Showing papers on "Actuator published in 1996"

Tracking control of a piezoceramic actuator

Abstract: The tracking control accuracy of piezoceramic actuators is limited due to their inherent hysteresis nonlinearity. This paper presents a computer-based tracking control approach for a piezoceramic actuator based on incorporating a feedforward loop with a PID (proportional-integral-derivative) feedback controller. The hysteresis nonlinearity of the piezoceramic actuator is modeled in the feedforward loop by using the classical Preisach model. Experiments were performed on a stacked piezoceramic actuator for tracking sinusoidal waveforms with signal frequencies ranging from 0.1-20 Hz. A comparison was made between a feedforward control scheme, a regular PID feedback control scheme, and a PID feedback control scheme with hysteresis modeling in the feedforward loop. The results show that the tracking control performance is greatly improved by augmenting the feedback loop with a model of hysteresis in the feedforward loop. The maximum error in tracking a sinusoidal waveform is about half that obtained using a regular PID controller.

Adaptive Control of Systems with Actuator and Sensor Nonlinearities

Abstract: From the Publisher: An in-depth examination of intelligent approaches to increasing the accuracy of a variety of system components. Utilizing a unified, adaptive, inverse approach, the book offers electrical, mechanical, chemical, aeronautical and computer engineers methods for controlling many of the "hard" nonlinearities of frequently-employed control systems such as dead-zone, backlash and hysteresis. Discusses such nonlinearities at both the input and output points of a linear part and within both continuous time designs and discrete time designs.

Process for in-plane and out-of-plane single-crystal-silicon thermal microactuators

Abstract: A process to manufacture single-crystal thermal actuators using silicon fusion bonding and electrochemical etch stop is presented. The process permits the simultaneous creation of in-plane and out-of-plane thermal actuators together with levers suitable for both directions of actuation. A final dry-release step is used, permitting the manufacture of MOS or bipolar devices in conjunction with actuators. Out-of-plane actuation of vertically levered devices has been demonstrated. The −3 dB response frequency of out-of-plane actuators is approximately 1000 Hz in air. Novel levered in-plane devices which achieve deflections of up to 200 μm have been fabricated. An estimate of the upper bound of thermal actuator efficiency is presented.

REVIEW: MEMS and Its Applications for Flow Control

Abstract: Emerging micromachining technology enables us to fabricate mechanical parts on the order of micron size. It provides us with micro-sensors and micro-actuators which facilitate the exploration of all areas of science. Furthermore, these miniature transducers can be integrated with microelectronics. With an integrated system, it then becomes possible to complete the loop of sensing, information processing, and actuation. This type of system enables us to perform real-time control of time varying events which are common in fluid dynamics. In this review paper, we will first briefly introduce Micro-Electro-Mechanical-Systems (MEMS) technology. Then, the applications of MEMS to flow control will be discussed.

Magnetically controlled shape memory alloys: A new class of actuator materials

Abstract: Materials that develop large strokes under precise and rapid control exhibit a great potential in mechanical engineering. Actuators made from those kinds of materials could replace hydraulic, pneumatic, and electromagnetic drives in many applications. However, no such materials are available to date. Piezoelectric and magnetostrictive materials exhibit rapid response, but their strokes are small. In shape memory alloys, strokes are large, but their control is slow due to thermomechanical control. Magnetic control of the shape memory effect was recently suggested by the present author for a principle of new kinds of actuator materials. These materials can develop strains of several percent, and their control is rapid and precise. Actuation of these materials is based on the reorienting of the twin structure of martensite or the motion of austenite-martensite interfaces by applied magnetic field. In the present report, magnetically induced motion of the austenite-martensite interfaces is demonstrated in an Fe-33.5Ni alloy.

Electro-mechanical impedance modeling of active material systems

Abstract: An active material system may be generalized as an electro-mechanical network because of the incorporation of actuators (electrically driven) and sensors (that convert mechanical energy into electrical energy). An investigation of the coupled electrical and mechanical aspects of an active material system will help reveal some of its most important characteristics, in particular regarding energy conversion and consumption issues. The research performed in the area of the electro-mechanical impedance (EMI) modeling of active material systems is herein summarized. In this paper, a generic EMI model to describe the electro-mechanical network behavior (time domain and frequency domain) of active material systems will be discussed. The focus of the discussion will be on the methodology and basic components of the EMI modeling technique and its application to assist in the design of efficient active control structures. This paper will first introduce the basic concept of the EMI modeling and its general utility in the area of active material systems. The methodology of the EMI modeling technique will be illustrated using an example of PZT actuator-driven mechanical systems. The basic components of the EMI modeling, including the electro-mechanics of induced strain actuators, the dynamic analysis of active material systems, and the electrical power consumption and requirements, will be discussed. Finally, some applications of the EMI modeling approach, including the determination of the optimal actuator locations, modal analysis using collocated PZT actuator - sensors, and the prediction of radiated acoustic power, will be presented.

Controller and actuating system for surgical instrument

Abstract: A surgical instrument controller and actuating system that allows precise hand operated control of a powered instrument based on the detection of variations on the gripping force by means of pressure sensors located on the instrument handle. The grip pressure signal is processed by an electronic actuator controller which in turn drives an actuator system. The actuator system produces an actuation force that is proportional to the gripping force change detected at the instrument handle. The actuation force is transmitted to the active members of the instrument allowing precision proportional activation of surgical instruments such as micro forceps and micro scissors. The system allows an operator to precisely regulate the action of a surgical instrument by variation of the griping force applied over the handle of the instrument.

Method and system for displayed menu activation using a matching distinctive arrangement of keypad actuators

Abstract: An apparatus for controlling equipment from a remote location is disclosed. A control keypad having a distinctive key arrangement such as an array is used to interact with a display device (e.g. TV), located independently from the control keypad. A control menu is displayed on the display device where the control menu has a background image which substantially matches the distinctive arrangement of the keypad, and a foreground image which is overlaid on the background image to associate menu options with each actuator on the keypad. Finally, responsive to the option selected by the keypad, the corresponding function is executed. The menu system is implemented in the context of a home-bus system such as CEBus.

Polyurethane-elastomer actuator

Abstract: A polyurethane elastomer actuator comprising a polyurethane elastomer 1 capable of deforming due to the orientation by an electric field, wherein the shrinkage displacement occurring at the time of the application of an electric field is transformed into other displacement. This polyurethane elastomer actuator does not require electrolyte and high voltage. Since it is not accompanied by chemical reactions and heat generation, its durability hardly deteriorates. This actuator deforms largely during driving.

Atomic force microscopy for high speed imaging using cantilevers with an integrated actuator and sensor

Abstract: A cantilever with an integrated ZnO piezoelectric actuator in feedback with a piezoresistive sensor is utilized in an atomic force microscope (AFM) to achieve a new high speed imaging technique. The imaging bandwidth is increased from 0.6 to 6 kHz by bending the cantilever over sample topography with the actuator rather than moving the sample with a 2 in. piezotube. Images taken in the constant force mode with a 3 mm/s tip velocity of a sample containing 2 μm vertical steps are presented. The effects of electrical coupling from the actuator were eliminated by measuring the piezoresistor sensor with a lock‐in amplifier.

A nonlinear approach to the control of magnetic bearings

Abstract: In this paper, nonlinear aspects of the control of magnetic bearings are studied. The authors design a nonlinear feedback law for the positioning of a shaft, and study the possibility of avoiding premagnetization currents, usually required when applying tangent linearization techniques. Using the flatness property, they propose simple solutions to the motion planning and stabilization problems according to the current complementarity condition or the current almost complementarity condition, that ensures that only one electromagnet in each actuator works at a time, or that one approaches arbitrarily close to this situation. The feedback synthesis is presented in both current and voltage control cases. In the latter case, a hierarchical control scheme, based on time-scale separation, is proposed, to avoid unbounded voltages at switchings that might result from the voltage linearizing feedback. Some implementation aspects are described and some experiments presented.

An Impedance-Based System Modeling Approach for Induced Strain Actuator-Driven Structures

Abstract: This paper presents the theoretical development and experimental verification of a system model of piezoelectric (PZT) patch actuators for induced strain actuation of two-dimensional active structures. The model includes the dynamic interaction between PZT actuators and their host structures. Analytical solutions of the output behavior of the PZT actuators have been developed based upon the actuator input impedance and the mechanical impedance of the host structures. The impedancebased model was then applied to thin plates and thin shells, and to beams. The case studies demonstrate the generality and utility of the impedance modeling approach. A simply-supported thin plate with surface-bonded PZT patches was built and tested so that the ability of the impedance model to accurately predict the dynamic performance of the actuator and the host structure has been verified. When compared with conventional static models, the impedance modeling method offers insight into the dynamic coupling of the integrated PZT/substrate systems.

Fracture mechanics for the design of ceramic multilayer actuators

Abstract: In a multilayer actuator, each internal electrode terminates an edge inside the active ceramic. Around the edge, the nonuniform electric field generates an incompatible strain field, which, in its turn, generates stresses and may cause the ceramic to crack. The industry has been exploring alternative electrode configurations to alleviate the stress concentration. The effort has been empirical and benefited little from numerical simulations. An inherent difficulty is that the actuator ceramics have nonlinear electro-mechanical interactions, of which no unified mathematical description is now available. In this paper, we develop a crack nucleation model that includes essential features of this nonlinearity. The model applies to both paraelectrics and ferroelectrics. Attention is focused on situations where the small-scale saturation conditions prevail. That is, the driving voltage is low enough so that the bulk of the ceramics is linearly dielectric, except for a cylinder of a small radius around the electrode edge. Inside the cylinder, large strains result from electrostriction or polar rotation. We identify a parameter group that determines the cracking condition; details in the material description only affect a dimensionless coefficient. Everything else being fixed, a critical layer thickness exists, below which a multilayer actuator will not crack around its internal electrode edges. Merits and limitations of the small-scale saturation model are discussed. We analyze this model analytically for a paraelectric with perfect polarization saturation, and estimate the value of the dimensionless coefficient in the model.

Implementation of sliding mode control with perturbation estimation (SMCPE)

Abstract: Experimental verification of a recently developed algorithm, sliding mode control with perturbation estimation (SMCPE), is performed, a two-axes planar SCARA type robot is used as the test platform. The controller is a PC-based microprocessor with transducer and actuator interfaces. The objective of trajectory tracking is achieved by directly controlling the joint torques, despite the modeling deficiencies and unknown disturbances. Two major practical issues are considered. One of them is the measurement noise and the other is the hard/software limitations on the control loop closure speed. Both of these issues affect the parametric selections with the SMCPE algorithm. A sample test result is presented, to compare the performance of SMCPE with the classical SMC.

Magnetic switching element for controlling a surgical device

Abstract: An apparatus for controlling a surgical device includes a housing (105) and a magnetic switching element (400) mounted on the housing (105). The magnetic switching element (400) includes a magnet (405), a magnetic sensor (500) configured to produce a control signal for controlling the surgical device, and an actuator (410) mounted on the housing (105) for movement between a first position in which a magnetic field of the magnet is decoupled from the magnetic sensor (500) and a second position in which the magnetic field is coupled to the magnetic sensor (500) so as to change a value of the control signal produced by the magnetic sensor (500). The magnetic switching element (400) may also include magnetically soft material positioned so that movement of the actuator causes relative movement between the magnet and the magnetically soft material.

Linear approximate dynamic model of ICPF (ionic conducting polymer gel film) actuator

Abstract: The ionic conducting polymer gel film (ICPF) actuator is a perfluorosulfonic acid membrane plated with platinum on its both surfaces. It bends in water and in wet condition by applying a low voltage of 1.5 V to its surfaces. This phenomenon was discovered in 1992. The principle of the motion is still unknown. This paper discusses 2-dimensional linear approximate modelling of the ICPF actuator. The authors are proposing a dynamic model of the actuator consisting of an electrical stage, a stress generation stage and mechanical stage. In the stress generation stage, time derivative of current generates the internal stress with a second degree delay. Expansion and contraction of each surface induce bending motion in the mechanical stage. Simulation results were in agreement with actual responses.

Micro mechatronics and micro actuators

Abstract: Micro mechatronics is the synergetic integration of both mechanical and electronic systems based on scaling effects in the micro world. A micro mechatronics system is expected to be the key component of the mechanical system, such as in electronic automotive technologies. Micro mechatronics requires the organic combination of micro devices such as micro processor, micro sensor, and micro actuator. Among the micro devices, the micro processor and micro sensor have been widely employed in advanced mechatronics products, but not the micro actuator. This paper surveys the state of the art of micro mechatronics and deals with micro actuators as new devices for micro mechatronics and advanced mechatronics, which play an important role in today's integrated mechanical products. Since micro actuators are still under development, the authors focus on micro actuators for further research and development in this paper.

Bistable microvalve with pneumatically coupled membranes

Abstract: The paper reports on a novel bistable electrostatic actuator with pneumatic coupling. Two buckled Si/SiO/sub 2/ membranes span over connected air filled cavities with enclosed driving electrodes. The membranes operate in counteraction. If one electrode is pulled down electrostatically, the other is pushed up pneumatically, and vice versa. The actuator module is designed to achieve a deflection of /spl plusmn/10 /spl mu/m and will be integrated in a microvalve for liquids. With first completed actuator modules the electrostatic/pneumatic driving principle could be demonstrated. Grey-tone lithography has been developed to fabricate curved driving electrodes on the cavity bottom. It is calculated that compared to flat electrodes the driving voltage then can be reduced up to a factor of five. The curved cavity bottom also improves the pneumatic coupling since the enclosed air volume is minimized.

Finite-element modeling of a smart cantilever plate and comparison with experiments

Abstract: The behavior of a cantilever plate instrumented with a piezoelectric sensor and actuator is described using finite-element modeling. To demonstrate the accuracy of the numerical model, a parallel experimental study was carried out in the laboratory for the same geometric dimensions. The two results are compared and show excellent agreement, demonstrating that finite-element modeling is a good approach for optimized smart structure design. A three-dimensional finite-element formulation is employed in the piezoelectric material region and a small neighboring region of the plate structure on which it is mounted. Shell elements, approximated by many flat-shell elements, are used in modeling the remaining part of the plate structure. Transition elements that connect the three-dimensional solid elements to the flat-shell element are used. For the cantilever plate example, the electrical input admittance as well as the sensor response are found from the finite-element analysis and they are compared with experimental measurements. From this, the accuracy and efficiency of this approach is demonstrated. In contrast to many other modeling techniques used for smart structures which are approximate and hence limited, the finite-element model is applicable to complicated geometries.

Electronic exercise enhancer

Abstract: An electronic exercise enhancer apparatus (10) and method for providing stimuli to a user while sensing the performance and condition of the user may rely on a controller (12) for programmably coordinating a tracking device (14) and a sensory interface device (16). The tracking device (14) may be equipped with sensors (60) for sensing position, displacement, motion, deflection, velocity, speed, temperature, humidity, heart rate, internal or external images, and the like. The sensory interface device (16) may produce outputs presented as stimuli to a user. The sensory interface device (16) may include one or more actuators (90) for providing aural, optical, tactile, and electromuscular stimulation to a user. The controller (12), tracking device (14), and sensory interface device (16) may all be microprocessor controlled for providing coordinated sensory perceptions of complex events.

Design and characterization of a low-profile micropositioning stage

Abstract: This paper discusses the design and characterization of a new, single-axis, low-profile, piezo-driven vertical motion micropositioning stage for use in laser welding applications. A low-profile configuration is attained by mounting the piezo actuator horizontally and using a novel lever arrangement to transfer the horizontal motion of the actuator into the desired vertical motion. An analytical model for the static and dynamic behavior of the stage is presented, along with finite element (FE) modeling verification. A 200 μm motion-range stage was built, and tests show that the stage has a vertical stiffness of 6.0 N/μm and a resonance frequency of 364 Hz. The results are in very close agreement to those predicted by the model.

Head rail-mounted actuator for window coverings

Abstract: A mini-blind actuator has a motor and a housing that holds the motor and a dc battery. The rotor of the motor is coupled to the baton of the mini-blind for rotating the baton and thereby opening or closing the slats of the mini-blind. Alternatively, the rotor is coupled to the tilt rod of the blind to rotate the tilt rod and thereby open or close the slats of the mini-blind. A control signal generator generates a control signal for completing the electrical circuit between the battery and the motor. The control signal can be generated in response to a predetermined amount of daylight or in response to a user-generated remote command signal. The actuator can be used to rotate the slats of horizontal or vertical blinds, or the sections of a pleated shade. Or, the actuator can be used to rotate the hollow rotatable tube of a roll-up shade.

A feasibility study of using smart materials for rotor control

Abstract: Rotor actuation in the rotating system promises a quantum jump in overall rotor craft performance. Smart material actuator technology for operation `on the blade' is now becoming available and has the potential to overcome the size, weight, and complexity issues of hydraulic and electric on-rotor actuation. The present paper is based on the results of a feasibility study to investigate the use of smart materials for primary and active control on the AH-64 helicopter. Based on the results of the study, it is seen that imbedded actuator concepts, i.e. pitch, twist, and camber control, are not practical at this time. Servoflap control, using hinged control surfaces driven by discrete actuators emerges as the most suitable candidate for smart material actuation. Preliminary data show that rotor control using smart materials might be feasible if a combination of smart materials is used and the rotor design is driven towards low control loads and motions.

An adaptive partial state-feedback controller for RLED robot manipulators

Abstract: An adaptive partial state-feedback controller is designed for rigid-link electrically driven (RLED) robot manipulators. The controller is based on structural knowledge of the electromechanical dynamics of the RLED robot and measurements of link position and electrical winding current in each of the brushed DC link actuators. The proposed controller is designed to adapt for parametric uncertainty in the electromechanical dynamics while utilizing a dynamic filter to generate link velocity tracking error information. The controller, adaptation laws, and the pseudovelocity filter are designed via a Lyapunov-like approach, the benefit of which is that at the end of the design procedure the controller can be mathematically shown to produce semiglobal asymptotic link position tracking. The basic design approach can be extended to many types of multiphase motors.

Metal-electroactive ceramic composite transducers

Abstract: A metal-ceramic device includes an electroactive ceramic substrate having a pair of opposed planar surfaces and a thickness aspect. Conductive electrodes sandwich the ceramic substrate and a first sheet metal cap having a concave shape, a substantially unchanging thickness and a rim is joined to a first planar surface of the ceramic substrate. A second sheet metal cap having a concave shape, a substantially unchanging thickness and a rim is bonded to a second planar surface of the ceramic substrate, the second planar surface opposed to the first planar surface. In an actuator embodiment, a potential is applied across the conductive electrodes to cause an expansion of the ceramic substrate in the thickness dimension and a concomitant contraction in its planar dimensions. The contraction causes a flexure of the sheet metal caps, which flexures are used for actuation purposes. In a sensor embodiment, the sheet metal caps are subjected to a displacement by an instrumentality, and a resulting change in voltage across the ceramic substrate is sensed.

Development of a piezoelectric servoflap for helicopter rotor control

Abstract: A servoflap that uses a piezoelectric bender to deflect a trailing edge flap for use on a helicopter rotor blade was designed, built, and tested. This servoflap design is an improvement over a design developed previously at MIT. The design utilizes a new flexure mechanism to connect the piezoelectric bender to the control surface. The efficiency of the bender was improved by tapering its thickness with length. Also, the authority of the actuator was increased by implementing a nonlinear circuit to control the applied electric field, allowing a greater range of actuator voltages. Experiments were carried out on a bench test article to determine the frequency response of the actuator, as well as hinge moment and displacement capabilities. Flap deflections of or more were demonstrated while operating under no-load conditions at frequencies up to 100 Hz. The data indicate that, if properly scaled, the actuator will produce flap deflections greater than at the 90% span location on a full-scale helicopter. In addition, the first mode of the actuator was at frequency of the target model rotor. Proper inertial scaling of this actuator could raise this modal frequency to greater than on an operational helicopter, which is adequate for most rotor control purposes. A linear state space model of the actuator was derived. Comparisons of this model with the experimental data highlighted a number of mild nonlinearities in the actuator's response. However, the agreement between the experiment and analysis indicate that the model is a valid tool for predicting actuator performance.

Adaptive, High Bandwidth Control of a Hydraulic Actuator

Abstract: Hydraulic servovalve controlled systems contain many time-varying dynamic characteristics that are difficult to model. Controllers for such systems must either adapt to these changing parameters or be robust enough to handle the parameter variations. In order to achieve the highest possible bandwidth, an adaptive controller is developed for the system that uses full-state feedback for simultaneous parameter identification and tracking control. This controller takes into account the hydraulic fluid compressibility with an on-line identification scheme. Experimental results demonstrate a four fold improvement in bandwidth as compared to a conventional fixed gain proportional controller.