Study On Positioning Control Method Or SPM And Application In Nano Iscoelasticity Measurement

As a basis of promoting the development of nanotechnology, scanning probemicroscopy (SPM) has been widely used in nano-manufacturing, materials processing,biomedical and other fields in recent years. The application of high precision andbroadband SPM technology is urgently required. However, the operation speed andpositioning accuracy have been the main factors to restrict the commercial applications ofSPM technology. Due to the characters of complex structure and strong nonlinearcharacteristics of SPM system, the existing SPM control methods can not eliminate thepositioning errors in the SPM broadband high-speed operation. Accounting for slow-speedoperation and low-accuracy positioning of SPM, the error factors of the piezoelectricpositioning system are analyzed, and the compensation methods of the positioning systemare explored by the control technology. The specific research ways are as follows:Firstly, the structure and working mechanism of SPM system are studied; the errorfactors of SPM positioning system are analyzed; the limitations of the traditional PIDcontrol methods applied in SPM system are discussed; the research achievements aboutthe SPM control compensation are introduced, and the necessity of the control compensat-ion method on the SPM system is clarified.Secondly, in order to solve narrow bandwidth and low precision problems in the SPMthree-dimensional scanning operation, two different iterative control methods are designedto compensate for the nonlinear effect factors in the x-axis and z-axis. An open-closedloop PD iterative learning control compensation method is proposed, and the scanningrange in the x-axis is increased through the iterative optimization in time domain. Afiltered-type iterative learning control compensation method is proposed. Based oninversion-iterative in frequency domain, the adverse dynamic characteristics effect iscompensated to realize the fast and high-precision positioning in the z-axis.What’s more, in the ultra high speed SPM scanning operation, a feed-forward plusfeedback control method is proposed to compensate for the dynamic coupling-causedpositioning errors. Based on the coupling model of the z-axis, the feed-forward input can be gained by the inverse iterative, and the errors of the feed-forward input caused by thecoupling model can be reduced by the feedback compensation, so as to enable high-speedand high-precision positioning of SPM.Finally, the proposed control method is applied in the broadband nano viscoelasticitymeasurement using SPM. The unfavorable dynamic characteristics of SPM system in thez-axis are compensated by using the proposed filtered-type control method, and the desir-ed excitation force profile is accurately tracked on a polydimethylsiloxane (PDMS)sample. Furthermore, the dynamics convolution errors on nanomechanical property meas-urement are analyzed. Based on the dynamic viscoelasticity model of the soft material, anapproach to compensate for dynamic convolution errors is proposed to improve the accur-acy of viscoelasticity measurement. The effectiveness of the proposed approach is verifiedby PDMS nano viscoelasticity measurement experiment.