Showing papers on "Actuator published in 1997"

Modeling piezoelectric stack actuators for control of micromanipulation

Abstract: A nonlinear lumped-parameter model of a piezoelectric stack actuator has been developed to describe actuator behavior for purposes of control system analysis and design, and, in particular, for microrobotic applications requiring accurate position and/or force control. In formulating this model, the authors propose a generalized Maxwell resistive capacitor as a lumped-parameter causal representation of rate-independent hysteresis. Model formulation is validated by comparing results of numerical simulations to experimental data. Validation is followed by a discussion of model implications for purposes of actuator control.

Linear Electric Actuators and Generators

Abstract: Linear electric actuators and generators (LEAGs) are electromagnetic devices which develop directly short-travel progressive (or oscillatory) linear motion. Machine tool sliding tables, pen recorders and free piston power machines are typical industrial applications for LEAGs. Their recent revival in applications in compressors, pumps, electromagnetic valve actuators, active shock absorbers, vibrators, etc. Prompts this review, which presents main LEAGs configurations, their principles of operations, comparative performance evaluation, motion control and existing as well as potential applications.

The selection of mechanical actuators based on performance indices

Abstract: A method is presented for selecting the type of actuator best suited to a given task, in the early stages of engineering design. The selection is based on matching performance characteristics of the actuator, such as force and displacement, to the requirements of the given task. The performance characteristics are estimated from manufacturers9 data and from simple models of performance limitation such as heat generation and resonance. Characteristics are presented in a graphical form which allows for a direct and systematic comparison of widely different systems of actuation. The actuators considered include man-made actuators (such as hydraulic, solenoid and shape memory alloy) and naturally occurring actuators (such as the muscles of animals and plants).

Bistable microelectromechanical actuator

Abstract: A bistable microelectromechanical (MEM) actuator is formed on a substrate and includes a stressed membrane of generally rectangular shape that upon release assumes a curvilinear cross-sectional shape due to attachment at a midpoint to a resilient member and at opposing edges to a pair of elongate supports. The stressed membrane can be electrostatically switched between a pair of mechanical states having mirror-image symmetry, with the MEM actuator remaining in a quiescent state after a programming voltage is removed. The bistable MEM actuator according to various embodiments of the present invention can be used to form a nonvolatile memory element, an optical modulator (with a pair of mirrors supported above the membrane and moving in synchronism as the membrane is switched), a switchable mirror (with a single mirror supported above the membrane at the midpoint thereof) and a latching relay (with a pair of contacts that open and close as the membrane is switched). Arrays of bistable MEM actuators can be formed for applications including nonvolatile memories, optical displays and optical computing.

Modeling and optimal design of piezoelectric cantilever microactuators

Abstract: A novel model is described for predicting the static behavior of a piezoelectric cantilever actuator with an arbitrary configuration of elastic and piezoelectric layers. The model is compared to deflection measurements obtained from 500-/spl mu/m-long ZnO cantilever actuators fabricated by surface micromachining. Modeled and experimental results demonstrate the utility of the model for optimizing device design. A discussion of design considerations and optimization of device performance is presented.

Generalized preisach model for hysteresis nonlinearity of piezoceramic actuators

Abstract: This paper presents a new approach for modeling the hysteresis nonlinearity of a piezoceramic actuator using a modified generalized Preisach model, and the use of this model in a linearizing control scheme. The developed generalized Preisach model relaxes the congruency requirement on the hysteresis loops of a piezoceramic actuator, which must be satisfied when using the classical Preisach model. The congruency property is experimentally proved to not hold when running the actuator on a minor hysteresis loop. A numerical expression of the model is derived in terms of first- and second-order reversal curve experimental datasets. Output prediction using this model is performed on both an exponentially decayed sinusoidal input signal and an arbitrary input signal, and the results show that the model can accurately reproduce the hysteresis response with an error of less than 2.7%. A tracking control system for a piezoceramic actuator is also developed by combining a PID feedback controller with a hysteresis linearizing scheme in a feed-forward loop. The results show that this new control system can achieve 0.25 μm tracking control accuracy, which is 80 and 50% less than that obtained when using an open-loop controller and a regular feedback control system, respectively.

Accurate position control of a pneumatic actuator using on/off solenoid valves

Abstract: The development of a fast, accurate, and inexpensive position-controlled pneumatic actuator that may be applied to a variety of practical positioning applications is described. A novel pulse width modulation (PWM) valve pulsing algorithm allows on/off solenoid valves to be used in place of costly servo valves. The open-loop characteristic is shown both theoretically and experimentally to be near symmetrical. A comparison of the open- and closed-loop responses of standard PWM techniques and that of the novel PWM technique shows that there has been a significant improvement in the control. A linear process model is obtained from experimental data using system identification. A proportional integral derivative controller with added friction compensation and position feedforward has been successfully implemented. A worst case steady-state accuracy of 0.21 mm was achieved with a rise time of 180 ms for step inputs from 0.11 to 64 mm. Following errors to 64-mm S-curve profiles were less than 2.0 mm. The controller is robust to a sixfold increase in the system mass. The actuator's overall performance is comparable to that achieved by other researchers using servo valves.

A Lumped Parameter Electromechanical Model for Describing the Nonlinear Behavior of Piezoelectric Actuators

Abstract: A lumped-parameter model of a piezoeletric stack actuator has been developed to describe actuator behavior for purposes of control system analysis and design, and in particular for control applications requiring accurate position tracking performance. In addition to describing the input-output dynamic behavior, the proposed model explains aspects of nonintuitive behavioral phenomena evinced by piezoelectric actuators, such as the input-output rate-independent hysteresis and the change in mechanical stiffness that results from altering electrical load. Bond graph terminology is incorporated to facilitate the energy-based formulation of the actuator model. The authors propose a new bond graph element, the generalized Maxwell resistive capacitor, as a lumped-parameter causal representation of rate-independent hysteresis. Model formulation is validated by comparing results of numerical simulations to experimental data.

Composite piezoelectric transducer with truncated conical endcaps "cymbal"

Abstract: This paper presents original results obtained in the development of the moonie-type transducers for actuator applications. The moonie-type actuators fill the gap between multilayer and bimorph actuators, but its position-dependent displacement and low generative force are unacceptable for certain applications. The moonie transducers were modified systematically by using finite element analysis combined with experimental techniques. A new transducer design, named "cymbal transducer", was developed with larger displacement, larger generative forces, and more cost-effective manufacturing. The cymbal transducers consist of a cylindrical ceramic element sandwiched between two truncated conical metal endcaps and can be used as both sensors and actuators. The cymbal actuator exhibits almost 40 times higher displacement than the same size of ceramic element. Effective piezoelectric charge coefficient, Eff. d/sub 33/, of cymbal is roughly 40 times higher than PZT itself.

Variable structure control of shape memory alloy actuators

Abstract: A shape memory alloy (SMA) actuator consisting of a number of thin NiTi fibers woven in a counter rotating helical pattern around supporting disks is first described. This structure accomplishes a highly efficient transformation between force and displacement overcoming the main mechanical drawback of shape memory alloys, that being limited strain. Time domain open loop experiments were then conducted to determine the intrinsic properties of the actuator. From these experiments and from the knowledge of the underlying physics of SMAs, a multiterm model, including linear and nonlinear elements, was proposed. After further investigation and simulation, it was found that most of these complexities did not need to be considered in order to explain the reported results, and that the model could be reduced to that of a single integrator. A variable structure controller was then applied to a pair of antagonist actuators. The feedback switches between the two actuators according to the sign of the displacement error. A further improvement was added to compensate for known gross nonlinearities by modulating the current magnitude in a discrete manner as a function of the state space position. It was therefore possible to realize smooth and robust control with very little cost in complexity.

Force actuator with dual magnetic operation

Abstract: An electromagnetic active vibration actuator configuration combines two modes of operation to obtain the advantages of long stroke and linearity of voice coil type actuators and high efficiency of dual-gap solenoid type actuators. A coaxial stator shell surrounds an axially vibratable armature. Either the stator or the armature can carry one or more coils and/or permanent magnets, however usually the magnets are located on the armature for their contribution to vibrating mass. Alternate coils and alternate magnets are made opposite in polarity, the stator armature pole pieces being held symmetrically staggered relative to the stator pole pieces by end springs or flexures that allow axial vibration when AC is applied to the coils. Two different types of flux loop paths are associated with each pair of permanent magnet prominent poles: a voice-coil-effect flux loop path including two air gaps, each traversing a coil, that remain relatively constant in separation distance and permeability under vibration, and a solenoid-effect loop flux path traversing a pair of gaps in series flanking a coil prominent pole, that vary in separation distance and permeability in a complementary manner under vibration in the manner of a solenoid type actuator. These two magnetic modes operate in a cooperative additive efficient manner. Multiples of a typical magnet/coil pair can be easily tandemed using common building block component elements, typically being made to have in total an odd number of prominent poles. Wide flexibility is provided in design and manufacture to customize the performance of the actuator by manipulating the proportion of voice coil effect and solenoid effect along with the mechanical spring effect and the vibrating mass.

Characterization and modelling of a conducting polymer muscle-like linear actuator

Abstract: The demand for actuators featuring biomimetic properties, such as linearity, high power density and compliance, is growing in microrobotics and bioengineering. In the present paper a novel linear actuator is presented. It exploits the electromechanochemical phenomena of -electron conjugated conducting polymers, occuring when ionic species are exchanged with the surrounding medium, i.e. solid or liquid electrolyte. In our experiments, a polypyrrole film doped with benzensulphonate anions is considered as the conducting polymer and a liquid electrolyte bath as the ionic reservoir. The actuating properties of the material are investigated and quantified in terms of both isotonic displacement and isometric developed force. A lumped parameter, muscle-like model of the system is proposed and verified with respect to the experimental data. The results of the electromechanical characterization and the goodness of fit of the model provide favourable indications for the utilization of the material as an effective muscle-like linear actuator, once the response time is decreased by means of a suitable scaling down of the film thickness.

Operating device for menu-controlled functions of a vehicle

Abstract: In an operating device for menu-controlled functions of a motor vehicle that can be shown symbolically on a screen and selected by an actuator, the actuator is movable between mechanical stops into a position that corresponds to the position of the symbol of the selectable function on the surface of the screen and which provides haptic feedback to the actuator when the selectable function is changed by moving the actuator.

Method and apparatus for providing high bandwidth force feedback with improved actuator feel

Abstract: A method and apparatus for providing low-cost, realistic force feedback including an improved actuator. Force sensations are provided to a user and an interface device coupled to a host computer allows a user to interact with a host application program. A user object, such as a joystick, is moveable by a user in at least one rotary degree of freedom. A sensor reports a locative signal to the host computer to indicate a position of the user object. An actuator outputs forces on the user object in response to signals from the host computer and program. The actuator includes a housing, a set of grounded magnets provided on opposing surfaces of the housing and creating a magnetic field, and a rotor coupled to the user object positioned between the magnets. The rotor rotates about an axis of rotation and includes a shaft and teeth spaced around the shaft. An electric current flows through one or more coils on the teeth to cause the rotor to rotate. The teeth and the magnets are provided in a skewed, helical arrangement relative to each other so that, as the rotor rotates, a first tooth gradually exits the magnetic field as the next consecutive tooth gradually enters the magnetic field, thereby significantly reducing a cogging effect of the rotor when the user object is moved by the user and increasing the fidelity of forces experienced by the user.

Active damage interrogation method for structural health monitoring

Abstract: An active damage interrogation (ADI) system (and method) which utilizes an array of piezoelectric transducers attached to or embedded within the structure for both actuation and sensing. The ADI system actively interrogates the structure through broadband excitation of the transducers. The transducer (sensor) signals are digitized and the transfer function of each actuator/sensor pair is computed. The ADI system compares the computed transfer function magnitude and phase spectrum for each actuator/sensor pair to a baseline transfer function for that actuator/sensor pair which is computed by averaging several sets of data obtained with the structure in an undamaged state. The difference between the current transfer function and the baseline transfer function for each actuator/sensor pair is normalized by the standard deviation associated with that baseline transfer function. The transfer function deviation for each actuator/sensor pair is then represented in terms of the number of standard deviations, or sigmas, from the baseline. This statistic, termed the TF Delta, is then processed by a windowed local averaging function in order to reduce minor variations due to random noise, etc. The Windowed TF Delta for each actuator/sensor pair is then integrated over the entire excitation frequency spectrum, to thereby produce the Cumulative Average Delta, which provides a single metric for assessing the magnitude of change (deviation from baseline) of that particular actuator/sensor transfer function. The Cumulative Average Delta (CAD) for each actuator/sensor transfer function provides key, first-level information which is required for detecting, localizing, and quantitatively assessing damage to the structure.

Use of a shape memory alloy to modify the disposition of a device within an implantable medical probe

Abstract: This invention is an implanting probe (100) having an elongated sheath (102) with provision for remotely positioning a device disposed within the elongated sheath. In one embodiment, the device is a circuit board (104), and a shape memory alloy (SMA), such as nitinol, is used to fabricate one or more actuators (108) that are coupled to the circuit board. The shape memory effect exhibited by the SMA is thermally activated. Electrical current is selectively applied to the actuator to resistively heat the SMA to a temperature sufficient to change the shape. When the shape of the SMA changes, the actuator moves the circuit board or other device longitudinally whithin the elongated sheath so that the light emitted is directed to a different portion of a treatment site. In another embodiment, the circuit board is rotated about is longitudinal axis within the sheath. In still another embodiment, the actuator moves a piston (272) so as to pump a fluid through a pair of lumens (204, 206) disposed within the sheath to dissipate heat produced by the light emitting diodes (128) in a remotely disposed heat exchanger. Another embodiment uses the actuator to both circulate the fluid and move a circuit board.

Modeling of a flexible beam actuated by shape memory alloy wires

Abstract: A thermomechanical model is developed to predict the structural response of a flexible beam with shape memory alloy (SMA) wire actuators. A geometrically nonlinear static analysis is first carried out to investigate the deformed shape of a flexible cantilever beam caused by an externally-attached SMA wire actuated electrically. The actuation force applied by the SMA actuator to the beam is evaluated by solving a coupled problem that combines a thermodynamic constitutive model of SMAs with the heat conduction equation in the SMA and the structural model of the beam. To calculate the temperature history of the SMA actuator for given electrical current input, the heat transfer equation is solved with the electrical resistive heating being modeled as a distributed heat source along the SMA wire. The steps in the formulation are connected together through an iterative scheme that takes into account the static equilibrium of the beam and the constitutive relation of SMAs, thus translating an electrical current history input into beam strain output. The proposed model is used to simulate the experimental results, thus demonstrating the feasibility of using SMA actuators for shape control of active flexible structural systems.

Adaptable controller for work vehicle attachments

Abstract: An adaptable control system for the efficient use of different implement attachments for a work vehicle is disclosed. The work vehicle has an actuator for attachment and operation of different implements. The actuator is controlled by a control unit. The control unit has an input coupled to a user operated control device. The control unit is coupled to the actuator and activates the actuator in response to the user operated control device. An attachable implement such as a loader bucket is attached to the actuator. An implement data input such as a card slot is coupled to the processor. A portable data storage device, such as a data card, corresponding with the specific implement is inserted in the data input. The data storage device transmits instruction data relating to the specific implement to the implement data input. The controller operates the actuator in accordance to the data read from the data storage device. Alteratively a sensor may read identification data from an identification indicator on the implement attachment. The controller then selects corresponding instruction data from a memory device.

Bistable microactuator with coupled membranes

Abstract: The invention concerns a bistable electrostatic actuator with pneumatic or liquid coupling. The electrostatic membrane actuator has enclosed metallic electrodes (21, 22; 23). It can be used for a microvalve or a micropump. Said actuator having buckled membrane sections (20a, 20b, 20x) in pairs and curved substrate electrodes (21, 22, 23), locally associated with said membrane sections (20a, 20b).

Read/write head including displacement generating means that elongates and contracts by inverse piezoelectric effect of electrostrictive effect

Abstract: A read/write head includes a slider provided with an electromagnetic transducer element (or an optical module), an actuator, and a suspension. The actuator includes a fixed part, a movable part, and at least two beam members for coupling them together. The beam members have a displacement generating means that elongates and contracts by inverse piezoelectric effect or electrostrictive effect. The fixed part is fixed to the suspension, and the movable part is fixed to the slider. Upon the elongation and contraction of the displacement generator, the displacement generator deflects and the movable part displaces linearly, circularly or rotationally with respect to the fixed part, and the electromagnetic transducer element displaces in a linear or circular orbit, so that the electromagnetic transducer element intersects recording tracks. In the actuator, the fixed part, movable part and beam members are formed as an integrated single piece by providing a hole and/or a cutout in a sheet-like member constructed of a piezoelectric or electrostrictive material. The actuator of the structure illustrated is used for the positioning of a direction intersecting recording tracks. In this case, the total sum of voltages applied on the displacement generating means is controlled in such a manner that it is constant at any time, thereby controlling position fluctuations of the electromagnetic transducer element in the direction vertical to the recording medium surface.

Automatic steering device for vehicle

Abstract: A first correction coefficient and a second correction coefficient are map-searched based on a steering force applied by a driver to a steering wheel. A steering actuator is controlled based on an actuator driving electric current obtained by adding the product of an automatic steering control electric current and a first correction coefficient to the product of a power steering control electric current and a second correction coefficient. With an increase of the steering force, the first correction coefficient decreases and the second correction coefficient increases, so that a proportion of power steering control increases with respect to a proportion of automatic steering control.

Control system for exhaust gas recovery system in an internal combustion engine

Abstract: A system and method for controlling an exhaust gas recirculation system in an internal combustion engine having two or more actuating devices on a supercharger-type pressure-charged internal combustion engine, or, in a turbocharger equipped pressure-charged internal combustion engine. In the disclosed embodiments, the actuating devices may include a variable gas pocket valve, an air intake throttle valve, an exhaust gas recirculation valve, a turbocharger back pressure valve, or the adjustable turbine blades in a variable gas turbine. In the disclosed embodiments, the control system includes a pair of actuators operatively coupled to an engine controller. The second actuator is operatively responsive to the first actuator when the first actuator command signal exceeds prescribed actuator limits. However, when the first actuator is commanded or operating within the prescribed actuator limits, the variance or feedback signal is zero and the second actuator operates more or less independently of the first actuator.

Actuator with opposing repulsive magnetic forces

Abstract: A new class of actuators and mechanisms use opposing repulsive magnetic forces. The repulsive forces are typically generated between a stationary magnet and a moving magnet, where the moving magnet is coupled to the mechanism output member. The mechanisms are generally configured such that the repulsive force from one electromagnet is opposed by a repulsive force from another electromagnet, where the opposing forces are simultaneously applied to the mechanism's output member. This configuration is similar in certain aspects to the way biological flexor and extensor muscles are configured in a musculoskeletal system. The opposing configuration allows for open loop control of position and stiffness. The actuator mechanism may have both rotary and linear motion output, and may have either a single degree of freedom or multiple degrees of freedom. Permanent magnets can be used to create a baseline repulsive force without electric power, and electromagnets can modulate the repulsive force magnitude. The actuator can provide high fidelity motion and force output, and is well suited for human interface devices, such as force feedback joysticks. Other applications include adjustable stiffness devices, and high bandwidth mechanisms.

Nonlinear vectorial backstepping design for global exponential tracking of marine vessels in the presence of actuator dynamics

Abstract: A nonlinear vectorial backstepping control law for commercial ships is derived by using the concept of vectorial backstepping. Vectorial backstepping is done in 3 steps corresponding to the state vectors of the ship dynamics, kinematics and actuator dynamics. Emphasis is placed on compensation of the actuator dynamics since the bandwidth of the propellers, thrusters and rudders often is close to the bandwidth of the ship dynamics. Global exponential tracking is proven by applying Lyapunov stability analysis. The case study is simultaneously global exponential tracking of the surge and sway positions (x,y) and the yaw angle /spl psi/ of a surface ship. This can only be done by applying nonlinear control theory due to the nonlinear structure of the kinematic equations, Coriolis and centripetal forces, and hydrodynamic damping forces.

Coupled Fluid-Structural Characteristics of Actuators for Flow Control

Abstract: The characteristics of a typical flow control actuator design are discussed. The device is based on a resonating structure that interacts with a closed volume of fluid to create a concentrated jet through an exit orifice. The resulting unsteady flow through the orifice introduces viscous effects that are characterized by the Stokes parameter based on the orifice diameter. An optimum operating Stokes parameter is then computed by matching this viscous dominated solution to an ideal, inviscid result. The actuator is modeled with a system of coupled equations that describe its fluid-structural behavior.

An experimental study of active vibration control of composite structures with a piezo-ceramic actuator and a piezo-film sensor

Abstract: In order to reduce the vibrational level of lightweight composite structures, active vibration control methods have been applied both numerically and experimentally. Using the classical laminated beam theory and Ritz method, an analytical model of the laminated composite beam with piezoelectric sensors and actuators has been developed. Smart composite beams and plates with surface-bonded piezoelectric sensors and actuators were manufactured and tested. It is found that the developed analytical model predicts the dynamic characteristics of smart composite plates very well. Utilizing a linear quadratic Gaussian (LQG) control algorithm as well as well known classical control methods, a feedback control system was designed and implemented. A personal computer (PC) was used as a controller with an analogue - digital conversion card. For a cantilevered beam the first and second bending modes are successfully controlled, and for cantilevered plates the simultaneous control of the bending and twisting modes gives a significant reduction in the vibration level. LQG has shown advantages in robustness to noise and control efficiency compared with classical control methods. In this study examples of control spillover are demonstrated via the instantaneous power spectrum of the sensor output.