Showing papers on "Actuator published in 2014"

Pneumatic Networks for Soft Robotics that Actuate Rapidly

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.

Actuator for releasing a tissue thickness compensator from a fastener cartridge

Abstract: A fastener cartridge assembly for use with a surgical end effector. The fastener cartridge assembly can comprise a cartridge body having fastener cavities, fasteners removably positioned in the fastener cavities, a layer of material releasably secured relative to the cartridge body, a connector configured to secure the layer of material to the cartridge body at a location distal to at least one fastener cavity, and an actuator. The layer of material can be a tissue thickness compensator. When actuated, the actuator can overcome the connector, and can overcome the connector prior to the removal of the fasteners from the fastener cavities. The actuator can be actuated at a location proximal to at least one fastener cavity, and can extend distally past at least one fastener cavity toward the connector.

Extended-State-Observer-Based Output Feedback Nonlinear Robust Control of Hydraulic Systems With Backstepping

Abstract: In this paper, an output feedback nonlinear control is proposed for a hydraulic system with mismatched modeling uncertainties in which an extended state observer (ESO) and a nonlinear robust controller are synthesized via the backstepping method. The ESO is designed to estimate not only the unmeasured system states but also the modeling uncertainties. The nonlinear robust controller is designed to stabilize the closed-loop system. The proposed controller accounts for not only the nonlinearities (e.g., nonlinear flow features of servovalve), but also the modeling uncertainties (e.g., parameter derivations and unmodeled dynamics). Furthermore, the controller theoretically guarantees a prescribed tracking transient performance and final tracking accuracy, while achieving asymptotic tracking performance in the absence of time-varying uncertainties, which is very important for high-accuracy tracking control of hydraulic servo systems. Extensive comparative experimental results are obtained to verify the high-performance nature of the proposed control strategy.

3D multifunctional integumentary membranes for spatiotemporal cardiac measurements and stimulation across the entire epicardium

Abstract: Means for high-density multiparametric physiological mapping and stimulation are critically important in both basic and clinical cardiology. Current conformal electronic systems are essentially 2D sheets, which cannot cover the full epicardial surface or maintain reliable contact for chronic use without sutures or adhesives. Here we create 3D elastic membranes shaped precisely to match the epicardium of the heart via the use of 3D printing, as a platform for deformable arrays of multifunctional sensors, electronic and optoelectronic components. Such integumentary devices completely envelop the heart, in a form-fitting manner, and possess inherent elasticity, providing a mechanically stable biotic/abiotic interface during normal cardiac cycles. Component examples range from actuators for electrical, thermal and optical stimulation, to sensors for pH, temperature and mechanical strain. The semiconductor materials include silicon, gallium arsenide and gallium nitride, co-integrated with metals, metal oxides and polymers, to provide these and other operational capabilities. Ex vivo physiological experiments demonstrate various functions and methodological possibilities for cardiac research and therapy.

High-Accuracy Tracking Control of Hydraulic Rotary Actuators With Modeling Uncertainties

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.

An instant multi-responsive porous polymer actuator driven by solvent molecule sorption

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.

Design and Control Considerations for High-Performance Series Elastic Actuators

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.

A review on shape memory alloys with applications to morphing aircraft

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.

Device and method for less forceful tissue puncture

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.

Carbon Nanotube and Graphene‐based Bioinspired Electrochemical Actuators

Abstract: Bio-inspired actuation materials, also called artificial muscles, have attracted great attention in recent decades for their potential application in intelligent robots, biomedical devices, and micro-electro-mechanical systems. Among them, ionic polymer metal composite (IPMC) actuator has been intensively studied for their impressive high-strain under low voltage stimulation and air-working capability. A typical IPMC actuator is composed of one ion-conductive electrolyte membrane laminated by two electron-conductive metal electrode membranes, which can bend back and forth due to the electrode expansion and contraction induced by ion motion under alternating applied voltage. As its actuation performance is mainly dominated by electrochemical and electromechanical process of the electrode layer, the electrode material and structure become to be more crucial to higher performance. The recent discovery of one dimensional carbon nanotube and two dimensional graphene has created a revolution in functional nanomaterials. Their unique structures render them intriguing electrical and mechanical properties, which makes them ideal flexible electrode materials for IPMC actuators in stead of conventional metal electrodes. Currently although the detailed effect caused by those carbon nanomaterial electrodes is not very clear, the presented outstanding actuation performance gives us tremendous motivation to meet the challenge in understanding the mechanism and thus developing more advanced actuator materials. Therefore, in this review IPMC actuators prepared with different kinds of carbon nanomaterials based electrodes or electrolytes are addressed. Key parameters which may generate important influence on actuation process are discussed in order to shed light on possible future research and application of the novel carbon nanomateials based bio-inspired electrochemical actuators.

Asymptotic Tracking Control of Uncertain Nonlinear Systems With Unknown Actuator Nonlinearity

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.

Linear Parameter-Varying Controller Design for Four-Wheel Independently Actuated Electric Ground Vehicles With Active Steering Systems

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.

Adaptive Fuzzy Observer-Based Active Fault-Tolerant Dynamic Surface Control for a Class of Nonlinear Systems With Actuator 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.

Adaptive optoelectronic camouflage systems with designs inspired by cephalopod skins

Abstract: Octopus, squid, cuttlefish, and other cephalopods exhibit exceptional capabilities for visually adapting to or differentiating from the coloration and texture of their surroundings, for the purpose of concealment, communication, predation, and reproduction. Long-standing interest in and emerging understanding of the underlying ultrastructure, physiological control, and photonic interactions has recently led to efforts in the construction of artificial systems that have key attributes found in the skins of these organisms. Despite several promising options in active materials for mimicking biological color tuning, existing routes to integrated systems do not include critical capabilities in distributed sensing and actuation. Research described here represents progress in this direction, demonstrated through the construction, experimental study, and computational modeling of materials, device elements, and integration schemes for cephalopod-inspired flexible sheets that can autonomously sense and adapt to the coloration of their surroundings. These systems combine high-performance, multiplexed arrays of actuators and photodetectors in laminated, multilayer configurations on flexible substrates, with overlaid arrangements of pixelated, color-changing elements. The concepts provide realistic routes to thin sheets that can be conformally wrapped onto solid objects to modulate their visual appearance, with potential relevance to consumer, industrial, and military applications.

Surgical instrument system comprising lockable systems

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.

Liquid Metal Actuator for Inducing Chaotic Advection

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.

Delay-Adaptive Control for Nonlinear Systems

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.

The Variable Stiffness Actuator vsaUT-II: Mechanical Design, Modeling, and Identification

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.

Fault-Tolerant Tracking Control of Spacecraft with Attitude-Only Measurement Under Actuator Failures

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.

Dynamics and control of quadrotor with robotic manipulator

Abstract: We show that the Lagrange dynamics of quadrotor-manipulator systems can be completely decoupled into: 1) the center-of-mass dynamics in E(3), which, similar to the standard quadrotor dynamics, is point-mass dynamics with under-actuation and gravity effect; and 2) the "internal rota- tional" dynamics of the quadrotor's rotation and manipulator configuration, which assumes the form of standard Lagrange dynamics of robotic manipulator with full-actuation and no gravity effect. Relying on this structure, we propose a novel backstepping-like end-effector tracking control law, which can allow us to assign different roles for the center-of-mass control and for the internal rotational dynamics control according to task objectives. Simulations using a planar quadrotor with a 2-DOF arm are also performed to show the theory. I. INTRODUCTION Quadrotors have been researched extensively in recent years due to their agile performance, relative-easiness to con- trol, and affordability, with the rapid advancements in sen- sors, actuators, materials, and embedded computing. These quadrotors are also promising to extend the ground-bound ability of the typical mobile robots to the three dimensional space. Some application examples include: remote landscape survey, aerial photography, surveillance and reconnaissance,

Development of a piezoelectrically actuated two-degree-of-freedom fast tool servo with decoupled motions for micro-/nanomachining

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.

Adaptive PID-Sliding-Mode Fault-Tolerant Control Approach for Vehicle Suspension Systems Subject to Actuator Faults

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.

Robust H∞ sliding mode control with pole placement for a fluid power electrohydraulic actuator (EHA) system

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.

Method and arrangement for pick-up point retrieval timing

Abstract: A method and arrangement are described for pick-up point retrieval timing in a vehicle having autonomous parking capabilities. The arrangement may include a communication interface arranged to receive data concerning a desired retrieval time. A processor may be arranged to monitor one or more parameters while the vehicle is performing autonomous driving along a route to a final slot until autonomous parking of the vehicle has been completed. The processor may be further arranged to calculate when to start autonomous return travel in order to be at the pick-up point at the desired retrieval time based on at least one monitored parameter. An actuator may be arranged to initiate autonomous travel to the pick-up point at the calculated return travel start time.

Robust fault reconstruction for linear parameter varying systems using sliding mode observers

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