Research On PID Parameter Optimization And Tool Path Generation Of Slow Tool Servo Turning Machine

Slow tool servo(STS)turning technology is a new precision turning processing technology,which is different from traditional turning.By the C axis,X axis and Z axis linkage,the STS lathe drive the tool relative to the workpiece in the cylindrical coordinates to achieve the tool spiral trajectory of a variety of complex surfaces.It is mainly used in the machining of various types of complex surfaces.Now for the study of slow tool servo turning technology,foreign countries started earlier and realized the industrial application;but the domestic related research in recent years has just started,was still in the laboratory research stage and did not form industrial processing capacity.Slow tool servo turning technology has been widely used in the field of national defense,military,space observation,optical measurement,civil consumption et al.In this paper,based on the independent research and development of the slow servo lathe,the relative research was studied about slow servo turning technology and the specific research contents are as follows:1)The control system parameter optimization of the slow tool servo turning machine.Taking the C axis as an example,the mathematical model of AC servo feed system with speed and acceleration feedforward PID control algorithm based on PMAC was deduced.A simplified control system block diagram was obtained by using the step response signal to system identification,which was simplified as the three order oscillation system.Then the PID parameters were optimized by the particle swarm optimization algorithm,and the effect of the velocity and acceleration feedforward on the tracking error was analyzed by simulation.2)Tool path generation for slow tool servo turning of complex surface.Based on the brief introduction of STS lathe construction,the method of mathematical expression of surface was determined,and the machinability of the pseudo machined surface was determined.Three kinds of cutting contact points discrete method was introduced,including equal angle discretization method,equal arc length discretization and integrated method,the advantages and disadvantages of each discretization method was analysised.According to the surface’s expressed mathematical expression method,two different Z direction tool geometry compensation method was put forward;The PVT interpolation method was chosen as the axis trajectory interpolation algorithm,which is provided by IMAC.Based on the analysis of the existing PVT entrance parameters algorithms:area method and the three points method,the triangle rotary method was proposed,and the related simulation results showed that the interpolation error can be reduced by about one order of magnitude by used the triangle rotary method.3)Design and slow tool servo turning of progressive-addition surface.The functional of the progressive-addition surface quality was established,the discrete points’ coordinate value of progressive-addition surface were calculated by the method of variational difference.Based on the discrete data points,The double high order uniform B-spline interpolation method and Zernike polynomial fitting method was analyzed to construct the progressive-addition surface,the caculation results showed that double high order uniform B-spline interpolation had a better interpolation accuracy.The order of double uniform B-spline had no obvious effect on the structural accuracy of the progressive-addition lenses,so double uniform three-order uniform B-spline was chosen as the surface construction method.The actual optical power degree distribution and astigmatism distribution of the designed surface had a good agreement with the ideal surface.Finally,the tool path genration and algorithm error analysis were carried out on the designed complete progressive-addition surface.4)The experiment of slow tool servo turning of typical complex surface.Based on C#,the control software of STS lathe and STS turning NC program generation software was written accoding to the tool path generation method proposed in chapter 3.The array surfcae(spherical array surface,sinusoidal array surface),toric surface and progressive-addition surface was machined by slow tool servo turning and the purpose of this experiment is to validate the correctness and feasibility of the related theories put forward in this paper.The experiments results showed that the toric surface and progressive-addition surface machining effect was good,the surface roughness was about 0.09 μm and the surface form error can be controlled at about ± 0.01 mm.Due to constraints of the lathe’s precision and structure,for the undulating surface structure such as the array surface,the machining effect was not satisfactory.The lathe produced a slight vibration when machining the array surface,which resulting in the form error and surface roughness of the machined surface was relatively large.