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Showing papers on "Actuator published in 2014"


Journal ArticleDOI
TL;DR: In this article, a pneumatic actuator can bend from a linear to a quasicircular shape in 50 ms when pressurized at Δ P = 345 kPa.
Abstract: Soft robots actuated by infl ation of a pneumatic network (a “pneu-net”) of small channels in elastomeric materials are appealing for producing sophisticated motions with simple controls. Although current designs of pneu-nets achieve motion with large amplitudes, they do so relatively slowly (over seconds). This paper describes a new design for pneu-nets that reduces the amount of gas needed for infl ation of the pneu-net, and thus increases its speed of actuation. A simple actuator can bend from a linear to a quasicircular shape in 50 ms when pressurized at Δ P = 345 kPa. At high rates of pressurization, the path along which the actuator bends depends on this rate. When infl ated fully, the chambers of this new design experience only one-tenth the change in volume of that required for the previous design. This small change in volume requires comparably low levels of strain in the material at maximum amplitudes of actuation, and commensurately low rates of fatigue and failure. This actuator can operate over a million cycles without signifi cant degradation of performance. This design for soft robotic actuators combines high rates of actuation with high reliability of the actuator, and opens new areas of application for them.

1,158 citations


Journal ArticleDOI
TL;DR: In this article, a robust integral of the sign of the error controller and an adaptive controller are synthesized via backstepping method for motion control of a hydraulic rotary actuator.
Abstract: Structured and unstructured uncertainties are the main obstacles in the development of advanced controllers for high-accuracy tracking control of hydraulic servo systems. For the structured uncertainties, nonlinear adaptive control can be employed to achieve asymptotic tracking performance. But modeling errors, such as nonlinear frictions, always exist in physical hydraulic systems and degrade the tracking accuracy. In this paper, a robust integral of the sign of the error controller and an adaptive controller are synthesized via backstepping method for motion control of a hydraulic rotary actuator. In addition, an experimental internal leakage model of the actuator is built for precise model compensation. The proposed controller accounts for not only the structured uncertainties (i.e., parametric uncertainties), but also the unstructured uncertainties (i.e., nonlinear frictions). Furthermore, the controller theoretically guarantees asymptotic tracking performance in the presence of various uncertainties, which is very important for high-accuracy tracking control of hydraulic servo systems. Extensive comparative experimental results are obtained to verify the high-accuracy tracking performance of the proposed control strategy.

443 citations


Journal ArticleDOI
TL;DR: P porous polymer actuators that bend in response to acetone vapour at a speed of an order of magnitude faster than the state-of-the-art, coupled with a large-scale locomotion.
Abstract: Fast actuation speed, large-shape deformation and robust responsiveness are critical to synthetic soft actuators. A simultaneous optimization of all these aspects without trade-offs remains unresolved. Here we describe porous polymer actuators that bend in response to acetone vapour (24 kPa, 20 °C) at a speed of an order of magnitude faster than the state-of-the-art, coupled with a large-scale locomotion. They are meanwhile multi-responsive towards a variety of organic vapours in both the dry and wet states, thus distinctive from the traditional gel actuation systems that become inactive when dried. The actuator is easy-to-make and survives even after hydrothermal processing (200 °C, 24 h) and pressing-pressure (100 MPa) treatments. In addition, the beneficial responsiveness is transferable, being able to turn 'inert' objects into actuators through surface coating. This advanced actuator arises from the unique combination of porous morphology, gradient structure and the interaction between solvent molecules and actuator materials.

430 citations


Journal ArticleDOI
TL;DR: In this paper, the design and control of a prismatic series elastic actuator with high mechanical power output in a small and lightweight form factor is discussed. And the actuator's performance is demonstrated through a series of experiments designed to operate at the limits of its mechanical and control capability.
Abstract: This paper discusses design and control of a prismatic series elastic actuator with high mechanical power output in a small and lightweight form factor. A design is introduced that pushes the performance boundary of electric series elastic actuators by using high motor voltage coupled with an efficient drivetrain to enable large continuous actuator force while retaining speed. Compact size is achieved through the use of a novel piston-style ball screw support mechanism and a concentric compliant element. Generic models for two common series elastic actuator configurations are introduced and compared. These models are then used to develop controllers for force and position tracking based on combinations of PID, model-based, and disturbance observer control structures. Finally, our actuator's performance is demonstrated through a series of experiments designed to operate the actuator at the limits of its mechanical and control capability.

332 citations


Journal ArticleDOI
TL;DR: Shape memory alloys (SMAs) as discussed by the authors are a unique class of metallic materials with the ability to recover their original shape at certain characteristic temperatures (shape memory effect), even under high applied loads and large inelastic deformations, or to undergo large strains without plastic deformation or failure (super-elasticity).
Abstract: Shape memory alloys (SMAs) are a unique class of metallic materials with the ability to recover their original shape at certain characteristic temperatures (shape memory effect), even under high applied loads and large inelastic deformations, or to undergo large strains without plastic deformation or failure (super-elasticity). In this review, we describe the main features of SMAs, their constitutive models and their properties. We also review the fatigue behavior of SMAs and some methods adopted to remove or reduce its undesirable effects. SMAs have been used in a wide variety of applications in different fields. In this review, we focus on the use of shape memory alloys in the context of morphing aircraft, with particular emphasis on variable twist and camber, and also on actuation bandwidth and reduction of power consumption. These applications prove particularly challenging because novel configurations are adopted to maximize integration and effectiveness of SMAs, which play the role of an actuator (using the shape memory effect), often combined with structural, load-carrying capabilities. Iterative and multi-disciplinary modeling is therefore necessary due to the fluid–structure interaction combined with the nonlinear behavior of SMAs.

307 citations


Patent
24 Oct 2014
TL;DR: In this paper, a device for penetrating tissue is provided that has a driving actuator with a body and motor shaft that is reciprocated, and a coupler is attached to the motor shaft.
Abstract: A device for penetrating tissue is provided that has a driving actuator with a body and motor shaft that is reciprocated. A coupler is attached to the motor shaft, and a key engages the driving actuator and coupler and limits rotational motion of the motor shaft and permits linear motion of the motor shaft. A penetrating member is carried by the coupler, and linear motion of the motor shaft is translated to the penetrating member to linearly reciprocate the penetrating member.

236 citations


Journal ArticleDOI
TL;DR: This technical note is concerned with the problem of adaptive tracking control for a class of nonlinear systems with parametric uncertainty, unknown actuator nonlinearity and bounded external disturbance, and two type of actuatorNonlinearities, symmetric dead-zone and Bouc-Wen hysteresis are considered.
Abstract: This technical note is concerned with the problem of adaptive tracking control for a class of nonlinear systems with parametric uncertainty, unknown actuator nonlinearity and bounded external disturbance. Two type of actuator nonlinearities, that is, symmetric dead-zone and Bouc-Wen hysteresis, are considered, respectively. First, an adaptive control scheme with positive integrable time-varying function is presented to compensate for the dead-zone nonlinearity. Then, the actuator nonlinearity under consideration is modeled as Bouc-Wen hysteresis, and desired compensation controller is designed based on the backstepping technique and Nussbaum gain approach. In both of the two schemes, the asymptotic tracking is guaranteed with the tracking error converging to zero. Finally, an illustrative example is provided to show the effectiveness of the proposed design methods.

213 citations


Journal ArticleDOI
TL;DR: A novel fault-tolerant (FT) robust linear quadratic regulator (LQR)-based H∞ controller using the LPV method to preserve stability and improve handling of a four-wheel independently actuated electric ground vehicle in spite of in-wheel motors and/or steering system faults is proposed.
Abstract: This paper presents a linear parameter-varying (LPV) control strategy to preserve stability and improve handling of a four-wheel independently actuated electric ground vehicle in spite of in-wheel motors and/or steering system faults. Different types of actuator faults including loss-of-effectiveness fault, additive fault, and the fault makes an actuator's control effect stuck-at-fixed-level, are considered simultaneously. To attenuate the effects of disturbance and address the challenging problem, a novel fault-tolerant (FT) robust linear quadratic regulator (LQR)-based $H_{\infty}$ controller using the LPV method is proposed. With the LQR-based $H_{\infty}$ control, the tradeoff between the tracking performance and the control input energy is achieved, and the effect from the external disturbance to the controlled outputs is minimized. The eigenvalue positions of the system matrix of the closed-loop system are also incorporated to tradeoff between the control inputs and the transient responses. The vehicle states, including vehicle yaw rate, lateral and longitudinal velocities, are simultaneously controlled to track their respective references. Simulations for different fault types and various driving scenarios are carried out with a high-fidelity, CarSim®, full-vehicle model. Simulation results show the effectiveness of the proposed FT control approach.

195 citations


Journal ArticleDOI
TL;DR: A novel fault diagnostic algorithm is proposed, which removes the classical assumption that the time derivative of the output error should be known, and an accommodation scheme is proposed to compensate for both actuator time-varying gain and bias faults.
Abstract: The problem of fault-tolerant dynamic surface control (DSC) for a class of uncertain nonlinear systems with actuator faults is discussed and an active fault-tolerant control (FTC) scheme is proposed. Using the DSC technique, a novel fault diagnostic algorithm is proposed, which removes the classical assumption that the time derivative of the output error should be known. Further, an accommodation scheme is proposed to compensate for both actuator time-varying gain and bias faults, and avoids the controller singularity. In addition, the proposed controller guarantees that all signals of the closed-loop system are semiglobally uniformly ultimately bounded, and converge to a small neighborhood of the origin. Finally, the effectiveness of the proposed FTC approach is demonstrated on a simulated aircraft longitudinal dynamics example.

191 citations


Patent
18 Dec 2014
TL;DR: In this paper, a surgical instrument system comprising a handle and a shaft assembly is disclosed, and the shaft assembly comprises an end effector, a release actuator, and a latch.
Abstract: A surgical instrument system comprising a handle and a shaft assembly is disclosed. The shaft assembly comprises an end effector, a release actuator, and a latch. The release actuator comprises a lock engaged with the handle when the release actuator is in a proximal position and disengaged from the handle when the release actuator is in a distal position. The latch is operably engaged with the release actuator and movable between a first position and a second position. The release actuator is configured to rotate the latch from the first position to the second position when the release actuator is moved toward the distal position. The latch comprises a catch configured to engage the handle when the latch is moved toward the second position. The catch is disengaged from the handle upon an additional manipulation of the release actuator. The additional manipulation is in a proximal direction.

174 citations


Journal ArticleDOI
TL;DR: In this paper, a soft actuator is presented which utilizes a droplet of Galinstan liquid metal to induce harmonic Marangoni fl ow at the surface of liquid metal when activated by a sinusoidal signal.
Abstract: Chaotic advection plays an important role in microplatforms for a variety of applications. Currently used mechanisms for inducing chaotic advection in small scale, however, are limited by their complicated fabrication processes and relatively high power consumption. Here, a soft actuator is reported which utilizes a droplet of Galinstan liquid metal to induce harmonic Marangoni fl ow at the surface of liquid metal when activated by a sinusoidal signal. This liquid metal actuator has no rigid parts and employs continuous electrowetting effect to induce chaotic advection with exceptionally low power consumption. The theory behind the operation of this actuator is developed and validated via a series of experiments. The presented actuator can be readily integrated into other microfl uidic components for a wide range of applications.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated model predictive control (MPC) of a single sea wave energy converter (WEC) and proposed a novel objective function, which can trade off the energy extraction, the energy consumed by the actuator and safe operation.

Journal ArticleDOI
TL;DR: This work studies two different frameworks for delay-adaptive prediction-based control design for nonlinear systems with unknown long actuator delay, and proves global asymptotic convergence of the proposed adaptive controller and local regulation.
Abstract: We present a systematic delay-adaptive prediction-based control design for nonlinear systems with unknown long actuator delay. Our approach is based on the representation of the constant actuator delay as a transport Partial Differential Equation (PDE) in which the convective speed is inversely proportional to the unknown delay. We study two different frameworks, assuming first that the actuator state is measured and relaxing afterward. For the full-state feedback case, we prove global asymptotic convergence of the proposed adaptive controller while, in the second case, replacing the actuator state by its adaptive estimate, we prove local regulation. The relevance of the obtained results are illustrated by simulations of a biological activator/repressor system.

Journal ArticleDOI
TL;DR: In this article, a finite-time controller integrated with disturbance observer is investigated for a rigid spacecraft in the presence of disturbance, actuator saturation and misalignment, and the closed-loop system/state is proved to be finite time stable and converges to the specified time-varying sliding mode surface.

Journal ArticleDOI
TL;DR: In this paper, the rotational variable stiffness actuator vsaUT-II is presented, which is characterized by the property that the apparent stiffness at the actuator output can be varied independently from its position.
Abstract: In this paper, the rotational variable stiffness actuator vsaUT-II is presented. This actuation system is characterized by the property that the apparent stiffness at the actuator output can be varied independently from its position. This behavior is realized by implementing a variable transmission ratio between the internal elastic elements and the actuator output, i.e., a lever arm with variable pivot point position. The pivot point is moved by a planetary gears mechanism, which acquires a straight motion from only rotations, thereby providing a low-friction transmission. The working principle details of the vsaUT-II are elaborated and the design is presented. The actuator dynamics are described by means of a lumped parameter model. The relevant parameters of the actuator are estimated and identified in the physical setup and measurements are used to validate both the design and the derived model.

Journal ArticleDOI
TL;DR: In this article, a velocity-measurement-free feedback control problem associated with attitude tracking for a rigid spacecraft in the presence of both actuator failures and actuator saturation is investigated.
Abstract: This paper investigates the velocity-measurement-free feedback control problem associated with attitude tracking for a rigid spacecraft in the presence of both actuator failures and actuator saturation. The decreased reaction torque fault and the increased bias torque fault in the reaction wheel are handled. By using only the measurable attitude, a terminal sliding-mode-based observer is developed to reconstruct all the states of the attitude system in finite time. With the reconstructed information, a novel attitude tracking controller is developed. A Lyapunov analysis shows that the desired attitude trajectories are followed even in the presence of external disturbances. The key features of the proposed control approach are that it is independent from the knowledge of actuator faults and fault-tolerant control is achieved without the need of angular velocity. The attitude tracking performance using the proposed strategy is evaluated through a numerical example.

Journal ArticleDOI
TL;DR: In this article, a fault tolerant control (FTC) strategy using virtual actuators and sensors for linear parameter varying (LPV) systems is proposed, which reconfigures the virtual actuator/sensor on-line taking into account faults and operating point changes.


Journal ArticleDOI
Zhiwei Zhu1, Xiaoqin Zhou1, Liu Zhiwei1, Rongqi Wang1, Lei Zhu1 
TL;DR: In this article, a 2DOF FTS-assisted diamond turning is proposed and demonstrated to enable the cutting tool to move along two directions with decoupled motions using a novel guidance flexural mechanism constructed using the newly proposed Z-shaped flexure hinges.
Abstract: The limited degrees of freedom (DOFs) of servo motions is an inherent deficiency in conventional, fast-tool-servo-(FTS)-assisted, diamond-turning, highly blocking applications of the FTS technique. In this paper, the concept of two-DOF FTS (2-DOF FTS)-assisted diamond turning is proposed and demonstrated. A piezoelectrically actuated 2-DOF FTS mechanism is developed to enable the cutting tool to move along two directions with decoupled motions. A novel guidance flexural mechanism constructed using the newly proposed Z-shaped flexure hinges (ZFHs) is introduced to generate motions along the z -axis, which is based on the bending deformation of the beams of the ZFHs. Additionally, using the differential moving principle (DMP), bi-directional motions in the x -axis direction can be achieved. Using the matrix-based compliance modeling method, the kinematics of the mechanism are analytically described, and the dynamics are also modeled using the Lagrangian principle. The theoretical results are then verified using finite element analysis (FEA). Certain increases in performances over conventional two-DOF flexural mechanisms are achieved: (a) a more compact structure with lower moving inertia, (b) theoretically decoupled motions of the output end, and (c) less than one actuator per DOF. To investigate the practical performance of the 2-DOF FTS system, both open-loop and closed-loop tests are conducted. Finally, the developed 2-DOF FTS technique is implemented to realize an innovative Pseudo-Random Diamond Turning (PRDT) method for the fabrication of micro-structured surfaces with scattering homogenization. The cutting results demonstrate not only the superiority of the concept but also the efficiency of the developed 2-DOF FTS system.

Journal ArticleDOI
TL;DR: A novel approach to fault-tolerant control design is proposed for a full-scale vehicle dynamic model with an active suspension system in the presence of uncertainties and actuator faults for mitigating three degrees of freedom heave-roll-pitch motion arising from road undulations.
Abstract: Advanced fault-tolerant control schemes are required for ensuring efficient and reliable operation of complex technological systems such as ground vehicles. A novel approach to fault-tolerant control design is proposed for a full-scale vehicle dynamic model with an active suspension system in the presence of uncertainties and actuator faults. The proposed control scheme uses a sliding-mode controller to generate the tracking signal to the valve for each of the four wheel subsystems for mitigating three degrees of freedom (3-DOF) heave-roll-pitch motion arising from road undulations. For each of the electrohydraulic valve-cylinder pair in each subsystem, an adaptive proportional-integralderivative (PID) controller is proposed. Designing an adaptation scheme for the PID gains to accommodate actuator faults is among the main contributions of this work. The focus on actuator faults is motivated by the fact that loss of actuator effectiveness is a critical fault scenario in vehicle suspension systems and that the probability of occurrence of faults in actuators is higher and more severe when compared with other components. To analyze the performance of the proposed approach, computer simulations are carried out to illustrate control performance, robustness, and fault tolerance. The performance of our approach is then compared with that of the sliding-mode control (SMC) approach presented by Chamseddine and Noura. Results clearly indicate the strength of the adaptation scheme and its ability to mitigate fault effects in a short time. Simplicity of the overall scheme and the stabilization of the system under both faulty and fault-free conditions are the main positive features of the proposed approach.

Journal ArticleDOI
TL;DR: In this paper, an integral sliding mode controller is proposed to design for a fluid power electrohydraulic actuator (EHA) system, where advanced techniques such as H∞ control and the regional pole placement are employed to derive the optimal feedback gain which can be calculated by solving a necessary and sufficient condition in the form of linear matrix inequality.
Abstract: In this paper, we exploit the sliding mode control problem for a fluid power electrohydraulic actuator (EHA) system. To characterize the nonlinearity of the friction, the EHA system is modeled as a linear system with a system uncertainty. Practically, it is assumed that the system is also subject to the load disturbance and the external noise. An integral sliding mode controller is proposed to design. The advanced techniques such as the H∞ control and the regional pole placement are employed to derive the optimal feedback gain which can be calculated by solving a necessary and sufficient condition in the form of linear matrix inequality. A sliding mode control law is developed such that the sliding mode reaching law is satisfied. Simulation and comparison results show the effectiveness of the proposed design method.

Journal ArticleDOI
TL;DR: In this article, a sliding mode observer based on a linear parameter varying system with fault reconstruction capability is proposed for detecting and isolating faults in an actuator and a sensor in a nonlinear model of a large transport aircraft.
Abstract: SUMMARY This paper presents a robust fault detection and isolation scheme using a sliding mode observer based on a linear parameter varying system, with fault reconstruction capability Both actuator and sensor fault reconstruction schemes are considered that possess robustness against a certain class of uncertainty and corrupted measurements For actuator fault reconstruction, the input distribution matrix (associated with the actuators being monitored) is factorized into fixed and varying components LMIs are used to design the key observer parameters in order to minimize the effect of uncertainty and measurement corruption on the fault reconstruction signal The faults are reconstructed using the output error injection signal associated with the nonlinear term of the sliding mode observer For sensor fault reconstruction, the idea is to reformulate the problem into an actuator fault reconstruction scenario so that the same design procedure can be applied This is achieved by augmenting the original system with the filtered sensors being monitored Simulations using a full nonlinear model of a large transport aircraft are presented and show good fault reconstruction performance Copyright © 2013 John Wiley & Sons, Ltd

Journal ArticleDOI
TL;DR: A piezoelectric actuator using the third and fourth bending vibration modes was proposed, designed, fabricated and tested with the aim of accomplishing rotary driving by boltclamped transducer.
Abstract: A piezoelectric actuator using the third and fourth bending vibration modes was proposed, designed, fabricated and tested with the aim of accomplishing rotary driving by boltclamped transducer. By superimposing the third and fourth bending vibrations, elliptical movements are formed on the two leading ends of the actuator. When a ring type rotor is in contact with the two diving tips and the vertical preload is applied, the horizontal movements of the driving tips generated by the third bending vibration will push the rotor into motion by frictional forces while the vertical movements produced by the fourth bending vibration will overcome the preload. A method of tuning the resonance frequency of the third bending mode to the fourth bending one was discussed. The horn shape was adjusted to make the two bending modes have nearly uniform frequencies. The vibration characteristic and mechanical ability of a prototype were tested, and the tested resonance frequencies agreed well with the calculated ones. The prototype achieved maximum speed and torque of 86 r/min and 2.5 Nm, respectively.

Journal ArticleDOI
TL;DR: In this article, an active fault-tolerant control scheme is proposed for a wind turbine power generating unit of a grid using adaptive filters obtained via the nonlinear geometric approach, which allows to obtain interesting decoupling property with respect to uncertainty affecting the wind turbine system.
Abstract: SUMMARY This paper describes the design of an active fault-tolerant control scheme that is applied to the actuator of a wind turbine benchmark. The methodology is based on adaptive filters obtained via the nonlinear geometric approach, which allows to obtain interesting decoupling property with respect to uncertainty affecting the wind turbine system. The controller accommodation scheme exploits the on-line estimate of the actuator fault signal generated by the adaptive filters. The nonlinearity of the wind turbine model is described by the mapping to the power conversion ratio from tip-speed ratio and blade pitch angles. This mapping represents the aerodynamic uncertainty, and usually is not known in analytical form, but in general represented by approximated two-dimensional maps (i.e. look-up tables). Therefore, this paper suggests a scheme to estimate this power conversion ratio in an analytical form by means of a two-dimensional polynomial, which is subsequently used for designing the active fault-tolerant control scheme. The wind turbine power generating unit of a grid is considered as a benchmark to show the design procedure, including the aspects of the nonlinear disturbance decoupling method, as well as the viability of the proposed approach. Extensive simulations of the benchmark process are practical tools for assessing experimentally the features of the developed actuator fault-tolerant control scheme, in the presence of modelling and measurement errors. Comparisons with different fault-tolerant schemes serve to highlight the advantages and drawbacks of the proposed methodology. Copyright © 2013 John Wiley & Sons, Ltd.

Journal ArticleDOI
TL;DR: In this paper, a general flexible method to redistribute wind turbine blade forces as permeable body forces in a computational domain is presented, which can take any kind of shape discretization, determine the intersectional elements with the computational grid, and use the size of these elements to reduce the computational cost of large wind farm wake simulations.
Abstract: Wind turbine wake can be studied in computational fluid dynamics with the use of permeable body forces (e.g. actuator disc, line and surface). This paper presents a general flexible method to redistribute wind turbine blade forces as permeable body forces in a computational domain. The method can take any kind of shape discretization, determine the intersectional elements with the computational grid and use the size of these elements to redistribute proportionally the forces. This method can potentially reduce the need for mesh refinement in the region surrounding the rotor and, therefore, also reduce the computational cost of large wind farm wake simulations. The special case of the actuator disc is successfully validated with an analytical solution for heavily loaded turbines and with a full-rotor computation in computational fluid dynamics. Copyright © 2013 John Wiley & Sons, Ltd.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated topology optimization of the piezoelectric actuator/sensor coverage attached to a thin-shell structure to improve the active control performance for reducing the dynamic response under transient excitations.

Journal ArticleDOI
TL;DR: In this article, a fabrication process is developed that uses accessible PDMS soft lithography techniques to produce compliant pneumatic actuators with a width of 7mm and a thickness of 0.65mm.
Abstract: Compliant pneumatic actuators have recently attracted the interests of the robotics community, especially for soft robotic applications where large strokes are needed in delicate environments. To date, these actuators have demonstrated the ability to generate contracting, expanding and bending strokes. This paper introduces a new actuator design that complements the existing actuators by generating twisting deformations upon pressurization. A fabrication process is developed that uses accessible PDMS soft lithography techniques. With this process, prototype actuators with a width of 7 mm and a thickness of 0.65 mm have been made that achieved a twisting rotation of 6.5°/mm actuator length at a pressure of 178 kPa. This paper also presents the integration of four twisting actuators into a 2 DOF tilting mirror platform which is capable of deflecting a mirror over 25° at a pressure of 231 kPa.

Journal ArticleDOI
TL;DR: In this paper, the analysis of the aerodynamic performance of ducted wind turbines is carried out by means of a nonlinear and semi-analytical actuator disk model, which returns the exact solution in an implicit formulation as superposition of ring vortices properly arranged along the duct surface and wake region.

Journal ArticleDOI
TL;DR: In this paper, the use of pleated pneumatic artificial muscles in a novel actuator system design allows for a higher torque range in a larger range of motion, and the proposed torque controller achieves the dynamic torques required for zero to full assistance at moderate walking speeds.
Abstract: Powered lower limb exoskeletons require high-performance actuator systems, capable of producing zero to high-assistive torque and at the same time yielding to human interaction torques. Such variable impedance can be achieved by the means of compliant actuators. Because of their intrinsic compliance and high force-to-weight ratio pneumatic muscles are a viable option. However, previous pneumatic muscle powered exoskeleton designs either used them as a position source or failed to meet the high-dynamic torque requirements when using them as a torque source. This paper contributes to the improvement of pneumatic muscle-based actuator systems as a torque source for exoskeleton-type robots. The use of pleated pneumatic artificial muscles in a novel actuator system design allows for a higher torque range in a larger range of motion. Performance evaluation results are given for a 1 DOF test setup and a powered knee exoskeleton. The proposed torque controller achieves the dynamic torques required for zero to full assistance at moderate walking speeds.