An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> A. Voltage-Based SSA <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> A. Voltage-Based SSA <s> A self-sensing actuator is a new concept for intelligent material, where a single piece of piezoelectric element simultaneously performs as both a sensor and an actuator. This idea should be advantageous especially for control of flexible structures. The key of this device is an electric bridge circuit that includes a piezoelectric element as a component. This circuit could give significant information about strain in the element if it were well-balanced. Our aim is to design controllers which enable practical self-sensing actuation in the presence of uncertainty that loses the balance of the circuit. In this paper, we proposed two approaches to realize self-sensing actuation which deal with this uncertainty differently. Experimental results proved the effectiveness of self-sensing actuation in both vibration suppression and tracking control of a cantilever. <s> BIB002 </s> An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> A. Voltage-Based SSA <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> A. Voltage-Based SSA <s> In this paper, self-sensing control of a micro-actuator for the hard disk drive is presented. The micro-actuator is a suspension driving type. The micro-actuator uses a PZT actuator pair, installed on the assembly of the suspension. The self-sensing micro actuator can be used to form a combined actuation and sensing mechanism. Direct velocity feedback control and positive position feedback control of a self-sensing microactuator for an HDD is presented. The experimental results show that the direct velocity feedback controller and the positive position feedback controller are effective in suppressing the vibration modes. Experiments successfully demonstrate that the self-sensing actuator can be used for active feedback control of the HDD suspension assembly vibration. <s> BIB004 </s> An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> A. Voltage-Based SSA <s> This article describes new perspectives on SPM-related science and technology, based on systems and control theory. These perspectives have led to a better understanding of SPM technology, overcome hurdles that limited the efficacy of SPM, and resulted in new modes of SPM-based interrogation. ThNcAFM, based on systems principles, has made it possible to image with resolution as high as 0.25 Aring in ambient conditions. The orders-of-magnitude improvements achieved in areas such as precision positioning, sample imaging, and sample detection rates emphasize the potential of systems tools in nanotechnology. The concept of using models in online operation has significant potential for SPM. For instance, TF-AFM, which uses models for online operation, resolves competing objectives of high resolution and detection rate by using a design from a systems perspective that makes detection bandwidth independent of the quality factor of the probe and, therefore, independent of resolution. The systems perspective also facilitates the interpretation of data since it provides a precise means for delineating the effects of the inherent dynamics of the interrogation system from the properties of the sample being probed. Devices such as SPMs are sensitive to operating conditions, ambient conditions, and modeling inaccuracies. Modern control theory provides a framework where such challenges can be effectively addressed. This aspect translates to reliable experiments in terms of repeatability, which is crucial in many nanoscience studies. <s> BIB005 </s> An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> A. Voltage-Based SSA <s> This paper presents the experimental validation of an active control approach to improve the damping of a spindle system for wood machining. The active control was implemented using piezoelectric actuators in push–pull configuration with real-time control capabilities. The adaptive control strategy based on the linear quadratic Gaussian is first modeled within MATLAB/Simulink and then implemented on the real spindle system. Experimental tests were performed on the small-scale planer prototype to validate the simulation models. Moreover a cutting force observer which can be used to continuously monitor the cutting process is also implemented and its performance is presented. <s> BIB006 </s> An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> A. Voltage-Based SSA <s> This paper presents a position control approach considering vibration suppression using self-sensing techniques in piezoelectric actuators. In order to achieve the high precision positioning using piezoelectric actuators, mechanical vibrations as well as nonlinear properties should be compensated. In this paper, a robust vibration suppression control system against resonant frequency variations is designed, where a minor loop aided by a self-sensing technique is added on the position control system. In the minor loop design, the reduction of sensitivity characteristic at around the vibration frequencies is considered to suppress the residual vibration for the reference and disturbance. Major loop for augmented plant including self-sensing minor loop, on the other hand, is designed by considering system stability and servo characteristic. The proposed approach has been evaluated by experiments using a piezo-driven stage. <s> BIB007 </s> An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> A. Voltage-Based SSA <s> The motorized spindle is the core component of CNC machine tools, and the vibration of it reduces the machining precision and service life of the machine tools. Owing to the fast response, large output force, and displacement of the piezoelectric stack, it is often used as the actuator in the active vibration control of the spindle. A piezoelectric self-sensing actuator (SSA) can reduce the cost of the active vibration control system and simplify the structure by eliminating the use of a sensor, because a SSA can have both actuating and sensing functions at the same time. The signal separation method of a SSA based on a bridge circuit is widely applied because of its simple principle and easy implementation. However, it is difficult to maintain dynamic balance of the circuit. Prior research has used adaptive algorithm to balance of the bridge circuit on the flexible beam dynamically, but those algorithms need no correlation between sensing and control voltage, which limit the applications of SSA in the vibration control of the rotor-bearing system. Here, the electromechanical coupling model of the piezoelectric stack is established, followed by establishment of the dynamic model of the spindle system. Next, a new adaptive signal separation method based on the bridge circuit is proposed, which can separate relative small sensing voltage from related mixed voltage adaptively. The experimental results show that when the self-sensing signal obtained from the proposed method is used as a displacement signal, the vibration of the motorized spindle can be suppressed effectively through a linear quadratic Gaussian (LQG) algorithm. <s> BIB008 </s> An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation <s> A. Voltage-Based SSA <s> This letter presents a displacement self-sensing method for piezoelectric actuators that takes into account the effect of the deformation of these latter on their electrical impedance. A self-updating digital electrical impedance equivalent to that of the piezoelement is suggested in order to overcome the mismatch problem met when considering a static analog electrical impedance as classically used. Then, the design of an observer that performs a thorough separation of the electric current due to the direct piezoelectric effect from the measured electric current is proposed in order to estimate the piezoelectric actuator displacement. The experimental results validate the proposed approach and demonstrate the efficiency of the developed self-sensing circuit and its observer to estimate the displacement of the piezoceramics actuator for long duration measurement of constant step signal. <s> BIB009
As shown in Fig. 2(b) , an additional voltage potential across the PEA v δ emerges from its deformation. The voltage v δ is  All the strain bridge's components are chosen so that the bridge circuit is balanced, that is, C pea C 1 = C r C 2 (and R r = R L only for lower frequency nearby dc) so that v s = 0 ∀ v c . The induced voltage v δ generated due to strain in the PEA creates an imbalance in the bridge. The voltage difference between the two branches provides a sensing signal, v s = v 2 − v 1 , proportional to the strain-induced voltage v δ . The sensing voltage v s of the bridge circuit is only related to the voltage v δ , which is derived from the PEA's strain and is independent of the control voltage v c . For C pea C 1 = C r C 2 , (1) can be rewritten as follows: (2) Fig. 3 . Self-sensing strain bridge for dielectric feedthrough cancellation in case of voltage-based SSA BIB002 . For this configuration, the hysteresis nonlinearity H(·) is neglected in the literature. The dashed (− − −) part is to be considered only for lower frequency nearby dc (R r = R L ). Thence, the displacement of the PEA can be estimated through the relationship where α v is denoted as the PEA voltage-displacement coefficient. Though simple to implement, this technique has several limitations in practice. The most relevant properties are given in the following. 1) The size of the reference capacitance C r has to be all the time equal to the PEA's capacitance C pea . However, C pea is greatly influenced by the ambient temperature, humidity, preload, and control input voltage, making the success of voltage-based SSA rely on a tedious continual tuning of the reference capacitance BIB003 , BIB006 . Since it is difficult to maintain a dynamic balance of the voltage-based SSA, this results in a significant error in signal separation, which hampers the applicability of this technique and adversely affects the performance and stability of the closed-loop control system. He et al. BIB008 proposed an adaptative signal separation algorithm to estimate the gain between half-bridges to automatically adjust the bridge circuit balance to eliminate the part of v s that is related to v c . Although innovative, this method does not consider the impact of the control input voltage v c on C pea . 2) Due to the electromechanical coupling nature of piezoelectric materials, C pea is not only influenced by ambient temperature, humidity, and so on but even more by its mechanical deformation. Indeed, due to the piezoelectric converse effect, the application of an electric field creates a mechanical deformation in the PEA's crystals, and with this deformation, the PEA maintains its volume but does not keep the same geometry due to the Poisson effect. This geometry change alters the PEA's electrical properties. Therefore, an equivalent electrical model that does not account for the variations of C pea due to v c would not accurately depict the electrical characteristics of piezoelectric materials BIB009 . 3) The flow of free electric charges responsible for generating v δ continues until they neutralize the polarization effect. Thus, bridge circuits BIB001 , BIB007 , BIB004 are often used for strain rate sensing and are effective in suppressing the vibration modes but are not easy to balance for long-term measurements. 4) The PEA's strain is said to be linear to the produced charges Q δ . Voltage-based SSA exploits v δ rather than According to BIB005 , the relationship between v δ and the PEA's strain depends on C pea behavior. Since C pea value varies according to several factors among which v c and F ext , a linear relationship between v δ and the PEA's generated displacement δ is not always guaranteed.