Inertial drives for micro- and nanorobots : analytical study

The need for high precision robots dedicated to the assembly of microsystems has led to the design of new kinds of actuators able to reach very high positional accuracy over large distances. Among these, inertial sliders have received considerable interest in the last years. They have the advantage of being based on a simple principle that leads to a simple mechanical design. However, because they are based on the nonlinearity of friction, it is not easy to predict their stepsize repeatability. In order to understand the most important parameters affecting the precision of inertial drives, a theoretical study of a 1 degree of freedom inertial slider has been established. Analytical formulas describing the influence of different parameters, such as static and dynamic friction and mass distribution, have been developed. The effect of applied functions (sawtooth and parabolic), have also been studied. The theoretical cut off frequency has been found for each of the different waveforms, allowing us to predict the maximal and minimal working frequencies of the system. Thus, for each curve form, the repeatability of inertial sliders can be evaluated taking into account the uncertainties in the friction coefficients. The best suited waveforms for given constraints can therefore be selected. Simulations carried out from this have been successfully compared to experimental results

A Body-Oriented Method For Dynamic Modeling And Adaptive Control Of Fully Parallel Robots

: In this paper we propose a method based on the virtual work principle to find a linear form of the dynamic equation of fully parallel robots. Compared to other methods, it has the advantage that it does not need to open the closed loop structure into a tree-structure robot. It considers rather each body separately using its Jacobian matrix to project the forces into the joint space of the robot. Thus, simplifications can be made at the very beginning of the modeling, that is very usefull for real-time nonlinear adaptive control implementation. As an example, the method is applied to the Hexaglide, a parallel machine tool with 6 degree-of-freedom. Based on this model, a simulation of a non-linear adaptive controller is performed, demonstrating the possibility to apply nonlinear adaptive control to complex parallel robots. Keywords: robot control, robot dynamics, adaptive control, parameter identification, parallel robot 1. INTRODUCTION The dynamic equation of robots is linear in its d..

High precision robots for automated handling of micro objects

Nanotechnology is a key issue in today’s and tomorrow’s development of advanced products. Soon new tools will be needed to automatically handle and assemble micro-sized objects with nanometer precision, or simply to give human beings the capability of operating in those tiny dimensions. Seeing emerging applications in this field, the Swiss Federal Institute of Technology at Zurich (ETHZ) decided to focus an interdisciplinary project on the theme “Nanorobotics”, ie automated handling of microparts with nanometer resolution. In this paper, after a short description of the goals and the approach taken in this project, some important aspects of the design of high precision robots are stressed. It is especially shown that if a minimum of 6 independent degrees-of-freedom (dof) is required to freely position an object in space, redundant robots will lead to less complicated and more efficient mechanical structures. It is then shown, that if a global sensor is used, measuring the relation gripper-object, the only requirement for the mechanical structure is a good resolution. Finally, two new 3 dof planar robot designs are presented. Both of them have unlimited range of motion while having a resolution down to 10 nm. One of them has been controlled using a vision feedback under a light microscope and showed very promising results