Structure Design And Experimental Investigation Of A Multi-function Stylus Profiling System For Characterization Of Engineering Surfaces At Micro/Nano Scales

Surfaces of materials,particularly the topmost layer,play an important role in their function and durability.The geometrical features of a surface and its mechanical and tribological properties are related to each other.The measurement of these properties in a wide range and correlated form is important and will help scientists and engineers understand the behaviors of surface materials and thus be able to modify the surface to achieve an optimum function.However,the existing instruments that can be used for this application are limited by either their force range or functions.This dissertation focuses on the development of a multi-function stylus profiling system for characterizing surface properties at micro/nanometer scales.The multi-function stylus profiling system provides,within one set-up arrangement,measurements of topography,friction,Young's modulus and hardness of a surface.The measurement is based on point-by-point scanning so that the four measured functions can be correlated in space and in time.Design,analysis,and experimental investigation of the multi-function stylus profiling system are carried out.Related theoretical and technological issues,such as structure design,construction,Finite Element Method(FEM)analysis,dynamic modeling,calibration,and so on,are addressed.Evaluations are carried out on certain material surfaces to demonstrate the capability of the system.The following innovative work has been completed:A triangular flexure structure featuring rotationally symmetric design has been proposed.Using stiffness matrix method,the analytical stiffness model of the triangular flexure structure has been established.Based on dynamic design theory and FEM analysis,the parameter optimization of the triangular flexure structure has been performed.The triangular flexure structure shows advantages such as compact size and high motion accuracy and can be utilized as the suspension for multi-function stylus profiling systems.A prototype of the multi-function stylus profiling system has been designed and fabricated.The essential part of the multi-function stylus profiling system is a special sensing probe,which has an electromagnetic force actuator and three precision capacitive sensors for simultaneous measurements of surface height/deformation and friction force between the probe tip and the surface being scanned.The system provides a controllable loading force in a range of 0.05–20 m N.The topography measurement has a maximum range of 20 ?m.The scanning area of 100 ?m × 100 ?m is closed-loop controlled with an accuracy of 1 nm.FEM is used to analyze the characteristics of the sensing probe.The performance of the sensing probe subjected to different load has been examined and the modal shapes,natural frequency and sinusoidal response of the sensing probe have also been obtained.Considering the sensing probe as a 3-DOF lumped-mass-spring system,the dynamic model has been developed.The analytic solution of the step responses of the sensing probe has also been derived using Laplace transform method.The cycloidal input signal is introduced to eliminate the overshoot of the step response.The multi-function stylus profiling system has been calibrated and experimentally tested to characterize the system's response and performance.The capability of the system for multi-function measurements has been demonstrated on certain material surfaces.The main advantage of the system is its rapid,single pass scanning to provide the multi-function characterization of surface topography,friction,Young's modulus and hardness.