Mokrane Boudaoud

An Overview on Gripping Force Measurement at the Micro and Nano-Scales Using Two-Fingered Microrobotic Systems

Two-fingered micromanipulation systems with an integrated force sensor are widely used in robotics to sense and control gripping forces at the micro and nano-scales. They became of primary importance for an efficient manipulation and characterization of highly deformable biomaterials and nanostructures. This paper presents a chronological overview of gripping force measurement using two-fingered micromanipulation systems. The work summarizes the major achievements in this field from the early 90s to the present, focusing in particular on the evolution of measurement technologies regarding the requirements of microrobotic applications. Measuring forces below the microNewton for the manipulation of highly deformable materials, embedding force sensors within microgrippers to increase their dexterity, and reducing the influence of noise to improve the measurement resolution are among the addressed challenges. The paper shows different examples of how these challenges have been addressed. Resolution, operating range and signal/noise ratio of gripping force sensors are reported and compared. A discussion about force measurement technologies and gripping force control is performed and future trends are highlighted.

Gain Scheduling Control of a Nonlinear Electrostatic Microgripper: Design by an Eigenstructure Assignment With an Observer-Based Structure

This paper deals with the modeling and the robust control of a nonlinear electrostatic microgripper dedicated to embedded microrobotics applications. We first propose a polynomial linear parameter varying model of the system, where the varying parameter is the mean position of the microgripper that is used for the linearization. The controller is then derived using a multimodel and scheduled observer-based control strategy. The structure and the order of the controller are defined a priori allowing the derivation of a robust low-order controller suitable for a real-time implementation in embedded on-chip environments. Results show that a very wide (several tens of micrometers) and fast positioning of the gripping arm can be achieved using the control strategy. A robustness analysis and experimental implementation results show the efficiency of the controller and the relevance of the theoretical approach.

Study of thermal and acoustic noise interferences in low stiffness atomic force microscope cantilevers and characterization of their dynamic properties

The atomic force microscope (AFM) is a powerful tool for the measurement of forces at the micro/nano scale when calibrated cantilevers are used. Besides many existing calibration techniques, the thermal calibration is one of the simplest and fastest methods for the dynamic characterization of an AFM cantilever. This method is efficient provided that the Brownian motion (thermal noise) is the most important source of excitation during the calibration process. Otherwise, the value of spring constant is underestimated. This paper investigates noise interference ranges in low stiffness AFM cantilevers taking into account thermal fluctuations and acoustic pressures as two main sources of noise. As a result, a preliminary knowledge about the conditions in which thermal fluctuations and acoustic pressures have closely the same effect on the AFM cantilever (noise interference) is provided with both theoretical and experimental arguments. Consequently, beyond the noise interference range, commercial low stiffness AFM cantilevers are calibrated in two ways: using the thermal noise (in a wide temperature range) and acoustic pressures generated by a loudspeaker. We then demonstrate that acoustic noises can also be used for an efficient characterization and calibration of low stiffness AFM cantilevers. The accuracy of the acoustic characterization is evaluated by comparison with results from the thermal calibration.

Nonlinear modeling for a class of nano-robotic systems using piezoelectric stick-slip actuators

This paper addresses modeling issues for a class of nano-robotic systems using piezoelectric stick-slip actuators. The work focuses on the friction force modeling to describe the dynamics of a stick-slip actuator in a wide operating range needed in nano-robotics. Based on the theory of the single state elasto-plastic model and on an experimental analysis, necessary conditions on presiding modeling are highlighted. The conditions allow describing the dynamics of stick-slip type actuators for both scanning mode and stepping mode in the time and the frequency domains and for backward and forward directions of the motion. The proposed dynamic model opens new perspective for closed loop control of nano-robotic system.

Robust Microscale Grasping Using a Self Scheduled Dynamic Controller

Abstract This paper deals with robust gripping force control at the microscale for a safe manipulation of deformable soft materials. Since mechanical properties of micrometer sized objects are uncertain, instability often occurs during a gripping task. In this article, the design of an output feedback self-scheduled dynamic controller is proposed considering parametric uncertainties of a set of 65 soft and resilient microspheres. The degrees of freedom of the controller are managed by the design of a set of elementary observers. Robustness with respect to parametric uncertainties is satisfied thanks to an iterative procedure based on an eigenstructure assignment methodology and a worst case analysis. The developed controller is of low order and can be implemented in real time. Simulations demonstrate the validity of the proposed control approach.

Robust control strategies of stick-slip type actuators for fast and accurate nanopositioning operations in scanning mode

This paper deals with robust closed-loop control of a nano-robotic system dedicated to fast scanning probe microscopy. The nano-robotic system is actuated by piezoelectric stick-slip actuators able to produce a millimeter range displacement with a nanometer resolution. In order to meet the requirements of fast scanning in terms of closed-loop bandwidth and vibration damping, robust control strategies are studied. We first show that a commonly used one degree of freedom (1-DOF) H∞ controller is limited to satisfy robust performances required for fast and accurate positioning of the actuators. As such, the control strategy is defined considering two closed-loops. Results show that the 2-DOF H∞ control scheme allows robust performances for the positioning of nanorobotic systems and lead to new perspectives for fast scanning probe microscopy using stick-slip actuators.

Voltage/frequency rate dependent modeling for nano-robotic systems based on piezoelectric stick-slip actuators

In order to define trajectory-tracking strategies for nano-robotic systems using piezoelectric stick-slip actuators, the dynamics of the elementary actuator must be studied and well modeled. The modeling of this class of actuators is complex because several nonlinear parameters are involved. In this paper, we propose a systematic modeling methodology of piezoelectric stick-slip actuators for nano-robotic systems control. The main idea is the proposition of an augmented voltage/frequency rate dependent modeling of the friction force based on a multi-state elasto-plastic formulation. Experimental and simulation results demonstrate the efficiency of the model in the time and the frequency domains. As a case of study, the proposed model is used to define a control strategy in order to detect collisions when the nano-robotic system is operating inside a Scanning Electron Microscope (SEM). This application demonstrates the need of a voltage/frequency rate dependent modeling.

Modeling and Experimental Characterization of an Active MEMS Based Force Sensor

Active force sensors are based on the principle of force balancing using a feedback control. They allow, unlike passive sensors, the measurement of forces in a wide range with nanoNewton resolutions. This capability is fundamental when dealing with the mechanical characterization of samples with a wide range of stiffness. This paper deals with the modeling and the experimental characterization of a new active MEMS based force sensor. This sensor includes folded-flexure type suspensions and a differential comb drive actuation allowing a linear force/voltage relationship. A control oriented electromechanical model is proposed and validated experimentally in static and dynamic operating modes using a stroboscopic measurement system. The sensor has a resonant frequency of 2.2 kHz, and a static passive measurement range of

Velocity characterization and control strategies for nano-robotic systems based on piezoelectric stick-slip actuators

\pm 2.45\mu \mathbf{N}

Kalman Filtering Applied to Weak Force Measurement and Control in the Microworld

. This work is the first step toward new dynamic measuring capabilities and sensing at the micro/nano-scales when high dynamic, large measurement range and nanoNewton resolution are required.