Showing papers on "Actuator published in 2009"

Compliant actuator designs

Abstract: In the growing fields of wearable robotics, rehabilitation robotics, prosthetics, and walking k robots, variable stiffness actuators (VSAs) or adjustable compliant actuators are being designed and implemented because of their ability to minimize large forces due to shocks, to safely interact with the user, and their ability to store and release energy in passive elastic elements. This review article describes the state of the art in the design of actuators with adaptable passive compliance. This new type of actuator is not preferred for classical position-controlled applications such as pick and place operations but is preferred in novel robots where safe human- robot interaction is required or in applications where energy efficiency must be increased by adapting the actuator's resonance frequency. The working principles of the different existing designs are explained and compared. The designs are divided into four groups: equilibrium-controlled stiffness, antagonistic-controlled stiffness, structure-controlled stiffness (SCS), and mechanically controlled stiffness.

Surgical attachment for use with a robotic surgical system

Abstract: A surgical attachment includes a surgical tool, an actuator configured to drive the surgical tool, and a power cell for providing electrical power to the actuator, the power cell being configured to accumulate stored electrical energy during an idle state of the actuator and to discharge at least a portion of the stored energy to power the actuator during a peak load of the actuator.

Optimization of Dielectric Barrier Discharge Plasma Actuators for Active Aerodynamic Flow Control

Abstract: This paper presents the results of a parametric experimental investigation aimed at optimizing the body force produced by single dielectric barrier discharge plasma actuators used for aerodynamic flow control. A primary goal of the study is the improvement of actuator authority for flow control applications at higher Reynolds number than previously possible. The study examines the effects of dielectric material and thickness, applied voltage amplitude and frequency, voltage waveform, exposed electrode geometry, covered electrode width, and multiple actuator arrays. The metric used to evaluate the performance of the actuator in each case is the measured actuator-induced thrust which is proportional to the total body force. It is demonstrated that actuators constructed with thick dielectric material of low dielectric constant produce a body force that is an order of magnitude larger than that obtained by the Kapton-based actuators used in many previous plasma flow control studies. These actuators allow operation at much higher applied voltages without the formation of discrete streamers which lead to body force saturation.

Control of Rotary Series Elastic Actuator for Ideal Force-Mode Actuation in Human–Robot Interaction Applications

Abstract: To realize ideal force control of robots that interact with a human, a very precise actuating system with zero impedance is desired. For such applications, a rotary series elastic actuator (RSEA) has been introduced recently. This paper presents the design of RSEA and the associated control algorithms. To generate joint torque as desired, a torsional spring is installed between a motor and a human joint, and the motor is controlled to produce a proper spring deflection for torque generation. When the desired torque is zero, the motor must follow the human joint motion, which requires that the friction and the inertia of the motor be compensated. The human joint and the body part impose the load on the RSEA. They interact with uncertain environments and their physical properties vary with time. In this paper, the disturbance observer (DOB) method is applied to make the RSEA precisely generate the desired torque under such time-varying conditions. Based on the nominal model preserved by the DOB, feedback and feedforward controllers are optimally designed for the desired performance, i.e., the RSEA: (1) exhibits very low impedance and (2) generates the desired torque precisely while interacting with a human. The effectiveness of the proposed design is verified by experiments.

Stacked dielectric elastomer actuator for tensile force transmission

Abstract: This paper presents a novel approach for active structures driven by soft dielectric electro-active polymers (EAPs), which can perform contractive displacements at external tensile load. The active structure is composed of an array of equal segments, where the dielectric films are arranged in a pile-up configuration. The proposed active structure has the capability of exhibiting uniaxial contractive deformations, while being exposed to external tensile forces. The serial arrangement of active segments has one contracting degree of freedom in the thickness direction of the dielectric EAP film layers. Due to the envisaged tension force transmission capability, special attention is paid to the electrode design which is of paramount importance with regard to functionality of the actuator. A compliant electrode system with anisotropic deformation properties is presented based on nano scale carbon powder. In experiments, the free deformation as well as the contractive motion under external tensile loading of several actuator configurations with different setups is characterized. These involve the study of various sizes and numbers of stacked film layers as well as different electrode designs.

Actuator Line Modeling of Wind Turbine Wakes

Abstract: This thesis contains a comprehensive 3D Navier-Stokes computational study of the characteristics of wakes of wind turbines operating in various flow conditions including interacting wakes between a row of turbines. The computations were carried out using the actuator line technique combined with the 3D Navier Stokes solver EllipSys3D and a LES turbulence model. Simple models, based on applying body forces in the computational domain, are developed for imposing sheared and turbulent inflow and their validity is discussed. A few computations on stand alone turbines are compared to measurements and good to fair agreement are shown in terms of respectively power coefficient and mean wake properties. The turbulence properties in the wake are generally characterized by its spectral characteristics and include estimation of spectral coherence, length scales and Reynolds stresses. Simulations of the wake from an isolated turbine operating in uniform inflow at tip-speed ratios ranging from λ = 3.21 to λ = 11.78 is presented and provides detailed information about the wake development including vortex properties and turbulence characteristics. Calculations on the wake of turbines subject to sheared inflow shows that besides an expected vertical skewed wake the wake also becomes increasingly asymmetric in the horizontal direction as it is convected downstream. The latter phenomena, which is also often observed in measurements, is argued to be caused by the rotation of the wake. A detailed study is presented to investigate the influence of including turbulence in the inflow. The study shows that the ambient turbulence causes the vortex system in the wake to become unstable much closer to the rotor and as a consequence the wake becomes fully turbulent earlier than if inflow turbulence is neglected. Furthermore, it is shown that the main effect governing the large scale meandering of wakes is the large scale structures of the ambient turbulence field. Finally studies are conducted on rows of respectively two and three turbines. The investigation includes evaluation of the loading on the rotors and it is shown that the turbines are subject to rather severe yaw moments, even in situations where the mean wind is oriented along the row. This observation is indicative of large scale dynamics of the wakes.

Device and method employing shape memory alloy

Abstract: A system for the metering and delivery of small discrete volumes of liquid is comprised of a small or minimal number of inexpensive components. One such component is a movable member, such as a miniature precision reciprocating displacement pump head, which is driven by an actuator that comprises a shape memory alloy material. The operating mechanism of the system is of little or minimal complexity. The system facilitates the precise metering and delivery of the small discrete volumes of liquid. Potential applications for the system include subcutaneous, long-term, automated drug delivery, for example, the delivery of insulin to a person with diabetes. In such an application, the small, simple and inexpensive nature of the invention would allow for its use as both a portable and a disposable system.

A compact soft actuator unit for small scale human friendly robots

Abstract: This paper presents the development of a new compact soft actuation unit intended to be used in multi degree of freedom and small scale robotic systems such as the child humanoid robot “iCub” [1]. Compared to the other existing series elastic linear or rotary implementations the proposed design shows high integration density and wider passive deflection. The miniaturization of the newly developed high performance unit was achieved with a use of a new rotary spring module based on a novel arrangement of linear springs.

A Recurrent Neural-Network-Based Sensor and Actuator Fault Detection and Isolation for Nonlinear Systems With Application to the Satellite's Attitude Control Subsystem

Abstract: This paper presents a robust fault detection and isolation (FDI) scheme for a general class of nonlinear systems using a neural-network-based observer strategy. Both actuator and sensor faults are considered. The nonlinear system considered is subject to both state and sensor uncertainties and disturbances. Two recurrent neural networks are employed to identify general unknown actuator and sensor faults, respectively. The neural network weights are updated according to a modified backpropagation scheme. Unlike many previous methods developed in the literature, our proposed FDI scheme does not rely on availability of full state measurements. The stability of the overall FDI scheme in presence of unknown sensor and actuator faults as well as plant and sensor noise and uncertainties is shown by using the Lyapunov's direct method. The stability analysis developed requires no restrictive assumptions on the system and/or the FDI algorithm. Magnetorquer-type actuators and magnetometer-type sensors that are commonly employed in the attitude control subsystem (ACS) of low-Earth orbit (LEO) satellites for attitude determination and control are considered in our case studies. The effectiveness and capabilities of our proposed fault diagnosis strategy are demonstrated and validated through extensive simulation studies.

Piezoelectric ultrasonic micro/milli-scale actuators

Abstract: A growing demand for actuators with a volume of less than 1 mm3 has driven researchers to produce a varied range of micro/milli-scale designs. By examining the underlying physics of the actuator operation we are able to demonstrate why piezoelectric ultrasonic actuators have the greatest potential to meet this need. Moreover, it allows us to create a new classification system for piezoelectric ultrasonic actuators, affording us a better understanding of the core characteristics of each class of actuator, which class is most suited to various applications, and highlights potential areas of future research.

Actuator Fault Detection and Isolation for a Network of Unmanned Vehicles

Abstract: This technical note investigates development, design and analysis of actuator fault detection and isolation (FDI) filters for a network of unmanned vehicles. It is shown that actuator fault signatures in a network of unmanned vehicles are dependent and the network can be considered as an over-actuated system. An isolability index mu is defined for a family of fault signatures and a new structured residual set is developed that is selectively capable of properly detecting and isolating mu multiple faults in linear systems with dependent fault signatures, such as over-actuated systems. Our proposed algorithm is then applied to the actuator FDI problem in a network of unmanned vehicles configured according to centralized, decentralized and semi-decentralized architectures. A comparative analysis in terms of the capabilities and limitations of these architectures is performed. Simulation results presented for the formation flight of multiple satellites demonstrate the effectiveness of our proposed FDI algorithm.

Magnetostrictive actuator of a medical ultrasound transducer assembly, and a medical ultrasound handpiece and a medical ultrasound system having such actuator

Abstract: Apparatus includes a magnetostrictive actuator of a medical ultrasound transducer assembly. The actuator comprises a magnetostrictive alloy chosen from a list. A medical ultrasound handpiece includes an ultrasound transducer assembly adapted to attachingly receive an end effector. The transducer assembly includes a magnetostrictive actuator having a magnetostrictive alloy, and includes a first coil surrounding the actuator and adapted to excite the actuator to substantially a desired medical resonant frequency and substantially a desired medical amplitude. A medical ultrasound system includes a handpiece housing, a first medical ultrasound transducer assembly, and a first medical end effector attachable to the first transducer assembly. The first transducer assembly includes a magnetostrictive first actuator having a first magnetostrictive alloy. At least a portion of the first transducer assembly is attachingly insertable in the handpiece housing without the use of tools, without damaging the handpiece housing, and without damaging the first transducer assembly.

Sensor-based occupancy behavioral pattern recognition for energy and comfort management in intelligent buildings

Abstract: There has been extensive research focusing on developing smart environments by integrating data mining techniques into environments that are equipped with sensors and actuators. The ultimate goal is to reduce the energy consumption in buildings while maintaining a maximum comfort level for occupants. However, there are few studies successfully demonstrating energy savings from occupancy behavioural patterns that have been learned in a smart environment because of a lack of a formal connection to building energy management systems. In this study, the objective is to develop and implement algorithms for sensor-based modelling and prediction of user behaviour in intelligent buildings and connect the behavioural patterns to building energy and comfort management systems through simulation tools. The results are tested on data from a room equipped with a distributed set of sensors, and building simulations through EnergyPlus suggest potential energy savings of 30% while maintaining an indoor comfort level when compared with other basic energy savings HVAC control strategies.

Integrated circuit amplifiers for multi-electrode intracortical recording.

Abstract: Significant progress has been made in systems that interpret the electrical signals of the brain in order to control an actuator. One version of these systems senses neuronal extracellular action potentials with an array of up to 100 miniature probes inserted into the cortex. The impedance of each probe is high, so environmental electrical noise is readily coupled to the neuronal signal. To minimize this noise, an amplifier is placed close to each probe. Thus, the need has arisen for many amplifiers to be placed near the cortex. Commercially available integrated circuits do not satisfy the area, power and noise requirements of this application, so researchers have designed custom integrated-circuit amplifiers. This paper presents a comprehensive survey of the neural amplifiers described in publications prior to 2008. Methods to achieve high input impedance, low noise and a large time-constant high-pass filter are reviewed. A tutorial on the biological, electrochemical, mechanical and electromagnetic phenomena that influence amplifier design is provided. Areas for additional research, including sub-nanoampere electrolysis and chronic cortical heating, are discussed. Unresolved design concerns, including teraohm circuitry, electrical overstress and component failure, are identified.

Disturbance-Observer-Based Hysteresis Compensation for Piezoelectric Actuators

Abstract: We present a novel hysteresis compensation method for piezoelectric actuators. We consider the hysteresis nonlinearity of the actuator as a disturbance over a linear system. A disturbance observer (DOB) is then utilized to estimate and compensate for the hysteresis nonlinearity. In contrast to the existing inverse-model-based approach, the DOB-based hysteresis compensation does not rely on any particular hysteresis model, and therefore provides a simple and effective compensation mechanism. We design and fabricate a lead magnesium niobate-lead titanate (PMN-PT) piezoelectric actuator for microscale tip-based power sintering process. Experimental validation of the proposed hysteresis compensation is performed on the PMN-PT cantilever piezoelectric actuator. The experimental results demonstrate the effectiveness and efficiency of the approach.

A scaling model for electrowetting-on-dielectric microfluidic actuators

Abstract: A hydrodynamic scaling model of droplet actuation in an electrowetting-on-dielectric (EWD) actuator is presented that takes into account the effects of contact angle hysteresis, drag from the filler fluid, drag from the solid walls, and change in the actuation force while a droplet traverses a neighboring electrode. Based on this model, the threshold voltage, VT, for droplet actuation is estimated as a function of the filler medium of a scaled device. It is shown that scaling models of droplet splitting and liquid dispensing all show a similar scaling dependence on [t/er(d/L)]1/2, where t is insulator thickness and d/L is the aspect ratio of the device. It is also determined that reliable operation of a EWD actuator is possible as long as the device is operated within the limits of the Lippmann–Young equation. The upper limit on applied voltage, Vsat, corresponds to contact-angle saturation. The minimum 3-electrode splitting voltages as a function of aspect ratio d/L < 1 for an oil medium are less than Vsat. However, for an air medium the minimum voltage for 3-electrode droplet splitting exceeds Vsat for d/L ≥ 0.4. EWD actuators were fabricated to operate with droplets down to 35pl. Reasonable scaling results were achieved.

Comparison of Mechanical Design and Energy Consumption of Adaptable, Passive-compliant Actuators

Abstract: Different, adaptable, passive-compliant actuators have been developed recently such as the antagonistic setup of two Series Elastic Actuators, the Mechanically Adjustable Compliance and Controllable Equilibrium Position Actuator, the Actuator with Mechanically Adjustable Series Compliance, and the Variable Stiffness Actuator. The main purpose of these designs is to reduce the energy consumption of walking/running robots and prostheses. This paper presents a design formulation to link the different mechanical designs together, and a study on the power consumption of these actuators.

Actuator properties of the complexes composed by carbon nanotube and ionic liquid: The effects of additives

Abstract: Two different types of additives were mixed into the electrode of carbon nanotube (CNT) actuators low-voltage-driven in air to investigate the influence of additives on the actuator performance. The electrode was composed by single-walled carbon nanotubes (SWNTs), an ionic liquid (IL), a base polymer, and an additive. The generated strain was estimated by measuring displacement changes of the actuator element in the frequency range between 5 mHz and 200 Hz. In case of a non-conductive additive, that is, mesoporous silica (MCM-41), the maximum strain of the actuator increased about 1.6 times as large as that of the non-additive actuator. On the contrary, a conductive additive, polyaniline (poly-An), caused a remarkable improvement of the strain (ca. 3 times) for the actuator. It is found that this improvement was achieved by the effective charge storage in the actuator element. The generated stress was also determined by Hooke's law with the parameter of the maximum strain and the Young's modulus of actuator composite.

Printing 3D dielectric elastomer actuators for soft robotics

Abstract: We present a new approach to the fabrication of soft dielectric elastomer actuators using a 3D printing process. Complete actuators including active membranes and support structures can be 3D printed in one go, resulting in a great improvement in fabrication speed and increases in accuracy and consistency. We describe the fabrication process and present force and displacement results for a double-membrane antagonistic actuator. In this structure controlled prestrain is applied by the simple process of pressing together two printed actuator halves. The development of 3D printable soft actuators will have a large impact on many application areas including engineering, medicine and the emerging field of soft robotics.

The Actuator Surface Model: A New Navier-Stokes Based Model for Rotor Computations

Abstract: This paper presents a new numerical technique for simulating two-dimensional wind turbine flow. The method, denoted as the 2D actuator surface technique, consists of a two-dimensional Navier-Stokes solver in which the pressure distribution is represented by body forces that are distributed along the chord of the airfoils. The distribution of body force is determined from a set of predefined functions that depend on angle of attack and airfoil shape. The predefined functions are curve fitted using pressure distributions obtained either from viscous-inviscid interactive codes or from full Navier-Stokes simulations. The actuator surface technique is evaluated by computing the two-dimensional flow past a NACA 0015 airfoil at a Reynolds number of 10 6 and an angle of attack of 10 deg and by comparing the computed streamlines with the results from a traditional Reynolds-averaged Navier-Stokes computation. In the last part, the actuator surface technique is applied to compute the flow past a two-bladed vertical axis wind turbine equipped with NACA 0012 airfoils. Comparisons with experimental data show an encouraging performance of the method.

An Electrothermal Tip–Tilt–Piston Micromirror Based on Folded Dual S-Shaped Bimorphs

Abstract: This paper presents the design, optimization, fabrication, and test results of an electrothermally actuated tip-tilt-piston micromirror with a large optical aperture of 1 mm. The fabrication of the device is a combination of thin-film surface micromachining and bulk silicon micromachining based on silicon-on-insulator wafers. The device has 3-DOF of actuations, including rotations around two axes in the mirror plane, and out-of-plane piston actuation. The micromirror shows an optical scan range of plusmn30deg about both x- and y-axes and displaces 480 mum in the z-axis, all at dc voltages that are less than 8 V. Dynamic testing of the micromirror shows that the thermal response time of each actuator is about 10 ms. Resonant frequencies of the piston and rotation motion are 336 and 488 Hz, respectively. The unique structural design of the device ensures that there is no lateral shift for the piston motion and no rotation-axis shift for the rotation scanning. With the large tip-tilt-piston scan ranges and low driving voltage, this type of device is very suitable for biomedical imaging and laser beam steering applications.

Disk drive to reduce head instability

Abstract: A disk drive to reduce head instability during disk drive manufacturing is disclosed. The disk drive comprises: a disk; a dynamic flying height (DFH) read/write head; a flying height actuator to control the spacing between the DFH read/write head and the disk; and a controller. The controller controls operations in the disk drive including applying a sloped increasing power between a first voltage and a second voltage to move the DFH read/write head towards the disk.

Robust adaptive sliding mode attitude maneuvering and vibration damping of three-axis-stabilized flexible spacecraft with actuator saturation limits

Abstract: This paper presents a dual-stage control system design method for flexible spacecraft attitude maneuvering control by use of on-off thrusters and active vibration suppression by embedded smart material as actuator. As a stepping stone, an adaptive sliding mode controller with the assumption of knowing the upper bounds of the lumped perturbation is designed that ensures exponential convergence or uniform ultimate boundedness (UUB) of the attitude control system in the presence of bounded parameter variation/disturbances and control input saturation as well. Then this adaptive controller is redesigned such that the need for knowing the upper bound in advance is eliminated. Lyapunov analysis shows that this modified adaptive controller can also guarantee the exponential convergence or UUB of the system. For actively suppressing the induced vibration, linear quadratic regulator (LQR) based positive position feedback control method is presented. Numerical simulations are performed to show that rotational maneuver and vibration suppression are accomplished in spite of the presence of disturbance torque/parameter uncertainty and saturation input.

Integrated locking device with active sealing

Abstract: Endoscope assemblies, biopsy caps, and methods for making and using the same. An example endoscope assembly may include an endoscope having a channel formed therein and a port that provides access to the channel. A cap may be coupled to the port. The cap may include a base and an outer shell. A locking member may be coupled to the outer shell. An inner seal member may be disposed within the outer shell. One or more openings may extend through the cap and into the channel. An actuator may be coupled to the base for shifting the inner seal member between an unsealed configuration and a sealed configuration.