Cédric Clévy

Complete Open Loop Control of Hysteretic, Creeped, and Oscillating Piezoelectric Cantilevers

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.

Modelling and Robust Position/Force Control of a Piezoelectric Microgripper

This paper deals with the control of a piezoelectric microgripper based on two piezocantilevers. To avoid the destruction of the manipulated micro-object and to permit a high accurate positioning, the microgripper is controlled on position and on force. Each piezocantilever is separately modelled and controlled: while the one is controlled on position, the second is controlled on force. Because the models are subjected to uncertainties and the micromanipulation requires good performances, a Hinfin robust controller is designed for each system. The experiments end the paper and show that good performances are obtained.

Hysteresis and vibration compensation in a nonlinear unimorph piezocantilever

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.

Prototyping of a highly performant and integrated piezoresistive force sensor for microscale applications

In this paper, the prototyping of a new piezoresistive microforce sensor is presented. An original design taking advantage of both the mechanical and bulk piezoresistive properties of silicon is presented, which enables the easy fabrication of a very small, large-range, high-sensitivity with high integration potential sensor. The sensor is made of two silicon strain gauges for which widespread and known microfabrication processes are used. The strain gauges present a high gauge factor which allows a good sensitivity of this force sensor. The dimensions of this sensor are 700 μm in length, 100 μm in width and 12 μm in thickness. These dimensions make its use convenient with many microscale applications, notably its integration in a microgripper. The fabricated sensor is calibrated using an industrial force sensor. The design, microfabrication process and performances of the fabricated piezoresistive force sensor are innovative thanks to its resolution of 100 nN and its measurement range of 2 mN. This force sensor also presents a high signal-to-noise ratio, typically 50 dB when a 2 mN force is applied at the tip of the force sensor.

Signal Measurement and Estimation Techniques for Micro and Nanotechnology

Signal Measurement and Estimation Techniques for Micro and Nanotechnology provides a state-of-the-art discussion on techniques and solutions to measure and estimate signals at the micro and nano scale. new technologies and applications such as micromanipulation (artificial components, biological objects), micro-assembly (MEMS, MOEMS, NEMS) and material and surface forces characterization are covered. The importance of sensing at the micro and nano scale is presented as a key issue in control systems, as well as for understanding the physical phenomena of these systems.

Precise Motion Control of a Piezoelectric Microgripper for Microspectrometer Assembly

The Fourier Transform (FTIR) microspectrometer discussed in this paper is an example of a complex Micro-Opto-Electro-Mechanical System (MOEMS) configured as an optical bench on a chip. It is an important benchmark application for microtechnology due to increased demands for the use of miniature wavelength detection instruments in bio, nano and material science. This device can be manufactured using automated microassembly and precision alignment of hybrid silicon and glass components, and in particular, of a micro-beamsplitter cube along 3 rotational degrees of freedom. In this paper, a piezoelectric microgripper with four degrees of freedom was attached to a precision robot in order to enhance its dexterity and align the beamsplitter to arcsecond angular tolerance. The modeling and control of the microgripper, and the alignment algorithm utilizing a novel spot-Jacobian servoing technique are discussed. Experimental results obtained during joint on-going work in Texas and in France are presented, demonstrating the advantage of using the microgripper for optical alignment of the microspectrometer.Copyright

Dynamic displacement self-sensing and robust control of cantilever piezoelectric actuators dedicated for microassembly

The main objective of this paper is the dynamic self-sensing of the motion of piezoelectric actuators. The proposed measurement technique is afterwards used for a closed-loop control. Aiming to obtain a self-sensing scheme that estimates the transient and steady-state modes of the displacement, we extend a previous static self-sensing scheme by adding a dynamic part. Analytical solutions are provided to compute the gains of this dynamic part. Afterwards, the proposed dynamic self-sensing result is used in a closed-loop control. The experimental results demonstrate the concept and evaluate the accuracy and the efficiency of the proposed technique for closed-loop applications.

A new micro-tools exchange principle for micromanipulation

This paper deals with the design, fabrication and characterization of a new micro-tools changer for a micromanipulation station including three translation stages (X-Y-Z manipulator) and a new piezoelectric microgripper. This system can be implemented in confined workspaces such as a scanning electron microscope (SEM) or more generally in a micro-factory station by the reduction of the manipulators size and the flexibility gain. The principle of this micro-tools changer is based on the use of a thermal glue whose state (liquid or solid) is controlled by surface mounted device (SMD) electrical resistances. Such system allows hundreds of automatic micro-tools exchanges with a maximum position error between two consecutive tools exchanges of respectively 4.2, 2.8 and 5.4 /spl mu/m on the X, Y and Z axis. To validate the use of the micromanipulation station in a SEM, an experimental comparison of the working principle in low (vacuum) and high (air) pressure has also been established through thermal and degassing studies.

High Bandwidth Microgripper With Integrated Force Sensors and Position Estimation for the Grasp of Multistiffness Microcomponents

At the microscale, small inertia and high dynamics of microparts increase the complexity of grasping, releasing, and positioning tasks. The difficulty increases especially because the position, the dimensions, and the stiffness of the micropart are unknown. In this paper, the use of a microgripper with integrated sensorized end effectors with high dynamic capabilities is proposed to perform stable and accurate grasps of multistiffness microcomponents. A dynamic nonlinear force/position model of the complete microgripper while manipulating a microcomponent is developed. The model takes into consideration not only free motion and constrained motion, but also, contact transitions which is a key issue at the microscale due to the predominance of surface forces. It enables us to estimate the position of the microgrippers end effectors, the contact position of the microcomponent, and the force applied on the microcomponent. Using the proposed microgripper and its model, both of the gripping forces are measured and the position of each of the microgrippers end effectors is estimated. This enables to perform a stable grasp of the micropart by providing force and position feedback. Moreover, using the developed microgripper and its model, the characterization of the microcomponent can be performed by estimating its dimensions and its stiffness.

Static/dynamic trade-off performance of PZT thick film micro-actuators

Piezoelectric actuators are widespread in the design of micro/nanorobotic tools and microsystems. Studies toward the integration of such actuators in complex micromechatronic systems require the size reduction of these actuators while retaining a wide range of performance. Two main fabrication processes are currently used for the fabrication of piezoelectric actuators, providing very different behaviors: (i) the use of a bulk lead zirconate titanate (PZT) layer and (ii) the use of thin film growth. In this paper, we propose a trade-off between these two extreme processes and technologies in order to explore the performance of new actuators. This resulted in the design and fabrication of thick film PZT unimorph cantilevers. They allowed a high level of performance, both in the static (displacement) and dynamic (first resonance frequency) regimes, in addition to being small in size. Such cantilever sizes are obtained through the wafer scale bonding and thinning of a PZT plate onto a silicon on insulator wafer. The piezoelectric cantilevers have a 26 μm thick PZT layer with a 5 μm thick silicon layer, over a length of 4 mm and a width of 150 μm. Experimental characterization has shown that the static displacements obtained are in excess of 4.8 μm V−1 and the resonance frequencies are up to 1103 Hz, which are useful for large displacements and low voltage actuators.