Research On The Service Performance Of 2-DOF Fast Tool Servo Mechanism

In this paper,the service performance of 2-DOF fast tool servo mechanism is researched,the 2-DOF-FTS is driven by piezoelectricity and guided by compliant structure.Theoretical analysis,simulation analysis and experimental study have been done to know how to ensure its performances,such as stroke,working frequency and fatigue life and so on.It is analyzed whether the contact between the actuator and the compliant structure will separate dynamically.The influences of the contact on the service performance is also analyzed.Besides it is analyzed that the influences of the machining error of the flexible guide structure and the assembling error on movement precision.The main contents and conclusions of this paper are as follows:(a)The design of the compliant guide structure is important to the design of the FTS mechanism.The compliant matrix model is an effective and accurate method to study the compliant structure.This paper introduces the latest research results and combines the relevant knowledge to describe the flexible matrix modeling method of the compliant structure,and gives the accurate calculation formula of the compliant matrix of the general series and parallel compliant structure and the basic flexible structure.The relationship between the input stiffness and the basic size parameters of the compliant structure can be obtained by using the compliant matrix modeling,this can be used to design the flexible guide structure theoretically.(b)Considering the influence of contact stiffness in FTS stroke design is needed,and the FTS stroke design formula considering contact stiffness is given by referring to any surface contact deformation formula.Through contact finite element simulation,it is found that the contact stiffness of the both is basically the same when the contact stiffness is large.Experiments show that the final travel is similar to the design travel.To reduce the stroke shrinkage,the compliant guide structure is designed as a concave cylindrical surface at the contact portion,so the stroke loss is reduced.The influence of preload on the contact stiffness is analyzed,and the preload is determined according to the contact stiffness and the contact force curve.(c)Whether the contact between the ball piezoelectric and the compliant structure will be separated by dynamic force is analyzed by the finite element harmonic response.It is found that the resonant frequency of the FTS device in the moving direction is mainly affected by the whole mode of the device,rather than a moderately flexible structure of the modal,When the working frequency exceeds the minimum resonant frequency of the compliant structure in the direction of motion,the contact may undergo dynamic separation and,on the contrary,no dynamic separation occurs.In summary,increasing the overall stiffness of the FTS in the direction of motion,including the stiffness of the piezoelectric,the stiffness of the contact,the stiffness of the compliant structure,is conducive to increasing the resonant frequency in the direction of movement of the FTS and improving the resonance frequency of the compliant structure in the direction of motion is conducive to improving the FTS working frequency and avoiding the occurrence of unstable dynamic separation.(d)The normal machining error and the assembly error of the FTS are substituted into the flexible matrix model.Then,the relationship between the machining error and the motion error of the symmetrical double four-link flexible structure can be obtained,and also the relationship between the motion precision and the basic dimension when the direction of motion is constant and the relationship between the assembly error and the motion accuracy.Through the analysis of the sensitivity of machining error and motion precision,it is found that the thickness tolerance of straight beam type flexible hinge has the greatest influence on the motion precision.In order to verify the correctness of the analysis,the sensitivity analysis module of ANSYS workbench was used to analyze the sensitivity.The results were in agreement with the theoretical analysis.