Development And Performance Analysis Of A 2-DOF Large Stroke FTS Device

The Non-Rotationally Symmertric Surface of revolution in optical free-form surface has its unique optical performance and design freedom,which greatly simplifies the complexity of optical system and makes it widely used and demanded in military and civil fields such as national defense,aerospace,etc.Among many ways of processing optical surfaces,Fast Tool Servo(hereinafter referred to as FTS)processing technology stands out among many Ultra-precision Diamond Turning due to its simple structure,high efficiency and good surface quality.Based on the research prospects of FTS devices in recent years,a 2-DOF large-stroke FTS device is developed in this paper and its performance analysis is carried out.The FTS device which is developed in this paper is mainly innovative in using rhombus flexible hinge to build the transmission structure.The rhombus structure is a plane structure without additional displacement in Y-axis,which simplifies the control system.Voice coil motor is chosen as actuator to extrude flexible hinge oppositely,which guarantees machining tracking accuracy and reduces inertia effect of motor rotor mass on the device and effectively reduces inertia force of the system.Static mathematical model of each part of the FTS device is established,and the static mathematical model of each component is established,and the transfer function of the device motion is obtained.The key mechanism is simulated by ANSYS,and the stiffness and natural frequency of the device under simulation conditions are obtained.By comparing with the solution of theoretical calculation,it is found that the performance of the designed device can fully meet the processing requirements.Modal analysis guides the work-piece processing conditions.It is beneficial to calculate the functional relationship between output displacement and input load of flexible hinge by flexibility matrix method and pseudo-rigid body method,which can guide subsequent tool path planning.In order to verify the characteristic index of the FTS device developed and test the off-line performance,the off-line test experimental platform of the FTS device is builded,and it completes the measurement of noise interference in the experimental environment,bi-directional stiffness value,step response test,resolution test and tracking test.The Z-direction stiffness of the developed FTS device is 0.1639N/μm,Xdirection stiffness is 0.276N/μm,Z-direction step response rise time is 4.43 ms,peak time is 9.30 ms,X-direction step response rise time is 3.49 ms,peak time is 5.31 ms,twoway overshoot is 0.Z-axis resolution 0.056μm,X-direction resolution 0.052μm.The total tracking error is 3.6%.The FTS device developed is comprehensively and rationally analyzed to ensure that the final cutting experiment can be carried out properly.An experimental system for free-form surface turning was built and the surface morphology and quality of the work-piece processed by the FTS device were analyzed.Feed volume 30μm/rec and main shaft speed of 30rec/min,the processing wavelength is 1mm and the amplitude is 5μm sine wave surface,observe the micro-morphology of the machined surface by white light interferometer.The surface Sq of the developed FTS device is 0.28188μm by function fitting of the machined surface interface,Sa0.23204μm.The FTS machining accuracy can reach sub-micron level.The test shows that the device has the ability to machine optical surfaces.