Displacement Of Actuator Research Articles

Experimental Analysis of Hysteresis in the Motion of a Two-Input Piezoelectric Bimorph Actuator

This article presents a comparison of hysteresis courses in the motion of a two-input actuator (bimorph) and hysteresis in the motion of a single-input actuator (unimorph). The comparison was based on the results of laboratory and numerical experiments, the subject of which was an actuator built of three layers: a carrier layer from a glass-reinforced epoxy laminate and two piezoelectric layers from Macro Fiber Composite. The layers were glued together, and electrodes in the Macro Fiber Composite layers were connected to a system that included an analogue/digital board and a voltage amplifier. The main purpose of this research was to compare the characteristic points of the hysteresis curves of the displacement of the bimorph actuator with the characteristic points of the hysteresis curves of the unimorph actuator. Based on the research results, it was noticed that, in the bimorph, the maximum hysteresis and mean hysteresis values increase faster than the maximum displacement of a beam tip. However, values of characteristic input voltages for hysteresis loops—voltage corresponding to a maximum displacement of the actuator beam tip and voltage corresponding to maximum hysteresis—are almost the same for the bimorph and unimorph. From a practical point of view, it was noticed that the unimorph is a better choice compared to the bimorph in applications in which high changes in frequencies of input voltages appear.

Relationships between pretreatment methods and properties of ion-electroactive polymers based on image analysis technology

In recent years, ion-electroactive polymers have attracted much attention because of their good flexibility, but the effect mechanisms of their pretreatment on the electrode and actuation property are not clear. In this paper, the intrinsic fractal characteristics of the interface contact of ion-electroactive polymers are characterized based on two-dimensional scanning images. The main objective of this study is to investigate the effects of different pretreatment methods on the property of ion-electroactive polymers. Based on the image analysis technology, the contact contour of the interface between the electrode and the polymer membrane was extracted using the processing software, and the fractal dimension and Hurst index of the interface were calculated by programming the calculation code using the root mean square (RMS) method and the rescaled range analysis (RRA) method. The obtained fractal parameters were then applied to the derivation of the capacitance at the interface and the effect of the fractal dimension on the displacement was discussed. The results show that the vertical preprocessing of the ion-electroactive polymer can significantly increase the capacitance and thus facilitate the output of the actuation displacement. It is a feasible way to analyze the fractal characteristics of interface by two-dimensional image analysis technology.

Quantitative analysis of time-varying delay for real-time hybrid simulation

Real-time hybrid simulation is an effective method to study the seismic performance of large or complex structures. Time delay of the hydraulic servo system is unavoidable, which affects test accuracy and may cause instability. Previous studies shown that the reality of time-varying delay has a substantial negative effect on system stability than the assumption of constant delay. However, there is currently a lack of research for the actuating system with time-varying delay in the reality time domain. Therefore, a quantitative analysis method of time-varying delay is proposed in this study. The advantage is that only the command and the measured displacement signals are needed to obtain the time-varying delay in the time domain without any prior knowledge of the system. To overcome the influence of the amplitude error on the solution results, a processing method for the amplitude modulation of the measured displacement is proposed. To accurately search for the command corresponding to the measured signal, it is proposed to solve the time-varying delay by taking segment operation on the signal according to the maximum and minimum points. The efficiency of the proposed method is verified by numerical simulation, actuator displacement tracking test, and RTHS.

Design of intelligent nonlinear robust controller for hydro-turbine governing system based on state-dynamic-measurement hybrid feedback linearization method

Due to the stochastic grid loads and intermittent renewable energy sources in today’s power grid, hydro-generator and grid system stability is increasingly dependent on the hydro-turbine governing system (HTGS). For the HTGS with external disturbances and system uncertainties, an intelligent nonlinear robust controller (INRC) based on state-dynamic-measurement feedback linearization (SDMFL) is proposed to enhance the HTGS’s control performance in this paper. This strategy establishes a dynamic output function including actuator displacement, generator rotor angle, and turbine parameters. The relationship between dynamic output and control input is derived based on this function to establish the corresponding linear state-space model. Then, the mixed H2/H∞ robust controller based on the linear model is designed to suppress the effects of external disturbances and system uncertainties on the system performance. In addition, the controller performance is optimized by levy flight and chaos theory-based gravitational search algorithm (LCGSA), resulting in the INRC. Simulations are performed in MATLAB, and the results are compared with the nonlinear robust controller (NRC) and PID controller. The results show that the proposed controller INRC improves the control performance of nonlinear HTGS with smaller overshoot and shorter adjustment time in all cases.

Sensorless force and displacement estimation in soft actuators.

Sensing forms an integral part of soft matter based robots due to their compliance, dependence on loading conditions, and virtually infinite degrees of freedom. Previous studies have developed several extrinsic sensors and embedded them into soft actuators for displacement and force estimation. What has not been investigated is whether soft robots themselves possess intrinsic sensing capabilities, especially in the case of pneumatically powered soft robots. Such an approach, that exploits the inherent properties of a system toward sensing is called sensorless estimation. Here, we introduce sensorless estimation for the first time in pneumatically powered soft actuators. Specifically, we show that the intrinsic properties of pressure and volume can be used to estimate the output force and displacement of soft actuators. On testing this approach with a bending actuator, we observed errors under 10% and 15% for force and displacement estimation respectively, with randomized and previously unseen test conditions. We also show that combining this approach with a conventional embedded sensor improves estimation accuracy due to sensing redundancy. By modelling soft actuators additionally as sensors, this work presents a new, readily implementable sensing modality that helps us better understand the highly complex behaviour of soft matter based robots.

Insight into the evolutions of microstructure and performance in bismuth ferrite modified potassium sodium niobate lead-free ceramics

In consideration of growing human health and ecological environment issues, lead-free piezoelectric ceramics have aroused heated research to develop their potential applications in electronic fields instead of toxic lead-based ones. In the present work, a ternary lead-free material system of (0.97- x )K 0.48 Na 0.52 Nb 0.96 Sb 0.04 O 3 –0.03Bi 0.5 Na 0.5 Zr 0.8 Sn 0.2 O 3 - x BiFeO 3 (KNNS-BNZS- x BF, 0 ≤ x ≤ 0.007) ceramics was designed, and the evolution mechanisms of microstructures and electrical behaviors at multiple applied fields were revealed in detail. The bimodal microstructure with an alternative fine and coarse grain size distribution feature is generally observed, while the BF doping tends to decrease grain size and increase the diffusion phase transition behaviors. As x = 0.005, the R-O-T multiphase boundary is formed at room temperature, accompanied by the presence of striped nanodomains with smaller size and regular distribution feature that exhibit the better polarization switching and the fast domain wall movement under external stimuli. In particular, an enhanced d 33 ~ 470 pC/N and a simultaneous higher T c ~ 260 °C are achieved in KNNS-BNZS-0.005BF, reflecting a better balanced development of performance by the present doping strategy. Most importantly, benefiting from the coexistence of R-O-T multiphase boundary and the lower domain wall energy, an excellent d 33 ⁎ ~ 530 pm/V is attained as well in this ceramic, which favors the better applications in high precision displacement or strain actuators. This work sheds insight into understanding the underlying physical mechanism of enhanced performance of KNN-based ceramics, substantially expanding the more applications of lead-free piezoelectric materials in electronic fields. • A new lead-free material system of KNNS-BNZS- x BF is designed. • Enhanced comprehensive performance is obtained by constructing R-O-T multiphase boundary. • The domain structures and polarization switching behaviors are revealed in detail. • The physical origin of enhanced performance is elaborated.

Design and Analysis of Mechanical Characteristics of EAP Flexible Drivers

Electroactive polymer(EAP) is a “smart material” with high energy density, high electromechanical energy conversion efficiency, simple structure, good adaptability to the working environment, etc. It can be made into various shapes to realize flexible drivers. At present, the common EAP actuator is mainly composed of EAP film wound on a spring, and the output performance of this type of actuator is related to the spring stiffness, film prestretching rate, voltage, and other factors. Its working process is actually an electromechanical coupling process. In this paper, two types of cylindrical actuators are designed and tested. The electromechanical coupling mathematical model is constructed to simulate the driver. According to the experimental and simulation results, the relationship between the output displacement and elongation strain of EAP actuator and voltage, spring stiffness, and tensile rate is analyzed. It provides a reference and basis for the design of similar actuators.

Design and analysis of optical nano electro-mechanical-system-based logic circuits relied on movable waveguides

An approach based on optical nano electro-mechanical-system (NEMS) switches is proposed in this paper to develop low-power logic circuits and processors. Based on the specific logic tasks expressed by sum-of-products (SOP) expressions, an array of switches can be appropriately arranged to implement various logic circuits. The logical output can be detected by translating the presence or absence of the light in the optical guided mode, which is controlled by the displacement of NEMS actuators under electrostatic forces. Therefore, to show the universality of the proposed method and its capability to extend processor circuits, the operation of a MUX (2:1) is analyzed. Furthermore, the presented switch’s functional characteristics and the logic circuits’ optical performance are obtained using the Finite Element Method (FEM) and Finite Difference Time Domain (FDTD) approaches. According to simulation results, the properties of the proposed switch, such as the operating voltage and the switching time, are 12 V and 2.6 μs, respectively. Consequently, the proposed fast and low-power actuator can be a promising choice for realizing low-power digital circuits, especially in the design of NEMS processors for low-power applications because of the significant reduction in its power consumption and immunity against electromagnetic radiation.

Disturbance Modeling and Prediction of Closed-Loop Micro-Actuator Stroke Usage in Dual-Stage Hard Disk Drives

Abstract This letter presents a method to model the disturbance environment of a dual-stage hard disk drive (HDD), which is then used to predict the actuator stroke usage (i.e., the range of actuator displacement used) of a closed-loop track-following controller. In particular, a data-driven disturbance modeling approach is proposed and the stochastic interpretation of the H2 norm is used to systematically estimate the micro-actuator (PZT) stroke usage of the HDD controller. Upper- and lower-bound models of the frequency response of the external disturbance environment are used to provide a range of possible stroke usage, which involves a data-driven calibration process. The accuracy of the prediction model is validated in experiments with a controller that differs from the controllers in the calibration data set.

Insights into the correlation between strain and electrostrictive coefficient of potassium sodium niobate based ceramics from relaxor structure

Eco-friendly (K, Na)NbO3 (KNN)-based electrostrictive materials have attracted increasing attention as potential candidates for high-precision displacement actuators. Although a series of breakthroughs have increased the electrostrictive coefficient of KNN-based materials with relaxor behaviour (Q33 > 0.0450 m4/C2), the electrostrictive strain is still low (<0.1%), making the improvement of the electrostrictive strain a crucial next step. Here, a KNN-based relaxor ceramic of 0.96K0.48Na0.52Nb1-xSbxO3-0.04Bi0.5Na0.5ZrO3-0.3%Fe2O3 (KNNSx-BNZ) was designed to simultaneously achieve high electrostrictive strain and Q33. The phase structure transformed from the T phase to the C phase with increasing Sb concentration, which also introduced fine grains and domains. A high electrostrictive strain (∼0.102%) and Q33 (∼0.0461 m4/C2) were obtained at x = 0.09 through a small adjustment of the structure of the relaxor, while an electrostrictive strain with low hysteresis (<10.5%) and an outstanding temperature stability (≥95%) were achieved in the broadened temperature range of 20–180 °C, representing properties superior to those of previous KNN-based and typical PZT-based materials. Our results will help researchers understand how to balance the strain and electrostrictive coefficient in lead-free materials, and thereby contribute toward accelerating the application of KNN-based electrostrictive materials in actuators.

Repeatable Actuations of Organic Single Crystal Fibers Driven by Thermosalient-Phase-Transition-Induced Buckling.

Thermosalient crystals are molecular solids that exhibit explosive motions, such as sudden breaks and jumps, due to temperature-induced structural phase transitions between two polymorphs. Therefore, the development of molecular actuators with superior speed and power by deriving mechanical work from explosive motion is a fascinating concept. However, thermosalient transitions often cause crystal disintegration, which hampers repeatable phase transitions between the polymorphs. Here, it is reported that single crystal nano/microfibers of 1, 2, 4, 5-tetrabromobenzene (TBB), whose bulk crystals exhibit thermosalient behavior at ≈40°C, can repeatedly transform between the low and high temperature polymorphs without disintegration. The structural tolerance against phase transition is attributed to the high flexibility of the nano/microfibers. It is observed that a structure consisting of a TBB fiber with both ends pinned to the substrate repeatedly buckles and straightens when the temperature is varied between 30 and 40°C. It is demonstrated that buckling can lead to large displacement actuation as compared to a simple length change of the fiber. Moreover, the force generated by the buckling fiber is estimated and it is found that it can generate a force large enough to flick an object ≈104 times heavier than the fiber itself into the air against gravity.

Linear displacement and force characterisation of a 3D-printed flexure-based delta actuator

Piezoelectric beams provide a fast, high-force and scalable actuation mechanism that could offer precise motion control to medical microdevices including invasive micromanipulators, catheters and diagnosis tools. Their small displacement range can be addressed by motion amplification mechanisms. In this paper, a piezoelectric-actuated delta-robot actuator is proposed for probe-based confocal laser endomicroscopy (pCLE) microsystems. A prototype is designed and fabricated using three-dimensional (3D) polymer compound printing for a multi-flexure compliant motion amplifier and commercial piezoelectric beams. The flexure material is optimised for maximum linear output motion. The overall robot length is 76 mm and its maximum lateral dimension is 32 mm, with 10 g overall mass, including three piezoelectric beams. An axial motion control range of 0.70 mm and a maximum axial force of 20 mN are demonstrated, at 140 V actuation voltage. The proposed actuator architecture is promising for controlling lens, fibre and micromanipulator components for medical microrobotic applications.

Biomechanical evaluation of locking versus nonlocking 2.0-mm malleable L-miniplate fixation of simulated caudal mandibular fractures in cats.

To evaluate the biomechanical properties of the mandibles of cats with experimentally created osteotomies simulating oblique ramus fractures, which were stabilized with malleable L-miniplates with either locking screws [locking construct (LC)] or nonlocking screws [nonlocking construct (NLC)], compared with those for intact mandibles. 20 mandibles from 10 adult cat cadavers. A block study design was adopted to allocate the mandibles of each cadaver to 2 of the 3 test groups (LC, NLC, or intact mandible). Mandibles within each cadaver were allocated systematically to a test group. For mandibles assigned to an LC and an NLC, a complete oblique osteotomy was performed from the mid rostral aspect of the ramus in a caudoventral direction. All mandibles were loaded in a single-load-to-failure test through cantilever bending. Load and actuator displacement were recorded simultaneously. Mode of failure and radiographic evidence of damage to tooth roots and the mandibular canal were evaluated. Biomechanical properties were compared among the groups. No iatrogenic tooth root damage was evident, but all mandibles with an LC and an NLC had evidence of screw invasion into the mandibular canal. Plated mandibles had significantly less stiffness and bending moment than intact mandibles. Stiffness was not significantly different between the LC and the NLC; the NLC had a greater bending moment at failure than the LC. The pre-yield stiffness of plated mandibles decreased when the number of screw holes overlapping the mandibular canal increased. The use of a malleable L-miniplate in a caudal mandibular fracture model is feasible. Both the LC and the NLC were inferior mechanically to intact mandibles. Type of construct used did not affect the construct stiffness significantly in tested mandibles.

Feed-forward Control of Vortices Using Real-Time Particle Image Velocimetry

Active flow control (AFC) is a topic with enormous potential for improving a wide array of technologies. This work presents the use and evaluation of a novel AFC system to apply feed-forward control to vortices formed in the wake of a wall-mounted spherical cap. A real-time particle image velocimetry (RT-PIV) system served as the sensor for the AFC system. The RT-PIV system produced 7.35 vector fields per second, each consisting of a two-dimensional grid of 5 × 37 velocity vectors. The actuator system consisted of a rubber surface that could deform using 16 independently controlled linear actuators. The actuators were controlled to apply wall-normal surface deformation at velocities proportional to wall-normal velocities measured by the RT-PIV system upstream of each of the 16 actuators. Analysis of the RT-PIV measurements in comparison to those from an offline PIV system run in parallel indicated that the RT-PIV system produced accurate flow measurements. As well, it was found that the RT-PIV system had a delay of approximately 0.09 seconds. The evaluation of the actuator system indicated that the actuator displacements were consistently damped by 20-25% and lagged the control signal by approximately 0.1 seconds relative to the input signal to the actuators. Therefore, the AFC system had a total delay of approximately 0.2 seconds and applied slightly weaker than specified actuations. These results were within anticipated values and, overall, the AFC system functioned adequately. The impacts of the flow control included disruption of the coherent ejection and sweep structures formed in the wake of the spherical cap and the formation of numerous smaller turbulent structures. As well, several of the control cases showed altered wall-normal velocity fluctuation variance fields in comparison to that of the unforced wake. This is a promising result for AFC using deformable surface actuators as it shows that the active control had a significant effect on an average quantity of the flow.

Perceived Intensities of Normal and Shear Skin Stimuli Using a Wearable Haptic Bracelet

Our aim is to provide effective interaction with virtual objects, despite the lack of co-location of virtual and real-world contacts, while taking advantage of relatively large skin area and ease of mounting on the forearm. We performed two human participant studies to determine the effects of haptic feedback in the normal and shear directions during virtual manipulation using haptic devices worn near the wrist. In the first study, participants performed significantly better while discriminating stiffness values of virtual objects when the feedback consisted of normal displacements compared to shear displacements. Participants also commented that they could detect normal cues much easier than shear, which motivated us to perform a second study to find the point of subjective equality (PSE) between normal and shear stimuli. Our results show that shear stimuli require a larger actuator displacement but less force than normal stimuli to achieve perceptual equality for our haptic bracelets. We found that normal and shear stimuli cannot be equalized through skin displacement nor the interaction forces across all users. Rather, a calibration method is needed to find the point of equality for each user where normal and shear stimuli create the same intensity on the user's skin.

Large electrostrictive coefficient with optimized Electro-Strain in BNT-based ceramics with ergodic state

Electric field-induced high strain with low hysteresis and large electrostrictive coefficient are necessary for high-precision displacement actuators. Many works focused on achieve large strain through electric field-induced nonergodic-ergodic phase transition, while the accompanied large hysteresis hinders their practical application. Here, (1-x)(Bi0.54Na0.46)0.94Ba0.06TiO3-xSrTiO3 (BNBT-xST, x = 0.1, 0.2, 0.3, 0.4 and 0.5) ceramics are fabricated by a conventional solid state reaction method. The ergodic relaxor phase in BNBT ceramics was effectively regulated by doping SrTiO3. Finally, we achieve a high electro-strain of 0.17% with ultra-low hysteresis of 7.2% (@70 kV/cm) for × = 0.3 ceramics, and a large electrostrictive coefficient Q33 of 0.0251 m4/C2 (@70 kV/cm) with low strain hysteresis of 8.3% for × = 0.4 ceramics. This work provides a method for optimizing the strain-hysteresis trade-off and improving electrostrictive coefficient Q33 of BNT-based ceramics.

Development of a Braking Device for a Step Drive of Vertical Displacement Actuators

The conceptual design scheme of an electric drive for control rod vertical displacement consisting of an electromagnetically excited inductor motor and a variable-pole permanent magnet generator, both interconnected by a common shaft, is substantiated. For this design scheme, an approach to determining the common bore diameter for both machines is proposed, which takes into account the drive inertia moment and includes the outer diameter determination by using the known motor designing methods. The sequence of determining the following generator parameters is described: the number of rotor poles, the number of phase winding turns, the winding wire diameter depending on the required steady-state rotor rotation frequency, and the shaft torque versus the control rod weight. A separate generator for limiting the control rod insertion speed has been designed and manufactured. This generator is a two-phase six-pole machine with barium-ferrite permanent magnets on the rotor, and with a thick-walled partition installed in the stator bore and containing magnetically soft steel inserts located in places of abutment to stator teeth. Field studies of the developed generator were carried out. The obtained test results confirm the advisability of making a shift to using the two-machine electromechanical converter design of the step drive for nuclear reactor control rod vertical displacement owing to a wider range of possible steady-state speeds and an increased generator braking torque.

Theoretical thermal-mechanical modelling and experimental validation of a novel 3D three-fingered electrothermal microgripper

This paper compared the static theoretical modelling, numerical simulation, and experimental results of a 3D electro-thermal actuator that is built by three fingers. Each finger is composed of a U-shaped (two DOFs) and a V-shaped (one DOF) electrothermal actuator for three DOFs. The heating source of those actuators is from polyimide films that is attaching with those beam actuators. When voltage or current (Joule heating) is applied to the polyimide film, the temperature of the beam increases since the thermal energy is transmitted from the film to the beam actuator. Then, the beam elongates due to the thermal expansion of the metal, resulting in displacement of the beam. In addition, we also perform the parameter analysis to discuss the effect of parameter change on the output displacement of actuator. Finally, the 3D electrothermal microgripper is used to implement micromanipulation experiments such as picking, moving and rotating on micro balls and zebrafish embryos in 3D space to verify its usability.

Design and Simulation of a Novel Magnetic Microactuator for Microrobots in Lab-On-a-Chip Applications

This article presents the design of a magnetic microactuator comprising soft magnetic material blocks and flexible beams. The modular layout of the proposed microactuator promotes scalability towards different microrobotic applications using low magnetic fields. The presented microactuator consists of three soft magnetic material (Ni-Fe 4750) blocks connected together via two Polydimethylsiloxane (PDMS) semi-circular beams. A detailed design approach is highlighted giving considerations toward compactness, range of motion and force characteristics of the actuator. The actuator displacement and force characteristics are approximately linear in the magnetic field strength range of 80-160 kA/m. It can achieve maximum displacements of 111.6 µm (at 160 kA/m) during extension and 10.7 µm (at 80 kA/m) during contraction under no-load condition. The maximum force output of the microactuator, computed through a contact simulation, was 404.3 nN at a magnetic field strength of 160 kA/m. The microactuator achieved stroke angles up to 18.4 in a study where the microactuator was integrated with a swimming microrobot executing rowing motion using an artificial appendage, providing insight into the capabilities of actuating untethered microrobots.

Large strain and reduced hysteresis of BiFeO3-xBaTiO3 lead-free ceramic via multiphase coexistence and relaxor behaviors

Ferroelectric ceramics with large strain response, low hysteresis and high Curie temperature (TC) are required for contemporary displacement actuator. In this work, (1-x)BiFeO3-xBaTiO3 ceramics were synthesized using traditional solid sintering technique. A high electric field-induced strain (0.25%), a relatively low hysteresis (22.5%) and a high Curie temperature (415 °C) were achieved in BiFeO3-0.35BaTiO3 ceramic. Meanwhile, the ceramics exhibited apparent relaxor behavior owing to the local structural heterogeneity. Aberration-corrected scanning transmission electron microscopy revealed that polar nano-regions with multiphase coexistence occur in the material, which is the microstructure origin of the enhanced strain and low hysteresis in BiFeO3-0.35BaTiO3 ceramics. This work indicates that BiFeO3–BaTiO3-based ceramics are good high-temperature ferroelectric materials and are promising candidates for high-precision actuator.