A 4-degrees-of-freedom microrobot with nanometer resolution

A new type of microrobot is described. Its simple and compact design is believed to be of promise in the microrobotics field. Stepping motion allows speeds up to 4mm/s. Resolution smaller than 10 nm is achievable. Experiments in an open-loop motion demonstrated a repeatability better than 50µm on a 10 mm displacement at an average speed of 0.25 mm/s. A position feedback based on a microvision system will be developed in order to achieve a submicron absolute position accurac

Pseudo-elastic Flexure-Hinges in Robots for Micro Assembly

The increasing tendency of products towards miniaturization makes the substitution of conventional hinges to flexure hinges necessary, since they can be manufactured almost arbitrarily small. On account of their multiple advantages like no backlash, no slip-stick-effects and no friction, their application is especially reasonable in high-precision robots for micro assembly. Particular pseudo-elastic shape memory alloys offer themselves as material for flexure hinges. Since flexible joints gain their mobility exclusively via the elastic deformation of matter, the attainable angle of rotation is strongly limited when using conventional metallic materials with approximately 0.4% maximal elastic strain. Using pseudo-elastic materials, with up to 15% elastic strain, this serious disadvantage of flexure hinges can be avoided. A further problem of flexible joints is their kinematic behavior since they do not behave exactly like conventional rotational joints. In order to examine the kinematics of the hinges an experimental set-up was developed whereby good compliance with theoretical computed values could be achieved. A three (+1) degree of freedom parallel robot with integrated flexure hinges is investigated showing its kinematic deviations to its rigid body model. The data of the kinematic model of the flexible joint can then be implemented into the control of this compliant mechanism in order to gain not only a higher repeatability but also a good absolute accuracy over the entire working space

Comparison of nanoindentation results obtained with Berkovich and cube-corner indenters

There is increasing interest in using sharp cube corner indenters in nanoindentation experiments to study plastic properties. In combination with finite element methods it is for instance possible to extract stress-strain curves from load-displacement curves measured with differently shaped pyramidal indenters. Another example is the fracture toughness of coatings, which can be studied using cracks produced during indentation with cube corner tips. We have carried out indentation experiments with Berkovich and cube corner indenters on eight different materials with different mechanical properties. To gain information about the formation of pile-up and cracks, indentation experiments with cube corner indenter were performed inside a Scanning Electron Microscope (SEM) using a custom-built SEMMicroindenter. The results show that reliable hardness and modulus values can be measured using cube corner indenters. However, the fit range of the unloading curve has a much bigger influence on the results for the cube corner than for the Berkovich tip. The unloading curves of a cube corner measurement should therefore be carefully inspected to determine the region of smooth curvature and the unloading fit range chosen warily. Comparison of the modulus results shows that there is no significant difference between cube corner and Berkovich measurements. Also for hardness, no fundamental difference is observed for most of the investigated materials. Exceptions are materials like silicon nitride, cemented carbide or glassy carbon, where a clear difference to the hardness reference value has been observed although the modulus difference is not pronounced

Compliant parallel robot with 6 DOF

In this paper a patented parallel structure1 will be presented in which conventional bearings are replaced by flexure hinges made of pseudo-elastic shape memory alloy. The robot has six degrees of freedom and was developed for micro assembly tasks. Laboratory tests made with the robot using conventional bearings have shown that the repeatability was only a couple of 1/100 mm instead of the theoretical resolution of the platform of < 1 pm. Especially the slip-stick effects of the bearings decreased the positional accuracy. Because flexure hinges gam their mobility only by a deformation of matter, no backlash, friction and slip-stick-effects exist in flexure hinges. For this reason the repeatability of robots can be increased by using flexure hinges. Joints with different degrees of freedom had to be replaced in the structure. This has been done by a combination of flexure hinges with one rotational degree of freedom. FEM simulations for different designs of the hinges have been made to calculate the possible maximal angular deflections. The assumed maximal deflection of 20° of the hinges restricts the workspace of the robot to 28x28 mm with no additional rotation of the working platform. The deviations between the kinematic behavior of the compliant parallel mechanism and its rigid body model can be simulated with the FEM

Some recent advances in nanomechanical testing: High strain rates, variable temperatures, fatigue and stress relaxation, combinatorial experimentation

In the first part of the talk, I will present two recently developed platforms for high temperature nanomechanical testing. The first platform allows for variable temperature and variable strain rate testing of micropillars in situ in the scanning electron microscope. By utilizing an intrinsically displacement-controlled micro-compression setup, which applies displacement using a miniaturized piezo-actuator, we’ve recently extended the attainable range of strain rates to up to~ 103 s−1, and enabled cyclic loading up to 107 cycles and load relaxation tests. Stable, variable temperature indentation/micro-compression in the range of -45°C to 600°C is achieved through independent heating and temperature monitoring of both the indenter tip and sample and by cooling the instrument frame. A second system allows for measurements at lower loads ex-situ in a dedicated vacuum chamber in the range of -150 °C to 700 °C. The cryo temperature is achieved by means of a liquid nitrogen line, while the high temperature is generated by three independent heat sources for the sample and the two tips of the differential displacement measurement system, establishing an infrared bath in the measurement area. In the second part several case studies will be presented. Using these new capabilities, we examine the plasticity of electrodeposited nanocrystalline Nickel, of combinatorial thin film libraries, of hard nanocrystalline ceramic thin films. Activation parameters such as activation volume and activation energy were determined and discussed in view of the most probable deformation mechanism. High strain rates and cyclic fatigue tests were performed on nanocrystalline Ni. The strain rate sensitivity seems to increase for strain rates higher than 10 s-1 suggesting a change in deformation mechanism with increasing strain rate. Cyclic fatigue tests up to 1 million cycles were performed on nanocrystalline Ni microbeams and compared with existing data from literature. Combinatorial libraries of bulk metallic glasses were synthesized by a combination of gradient sputtering and evaporation. Hardness and Young’s modulus was mapped as a function of temperate, strain rate and composition. The results are discussed in the light of shear band kinetics. Finally, a wide range of chromium nitride-based hard coatings was investigated using in situ micro-cantilever bending and compression testing. This allowed the first direct measurement of the high temperature compressive strength and fracture toughness

A new dynamic module for in-situ nanomechanical testing at high strain rate

In-situ nanomechanical testing is commonly used to probe surface mechanical properties of bulk materials or thin films, like hardness, Young’s modulus, Yield stress…Actually most of the instruments can measure these properties only statically, i.e. a low frequency, leading to property measurement only at low strain rate (usually 10-1s-1 by nanoindentation). This is mainly caused by the low resonance frequency of the system, preventing making tests at higher speed. Performing high dynamic measurements could bring new information on materials properties like deformation mechanism at high strain rate, or high dynamic fatigue properties. A new high dynamic module usable for in-situ mechanical testing has been developed. It is composed of a small piezotube attached directly behind the tip. Because of the small dimensions of the module, his resonance frequency is very high (higher than 50kHz) in comparison to classical nanomechanical testers, permitting to perform and measure precisely the signals at very high frequency. Moreover, it can be used as a sensor and as an actuator, in x, y and z directions which gives to this module a very large range of measurements. Firstly, the characteristics, the performances and the limits of the new high dynamic module will be presented. Secondly some indentations experiments performed at high strain rate on nanocrystalline nickel with the in-situ nanomechanical tester (Alemnis Gmbh) equipped with the high dynamic will be presented and discussed (Fig. 1). Finally, some micropillar compression at high strain rate on the same material will be described and discussed

Cleavage Fracture of Brittle Semiconductors from the Nanometer to the Centimeter Scale

The objective of this paper is to present the fundamental phenomena occurring during the scribing and subsequent fracturing process usually performed when preparing surfaces of brittle semiconductors. In the first part, an overview of nano-scratching experiments of different semiconductor surfaces (InP, Si and GaAs) is given. It is shown how phase transformation can occur in Si under a diamond tip, how single dislocations can be induced in InP wafers and how higher scratching load of GaAs wafer leads to the apparition of a crack network below the surface. A nano-scratching device, inside a scanning electron microscope (SEM), has been used to observe how spalling (crack and detachment of chips) and/or ductile formation of chips may happen at the semiconductor surface. In the second part cleavage experiments are described. The breaking load of thin GaAs (100) wafers is directly related to the presence of initial sharp cracks induced by scratching. By performing finite element modelling (FEM) of samples under specific loading conditions, it is found that the depth of the median crack below the scratch determines quantitatively the onset of crack propagation. By carefully controlling the position and measuring the force during the cleavage, it is demonstrated that crack propagation through a wafer can be controlled. Besides, the influence of the loading configuration on crack propagation and on the cleaved surface quality is explained. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Security against individual attacks for realistic quantum key distribution

I prove the security of quantum key distribution against individual attacks for realistic signals sources, including weak coherent pulses and downconversion sources. The proof applies to the BB84 protocol with the standard detection scheme (no strong reference pulse). I obtain a formula for the secure bit rate per time slot of an experimental setup which can be used to optimize the performance of existing schemes for the considered scenario.Comment: 10 pages, 4 figure