High positioning accuracy with micropositioning robots (MPRs) is required to successfully perform many complex tasks, such as microassembly, manipulation, and characterization of biological tissues and minimally invasive inspection and surgery. Despite the widespread use of high-resolution micro- and nanopositioning robots, there is very little knowledge about the real positioning accuracy that can be obtained and what the main influential factors are. Indeed, very few notable methods are available to measure multi-degree-of-freedom motions with adapted range, resolution, and dynamic capabilities. The main objective of this paper is to quantify the positioning accuracy of serial MPRs and to identify the main influential factors (a typical XY Θ serial robot is chosen as a case study). To reach this goal, a measuring system that combines vision and pseudoperiodic patterns with an extremely large range-to-resolution ratio is introduced as a new way to quantify the positioning accuracy of MPRs for in-plane motions. Then, an open-loop control approach based on MPR calibration is chosen for several reasons: the use of different models to identify influential factors, the quantification of the positioning accuracy, and the necessity of the method when sensor integration is too complex. Experiments using five different calibration models were conducted to classify factors influencing the positioning accuracy of MPRs. The results show that positioning accuracy can be improved by more than 35 times from 96 μ with no imperfection compensation to 2.5 μ by compensating for geometric, position-dependent, and angle-dependent errors through the MPR calibration approach.

Accuracy is an important issue for microrobotic applications. High accuracy is usually a necessary condition for reliable system performance. However there are many sources of inaccuracy acting on the microrobotic systems. Characterization and compensation enable reduction of the systematic errors of the micropositioning stages and improve the positioning accuracy. In this paper, we propose a novel method based on vision and pseudo-periodic encoded patterns to characterize the position-dependent errors along XY stages. This method is particularly suitable for microscale motion characterization thanks to its high range-to-resolution ratio and avoidance of camera calibration. Based on look-up tables and interpolation techniques, we perform compensation and get improved accuracy. The experimental results show an accuracy improved by 84% for square tracking and by 68% for random points reaching (respectively from 22 μm to 3.5 μm and from 22 μm to 7 μm).

In micromanipulation, especially microassembly, accuracy is a criterion useful for characterizing the performance of microrobots. The increase of positioning accuracy is a very important issue before making automatic assembly or other micro-tasks such as characterization. Thermal drift is one of the major sources of inaccuracy for automatic micromanipulation in ambient conditions and even in clean room. This paper addresses the calibration of a 1-DOF (Degree Of Freedom) nanopositioning cell including thermal drift compensation. The nanopositioning cell consists of a single-axis PZT stage and a XYZ manual stage which is usually used for fine positioning in microassembly platform. Subsequently, validations are implemented to test the performance by integrating the calibrated model. The experimental results show an effective improvement of the accuracy by a factor of 7 when temperature changes in the range of temperature for training, and 2.4 times improvement is achieved when temperature goes out of the training range.

The paper documents the principle and experiments of the "2mm dash" winner at NIST IEEE Mobile Microrobotics Challenge held at ICRA2010 in Alaska [1]. Submission is made for the special session "ICRA Robot Challenge: Advancing Research Through Competitions". The new MagPieR microrobot was specially designed for breaking the speed record, providing a planar magnetic actuation with an optimised coils setup and a subsequent piezoelectric actuation for improved sliding condition. The paper describes the principle of actuation, the microrobot manufacturing flowchart and the assembly setup. Some simulations are provided with a first series of experimental data and conclusions.

Many tasks related to the micro/nanoworld require, not only high performances like submicrometric accuracy, but also a high dexterity. Such performances are only obtained using micromanipulators and microrobots with multiple degrees of freedom (DOF). Unfortunately, these multi-DOF systems usually present a strong coupling between the different axis making them very hard to control. The aim of this work is the modeling and control of a 2-DOF piezoelectric cantilever dedicated to microassembly/micromanipulation tasks. In addition to the coupling between the two axis, the piezocantilever is very oscillating and strongly nonlinear (hysteresis and creep). In the proposed approach, the nonlinearity and vibration are first compensated thanks to the feedforward technique. Afterwards, we derive a decoupled model in order to synthesize a linear robust H∞controller. The experimental results show the efficiency of the proposed approach and their convenience to the micromanipulation/microassembly requirements. Note to Practitioners-The main motivation of this paper is the need of both high performances and high dexterity in micromanipulation and microassembly tasks. In such a case, not only a sub micrometric accuracy and stability are needed, but also numerous degrees of freedom. For that, in the literature, there exist piezoelectric based structures with two or more DOF. Unfortunately, the coupling between its axis, the nonlinearities (hysteresis and creep) and the structure vibration make them very difficult to control and therefore make performances lost. A classical feedback con troller can be employed but when the nonlinearities and vibration become strong, it is impossible to synthesize a linear controller. In this paper, we show that the combination of feedforward techniques, to minimize the nonlinearities and vibration, and feedback techniques makes possible to reach the high performances required in micromanipulation/microassembly. We notice that the proposed approach can also be applied to other nonlinear, oscillating and multi-DOF systems, such as piezotubes.

Micro and nano-particles can be trapped by a non uniform electric field through the effect of dielectrophoretic principle. Dielectrophoresis (DEP) is used to separate, manipulate and detect micro particles in several domains, such as in biological or Carbon Nano-Tubes (CNTs) manipulations. Current methods to simulate the trajectory of micro-particles under a DEP force field are based on Finite Elements Modeling (FEM) which requires new simulations when the electrodes potentials are changed, or on analytic equations which are limited to very simple geometries. In this paper, we propose an hybrid method between analytical and numerical calculations able to simulate complex geometries and to easily change the electrode voltages along the trajectory. In this method a few FEM simulations are used to create a database which enables online calculation of the object trajectory in function of the electrode potentials. In order to verify the simulation results, experiments are done and compared to the simulations.

Micro and nano-particles can be trapped by a non uniform electric field through the effect of the dielectrophoretic force. Dielectrophoresis (DEP) is used to separate, manipulate and sense micro particles in several domains, such as in biological or Carbon Nano-Tubes (CNTs) manipulations. This paper tackles the creation of a closed loop strategy in order to control, using DEP, the trajectory of micro objects using vision feedback. A modeling of the dielectrophoresis force is presented to illustrate the non linearity of the system and the high dynamics of the object under dielectrophoresis. A control strategy based on the generalized predictive control method is proposed with the aim of controlling the trajectory, taking advantage of the high dynamics despite the non linearity. Simulated results are shown to evaluate our control strategy.

Piezoelectric cantilevers have proved their performances for actuating microgrippers dedicated to micromanipulation and microassembly tasks. While the control of one degree-of-freedom (dof) piezocantilevers have been well whelmed, the control of multi-dof one has not been addressed. Indeed, to assemble complex structures, the use of multidof microgrippers is recognized. Unfortunately, strong coupling between the axis and nonlinearities indeniably limit their performances. This paper deals with the modeling and control of a piezocantilever that has 2 degrees of freedom: in-plane and out of plane deflections. While such a characteristic allows the microgrippers perform both orientation and translation during micromanipulation/microassembly tasks, the strong coupling between the two dof makes difficult their control. Moreover, nonlinearities (hysteresis and creep) raise when the piezocantilever is used in high deformation. To overcome these, we consider the coupling as a disturbance, model the nonlinearities with the quadrilateral approximation and we apply a robust H¿controller that accounts them. The experiments show the efficiency of the synthesized controller and the obtained performances are convenient for micromanipulation/ microassembly tasks.

The development of reliable and repeatable strategies to manipulate and assemble microobjects lies in the efficiency, reliability, and precision of the handling processes. In this paper, we propose a thermal-based microgripper working in an aqueous medium. Manipulating and assembling in liquid surroundings can indeed be more efficient than in dry conditions. A comparative analysis of the impact of dry and liquid media on surface forces, contact forces, and hydrodynamic forces is shown. In addition, ice grippers represent flexible manipulation solutions. Nevertheless, when micromanipulation tasks are performed in air, capillary forces can drastically perturb the release. Our submerged freeze microgripper exploits the liquid surroundings to generate an ice droplet to catch microobjects, and to avoid capillary forces during the release. The thermal principle, the first microgripper prototype, an ice generation simulation, and the first tests are presented. The main objective is to validate the manipulation principle. Further research will be focused on control and optimization of the ice generation and the miniaturization of the system.

Efficient, reliable and flexible handling is still very challenging in micromanipulation and micro-assembly. In this paper, we propose an original thermally actuated gripper based on the use of ice to manipulate submerged artificial micro-objects sized under 100 mum. Manipulating in liquid surroundings can indeed be more interesting than in dry conditions. A comparative analysis on the impact of dry and liquid media on surface forces, contact forces and hydrodynamic forces shortly given first shows it. Concerning the use of ice for micromanipulation, cryogenic grippers are a flexible solution. Nevertheless, as they currently work in air, water must be provided by an external device and capillary force occurs during the release. Our submerged freeze microgripper takes advantages of the aqueous surroundings for the handling process as explained. The thermal principle, based on the Peltier effect, the characteristics of the microgripper prototype and the first micromanipulation tests are also presented. To control and optimize the heat exchanges in the developed gripper, a static thermal model using electrical analogy has been developed and validated for the Peltier elements and a 3D heat sink of the gripper. Further work will focus on the dynamic equivalent electric model.

Magnetic shape memory alloys (MSMA) are relatively new active materials but at this time they are not actually very used as actuators despite a high strain and a small response time. This is probably due in part to a large hysteresis and a strong non-linear behaviour. In this paper, an original hybrid control is designed taking into account dynamical effects and hysteretic behaviour in order to increase static gain of the system. After a short presentation of MSMA behaviour, a modelling is proposed to obtain two different control strategies. Some experimental results are also given.

This paper presents a new method developed for the optimal design of microrobotic compliant mechanisms. It is based on a flexible building block method, called Flexln, which uses an evolutionary approach, to optimize a truss-like structure made of building blocks. From the first design step, in addition to conventional mechanical criteria, dynamic gramian- based metrics can be considered in the optimization procedure to fit expected frequency responses of the synthesized mechanisms. A planar monolithic compliant coupling structure is obtained by the optimal design method to act as a stroke amplifier for piezoelectric stacked actuators, to operate in both static and dynamic motions, and to passively filter out undesirable vibrations. Finally, performance comparisons between some of the pseudo-optimal Flexln synthetized compliant mechanisms demonstrate the interests of the proposed optimization method for the design of dynamic operating smart microrobotic structures.

The purpose of this paper is to present a temporary fixing system based on a thermal glue that is well-adapted to micro-robotics. In the paper, this system is used to design a tool changer but can be generalized to other micro-robotic applications. A thermal modeling and an identification procedure are presented to propose a strategy to control the system. This system takes place into a micromanipulation station to gain flexibility, space and complexity. Indeed, to perform sequences of micromanipulation tasks (i.e. micro-assembly sequences), only one manipulator, able to use sequentially several end-effectors, has to be used instead of several dedicated to one specific task

Manipulating microscopic objects with the necessary dexterity still remains a very challenging task. In this paper, we propose a freeze gripper able to manipulate micro-objects in an innovative way, i.e. in submerged surroundings. We first review the influences of dry and liquid media on contact forces and non contact forces. This comparative analyse clearly shows the interest of the liquid medium. A survey of different microhandling systems based on the use of ice is also given. Then submerged microgripper with frozen water as an active end-effector is proposed as a promising new approach for manipulating low thermal conductive micro-objects. A prototype using the Peltier effect has been numerically modeled and developed. It is described in the paper. Experimental results validate the cooling and warming of the freeze gripper. A generic micromanipulation task is the purpose of further work

This paper deals with the design, fabrication and characterization of a new micro-tools changer for a micromanipulation station including three translation stages (X-Y-Z manipulator) and a new piezoelectric microgripper. This system can be implemented in confined workspaces such as a scanning electron microscope (SEM) or more generally in a micro-factory station by the reduction of the manipulator's size and the flexibility gain. The principle of this micro-tools changer is based on the use of a thermal glue whose state (liquid or solid) is controlled by surface mounted device (SMD) electrical resistances. Such system allows hundreds of automatic micro-tools exchanges with a maximum position error between two consecutive tools exchanges of respectively 4.2, 2.8 and 5.4 /spl mu/m on the X, Y and Z axis. To validate the use of the micromanipulation station in a SEM, an experimental comparison of the working principle in low (vacuum) and high (air) pressure has also been established through thermal and degassing studies.

The work presented in this paper concerns the study, the design, the fabrication and the experimentation of a legged microrobot. Legs were developed by integrating in each two thermal bimorph actuators, which give two degrees of freedom. After their fabrication and their experimentation, the legs were integrated on a body to realize the complete structure of the microrobot in a monolithic way. This microrobot was totally made by microfabrication in a clean room. The microrobot has a total volume of 6 mm/spl times/3.5 mm/spl times/0.5 mm and possesses six legs. Its experimentation allowed to determine its potential performances. This microrobot can find numerous applications in microrobotics, such as the inspection of stuffy environments, the micro-escorting or as a plug and play function in a system.

In this paper, three peculiar in-pipe microrobots are presented. They are the result of investigations of 3 laboratories involved in the microrobotics workgroup of the French National Centre of the Scientific Research (CNRS). They have been conceived to answer the locomotion problem inside industrial tubes of small diameter. Each of them is specific to a particular set of conditions.

The manipulation of very small objects is one of the most important tasks in microrobotics. Micromanipulators are required in all fields where precise manipulation of very small objects must be performed like microsurgery or assembly of MEMS. It is well known that downsizing the tools used in the macroworld is not appropriate to achieve tasks in the microworld. In this paper we present a prototype of a microgripper made up of piezoelectric bending unimorphs. A dynamic model of the piezoelectric unimorphs is developed. Various identification methods have been applied in order to verify the validity of the model. An observer has been built in order to estimate the forces applied at the tip of the fingers. Knowing these forces is very important to avoid destruction of objects during manipulation. The microgripper is able to handle microobjects in a wide range of size by changing the initial distance between the fingers. The resolution of positioning obtained is better than 10 nm for each finger. Every finger can be actuated individually so that dexterous handling can be achieved. This system allows us to perform precise micromanipulation tasks.

A microrobot is a complex microsystem that requires the integration of different functions in a very small volume - a mechanical structure, actuators, sensors, coordinated by a control system. This paper presents some prototypes of microrobots, with diameter of 2 mm and 3D mobility. They are realized by microstereophotolithography (/spl mu/SPL) and are actuated by shape memory alloy wires. We also present some results concerning the identification and control of our prototypes.

This paper deals with the design optimization and development of cooperative microrobots. We realize several prototypes by micro-stererophotolithographic (/spl mu/SPL) process, actuated by shape memory alloy (SMA) wire micromotors. The integration of displacement and temperature microsensors is considered. Our aim is to realise cooperative micromanipulation of microobjects in the applications such as microcatheters and micro-assembling devices. The compliance and impedance controls of the microrobots are considered. We introduce the thermomechanical behavior of the SMA microactuators and the mechanical characteristics of polymer robot in an incremental dynamic model of the microrobot. We obtain the impedance model of the integrated microsystem and identify the main influencing design parameters. We also develop a neuronal bond graph formalism that is used for the adaptive modeling of partial dynamic hysteresis cycles.

This paper describes a micro-conveying station for micro-component assembly. It incorporates micro-grippers joined up a micro-conveyer stage. The micro-grippers are fabricated from a mechanical structure in polymer using micro-stereophotolithography process and actuated by shape memory alloy wires. The micro-grippers can work in a space of 10 mm diameter and can carry out opening and closing movements. Neural network identification and PID control are proposed for the closed-loop control the micro-grippers, and trajectory control is realized on one finger. The micro-conveyer stage uses surface acoustic waves generated from interdigital transducers to move a slider onto the surface of the substrate with a high degree of resolution (nanometer) and in several centimetres of operation length. A mechanical model for the energy transfer from the acoustic wave to the slider is proposed. A good agreement between the theory and the experiment is obtained.

Presents a method for robot modelling called "double dynamic modelling". This method is based on an improvement of the classic dynamic model which takes into account the gear trains included in the robot axes, especially the gear yields and the direction of power transmission in the gears. According to this direction the dynamic model becomes different. Experimental results on a biped robot are given, which show the improved accuracy of the new dynamic model and better performances of the computed-torque control implemented in the biped robot and based on this model.>