Mehdi Boukallel

Mechanical and Control-Oriented Design of a Monolithic Piezoelectric Microgripper Using a New Topological Optimization Method

This paper presents a new method developed for the optimal design of piezoactive compliant micromechanisms. It is based on a flexible building block method, called FlexIn (flexible innovation), which uses an evolutionary approach, to optimize a truss-like planar structure made of passive and active building blocks, made of piezoelectric material. An electromechanical approach, based on a mixed finite-element formulation, is used to establish the model of the active piezoelectric blocks. From the first design step, in addition to conventional mechanical criteria, innovative control-based metrics can be considered in the optimization procedure to fit the open-loop frequency response of the synthesized mechanisms. In particular, these criteria have been drawn here to optimize modal controllability and observability of the system, which is particularly interesting when considering control of flexible structures. Then, a planar monolithic compliant microactuator has been synthesized using FlexIn and prototyped. Finally, simulations and experimental tests of the FlexIn optimally synthesized device demonstrate the interests of the proposed optimization method for the design of microactuators, microrobots, and more generally for adaptronic structures.

Modeling and Robust Control Strategy for a Control-Optimized Piezoelectric Microgripper

In this paper, modeling and robust control strategy for a new control-optimized piezoelectric microgripper are presented. The device to be controlled is a piezoelectric flexible mechanism dedicated to micromanipulation. It has been previously designed with an emphasis to control strategy, using a new topological optimization method, by considering innovative frequency-based criteria. A complete nonlinear model relating the voltage and the resulting deflection is established, taking into account hysteresis as a plurilinear model subjected to uncertainties. The approach used for controlling the actuator tip is based on a mixed high authority control (HAC)/low authority control (LAC) strategy for designing a wideband regulator. It consists of a positive position feedback damping controller approach combined with a low-frequency integral controller, which is shown to have robustness performances as good as a RST-based robust pole placement approach for the microgripper. The rejection of the vibrations, naturally induced by the flexible structure, and the control of the tip displacement have been successfully performed. Because we had taken into account frequency-based criteria from the first designing step of our device, we demonstrate that the tuning of the HAC/LAC can be easily performed and leads to low-regulator order.

Actuation means for the mechanical stimulation of living cells via microelectromechanical systems: A critical review

Within a living body, cells are constantly exposed to various mechanical constraints. As a matter of fact, these mechanical factors play a vital role in the regulation of the cell state. It is widely recognized that cells can sense, react and adapt themselves to mechanical stimulation. However, investigations aimed at studying cell mechanics directly in vivo remain elusive. An alternative solution is to study cell mechanics via in vitro experiments. Nevertheless, this requires implementing means to mimic the stresses that cells naturally undergo in their physiological environment. In this paper, we survey various microelectromechanical systems (MEMS) dedicated to the mechanical stimulation of living cells. In particular, we focus on their actuation means as well as their inherent capabilities to stimulate a given amount of cells. Thereby, we report actuation means dependent upon the fact they can provide stimulation to a single cell, target a maximum of a hundred cells, or deal with thousands of cells. Intrinsic performances, strengths and limitations are summarized for each type of actuator. We also discuss recent achievements as well as future challenges of cell mechanostimulation.

Calibration of lateral force measurements in atomic force microscopy with a piezoresistive force sensor

We present here a method to calibrate the lateral force in the atomic force microscope. This method makes use of an accurately calibrated force sensor composed of a tipless piezoresistive cantilever and corresponding signal amplifying and processing electronics. Two ways of force loading with different loading points were compared by scanning the top and side edges of the piezoresistive cantilever. Conversion factors between the lateral force and photodiode signal using three types of atomic force microscope cantilevers with rectangular geometries (normal spring constants from 0.092 to 1.24 N/m and lateral stiffness from 10.34 to 101.06 N/m) were measured in experiments using the proposed method. When used properly, this method calibrates the conversion factors that are accurate to +/-12.4% or better. This standard has less error than the commonly used method based on the cantilevers beam mechanics. Methods such of this allow accurate and direct conversion between lateral forces and photodiode signals without any knowledge of the cantilevers and the laser measuring system.

Smart Microrobots for Mechanical Cell Characterization and Cell Convoying

This paper deals with the effective design of smart microrobots for both mechanical cell characterization and cell convoying for in vitro fertilization. The first microrobotic device was developed to evaluate oocyte mechanical behavior in order to sort oocytes. A multi-axial micro-force sensor based on a frictionless magnetic bearing was developed. The second microrobotic device presented is a cell convoying device consisting of a wireless micropusher based on magnetic actuation. As wireless capabilities are supported by this microrobotic system, no power supply connections to the micropusher are needed. Preliminary experiments have been performed regarding both cell transporting and biomechanical characterization capabilities under in vitro conditions on human oocytes so as to demonstrate the viability and effectiveness of the proposed setups.

Passive diamagnetic levitation: theoretical foundations and application to the design of a micro-nano force sensor

Mechanical friction and more generally adhesion forces are some problems, which can severely limit the performances of micromechanical devices. One way to avoid friction problem, is to use levitation methods. Levitation in static magnetic field is very easy to achieve by the use of diamagnetic materials. Thus, it is possible to freely suspend a light magnet and let it in a stable equilibrium state. We have developed a prototype of a micro-nano force sensor using a passive levitation approach. This paper explains diamagnetic levitation in the simple case of a small cylindrical magnet with a mass and volume of 11 mg and 1.65 mm/sup 3/ respectively. The forces applied to the suspended magnet are presented and the natural stability of the diamagnetic levitation is explained. Finally, we present the design of our micro-nano force sensor using diamagnetic levitation.

Levitated micro-nano force sensor using diamagnetic materials

Under suitable conditions, diamagnetic materials allow to achieve stable levitation of permanent magnets in entirely passive configuration. Using NdFeB magnets and diamagnetic materials such as graphite in a particular configuration, we build a passive levitated force sensor with a variable stiffness and linear output. The suspended part is used as the sensing device and two directions of force measurement are possible. The absence of friction makes the sensor highly sensitive and forces around nN can be measured. The established model of both magnetic and diamagnetic forces allows to calculate the applied force on the end point of the levitating device after measuring the position of the levitating part. This paper presents the description of the levitated sensor, force calculation and experimental results.

Characterization of cellular mechanical behavior at the microscale level by a hybrid force sensing device

This paper deals with the development of an open design platform for characterization of mechanical cellular behavior. The resulting setup combines Scanning Probe Microscopy (SPM) techniques and advanced robotic approaches in order to carry out both prolonged observations and spatial measurements on biological samples. Visual and force feedback is controlled to achieve automatic data acquisition and to monitor process when high skills are required. The issue of the spring constant calibration is addressed using an accurate dynamic vibration approach. Experimentation on the mechanical cell characterization under in vitro conditions on human adherent Epithelial Hela cells demonstrates the viability and effectiveness of the proposed setup. Finally, the JKR (Johnson, Kendall and Roberts), the DMT (Derjaguin, Muller and Toporov) and Hertz contact theories are used to estimate the contact area between the cantilever and the biological sample.

Modeling Soft Contact Mechanism of Biological Cells Using an Atomic Force Bio-Microscope

The development of a mechanical force sensing device system based on force/vision feedback control for exploring in vitro the contact mechanics of human adherent cervix Epithelial Hela cells is presented in this paper. The design of the prototype combines scanning probe microscopy (SPM) techniques with advanced robotics approaches. Some important issues in the design process, such as in vitro environment constraints and calibration of the force sensing probe are also addressed in this paper. The system is then used for accurate and non-destructive mechanical characterization based on soft contact interactions on biological samples. Finally, some mechanical properties of the studied biological samples are estimated using two appropriate models describing the contact mechanism taking into account adhesion forces

Indoor pedestrian localisation solution based on anemometry sensor integration with a smartphone

The paper deals with the design, calibration and experimental validation of a novel infrastructure-less solution dedicated to indoor pedestrian localisation issues. The approach involves aerodynamic fluid computation for instantaneous speed estimation of a pedestrian handling a smartphone. For this purpose, a differential pressure-based MEMS anemometer is integrated to an Android smartphone by means of a dedicated PIC 32 bits microcontroller. Measurements of the pedestrian orientation are ensured by a gyroscope sensor coupled with the smartphone. Consequently, both instantaneous speed and heading measurements are combined to the dead reckoning technique for estimating the 2D relative position of the user. Theoretical modeling is conducted in order to calibrate and quantify the accuracy of the sensor. In situ experiments along straight paths demonstrate that the sensors coupled with a smartphone achieve pedestrian localisation with average accuracy of less than 6 % of the total travelled distance.