Feedforward control with rate-dependent hysteresis compensator for piezoelectric micro stage (Conference Presentation)

This paper presents a novel piezoelectric XY micro-displacement scanning stage (MDSS), which features a parallel structure based on compliant mechanisms and has a compact configuration. Since the coupling problem between two motion axes, an innovative elliptical compliant restraint mechanism (ECRM) with a compact layout is proposed and utilized in XY MDSS to obtain high motion accuracy. And the XY MDSS can realize compact structure and lower input stiffness for a large workspace owing to the ECRM simultaneously. Due to the limited displacement of the piezoelectric stack actuator, compliant amplification mechanism is applied to achieve a large stroke. In order to estimate the static and dynamic characteristics theoretically, Castigliano’s second theorem and Lagrange’s method are utilized to establish the analytical models of the newfangled ECRM, compliant amplification mechanism, and XY MDSS. The finite element analysis and experimental tests are carried out to evaluate the performances of XY XDSS, and the results are all in correspondence with analytic solutions, which further validate the correctness of the analytical modeling methodologies. Experimental results show that the XY MDSS can realize a workspace of 58.8 μm × 51.5 μm with a resonance frequency of 576.5 Hz and nanometer-level resolution. The effectiveness of the designed ECRM is also proved simultaneously, which could well limit the coupling motion. The theoretical studies, finite element analysis, and experimental testing all demonstrate that the designed XY MDSS with ECRM has good performance while having a compact structure.

We present a distributed compliant mechanism, which acts like a transmission between a flapping wing of a micro air vehicle and a laminated piezoelectric actuator. The piezoelectric bimorph actuator is connected in cantilever configuration with the compliant mechanism at its free end. The mechanism takes translational deflection at its input from the piezoelectric actuator to provide angular deflection at its output, which causes flapping. We used spring-level model and topology optimization to obtain the design of the mechanism. The design of the mechanism has been finalized by analyzing the design considering beam model with geometric nonlinearity. The final mechanism is a planar structure of 1 mm thickness and 40 mm ×24 mm in-plane footprint. The input stiffness of the compliant mechanism is 711 N/m and the output torsional stiffness is 0.014 Nm/rad. The compliant mechanism is tested with a piezoelectric bimorph actuator. The mechanism takes ±1 mm deflection with ±0.2 N block force at 30 Hz as an input and produces ±6° flap angle at 30 Hz as an output. The first fundamental frequency of the mechanism is 391 Hz, which is almost 13 times greater than our assumed wing flapping frequency 30 Hz. The final mechanism is prototyped with a 3D printer using VeroWhitePlus RGD835 material and tested with a piezoelectric bimorph actuator using a bench-top experimental set-up.

Piezoelectric actuator (PEA) is one of the key component in micro/nano manipulation equipment. However, the inherent hysteresis significantly limits its motion accuracy. In this paper, a Prandtl-Ishlinskii (PI) based feedforward and feedback compound control strategy is designed to eliminate the hysteretic nonlinearity of PEA, and thus linearizing the input/output relationship. An inverse hysteresis model is directly identified and validated using the open loop characteristics of the PEA. The inverse hysteresis model is used as the feedforward compensator. In order to further improve the performance of the PEA, a feedforward and feedback compound control strategy is also designed and tested. A PEA equipped with strain gauges is selected in the experimental investigation. Experimental results show that the hysteresis can be successfully compensated using only feedforward control, and better performance is achieved using the feedforward and feedback compound control.

Piezo-driven compliant actuators capable of out-of-plane displacement from the substrate are urgently required in the fields of micro/nano manipulations and active optics, where compact size and low-profile configurations are often critical. In this paper, a two-stage amplification mechanism is developed by orthogonal series connection of a bridge-type mechanism and a Scott-Russell mechanism, for the sake of a large amplification ratio and high stiffness. The low-profile configuration is realized by horizontally mounting the piezoelectric actuator within the planar bridge-type amplification mechanism. The bridge-type mechanism initially amplifies the output displacement of the piezoelectric actuator. A compound guiding mechanism at the output end significantly enhances the equivalent stiffness and constrains parasitic displacements of the bridge-type mechanism. The second-stage Scott–Russell mechanism, further amplifies and converts the in-plane displacement into out-of-plane motion. The kinematic and static model of the developed mechanism is established using the compliance matrix method, enabling precise prediction of the amplification ratio and input/equivalent stiffness. Finite element simulations and experimental tests on the prototype validate the modeling accuracy and mechanical performance of the proposed low-profile amplification mechanism, demonstrating a large amplification ratio of 15.70, a high resonant frequency of 312.50 Hz, and a load-bearing capacity up to 20 N.

To enhance the performance for high-speed tracking control of a piezoelectric tube actuator (PTA), an improved direct inverse rate-dependent PI model is obtained in this paper, and then adopted to design a practical feedforward controller achieving high-speed tracking control for a high-frequency trajectory with strong robustness. Specifically, based on the Prandtl-Ishlinskii (PI) model, an improved direct rate-dependent inverse model is set up for the PTA, with a polynomial function module introduced to eliminate the influence caused by the structure nonlinearity. Then, considering the features of the PTA structure, some preprocessing procedure is proposed to handle the collected experimental data, with the results utilized to identify all the unknown parameters over a wide bandwidth. Based on the obtained model, a practical feedforward controller, which presents the advantages of high-speed response, simple structure and convenient implementation, is then designed to enable the PTA to track high-frequency trajectories with satisfactory precision. Some experimental results are provided, which clearly demonstrate the high precision of the constructed/identified model, and the satisfactory performance of the proposed practical feedforward tracking control law.

Piezoelectric actuator can cause severe non-linearity deformation under higher electrical field, the position accuracy of it will be damaged. The nonlinearity of piezoelectric actuator is related not only to nonlinearity of material, creep and hysteresis, but also to the dynamic performance of actuator. The hysteresis and nonlinearity of dynamic performance is a key factor for piezoelectric actuator to affect improvement of controlling accuracy. With the compound control algorithm of feed-forward and digital PID control, the closed-loop system is established to adjust dynamic response of the compliant lever mechanism of single degree of freedom. It is indicated by experiment that the time of dynamic response declines from 90ms to 50ms, the rapid response of mechanism is realized.

A driving power for piezoelectric actuators is presented in this paper. The power supply is the key component in piezoelectric micro displacement system. The dedicated DC driving power is designed toward the piezoelectric micro angle actuator, through changing the charging current of piezoelectric ceramic to control its movement speed, thereby control the displacement. The positive voltage float regulating expansion circuit is consisted of LM723CN, to realize the stable controllable voltage output with high precision. The high voltage linear amplification circuit uses discrete components design method. Through the two stage amplifying drive signal, a closed loop negative feedback circuit system is set, and it have small output resistance, strong load capacity. The stability of the output voltage is improved. The system meets the requirements of the high precision, strong drive capabilities, simple structure and good stability.

This paper proposes a new compliant mechanism for the stroke amplification of piezoelectric actuators. Compared with the existing ones, this compliant stroke amplification mechanism (CSAM) has several advantages including lightweight, less stress concentration, large motion range, as well as ease of manufacture in macro- and micro-scales, mainly due to the completely distributed compliance and largely reduced moving mass. Kinetostatic models of the CSAM, with consideration of the payloads applied on the output stage, are derived for quick and insightful determinate analysis, which enables optimization of the associated parameters to achieve different objectives. The results obtained from the kinetostatic models are in reasonable agreement with the FEA simulation results, with less than 3.8% difference when the input displacement is less than 10 µm. An optimization method, based on the analytical models, is introduced and employed to increase the amplification ratio of the CSAM by up to 240%. The optimized CSAM is an excellent candidate for the stroke amplification of piezoelectric actuators, which is fabricated and experimentally tested. The optimization method is able to be extended to design other compliant mechanisms with optimized size, shape and topology configuration simultaneously.

A bioinspired tethered MAV model is designed, constructed and studied for structural dynamic characteristics using novel materials and methods. The model consists of two flapping wings, a compliant flapping mechanism, and a supporting chassis. Large size insects such as dragonfly and cicada are considered as inspiration for the designing purposes. The wings and mechanism designed in this study are a simplified form of the natural counterparts. These idealized bioinspired structures are first studied for structural dynamic characteristics using finite element methods. Carbon nanotubes/polypropylene (CNTs/PP) nanocomposite stiffeners and a thin LDPE membrane are used to realize the designed wing model. The use of this novel material composition resulted in a lightweight, thin, and flexible wing capable of large amplitude passive bending-twisting motion. For constructing the flapping mechanism, a novel compliant mechanism is fabricated and attached with a piezoelectric actuator of cantilever form. The compliant mechanism is designed with CNTs/PP nanocomposite flexure joints supported using rigid carbon fiber/epoxy composite linkages. The fabrication of wing stiffeners and mechanism flexures from lab developed CNTs/PP nanocomposite materials is carried out using laser micromachining based manufacturing technique. The complete MAV model is constructed by assembling the wings and mechanism with a carbon fiber/epoxy composite chassis. The final assemblage is a two-winged MAV model of a total mass, body length, and wingspan of 0.6 1g, 60.46 mm, and 90.14 mm, respectively. An external customized power supply is developed and used with a microcontroller to actuate the flapping mechanism and wings during experiments. The computational structural analysis showed that no resonance occurs at the mechanism, all the first four fundamental modes are at the wings. This is advantageous for accurate and efficient motion transmission to the wings. The model generates large-amplitude wing deflections with a very small amplitude input excitation from the actuator - useful for higher aerodynamic performance. Experimentally, the structural dynamic analysis of the MAV model is carried out using an in-house high-speed 3D digital image correlation (DIC) technique, which reveals that the wings generate bending dominated deforming shape with marginal twisting and positive camber (during downstroke). Structural dynamic results from computations are in good agreement with the experiments that validates both of the approaches for further advancements in the developed MAV model. Overall outcome of the current work is a simplified biomimetic MAV design, a potential candidate for developing mechanically efficient MAV models.

Compliant mechanism flexure hinge was frequently utilized in precision enginering in recently years such as bridge-type and rhombus-type compliant mechanism. The previous study used approximation mathamatic model to estimate displacement amplification ratio. But the result of this investigations obtain displacement amplification ratio aproximatly 30. It identify so difficult to obtain maximum and precision value. Therefore, in this paper designed new model for bridge-type compliant flexure in SOLIDWORK. Displacment amplification ratio was calculated by using finite element method in ANSYS. The simualtion result reveal that ouput displacement increase from 0.506 mm to 0.648 mm when length of input body increase from 5 mm to 15 mm with thickness of flexure hinge of 0.3 mm and input displacement of 0.01 mm. The displacement amplifycation obtained from 50.6 to 64.8. concentration stress increase from 78.7 MPa to 101.5 MPa. Moreover, input incline angle between two flexure changes from 1.2 degree to 1.6 degree, with length of input body of 5 mm and the input displacement of 0.01 mm, output displacemt increases from 0.505 mm to 0.521 mm. The displacement amplification ratio obtained from 50.5 to 52.1 and concentration stress increased from 78.7 MPa to 80.16 MPa and then reduce to 74.19 MPa. The length of input body has significant effected while the incline angle between two flexure hinge from 1.2 degree to 1.6 degree has slightly effected on the displacement amplification of bridge-type compliant mechanism.

Adaptive sliding mode control with hysteresis compensation-based neuroevolution for motion tracking of piezoelectric actuator

Micro actuators are irreplaceable part of motion control in minimized systems. The current study presents an analytical model for a new Hybrid Thermo Piezoelectric micro actuator based on the combination of piezoelectric and thermal actuation mechanisms. The micro actuator structure is a double PZT cantilever beam consisting of two arms with different lengths. The presented micro actuator uses the structure of electrothermal micro actuator in which polysilicon material is replaced by PZT. Also the voltage and poling directions are considered in the lengthwise of PZT beams. As a result, the piezoelectric actuation mechanism is based on d 33 strain coefficient. The tip deflection of micro actuator is obtained using Timoshenko beam theory. Analytical results are compared with FEM results along with other reported results in the literature. The effects of geometrical parameters and PZT material constants on actuator tip deflection are studied to provide an efficient optimization of HTP micro actuator.

In this paper, a probabilistic design approach is presented to evaluate the reliability of piezoelectric micro actuators. Based on the relationship between the lifetime, and degradation mechanism of piezoelectric actuators, and the electric field strength, the concept of "electric strength" is proposed to indicate the electric field strength of the piezoelectric actuators at a specified lifetime. The lifetime (number of cycles to failure) of the piezoelectric actuator, electric strength, and electric load are considered as the random variables; and their probability distributions are discussed. The interference model of electric load, and electric strength is introduced to the reliability design of piezoelectric micro actuators. By this approach, the relationship between the reliability, and the lifetime of the piezoelectric actuator can be given. A case study of the disk drive head positioning system demonstrates the application of the approach.

In this paper, we investigate the attitude manoeuver planning and tracking control of the flexible satellite equipped with a coilable mast. Due to its flexible beamlike structure, the coilable mast experiences bending and torsional modal vibrations in multi-direction. The complex nonlinear coupling and other external disturbances significantly impact the achievement of high-precision attitude control. To overcome these challenges, a robust attitude tracking controller is proposed for easy implementation by the Attitude Determination and Control System (ADCS). The controller consists of a disturbance compensator, feedforward controller and output feedback controller. The compensator, based on a Nonlinear Disturbance Observer (NDO), effectively compensates for the cluster disturbances caused by vibrations, environmental factors and parameter perturbations. The feedforward controller tracks the desired path in the nominal satellite model. Furthermore, the output feedback controller enables large-angle manoeuver control of the satellite and evaluates the suppression effect of the controlled output on the observation error of cluster disturbances used the${L_2}$-gain. Simulation results demonstrate that the proposed controller successfully achieves high-precision attitude tracking control during large-angle manoeuvering.

Coupled dynamic modeling of piezo-actuated compliant mechanisms subjected to external loads