An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> I. INTRODUCTION <s> A technique has been developed which allows a single piece of piezoelec tric material to concurrently sense and actuate in a closed loop system. The motivation behind the technique is that such a self-sensing actuator will be truly collocated and has applications in active and intelligent structures, such as vibration suppression. A theoreti cal basis for the self-sensing actuator is given in terms of the electromechanical consti tutive equations for a piezoelectric material. In a practical implementation of the self- sensing actuator an electrical bridge circuit is used to measure strain. The bridge circuit is capable of measuring either strain or time rate of strain in the actuator. The usefulness of the proposed device was experimentally verified by actively damping the vibration in a cantilever beam. A single piezoceramic element bonded to the base of the beam functioned both as a distributed moment actuator and strain sensor. Using a rate feedback control law, the first mode of vibration was suppressed, reducing the settling from 35 seconds to 2.5 seconds. Using a positive position feedback law the first two modes of vibration were suppressed; the first mode settling time was reduced from 35 to 0.3 sec onds and the second mode settling time was reduced from 7 seconds to 0.9 seconds. <s> BIB001 </s> An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> I. INTRODUCTION <s> This paper deals with a displacement control method of a piezoelectric actuator (piezo). When voltage is applied to a piezo with conductive plates attached on both ends of the piezo, charges are induced on the conductive plates. This induced charge indicates the deformation of the piezo. The ratio of the displacement to the induced charge does not depend on the amplitude and the bias of the applied voltage. The hysteresis of the displacement to the induced charge is 2% though the hysteresis to the applied voltage is 14%. The induced charge has high response as the displacement. The displacement of the piezo can be controlled by the feedback of the induced charge as well as by a feedback of the displacement with other measuring instruments. This method can be used at a high driving frequency since the piezo is driven with a voltage source with a low output impedance in this method. <s> BIB002 </s> An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> I. INTRODUCTION <s> Research on shunted piezoelectric transducers, per- formed mainly over the past decade, has generated new opportuni- ties for control of vibration and damping in flexible structures. This is made possible by the strong electromechanical coupling associ- ated with modern piezoelectric transducers. In vibration control applications, a piezoelectric transducer is bonded to, or embedded in a base structure. As the structure deforms, the piezoelectric el- ement strains and converts a portion of the structural vibration energy into electrical energy. By shunting the piezoelectric trans- ducer to an electrical impedance, a part of the induced electrical energy can be dissipated. Hence, the impedance acts as a means of extracting mechanical energy from the base structure. This paper reviews recent research related to the use of shunted piezoelec- tric elements for vibration damping and control. In particular, the paper presents an overview of the literature on piezoelectric shunt damping and discusses recent observations on the feedback nature of piezoelectric shunt damping systems. <s> BIB003 </s> An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> I. INTRODUCTION <s> In this paper, a charge amplifier adapted for piezoelectric tube scanners is presented. Previous problems involved with the implementation of such amplifiers are resolved to provide dc accurate performance with zero voltage drift. In our experiment, hysteresis was reduced by 89% when compared to a voltage amplifier. <s> BIB004 </s> An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> I. INTRODUCTION <s> Position sensors other than the R/W heads are not embedded into current hard-disk drives (HDDs) due to cost, resolution, and signal-to-noise ratio (SNR) issues. Moreover, the "optimal" location for placing these sensors is still unknown. In this paper, the Pb-Zr-Ti (PZT) elements in the PZT suspension-based microactuator are used as a secondary actuator and a displacement sensor simultaneously with self-sensing actuation. The proposed displacement estimation circuit produces an estimated PZT microactuator's displacement with high SNR and nanometer resolution comparable to that measured from the laser doppler vibrometer (LDV). A robust active mode damping controller is then designed to damp the PZT microactuator suspension's torsion modes and sway mode, as well as decoupling the HDD dual-stage servo into two distinct loops for individual sensitivity optimization. Our results show attenuation of PZT microactuator's suspension modes by 5 dB and sway mode by 30 dB with low sensitivity. A reduction of up to 20% in 3/spl sigma/ position error signal is also observed. <s> BIB005 </s> An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> I. INTRODUCTION <s> Piezoelectric tube scanners are employed in high-resolution positioning applications such as scanning probe microscopy and nanofabrication. Much research has proceeded with the aim of reducing hysteresis and vibration-the two foremost problems associated with piezoelectric tube scanners. In this paper, two simple techniques are proposed for simultaneously reducing hysteresis and vibration: 1) A new dc accurate charge amplifier is shown to significantly reduce hysteresis while avoiding characteristic voltage drift. 2) Piezoelectric shunt damping, a technique previously resident in the field of smart structures, has been applied to damp tube vibration. By attaching an LCR impedance to a single tube electrode, the first mechanical mode is reduced in magnitude by more than 20 dB. <s> BIB006 </s> An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> I. INTRODUCTION <s> Nanotechnology is the science of understanding matter and the control of matter at dimensions of 100 nm or less. Encompassing nanoscale science, engineering, and technology, nanotechnology involves imaging, measuring, modeling, and manipulation of matter at this level of precision. An important aspect of research in nanotechnology involves precision control and manipulation of devices and materials at a nanoscale, i.e., nanopositioning. Nanopositioners are precision mechatronic systems designed to move objects over a small range with a resolution down to a fraction of an atomic diameter. The desired attributes of a nanopositioner are extremely high resolution, accuracy, stability, and fast response. The key to successful nanopositioning is accurate position sensing and feedback control of the motion. This paper presents an overview of nanopositioning technologies and devices emphasizing the key role of advanced control techniques in improving precision, accuracy, and speed of operation of these systems. <s> BIB007 </s> An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> I. INTRODUCTION <s> Piezoelectric materials exhibit high electromechanical coupling that allows them to both generate an electrical signal when strained and, conversely, to produce a strain under an applied electric field. This coupling has led to the use of these materials for a variety of sensing and actuation purposes. One unique application of these materials is their use as self-sensing actuators where both the sensing and actuation functions are performed by a single patch of material. Since the actuation and sensing voltages both exist simultaneously in the piezoelectric material, a specially designed electric circuit, referred to as a bridge circuit, is required to realize the concept. Configuration of the material in this manner is advantageous for control systems due to the enhanced stability associated when collocated control is applied. While certain advantages result from this type of system, precise equilibrium of the bridge circuit is required to achieve stability. This equilibrium is easy to achieve in theory, but difficult in practice due to the thermal dependence of the piezoelectric material's dielectric constant. This study will investigate a novel method of accounting for these changes through the use of thermal switches to passively adjust the bridge circuit and maintain a balanced state. The proposed concept will be theoretically modeled and simulated in a vibration control application to identify the thermal range for stability with and without the array of switches. It will be shown that, through the use of nine thermal switches, the stable operating range can be increased by 95 °C while maintaining vibration control performance. <s> BIB008 </s> An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> I. INTRODUCTION <s> This paper discusses a self-sensing vibration suppression method that measures only the value of the piezoelectric voltage. The method separates the electrical status into two cases concerning electrical current and characterizes each of these to establish a self-sensing system using extended system equations and a Kalman filter. Our self-sensing system can avoid estimation blackout during closed-circuit status and lessen harmful influences from residual modes. Experiments revealed that the self-sensing system suppressed vibrations in cooperation with state-switching and synchronized-switching controls. We confirmed that the self-sensing method is robust against model errors in a vibration suppression experiment in which there are model errors caused by an intentional frequency shift. <s> BIB009 </s> An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> I. INTRODUCTION <s> Nanomanipulation with atomic force microscopes (AFMs) for nanoparticles with overall sizes on the order of 10 nm has been hampered in the past by the large spatial uncertainties encountered in tip positioning. This paper addresses the compensation of nonlinear effects of creep and hysteresis on the piezo scanners which drive most AFMs. Creep and hysteresis are modeled as the superposition of fundamental operators, and their inverse model is obtained by using the inversion properties of the Prandtl-Ishlinskii operator. Identification of the parameters in the forward model is achieved by a novel method that uses the topography of the sample and does not require position sensors. The identified parameters are used to compute the inverse model, which in turn serves to drive the AFM in an open-loop, feedforward scheme. Experimental results show that this approach effectively reduces the spatial uncertainties associated with creep and hysteresis, and supports automated, computer-controlled manipulation operations that otherwise would fail. <s> BIB010 </s> An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> I. INTRODUCTION <s> Inverse-feedforward control can substantially improve the performance of piezoelectric positioners (piezopositioners). The feedforward-input is found by modeling and inverting the piezopositioner dynamics. The primary challenge in such an approach is the complexity of modeling and inverting the hysteresis nonlinearity in the piezopositioner dynamics. The main contribution of this work is to alleviate this complexity by using charge control to linearize the overall dynamics and then model and invert the simplified (linearized) dynamics. The proposed approach is applied to an experimental piezopositioner and results are presented to contrast the feedforward-based positioning performance with and without the use of charge control to linearize the dynamics. <s> BIB011 </s> An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> I. INTRODUCTION <s> Piezoelectric tube scanners have emerged as the most widely used nanopositioning technology in modern scanning probe microscopes. Despite their impressive properties, their fast and accurate operations are hindered due to complications such as scan induced mechanical vibrations, hysteresis nonlinearity, creep, and thermal drift. This paper presents an overview of emerging innovative solutions inspired from recent advances in fields such as smart structures, feedback control, and advanced estimation aimed at maximizing positioning precision and bandwidth of piezoelectric tube scanners. The paper presents a thorough survey of the related literature and contains suggestions for future research prospects. <s> BIB012 </s> An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> I. INTRODUCTION <s> Control can enable high-bandwidth nanopositioning needed to increase the operating speed of scanning probe microscopes (SPMs). High-speed SPMs can substantially impact the throughput of a wide range of emerging nanosciences and nanotechnologies. In particular, inversion-based control can find the feedforward input needed to account for the positioning dynamics and, thus, achieve the required precision and bandwidth. This article reviews inversion-based feedforward approaches used for high-speed SPMs such as optimal inversion that accounts for model uncertainty and inversion-based iterative control for repetitive applications. The article establishes connections to other existing methods such as zero-phase-error-tracking feedforward and robust feedforward. Additionally the article reviews the use of feedforward in emerging applications such as SPM-based nanoscale combinatorial-science studies, image-based control for subnanometer-scale studies, and imaging of large soft biosamples with SPMs. <s> BIB013 </s> An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> I. INTRODUCTION <s> We proposed a dynamic model identification and design of an H-Infinity (i.e. H∞) controller using a Lightweight Piezo-Composite Actuator (LIPCA). A second-order dynamic model was obtained by using input and output data, and applying an identification algorithm. The identified model coincides well with the real LIPCA. To reduce the resonating mode that is typical of piezoelectric actuators, a notch filter was used. A feedback controller using the H∞ control scheme was designed based on the identified dynamic model; thus, the LIPCA can be easily used as an actuator for biomemetic applications such as artificial muscles or macro/micro positioning in bioengineering. The control algorithm was implemented using a microprocessor, analog filters, and power amplifying drivers. Our simulation and experimental results demonstrate that the proposed control algorithm works well in real environment, providing robust performance and stability with uncertain disturbances. <s> BIB014 </s> An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> I. INTRODUCTION <s> Angle Sensor for Measurement of Surface Slope and Tilt Motion.- Laser Autocollimator for Measurement of Multi-axis Tilt Motion.- Surface Encoder for Measurement of In-plane Motion.- Grating Encoder for Measurement of In-plane and Out-of-plane Motion.- Scanning Multi-probe System for Measurement of Roundness.- Scanning Error Separation System for Measurement of Straightness.- Scanning Micro-stylus System for Measurement of Micro-aspherics.- Large Area Scanning Probe Microscope for Micro-textured Surfaces.- Automatic Alignment Scanning Probe Microscope System for Measurement of 3D Nanostructures.- Scanning Image-sensor System for Measurement of Micro-dimensions. <s> BIB015 </s> An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> I. INTRODUCTION <s> 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. <s> BIB016 </s> An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> I. INTRODUCTION <s> Abstract Piezoelectric displacement contains hysteresis and creep properties. Therefore, a displacement sensor is indispensable in precise positioning devices; however, the additional space and cost are problems. On the other hand, self-sensing methods that utilize the piezoelectric actuator itself as the displacement sensor have been proposed. With these self-sensing methods, precise positioning becomes possible without an additional displacement sensor. We developed a self-sensing method utilizing the non-hysteresis relationship between the permittivity change and the piezoelectric displacement. Furthermore, a differential current measurement method using two piezoelectric elements with a bimorph actuator could improve the positioning accuracy. In this study, we examine the control of a positioning stage using two multilayered piezoelectric actuators by applying the differential current measurement method for self-sensing control. The results indicate that the differential current measurement method is effective for precise positioning control. The positioning errors due to hysteresis decreased from 0.8 μm to 0.1 μm for a 10 μm displacement range. In addition, permittivity feedback control could compensate for the creep property. <s> BIB017 </s> An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> I. INTRODUCTION <s> Self-sensing technique consists of using an actuator as a sensor at the same time. This is possible for most actuators with physically reversible principle such as piezoelectric materials. The main advantages of self-sensing are: 1) the embeddability of the measurement technique, and 2) its low cost as no additional sensor is required. This paper presents a self-sensing technique for piezoelectric actuators used in precise positioning applications like micromanipulation and microassembly. The main novelty is that both displacement and force signals can be simultaneously estimated. This allows a feedback control using one of these two signals with a display of the other signal. To demonstrate this advantage, a robust $H_\infty$ feedback control on displacement with real-time display of the force is used as an application of the proposed self-sensing technique. In this paper, experimental results obtained with a piezoelectric cantilever actuator validate and demonstrate the efficiency of the proposed self-sensing. <s> BIB018
P IEZOELECTRIC-BASED nanopositioning systems generally refer to flexure-hinge-guided mechanisms driven by piezoelectric actuators (PEAs). PEAs are electrically controllable positioning element with high precision which have been widely applied in precision types of equipment, such as micromanipulators, atomic force microscopes, and ultraprecision machine tools. These kinds of actuators are designed Manuscript The authors are with the Department of Automatic Control and Micro-Mechatronic Systems, FEMTO-ST Institute, Univ. Bourgogne Franche-Comté, CNRS, F-25000 Besançon, France (e-mail: jbafumba@femto-st.fr; joel.agnus@femto-st.fr; philippe.lutz@femto-st.fr; mratoton@femto-st.fr). Color versions of one or more of the figures in this article are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TIM.2019.2950760 based on the piezoelectric reverse effect. The piezoelectric reverse effect, the key effect used to realize piezo actuator functions, consists in the deformation of a piezoelectric material due to the applied electric field. PEAs play a pivotal role for experimental investigation and manipulation of nanoscale biological, chemical, material, and physical processes. The high resolution, high bandwidth, small size, and high force density of piezoelectric materials make them a good contender as actuators when developing systems acting at the nanoscale. However, nonlinear effects, such as hysteresis and creep, affect the position accuracy of piezoelectric-based positioning systems if not compensated BIB007 . Often, feedback position sensors are mounted to the systems to eliminate the hysteresis and creep BIB014 - BIB013 . Nonetheless, the integration of sensors, to enable quality and robust servo control, poses specific problems for microrobots, and this is especially true when the number of degrees of freedom (DOFs) increases. There are sensors with very good resolutions, sometimes associated with a fairly large range. However, we can note that the best performances on this subject are at the expense of a higher price and a larger footprint (interferometry, encoders). In addition, these sensors mostly only perform measurements with a single DOF, which therefore implies the multiplicity of sensors as soon as a complex measurement is necessary BIB015 -  . Alternative solutions to the integration of external position sensors can be grouped into three categories as follows. 1) With feedforward voltage control schemes BIB016 , BIB010 whose performance depends on the accuracy of the PEA's model. Feedforward voltage control schemes do not account for model uncertainties and external disturbances. 2) With the use of charge amplifiers (charge control scheme), where the PEA is driven by a charge input instead of voltage input BIB002 , BIB004 . Their performance is related to the hardware complexity. As for feedforward voltage control schemes, charge amplifiers do not account for model uncertainties and external disturbances, 3) By simultaneously using the piezoelectric material as an actuator and its own sensor, also called self-sensing actuation (SSA) techniques BIB017 - BIB018 . For further performance improvement, combined control schemes, such as feedforward-feedback voltage control 0018-9456 © 2019 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. scheme  and integrated voltage-charge control strategy BIB011 , were introduced to overcome the limitations imposed by the need to balance a high-bandwidth precision positioning with robust closed-loop stability in the presence of unmodeled dynamics, uncertainties, and disturbances. In the integrated voltage-charge control scheme, the charge-based technique handles the hysteresis nonlinearity, while the voltage feedforward accounts for the dynamics. In this architecture, the charge amplifier is used for a traditional charge-based control. This can successfully reduce the hysteresis nonlinearity. However, the charge control cannot guarantee the position accuracy in the presence of higher dynamics or external disturbances. The integrated voltage-charge control strategy allows a control of a linearized PEA but lacks robustness against external disturbances and is likely to induce a loss in accuracy during the positioning. Feedforward-feedback voltage control scheme, if properly designed, can be robust to both internal uncertainties in the modeling and external disturbances; however, the feedback branch requires sensors. As already mentioned, unfortunately, accurate sensors are bulky, making them difficult to use for downscaling manipulation systems. Soft sensors aid in solving the problem created by the unavailability of embeddable and precise sensors by providing a software backup for it. They are inferential estimators that established themselves as a valuable alternative to the traditional means for the acquisition of process observations when hardware sensors are unavailable or unsuitable. They are based on control theory and provide an estimate of the internal state of a given real system, from available measurements thereof. Software sensors use more suitable hardware sensors that do not directly measure the physical signal of interest; however, associated with an algorithm, they make it possible to reconstruct the signal of interest. SSA is the PEA's soft-sensor implementation. As for soft sensors, SSA methods do not intend to completely get rid of the hardware sensors but rather to use less bulky and inexpensive sensors associated with an observer/estimator to reconstruct the signal of interest with at least the same resolution as the substituted sensor. The surrogate sensor measures physical signals produced by the PEA itself (throughout current, voltage drop, and so on) and allows, thanks to the observer/estimator, to derive its displacement, its perceived strength, or even the temperature variation of its surroundings. Piezoelectric SSA allows actuating a piezoelectric device while measuring its strain and/or the stress applied upon it by using itself as its proper sensor. In a piezoelectric SSA, the sensor and actuator are truly collocated. Thus, this intrinsic technique may be used in a closed loop and benefits from a number of advantages related to the closed-loop stability known to collocated control  , BIB008 . The piezoelectric SSA technique was first proposed in BIB001 for structures' vibration suppression. Sooner, several independent applications began to emerge from vibration suppression of beams BIB003 , BIB009 and scanning tubes BIB012 to control applications for precise positioning BIB005 , BIB006 . The main advantage of SSA is the reduction of space occupancy, allowing for better miniaturization of micromanipulation/microassembly cells. An additional Goldfarb and Celanovic [27] . This model comprises an electrical domain made of the piezoelectric capacitance C pea and the operator, which describes the hysteresis nonlinearity H(·). A mass (M) spring (k) damper (b) system shows the mechanical domain. The transduction factor is from the mechanical to the electrical domain α me and from the electrical to the mechanical domain α em . advantage is that the dynamics of the PEA is not affected because no sensor is mechanically attached thereto. SSA can be classified into two approaches as follows: 1) SSA based on the piezoelectric direct effect; 2) SSA based on the PEA's change of electrical properties. This article, which reviews the SSA techniques used for both precise positioning and handling force in piezoelectricbased nanopositioning systems, is organized as follows. We begin by reviewing the SSA based on the piezoelectric direct effect techniques, i.e., SSA techniques that employ the PEA's strain-induced charges as a means to estimate its generated displacement. The electrical circuits and constraints on the physical properties of the PEA to be considered for its implementation are presented in this section. This is followed by an overview of the SSA based on the PEA's change of electrical properties techniques in Section III. Methods used for the real-time evaluation of the PEA's impedance variation are outlined, accompanied by simplified block diagrams in order to highlight the differences, advantages, and disadvantages to be known before adopting one of these two SSA approaches. Then, a review of emerging solutions for the simultaneous displacement and force estimation from either charge or impedance measurement is provided in Section IV.