Showing papers on "Actuator published in 1998"

Ionic polymer-metal composites (IPMCs) as biomimetic sensors, actuators and artificial muscles - a review

Abstract: This paper presents an introduction to ionic polymer-metal composites and some mathematical modeling pertaining to them. It further discusses a number of recent findings in connection with ion-exchange polymer-metal composites (IPMCS) as biomimetic sensors and actuators. Strips of these composites can undergo large bending and flapping displacement if an electric field is imposed across their thickness. Thus, in this sense they are large motion actuators. Conversely by bending the composite strip, either quasi-statically or dynamically, a voltage is produced across the thickness of the strip. Thus, they are also large motion sensors. The output voltage can be calibrated for a standard size sensor and correlated to the applied loads or stresses. They can be manufactured and cut in any size and shape. In this paper first the sensing capability of these materials is reported. The preliminary results show the existence of a linear relationship between the output voltage and the imposed displacement for almost all cases. Furthermore, the ability of these IPMCs as large motion actuators and robotic manipulators is presented. Several muscle configurations are constructed to demonstrate the capabilities of these IPMC actuators. This paper further identifies key parameters involving the vibrational and resonance characteristics of sensors and actuators made with IPMCS. When the applied signal frequency varies, so does the displacement up to a critical frequency called the resonant frequency where maximum deformation is observed, beyond which the actuator response is diminished. A data acquisition system was used to measure the parameters involved and record the results in real time basis. Also the load characterizations of the IPMCs were measured and it was shown that these actuators exhibit good force to weight characteristics in the presence of low applied voltages. Finally reported are the cryogenic properties of these muscles for potential utilization in an outer space environment of a few Torrs and temperatures of the order of - 140 degrees Celsius. These muscles are shown to work quite well in such harsh cryogenic environments and thus present a great potential as sensors and actuators that can operate at cryogenic temperatures.

Thin-film shape-memory alloy actuated micropumps

Abstract: Micropumps capable of precise handling of low-fluid volumes have the potential to revolutionize applications in fields such as drug delivery, fuel injection, and micrototal chemical analysis systems (/spl mu/TAS). Traditional microactuators used in micropumps suffer from low strokes and, as a result, are unsuitable for achieving large fluid displacement. They also suffer low-actuation work densities, which translate to low forces. We investigate the use of the shape-memory effect (SMA) in sputter-deposited thin-film shape-memory alloy (SMA) titanium nickel (TiNi) as an actuator for microelectromechanical systems (MEMS)-based microfluidic devices, as it is capable of both high force and high strains. The resistivity of the SMA thin film is suitable for Joule heating, which allows direct electrical control of the actuator. Two micropump designs were fabricated-one with a novel complementary actuator and the other with a polyimide-biased actuator-which provided thermal isolation between the heated microactuator and the fluid being pumped. A maximum water flow rate of 50 /spl mu/l/min was achieved.

Universal tactile feedback system for computer video games and simulations

Abstract: A universal tactile feedback system for comptuer and video game systems which provides real time tactile feedback. The system includes a microcontroller based circuit that can operate in either a host-independent or a host-dependent mode. The host-independent mode is responsive to an audio signal which is typically generated by a computer while it is executing a game. The digital post-processing utilizes an algorithm with reprogrammable parameters that can be uniquely set for any given game or simulation. After the audio signal is processed, the results are used to generate multiple independent control signals for multiple independent tactile sensation generators (510, 520, 530, 540, 535, 545, 550, 560, 570, 575, 585, 595 and 598). Alternatively, the host-dependent mode is directly responsive to control commands generated by a computer while it is executing a game. All reconfigurable parameters are reprogrammable in real time by sending a communication to the controller (110) via any typical digital I/O port. The system's tactile sensation generators include independent groups of one or more actuators that are embedded within or attached to various devices.

Autopilot: adaptive control of distributed applications

Abstract: With increasing development of applications for heterogeneous, distributed computing grids, the focus of performance analysis has shifted from a posteriori optimization on homogeneous parallel systems to application tuning for heterogeneous resources with time varying availability. This shift has profound implications for performance instrumentation and analysis techniques. Autopilot is a new infrastructure for dynamic performance tuning of heterogeneous computational grids based on closed loop control. The paper describes the Autopilot model of distributed sensors, actuators, and decision procedures, reports preliminary performance benchmarks, and presents a case study in which the Autopilot library is utilized in the development of an adaptive parallel input/output system.

Detection and diagnosis of sensor and actuator failures using IMM estimator

Abstract: An approach to detection and diagnosis of multiple failures in a dynamic system is proposed. It is based on the interacting multiple-model (IMM) estimation algorithm, which is one of the most cost-effective adaptive estimation techniques for systems involving structural as well as parametric changes. The proposed approach provides an integrated framework for fault detection, diagnosis, and state estimation. It is able to detect and isolate multiple faults substantially more quickly and more reliably than many existing approaches. Its superiority is illustrated in two aircraft examples for single and double faults of both sensors and actuators, in the forms of "total", "partial", and simultaneous failures. Both deterministic and random fault scenarios are designed and used for testing and comparing the performance fairly. Some new performance indices are presented. The robustness of the proposed approach to the design of model transition probabilities, fault modeling errors, and the uncertainties of noise statistics are also evaluated.

Toward improvement of tracking performance nonlinear feedback for linear systems

Abstract: A composite nonlinear feedback tracking control law based on a nominal linear controller is proposed. The design yields nonlinear feedback laws that both increase the speed of the closed-loop system response to the command input and reduce the overshoot, while not imperilling the small signal performance achieved by the nominal linear feedback controller in the face of actuator amplitude saturation. A modern flight control application is used to demonstrate the effectiveness of the design.

Electrostrictive polymer artificial muscle actuators

Abstract: Many new robotic and teleoperated applications require a high degree of mobility or dexterity that is difficult to achieve with current actuator technology. Natural muscle is an actuator that has many features, including high energy density, fast speed of response, and large stroke, that are desirable for such applications. The electrostriction of polymer dielectrics with compliant electrodes can be used in electrically controllable, muscle-like actuators. These electrostrictive polymer artificial muscle (EPAM) actuators can produce strains of up to 30% and pressures of up to 1.9 MPa. The measured specific energy achieved with polyurethane and silicone polymers exceeds that of electromagnetic, electrostatic, piezoelectric, and magnetostrictive actuators. A simple model using linear elastic theory can predict EPAM actuator performance from mechanical and electrical material properties and load conditions. A spherical joint for a highly articulated (snake-like) manipulator using EPAM actuator elements has been demonstrated. A rotary motor using EPAM actuator elements has been shown to produce a specific torque of 19 mNm/g and a specific power of 0.1 W/g. An improved EPAM motor could produce greater specific power and specific torque than could electric motors.

Hysteresis Modeling of SMA Actuators for Control Applications

Abstract: Active material actuators, sometimes referred to as "smart" actuators, are gaining widespread use for control actuation. Many of these actuators exhibit hysteresis to some degree between their input and output response. There exists an extensive body of research concerning the modeling of hysteresis for the linearization, or compensation, of these hysteresis nonlinearities. However, the models have typically been identified off-line and mainly used in open-loop compensation. When the identified models do not exactly match the actuator nonlinearities, the compensation can create an error between the desired and actual control output. The hysteresis for several of these actuators has been shown to evolve over time, and can render a fixed hysteresis model inadequate to linearize the hysteretic nonlinearities. This paper presents an adaptive hysteresis model for on-line identification and closed-loop compensation. Laboratory experiments with a shape memory alloy wire actuator provide evidence of the success o...

Micro-electromechanical (MEM) optical resonator and method

Abstract: An integrated micro-electromechanical (MEM) optical resonator comprises a cantilever beam which is fixed to a substrate at one end and extends freely over the substrate at the other end, and a bimorph actuator stacked atop the beam at its fixed end. A reflective surface partially covers the top of the beam at its free end. The bimorph actuator comprises material layers having different thermal expansion coefficients. A DC-biased AC voltage connected across the actuator causes it to heat and cool as the current passing through it increases and decreases, creating a thermal bimorph effect which causes the cantilever beam and the reflective surface to oscillate in accordance with the varying current, preferably at the beam and actuator structure's fundamental resonant frequency. Combining the resonator with a light source and actuator excitation circuitry creates an optical scanner engine which delivers a scan angle in excess of 20 degrees and a scan rate of up to 2000 Hz, using a driving voltage of only 2 Vp-p.

A New Approach for the Dynamic Analysis of Parallel Manipulators

Abstract: A new approach for the dynamic analysis of parallel manipulators is presented in this paper. This approach is based on the principle of virtual work. The approach is firstly illustrated using a simple example, namely, a planar four-bar linkage. Then, the dynamic analysis of a spatial six-degree-of-freedom parallel manipulator with prismatic actuators (Gough–Stewart platform) is performed. Finally, a numerical example is given in order to illustrate the results. The approach proposed here can be applied to any type of planar and spatial parallel mechanism and leads to faster computational algorithms than the classical Newton–Euler approach when applied to these mechanisms.

Low cost force feedback device with actuator for non-primary axis

Abstract: A force feedback interface and method including an actuator in a non-primary axis or degree of freedom. The force feedback interface device is connected to a host computer that implements a host application program or graphical environment. The interface device includes a user manipulatable object, a sensor for detecting movement of the user object, and an actuator to apply output forces to the user object. The actuator outputs a linear force on the user object in non-primary linear axis or degree of freedom that is not used to control a graphical object or entity implemented by the host computer, and movement in the non-primary degree of freedom is preferably not sensed by sensors. The axis extends through the user object, and there are preferably no other actuators in the device, thus allowing the force feedback device to be very cost effective. Force sensations such as a jolt, vibration, a constant force, and a texture force can be output on the user object with the actuator. The force sensations can be output in a direction perpendicular to a planar degree of freedom, radial to spherical degree of freedom, and/or along a lengthwise axis of the user object.

Performance analysis of piezoelectric cantilever bending actuators

Abstract: Bimorph and unimorph are two typical bending mode actuators, either consisting two piezoelectric layers or one piezoelectric layer and one elastic layer. In the case of bimorph actuator, when an electric field is applied to the piezoelectric layers, one layer expands while the other contract along length direction, producing a pure bending deformation. In unimorph actuator, when piezoelectric layer is driven to expand or contract, the elastic layer will resist this dimension change, both bending and stretching deformation will be resulted. These actuators can generates very large tip displacement, in the range of tens micron to several millimeters, depending on the geometrical dimensions of actuators. In this paper, to describe the performance of cantilever bimorph/unimorph actuators in quasi-static driving condition, analytical expressions are derived to relate bending resonance frequency, tip deflection, blocking force and equivalent moment with actuator geometrical dimensions. Young's modulus,...

Modeling, identification, and control of a pneumatically actuated, force controllable robot

Abstract: Focuses on modeling and control of a light-weight and inexpensive pneumatic robot that can be used for position tracking and for end-effector force control. Unlike many previous controllers, our approach more fully accounts for the nonlinear dynamic properties of pneumatic systems such as servovalve flow characteristics and the thermodynamic properties of air compressed in a cylinder. We show with theory and experiments that pneumatic actuators can rival the performance of more common electric actuators. Our pneumatic robot is controlled by extending existing manipulator control algorithms to handle the nonlinear flow and compressibility of air. The control approach uses the triangular form of the coupled rigid body and air flow dynamics to establish path tracking. In addition to the trajectory tracking control law, a hybrid position/force control algorithm is developed. The experimental results indicate that the tip forces on the robot can be controlled without the need for an expensive force/torque sensor usually required by electric motors driven systems.

Corrugated MEMS heater structure

Abstract: A thermal actuator comprising a first conductive material encased in a second non-conductive expansive material wherein said first conductive material is constructed in the form of a corrugated heater element so as to increase the rate of thermal transfer to said second non-conductive expansive material.

Computer controlled hydraulic resistance device for a prosthesis and other apparatus

Abstract: A computer controlled hydraulic resistance device for apparatus such as a prosthetic knee for above knee amputees, includes a two stage pilot operated solenoid valve connected to control the flow of hydraulic fluid to and from a hydraulic actuator which applies resistance to the prosthetic knee or other apparatus through a coupling Hydraulic pressure is sensed on the high and low side of the actuator by a spring biased magnet and a magnetically actuated electronic sensor and is used by a micro-controller in a closed-loop manner to compensate automatically for variations in the device and in the hydraulic fluid viscosity The device also has magnetically actuated electronic sensors which sense positions of the apparatus and feed back to the micro-controller for applying a predetermined resistance profile to the apparatus

Active control of streamwise vortices and streaks in boundary layers

Abstract: Coherent structures play an important role in the dynamics of turbulent shear flows. The ability to control coherent structures could have significant technological benefits with respect to flow phenomena such as skin friction drag, transition, mixing, and separation. This paper describes the development of an actuator concept that could be used in large arrays for actively controlling transitional and turbulent boundary layers. The actuator consists of a piezoelectrically driven cantilever mounted flush with the flow wall. When driven, the resulting flow disturbance over the actuator is a quasi-steady pair of counter-rotating streamwise vortices with common-flow away from the wall. The vortices decay rapidly downstream of the actuator; however, they produce a set of high- and low-speed streaks that persist far downstream (well over 40 displacement thicknesses). The amplitude of the actuator drive signal controls the strength of the generated vortices. The actuator is fast, compact, and generates a substantial disturbance in the flow. Its performance has been demonstrated using a small array of sensors and actuators in low-speed water laminar boundary layers with imposed steady and unsteady disturbances. Experiments are reported in which transition from a large disturbance was delayed by 40 displacement thicknesses, and in which the mean and spanwise variation of wall shear under an array of high- and low-speed streaks was substantially reduced downstream of a single transverse array of actuators.

Master/slave system for the manipulation of tubular medical tools

Abstract: A master/slave system is used for performing a surgical procedure such as theterization of cardiac or peripheral vasculature. Movements of catheters or similar tools within a patient are remotely controlled by a surgeon, and the surgeon receives haptic or tactile feedback caused by the movement of the tools within the patient. The system employs a master actuator with cylindrical controls and a slave actuator that engages the tools. The master actuator and slave actuator are electrically coupled to electrical interface circuitry by drive signals and sense signals. A fluid system is coupled to the slave actuator by fluid-carrying tubes for the delivery of contrast and other solutions to be injected into the vasculature for improved imaging and also to pressurize the balloon on a balloon catheter. The master and slave actuators contain sensors that sense translation and rotation of the controls and tools with respect to their longitudinal axes, and provide sense signals indicative of these motions to the interface circuitry. The master and slave actuators also contain motors respectively engaging the controls and tools to cause translational and rotational movement of these components in response to the drive signals generated by the interface circuitry. The interface circuitry contains a processor executing a master/slave control program via which the relative positions of each control and the corresponding tool are made to track each other. The control program can optionally implement force scaling, position scaling, tremor reduction, and other features to enhance the system's performance.

A benchmark problem for nonlinear control design

Abstract: This paper describes a nonlinear control design problem involving the nonlinear interaction of a translational oscillator and an eccentric rotational proof mass. This problem provides a benchmark for examining nonlinear control design techniques within the framework of a nonlinear fourth-order dynamical system. The problem is posed in the spirit of the linear benchmark problem described in Reference 1. This system was originally studied as a simplified model of a dual-spin spacecraft to investigate the resonance capture phenomenon.2 More recently, it has been studied to investigate the utility of a rotational proof-mass actuator for stabilizing translational motion.3~5 Viewed in this way, the rotational/translational proof-mass actuator (RTAC) has the feature that the nonlinearities associated with the actuator stroke limitation are implicit in the system dynamics. In contrast, the stroke limitation constraint must be considered separately in linear translational proof-mass actuators.6 A similar system has been studied as a rotating unbalanced mass (RUM) actuator in References 7 and 8.

Vertical comb drive actuated deformable mirror device and method

Abstract: A deformable mirror includes a vertical comb actuator having a reflective surface attached thereto. The vertical comb drive includes stationary elements interspersed with moving elements. When a potential difference is provided between these elements, the moving elements are pulled downward, thereby deforming the reflective surface. The vertical comb drive typically includes a plurality of actuators, which are individually electrically addressed. Each actuator may be an array of interspersed elements or a cavity and corresponding tooth. Springs support the moving elements and bias the reflective surface in an original position. The vertical comb drive provides a large stroke and substantially linear voltage-versus-displacement curve throughout the stroke.

Advanced touchless plumbing systems

Abstract: The present invention is a system for controlling a plumbing fixture. The system includes at least two sensors, each sensor including a receiver, and a controller coupled to receive detection signals from the sensors and to generate a control signal in response to the received signals. An actuator is coupled to receive the control signal from the controller and couplable to the plumbing device to act on the bathroom device. The invention is also a method of controlling plumbing fixtures that includes receiving detection signals from a plurality of sensors in a central controller, selecting, in the central controller, which of a plurality of actuators attachable to the plumbing fixtures to operate and directing control signals to the selected actuator to operate the selected actuator.

Preisach model identification of a two-wire SMA actuator

Abstract: In recent years, the Preisach hysteresis model (1935) has emerged as the model of choice for the behaviour of many smart materials, such as shape memory alloys (SMA). This research treats the identification of Preisach models for a differential SMA actuator. The traditional identification technique is applied, and several models are derived for the actuator. It is seen that the classical Preisach model is able to model its behaviour. However, the results raise questions concerning the robustness of the traditional identification technique, as well as the conservative nature of current passivity-based control results for the Preisach model.

Modeling and L/sub 2/-stability of a shape memory alloy position control system

Abstract: Shape memory alloys (SMAs) are inherently nonlinear devices exhibiting significant hysteresis in their stress-strain-temperature characteristic. As a consequence most SMA actuator systems presented in the literature employ some form of proportional-integral-derivative (PID) or pulse-width modulated (PWM) control. However, due to the hysteresis of the SMA, the theoretical stability of these systems has been largely ignored. This paper extends the work of Ikuta et al. (1991) to arrive at a new model of an SMA actuator. The key feature of the model is its ability to model minor hysteresis loops. The model is suitable for computer simulation, even of closed-loop control systems, as well as control system analysis. Indeed, the model is used to prove the L/sub 2/-stability of a position control system.

A Nonlinear Vibration Absorber for Flexible Structures

Abstract: An approach for implementing an active nonlinear vibration absorber for flexible structures is presented. The technique exploits the saturation phenomenon exhibited by multidegree-of-freedom systems with quadratic nonlinearities possessing two-to-one autoparametric resonances. The strategy consists of introducing second-order controllers and coupling each of them with the plant through a sensor and an actuator, where both the feedback and control signals are quadratic. Once the structure is forced near its resonances, the oscillatory response is suppressed through the saturation phenomenon. We present theoretical and experimental results of the application of the proposed vibration absorber. The structure consists of a cantilever beam, the feedback signal is generated by a strain gage, and the actuation is achieved through piezoceramic patches. The equations of motion are developed and analyzed through perturbation techniques and numerical simulation. Then, the strategy is tested by assembling the controllers in electronic components and suppressing the vibrations of the first and second modes of two beams.

Method of manufacture of a planar thermoelastic bend actuator ink jet printer

Abstract: A method of manufacturing an ink jet printhead includes providing a substrate A doped layer is deposited on the substrate and is etched to create an array of nozzles on the substrate with a nozzle chamber in communication with each nozzle Planar monolithic deposition, lithographic and etching processes are used to form a thermoelastic bend actuator arranged in the nozzle chamber and being displaceable, when activated, towards the nozzle to effect ink ejection, at least that surface of the actuator facing a floor of the nozzle chamber being hydrophobic to facilitate the formation of an air bubble between the actuator and the floor

A bistable microrelay based on two-segment multimorph cantilever actuators

Abstract: A surface micromachined bistable microrelay based on the latching of a novel two-segment multimorph cantilever actuator is presented. The two-segment multimorph actuator is composed of two bimorph segment actuators that are connected with each other, one is normally open (NO) and the other is normally closed (NC). The two bimorph segments can be actuated independently in such a way that the device has two stable mechanical latching states, namely, "on" and "off", which can be electrically read out with large off/on resistance ratios. This bistable relay is operated by two separate thermal power pulses at 12 mW and 10 mW respectively. The latching "on" and unlatching "off" operation times are less than 0.5 msec and 0.1 msec respectively. The "on" resistance is in the range of 2.1 /spl sim/35.6 ohms. The "off" resistance is greater than 10/sup 12/ ohms. The breakdown voltage between the open electrodes is above 400 V. Keeping the NO bimorph segment of the bistable relay activated, a normally closed microrelay is also demonstrated.

Disk drive with dual stage actuator radial offset calibration

Abstract: In a disk drive having a dual stage actuator, a method to improve head switching time by aligning a target head with a target track before a head switch occurs by using a second stage actuator attached to the target head to align the target head with the new track. The radial offset required to align the target head with the target track is either calibrated at startup or is measured dynamically during normal disk operations. A dual stage actuator with either a milli-actuator second stage or a micro-actuator second stage, positions a read/write head over a disk surface. The disk drive has a radial offset table for storage of radial offsets for head switches.