Ioan Alexandru Ivan

Development and Force/Position Control of a New Hybrid Thermo-Piezoelectric MicroGripper Dedicated to Micromanipulation Tasks

A new microgripper dedicated to micromanipulation and microassembly tasks is presented in this paper. Based on a new actuator, called thermo-piezoelectric actuator, the microgripper presents both a high range and a high positioning resolution. The principle of the microgripper is based on the combination of the thermal actuation (for the coarse positioning) and the piezoelectric actuation (for the fine positioning). In order to improve the performances of the microgripper, its actuators are modeled and a control law for both the position and the manipulation force is synthesized afterwards. A new control scheme adapted for the actuators of the hybrid thermo-piezoelectric microgripper is therefore proposed. To prove the interest of the developed microgripper and of the proposed control scheme, the control of a pick-and-release task using this microgripper is carried out. The experimental results confirm their efficiency and demonstrate that the new microgripper and the control law are well suited for micromanipulation and microassembly applications.

Simultaneous Displacement/Force Self-Sensing in Piezoelectric Actuators and Applications to Robust Control

Self-sensing technique consists of using an actuator as a sensor at the same time. This is possible for most actuators with physically reversible principle such as piezoelectric materials. The main advantages of self-sensing are: 1) the embeddability of the measurement technique, and 2) its low cost as no additional sensor is required. This paper presents a self-sensing technique for piezoelectric actuators used in precise positioning applications like micromanipulation and microassembly. The main novelty is that both displacement and force signals can be simultaneously estimated. This allows a feedback control using one of these two signals with a display of the other signal. To demonstrate this advantage, a robust H∞ feedback control on displacement with real-time display of the force is used as an application of the proposed self-sensing technique. In this paper, experimental results obtained with a piezoelectric cantilever actuator validate and demonstrate the efficiency of the proposed self-sensing.

Quasistatic displacement self-sensing method for cantilevered piezoelectric actuators

Piezoelectric meso- and microactuator systems required for manipulation or assembly of microscale objects demand reliable force and/or displacement information. Available sensors are prone to dimension restrictions or precision limitation. Self-sensing method, based on the electric charge measurement, may represent a solution in terms of cost-effectiveness and integration, the actuator performing simultaneously as its own sensor. This paper presents a self-sensing method dedicated to free uni- and bimorph piezocantilevers but can also be adapted to other piezoactuator types. The integrated electric current, used to convert the charge, can be compensated against piezoelectric material nonlinearities to provide accurate displacement information. The advantages relative to existing self-sensing methods consist in the ability to keep this displacement information for long-term periods (more than a thousand seconds) and in the reduction in signal noise. After introductive issues related to the method the base principle allowing the estimation of tip displacement is presented. Then, the identification procedure of the estimator parameters is depicted and representative experimental results are shown. Finally, a series of aspects related to electronic circuits are discussed, useful for successful system implementation.

First experiments on MagPieR: A planar wireless magnetic and piezoelectric microrobot

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.

Current integration force and displacement self-sensing method for cantilevered piezoelectric actuators

This paper presents a new method of self-sensing both of the displacement and the external applied force at the tip of piezoelectric cantilevers. Integrated electric current across piezoelectric actuators is compensated against material nonlinearities (creep, hysteresis) to provide reliable information. We propose to compensate the hysteresis by using the Prandtl-Ishlinskii static approach while an auto regressive and moving average exogenous (ARMAX) model is used to minimize the creep influence. The quasistatic estimation, electronic circuit, and aspects related to long-term charge preservations are described or referenced. As an experiment, we tested the actuator entering in contact with a fixed force sensor. An input signal of 20 V peak-to-peak (10% of maximum range) led to force self-sensing errors inferior to +/-8%. A final discussion about method accuracy and its limitations is made.

Self-Sensing Measurement in Piezoelectric Cantilevered Actuators for Micromanipulation and Microassembly Contexts

This chapter aims to develop a self-sensing technique to measure the displacement and the force in piezoelectric microactuators dedicated to micromanipulation and microassembly contexts. In order to answer the requirements in these contexts, the developed self-sensing should perform a long duration measurement of constant signals (displacement and force) as well as a high precision. Furthermore, we propose to consider the dynamics in the displacement self-sensing measurement such that a positioning feedback is possible and therefore a high micro/nanopositioning accuracy is obtained. The experimental results validate the proposed technique and demonstrate its conveniency for micromanipulation and microassembly contexts.

NIST and IEEE Challenge for MagPieR: The Fastest Mobile Microrobots in the World

Recent advances in micro/nanotechnologies and microelectromechanical systems have enabled micromachined mobile agents. Highly dynamic mobile microrobots are believed to open the gate for various future applications. However, at the submillimeter scale, the adhesion effects dominate physics, especially in the air environment. Although many studies have been performed to avoid or reduce this effect, the sticking phenomena are still one of the biggest challenges in achieving highly dynamic micromobile robots. Subsequently, intrinsic challenges at the given scale (hundreds of micrometers) are the powering technique themselves. Although often designed from active materials, actuation may only be performed by means of various external fields that often require a lot of space around the scene. In this context, the National Institute of Standards and Technology (NIST) and the IEEE initiated an annual state-of-the art microrobotics challenge, boosting the development of novel mobile agents with precise and highly dynamic propulsion mechanisms and controllability. During our first participation in this competition in 2010, the French team Centre National de la Recherche Scientifique (CNRS) proposed a magnetic and piezoelectric mobile microrobot called MagPieR, which dramatically enhanced the propulsion speed to 28 ms for the so-called 2-mm dash task. It literally cut the former record to a quarter. In the meantime, during the 2011 challenge, MagPieR won the mobility challenge thanks to some optimized coil setup and control law. The continuous technical advances in terms of dynamic performance are now shifting, and the focus of the next challenge is more agile-demanding and controllable tasks. Combining different physical effects is a promising key for the future of highly dynamic mobile microsystems and associated applications in micromanipulation, microassembly, or minimally invasive surgery.

Development and Dynamic Modeling of a New Hybrid Thermopiezoelectric Microactuator

This paper presents a new hybrid microactuator based on the combination of piezoelectric and thermal effects. The proposed actuator can perform both a high-stroke coarse positioning through the thermal actuation and a high-resolution fine positioning through the piezoelectric actuation. The microactuator structure is a unimorph piezoelectric cantilever, which also constitutes a thermal bimorph that is very sensitive to temperature variation. While electrical voltage is used to control the piezoelectric actuation, we use a Peltier module to provide the temperature variation and to control the thermal functioning. In order to understand the behavior of the hybrid actuator, a model is developed. For better precision, but at the same time for model simplicity, the thermal part is modeled with the thermal network, whereas the Prandtl-Ishlinskii (PI) hysteresis approach is used to model the nonlinearity of the piezoelectric part. Finally, a series of experimental results validate the developed model.

High dynamics and precision optical measurement using a position sensitive detector (PSD) in reflection-mode: application to 2D object tracking over a Smart Surface.

When related to a single and good contrast object or a laser spot, position sensing, or sensitive, detectors (PSDs) have a series of advantages over the classical camera sensors, including a good positioning accuracy for a fast response time and very simple signal conditioning circuits. To test the performance of this kind of sensor for microrobotics, we have made a comparative analysis between a precise but slow video camera and a custom-made fast PSD system applied to the tracking of a diffuse-reflectivity object transported by a pneumatic microconveyor called Smart-Surface. Until now, the fast system dynamics prevented the full control of the smart surface by visual servoing, unless using a very expensive high frame rate camera. We have built and tested a custom and low cost PSD-based embedded circuit, optically connected with a camera to a single objective by means of a beam splitter. A stroboscopic light source enhanced the resolution. The obtained results showed a good linearity and a fast (over 500 frames per second) response time which will enable future closed-loop control by using PSD.

Design and first experiments on MagPieR, the magnetic microrobot

This article deals with the design, the actuation and the control of magnetic microrobots. The interest in such microscale robots actuated by remote force fields is increasing since a large range of application fields could benefit from these small size manipulators. However major scientific challenges such as the optimization of the actuation platform, or the reduction of the adhesion between the robot and the substrate must still be overcome to perform complex micromanipulations. This article presents an example of a magnetic microrobot, MagPieR. Its design, fabrication, actuation and control are detailed. First experiments are presented, and the issues that must still be overcome are highlighted.