Multi-axis Force Sensing with Pre-stressed Resonant Composite Plates : An Alternative to Strain Gauge Force Sensors

International audienceIndustrial robots embedding multi-axis force sensors at the robot/environment interface presents numerous advantages in terms of safety, dexterity and collaborative perspectives. The key-point of these developments remains the availability of cheap but sufficiently precise multi-axis force sensors. This paper proposes a model-based approach to design a new alternative to commonly used strain gauge sensors. The principle of the device relies on pre-stress resonant composite plates where feedback control and measurement are achieved with piezoelectric transducers. The main originality of this work is that the force to be measured may present multi-axis components. Based on pre-stress and piezoelectric theories, a complete electromechanical model is proposed. This one is used during the design of a resonating composite Mindlin plate, embedding piezoelectric patches. It is shown that the effects of in-plane and out-of-plane external forces can be considered as pre-stress components. These ones, at the root of buckling phenomena, alter the stiffness of the structure and shift the plate resonance frequencies. Then, by solving the eigenvalue problem of the pre-stress vibrating structure, we can find the relationship between the natural frequencies of the structure and the externally applied multi-axis force. The proof of concept of this sensor is achieved on a case study. Finally, numerical results from both, home-made and commercial, finite element software demonstrates the interest of our approach to design integrated and inexpensive multi-axis force sensors solutions

Gramian-based optimal design of a dynamic stroke amplifier compliant micro-mechanism.

International audienceThis paper presents a new method developed for the optimal design of microrobotic compliant mechanisms. It is based on a flexible building block method, called FlexIn, 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 synthetized 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 FlexIn synthetized compliant mechanisms demonstrate the interests of the proposed optimization method for the design of dynamic operating smart microrobotic structures

Mechanical and control-oriented design of a monolithic piezoelectric microgripper using a new topological optimisation method.

International audienceThis 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, 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 synthetized 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 micro-actuator has been synthetized using FlexIn and prototyped. Finally, simulations and experimental tests of the FlexIn optimally synthetized device demonstrate the interests of the proposed optimization method for the design of micro-actuators, microrobots, and more generally for adaptronic structures

Modeling and robust control strategy for a control-optimized piezoelectric microgripper.

International audienceIn 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 non-linear 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 wide-band regulator. It consists of a Positive Position Feedback (PPF) 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

Synthèse et commande robuste d'une micropince piézoélectrique intégrée.

National audienceWe have developed a new method to make the synthesis of monolithic flexible structures for designing integrated actuators. Our synthesis method is based on the optimal placement of building blocks. These elementary blocks can be made in passive materials or in active piezoelectric ceramics. Thanks to a dynamic representation of the input/output behavior of these mechanisms, some new specifications which can guaranty interesting performances for the identification and control of these systems are taken into account, from the first designing step. These last criteria helped us to draw an original design strategy for their robust control. MOTS-CLÉS : structure flexible, piézoélectricité, optimisation topologique multi-critères, grammiens, commandabilité, observabilité

Observation-Oriented design of a Monolithic Piezoelectric Microactuator with Optimally integrated Sensor.

International audienceThis paper presents an evolution in an optimization method, called FlexIn, developed for the optimal design of piezoelectric compliant smart structures. FlexIn is based on a flexible building block method that uses a genetic algorithm approach, to optimize a truss-like planar structure made of piezoelectric passive, active and, with the work reported in this paper, sensitive building blocks. The model of these blocks is established by means of a finite-element electromechanical formulation. The main contribution of this paper is to present a new observation-oriented criterion, along with a static electromechanical one, considered in the optimization procedure for the optimal placement of piezoactuating and piezosensing parts in the compliant micro-structure. In order to underline the interests of such a criterion, performances of three pseudo-optimal piezoelectric smart structures are drawn. Their analysis and comparison illustrate the role of the optimization method and the observation-oriented criterion, in the design of smart structures and in simplifying their control afterwards

Optimal Observability-based Modelling, Design and Characterization of Piezoelectric Microactuators.

International audienceThis paper deals with the optimal design of monolithic piezoelectric microactuators with integrated proprioceptive sensors. Dedicated to the microrobotic and micromechatronic fields, these works detail the modelling and the characterization of compliant structures with integrated actuating and sensing elements. The proposed optimal design procedure adresses not only static criteria but also dynamic ones. This leads to microdevices which are more performant with regards to mechanical (displacement, force...) and control (dynamics, stability, precision) characteristics. Efficient design of such devices is achieved using a flexible building block method. A topological optimization method combined with an evolutionary algorithm is used to optimize the design of truss-like planar structure. This method chooses the best location among the different piezoelectric elements. Different mechanical, actuation or sensing elements are accordingly chosen from a data bank. From the control point of view, optimisation criteria are considered to enforce the observability of the vibrational dominant modes of the structure. Therefore, control and observation Gramians are exploited in the optimal design to shape the open loop frequency response of both, actuation and sensing functions of the integrated device. In the last part of the paper, based on these results, the optimal design and manufacturing of an innovative piezoelectric flexible microgripper is proposed. The prototype is manufactured from a monolithic piezoelectric material (PIC 151). Its reduced size (15 mm x 18 mm) fits the requirement of both microrobotics and micromechatronics applications, which is suitable for micromanipulation tasks. The characterization and the performance of this integrated microactuator finally close the paper and the efficiency of the optimal design procedure for micromechatronics applications are shown

Optimal design and control simulation of a monolithic piezoelectric microactuator with integrated sensor.

International audienceThis paper presents an important evolution in an optimization method, called FlexIn, developed for the optimal design of piezoelectric compliant micromechanisms. It is based on a flexible building block method that uses an evolutionary approach, to optimize a truss-like planar structure made of piezoelectric passive, active and now sensitive building blocks. The model of these blocks is established by means of a finiteelement electromechanical formulation. The main contribution of this paper is to present an new control-observation-oriented criterion considered in the optimization procedure, among other conventional mechanical criteria, to optimize modal observability of the structure, for the placement of piezoactuating and piezosensing parts. In order to point out the underlying interests of this method for the design of smart structures with integrated actuators and sensors, a planar piezoelectric compliant smart micro-mechanism is optimally synthesized. Simulations of the device are finally performed illustrating the role of the observation-oriented criterion in simplifying the control of such smart structures

Méthode des blocs sensitifs pour la synthèse optimale de mécanismes flexibles à mesure piézoélectrique intégrée.

National audienceCet article présente une méthode de synthèse optimale pour la conception préliminaire de mécanismes flexibles monolithiques piézoélectriques. La construction d'un tel mécanisme, selon cette méthode baptisée FlexIn, est basée sur l'agencement de blocs flexibles piézoélectriques élémentaires qui peuvent être structurels, actionneurs et/ou capteurs, sélectionnés respectivement dans trois bibliothèques. Cet article décrit plus particulièrement l'approche utilisée pour établir le modèle aux éléments finis multi-physiques des blocs capteurs piézoélectriques, de type treillis de poutre, en vue de son intégration dans le logiciel de synthèse optimale. Les résultats obtenus présentent un écart de quelques pourcents avec ceux issus d'un code aux éléments finis commercial. A titre d'exemple, le modèle capteur est appliqué à une micropince monolithique existante ; le résultat de mesure est d'un ordre de grandeur satisfaisant. Ces résultats permettent de dresser les perspectives de la méthode de synthèse optimale proposée dans le cadre général de la conception de structures intelligentes pour la microrobotique