Tip Motion Control and Scanning of a Reorientable Micromanipulator With Axially Located Tip

Two-axis micromanipulators, whose tip orientation and position can be controlled in real time in the scanning plane, enable versatile probing systems for 2.5-D nanometrology. The key to achieve high-precision probing systems is to accurately control the interaction point of the manipulator tip when its orientation is changed. This paper presents the development of a probing system wherein the deviation in the end point due to large orientation changes is controlled to within 10 nm. To achieve this, a novel micromanipulator design is first proposed, wherein the end point of the tip is located on the axis of rotation. Next, the residual tip motion caused by fabrication error and actuation crosstalk is modeled and a systematic method to compensate it is presented. The manipulator is fabricated and the performance of the developed scheme to control tip position during orientation change is experimentally validated. Subsequently, the two-axis probing system is demonstrated to scan the full top surface of a micropipette down to a diameter of 300 nm

Design and Modeling of an Active Five-Axis Compliant Micromanipulator

This paper presents the design and modeling of an active five-axis compliant micromanipulator whose tip orientation can be independently controlled by large angles about two axes and the tip-position can be controlled in three dimensions. These features enable precise control of the contact point of the tip and the tip-sample interaction forces with three-dimensional nanoscale objects, including those features that are conventionally inaccessible. Control of the tip-motion is realized by means of electromagnetic actuation combined with a novel kinematic and structural design of the micromanipulator, which, in addition, also ensures compatibility with existing high-resolution motion-measurement systems. The design and analysis of the manipulator structure and those of the actuation system are first presented. Quasi-static and dynamic lumped-parameter (LP) models are then derived for the five-axis compliant micromanipulator. Finite element (FE) analysis is employed to validate these models, which are subsequently used to study the effects of tip orientation on the mechanical characteristics of the five-axis micromanipulator. Finally, a prototype of the designed five-axis manipulator is fabricated by means of focused ion-beam milling (FIB)

One-dimensional dynamic microslip friction model

A one-dimensional dynamic microslip friction model, including the damper inertia, is presented in this paper. An analytical approach is developed to obtain the steady-state solution of the resulting nonlinear partial differential equations when subjected to harmonic excitation. In the proposed approach, according to the excitation frequency, a single mode of the system is considered in the steady-state solution for simplicity; consequently, phase difference among spatially distributed points is neglected. Three types of normal load distributions, resulting in distinct stick-slip transitions along the contact interface, are studied. The resulting hysteresis curves and the associated Fourier coefficients are obtained and compared with each other. An equivalent point contact friction model is established and compared with the proposed microslip model, illustrating the effects of partial slip in the contact interface for low amplitude or high normal load applications

Reduced Order Modeling of Bolted Joints in Frequency Domain

Most of the structural systems assembled by using bolted joints. Therefore, bolted joint models have a critical importance to estimate the behavior of the overall assembled system. There are several linear bolted joint models which consist of spring and dashpot elements in literature. While they can estimate the resonant frequency of the overall system with a sufficient accuracy, linear bolted joint models are inadequate for approximating the damping which arises from the friction in the contact interface of assembled system. On the other hand, there are examples of nonlinear bolted joint models which utilize 3D contact models to account for the frictional damping behavior in the literature. However, modeling the structures with many bolted joints by using high fidelity 3D contact models is very time consuming. Therefore, reduced order bolted joint models with sufficient accuracy are in need. In this paper, a method for modeling bolted joints in frequency domain is introduced. The joint model consists of microslip friction elements each one of which is constructed by several Coulomb friction elements in parallel and located at both sides of bolt holes

Reduced-Order Modeling Friction for Line Contact in a Turbine Blade Damper System

Under-platform damper is used to attenuate resonant response and further prevent high cycle fatigue failure of turbine blades. The aim of this work is to improve the representation of contact interfaces in modeling an asymmetrical under-platform damper. A new reduced-order contact model with a lumped parameter form is proposed, which is based on a modification of the classical Iwan model. This model can explicitly consider the normal contact pressure on line contact. In modeling process, a method to relate the physical Hertzian normal contact pressure with the probability density function (PDF) of slider sliding force for continuous Iwan model is developed. Experimental results from a laboratory asymmetrical under-platform damper test rig are employed to validate the proposed model. For comparison, different normal contact pressure distributions are considered. The out-of-phase motion of the damper is numerically investigated, and the results show that the proposed model can give an accurate prediction of the damper’s nonlinear mechanics behavior

Nonlinear time-varying dynamic analysis of a spiral bevel geared system

In this paper, a nonlinear time-varying dynamic model of a drivetrain composed of a spiral bevel gear pair, shafts and bearings is developed. Gear shafts are modeled by utilizing Timoshenko beam finite elements, and the mesh model of a spiral bevel gear pair is used to couple them. The dynamic model includes the flexibilities of shaft bearings as well. Gear backlash and time variation of mesh stiffness are incorporated into the dynamic model. Clearance nonlinearity of bearings is assumed to be negligible, which is valid for preloaded rolling element bearings. Furthermore, stiffness fluctuations of bearings are disregarded. Multi-term harmonic balance method (HBM) is applied on the system of nonlinear differential equations in order to obtain a system of nonlinear algebraic equations. Utilizing receptance method, system of nonlinear algebraic equations is grouped in nonlinear and linear sets of algebraic equations where the nonlinear set can be solved alone decreasing the number of equations to be solved significantly. This reduces the computational effort drastically which makes it possible to use finite element models for gear shafts. In the calculation of Fourier coefficients, continuous-time Fourier transform as opposed to the gear dynamics studies that utilize discrete Fourier Transform is used. Thus, convergence problems that arise when the number of nonlinear DOFs is large are avoided. Moreover, analytical integration is employed for the calculation of Fourier coefficients rather than numerical integration in order to further reduce the computational time required. Nonlinear algebraic equations obtained are solved by utilizing Newton's method with arc-length continuation. Direct numerical integration is employed to verify the solutions obtained by HBM. Several case studies are carried out, and the influence of backlash amount, fluctuation of gear mesh stiffness and variation of bearing stiffness are investigated. In addition to these, the response of the coupled gear system model is compared with that of gear torsional model in order to study the influence of the coupling on dynamics of the system