Vibrational piezoelectric energy harvesters (vPEH) are of great interest in several fields such as autonomous sensors and wireless sensor networks, bird tracking devices, or autonomous miniaturized robotic systems. They capture energy from mechanical vibrations available in the ambient environment and convert it into electrical one to power those systems. Basically, a vPEH is composed of three main parts: the transducer mechanical structure, an electronic interface and the storage unit. In this paper, we focus on the optimization of the mechanical structure of the harvester. To this end, an optimization framework based on topology optimization is proposed. It consists to combine the Solid Isotropic Material with Penalization (SIMP) approach and frequency tuning technique to further increase the efficiency of the harvesters. The fundamental frequency of the design is tuned by considering the mass of the attachment as an optimization variable in addition to the classical density and polarity variables. Two numerical examples, including a new piezoelectric energy harvester configuration, are investigated to demonstrate the effectiveness of the topology optimization framework.

Due to their inherent crystalline properties piezoelectric actuators have a limited deformation. This intrinsic drawback deprives to exploit the potential of these actuators such as, high bandwidth and high resolution in applications that require large displacement range. To overcome this limitation, classical as well as systematic approaches were proposed to design amplification mechanisms. The classical approach leads to empirical mechanisms which are not trivial and needs much experience and intuition. In contrast, systematic approach uses topology optimization method which permits to automatically derive optimal designs that can satisfy specified performances and imposed constraints simultaneously, this with a reasonable time and cost. This paper proposes the design of a mechanism devoted to amplify the displacement of a piezoelectric actuators (PEA). Based on the SIMP topology optimization method, the approach permits to derive a design with a displacement amplification ratio of 4.5, which is higher than with the existing method of Rhombus mechanism. Both finite element (FE) simulation and experimental results confirm and demonstrate the efficiency of the approach.

This paper presents the control of a two-degree-of-freedom piezoelectric actuator that exhibits hysteresis nonlinearity, creep nonlinearity, badly damped vibration, and cross couplings without using feedback sensors. The principle consists in compensating first the hysteresis, then the creep, and finally the vibration. The proposed compensation technique is multivariable and therefore is also able to reduce the cross couplings that are unwanted phenomena. The experimental tests demonstrate that the hysteresis that initially exceeds 19% is reduced to about 0.01%, while the creep is reduced from 5.5% to 0.04%. Regarding the vibration, the related overshoot that was initially 45% is completely removed. Note to Practitioners-This paper describes an approach to control and to automate dexterous precise positioning systems based on multiaxes piezoelectric actuators (PEAs). Two problems have motivated the approach investigated in this paper: 1) the presence of nonlinearities (hysteresis and creep), of badly damped vibration and of cross couplings in the multiaxes PEAs and 2) the lack of convenient sensors to feedback control them. Therefore, this paper proposes multivariable and complete feedforward control approach that does not require external sensors. This sensorless control architecture permits a low-cost and a high integration feature additionally to the fact that it is of great interest in applications at small scales where implementation of real-time measurement system is often difficult.

A new methodology that employs the rate-dependent Prandtl-Ishlinskii model (RDPI) as a model and a compensator is suggested in this study for modeling and compensation of rate-dependent hysteresis nonlinearities of a piezoelectric actuator. The technique employs a restructuration of the model that ignores the need to derive an inverse model, which avoids the additional calculations required to formulate a compensator. The simulation results are presented to demonstrate the effectiveness of the strategy on modeling and compensation of hysteresis nonlinearities at various frequencies. The simulation results were followed by experimental study on a piezoelectric actuator that exhibits rate-dependent hysteresis nonlinearities. The results demonstrate that the proposed methodology can be employed effectively for compensation of rate-dependent hysteresis nonlinearities without developing an inverse model.

This paper presents a new control method devoted to improve the performances of 2-DOF piezoelectric actuator for precise positioning tasks. The piezoelectric actuator exhibits strong cross-couplings between its two axes and strong hysteresis and creep nonlinearities. These unwanted phenomena undeniably compromised therefore the final precision of the targeted tasks (micromanipulation) and should be conveniently accounted during the controller synthesis. In this paper, we proposed a combination of the discrete linear Kalman filtering with a closed-loop scheme to suppress the effects of the couplings and of the nonlinearities. The suggested method permits to improve the performances of the piezoelectric actuator without specific and detailed characterization and knowledges on the hysteresis and on the creep models. Extensive experiments were carried out with complex desired trajectories and demonstrate the efficiency of the novel approach.

In this paper, a method to predict the precision of parallel microstructures made of carbon fibers, polyimide layers and piezoelectric materials is proposed. To this aim, we propose to combine the exponential representation of transformation matrix with intervals to bound the uncertainties in each flexure joint of the microstructures. Based on interval techniques and algorithms, the derived model permits to guarantee a bound on the precision value of the end effector. The method has been demonstrated with a numerical example of parallel microrobot devoted to orient the laser spot towards vocal fold during phonomicrosurgery. This example considers the uncertainties that occur in the compliant joints caused by the fabrication technique.

The scope of this paper is the modeling, identification and compensation of multivariable creep in piezoelectric actuators. Based on the inverse multiplicative scheme, we propose an approach to model and reduce the creep when the actuators have multiple degrees of freedom. The approach is simple to compute and easy to implement. The experimental results demonstrate the efficiency of the proposed approach on piezoelectric actuators.

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.

A new approach to compensate the strong hysteresis nonlinearity in piezoelectric materials is proposed. Based on the inverse multiplicative scheme, the approach avoids models inversion as employed in existing works. The compensator is therefore simple to implement and does not require additional computation as soon as the direct model is available. The proposed compensation technique is valuable for hysteresis that are modeled with the Bouc-Wen set of equations.

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.

Many tasks related to the micro/nanoworld require, not only high performances like submicrometric accuracy, but also a high dexterity. Such performances are only obtained using micromanipulators and microrobots with multiple degrees of freedom (DOF). Unfortunately, these multi-DOF systems usually present a strong coupling between the different axis making them very hard to control. The aim of this work is the modeling and control of a 2-DOF piezoelectric cantilever dedicated to microassembly/micromanipulation tasks. In addition to the coupling between the two axis, the piezocantilever is very oscillating and strongly nonlinear (hysteresis and creep). In the proposed approach, the nonlinearity and vibration are first compensated thanks to the feedforward technique. Afterwards, we derive a decoupled model in order to synthesize a linear robust H∞controller. The experimental results show the efficiency of the proposed approach and their convenience to the micromanipulation/microassembly requirements. Note to Practitioners-The main motivation of this paper is the need of both high performances and high dexterity in micromanipulation and microassembly tasks. In such a case, not only a sub micrometric accuracy and stability are needed, but also numerous degrees of freedom. For that, in the literature, there exist piezoelectric based structures with two or more DOF. Unfortunately, the coupling between its axis, the nonlinearities (hysteresis and creep) and the structure vibration make them very difficult to control and therefore make performances lost. A classical feedback con troller can be employed but when the nonlinearities and vibration become strong, it is impossible to synthesize a linear controller. In this paper, we show that the combination of feedforward techniques, to minimize the nonlinearities and vibration, and feedback techniques makes possible to reach the high performances required in micromanipulation/microassembly. We notice that the proposed approach can also be applied to other nonlinear, oscillating and multi-DOF systems, such as piezotubes.

This paper presents a new actuator based on a unimorph piezocantilever and on the thermal bimorph principle, called hybrid thermo-piezoelectric actuator. The main advantage of the proposed actuator is the high range of positioning from the thermal actuation and the high resolution and bandwidth from the piezoelectric one. A characterization and linear modeling are proposed. Finally, we propose an adapted control law to manage the two possible actuation types.

The feedforward compensation of nonlinearities, i.e., hysteresis and creep, and unwanted vibrations in micromanipulators is presented in this paper. The aim is to improve the general performances of piezocantilevers dedicated to micromanipulation/microassembly tasks. While hysteresis is attenuated using the Prandtl-Ishlinskii inverse model, a new method is proposed to decrease the creep phenomenon. As no model inversion is used, the proposed method is simple and easy to implement. Finally, we employ an input shaping technique to reduce the vibration of the piezocantilevers. The experimental results show the efficiency of the feedforward techniques and their convenience to the micromanipulation/microassembly requirements.

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.

This paper presents the estimation of the force applied by a piezocantilever dedicated to micro-manipulation/microassembly. Relative to previous works, the presented method avoids the reliance on the force dynamics on the characteristics of the micro-objects. Furthermore, the estimation is a closed-loop kind technique so that convergency can be ensured efficiently. To perform these, we consider the force at the tip of a piezocantilever as an unknown input and we use an unknown input observation technique. We especially use the inverse-dynamics-based UIO technique because it is well suited for a piezo-cantilever model. The experiments show that the performances of the observer are convenient for micromanipulation/microassembly tasks.

Piezoelectric cantilevers have proved their performances for actuating microgrippers dedicated to micromanipulation and microassembly tasks. While the control of one degree-of-freedom (dof) piezocantilevers have been well whelmed, the control of multi-dof one has not been addressed. Indeed, to assemble complex structures, the use of multidof microgrippers is recognized. Unfortunately, strong coupling between the axis and nonlinearities indeniably limit their performances. This paper deals with the modeling and control of a piezocantilever that has 2 degrees of freedom: in-plane and out of plane deflections. While such a characteristic allows the microgrippers perform both orientation and translation during micromanipulation/microassembly tasks, the strong coupling between the two dof makes difficult their control. Moreover, nonlinearities (hysteresis and creep) raise when the piezocantilever is used in high deformation. To overcome these, we consider the coupling as a disturbance, model the nonlinearities with the quadrilateral approximation and we apply a robust H¿controller that accounts them. The experiments show the efficiency of the synthesized controller and the obtained performances are convenient for micromanipulation/ microassembly tasks.

Due to their rapidity and their high resolution, piezoelectric materials are very prized in microactuators and microrobotics. The classical example is the piezocantilevers. Notwithstanding, piezoecantilevers present nonlinearities (hysteresis and creep) when the applied electric field becomes large. On the other hand, they present lightly damped vibration. Feedback control is a classical issue to eliminate this unwanted behavior but it involves the use of sensors. In micromanipulation and in microassembly, sensors still remain one of the problematic because of their sizes and difficulty of packaging. This paper presents the feedforward compensation of the hysteresis and the vibrations in piezocantilevers. While the Prandtl-Ishlinskii (PI) static hysteresis model is used to compute the hysteresis compensator, we employ the Input-Shaping method to reject the unwanted vibration. The experiments show that the accuracy can be highly increased while the setling time ameliorated and the vibration largely decreased.

A new control type for stick-slip microsystems is proposed in this paper: the voltage/frequency (U/f) proportional control. It gives a best resolution relatively to the classical control algorithm. It is also an englobalization of three classical controllers: the sign controller, the classical proportional controller and the frequency proportional controller. A high stroke model of a stick-slip microsystem is first given. Then, we theoretically analyze the performances of the closed loop process with the U/f controller. Finally, we give some experimental results obtained with different values of the proportional gains.

The effect of the temperature variation on a unimorph piezoelectric cantilever is studied. Its influences on the thermal expansion, the piezoelectric constant, the transient part and the creep are experimentally analyzed. Afterwards, a Hinfincontroller is synthesized in order to reject the thermal disturbance and to reach performances required in micromanipulation. Finally, the closed-loop experiments end the paper.

During a micromanipulation, it is important to have the same performances whatever the manipulated object is. We present in this paper the control of the force applied to flexible and rigid micro-objects by a piezoelectric cantilever. First, the voltage-force transfer function is modeled. The hysteresis and creep phenomena are taken into account. The reliance of the model on the characteristics of the micro-objects is clearly detailed. Then, in order to reject disturbances and maintain tracking performances required in micromanipulation, a Hinfincontroller is designed. Finally, the experimental results end the paper.

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

This paper presents the design, the development and the experiments on a two degrees of freedom (2DoF) microsystem. The originality of the microsystem is its ability to do angular and linear motions independently with a very high stroke and a submicrometric precision. The target performances are first presented. Afterwards the stick-slip piezoelectric microactuators that are used are presented. Then, their integration inside the microsystem is detailed. Finally, results of experiments are given

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.