Showing papers on "Actuator published in 2007"

Manipulator for medical use

Abstract: In a manipulator, an actuator block contains motors and rotary shafts extending from the motors. A working unit of the manipulator contains a connecting portion, attachable to and detachable from the actuator block. The connecting portion has pulleys connectable to ends of the rotary shafts, and has a locking plate movable by alignment pins. The locking plate has slits, which are engaged with plate-shaped portions formed on the upper ends of the pulleys. A coil spring is placed between the locking plate and a top plate.

Optimization of a dielectric barrier discharge actuator by stationary and non-stationary measurements of the induced flow velocity: application to airflow control

Abstract: Several studies have shown that a surface dielectric barrier discharge (DBD) may be used as an electrohydrodynamic (EHD) actuator in order to control airflows In this paper, a parametric study has been performed in order to increase the velocity of the ionic wind induced by such actuators The results show that an optimization of geometrical and electrical parameters allows us to obtain a time-averaged ionic wind velocity up to 8 m/s at 05 mm from the wall Moreover, non-stationary measurements of the induced wind have been performed with synchronized records of current and voltage signals These experiments show that the DBD actuator seems to generate a pulsed velocity at the same frequency than the applied high voltage

Control system configured to compensate for non-ideal actuator-to-joint linkage characteristics in a medical robotic system

Abstract: A medical robotic system having non-ideal actuator-to-joint linkage characteristics, includes a control system including a proximal control loop with actuator sensor feedback to control dynamic response of an actuator coupled to a distal joint which in turn, is coupled to an end effector to provide a degree of freedom movement of the end effector, a distal control loop with distal joint sensor feedback and feedforward to the actuator to ensure steady-state convergence of the distal joint position, and an end effector control loop with end-point sensor feedback to control the end effector position to reach a commanded end effector position.

Feedforward Controller With Inverse Rate-Dependent Model for Piezoelectric Actuators in Trajectory-Tracking Applications

Abstract: Effective employment of piezoelectric actuators in microscale dynamic trajectory-tracking applications is limited by two factors: 1) the intrinsic hysteretic behavior of piezoelectric ceramic and 2) structural vibration as a result of the actuator's own mass, stiffness, and damping properties. While hysteresis is rate-independent, structural vibration increases as the piezoelectric actuator is driven closer to its resonant frequency. Instead of separately modeling the two interacting dynamic effects, this work treats their combined effect phenomenologically and proposes a rate-dependent modified Prandtl-Ishlinskii operator to account for the hysteretic nonlinearity of a piezoelectric actuator at varying actuation frequency. It is shown experimentally that the relationship between the slope of the hysteretic loading curve and the rate of control input can be modeled by a linear function up to a driving frequency of 40 Hz

Mechanical behavior of an acrylic elastomer used in dielectric elastomer actuators

Abstract: The paper reports on extensive experimental work for the characterization of a dielectric elastomer used as base material for electroactive polymer (EAP) actuators. The mechanical behavior of the acrylic elastomer VHB 4910 is characterized using large strain experiments (uniaxial and equibiaxial deformation) under force and displacement controlled loading conditions. Next to tensile and relaxation tests, experiments were conducted also using the so-called circular actuators. Over 40 actuators were produced (with different in-plane pre-strain levels) and activated with voltages between 2000 and 3500 V. The experimental data are useful for determining constitutive model parameters as well as for validating models and simulation procedures for electromechanical coupling in EAP actuators. A novel approach is proposed for finite element analysis of dielectric elastomer actuator, which has been used in the present work for the evaluation of the experimental observations from circular actuators. Material parameters of different visco-hyperelastic models have been determined from a subset of the experimental data and the predictive capabilities of the models evaluated through comparisons with the remaining data. The prediction of the circular actuator behavior was satisfactory so that the proposed models might be useful for actuator design and optimization purposes. Limitations of the proposed constitutive model formulation are presented.

A Bending Pneumatic Rubber Actuator Realizing Soft-bodied Manta Swimming Robot

Abstract: This paper shows a new design and prototyping method for a bending pneumatic rubber actuator and its application to a soft-bodied manta swimming robot. The design is based on optimal design using non-linear finite element method, in which geometrical and material non-linearity are considered and fabrication process is based on a rapid and efficient prototyping system using a CAD/CAM based rubber molding process. In this paper, the characteristics of several possible actuators are analyzed and evaluated to lead to an optimal actuator design. The actuator works very well with smooth and soft motion. The manta swimming robot in which the developed actuators are embedded is also designed based on non-linear finite element method. The developed manta swimming robot is made only of rubber and it swims in water smoothly as if it was a living fish. The experimental results of the manta robot motion show that good agreement with those of analytical results.

Haptic interface for touch screen embodiments

Abstract: A haptic feedback touch control used to provide input to a computer. A touch input device includes a planar touch surface that provides position information to a computer based on a location of user contact. The computer can position a cursor in a displayed graphical environment based at least in part on the position information, or perform a different function. At least one actuator is also coupled to the touch input device and outputs a force to provide a haptic sensation to the user. The actuator can move the touchpad laterally, or a separate surface member can be actuated. A flat E-core actuator, piezoelectric actuator, or other types of actuators can be used to provide forces. The touch input device can include multiple different regions to control different computer functions.

Dynamic Model Identification for Industrial Robots

Abstract: The use of periodic excitation is the key feature of the presented robot identification method. Periodic excitation allows us to integrate the experiment design, signal processing, and parameter estimation. This integration simplifies the identification procedure and yields accurate models. Experimental results on an industrial robot manipulator show that the estimated dynamic robot model can accurately predict the actuator torques for a given robot motion. Accurate actuator torque prediction is a fundamental requirement for robot models that are used for offline programming, task optimization, and advanced model-based control. A payload identification approach is derived from the integrated robot identification method, and possesses the same favorable properties.

Complementary Stability and Loop Shaping for Improved Human–Robot Interaction

Abstract: Robots intended for high-force interaction with humans face particular challenges to achieve performance and stability. They require low and tunable endpoint impedance as well as high force capacity, and demand actuators with low intrinsic impedance, the ability to exhibit high impedance (relative to the human subject), and a high ratio of force to weight. Force-feedback control can be used to improve actuator performance, but causes well-known interaction stability problems. This paper presents a novel method to design actuator controllers for physically interactive machines. A loop-shaping design method is developed from a study of fundamental differences between interaction control and the more common servo problem. This approach addresses the interaction problem by redefining stability and performance, using a computational approach to search parameter spaces and displaying variations in performance as control parameters are adjusted. A measure of complementary stability is introduced, and the coupled stability problem is transformed to a robust stability problem using limited knowledge of the environment dynamics (in this case, the human). Design examples show that this new measure improves performance beyond the current best-practice stability constraint (passivity). The controller was implemented on an interactive robot, verifying stability and performance. Testing showed that the new controller out-performed a state-of-the-art controller on the same system

Actuator Saturation Control

Abstract: Uniting local and global controllers for anti-windup design LQR/LQG theory for systems with saturated actuators - a stochastic linearization approach LPV-based control of systems with amplitude and rate actuator saturation constraints analysis and control of linear systems with saturation using convex optimization an LPV approach for disturbance attentuation of systems with bounded inputs regional H2 performance analysis and synthesis with saturating control control of discrete-time systems with actuator amplitude and rate nonlinearities null controllability and stabilization of linear systems subject to asymmetric actuator saturation internal stabilization and Lp(1p) performance for linear plants with actuators subject to amplitude and rate saturations optimal windup and directionality compensation in input-constrained nonlinear systems output feedback compensators for linear systems with position and rate bounded actuators.

Kinematic analysis of a 3-PRS parallel manipulator

Abstract: Although the current 3-PRS parallel manipulators have different methods on the arrangement of actuators, they may be considered as the same kind of mechanism since they can be treated with the same kinematic algorithm. A 3-PRS parallel manipulator with adjustable layout angle of actuators has been proposed in this paper. The key issues of how the kinematic characteristics in terms of workspace and dexterity vary with differences in the arrangement of actuators are investigated in detail. The mobility of the manipulator is analyzed by resorting to reciprocal screw theory. Then the inverse, forward, and velocity kinematics problems are solved, which can be applied to a 3-PRS parallel manipulator regardless of the arrangement of actuators. The reachable workspace features and dexterity characteristics including kinematic manipulability and global dexterity index are derived by the changing of layout angle of actuators. Simulation results illustrate that different tasks should be taken into consideration when the layout angles of actuators of a 3-PRS parallel manipulator are designed.

Artificial annelid robot driven by soft actuators

Abstract: The annelid provides a biological solution of effective locomotion adaptable to a large variety of unstructured environmental conditions. The undulated locomotion of the segmented body in the annelid is characterized by the combination of individual motion of the muscles distributed along the body, which has been of keen interest in biomimetic investigation. In this paper, we present an annelid-like robot driven by soft actuators based on dielectric elastomer. To mimic the unique motion of the annelid, a novel actuation method employing dielectric elastomer is developed. By using the actuator, a three-degree-of-freedom actuator module is presented, which can provide up-down translational motion, and two rotational degree-of-freedom motion. The proposed actuation method provides advantageous features of reduction in size, fast response and ruggedness in operation. By serially connecting the actuator modules, a micro-robot mimicking the motion of the annelid is developed and its effectiveness is experimentally demonstrated.

An arm wrestling robot driven by dielectric elastomer actuators

Abstract: The first arm wrestling match between a human arm and a robotic arm driven by electroactive polymers (EAP) was held at the EAPAD conference in 2005. The primary objective was to demonstrate the potential of the EAP actuator technology for applications in the field of robotics and bioengineering. The Swiss Federal Laboratories for Materials Testing and Research (Empa) was one of the three organizations participating in this competition. The robot presented by Empa was driven by a system of rolled dielectric elastomer (DE) actuators. Based on the calculated stress condition in the rolled actuator, a low number of pre-strained DE film wrappings were found to be preferential for achieving the best actuator performance. Because of the limited space inside the robot body, more than 250 rolled actuators with small diameters were arranged in two groups according to the human agonist–antagonist muscle configuration in order to achieve an arm-like bidirectional rotation movement. The robot was powered by a computer-controlled high voltage amplifier. The rotary motion of the arm was activated and deactivated electrically by corresponding actuator groups. The entire development process of the robot is presented in this paper where the design of the DE actuators is of primary interest. Although the robot lost the arm wrestling contest against the human opponent, the DE actuators have demonstrated very promising performance as artificial muscles. The scientific knowledge gained during the development process of the robot has pointed out the challenges to be addressed for future improvement in the performance of rolled dielectric elastomer actuators.

Iterative Control Approach to Compensate for Both the Hysteresis and the Dynamics Effects of Piezo Actuators

Abstract: In this brief, the compensation for both the nonlinear hysteresis and the vibrational dynamics effects of piezo actuators is studied. Piezo actuators are the enabling device in many applications such as atomic force microscopy (AFM) to provide nano- to atomic-levels precision positioning. During high-speed, large-range positioning, however, large positioning errors can be generated due to the combined hysteresis and dynamics effects of piezo actuators, making it challenging to achieve precision positioning. The main contribution of this brief is the use of an inversion-based iterative control (IIC) technique to compensate for both the hysteresis and vibrational dynamics effects of piezo actuators. The convergence of the IIC algorithm is investigated by capturing the input-output behavior of piezo actuators with a cascade model consisting of a rate-independent hysteresis at the input followed by the dynamics part of the system. The size of the hysteresis and the vibrational dynamics variations that can be compensated for (by using the IIC method) is quantified. The IIC approach is illustrated through experiments on a piezotube actuator used for positioning on an AFM system. Experimental results show that high-speed, large-range precision positioning can be achieved by using the proposed IIC technique. Furthermore, the proposed IIC algorithm is also applied to experimentally validate the cascade model and the rate-independence of the hysteresis effect of the piezo actuator.

Thermal energy harvesting device using ferromagnetic materials

Abstract: A unique concept for harvesting electrical energy from thermal energy is presented A thermomechanical actuator was fabricated using ferromagnetic material The device converts thermal energy into mechanical energy, which can be converted into electrical energy using piezoelectric materials Magnetic force and operating frequency were measured on the device Results show that the current power density at ΔT=50K is between 185 and 361mW∕cm2 A thermal finite element analysis model is also presented to understand the influence of thermal interface, suggesting that increases of 185mW∕cm2 or higher are achievable

Critical review of current trends in shape memory alloy actuators for intelligent robots

Abstract: Purpose – The purpose of this paper is to review the current application areas of shape memory alloy (SMA) actuators in intelligent robotic systems and devices.Design/methodology/approach – This paper analyses how actuation and sensing functions of the SMA actuator have been exploited and incorporated in micro and macro robotic devices, developed for medical and non‐medical applications. The speed of response of SMA actuator mostly depends upon its shape and size, addition and removal of heat and the bias force applied. All these factors have impact on the overall size of the robotic device and the degree of freedom (dof) obtained and hence, a comprehensive survey is made highlighting these aspects. Also described are the mechatronic aspects like the software and hardware used in an industrial environment for the control of such nonlinear actuator and the type of sensory feedback devices incorporated for obtaining better control, positioning accuracy and fast response.Findings – SMA actuators find wide ap...

Modeling of Magnetically Levitated Planar Actuators With Moving Magnets

Abstract: This paper presents three types of magnetostatic models of ironless planar actuators with moving magnets. The models predict the force and torque exerted on the translator of the actuator, which can be positioned in six degrees-of-freedom with respect to the stator coils. The force and torque are calculated with the Lorentz force law. The analytical and numerical models can be used for the design of large planar actuators, for the fast comparison of actuator topologies, and in the decoupling and commutation algorithm. The models have been verified with experiments

Passive and accurate torque control of series elastic actuators

Abstract: The principle of series elastic actuation offers considerable advantages for haptic displays compared to stiff actuators. The interaction force between motor and load is directly proportional to their relative position, which corresponds to the elongation of the elastic element. This way, the torque control task is transformed to a position control task, which comes natural to traditional DC motors. In this paper, several existing control strategies are analyzed and compared with respect to passivity concerns. Cascaded control with a fast inner velocity loop results to be the best option. Based on the analysis, boundaries for the parameters are presented, such that the force controller may contain integral action without jeopardizing passivity.

Flow control with plasma synthetic jet actuators

Abstract: This paper presents an experimental investigation of the characteristics of a plasma actuator design for flow control consisting of an annular electrode in quiescent and flat plate boundary layer flows. In quiescent flow, the circular plasma region produced on actuation was observed to generate a vertical zero-net mass flux (or synthetic) jet, hence the name plasma synthetic jet actuator, the characteristics of which were found to be affected by the actuator operation mode (steady or unsteady). Pulsed operation of the actuator results in the formation of a starting vortex ring that advects ahead of the jet and secondary vortex rings near the actuator surface due to the additional plasma-induced fluid entrainment in the boundary layer. By varying the actuator pulsing frequency, multiple vortex rings were created in the flowfield and the resulting vortex ring interactions were found to increase both the peak velocity and streamwise extent of the jet. The interaction of the actuator with a crossflow was observed to be similar to that seen in conventional or non zero-net mass flux jets with the plasma synthetic jet penetrating into the mean flow. As expected, the influence of the jet on the freestream was found to decrease with increasing mean velocity and the impact on displacement and momentum thickness values diminishes as well.

Method for defining a touch-down power for head having a flying height actuator

Abstract: A novel method for defining a touch-down power for a head that has a head-based flying height actuator is disclosed and claimed. A linear relationship between power and spacing is derived by fitting to first and second transducer-disk spacings corresponding to first and second electrical powers applied to the head-based flying height actuator. A third spacing between the transducer and the disk is determined when a greater third electrical power is applied to the flying height actuator. An estimated third spacing between the transducer and the disk, corresponding to application of the third electrical power to the flying height actuator, is calculated using the derived linear relationship and the third electrical power. The touch-down power is defined to be substantially equal to the second electrical power if an error between the third spacing and the estimated third spacing is larger than a first threshold.

Mechanical design of the humanoid robot platform, HUBO

Abstract: The Korea Advanced Institute of Science and Technology (KAIST) humanoid robot-1 (KHR-1) was developed for the purpose of researching the walking action of bipeds. KHR-1, which has no hands or head, has 21 d.o.f.: 12 d.o.f. in the legs, 1 d.o.f. in the torso and 8 d.o.f. in the arms. The second version of this humanoid robot, KHR-2 (which has 41 d.o.f.) can walk on a living-room floor; it also moves and looks like a human. The third version, KHR-3 (HUBO), has more human-like features, a greater variety of movements and a more human-friendly character. We present the mechanical design of HUBO, including the design concept, the lower-body design, the upper-body design and the actuator selection of joints. Previously we developed and published details of KHR-1 and KHR-2. The HUBO platform, which is based on KHR-2, has 41 d.o.f., stands 125 cm tall and weighs 55 kg. From a mechanical point of view, HUBO has greater mechanical stiffness and a more detailed frame design than KHR-2. The stiffness of the frame was...

Multiple mode haptic feedback system

Abstract: A haptic effect device includes a housing and a touchscreen coupled to the housing through a suspension. An actuator is coupled to the touchscreen. The suspension is tuned so that when the actuator generates first vibrations at a first frequency, the first vibrations are substantially isolated from the housing and are applied on the touchscreen to simulate a mechanical button. Further, when the actuator generates second vibrations at a second frequency, the second vibrations are substantially passed through to the housing to create a vibratory alert.

Adaptive unknown input observer approach for aircraft actuator fault detection and isolation

Abstract: In this paper, an adaptive unknown input observer (UIO) approach is developed to detect and isolate aircraft actuator faults. In a multiple-model scheme, a bank of parallel observers are constructed, each of which is based on a model that describes the system in the presence of a particular actuator fault. The observers are constructed based on a modified form of the standard UIO to generate fault-dependant residual signals, such that when a model matches the system, the residual signal will be zero. Otherwise, the residual will be definitely non-zero and governed uniquely by the faulty signal. For locked actuators and loss of actuator effectiveness, in which the locked position and the reduced effectiveness are additional unknowns, we develop an adaptive scheme to estimate these unknown parameters. To the best of our knowledge, this is the first adaptive UIO presented. We prove that the proposed adaptive algorithms guarantee that both the residual signals and the estimation errors of the unknown parameters converge exponentially when a model matches the plant. By further designing a model-matching index, the fault can be isolated accurately. A condition for the approach is that for an nth order system, there must be n independent measurements available. This requirement limits the applicability of our proposed approach. The condition is certainly satisfied by all state-feedback control systems. However, for some other systems, extra efforts may be needed to increase the number of measurements. The method is applied to a linear model of the F-16 aircraft with controller. The results show that the approach is effective. Copyright © 2006 John Wiley & Sons, Ltd.

Vehicle suspension system

Abstract: A vehicle suspension system including: (a) a suspension spring interconnecting a vehicle body and a wheel; (b) an actuator having an electric motor, such that the actuator is capable of generating, based on a force of the electric motor, an actuator force forcing the body and the wheel toward and away from each other, and causing the generated actuator force to act as a damping force against displacement of the body and the wheel; and (c) a control device for controlling the actuator force generated by the actuator, by controlling operation of the electric motor. The control device is capable of establishing a constant-force generating state in which the actuator force is constantly generated as a constant actuator force by the actuator with supply of an electric power thereto from a battery as an electric power source of the electric motor such that the generated constant actuator force acts in a rebound direction or a bound direction. The control device controls the constant-force generating state, based on a charge state of the battery.

A new approach to develop ionic polymer-metal composites (IPMC) actuator: Fabrication and control for active catheter systems

Abstract: The ionic polymer–metal composite (IPMC) is one type of electro-active materials with the characteristics of low electric driving potential, large deformation and aquatic manipulation. It is highly attractive to biomedical applications as an actuator or a sensor. The main purpose of this study was to develop an IPMC actuator for active catheter systems. The first step was to develop a low cost and high reliability fabrication procedure to yield an IPMC actuator. In the second step, the dynamic behavior of the actuator was tested in an aqueous environment. An empirical model was then constructed, which consisted of a fourth-order linear system, a nonlinear gain and a time delay. To linearize the dynamic behavior of this actuator for better actuating performance, a nonlinearity compensation method by a second-order polynomial was proposed. In the final step, the bending behavior of the constructed IPMC actuator with an open-loop and a closed-loop controller design was investigated. The results indicated that a low cost but reliable IPMC actuator was fabricated successfully. Its production time was less than half of current manufacturing time (more than 48 h). The bending motion at low operation frequencies was well controlled by a conventional PID controller without adding complicated control algorithm. Our proposed algorithm decreased the maximum overshot from 30 to 4.2%, and the steady-state error from 15 to 4%. Though the rise time was increased from 0.084 to 0.325 s, it was within the limit for many biomedical applications.

Active health monitoring of an aircraft wing with an embedded piezoelectric sensor/actuator network: II. Wireless approaches

Abstract: The objective of this study is to develop a wireless ultrasonic structural health monitoring (SHM) system for aircraft wing inspection. In part I of the study (Zhao et al 2007 Smart?Mater.?Struct. 16 1208?17), small, low cost and light weight piezoelectric (PZT) disc transducers were bonded to various parts of an aircraft wing for detection, localization and growth monitoring of defects. In this part, two approaches for wirelessly interrogating the sensor/actuator network were developed and tested. The first one utilizes a pair of reactive coupling monopoles to deliver 350?kHz RF tone-burst interrogation pulses directly to the PZT transducers for generating ultrasonic guided waves and to receive the response signals from the PZTs. It couples enough energy to and from the PZT transducers for the wing panel inspection, but the signal is quite noisy and the monopoles need to be in close proximity to each other for efficient coupling. In the second approach, a small local diagnostic device was developed that can be embedded into the wing and transmit the digital signals FM-modulated on a 915?MHz carrier. The device has an ultrasonic pulser that can generate 350?kHz, 70?V tone-burst signals, a multiplexed A/D board with a programmable gain amplifier for multi-channel data acquisition, a microprocessor for circuit control and data processing, and a wireless module for data transmission. Power to the electronics is delivered wirelessly at X-band with an antenna?rectifier (rectenna) array conformed to the aircraft body, eliminating the need for batteries and their replacement. It can effectively deliver at least 100?mW of DC power continuously from a transmitter at a range of 1?m. The wireless system was tested with the PZT sensor array on the wing panel and compared well with the wire connection case.