Actuator Research Articles

Stability Improvement of Segway Based on Tire Model Using the SEA

SUMMARYThis study proposes the use of a series elastic actuator (SEA) in a Segway to improve the stability of the tires during linear and curved driving, thus improving the comfort of the driver and ensuring driving stability. Recently, Segway has been developed continuously for intelligent mobile vehicles and the performance of Segway is being enhanced. Therefore, safety factors during the Segway driving have been considered seriously. In most of the developments and studies on Segway, the optimization and improvement of the controller component have been tackled and there are few studies on the safety devices and the stability of driving. The impact and vibration generated from the ground due to uneven road surfaces considerably influence the force exerted on the tire, which further affects driving stability. This research focuses on the control of the SEA based on the tire model to improve the driving stability of Segway. The performance of the proposed algorithm to improve the stability of the driver has been verified by straight and curved paths driving experiments with the tire model.

Modeling and Control of a Cable-Driven Rotary Series Elastic Actuator for an Upper Limb Rehabilitation Robot.

This paper focuses on the design, modeling, and control of a novel remote actuation, including a compact rotary series elastic actuator (SEA) and Bowden cable. This kind of remote actuation is used for an upper limb rehabilitation robot (ULRR) with four powered degrees of freedom (DOFs). The SEA mainly consists of a DC motor with planetary gearheads, inner/outer sleeves, and eight linearly translational springs. The key innovations include (1) an encoder for direct spring displacement measurement, which can be used to calculate the output torque of SEA equivalently, (2) the embedded springs can absorb the negative impact of backlash on SEA control performance, (3) and the Bowden cable enables long-distance actuation and reduces the bulky structure on the robotic joint. In modeling of this actuation, the SEA's stiffness coefficient, the dynamics of the SEA, and the force transmission of the Bowden cable are considered for computing the inputs on each powered joint of the robot. Then, both torque and impedance controllers consisting of proportional-derivative (PD) feedback, disturbance observer (DOB), and feedforward compensation terms are developed. Simulation and experimental results verify the performance of these controllers. The preliminary results show that this new kind of actuation can not only implement stable and friendly actuation over a long distance but also be customized to meet the requirements of other robotic system design.

The light-controlled actuator driven by the novel opto-electrostatic hybrid driving method based on PLZT ceramic

The light-controlled actuator driven by the novel opto-electrostatic hybrid driving method based on PLZT ceramic

A combined series-elastic actuator & parallel-elastic leg no-latch bio-inspired jumping robot

Compared with the catapult mechanism widely employed by small jumping robots, recently proposed jumping strategies based on series-elastic actuators (SEA) without latch mechanisms perform better in terms of agility, structural robustness and maneuverability. However, in some practical applications, they have difficulty in effectively storing energy before the push-off. This paper presents a novel no-latch jumping strategy inspired by frogs, achieving highly effective energy storage. The jumping strategy combines an SEA with a parallel-elastic linkage, which allows one motor to rotate in one direction to store the elastic energy and automatically trigger its release. Combined with this strategy, a frog-inspired robotic leg mechanism is designed. The jumping process is analysed in detail and the kinematic and dynamic models are derived. Bars’ dimensions and springs’ parameters are determined by the optimization to maximize the energy-storing capacity. The simulation is performed to predict the jumping performance. A 100.7 g prototype is fabricated and jumps to a height of 1.3 m with slight aerial body rotation. The energy-storing capacity of the robot is 18.1 J/Kg.

Dynamic Modeling and Simulation of a Body Weight Support System.

This paper proposes a body weight support (BWS) system with a series elastic actuator (SEA) to facilitate walking assistance and motor relearning during gait rehabilitation. This system comprises the following: a mobile platform that ensures movement of the system on the ground, a BWS mechanism with an SEA that is capable of providing the desired unloading force, and a pelvic brace to smooth the pelvis motions. The control of the body weight support is realized by an active weight-offload method, and a dynamic model of the BWS system with offload mass of a human is conducted to simulate the control process and optimize the parameters. Preliminary results demonstrate that the BWS system can provide the desired support force and vertical motion of the pelvis.

Real-time hybrid substructuring of a base isolated building considering robust stability and performance analysis

This paper demonstrates a real-time hybrid substructuring (RTHS) shake table test to evaluate the seismic performance of a base isolated building. Since RTHS involves a feedback loop in the test implementation, the frequency dependent magnitude and inherent time delay of the actuator dynamics can introduce inaccuracy and instability. The paper presents a robust stability and performance analysis method for the RTHS test. The robust stability method involves casting the actuator dynamics as a multiplicative uncertainty and applying the small gain theorem to derive the sufficient conditions for robust stability and performance. The attractive feature of this robust stability and performance analysis method is that it accommodates linearized modeled or measured frequency response functions for both the physical substructure and actuator dynamics. Significant experimental research has been conducted on base isolators and dampers toward developing high fidelity numerical models. Shake table testing, where the building superstructure is tested while the isolation layer is numerically modeled, can allow for a range of isolation strategies to be examined for a single shake table experiment. Further, recent concerns in base isolation for long period, long duration earthquakes necessitate adding damping at the isolation layer, which can allow higher frequency energy to be transmitted into the superstructure and can result in damage to structural and nonstructural components that can be difficult to numerically model and accurately predict. As such, physical testing of the superstructure while numerically modeling the isolation layer may be desired. The RTHS approach has been previously proposed for base isolated buildings, however, to date it has not been conducted on a base isolated structure isolated at the ground level and where the isolation layer itself is numerically simulated. This configuration provides multiple challenges in the RTHS stability associated with higher physical substructure frequencies and a low numerical to physical mass ratio. This paper demonstrates a base isolated RTHS test and the robust stability and performance analysis necessary to ensure the stability and accuracy. The tests consist of a scaled idealized 4-story superstructure building model placed directly onto a shake table and the isolation layer simulated in MATLAB/Simulink using a dSpace real-time controller.

Singular Wire-Driven Series Elastic Actuation with Force Control for a Waist Assistive Exoskeleton, H-WEXv2

This article presents a design of an electrically powered waist-assistive exoskeleton H-WEXv2 to reduce back-muscle fatigue and prevent back-injury of industrial workers. It utilizes a wire-driven mechanism based on a singular series elastic actuation to achieve system performances in aspect of cost, weight, operational time, and system endurance and maintainability for industrial feasibility. This proposed mechanism consisting of a ball screw drive and a series elastic actuator enables H-WEXv2 to accomplish better control maneuverability on powered flexion/extension while maintaining the advantage of allowing natural human walking with almost zero impedance. Also, to transfer torque determined by a high-level controller, a SEA force controller was implemented by measuring elastic displacements of installed spring elements at both hip joints. In order to evaluate the effectiveness of the developed robot installed with the proposed mechanism, electromyographic (EMG) signals of relevant muscles of ten subjects related to target waist motions were measured and compared for three cases: 1) wearing H-WEXv1, 2) wearing H-WEXv2, and 3) wearing nothing. Finally, the statistical analysis on acquired EMG signals verified the effectiveness of waist assistance provided by H-WEXv2.

Design, Modelling and Control of Novel Series-Elastic Actuators for Industrial Robots

This paper describes data-driven modelling methods and their use for the control of a novel set of series-elastic actuators (SEAs). A set of elastic actuators was developed in order to fulfill the end-user needs for tailored industrial collaborative robot manipulators of different morphologies and payloads. Three different types of elastic actuation were investigated, namely, disc springs, coil springs and torsion bars. The developed algorithms were validated both on single actuators and on a 6-DOF robotic arm composed of such actuators.

A Compact, Lightweight Robotic Ankle-Foot Prosthesis: Featuring a Powered Polycentric Design.

Robotic ankle-foot prostheses aim to improve the mobility of individuals with belowknee amputations by closely imitating the biomechanical function of the missing biological limb. To accomplish this goal, they must provide biomechanically accurate torque during ambulation. In addition, they must satisfy further requirements such as build height, range of motion (ROM), and weight. These requirements are critical for determining the potential number of users, range of activities that can be performed, and clinical outcomes. Previous studies have proposed addressing this challenge through the use of advanced actuation systems with series and parallel elastic actuators, clutchable leverages, and pneumatic artificial muscles. These ad vanced actuation systems have shown improved mechanical and electrical efficiency compared to conventional servo motors, making powered ankle prostheses possible. However, the improved efficiency comes at the expense of a tall build height, reduced ROM, and significant increase in weight, thus limiting the clinical viability of currently available powered prostheses.

Human postural ankle torque control model during standing posture with a series elastic muscle-tendon actuator

The main motivation behind the creation of a compliant actuation system is to provide safety, capability of storing energy, and improved performance levels in dynamic behavior of the mechanical human ankle. In this paper, a torsional flat spring (TFS) is proposed to provide high compliance and deformation values for human ankle series elastic muscle-tendon actuator system (HA-SEMTAS). The proposed torsional flat spring uses two torsional flat spiral spring in opposite directions, as the torsional flat spiral spring generates torque only in one direction. First, we present the characteristics of the TFS for an ankle joint, and the design and modeling of the HA-SEMTAS are developed. Modelling of the HA-SEMTAS simulates the responses of fluctuations in the center of mass and center of pressure and offers the possibility of measuring sensor activation, decomposition of reactive torque and participation of each set of muscle groups to balance posture. In order to control ankle angles and torque of Human system, torque controllers (PID and PD-feedforward) are generated for (HA-SEMTAS). The controller inputs are torsional flat spring position errors and error rates. Feedforward and integral action were applied to reduce the steady-state error of the system. It is seen that PID + ff of the system developed here is robust to step and ramp-type disturbances. Real-time controllers are embedded in GoogolTech GT-800 Industrial PC. Experimental results confirm that the step tracking of human upright posture behavior is satisfactory and overall system stability has improved using the proposed controller and compliant actuation system. It is also shown that PD + feedforward yields better performance than PID controller.

Improving the Dynamic Force Control of Series Elastic Actuation Using Motors of High Torque-to-Inertia Ratios

A series elastic actuator (SEA) includes an elastic spring in series with an actuator. SEAs provide more accurate force and impedance control than conventional rigid actuators. They are ideal for robots and machines that need to interact safely with the environment. The majority of existing SEAs uses brushless or brushed DC motors as the actuators. The advantages of using step motors as the actuators of SEAs have not received enough attention. Step motors have much higher torque-to-weight ratio and torque-to-inertia ratio than other DC motors. Hence they can provide better stability and high-speed accuracy of force control while maintaining lightweight. When the rotor position feedback is used, step motors can achieve accurate dynamic position response smoothly. This paper develops the dynamic model of a linear series elastic step motor and presents its prototype. Force and impedance control responses will be provided to show the advantages due to the high torque-to-inertia ratio of step motors. It is expected that the results presented here can offer a better actuator selection of SEAs when high-performance dynamic force control is required.

Low-delay Admittance Control of Hydraulic Series Elastic Actuator for Safe Human-Robot Collaboration

Current industrial manufacturing standards highlight safe human-robot collaboration. Therefore, compliance solutions, whether passive or active, are necessary. In this regard, series elastic actuators (SEAs) have attracted extensive interest for applications in industrial robotics owing to the low output impedance of these actuators, which can enhance interaction safety. Although considerable efforts have been expended to improve the control accuracy of SEAs, the time delay in impedance/admittance control has remained an unexplored problem. The use of filters in conventional methods can result in large time delay and considerable amplitude errors that degrade the performance and increase the risk of injury. This study resolves this problem by developing a method for low-delay admittance control of hydraulic SEAs. An external force observer (EFO)-based admittance scheme is first formulated. Thereafter, adaptive time series (ATS) compensators are introduced to improve position control and EFO. Based on the improved position controller and the ATS-based EFO (ATS-EFO), a novel low-delay admittance control scheme is developed. The proposed method only uses the load mass and spring stiffness information, thereby facilitating its application. Simulation experiments are performed to demonstrate the SEA control performance on position tracking, external force estimation, and stiffness tracking. The results confirm that the time delay and the amplitude error in these tests are significantly reduced by the proposed method.

Investigations on state estimation of smart structure systems

This paper aims at enlightening the properties, computational and implementation issues related to Kalman filter based state estimation algorithms and sliding mode observers, by applying them for estimating the states of a smart structure system. The Kalman based estimators considered in this work are Kalman filter and information filter and, the sliding mode observers considered are Utkin observer and higher order sliding mode observer. A fourth order linear time invariant model of a piezo actuated beam is used in this work. This structure is embedded with four number of piezo patches, of which two act as sensors, one as disturbance actuator and the other as control actuator. The performance of the state estimation algorithms is evaluated through simulation, for the first two vibrating modes of the piezo actuated structure, when the structure is maintained at first mode and second mode resonance.

Design, Optimization and Energetic Evaluation of an Efficient Fully Powered Ankle-Foot Prosthesis With a Series Elastic Actuator

The use of powered ankle-foot prostheses for below-knee amputees leads to challenges like the peak power of the applied actuator and biomechanical features of the prosthesis foot. This paper proposes an efficient powered ankle-foot prosthesis with a series elastic actuator. By combining the geared five-bar spring (GFBS) mechanism and the traditional series elastic actuator (SEA), a series elastic with geared five-bar (SGFB) actuator is built. The new SGFB actuator has the benefits of both the GFBS and the SEA on mimicking biomechanics of the human ankle and reducing the peak power of the motor. The healthy walking gait in the experiment results indicates that the optimized SGFB prosthesis foot including a 150W Maxon DC motor can provide a 70kg subject enough net positive energy with an energy efficiency of 35.3% during normal speed walking in the treadmill trials. The experiment of the SGFB prosthesis foot in semi-active mode shows the advantage on closely mimicking the human biomechanics during the control dorsiflexion phase and the importance of injecting positive energy during the powered plantarflexion phase. The experiment results also show that the optimization of different parameters within the electromechanical model considering the efficiency of the whole drive train can effectively reduce the motor's peak power to 132 W by making the motor more effective in high-power conditions.

Mechanical characterization of millimetric agarose spheres using a resonant technique

This paper presents a methodology for the mechanical characterization of agarose millimetric spheres using resonant principles. Detection of the modes of vibration was conducted using a low-cost experimental setup based on an electret microphone adapted with a thin latex elastic membrane for the sensing stage and a piezoelectric actuator driven by a conventional transformer for the excitation stage. The identification of vibration modes is supported through an ANSYS Finite Element model of the experimental setup. Experimental and numerical results demonstrate that two modes of vibration, known as Quadrupole and Octupole, appear in the amplitude spectrum and can be used to obtain stiffness values for the samples. Following this approach, Young’s modulus of 209 ± 19.80, 338 ± 35.30 and 646 ± 109 kPa for 2%, 3% and 4% agarose millimetric spheres were calculated.

Surface and small scale effects on the dynamic buckling of carbon nanotubes with smart layers assuming structural damping

In this paper, dynamic buckling of a smart sandwich nanotube is studied. The nanostructure is composed of a carbon-nanotube with inner and outer surfaces coated with ZnO piezoelectric layers, which play the role of sensor and actuator. Nanotube is under magnetic field and ZnO layers are under electric field. The nanostructure is located in a viscoelastic environment, which is assumed to obey Visco-Pasternak model. Non-local piezo-elasticity theory is used to consider the small-scale effect, and Kelvin model is used to describe the structural damping effects. Surface stresses are taken into account based on Gurtin-Murdoch theory. Hamilton principle in conjunction with zigzag shear-deformation theory is used to obtain the governing equations. The governing equations are then solved using the differential quadrature method, to determine dynamic stability region of the nanostructure. To validate the analysis, the results for simpler case studies are compared with others reported in the literature. Then, the effect of various parameters such as small-scale, surface stresses, Visco-Pasternak environment and electric and magnetic fields on the dynamic stability region is investigated. The results show that considering the surface stresses leads to an increase in the excitation frequency and the dynamic stability region happens at higher frequencies.

Ионные полимерные электроактивные актюаторы на основе ионообменной мембраны МФ-4СК. Часть 2. Ионные полимер-графеновые композиты

Впервые исследована специфика работы актюатора на основе отечественного электроактивного полимера МФ-4СК в комбинации с графеновыми электродами. Система показала ряд преимуществ по сравнению с теми, в которых используются традиционные гибкие металлические электроды, а также нафионовые мембраны, в частности лучшую взаимную адгезию материалов. Построена модель электроактивного полимера, связывающая размеры и структуру водонаполненных пор с геометрическими характеристиками полимера и ориентированная на сопоставление свойств полимера МФ-4СК и нафиона.

Ионные полимерные электроактивные актюаторы на основе ионообменной мембраны МФ-4СК. Часть 1. Ионные полимер-металлические композиты

Впервые исследована работа актюаторов на основе ионного полимер-металлического композита, в которых в качестве материала полимерной мембраны выступает отечественный полимер МФ-4СК, обеспечивающий ряд преимуществ по сравнению с зарубежным аналогом (Нафионом). Несмотря на известный эффект снижения ионной подвижности, композит демонстрирует усиление актюационных характеристик: увеличение амплитуды отклонения мембраны и блокирующей силы под действием как постоянного, так и синусоидального напряжения.

Thermo-electro-elastic nonlinear stability analysis of viscoelastic double-piezo nanoplates under magnetic field

The nonlinear thermo-electro-elastic buckling behavior of viscoelastic nanoplates under magnetic field is investigated based on nonlocal elasticity theory. Employing nonlinear strain-displacement relations, the geometrical nonlinearity is modeled while governing equations are derived through Hamilton\'s principle and they are solved applying semi-analytical generalized differential quadrature (GDQ) method. Eringen\'s nonlocal elasticity theory considers the effect of small size, which enables the present model to become effective in the analysis and design of nano-sensors and nano actuators. Based on Kelvin-Voigt model, the influence of the viscoelastic coefficient is also discussed. It is demonstrated that the GDQ method has high precision and computational efficiency in the buckling analysis of viscoelastic nanoplates. The good agreement between the results of this article and those available in literature validated the presented approach. The detailed mathematical derivations are presented and numerical investigations are performed while the emphasis is placed on investigating the effect of the several parameters such as electric voltage, small scale effects, elastomeric medium, magnetic field, temperature effects, the viscidity and aspect ratio of the nanoplate on its nonlinear buckling characteristics. It is explicitly shown that the thermo-electro-elastic nonlinear buckling behavior of viscoelastic nanoplates is significantly influenced by these effects. Numerical results are presented to serve as benchmarks for future analyses of viscoelastic nanoplates as fundamental elements in nanoelectromechanical systems.

Designing interconnected haptic interfaces and actuators for teleoperations in mobile ad hoc networks

Designing interconnected haptic interfaces and actuators for teleoperations in mobile ad hoc networks