Yassine Haddab

Development, Modeling, and Control of a Micro-/Nanopositioning 2-DOF Stick–Slip Device

The studies presented in this paper are motivated by the high performances required in micromanipulation/microassembly tasks. For that, this paper presents the development, the modeling, and the control of a 2-DOF (in linear and angular motion) micropositioning device. Based on the stick-slip motion principle, the device is characterized by unlimited strokes and submicrometric resolutions. First, experiments were carried out to characterize the performances of the micropositioning device in resolution and speed. After that, a state-space model was developed for the substep functioning. Such functioning is interesting for a highly accurate task like nanopositioning. The model is validated experimentally. Finally, a controller was designed and applied to the micropositioning device. The results show good robustness margins and a response time of the closed-loop system.

Plurilinear Modeling and discrete μ-Synthesis Control of a Hysteretic and Creeped Unimorph Piezoelectric Cantilever

First, we present a survey on modeling and control of bending piezoelectric microactuators. Second, a simple model for nonlinear piezoelectric actuators (hysteresis and creep) is presented. It is based on the multilinear approximation. This model requires low computing power and is well adapted for embedded systems. Finally, a μ-synthesis controller is implemented. Experiments show that the obtained performances are compatible with the requirements of micromanipulation tasks

Modelling of a MEMS-based microgripper: application to dexterous micromanipulation

MEMS-based microgrippers with integrated force sensor have proved their efficiency to perform dexterous micromanipulation tasks through gripping forces sensing and control. For force control, knowledge based models are more relevant and gives better physical significance than the use of black box models. However this approach is often limited by many problems commonly encountered in the MEMS (micro electromechanical systems) structures such as: complex architectures, nonlinear behaviors and parameters uncertainties due to fabrication process at the micrometer scale. For these reasons theoretical approaches must be compared with experiments. This paper describes a modelling approach of a MEMS-based microgripper with integrated force sensor while handling micro-glass balls of 80µm diameter. Therefore, a state space representation is developed to couple both the dynamics of the actuation and sensing subsystems of the gripper through the stiffness of the manipulated object. A knowledge based model is obtained for small displacements at the tip of the gripper arms (small gripping forces) and is compared with experimental approaches. Good agreements are observed allowing interesting perspectives for the control.

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.

Gain scheduled control strategies for a nonlinear electrostatic microgripper: Design and real time implementation

This paper deals with the accurate and fast positioning control of a nonlinear electrostatically actuated microgripper. Considering the importance of nonlinearities, performances are achieved through the design of gain scheduled controllers. To this end, a nonlinear model of the studied system is proposed and is reformulated into a polynomial LPV (Linear Parameter Varying) model. Controllers are designed considering the particular polynomial parametric dependence of the LPV model. In a first instance, a controller is synthesized using an affine LPV descriptor representation of the system and LMI (Linear Matrix Inequality) constraints. In a second instance, to deal with real time implementation constraints, a second controller is designed based on an iterative procedure using the eigenstructure assignment methodology and a worst case analysis. For embedded applications, requiring simple controller structures, we show experimentally the interest of the iterative procedure which can achieve good results relatively with the ones obtained using recent advances of robust controllers based on LMI conditions.

Effects of environmental noise on the accuracy of millimeter sized grippers in cantilever configuration and active stabilisation

This paper presents a study about the effects of environmental noise on millimeter sized grippers in cantilever configuration. The study is motivated and conducted aiming at assessing the level of accuracy loss when performing micromanipulation/microassembly tasks in noisy environments as well in typical microrobotics laboratories as in industrial locations or operating rooms. Ground motion and acoustic noises within a typical microrobotic laboratory are characterized in the frequency domain and their effects on cantilevers of different lengths are inspected. The relevance of a typical vibration isolation table is evaluated and the effects of low and high acoustic noises are assessed. A modeling of a cantilever with base excitation is thereafter conducted in the state space using finite difference formulation and a stabilization of a disturbed cantilever is obtained at the nanometer level in noisy environments allowing perspectives to high precision micromanipulation tasks in hostile locations.

Step Modelling of a High Precision 2DoF (Linear-Angular) Microsystem

In this paper, a new type of microsystem is presented : a system able to perform linear and angular motion. First, the microactuator used is studied. An approximation of the working equations is proposed in accordance with Finite-Element simulation. The microactuator used is inserted in the microsystem and a separated modelling of the whole system in linear and in angular motion is given. Stick and skid phases of each motion are independently studied.

Analysis of the dynamic behavior of a doped silicon U-shaped electrothermal actuator

The dynamic behavior of a U-shaped electrothermal actuator is investigated in this paper based on experimental findings and FEM simulations. Few previous works are found in the literature that have addressed the dynamic response of U-shaped actuators. A lack of data on the transient displacement of the actuator in the heating and cooling cycles is noted. Experiments are made in order to characterize the dynamic response of the actuator. The actuators are micro-fabricated on doped SOI wafers and the displacement is recorded with a high speed camera. FEM simulations are in good agreement with the experimental findings. Simulations and experiments show that the shape of displacement follows evolution of the temperature distribution inside the actuator. The influence of the dynamic behavior on the control of the actuator is finally discussed.

Trajectory Planning for Micromanipulation With a Nonredundant Digital Microrobot: Shortest Path Algorithm Optimization With a Hypercube Graph Representation

Microrobotics is an ongoing study all over the world for which design is often inspired from macroscale robots. We have proposed the design of a new kind of microfabricated microrobot based on the use of binary actuators in order to generate a highly accurate and repeatable tool for positioning tasks at microscale without any sensor (with open-loop control). Our previous work consisted in the design, modeling, fabrication, and characterization of the first planar digital microrobot. In this paper, we focus on the motion planning of this robot for micromanipulation tasks. The complex motion pattern of this robot requires the use of algorithms. Graph theory is well suited for the discrete workspace generated by this robot. The comparison between several well-known trajectory-planning algorithms is done. A new graphical representation, named the hypercubic graph, is used for improving the computation speed of the algorithm. This is particularly useful for large workspace robots.

Extended high-gain observer for robust position control of a micro-gripper in air and vacuum

This paper aims to develop a position tracking controller for a micro-grippers tip. The controller should be robust, able to compensate external disturbances and perform precise reference tracking under parameter variation and incertitudes. It becomes clear when considering the grippers response on two different environments: air and vacuum. In this work, two models were identified based on experimental data, one for each case of study, and an extended high-gain observer controller based on output feedback is proposed. Simulations show that the controller, chosen to achieve a desired performance for the system in air, is able to maintain similar results in vacuum. The proposed setup was implemented in real-time for the system in air and simulated for vacuum.