Model Of Actuator Research Articles

An efficient technique in dynamic modeling and analysis of soft fluidic actuator

Soft actuators with embedded fluidic channels are promising for soft robotics, but their continuous nature presents challenges in accurate and efficient modeling. Existing studies on dynamic behavior have shown that both approximate and exact methods have limitations in accurately predicting the deflection of soft actuators. Additionally, conventional methods require experimental parameter extraction for each individual actuator. To address these challenges, we propose a modified analytical method and use finite element analysis as the defined correction functions to improve accuracy and computational efficiency, providing a promising tool for the design and control of soft robotic systems. In this work, we propose a solution methodology for simulating the dynamic behavior of fluidic soft actuators, which are widely used in soft robotics applications. Our approach takes into account the cross-sectional geometry and the number of channels in the actuator’s configuration. By scrutinizing various fluidic actuation designs, we can deduce the most suitable cross-sectional configuration for optimal performance. Compared to existing analytical methods, our approach is more accurate and does not require additional calculation time. As the method is adaptable with experimental models, it can be used to design and optimize soft actuators while can be refined and improved through experimental model updating.

Adaptive neural controller with predefined boundary constraints for 3D printed cable-driven soft actuators

It is difficult to build dynamic models for 3D-printed soft actuators because of their material and structural flexibility and the complex intrinsic and extrinsic interactions encountered in human-centric or complex non-structural environments. Soft actuators require the control error during motion to be limited. However, existing control methods with predefined boundary constraints are designed for rigid actuators and are not directly applicable to soft actuators. In this paper, an adaptive neural controller based on a quasi-static model is proposed. The quasi-static model of the soft actuator is used to determine how the viscoelasticity of the flexible material influences the neural network, enabling the neural network to identify a better fit to the dynamic model of the soft actuator. Finally, experimental results verify that the proposed controller constrains the tracking error of the soft actuator to within the predefined boundary.

Extended High-Order Disturbance Observer-Based Clutch Actuator Model Uncertainty Estimation of Ball-Ramp Dual-Clutch Transmission

The ball-ramp dual-clutch transmission (BR-DCT) was proposed to overcome the disadvantages of conventional DCT. Specifically, BR-DCT is designed to reduce the amount of clutch actuator energy consumption and reverse torque during tie-up, in which two clutches are engaged simultaneously. In addition, since the self-energizing principle is used, the actuator model can be used without the friction coefficient, which is the main uncertainty of the clutch actuator. These features can greatly contribute to enhancing the shift control performance of the BR-DCT. However, the measurement error due to friction between actuator parts causes a small amount of uncertainty. In this article, a method using extended high-order disturbance observer (EH-DOB) is proposed to estimate this uncertainty. The EH-DOB used in the proposed method guarantees convergence even in a system in which the gain of the disturbance is time-varying. The convergence of the estimation error was verified through proof of the proposed algorithm. Experimental verification of the proposed algorithm was performed using a test bench that simulates a powertrain equipped with BR-DCT. As a result, it was confirmed that the uncertainty estimation result using EH-DOB showed high accuracy. As a result, it was verified that the uncertainty estimation method using the proposed algorithm has high accuracy and stability enough to perform disturbance rejection control.

Modeling of a Soft Actuator With a Semicircular Cross Section Under Gravity and External Load

Compared to rigid robotic actuators, soft actuators based on fibre-reinforced elastomeric actuators (FREAs) have great potential for use in exploring complex terrain, medical operations, and flexible capture of targets. However, it is still challenging to model the mechanical behaviour of soft actuators because of the large deformation and nonlinear characteristics of elastic materials. This paper proposes an analytical model to predict the shape of a soft actuator to better describe the relationship between its deformation and input pressure, gravity, and other external forces. We first derive the relationship between soft actuator deformation and pressure using volume maximisation and the principle of virtual work. We further use Euler–Bernoulli beam theory to investigate the influence of self-gravity and external forces on the soft actuator configuration. The model is verified by fabricating a soft actuator prototype via mold casting. Finally, we perform a series of experiments to evaluate the accuracy of our proposed model. The longest total time to solve the model is 0.035 s. Experimental results show that the model's maximum error rate is between 2.89% and 9.75%. This indicates that the model can effectively predicts the deformation of soft actuators considering gravity and other external forces.

Development of an ANC System with a Giant Magnetostrictive Actuator for Ultra-Compact Electric Vehicles: Thrust Force Characteristics Including Road Noise Range

Ultra-compact electric vehicles (EVs) have been recently sold as next-generation vehicles. However, they are yet to reach a notable phase of expansion and use. Ultra-compact EVs have compact and lightweight bodies. As the outer plate of an ultra-compact EV has low rigidity, the road noise generated by the tires and the wind noise generated from the vehicle’s projection shape are transmitted to the interior of the vehicle. Therefore, a new active noise control (ANC) system with a giant magnetostrictive actuator for ultra-compact EVs has been recently proposed. The giant magnetostrictive actuator is required to produce sufficient thrust, with less distortion, and delayed sound waves. In this work, we studied the thrust force characteristics of the giant magnetostrictive material, including in the road noise range. We considered the giant magnetostrictive thrust for output, including in the road noise range, using a finite element model of the giant magnetostrictive actuator by conducting an electromagnetic field analysis. The results showed that the effect of the thrust on the frequency changes depending on the length of the giant magnetostrictive material.

Computational Analysis of Semi-Analytical Modeling Techniques for a Novel PM-Based Planar Actuator

A novel type of permanent magnet planar actuator is proposed which consists of a permanent magnet mover that interacts with individually mechanically controllable permanent magnets in the stator. A state of levitation and actuation is obtained by mechanically altering the orientation of the stator magnets to control the forces and torques on the mover. To design and control the actuator, fast and accurate electromagnetic models are required. In this study, the harmonic modeling technique is applied to rotating and translating cuboidal and cylindrical permanent magnets and is compared to the equivalent charge model in terms of accuracy and computational effort. The models are compared for a finite stator topology which demonstrates that the harmonic model has a substantial computational advantage over the equivalent charge method in a non-periodic system while both models are in good agreement in terms of accuracy.

A flexoelectric actuator model with shear-lag and peel stress effects

Flexoelectric materials are being extensively studied in recent years for potential sensing, actuation, energy harvesting and structural health monitoring applications. However, no analytical model exists in the literature to predict the stress transfer between a flexoelectric transducer and the host structure, considering bonding compliance. In this article, we present an analytical model for the interfacial stresses and deformations of flexoelectric patch actuator(s) bonded to an isotropic host plate considering both shear-lag and peel stress effects at the interface(s). The model is valid for both piezoelectric and flexoelectric effects. The system’s one-dimensional governing equations are derived consistently from the three-dimensional equations for linear dielectric solids obtained using the bulk electric Gibbs energy density function and extended Hamilton’s principle. The transducer and substrate, modelled as classical Kirchhoff plates, undergo both extension and bending deformations. The formulation produces a seventh-order differential equation for the interfacial shear stress, which is solved analytically, satisfying all boundary conditions. The solution is validated by comparing with the available results for piezoelectric actuators with a non-rigid interface and those of flexoelectric actuators based on the pin-force-moment model assuming a rigid interface. Detailed numerical studies are presented to show the effect of the plate, actuator and adhesive parameters on the interfacial stresses and deformations. Finally, the size effect of the actuators at the micro-scale is illustrated.

Forward Kinematics Based Prediction for Bending Motion of Soft Pneumatic Actuators with Various Air Chambers

This study proposes a forward kinematic model for soft actuators that utilize pneumatic control to predict their bending motion, which is simulated using Ansys software. Firstly, a bending motion test is conducted with a 2-air chamber actuator to derive an equation that establishes the relationship between the bending angle and input pressure. Next, a serial model for the overall soft actuator is developed using forward kinematics with the DH method. The angle variables in the soft actuator are then replaced with an equation that relates the deformed angle and compressed air. Finally, the proposed serial model is used to predict the bending motion of 4-air and 6-air chamber actuators, and the results are compared to simulations and real experiments. The comparison shows that the proposed model could accurately predict the bending motion of the real actuators within an acceptable tolerance of 10%.

Functionally graded structure design for magnetic field applications

This study presents topology optimization methodology of anisotropic magnetic composites, which consist of two ferromagnetic materials with low and high reluctivity values, considering the nonlinear magnetic saturation effect. Instead of employing the asymptotic homogenization theory, the representative volume element method combined with the machine learning is used to build the continuous function model and it is applied to obtain the material property according to the design variable change. Finally, the micro-scale functionally graded structure composed of two ferromagnetic materials with the macro-scale topological morphology is simultaneously designed to improve the magnetic performance of actuators. Numerical examples for symmetric and asymmetric magnetic actuator models are provided to validate the effectiveness of proposed design process. In the numerical results, optimized configurations and objective values obtained with the nonlinear magnetic composite material, which depend on the intensity of the magnetic flux density, are compared with those of the linear magnetic composite material.

Modeling of Fiber-Constrained Planar PVC Gel Actuators.

In recent years, plasticized poly (vinyl chloride) (PVC) gel has attracted increasing attention in soft robotics. However, there is scarce research on the deformation mechanism and modeling of PVC gel actuators. In this study, to investigate the deformation mechanism of fiber-constrained planar PVC gel actuators, we propose a complex nonlinear model based on traditional thermodynamic electroactive polymer (EAP) multi-field coupling theory. The proposed model can reveal the dielectric breakdown strength of PVC gels and predict the deformation of planar PVC gel actuators with varying levels of pre-stretching. The theoretical results were in good agreement with the experimental results, indicating the feasibility of the proposed model.

Wax actuator’s empirical model development and application to underfloor heating control with varying complexity of controller modelling detail

This paper investigates how a simulated room’s energy and temperature performance are affected if its underfloor heating control is modelled with increasing detail. Experiments were performed to develop and calibrate an empirical model of wax motor and to calibrate the valve curve. These models were used to implement and test the On/Off and proportional-integral (PI) control processes at various levels of modelling detail. Controllers were implemented by gradually adding optimized control parameters, signal delay, calibrated valve curve, signal modulation, and actuator modelling. The On/Off control dead band and PI parameters exhibited the largest impact, reducing energy use (1%–5%) and temperature fluctuations (ca 1 K). Modulating the PI output signal increased temperature fluctuations to the same amplitude as On/Off with 0.5 K dead band, increasing space heating demand by 1.3%. The wax actuator counted for less than 1%; however, it increased time delays to maximally 7 min and remarkably changed the mass flows.

Design of Piezoelectric Inertial Actuator with Wedge‐shaped Foot Structure for Cell Manipulation

AbstractAiming at the performance requirements of positioning accuracy and stability of piezoelectric inertial actuators in fields including micro‐operation and biomedical engineering, a piezoelectric inertial actuator with wedge‐shaped friction foot structure using bimorph films is proposed in this paper. The wedge‐shaped friction foot structure can adjust the friction force in different driving stages, which suppresses the backward motion and effectively improves the output performance of the actuator. And the bimorph films are processed by Micro Electromechanical Systems (MEMS) manufacturing process technology. It enables the actuator to move steadily with a small tip mass and facilitates the miniaturization of actuator. The simulation model is constructed based on the dynamic model of actuator and the prototype parameters are optimized from the results of simulation tests. Then a series of output performance experiments are carried out. Experimental results show that the proposed actuator has the advantages of high resolution, stability, and displacement linearity. And the highest resolution of 0.035 µm is achieved. Depending on above results, the cell drug injection simulation experiments are successfully conducted. The success of experiments shows that the prototype has good output performance and great application potential and value in the field of cell manipulation.

Position-based impedance torque control for automatic clutch with robust predefined-time stability guarantee

Accurate clutch torque control is essential in improving vehicle comfort, drivability, and fuel economy. In this article, for automatic clutch system with electro-hydraulic clutch actuator, a clutch torque control strategy with a robust predefined-time stability guarantee based on position closed-loop impedance control is proposed and evaluated. For this purpose, a general second order model of electro-hydraulic clutch actuator with a disturbance term is established. Based on this model, a reference position compensator based on force control in the outer loop and a predefined-time backstepping position controller in the inner loop are developed. In addition, to obtain the release load of the release bearing, a virtual sensor is designed, composed of an online adaptive sliding mode disturbance observer with predefined-time stability and an offline Gaussian process model of uncertain disturbance based on the Gaussian process machine learning method. Finally, simulations and experiments are completed to verify the proposed control strategy. The results show that the control strategy can realize the precise clutch torque tracking control and achieve satisfactory performance.

Uncovering the Origins of Instability in Dynamical Systems: How Can the Attention Mechanism Help?

The behavior of the network and its stability are governed by both dynamics of the individual nodes, as well as their topological interconnections. The attention mechanism as an integral part of neural network models was initially designed for natural language processing (NLP) and, so far, has shown excellent performance in combining the dynamics of individual nodes and the coupling strengths between them within a network. Despite the undoubted impact of the attention mechanism, it is not yet clear why some nodes of a network obtain higher attention weights. To come up with more explainable solutions, we tried to look at the problem from a stability perspective. Based on stability theory, negative connections in a network can create feedback loops or other complex structures by allowing information to flow in the opposite direction. These structures play a critical role in the dynamics of a complex system and can contribute to abnormal synchronization, amplification, or suppression. We hypothesized that those nodes that are involved in organizing such structures could push the entire network into instability modes and therefore need more attention during analysis. To test this hypothesis, the attention mechanism, along with spectral and topological stability analyses, was performed on a real-world numerical problem, i.e., a linear Multi-Input Multi-Output state-space model of a piezoelectric tube actuator. The findings of our study suggest that the attention should be directed toward the collective behavior of imbalanced structures and polarity-driven structural instabilities within the network. The results demonstrated that the nodes receiving more attention cause more instability in the system. Our study provides a proof of concept to understand why perturbing some nodes of a network may cause dramatic changes in the network dynamics.

Modeling and analysis of a thrust anti-torque sensing actuator

In the field of intelligent drive and sense, the traditional actuator can realize linear actuation and lacks sensing function. Therefore, a new sensing actuator is designed, which can not only output force and displacement, but also have thrust anti-torque sensing function. Firstly, the model of piezoelectric actuator is designed, and the geometric and mechanical models are established. Furthermore, the geometric relationship of mechanical and electrical parameters is analyzed. Secondly, the optimal included angles are determined after finite element analysis and optimization. Finally, the maximum output displacement is obtained through finite element analysis, and the maximum strain position is pointed out. Besides, the rotational stiffness is obtained. The results show that the modeling method and simulation results are accurate.

A novel inchworm piezoelectric actuator using two-stage amplification mechanism with high speed: design, modeling, and experimental evaluation

The inchworm piezoelectric actuator has a wide application prospect in the field of precision instruments. However, in view of the complex structure of the existing inchworm piezoelectric actuator and the far distance between the driving feet of the actuator, it is difficult to realize alternate driving and the high output speed of the driving feet, etc. In this paper, an inchworm piezoelectric linear actuator based on two-stage amplification mechanism is designed, which amplifies the output displacement of the driving feet by two-stage amplification mechanism, and improves the driving efficiency of the actuator stator by the way of alternating driving. We present an inchworm piezoelectric actuator with three piezoelectric stacks and a two-stage amplification mechanism, which is simple in structure design, compact in actuator structure and easy to realize alternate driving. The kinematics and dynamics models of the inchworm piezoelectric actuator are established by analyzing the flexible hinge and its structure with the pseudo-rigid body method. The length of the lever structure and the angle of the triangular structure of the piezoelectric actuator are solved by kinematics, and the natural frequency of the whole structure is calculated by dynamics. Through finite element analysis, the simulation magnification ratio of the piezoelectric actuator is obtained, so as to evaluate and verify the theoretical calculation and further optimize the structure. The experimental results show that the inchworm piezoelectric linear actuator using two-stage amplification mechanism has a high driving speed of 5.53 mm s−1 under voltage of 135 V and frequency of 70 Hz.

Fault Diagnosis and Its Applications to Fault Tolerant Control of a Turbojet Engine

This paper presents a comprehensive study of model-based fault diagnosis (FD) and a fault-tolerant control (FTC) scheme for sensor and actuator faults of turbojet engines. For actuator FD, an unbiased estimation scheme with a modified Kalman filter (KF) was developed. For sensor FD, two approaches, the generalized likelihood ratio with robust KF and the pseudo actuator model with modified KF, were investigated in a comparative study. For fault detection and isolation, test statistics are commonly employed to detect fault behavior. For FTC, integral-type sliding mode control using control reconfiguration and the reconstruction of the sensor signal was adopted with the FD schemes. The effectiveness of the employed methods was demonstrated in this study and discussed with numerical simulations.

Dynamic modeling with quantifying dissipated power density and experimental validation of dielectric elastomer actuators

This paper proposes a dynamic electromechanical model for dielectric elastomer actuators (DEAs) with dissipative processes. Dielectric loss of elastomers, resistance of electrodes, actuator geometry, elastomer viscoelasticity and nonlinear electromechanical coupling are considered, and a new visco-hyperelastic constitutive model with frequency-dependent parameters is developed for large-strain elastomers. The dynamic responses of DEAs at different driving frequencies are experimentally measured and comprehensively compared with those predicted results. The relative errors over the time period of 0–50 s at 5 and 7 Hz are respectively 3.6% and 3.4%, demonstrating the effectiveness of the model. The proposed dynamic model can not only predict the frequency response of DEAs but also characterize the creep and hysteresis behavior with reasonable accuracy. The power density dissipated during dielectric elastomer actuation is calculated and analyzed. The results suggest that selecting low-resistance electrodes and elastomers with short dielectric relaxation time and low viscous loss is a feasible way to achieve high energy conversion efficiency for DEAs. This work can be helpful for the design and control of DEAs, paving the way for their practical applications.

Nafion-Pt IPMC electroactive behavior changes in response to environmental nonequilibrium conditions

Electroactive polymers (EAPs) continue to gain attention for their potential to offer unique and versatile solutions in the soft robotic and flexible electronic industries. Ionic polymer-metal composites (IPMCs) are a class of ionic-type EAPs which can be configured as capacitor actuators with very low voltage requirements (⩽5 V AC or DC). Their compact, portable, and lightweight properties, coupled with a biomimetic bending actuation response make them ideal for human-machine integrated technologies such as medical implants, active skins, and artificial muscles. This work tested the IPMC’s actuation and electrical response in varying saturation conditions (70% RH, 85% RH, 95% RH, and DI water liquid immersion) and voltage application schemes (direct current voltage (DCV) cycled, continuously applied, and relaxation responses upon voltage removal). This information was then used to establish actuation and back-relaxation response patterns through repetitive testing for statistical certainty. These demonstrated maximized actuation in water vapor conditions where the IPMC’s dielectric permittivity is maximized (), and the dissipation factor is minimized (). The response trends in vapor conditions are gradual but yield larger actuation ranges with increasing hydration. Liquid immersion restricts the IPMC’s range of motion but produces a sharper response pattern. These trends were validated against previously published IPMC actuator models. All of this creates a more pragmatic perspective on the potential of this technology which aids in the advancement of this material’s evolution towards viable real-world application configurations which capitalize on the material’s natural responses.

Development of Pneumatic Force-Controlled Actuator for Automatic Robot Polishing Complex Curved Plexiglass Parts

Due to the temperature-sensitive characteristic of plexiglass materials, it is necessary to maintain a constant small contact force to avoid surface burn damage when polishing complex curved plexiglass parts. To handle the issue, in this paper a pneumatic force-controlled actuator was developed to keep the normal contact force between the polishing tool and the workpiece constant during the robotic polishing process. The force-controlled actuator is configured with a double-acting cylinder as the driving element, and two electrical proportional valves are used to control the output force by adjusting the pressure difference between the two air chambers of the cylinder. In this case, a small contact force can be exactly achieved, and the cylinder can always work within the optimal pressure range. In order to judge the stability of the system and reduce the commissioning time of the force-controlled actuator, a mathematical model of the force-controlled actuator is established. Meanwhile, for eliminating the influence of the gravity of the polishing tool on the contact force control, a gravity compensation algorithm is also given according to the roll-pitch-yaw (RPY) angle calculation method. Since there are some nonlinear factors in the operation of the force-controlled actuator, a fuzzy proportion-integral-derivative (PID) control strategy is adopted without steady-state errors. Finally, the polishing experiment of a complex curved plexiglass part was carried out by using the robot automatic polishing system. The experimental results show that the contact force control effect of the force-controlled actuator meets the processing requirements, and the curved plexiglass part has good surface quality and optical performance after polishing.