Showing papers on "Actuator published in 2013"

Bio-Inspired Polymer Composite Actuator and Generator Driven by Water Gradients

Abstract: Here we describe the development of a water-responsive polymer film. Combining both a rigid matrix (polypyrrole) and a dynamic network (polyol-borate), strong and flexible polymer films were developed that can exchange water with the environment to induce film expansion and contraction, resulting in rapid and continuous locomotion. The film actuator can generate contractile stress up to 27 megapascals, lift objects 380 times heavier than itself, and transport cargo 10 times heavier than itself. We have assembled a generator by associating this actuator with a piezoelectric element. Driven by water gradients, this generator outputs alternating electricity at ~0.3 hertz, with a peak voltage of ~1.0 volt. The electrical energy is stored in capacitors that could power micro- and nanoelectronic devices.

System and method for server based control

Abstract: A system and method in a building or vehicle for an actuator operation in response to a sensor according to a control logic, the system comprising a router or a gateway communicating with a device associated with the sensor and a device associated with the actuator over in-building or in-vehicle networks, and an external Internet-connected control server associated with the control logic implementing a PID closed linear control loop and communicating with the router over external network for controlling the in-building or in-vehicle phenomenon. The sensor may be a microphone or a camera, and the system may include voice or image processing as part of the control logic. A redundancy is used by using multiple sensors or actuators, or by using multiple data paths over the building or vehicle internal or external communication. The networks may be wired or wireless, and may be BAN, PAN, LAN, WAN, or home networks.

Towards a soft pneumatic glove for hand rehabilitation

Abstract: This paper presents preliminary results for the design, development and evaluation of a hand rehabilitation glove fabricated using soft robotic technology. Soft actuators comprised of elastomeric materials with integrated channels that function as pneumatic networks (PneuNets), are designed and geometrically analyzed to produce bending motions that can safely conform with the human finger motion. Bending curvature and force response of these actuators are investigated using geometrical analysis and a finite element model (FEM) prior to fabrication. The fabrication procedure of the chosen actuator is described followed by a series of experiments that mechanically characterize the actuators. The experimental data is compared to results obtained from FEM simulations showing good agreement. Finally, an open-palm glove design and the integration of the actuators to it are described, followed by a qualitative evaluation study.

Access door with integrated switch actuator

Abstract: An apparatus and method are disclosed for creating an integrated access door and switch actuator. The integrated access door and switch actuator are created from a single composite material. The composite material is flexible to allow movement, but is also durable to provide a protective covering. The integrated access door and switch actuator include a living hinge, which allows the access door to move to an open and closed position while the switch actuator is stationary in a fixed position.

Tunable Lenses Using Transparent Dielectric Elastomer Actuators

Abstract: Focus tunable, adaptive lenses provide several advantages over traditional lens assemblies in terms of compactness, cost, efficiency, and flexibility. To further improve the simplicity and compact nature of adaptive lenses, we present an elastomer-liquid lens system which makes use of an inline, transparent electroactive polymer actuator. The lens requires only a minimal number of components: a frame, a passive membrane, a dielectric elastomer actuator membrane, and a clear liquid. The focal length variation was recorded to be greater than 100% with this system, responding in less than one second. Through the analysis of membrane deformation within geometrical constraints, it is shown that by selecting appropriate lens dimensions, even larger focusing dynamic ranges can be achieved.

Mechanically programmable bend radius for fiber-reinforced soft actuators

Abstract: Established design and fabrication guidelines exist for achieving a variety of motions with soft actuators such as bending, contraction, extension, and twisting. These guidelines typically involve multi-step molding of composite materials (elastomers, paper, fiber, etc.) along with specially designed geometry. In this paper we present the design and fabrication of a robust, fiber-reinforced soft bending actuator where its bend radius and bending axis can be mechanically-programed with a flexible, selectively-placed conformal covering that acts to mechanically constrain motion. Several soft actuators were fabricated and their displacement and force capabilities were measured experimentally and compared to demonstrate the utility of this approach. Finally, a prototype two-digit end-effector was designed and programmed with the conformal covering to shape match a rectangular object. We demonstrated improved gripping force compared to a pure bending actuator. We envision this approach enabling rapid customization of soft actuator function for grasping applications where the geometry of the task is known a priori.

Adaptive Robust Vibration Control of Full-Car Active Suspensions With Electrohydraulic Actuators

Abstract: This paper investigates the problem of vibration suppression in vehicular active suspension systems, whose aim is to stabilize the attitude of the vehicle and improve the riding comfort. A full-car model is adopted, and electrohydraulic actuators with highly nonlinear characteristics are considered to form the basis of accurate control. In this paper, the H∞ performance is introduced to realize the disturbance suppression by selecting the actuator forces as virtual inputs, and an adaptive robust control technology is further used to design controllers which help real force inputs track virtual ones. The resulting controllers are robust against both actuator parametric uncertainties and uncertain actuator nonlinearities. The stability analysis for the closed-loop system is given within the Lyapunov framework. Finally, a numerical example is given to illustrate the effectiveness of the proposed control law, where different road conditions are considered in order to reveal the closed-loop system performance in detail.

Fuzzy-Model-Based Fault-Tolerant Design for Nonlinear Stochastic Systems Against Simultaneous Sensor and Actuator Faults

Abstract: This paper addresses the problem of fault estimation and fault-tolerant control for a class of Takagi-Sugeno (T-S) fuzzy Ito stochastic systems subject to simultaneously sensor and actuator faults. The main difficulty in this study is that sensor faults, actuator faults, and stochastic noise that are governed by Brownian motion are taken into simultaneous consideration in a unified framework, and traditional fault-tolerant approaches are not effective to solve this research issue. A new descriptor fuzzy sliding-mode observer approach is presented in this paper to obtain the simultaneous estimates of system state, sensor fault, and actuator fault vectors. Based on the state estimates, an observer-based fault-tolerant control (FTC) scheme is developed to stabilize the resulting closed-loop system. Finally, a simulation example is provided to show the effectiveness of the proposed fault-tolerant approach.

Modeling and Robust Discrete-Time Sliding-Mode Control Design for a Fluid Power Electrohydraulic Actuator (EHA) System

Abstract: This paper studies the design of a robust discrete-time sliding-mode control (DT-SMC) for a high precision electrohydraulic actuator (EHA) system Nonlinear friction in the hydraulic actuator can greatly influence the performance and accuracy of the hydraulic actuators, and it is difficult to accurately model the nonlinear friction characteristics In this paper, it is proposed to characterize the frictions as an uncertainty in the system matrices Indeed, the effects of variations of the nonlinear friction coefficients are considered as norm-bounded uncertainties that span a bounded region to cover a wide range of the real actuator friction For such a discrete-time dynamic model, for the EHA system with system uncertainty matrices and a nonlinear term, a sufficient condition for existence of stable sliding surfaces is proposed by using the linear matrix inequality approach Based on this existence condition, a DT-SMC is developed such that the reaching motion satisfies the discrete-time sliding mode reaching condition for uncertain systems Simulation and experimental studies on the EHA system illustrate the effectiveness and applicability of the proposed method

Omega-Shaped Inchworm-Inspired Crawling Robot With Large-Index-and-Pitch (LIP) SMA Spring Actuators

Abstract: This paper proposes three design concepts for developing a crawling robot inspired by an inchworm, called the Omegabot. First, for locomotion, the robot strides by bending its body into an omega shape; anisotropic friction pads enable the robot to move forward using this simple motion. Second, the robot body is made of a single part but has two four-bar mechanisms and one spherical six-bar mechanism; the mechanisms are 2-D patterned into a single piece of composite and folded to become a robot body that weighs less than 1 g and that can crawl and steer. This design does not require the assembly of various mechanisms of the body structure, thereby simplifying the fabrication process. Third, a new concept for using a shape-memory alloy (SMA) coil-spring actuator is proposed; the coil spring is designed to have a large spring index and to work over a large pitch-angle range. This large-index-and-pitch SMA spring actuator cools faster and requires less energy, without compromising the amount of force and displacement that it can produce. Therefore, the frequency and the efficiency of the actuator are improved. A prototype was used to demonstrate that the inchworm-inspired, novel, small-scale, lightweight robot manufactured on a single piece of composite can crawl and steer.

Characterization of silicone rubber based soft pneumatic actuators

Abstract: Conventional pneumatic actuators have been a popular choice due to their decent force/torque output. Nowadays, new generation of pneumatic actuator made out of highly compliant elastomers, which we call soft pneumatic actuators (SPA), are drawing increasing attention due to their ease of fabrication, high customizability and innately softness. However, there is no effective method presented to characterize and understand these actuators, such as to measure the force and torque output, range of motion and the speed of actuation. In this work, we present two types of SPAs: bending and rotary actuators. In addition, we have developed two measurement setups to characterize actuators of different geometries. The measured force/torque outputs of different actuators are presented and analyzed. Step responses to certain pressure input are presented and discussed. A simple model is presented to provide physical insight to the observed behavior of the soft actuators. This work provides the basis for designing customized SPAs with application-specific requirements.

A Novel Intrinsically Energy Efficient Actuator With Adjustable Stiffness (AwAS)

Abstract: In this paper, a new actuator with adjustable stiffness (AwAS) is presented. AwAS is capable of controlling the position and stiffness of a joint, independently. The proposed actuator can regulate the joint stiffness through a wide range with minimum energy consumption by means of a small motor. This is possible due to its novel mechanical configuration that achieves the stiffness regulation not through the control of spring pretension (as in most of the existing variable stiffness joints) but by using the variable lever arm principle. The regulation of the lever arm length is achieved through the displacement of the spring elements. An important consequence of this mechanism is that the displacement needed to change the stiffness is perpendicular to the forces generated by the spring. This helps to reduce the energy/power required to regulate the stiffness. It is experimentally shown that AwAS is capable of minimizing energy consumption through exploiting the natural dynamics in real time for both fixed and variable frequency motions.

Inverse Rate-Dependent Prandtl–Ishlinskii Model for Feedforward Compensation of Hysteresis in a Piezomicropositioning Actuator

Abstract: Piezomicropositioning actuators, which are widely used in micropositioning applications, exhibit strong rate-dependent hysteresis nonlinearities that affect the accuracy of these micropositioning systems when used in open-loop control systems, and may also even lead to system instability of closed-loop control systems. Feedback control techniques could compensate for the rate-dependent hysteresis in piezomicropositioning actuators. However, accurate sensors over a wide range of excitation frequencies and the feedback control techniques inserted in the closed-loop control systems may limit the use of the piezomicropositioning and nanopositioning systems in different micropositioning and nanopositioning applications. We show that open-loop control techniques, also called feedforward techniques, can compensate for rate-dependent hysteresis nonlinearities over different excitation frequencies. An inverse rate-dependent Prandtl-Ishlinskii model is utilized for feedforward compensation of the rate-dependent hysteresis nonlinearities in a piezomicropositioning stage. The exact inversion of the rate-dependent model holds under the condition that the distances between the thresholds do not decrease in time. The inverse of the rate-dependent model is applied as a feedforward compensator to compensate for the rate-dependent hysteresis nonlinearities of a piezomicropositioning actuator at a range of different excitation frequencies between 0.05-100 Hz. The results show that the inverse compensator suppresses the rate-dependent hysteresis nonlinearities, and the maximum positioning error in the output displacement at different excitation frequencies.

A Data-Driven Constrained Norm-Optimal Iterative Learning Control Framework for LTI Systems

Abstract: This brief presents a data-driven constrained norm-optimal iterative learning control framework for linear time-invariant systems that applies to both tracking and point-to-point motion problems. The key contribution of this brief is the estimation of the system's impulse response using input/output measurements from previous iterations, hereby eliminating time-consuming identification experiments. The estimated impulse response is used in a norm-optimal iterative learning controller, where actuator limitations can be formulated as linear inequality constraints. Experimental validation on a linear motor positioning system shows the ability of the proposed data-driven framework to: 1) achieve tracking accuracy up to the repeatability of the test setup; 2) minimize the rms value of the tracking error while respecting the actuator input constraints; 3) learn energy-optimal system inputs for point-to-point motions.

Modeling and High Dynamic Compensating the Rate-Dependent Hysteresis of Piezoelectric Actuators via a Novel Modified Inverse Preisach Model

Abstract: Hysteresis of a piezoelectric actuator is rate-dependent, but most hysteresis models are based on elementary rate-independent models, which are not suitable for modeling actuator behavior across a wide range of frequencies. This paper presents a novel modified inverse Preisach model to compensate the hysteresis of a piezoelectric actuator at varying frequency ranges. The classical Preisach model for hysteresis is introduced first, the identification of μ-function through least square method is conducted afterwards. The linearity property of the Preisach model is analyzed and verified by experiment. A novel modified inverse Preisach model featured with weighed sum of μ-density functions is proposed, which is based on the linearity property. The fast Fourier transform method is adopted to select the proper μ-density functions and weights to form a real-time online rate-dependent compensator for piezoceramic (PZTs) hysteresis. During experiments with tracking multifrequency composed signals, we have observed that the hysteresis features of the PZT can be consistently compensated. The experimental results show that the proposed open-loop hysteresis adjust method greatly improves the tracking control accuracy of the PZT.

Fuzzy Logic System-Based Adaptive Fault-Tolerant Control for Near-Space Vehicle Attitude Dynamics With Actuator Faults

Abstract: This paper addresses the problem of fault-tolerant control (FTC) for near-space vehicle (NSV) attitude dynamics with actuator faults, which is described by a Takagi-Sugeno (T-S) fuzzy model. First, a general actuator fault model that integrated varying bias and gain faults, which are assumed to be dependent on the system state, is proposed. Then, sliding mode observers (SMOs) are designed to provide a bank of residuals for fault detection and isolation. Based on Lyapunov stability theory, a novel fault diagnostic algorithm is proposed, which removes the classical assumption that the time derivative of the output error should be known. Further, for the two cases where the state is available or not, two accommodation schemes are proposed to compensate for the effect of the faults. These schemes do not need the condition that the bounds of the time derivative of the faults should be known. In addition, a sufficient condition for the existence of SMOs is derived according to Lyapunov stability theory. Finally, simulation results of NSV are presented to demonstrate the efficiency of the proposed FTC approach.

Approximation-Based Robust Adaptive Automatic Train Control: An Approach for Actuator Saturation

Abstract: This paper addresses an on-line approximation-based robust adaptive control problem for the automatic train operation (ATO) system under actuator saturation caused by constraints from serving motors. A robust adaptive control law is proposed, which is proved capable of on-line estimating of the unknown system parameters and stabilizing the closed-loop system. To cope with actuator saturation, another robust adaptive control is proposed for the ATO system, by explicitly considering the actuator saturation nonlinearity other than unknown system parameters, which is also proved capable of stabilizing the closed-loop system. Simulation results are presented to verify the effectiveness of the two proposed control laws.

Experimental Test of a Two-Stage Kalman Filter for Actuator Fault Detection and Diagnosis of an Unmanned Quadrotor Helicopter

Abstract: This paper addresses the problem of Faut Detection and Diagnosis (FDD) of a quadrotor helicopter system in the presence of actuator faults. To this end a Two-Stage Kalman Filter (TSKF) is used to simultaneously estimate and isolate possible faults in each actuator. The faults are modelled as losses in control effectiveness of rotors. Three fault scenarios are investigated: loss of control effectiveness in one single actuator, simultaneous loss of control effectiveness in all motors, and loss of control effectiveness in three motors with different magnitudes. The developed FDD algorithm is evaluated through experimental application to an unmanned quadrotor helicopter testbed available at the Department of Mechanical and Industrial Engineering of Concordia University, called Qball-X4. The obtained results show the effectiveness of the proposed FDD method.

Appendage Mountable Electronic Devices COnformable to Surfaces

Abstract: Disclosed are appendage mountable electronic systems and related methods for covering and conforming to an appendage surface. A flexible or stretchable substrate has an inner surface for receiving an appendage, including an appendage having a curved surface, and an opposed outer surface that is accessible to external surfaces. A stretchable or flexible electronic device is supported by the substrate inner and/or outer surface, depending on the application of interest. The electronic device in combination with the substrate provides a net bending stiffness to facilitate conformal contact between the inner surface and a surface of the appendage provided within the enclosure. In an aspect, the system is capable of surface flipping without adversely impacting electronic device functionality, such as electronic devices comprising arrays of sensors, actuators, or both sensors and actuators.

Wing morphing control with shape memory alloy actuators

Abstract: Aircraft morphing is referred to as the ability for an aircraft to change its geometry in flight. Formally, flaps, spoilers, and control devices are considered morphing, but in general, morphing in aerospace is associated with geometrical changes using smart materials such as shape memory alloys. Shape memory alloy is a material that changes shape under heating and produces force and deflections, which make it potential actuator for a wing morphing system. The motivation behind this study is the application to small-sized and medium-sized unmanned air vehicles and the potential to increase range or endurance for a given fuel load through improved lift-to-drag ratio. The camber line of an airfoil section, the predominant parameter affecting lift and drag, is changed by resistive heating of a shape memory alloy actuator and cooling in the surrounding air. Experiments were conducted under wind tunnel conditions to verify analysis and to investigate the effects of its application on the aerodynamic behavior o...

Adaptive time series compensator for delay compensation of servo-hydraulic actuator systems for real-time hybrid simulation

Abstract: SUMMARY Hydraulic actuators are typically used in a real-time hybrid simulation to impose displacements to a test structure (also known as the experimental substructure). It is imperative that good actuator control is achieved in the real-time hybrid simulation to minimize actuator delay that leads to incorrect simulation results. The inherent nonlinearity of an actuator as well as any nonlinear response of the experimental substructure can result in an amplitude-dependent behavior of the servo-hydraulic system, making it challenging to accurately control the actuator. To achieve improved control of a servo-hydraulic system with nonlinearities, an adaptive actuator compensation scheme called the adaptive time series (ATS) compensator is developed. The ATS compensator continuously updates the coefficients of the system transfer function during a real-time hybrid simulation using online real-time linear regression analysis. Unlike most existing adaptive methods, the system identification procedure of the ATS compensator does not involve user-defined adaptive gains. Through the online updating of the coefficients of the system transfer function, the ATS compensator can effectively account for the nonlinearity of the combined system, resulting in improved accuracy in actuator control. A comparison of the performance of the ATS compensator with existing linearized compensation methods shows superior results for the ATS compensator for cases involving actuator motions with predefined actuator displacement histories as well as real-time hybrid simulations. Copyright © 2013 John Wiley & Sons, Ltd.

A piezoelectric-driven rotary actuator by means of inchworm motion

Abstract: This paper presents a piezoelectric-driven stepping rotary actuator based on the inchworm motion. With the help of nine piezoelectric stacks and the flexure hinges, the designed actuator can realize large rotary ranges and high rotary speed with high accuracy. Three kinds of working units that compose the actuator are described and calculated: the clamping unit to hold the rotor, the adjusting unit to preload the piezoelectric stacks and the driving unit to produce the driving torque. To test the working performance, a prototype actuator was fabricated, and the experimental results indicate that the minimum stepping angle is 4.95 μrad when the driving voltage is 20 V and the frequency is 1 Hz, the maximum output torque is 93.1 N mm under the driving voltage of 100 V and the maximum velocity can be 6508.5 μrad/s when the frequency reaches 30 Hz. The experimental results verify that the proposed actuator can realize different stepping angles and rotation speeds with high accuracy under different driving voltages and frequencies.

Accuracy of the actuator disc-RANS approach for predicting the performance and wake of tidal turbines.

Abstract: The actuator disc-RANS model has widely been used in wind and tidal energy to predict the wake of a horizontal axis turbine. The model is appropriate where large-scale effects of the turbine on a flow are of interest, for example, when considering environmental impacts, or arrays of devices. The accuracy of the model for modelling the wake of tidal stream turbines has not been demonstrated, and flow predictions presented in the literature for similar modelled scenarios vary significantly. This paper compares the results of the actuator disc-RANS model, where the turbine forces have been derived using a blade-element approach, to experimental data measured in the wake of a scaled turbine. It also compares the results with those of a simpler uniform actuator disc model. The comparisons show that the model is accurate and can predict up to 94 per cent of the variation in the experimental velocity data measured on the centreline of the wake, therefore demonstrating that the actuator disc-RANS model is an accurate approach for modelling a turbine wake, and a conservative approach to predict performance and loads. It can therefore be applied to similar scenarios with confidence.

Dielectric elastomer actuators used for pneumatic valve technology

Abstract: Dielectric elastomer actuators have been investigated for applications in the field of pneumatic automation technology. We have developed different valve designs with stacked dielectric elastomer actuators and with integrated high voltage converters. The actuators were made using VHB-4910 material and a stacker machine for automated fabrication of the cylindrical actuators. Typical characteristics of pneumatic valves such as flow rate, power consumption and dynamic behaviour are presented. For valve construction the force and stroke parameters of the dielectric elastomer actuator have been measured. Further, benefits for valve applications using dielectric elastomers are shown as well as their potential operational area. Finally, challenges are discussed that are relevant for the use of elastomer actuators in valves for industrial applications.

Passive Actuator Fault-Tolerant Control for a Class of Overactuated Nonlinear Systems and Applications to Electric Vehicles

Abstract: This paper presents a passive actuator fault-tolerant (FT) controller for a class of overactuated nonlinear systems and its experimental investigations on an electric vehicle. As the actuator fault information is unknown before the fault detection and diagnosis procedure finishes, the passive FT control is of great necessity in maintaining system stability and achieving acceptable performance. In this paper, three types of actuator faults are considered, and a passive FT controller that works for all of the studied fault types is designed. By grouping control efforts that have similar effects on the system into the same subsystem, the proposed control method can automatically distribute the higher level control signals to the actuators while minimizing a defined cost function. The FT control method was applied to control of a four-wheel-independently-actuated (FWIA) electric ground vehicle. Experimental results obtained on a FWIA electric vehicle show the effectiveness of the proposed method.

Attitude Stabilization of Spacecrafts Under Actuator Saturation and Partial Loss of Control Effectiveness

Abstract: A practical solution is presented to the problem of fault tolerant attitude stabilization for a rigid spacecraft by using feedback from attitude orientation only. The attitude system, represented by modified Rodriguez parameters, is considered in the presence of external disturbances, uncertain inertia parameters, and actuator saturation. A low-cost control scheme is developed to compensate for the partial loss of actuator effectiveness fault. The derived controller not only has the capability to protect the control effort from actuator saturation but also guarantees all the signals in the closed-loop system to be uniformly ultimately bounded. Another feature of the approach is that the implementation of the controller does not require any rate sensor to measure angular velocity. An example is included to verify those highly desirable features in comparison with the conventional velocity-free control strategy.