrorheological polishing aspherical parts has its advantage in polishing micro aspherical parts,but we still quest for the mechanism of electrorheological polishing,so it's indispensable to design and establish a experiment platform which is used to polish micro aspherical parts.The paper study subject is related to the project on the outstanding youthful research plan in Jilin Province, which is the research of ER polishing micro aspheric mould,and the contract number is 20050121.The primary work and conclusions are expressed as follow:(1) The design of experimental platform is the major work in this paper.The experiment platform is composed of X table,Y table,Z table,deflexion setup and precision electric rotational table.The paper making the parameters of experiment platform based on the need of ER polishing aspheric parts,and design three projects and discuss their advantage and shortcoming,and choose a best project in them,and design the parts according to the best project.(2) The distortion of the shaft-coupling and the joint block can affect the precision of the experiment platform,so it's necessary to make the static analysis of their structures,and find out the max distortion.We can use ANSYS to analyse the distortion of the shaft-coupling and the joint block, and we can find that the distortion of the shaft-coupling and the joint block is smaller than the precision of the experimental platform, so the design of the shaft-coupling and the joint block is right.In addition,the vibration of thebase of the table also can affect the precision of the experiment platform,so it's indispensable to make vibration analysis of their bases.We can use ANSYS to analyse the vibration model of X base and find the design of X base is right.(3) The models are used to assemble in Pro/E,then check out whether there are some interferences in the assembly model of the experiment platform,if there are some interferences,and we will redesign the model till there isn't interference.We can check out whether there are some interferences in the assembly model of the experiment platform by using Pro/E, at last, we can make sure that there isn't any interference, so we can think the design of the assembly model of experiment platform is right.
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