An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> IV. SIMULTANEOUS FORCE AND POSITION ESTIMATION THROUGH SSA <s> Summary form only given as follows. A nano-metric precision three degrees of freedom (DOF) positioner is designed and fabricated. Actuation is based on piezo-electric stack actuators. Capacitive gap sensors with less than 1.0 nanometer resolution are used for position feedback. In order to design a proper closed loop controller, the open loop characteristics of the nano-positioner (hysteresis, static stiffness, drift, frequency response, and the coupling effects) are experimentally investigated. A CMAC neural network control algorithm was applied in order to provide online learning and better tracking capability compared to a standard PID control algorithm. The closed loop controller was implemented using C language on a DSP based PC bus board. The learning CMAC control provides significantly better tracking accuracy and robustness against hysteresis and drift effects. <s> BIB001 </s> An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> IV. SIMULTANEOUS FORCE AND POSITION ESTIMATION THROUGH SSA <s> High-performance actuation is always desirable in a dexterous high-precision manipulation system. In this paper, we first develop a single-degree-of-freedom piezoelectric translator composed of a piezoelectric stack, a monolithic leaf spring and a preload mechanism. The displacement resolution reached by this translator is better than 10 nm, while its natural frequency is over 2 kHz. Based on the developed piezoelectric translator, a micro-manipulator is then designed, which is capable of producing micro-motions in six degrees of freedom. The design characteristics and kinematics of this micro-manipulator are investigated. An effective kinematic model used for the real-time control is presented, and the operation performance of the micro-manipulator is discussed further. <s> BIB002 </s> An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> IV. SIMULTANEOUS FORCE AND POSITION ESTIMATION THROUGH SSA <s> Ultra-precision positioning mechanisms with a high displacement resolution and long travelling range are becoming increasingly popular in industrial applications. In this design note, we discuss the design and characterization of a new piezo-driven ultra-precision stepping positioner composed of three piezoelectric actuators and a monolithic flexure hinge mechanism. The analytical models are presented, the formulae for static and dynamic characteristics are derived and the design process is described. It follows that the performance characterization is carried out. It is confirmed that this device is capable of performing a stepping motion with a high reproducibility, as well as a single movement with a displacement resolution of over 10 nm and a natural frequency of over 432 Hz. <s> BIB003 </s> An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> IV. SIMULTANEOUS FORCE AND POSITION ESTIMATION THROUGH SSA <s> Abstract The design, fabrication, modelling, and control of a two-axis electrostatic microactuator for precision manipulation tasks is described. A high-yield fabrication process using deep reactive ion etching (DRIE) on silicon-on-insulator (SOI) wafers forms the 3-D high aspect ratio transverse comb drives that produce a relatively large electrostatic force. The structure is suspended by removing the substrate beneath the comb drives, therefore, a ground plane is not needed in order to compensate for electrostatic levitation. Among other advantages of the developed process is a dice-free release of wafer structures, allowing fragile structures to be individually packaged. Notching or footing effects and bowing effects are well-known problems in DRIE on SOI wafers. Techniques to overcome notching and bowing effects using a PlasmaTherm SLR-770 etcher are presented that do not require hardware modifications. A capacitive position sensing mechanism, capable of measuring displacements up to 4.5 μm with a resolution of 0.01 μm in both X and Y is integrated to provide position feedback. A nonlinear model inversion technique is proposed for nonlinear electrostatic microactuation system identification and improving system linearity and response. Pull-in instability limits the travel distance of transverse comb drive actuators. Using a nonlinear model inversion technique, a stable travel distance of 3.7 μm with a 4.5 μm gap has been achieved. <s> BIB004 </s> An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> IV. SIMULTANEOUS FORCE AND POSITION ESTIMATION THROUGH SSA <s> This paper describes an approach to controlling the force generated by a piezoelectric actuator (PEA) accurately without using any force sensor. A model PEA is proposed that includes a new asymmetric hysteresis operator and that takes the external force into account. A detection model is deduced that allows computation in real time of the PEA elongation and generated force starting from the measurement of the driving voltage and current. This detection model is used to replace a force sensor for closed-loop force control of a PEA. Experiments are carried out using 2 PEAs in an experimental setup. The first actuator is the controlled actuator, and the second one is used as a dynamic controllable mechanical load. It is shown that a good control performance can be obtained whatever the mechanical loading conditions. <s> BIB005 </s> An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> IV. SIMULTANEOUS FORCE AND POSITION ESTIMATION THROUGH SSA <s> This paper presents a new method of self-sensing both of the displacement and the external applied force at the tip of piezoelectric cantilevers. Integrated electric current across piezoelectric actuators is compensated against material nonlinearities (creep, hysteresis) to provide reliable information. We propose to compensate the hysteresis by using the Prandtl-Ishlinskii static approach while an auto regressive and moving average exogenous (ARMAX) model is used to minimize the creep influence. The quasistatic estimation, electronic circuit, and aspects related to long-term charge preservations are described or referenced. As an experiment, we tested the actuator entering in contact with a fixed force sensor. An input signal of 20 V peak-to-peak (10% of maximum range) led to force self-sensing errors inferior to +/-8%. A final discussion about method accuracy and its limitations is made. <s> BIB006 </s> An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> IV. SIMULTANEOUS FORCE AND POSITION ESTIMATION THROUGH SSA <s> 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. <s> BIB007 </s> An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> IV. SIMULTANEOUS FORCE AND POSITION ESTIMATION THROUGH SSA <s> Self-sensing techniques is defined as the use of an actuator as a sensor at the same time. The main advantage of such techniques is the embeddability and the packageability of the systems. This paper deals with the development of a self-sensing technique able to estimate the displacement, the force and the state in piezoelectric cantilevered actuators. The main novelties relative to previous works are: 1) three signals (displacement, force and states) are provided at the same time instead of only two (displacement and force), 2) and these three signals are provided in a complete way, i.e. low and high frequency information can be provided (instead of exclusively low or high frequency). It is therefore possible to further use the measurement for a displacement control or for a force control by using the output feedback methods or by using modern control methods (state-feedback). In order to allow such measurement possibilities, the proposed approach consists in combining an unknown-input-observer (UIO) with the classical electrical circuit of a self-sensing. The experimental results confirm the effectiveness of the proposed approach. <s> BIB008 </s> An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> IV. SIMULTANEOUS FORCE AND POSITION ESTIMATION THROUGH SSA <s> This paper describes a self-sensing technique for a piezoelectrically driven magnetic resonance imaging (MRI)-compatible tweezer style end effector, suitable for robot assisted MRI guided surgery. Nested strain amplification mechanisms are used to amplify the displacement of the piezo actuators to practical levels for robotics. By using a hysteretic piezoelectric model and a two port network model for the compliant nested strain amplifiers, it is shown that force and displacement at the tweezer tip can be estimated if the input voltage and charge are measured. One piezo unit is used simultaneously as a sensor and an actuator, preserving the full actuation capability of the device. An on-site calibration procedure is proposed that calibrates the combined electromechanical model without requiring specific loading conditions on the inner piezoelectric actuators. Experimental validation shows an average of 12% error between the self-sensed and true values. <s> BIB009 </s> An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> IV. SIMULTANEOUS FORCE AND POSITION ESTIMATION THROUGH SSA <s> Abstract Due to the trend of miniaturization of devices, micromanipulation has been a hot topic in the last two decades. Unlike the macro world, the micro object is easy to be damaged if the contact force is not reliably detected and controlled. Hence, micro-force sensing is of great importance in micromanipulation, microassembly, medical applications, biomedical applications, materials science, dimension measurements and MEMS/NEMS for protecting micro-parts and micro-gripper from being damaged and ensuring the success of the manipulation process. This paper presents a survey of the recent methods of micro-force sensing. The working principle, detection accuracy, advantage and disadvantage of seven widely used force sensing methods are presented. Typical applications of each method in micro-assembly and micromanipulation are discussed. In addition, the comparisons among different kinds of force sensing approaches have been addressed. Moreover, another five promising micro-force sensing methods, which are confined to special component measurements or not widely used, are briefly introduced. Furthermore, two popular types of commercial micro-force sensors are listed to provide a guideline of selection for a specific application. The presented state-of-the-art overview is helpful to those engaged in micro-force sensing area to know the recent development and research tendency on micro-force sensing. <s> BIB010 </s> An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> IV. SIMULTANEOUS FORCE AND POSITION ESTIMATION THROUGH SSA <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> BIB011 </s> An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> IV. SIMULTANEOUS FORCE AND POSITION ESTIMATION THROUGH SSA <s> In this study a new relationship between effective capacitance, position, and force of a piezoelectric actuator is presented. This relationship in combination with an existing constitutive relationship between charge, position, and force, can pave the way for simultaneous sensorless position and force identification. A test setup is built to study the feasibility of using the proposed relationship. Satisfying experimental correlation between effective capacitance, force, and position has been achieved using a second order Taylor series. <s> BIB012 </s> An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> IV. SIMULTANEOUS FORCE AND POSITION ESTIMATION THROUGH SSA <s> Microelectromechanical system (MEMS) reveals excellent flexibility and adaptability in miniaturization devices owing to its compact dimension, low power consumption, and fine performance. As a typical type of miniaturization tool, MEMS-based robotic microgripper has been widely employed in the manipulation of tiny micro-objects, material characterizations, and so on. This paper presents the state-of-the-art survey of prevalent MEMS-based actuation and sensing techniques, which can be applied in microgrippers. Five main types of actuators are reviewed in this survey, namely, electro-thermal actuators, electrostatic actuators, shape memory alloy actuators, piezoelectric actuators, and electromagnetic actuators. A review of recent sensing techniques is also conducted, which includes four popular sensing approaches in terms of capacitive sensors, electrothermal sensors, piezoresistive sensors, and piezoelectric sensors. Their advantages, disadvantages, and applications have been discussed in detail. Some perspectives on the future development are presented. <s> BIB013 </s> An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> IV. SIMULTANEOUS FORCE AND POSITION ESTIMATION THROUGH SSA <s> This article is devoted to simultaneous displacement and force self-sensing using a single piezoelectric stack actuator. Values of displacement and force are estimated from measurements of charge and applied voltage. To calibrate the self-sensing algorithm, a parameter identification procedure is presented that accounts for hysteresis under varying displacement and force conditions using a standard Prandtl–Ishlinskii hysteresis operator. Quasi-static validation experiments are carried out on a custom-built test rig that shows low average estimation errors of $0.5 \%$ and $-0.4\%$ with standard deviations of $2.7\%$ and $3.1\%$ in displacement and force, respectively. <s> BIB014 </s> An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> IV. SIMULTANEOUS FORCE AND POSITION ESTIMATION THROUGH SSA <s> Abstract This article extends the conventional permittivity change based displacement self-sensing technique for piezoelectric actuators to an impedance change based displacement–force self-sensing technique. The presented methodology evaluates changes in capacitance and resistance at an electrical resonance frequency and uses a third order polynomial fit to estimate displacement and force. Experimental validations show a mean error of 1.8%, and an error standard deviation of 1.9% for displacement and a mean error of 1.7%, and an error standard deviation of 1.8% for force. <s> BIB015 </s> An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> IV. SIMULTANEOUS FORCE AND POSITION ESTIMATION THROUGH SSA <s> This paper describes a new self-sensing technique for piezoelectric actuators that estimates both displacement and force from voltage and charge measurements. The novelty of this technique lies in the use of a constitutive model with nonlinear capacitance and an exponential hysteresis model. The advantage of the presented self-sensing technique over similar techniques in the literature is that it only requires one parameter identification experiment and its hysteresis model is computationally efficient. The control performance of the self-sensing technique is evaluated in a sensorless displacement and force control structure. Validation experiments are carried out on a two degree of freedom test setup that mimics micropositioners by generating simultaneously varying displacements and forces. Less than $\text{3}\%$ absolute average errors are obtained for both displacement and force. <s> BIB016
Nanopositioners could perform a variety of precision machining operations BIB003 , BIB001 , and they might be configured to assemble micrometer-sized parts BIB002 - BIB004 . However, it is worth noting that microscopic objects are generally fragile (objects of small dimensions that are often made of special materials) so that the forces exerted during their handling must be adapted and controlled. Whereas all the listed SSA techniques in the previous sections have often been used for constant force operating conditions, applications, such as microgrippers BIB013 , BIB010 , exhibit both varying displacement and force. Due to the additional constraint of the handling force of micro-objects, some researchers have focused on the development of SSA's techniques that allow the simultaneous estimation of displacement and force. These techniques exploit either the piezoelectric direct effect or the PEA's change of electrical properties. Two measurements are required to simultaneously estimate displacement and force. The first attempts for simultaneous displacement and force estimation were the extensions of charge-based SSA techniques. Badel et al. BIB005 proposed a model that computes the generated force and the elongation of the PEA from the measurements of the produced electrical charges and input voltage applied to the PEA. This model included a dedicated hysteresis operator that allowed the hysteretic properties of the PEA to be considered. The detection model combined with a PID controller has been used successfully, and experiments conducted to show the feasibility of SSA for force control of a PEA. An identical approach was used by McPherson and Ueda BIB009 to estimate the force and displacement at the tip of a piezoelectric-based driven magnetic resonance imaging (MRI)-compatible tweezer and by Mansour and Seethaler BIB014 , BIB016 for simultaneous displacement and force estimation of piezoelectric stack actuators. Ivan et al. BIB006 , such as in BIB009 , BIB005 , and BIB014 , used the measured electrical charges, the input voltage, and an hysteresis operator and added an ARMAX model to account for the creep effect and provide a more reliable estimate of the steady-state PEA's generated displacement and force applied thereto. Rakotondrabe et al. BIB011 extended the proposed scheme in BIB006 to include the SSA scheme for dynamic displacement estimation suggested in BIB007 and  and thus allow the estimation of the PEA's generated displacement in both steady state and dynamics, while the force estimation remained in the steady state. In the proposed approach, the estimated displacement was used as a feedback signal, whereas the estimated force was only being displayed. In order to estimate the PEA's generated displacement, the force applied thereto, and state, all in a full way (steady state and dynamics, i.e., low and high frequencies), Rakotondrabe BIB008 introduced an unknown input observer (UIO) in the SSA approach proposed in BIB007 . The main advantages of the latter over previous SSA approaches are: 1) the possibility of feedback control for the displacement and for the force and 2) the possibility to use modern control such as state-feedback. The SSA technique introduced in BIB006 was destined for the simultaneous estimation of the PEA's generated displacement and force applied thereto for steady state. One drawback of this method is having relatively large transient errors, which makes it hard to be used in fast applications. Before its extension to a full (i.e., low and high frequencies) displacement, force, and state estimation BIB008 , Mansour and Seethaler BIB012 proposed an alternative approach for simultaneous estimation of the displacement and force for both the transient and steady state. Rather than using measurements of produced charges and the input voltage, this method utilizes the measurements of the produced charges and effective capacitance. This approach eliminates the need for a mathematically complex inverse hysteresis models and is supposed to be largely rate independent as well as robust against the creep. More recently, Mansour and Seethaler BIB015 proposed a technique for real-time detection of the variation of the capacitance and resistance of the PEA at a resonance frequency and a third-order polynomial fit for the simultaneous estimation of the displacement and force. Conducted experiments with this technique have provided the estimates of the displacement and force equivalent or better than the previously reported displacement-force SSA techniques that use charge and voltage measurements. However, the performances for dynamic operations of the technique proposed in BIB015 yet need to be investigated.