Showing papers on "Actuator published in 2012"

Interchangeable clip applier

Abstract: A surgical device for clipping tissue can include an actuator, such as a handle or a robotic arm, for example, and a replaceable end effector including a plurality of clips contained therein. After the replaceable end effector has been used, the end effector can be detached from the actuator and a new end effector can be operably coupled with the actuator. Each replaceable end effector can include a firing drive for advancing clips into a receiver of the end effector and a crimping drive configured to deform a clip positioned within the receiver.

Three-dimensional graphene architectures

Abstract: Graphene has been widely explored for applications in electronics, sensors, actuators, catalysis and bio- or energy related systems. For these purposes, graphene materials usually have to be fabricated or assembled into desired micro-/nano-architectures for tuning and/or controlling their electrical, optical, mechanical, chemical or electrochemical properties. In this feature article, we review recent achievements in the studies of three-dimensional (3D) graphene architectures. The methodology for preparing these 3D graphene micro-/nano-architectures and their potential applications have been summarized.

Adaptive Sliding Mode Fault Tolerant Attitude Tracking Control for Flexible Spacecraft Under Actuator Saturation

Abstract: A novel fault tolerant attitude tracking control scheme is developed for flexible spacecraft with partial loss of actuator effectiveness fault. Neural networks are first introduced to account for system uncertainties, and an adaptive sliding mode controller is derived by using on-line updating law to estimate the bound of actuator fault such that any information of the fault is not required. To further address actuator saturation problem, a modified fault tolerant control law is then presented to ensure that the resulting control signal will never incur saturation. It is shown that the roll, pitch and yaw angle trajectories can globally asymptotically track the desired attitude in the face of faulty actuator, system uncertainties, external disturbances and even actuator saturation. A simulation example of a flexible spacecraft is given to illustrate the effectiveness of the proposed controller.

Medical devices having releasable coupling

Abstract: This invention is directed to a medical device having a longitudinal axis, and including a handle and a catheter. The handle can include a body having a proximal end and a distal end, an actuator moveably coupled to the body, and a handle control member coupled to the actuator, wherein the actuator can be configured to move relative to the body to move the handle control member. The catheter can include a shaft having a proximal end and a distal end, wherein the proximal end of the shaft and the distal end of the body can be configured for releasable coupling. The catheter can also include a steering section located along the shaft and a catheter control member coupled to the steering section, wherein the catheter control member can be configured to move relative to the shaft to move the steering section relative to the longitudinal axis. The medical device can also include a securing member configured to move relative to at least one of the handle and the catheter to releasably couple the handle control member to the catheter control member.

A Compact Rotary Series Elastic Actuator for Human Assistive Systems

Abstract: Precise and large torque generation, back drivability, low output impedance, and compactness of hardware are important requirements for human assistive robots. In this paper, a compact rotary series elastic actuator (cRSEA) is designed considering these requirements. To magnify the torque generated by an electric motor in the limited space of the compact device, a worm gear is utilized. However, the actual torque amplification ratio provided by the worm gear is different from the nominal speed reduction ratio due to friction, which makes the controller design challenging. In this paper, the friction effect is considered in the model of cRSEA, and a robust control algorithm is designed to precisely control the torque output in the presence of nonlinearities such as the friction. The mechanical design and dynamic model of the proposed device and the design of a robust control algorithm are discussed, and actuation performance is verified by experiments. Experimental results with a human subject are also presented to show the performance of the cRSEA while interacting with humans.

Design and Analysis of a Robust, Low-cost, Highly Articulated manipulator enabled by jamming of granular media

Abstract: Hyper-redundant manipulators can be fragile, expensive, and limited in their flexibility due to the distributed and bulky actuators that are typically used to achieve the precision and degrees of freedom (DOFs) required. Here, a manipulator is proposed that is robust, high-force, low-cost, and highly articulated without employing traditional actuators mounted at the manipulator joints. Rather, local tunable stiffness is coupled with off-board spooler motors and tension cables to achieve complex manipulator configurations. Tunable stiffness is achieved by reversible jamming of granular media, which—by applying a vacuum to enclosed grains—causes the grains to transition between solid-like states and liquid-like ones. Experimental studies were conducted to identify grains with high strength-to-weight performance. A prototype of the manipulator is presented with performance analysis, with emphasis on speed, strength, and articulation. This novel design for a manipulator—and use of jamming for robotic applications in general—could greatly benefit applications such as human-safe robotics and systems in which robots need to exhibit high flexibility to conform to their environments.

Robust adaptive fault-tolerant control for uncertain linear systems with actuator failures

Abstract: This study is concerned with the robust adaptive fault-tolerant compensation control problem for linear systems with parameter uncertainty, disturbance and actuator faults including outage, loss of effectiveness and stuck. It is assumed that the lower and upper bounds of actuator efficiency factor, the upper bounds of disturbance and the unparametrisable time-varying stuck fault, are unknown. Then, according to the information from the adaptive mechanism, the effect of actuator fault, exogenous disturbance and parameter uncertainty can be eliminated completely by designing adaptive state feedback controller. Furthermore, it is shown that the solutions of the resulting adaptive closed-loop system are uniformly bounded, the states converge asymptotically to zero. Finally, two examples are given to illustrate the effectiveness and applicability of the proposed design method.

Fault-Tolerant Control for T–S Fuzzy Systems With Application to Near-Space Hypersonic Vehicle With Actuator Faults

Abstract: This paper addresses the problem of fault-tolerant control for Takagi-Sugeno (T-S) fuzzy systems with actuator faults First, a general actuator fault model is proposed, which integrates time-varying bias faults and time-varying gain faults 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 to estimate the actuator fault, which removes the classical assumption that the time derivative of the output errors should be known as in some existing work Further, a novel fault-estimation observer is designed Utilizing the estimated actuator fault, an accommodation scheme is proposed to compensate for the effect of the fault In addition, a sufficient condition for the existence of SMOs is derived according to Lyapunov stability theory Finally, simulation results of a near-space hypersonic vehicle are presented to demonstrate the efficiency of the proposed approach

Active Suspension Control With Frequency Band Constraints and Actuator Input Delay

Abstract: This paper investigates the problem of vehicle active suspension control with frequency band constraints and actuator input delay. First, the mathematical model of suspension systems is established, and the problem of suspension control with finite-frequency constraints is formulated to match the characteristics of the human body. Then, the finite-frequency method is developed to deal with the problem of suspension control with actuator input delay, based on the generalized Kalman-Yakubovich-Popov lemma. Compared with the traditional entire-frequency approach for active suspension systems, the finite-frequency approach proposed in this paper achieves better disturbance attenuation performance for the chosen frequency range while the constraints required by real situation are guaranteed in the controller design. The effectiveness and merits of the proposed method are verified by a number of simulations with several types of road disturbances.

Actuator design for high force proprioceptive control in fast legged locomotion

Abstract: High speed legged locomotion involves high acceleration and extensive loadings of the leg, which impose critical challenges in actuator design. We introduce actuator dimensional analysis for maximizing torque density and transmission ‘transparency’. A front leg prototype developed based on insight from the analysis is evaluated for direct proprioceptive force control without force sensors. The vertical stiffness controlled leg was tested on a material testing device to calibrate the mechanical impedance of the leg. By compensating transmission impedance from commanded torque, the leg was able to estimate impact force. For the impact test, the mean absolute error as a ratio of full scale sensor force is 0.041 in the 3406 N/m stiffness experiment and is 0.049 in the 5038 N/m experiment. The results indicate that prescribed force profile control is possible during high speed locomotion.

Fuzzy-Model-Based Control of an Overhead Crane With Input Delay and Actuator Saturation

Abstract: This paper investigates the problem of a Takagi-Sugeno (T-S) fuzzy-model-based control of a nonlinear overhead crane system with input delay and actuator saturation. The complex nonlinear dynamic system of the crane is modeled as a three-rule T-S fuzzy model with a saturated input. Based on the fuzzy model, a state-feedback controller is designed so that trajectories of the system that start from an ellipsoid will remain in it, where a decay rate is introduced to accelerate the response speed. Besides, since the input delay often appears in real equipment, the delayed feedback control is also considered with respect to the actuator saturation. Delay-dependent existence conditions of the fuzzy controller are established such that the load can be placed in a desired position by the crane with a much suppressed swing angle, where trajectories of the closed-loop system that start from a bounded set will asymptotically converge to a contractively invariant ellipsoid. The results are formulated in the form of linear matrix inequalities, which can be readily solved via standard numerical software. Simulations on the true plant are illustrated to show the feasibility and effectiveness of the proposed control method.

Reliable $H_\infty$ Control for Discrete-Time Fuzzy Systems With Infinite-Distributed Delay

Abstract: In this paper, the problem of reliable H∞ control is investigated for discrete-time Takagi-Sugeno (T-S) fuzzy systems with infinite-distributed delay and actuator faults. A discrete-time homogeneous Markov chain is used to represent the stochastic behavior of actuator faults. In terms of a stochastic fuzzy Lyapunov functional, a sufficient condition is proposed to ensure that the resultant closed-loop system is exponentially stable in the mean-square sense with an H∞ performance index. Based on the derived condition, the reliable H∞ control problem is solved, and an explicit expression of the desired controller is also given. The case of no failure in the actuator is also considered. A numerical example is given to demonstrate that our results are effective and less conservative.

Medical tool for reduced penetration force with feedback means

Abstract: A medical device for reducing the force necessary to penetrate living being tissue using a variety of reciprocating motion actuators, including piezoelectric, voice coil, solenoids, pneumatics or fluidics. The reciprocating actuator drives a penetrating member, such as a needle, through the tissue at a reduced force while the device detects the passage of the penetrating member through the tissue. Upon passage of the penetrating member through the tissue, electrical power to the reciprocating actuator is automatically terminated. One exemplary method for detecting this passage is via a fluid-containing syringe that is coupled to a channel within the penetrating member. Once the penetrating member tip has passed through the living tissue, the fluid within the syringe no longer experiences any pressure and a plunger within the syringe displaces indicating passage of the penetrating member tip. This motion can provide direct tactile feedback to an operator of the medical device or can automatically open a switch providing electrical power to the medical device. Alternatively, a pressure transducer can also monitor the pressure within the penetrating member channel and automatically activate the switch to cut off the electrical power.

Fluorescent Actuator Based on Microporous Conjugated Polymer with Intramolecular Stack Structure

Abstract: IO N Artifi cial smart materials that respond to external stimuli, such as heat, light, chemicals, and electric fi elds, have recently attracted considerable attention for applications to actuators and sensors. [ 1 ] An wide range of conjugated polymers have been developed as functional active materials not only for soft actuation but also for optical sensing. [ 1h , 2 ] To our best knowledge, however, there are no reports on conjugated polymers showing a simultaneous optical output signal and actuation behavior. The actuation of soft materials in response to chemical stimuli is based on a reversible expansion/contraction in volume. [ 3 ]

Electromechanical Actuator with Controllable Motion, Fast Response Rate, and High-Frequency Resonance Based on Graphene and Polydiacetylene

Abstract: Although widely investigated, novel electromechanical actuators with high overall actuation performance are still in urgent need for various practical and scientific applications, such as robots, prosthetic devices, sensor switches, and sonar projectors. In this work, combining the properties of unique environmental perturbations-actuated deformational isomerization of polydiacetylene (PDA) and the outstanding intrinsic features of graphene together for the first time, we design and fabricate an electromechanical bimorph actuator composed of a layer of PDA crystal and a layer of flexible graphene paper through a simple yet versatile solution approach. Under low applied direct current (dc), the graphene–PDA bimorph actuator with strong mechanical strength can generate large actuation motion (curvature is about 0.37 cm–1 under a current density of 0.74 A/mm2) and produce high actuation stress (more than 160 MPa/g under an applied dc of only 0.29 A/mm2). When applying alternating current (ac), this actuator ...

Engineering design framework for a shape memory alloy coil spring actuator using a static two-state model

Abstract: A shape memory alloy (SMA) coil spring actuator is fabricated by annealing an SMA wire wound on a rod. Four design parameters are required for the winding: the wire diameter, the rod diameter, the pitch angle and the number of active coils. These parameters determine the force and stroke produced by the actuator. In this paper, we present an engineering design framework to select these parameters on the basis of the desired force and stoke. The behavior of the SMA coil spring actuator is described in detail to provide information about the inner workings of the actuator and to aid in selecting the design parameters. A new static two-state model, which represents a force?deflection relation of the actuator at the fully martensitic state (M100%) and fully austenitic state (A100%), is derived for use in the design. Two nonlinear effects are considered in the model: the nonlinear detwinning effect of the SMA and the nonlinear geometric effect of the coil spring for large deformations. The design process is organized into six steps and is presented with a flowchart and design equations. By following this systematic approach, an SMA coil spring actuator can be designed for various applications. Experimental results verified the static two-state model for the SMA coil spring actuator and a case study showed that an actuator designed using this framework met the design requirements. The proposed design framework was developed to assist application engineers such as robotics researchers in designing SMA coil spring actuators without the need for full thermomechanical models.

Artificial ankle-foot system with spring, variable-damping, and series-elastic actuator components

Abstract: An artificial foot and ankle joint consists of a curved leaf spring foot member having a heel extremity and a toe extremity, and a flexible elastic ankle member that connects the foot member for rotation at the ankle joint. An actuator motor applies torque to the ankle joint to orient the foot when it is not in contact with the support surface and to store energy in a catapult spring that is released along with the energy stored in the leaf spring to propel the wearer forward. A ribbon clutch prevents the foot member from rotating in one direction beyond a predetermined limit position. A controllable damper is employed to lock the ankle joint or to absorb mechanical energy as needed. The controller and sensing mechanisms control both the actuator motor and the controllable damper at different times during the walking cycle for level walking, stair ascent, and stair descent.

A clutched parallel elastic actuator concept: Towards energy efficient powered legs in prosthetics and robotics

Abstract: Parallel passive-elastic elements can reduce the energy consumption and torque requirements for motors in powered legged systems. However, the hardware design for such combined actuators is challenged by the need to engage and disengage the parallel elasticity depending on the gait phase. Although clutches in the drive train are often proposed, compact and low cost solutions of clutched parallel elastic actuators have so far not been established. Here we present the design and control of an initial prototype for a parallel elastic actuator. The actuator combines a DC motor with a parallel spring that is engaged and disengaged by a commercially available, compact and low-cost electric clutch. In experiments that mimic the torque and motion patterns of knee extensor muscles in human rebounding tasks we find that the parallel spring in the prototype reduces the energy consumption of the actuator by about 80% and the peak torque requirement for the DC motor by about 66%. In addition, we find that a simple trigger-based control can reliably engage and disengage the electric clutch during the motion, allowing the spring to support the motor in rebound, to remove stored energy from the system as necessary for stopping, and to virtually disappear at the actuator output level. On the other hand, the hardware experiments also reveal that our initial design limits the precision in the torque control, and we propose specific improvements to overcome these limitations.

Design of soft robotic actuators using fluid-filled fiber-reinforced elastomeric enclosures in parallel combinations

Abstract: Complex controlled motions, soft human interaction, and minimal moving mass all drive the need for soft robots using fluid filled fiber reinforced elastomer enclosures (FREEs). While a narrow class of FREEs known as McKibben's actuators have been extensively studied, there is a wide unexplored class with complex sets of motion patterns. Combining these actuators in parallel can yield versatile motion patterns resulting in a large overall workspace. Mobility of individual actuators is enforced by inextensibility of fibers and incompressibility of fluids, which in turn drives the net attainable motions. In this paper, we map the mobility of individual FREE actuators to all possible resultant motions that a combination of three sets of actuators arranged in a triangular configuration would undergo. This understanding has resulted in a preliminary design tool that determines individual FREE topologies for a required set of motion patterns. Five case studies that result from this methodology are prototyped and tested for comparison of the predicted and obtained motion directions.

A compact dielectric elastomer tubular actuator for refreshable Braille displays

Abstract: Electroactive polymer actuators stimulated by appropriate levels of electric field are particularly attractive for human-assist devices such as Braille. The development of a full page refreshable Braille display is very important for the integration of the visually impaired into the new era of communication. In this paper, development of a compact dielectric elastomer actuator suitable for Braille application is reported. The actuators are fabricated from commercially available silicone tubes. The tube has been rendered mechanically anisotropic through asymmetric levels of applied pretension in circumferential and axial directions in order to direct the actuation strain in the axial direction of the actuator. Key performance parameters, such as displacement, force, and response time of the actuator are investigated. The test results demonstrate the potential of the compact, lightweight, and low cost dielectric elastomer as actuators for a refreshable full page Braille display.

Design and Control of a Variable Stiffness Actuator Based on Adjustable Moment Arm

Abstract: For tasks that require robot-environment interaction, stiffness control is important to ensure stable contact motion and collision safety. The variable stiffness approach has been used to address this type of control. We propose a hybrid variable stiffness actuator (HVSA), which is a variable stiffness unit design. The proposed HVSA is composed of a hybrid control module based on an adjustable moment-arm mechanism, and a drive module with two motors. By controlling the relative motion of gears in the hybrid control module, position and stiffness of a joint can be simultaneously controlled. The HVSA provides a wide range of joint stiffness due to the nonlinearity provided by the adjustable moment arm. Furthermore, the rigid mode, which behaves as a conventional stiff joint, can be implemented to improve positioning accuracy when a robot handles a heavy object. In this paper, the mechanical design features and related analysis are explained. We show that the HVSA can provide a wide range of stiffness and rapid responses according to changes in the stiffness of a joint under varying loads by experiments. The effectiveness of the rigid mode is verified by some experiments on position tracking under high-load conditions.

Design and Development of a Flexure-Based Dual-Stage Nanopositioning System With Minimum Interference Behavior

Abstract: Dual-servo systems (DSSs) are highly desirable in micro-/nanomanipulation when high positioning accuracy, long stroke motion, and high servo bandwidth are required simultaneously. This paper presents the design and development of a new flexure-based dual-stage nanopositioning system. A coarse voice coil motor (VCM) and a fine piezoelectric stack actuator (PSA) are adopted to provide long stroke and quick response, respectively. A new decoupling design is carried out to minimize the interference behavior between the coarse and fine stages by taking into account actuation schemes as well as guiding mechanism implementations. Both analytical results and finite-element model (FEM) results show that the system is capable of over 10 mm traveling, while possessing a compact structure. To verify the decoupling property, a single-input-single-output (SISO) control scheme is realized on a prototype to demonstrate the performance of the DSS without considering the interference behavior. Experimental results not only confirm the superiority of the dual-servo stage over the standalone coarse stage but reveal the effectiveness of the proposed idea of decoupling design.

Novel Soft Actuator Using Magnetorheological Elastomer

Abstract: This paper describes a novel soft actuator using a magnetorheological elastomer. First, the material characteristics in the magnetization process and major contributing factors to magnetization of the magnetic elastomer are shown. Second, an actuator using a magnetorheological elastomer combined with an embedded electromagnet is proposed. The magnetic circuit when a current is applied is described and its operating principle is explained. Finally, the static and dynamic motions and dynamic stress of the actuator are determined by an experimental prototype and measurement setup.

Disk drive adjusting microactuator gain by injecting a sinusoid into a servo control system

Abstract: A disk drive is disclosed comprising a head, a disk surface, and a dual stage actuator (DSA) servo loop comprising a voice coil motor (VCM) servo loop and a microactuator servo loop operable to actuate the head over the disk surface. A microactuator compensator in the microactuator servo loop is disabled, a sinusoid is injected into a control signal applied to the microactuator, and coefficients of a corresponding sinusoidal response in a DSA error signal of the DSA servo loop is measured. The sinusoid is injected into a model of the microactuator to generate a compensation signal. A gain of the microactuator is adjusted based on a VCM error signal and the coefficients of the sinusoidal response in the DSA error signal.

Flexure apparatus, system, and method

Abstract: An actuator module is disclosed. The actuator module includes an actuator having at least one elastomeric dielectric film disposed between first and second electrodes. A suspension system having at least one flexure is coupled to the actuator. The flexure enables the suspension system to move in a predetermined direction when the first and second electrodes are energized. A mobile device that includes the actuator module and a flexure where the actuator module assembly is used to provide haptic feedback also are disclosed.

Control allocation for fault tolerant control of a VTOL octorotor

Abstract: For the fault tolerant control of an eight-rotor VTOL Unmanned Air Vehicle (UAV), a control allocation scheme is proposed. The eight-rotor configuration provides actuator redundancy to ensure safe operation under rotor/motor failures. A PD controller is used to generate total thrust and moment demands. A cascade inverse method of control allocation is proposed to allocate the controller commands to the actuators whilst ensuring that actuator saturation does not occur. If the vehicle is subjected to rotor failures, the scheme re-allocates the commands to maintain the vehicle stability and performance. Until actuator saturation occurs the response of the vehicle is the same when operating with all motors or fewer. The response of the vehicle to several combinations of complete actuator failures is investigated by simulation and it is shown that the proposed method is able to maintain control after failure of up to four actuators. The controller is invarient and the vehicle response to commands is identical until motor saturation occurs.