Showing papers on "Actuator published in 1995"

Series elastic actuators

Abstract: It is traditional to make the interface between an actuator and its load as stiff as possible. Despite this tradition, reducing interface stiffness offers a number of advantages, including greater shock tolerance, lower reflected inertia, more accurate and stable force control, less inadvertent damage to the environment, and the capacity for energy storage. As a trade-off, reducing interface stiffness also lowers zero motion force bandwidth. In this paper, the authors propose that for natural tasks, zero motion force bandwidth isn't everything, and incorporating series elasticity as a purposeful element within the actuator is a good idea. The authors use the term elasticity instead of compliance to indicate the presence of a passive mechanical spring in the actuator. After a discussion of the trade-offs inherent in series elastic actuators, the authors present a control system for their use under general force or impedance control. The authors conclude with test results from a revolute series-elastic actuator meant for the arms of the MIT humanoid robot Cog and for a small planetary rover.

Parallel atomic force microscopy using cantilevers with integrated piezoresistive sensors and integrated piezoelectric actuators

Abstract: We have fabricated and operated two cantilevers in parallel in a new mode for imaging with the atomic force microscope (AFM). The cantilevers contain both an integrated piezoresistive silicon sensor and an integrated piezoelectric zinc oxide (ZnO) actuator. The integration of sensor and actuator on a single cantilever allows us to simultaneously record two independent AFM images in the constant force mode. The ZnO actuator provides over 4 μm of deflection at low frequencies (dc) and over 30 μm deflection at the first resonant frequency. The piezoresistive element is used to detect the strain and provide the feedback signal for the ZnO actuator.

Modeling hysteresis in piezoceramic actuators

Abstract: A major deficiency of piezoceramic actuators is that their open-loop control accuracy is seriously limited by hysteresis. This paper discusses the adaptation of the Preisach model to describe the nonlinear hysteresis behavior of these actuators. The adapted model is used to predict the response of a piezoceramic actuator to a sinusoidal input and a triangular input. The predictions are compared with experimental measurements on a stacked piezoceramic actuator. The model reproduces the hysteresis loop of the actuator to within 3% over the entire working range of 0–15 μm. This opens the possibility of incorporating the model into a control loop in order to overcome the accuracy problem.

Control of pneumatic muscle actuators

Abstract: Problems with the control and compliance of pneumatic systems have prevented their widespread use in advanced robotics. However, their compactness, power/weight ratio, and simplicity are factors that could potentially be exploited in sophisticated dextrous manipulator designs. This paper considers the development of a new high power/weight and power/volume braided pneumatic muscle actuator (PMA) having considerable power output potential, combined with controllable motion and inherent compliance to prevent damage to handled objects. Control of these muscles is explored via adaptive pole-placement controllers. Experimental results indicate that accurate position control of 1/spl deg/ is feasible, with power/weight outputs in excess of 1kW/kg at 200kPa. >

High bandwidth force feedback interface using voice coils and flexures

Abstract: A method and apparatus for interfacing the motion of a user-manipulable object with an electrical or computer system includes a user object physically contacted by a user. A gimbal mechanism is coupled to the user object, such as a joystick or a medical tool, and provides at least two degrees of freedom to the user object. The gimbal mechanism preferably includes multiple members, at least two of which are formed as a unitary member which provides flex between the selected members. An actuator applies a force along a degree of freedom to the user object in response to electrical signals produced by the computer system. A sensor detects a position of the user object along the degree of freedom and outputs sensor signals to the computer system. Another embodiment includes a host computer system and a local microprocessor, separate from the host computer, for communicating with the host computer and controlling the forces output by the actuators according to a processor subroutine selected in accordance with a host command, sensor signals, and timing information. Another embodiment of the interface apparatus uses voice coil actuators that produce forces in either linear or rotary degrees of freedom using currents applied in a magnetic fields. A friction drive mechanism of the present invention can be coupled between an actuator and a gimbal mechanism. Force from the actuator is transmitted to the gimbal mechanism through frictional contact of members of the friction drive mechanism.

An analysis package comparing PID anti-windup strategies

Abstract: This article describes software developed in SIMULINK that enables the behavior of feedback control systems with actuator saturation and PID controllers to be evaluated. The software, which is part command- and part menu-driven, allows a choice of four PID controllers using different integral wind-up strategies and transfer function entry of the actuator and plant dynamics. Most realistic control systems contain nonlinearities of some form. One nonlinearity commonly found in control systems is a saturating element. If integral control is applied to such a system to eliminate steady state error, an undesired side effect known as integrator windup may occur when large setpoint changes are made. This effect leads to a characteristic step response with a large overshoot and a very high settling time. To avoid this situation, many different anti-windup strategies have been suggested. This article discusses a software package that has been developed in the SIMULINK/MATLAB environment to investigate and compare the performance of four different anti-windup implementations for PI or PID controllers. The software is partially menu-driven and enables the user to easily enter his own actuator and plant transfer functions to study the performance with the different controllers. >

Method and apparatus for providing passive force feedback to human-computer interface systems

Abstract: A method and apparatus for interfacing the motion of an object with a digital processing system includes a sensor which has a sensing resolution and detects movement of the object along a degree of freedom. An amount of play less than the sensing resolution exists between the sensor and the object. A passive actuator is coupled to the mechanism to transmit a resistive force to the object along the degree of freedom. A play mechanism is coupled to the actuator to provide a desired amount of play between the actuator and the object along the degree of feedom. The desired amount of play is greater than the sensing resolution of the sensor so that the sensor can detect the desired play when the user moves the object, even when the actuator has locked the object into place. Such desired play can be torsion flex (compliance) or rotary backlash. The actuator and the sensor provide an electromechanical interface between the object and the digital processing system. A gimbal mechanism or slotted yoke mechanism can be coupled between the actuator and the object. The interface is well suited for simulations of medical procedures and simulations in which an object such as a stylus or a joystick is moved and manipulated by the user.

Electrostatic curved electrode actuators

Abstract: This paper presents the design and performance of an electrostatic actuator consisting of a laterally compliant cantilever beam and a fixed curved electrode, both suspended above a ground plane. A theoretical description of the static behavior of the cantilever as it is pulled into contact with the rigid fixed-electrode structure is given. Two models are presented: a simplified semi-analytical model based on energy methods, and fully three-dimensional (3-D) coupled electromechanical numerical simulations using CoSolve-EM. The two models are in qualitative agreement with each other, and predict stable actuator behavior when the beam deflection becomes constrained by the curved electrode geometry before electrostatic pull-in can occur. The pull-in behavior depends on the shape of the curved electrode. Test devices have been fabricated by polysilicon surface micromachining techniques. Experimental results confirm the basic theoretical results. Stable behavior with relatively large displacements and forces can be generated by these curved electrode actuators. Depending on the design, or as a result of geometrical imperfections, regions of unstable (pull-in) deflection behavior are also observed.

Role of Control-Structure Interaction in Protective System Design

Abstract: Most of the current research in the field of structural control for mitigation of responses due to extreme environmental loads does not directly account for the effects of control-structure interaction and actuator/sensor dynamics in analysis and design The importance of including control-structure interaction when modeling a control system is discussed herein, and a general framework within which one can study its effect on protective systems is presented A specific model for hydraulic actuators typical of those used in many protective systems is developed, and a natural velocity feedback link is shown to exist which tightly couples the dynamics of the hydraulic actuator to the dynamics of the structure to which it is attached Experimental verification of this model is given Numerical examples are provided that use seismically excited structures configured with active bracing, active tendon, and active mass driver systems These examples show that accounting for control-structure interaction and actu

Active Control of Structures Using Neural Networks

Abstract: A new neural-network-based control algorithm has been developed and tested in the computer simulation of active control of a three-story frame structure subjected to ground excitations. First, an emulator neural network has been trained to forecast the future response of the structure from the immediate history of the system's response, which consists of the structure plus an actuator. The trained emulator has been used in predicting the future responses and in evaluating the sensitivities of the control signal with respect to those responses. At each time step of the simulation, the control signal has been adjusted to induce the required control force in the actuator based in a control criterion. A controller neural network has been trained to learn the relation between the immediate history of response of the structure and actuator, and the adjusted control signals. The trained neurocontroller has been used in controlling the structure for different dynamic loading conditions. Results of this initial st...

Magnetic recording-head positioning at very high track densities using a microactuator-based, two-stage servo system

Abstract: The storage capacities and areal densities found in magnetic disk drives are increasing very rapidly. Data is recorded in ever-narrower tracks which must be followed with extreme precision. Also, the advent of portable applications exposes these smaller drives to higher levels of vibration and shock. A description is given of the many factors which contribute to recording track misregistration (TMR) in today's drives. The mechanics of the drive and actuator and the architecture of the servo control system are also described. A projection is made for the TMR sensitivities and control system at an areal density of 10 Gb/in/sup 2/, having roughly 25000 tracks/in. A two-stage servo may be needed to achieve such track densities. This would comprise a high bandwidth microactuator for rapid position corrections of the recording head, coupled with a conventional actuator. The characteristics of such a microactuator are discussed, and operational examples of fabricated electroplated microactuators, driven electrostatically, are shown. The mechanical behavior of the devices and some of the factors which would affect their implementation are also described. >

Packaged strain actuator

Abstract: A modulator actuator assembly includes one or more plates or elements of electro-active material (71, 73) bonded to an electroded sheet to form a card. The card is sealed, and may itself constitute a practical device, such as a vane, shaker, stirrer, lever, pusher or sonicator for direct contact with a solid or immersion in a fluid, or may be bonded by a stiff adhesive to make a surface-to-object mechanical coupling of the plates through the sheet to a solid workpiece, device, substrate, machine, sample or other article. The laminated assembly supports the plates and provides a bending stiffness such that the tin plates do not deform to a breaking point, and a mechanical stiffness such that shear forces are efficiently coupled from the plates to the workpiece. In further embodiments, the card may include active circuit elements (75, 77, 78, 79) for switching, powering or processing signals, and/or passive circuit elements for filtering, matching or damping signals, so few or no connections to outside power or circuitry are required.

Sensor/actuator failure detection in the Vista F-16 by multiple model adaptive estimation

Abstract: Multiple model adaptive estimation (MMAE) is applied to the Variable-In-flight Stability Test Aircraft (VISTA) F-16 flight control system at a low dynamic pressure flight condition (0.4 M at 20000 ft). Single actuator and sensor failures are addressed first, followed by dual actuator and sensor failures. The system is evaluated for complete or "hard" failures, partial or, "soft" failures, and combinations of hard and soft actuator and sensor failures. Residual monitoring is discussed for single and dual failure scenarios. Performance is enhanced by the application of a modified Bayesian form of MMAE, scalar residual monitoring to reduce ambiguities, automatic dithering where advantageous, and purposeful commands. >

Stiffness Isn't Everything

Abstract: Most robot designers make the mechanical interface between an actuator and its load as stiff as possible[9][10]. This makes sense in traditional position-controlled systems, because high interface stiffness maximizes bandwidth and, for non-collocated control, reduces instability. However, lower interface stiffness has advantages as well, including greater shock tolerance, lower reflected inertia, more accurate and stable force control, less damage during inadvertent contact, and the potential for energy storage. The ability of series elasticity (usually in the form of a compliant coating on an end-effector) to stabilize force control during intermittent contact with hard surfaces is well known. This paper proposes that for natural tasks where small-motion bandwidth is not of paramount concern, actuator to load interfaces should be significantly less stiff than in most present designs. Furthermore, by purposefully placing the majority of interface elasticity inside of an actuator package, a new type of actuator is created with performance characteristics more suited to the natural world. Despite common intuition, such a series-elastic actuator is not difficult to control.

Preisach modeling of piezoceramic and shape memory alloy hysteresis

Abstract: Smart materials such as piezoceramics and shape memory alloys (SMAs) exhibit significant hysteresis and in order to estimate the effect on open and closed loop control a suitable model is needed. One promising candidate is the Preisach independent domain hysteresis model that is characterized by the congruent minor loop and wiping out properties. Comparable minor loop and decaying oscillation test data for a multi-sheet piezoceramic actuator (made of lead zirconate titanate) attached to a flexible beam are presented and are seen to be very consistent with the two Preisach model properties. The commanded parameter is the sheet transverse electric field while the measured parameter is an approximately colocated strain induced in the beam. Equivalent data for a Nitinol SMA wire muscle, attached to the same beam, are also presented. The input and output parameters are the SMA current and a beam strain respectfully. The minor loop and wiping out evidence is less strong than that of the piezoceramic case, but encouraging. In all experiments the quasi-steady state responses were generated in order to avoid exciting beam flexible modes which would complicate the analysis.

Dynamic feedback linearization for electrohydraulically actuated control systems

Abstract: Using the dynamic inversion principal, a globally linearizing feedback control law is developed for an electrohydraulic servo system. The proposed control law is implemented on a rotational joint driven by a linear actuator. The results from experiments indicate that better uniformity of response is achieved across a wider range of operating conditions than would otherwise be possible. Improved symmetry is obtained for the extension and retraction phases of motion for an asymmetric actuator under various loading conditions and actuator positions. As a result of the improvements in linearity, significantly better performance is achieved when using linear controllers. To incorporate the effects of parametric uncertainties on the feedback linearization, a state space linear fractional representation of the parametrically uncertain linearized system is also developed. This uncertainty model is specifically suited for the design of robust control systems using the μ-synthesis and H∞ based approach.

Local-area health monitoring of aircraft via piezoelectric actuator/sensor patches

Abstract: A high-frequency-electrical-impedance-signature-based technique for structural integrity monitoring is presented. The technique which has been under investigation at the Center for Intelligent Material Systems and Structures at Virginia Tech for the last 18 months is unique and different from conventional non-destructive damage identification and structural integrity monitoring methods. It relies on tracking the high-frequency (typically > 50 kHz) point impedance of the structure to identify damage. At such high frequencies, the technique is comparable in sensitivity to sophisticated traditional NDE techniques, such as ultrasonics, and is capable of qualitatively detecting incipient-type damage by looking at changes in structural impedance. As yet, it can be implemented in a remote sensing scenario with small non- intrusive piezoelectric (PZT) materials. The structure's high-frequency electrical impedance signature, which is functionally equivalent to its mechanical impedance signature, is obtained through a bonded PZT functioning both as actuator and sensor. A statistic algorithm based on the difference in the electrical impedance of a healthy and a damaged structure, is then applied to extract an index of the health of the structure. High-frequency excitation, which is greatly facilitated by the electrically driven low-power compact PZT patch, assures a clearly visible change in the impedance/vibration signature even for very minor damage/changes. It also limits the actuation/sensing area to a small region, `local-area', close to the PZT patch. Because of the limited actuation/sensing area, the impedance signature is affected only by changes in the structural properties close to the sensor-actuator and is insensitive to changes in far-field boundary conditions, mass loading, etc., which may be part of the normal usage of the structure. As a case study, an application to a real complex aircraft structure is presented. Experimental proof that very minor alterations in the structure are easily identified and the fact that the detection range of the bonded PZT actuator/sensor is constrained to its immediate neighborhood is presented.

Operational principle, fabrication and displacement characteristics of a functionally gradient piezoelectric ceramic actuator

Abstract: In this paper, the theoretical relationship between the bending displacement at the free end of a functionally gradient material (FGM) actuator and the FGM coefficient of the sandwich has been derived from the structure of an FGM actuator. FGM actuators based on PNN-PZT piezoelectric ceramics have been developed by the powder mould stacking press method and their displacement characteristics have also been measured. The results show that the bending displacement at the free end of a 20 mm×8 mm×0.7 mm FGM actuator is about 20 μm when a voltage of 1000 V is applied. The morphology and the compositional distribution across the profile of the FGM actuator are examined by using SEM and EDS, respectively.

Shape memory alloy microactuator having an electrostatic force and heating means

Abstract: A microactuator and method of operation is disclosed for use in actuating valves, electrical contacts, light beams, sensors and other elements between different actuation modes. An actuator member comprised of a shape memory alloy layer is mounted on an elastic substrate, and the proximal end of the actuator member is carried by a base. The shape memory alloy material is heated through its phase change transition temperature so that it deforms by changing volume to bend the distal end of the actuator member in a first direction relative to the base. Stress forces in the substrate oppose the bending movement, and when the shape change layer is cooled below the transition temperature the stress forces move the distal in a second direction which returns the shape change layer to its low temperature shape. Electrostatic forces are selectively applied between the actuator member and base for clamping the actuator member in one of its positions. In another embodiment a bistable actuator is provided in which the actuator member can be operated between two stable positions.

Sliding Mode Control for Nonlinear and Hysteretic Structures

Abstract: Control methods based on the theory of variable structure system or sliding mode control are presented for applications to seismically excited nonlinear and hysteretic civil engineering structures. These control methods are robust with respect to parametric uncertainties of the structure. The controllers have no adverse effect should the actuator be saturated due to unexpected extreme earthquakes. Emphasis is placed on continuous sliding mode control methods that do not have possible chattering effects. Static output feedback controllers using only the measured information from a limited number of sensors installed at strategic locations are also presented. When a controller is installed in each story unit of a building, a complete compensation of the structural response can be achieved and the response state vector can be reduced to zero. Among the contributions of this paper are the establishment of saturated controllers and controllers for static output feedback. The robustness of the control methods, the applications of the static output controllers, and the control effectiveness in case of actuator saturation are all demonstrated by numerical simulation results. Simulation results indicate that the performance of the sliding mode control methods is remarkable.

Precision position control of piezoelectric actuators using charge feedback

Abstract: The issue of precision position control is critical if piezoelectric actuator technology is to be applied in increasingly demanding applications. In one particular application, the NASA NAOMI project, piezoelectric actuators have been proposed as the pointing and focusing elements for thousands of small mirror-lenslets because of their fast response time and load- carrying ability. In this application the positions of these actuators must be precisely controlled both statically and dynamically to the nanometer level. This requirement necessitates a careful study of the concept and design of the driving electronics of the system. This paper is focused on finding an appropriate method for driving piezoelectric stack actuators for ultraprecision position and motion control. In this paper the theoretical basis of the electrical control of piezoelectric stack actuators is derived using the fundamental physical laws governing dielectrics and piezoceramics. It is shown that the relationships used for voltage control of piezoelectric actuators result from an approximation of the constitutive equations. An exact input/output relationship for piezoelectric actuators is derived and shows that displacement relies fundamentally on charge, not voltage. Experimental verification was obtained to illustrate the differences between driving piezoactuators with voltage control and charge control.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Handle for surgical clip applicator systems

Abstract: An improved actuator handle for a surgical instrument that can be used in endoscopic surgery with the emphasis on applying hemostatic clips. The instrument receives a longitudinal input from the actuator handle and translates the input into relative component motion to apply the hemostatic clips. The improved handle is fabricated primarily from a reusable, engineering resin having exceptional resistance to degradation by steam sterilization. Other improvements to the actuator handle include a drive stem mechanism of unitary construction that can be removed from the actuator handle as an assembled unit to facilitate sterilization. The actuator handle is provided with a quick release mechanism to facilitate the removal and replacement of the drive stem mechanism. The improved actuator handle also features a ratchet mechanism that enables the user to incrementally adjust the longitudinal input force that is transmitted to the surgical instrument and includes a switch for selective operation of the same. The actuator handle also includes a safety lock mechanism integrated into the drive stem mechanism for selective engagement of the surgical instrument and the actuator handle to prevent accidental disconnection during a surgical procedure.

Virtual environment tactile system

Abstract: A method for providing a realistic sense of touch in virtual reality by means of programmable actuator assemblies is disclosed. Each tactile actuator assembly consists of a number of individual actuators whose movement is controlled by a computer and associated drive electronics. When an actuator is energized, the rare earth magnet and the associated contactor, incorporated within the actuator, are set in motion by the opposing electromagnetic field of a surrounding coil. The magnet pushes the contactor forward to contact the skin resulting in the sensation of touch. When the electromagnetic field is turned off, the rare earth magnet and the contactor return to their neutral positions due to the magnetic equilibrium caused by the interaction with the ferrous outer sleeve. The small size and flexible nature of the actuator assemblies permit incorporation into a glove, boot or body suit. The actuator has additional applications, such as, for example, as an accelerometer, an actuator for precisely controlled actuations or to simulate the sensation of braille letters.

Synthetic jet actuator and applications thereof

Abstract: A synthetic jet actuator, which can be micromachined if desired, generates a synthetic jet stream characterized by a series of successive vortices that can be used for effectively entraining adjacent fluid. The synthetic jet actuator can be used to bend, or vector, a jet stream from another jet actuator. Further, because the synthetic jet actuator exhibits zero net mass flux, the synthetic jet actuator can be used within a bounded volume. In structure, the synthetic jet actuator comprises a housing defining an internal chamber and having an orifice. A flexible metallized diaphragm forms a wall of the housing and can change the volume of the chamber when moved. An electrode is disposed adjacent to and spaced from the diaphragm, and an electrical bias is imposed between the metallized diaphragm and the electrode by a control system to force movement of the diaphragm. As the diaphragm moves, the volume in the internal chamber changes and vortices are ejected from the chamber through the orifice.

Elastic actuator for precise force control

Abstract: The invention provides an elastic actuator consisting of a motor and a motor drive transmission connected at an output of the motor. An elastic element is connected in series with the motor drive transmission, and this elastic element is positioned to alone support the full weight of any load connected at an output of the actuator. A single force transducer is positioned at a point between a mount for the motor and an output of the actuator. This force transducer generates a force signal, based on deflection of the elastic element, that indicates force applied by the elastic element to an output of the actuator. An active feedback force control loop is connected between the force transducer and the motor for controlling the motor. This motor control is based on the force signal to deflect the elastic element an amount that produces a desired actuator output force. The produced output force is substantially independent of load motion. The invention also provides a torsional spring consisting of a flexible structure having at least three flat sections each connected integrally with and extending radially from a central section. Each flat section extends axially along the central section from a distal end of the central section to a proximal end of the central section.

Use of thickness-shear mode in adaptive sandwich structures

Abstract: A new adaptive sandwich structure is constructed using the shear mode of piezoelectric materials. A comparative study of the sandwich structure and the corresponding surface-mounted actuation structure is performed using finite-element analysis. The effects of actuator length and location on actuation performance of the structures are studied. The stress distributions under mechanical and electrical loads are investigated for both the sandwich beam and the surface-mounted actuation beam. It is shown that the stress level within the actuators is more severe for the surface-mounted actuation beam than for the sandwich. Also, the interface-stress distribution between actuator and host structure is analysed. It is shown that sandwich construction offers many advantages over conventional surface-mounted actuation constructions.

Micro catheter system with active guide wire

Abstract: In this paper, we propose a new prototype model of micro-catheter with active guide wire that has two bending degrees of freedom. The design and fabrication methods of this micro active catheters (MAC) are described. Prototype models are 3Fr, 4Fr, 6Fr (1Fr=1/3 mm) in diameter and consist of catheter tube and active guide wire with ionic conducting polymer film actuator on its front end as the servo actuator. The bending characteristics of the MAC have been measured by application of electricity in physiological saline solution. We also modeled this MAC for characteristic evaluation. Experimental results show that the model of the active catheter is reasonable for practical applications. By using simulators (whose conditions are similar to those of a body cavity), we also carried out simulation experiments "in vitro". The experimental results indicate that the proposed MAC is applicable to intracavity operations.

Piezoelectric ultrasonic motors

Abstract: Piezoelectric ultrasonic motors are a new type of actuator. They are characterized by high torque at low rotational speed, simple mechanical design and good controllability. They also provide a high holding torque even if no power is applied. Compared to electromagnetic actuators the torque per volume ratio of piezoelectric ultrasonic motors can be higher by an order of magnitude. Recently various types of piezoelectric ultrasonic motors have been developed for industrial applications such as cameralens drive or as actuator in the head restraint of automobile seats. This paper describes several types of piezoelectric ultrasonic motors. In the first part the working principle of the travelling wave motor is explained. In the second part other types of piezoelectric ultrasonic motors are described and classified with respect to the vibration modes and contact mechanisms used in their design. Finally some open problems in piezoelectric ultrasonic motor research are addressed.

Thermal microactuators for surface-micromachining processes

Abstract: Microelectromechanical systems must include large-deflection actuators to create devices which can interact mechanically with their surroundings. Electrostatic actuators with large nonresonant motion require high voltages and large surface areas to produce useful forces. Large-deflection thermal actuators have been fabricated in electroplated metal processes, but the choice of materials is limited, and the high conductivity of metal means these devices need a high current to generate the required heat. Thus, there is a need for a low voltage actuator with a large nonresonant deflection which can be fabricated in integrated circuit compatible surface-micromachining processes. The device described in this paper has a simple, flexible, and reliable design which overcomes the limitations of other actuators. It is a low voltage, medium current thermal actuator which can be designed to move laterally in a controllable, nonresonant motion. Typical actuators are 200 micrometers long, 18 micrometers wide, and deflect 10 micrometers at the tip with a drive current of 5 mA at 5 volts. A wide range of layout geometries allows this type of actuator to be fabricated in any surface-micromachining process that includes a releasable, current-carrying layer. An empirical model is presented to describe the devices fabricate in a commercially available surface-micromachining process. Arrays of actuators were fabricated to test the effect of different device dimensions on maximum achievable deflection as a funciton of applied current. Actuators can be combined to produce more force and have been integrated with other micromechanical structures. Applications of these actuators include linear and rotating motors, compliant micromechanisms, latches, micro-relays, variable capacitators and tweezers.

A force-controlled pneumatic actuator

Abstract: This paper presents a new pneumatic actuator for applications requiring moderate, but accurate, force control, such as teleoperation masters and robot wrists. The actuator uses voice-coil flapper valves and low-friction cylinders. Its force is controlled by servoing differential pressure. Aspects of valve design, system modeling, controller design, and experimental results are presented.