Research On The Type Synthesis And Dynamic Balance Of A Novel Planetary Polishing Head

With the increasing of precision requirements of optical lens,the manufacturing methods are facing new challenges.Traditional polishing equipment based on the machine tools is difficult to meet the requirements of flexible manufacturing of optical lens.Therefore,robot polishing equipment have attracted extensive attentions,and become an effective way for high-efficiency,high-precision and flexibility polishing of large optical lens.The planetary polishing head is the end-effector installed on the end of the polishing robot.Due to the periodicity of the planetary polishing motion,additional shaking force and shaking moment are produced to the end of the robots.Therefore,the investigation on the dynamic balance of the polishing head has great significance to improve the stabilization,precision and polishing quality.Aiming at the high precision polishing requirements of optical lens,this paper presents a type synthesis method of the planetary polishing head based on AKC(Assur kinematic chain).According to the composition principle of planar mechanisms,AKC is selected as the basic unit,which is disassembled according to the number of the components to obtain the original types.Then,the topological synthesis of the original types is presented to obtain homologous types of single or multiple degrees of freedom.The redundant degrees of freedom are constrained by the double sliding block structure,sliding block parallelogram structure and bi-parallelogram structure,respectively.Finally,three topological types of planetary polishing head that meet the functional requirements are achieved based on the type synthesis and design requirements,one of which is selected to give the detailed design.In order to reduce the shaking force/moment produced by the planetary polishing motion,the dynamic balance of the planetary polishing head is investigated.Based on the kinematic model of the mechanism,the rigid-body dynamic model of the mechanism is derived by using the principle of virtual work.The correctness of the derived model is verified by simulation.By analyzing the topological characteristics of the mechanism,the linear weighted method is adopted to optimize the length of the transmission branch by minimizing the shaking force/moment and input torque at the reference point on the frame,and taking the lengths of links and the transmission angle as the constraint function.Then,the genetic algorithm is used to optimize the masses and centers of masses of the counterweights connected to the side links to reduce the shaking force/moment.The results show that the proposed method can significantly reduce the shaking force compared with the mass static substitution approach.Finally,the effectiveness of the result is verified by simulation.