Showing papers in "IEEE-ASME Transactions on Mechatronics in 2012"

Design and Control of a Three-Axis Serial-Kinematic High-Bandwidth Nanopositioner

Abstract: The development of a high-performance three-axis serial-kinematic nanopositioning stage is presented. The stage is designed for high-bandwidth applications that include video-rate scanning probe microscopy and high-throughput probe-based nanofabrication. Specifically, the positioner employs vertically stiff, double-hinged serial flexures for guiding the motion of the sample platform to minimize parasitic motion (runout) and off-axis effects compared to previous designs. Finite element analysis (FEA) predicts the dominant resonances along the fast ( x-axis) and slow (y-axis) scanning axes at 25.9 and 6.0 kHz, respectively. The measured dominant resonances of the prototype stage in the fast and slow scanning directions are 24.2 and 6.0 kHz, respectively, which are in good agreement with the FEA predictions. In the z-direction, the measured dominant resonance is approximately 70 kHz. The lateral and vertical positioning ranges are approximately 9 μm × 9 μm and 1 μm, respectively. Four approaches to control the lateral motion of the stage are evaluated for precision tracking at high-scan rates: (1) open-loop smooth inputs; (2) PID feedback; (3) discrete-time repetitive control implemented using field-programmable gate array (FPGA) hardware; and (4) model-based feed forward control. The stage is integrated with a commercial scan-by-probe atomic force microscope (AFM) and imaging and tracking results up to a line rate of 7 kHz are presented. At this line rate, 70 frames/s atomic force microscope video (100 × 100 pixels resolution) can be achieved.

Algorithms for Real-Time Estimation of Individual Wheel Tire-Road Friction Coefficients

Abstract: It is well recognized in the automotive research community that knowledge of the real-time tire-road friction coefficient can be extremely valuable for active safety applications, including traction control, yaw stability control and rollover prevention. Previous research results in literature have focused on the estimation of average tire-road friction coefficient for the entire vehicle. This paper explores the development of algorithms for reliable estimation of independent friction coefficients at each individual wheel of the vehicle. Three different observers are developed for the estimation of slip ratios and longitudinal tire forces, based on the types of sensors available. After estimation of slip ratio and tire force, the friction coefficient is identified using a recursive least-squares parameter identification formulation. The observers include one that utilizes engine torque, brake torque, and GPS measurements, one that utilizes torque measurements and an accelerometer and one that utilizes GPS measurements and an accelerometer. The developed algorithms are first evaluated in simulation and then evaluated experimentally on a Volvo XC90 sport utility vehicle. Experimental results demonstrate the feasibility of estimating friction coefficients at the individual wheels reliably and quickly. The sensitivities of the observers to changes in vehicle parameters are evaluated and comparisons of robustness of the observers are provided.

A Compact Rotary Series Elastic Actuator for Human Assistive Systems

Abstract: Precise and large torque generation, back drivability, low output impedance, and compactness of hardware are important requirements for human assistive robots. In this paper, a compact rotary series elastic actuator (cRSEA) is designed considering these requirements. To magnify the torque generated by an electric motor in the limited space of the compact device, a worm gear is utilized. However, the actual torque amplification ratio provided by the worm gear is different from the nominal speed reduction ratio due to friction, which makes the controller design challenging. In this paper, the friction effect is considered in the model of cRSEA, and a robust control algorithm is designed to precisely control the torque output in the presence of nonlinearities such as the friction. The mechanical design and dynamic model of the proposed device and the design of a robust control algorithm are discussed, and actuation performance is verified by experiments. Experimental results with a human subject are also presented to show the performance of the cRSEA while interacting with humans.

Sliding-Mode Antisway Control of an Offshore Container Crane

Abstract: In this paper, a sliding-mode control for an offshore container crane is discussed. The offshore container crane is used to load/unload containers between a huge container ship (called the “mother ship”) and a smaller ship (called the “mobile harbor”), on which the crane is installed. The purpose of the mobile harbor is to load/unload containers in the open sea and transport them to shallower water where they can be offloaded at existing conventional ports, thereby obviating the need for expansive and expensive new facilities. The load/unload control objective is to suppress the pendulum motion (i.e., “sway”) of the load in the presence of the wave- and wind-induced movements (heave, roll, and pitch) of the mobile harbor. A new mechanism for lateral sway control, therefore, is proposed as well. A sliding surface is designed in such a way that the longitudinal sway of the load is incorporated with the trolley dynamics. The asymptotic stability of the closed-loop system is guaranteed by a control law derived for the purpose. The proposed new mechanism can suppress lateral sway, which functionality is not possible with conventional cranes. Simulation results are provided.

Girona 500 AUV: From Survey to Intervention

Abstract: This paper outlines the specifications and basic design approach taken on the development of the Girona 500, an autonomous underwater vehicle whose most remarkable characteristic is its capacity to reconfigure for different tasks. The capabilities of this new vehicle range from different forms of seafloor survey to inspection and intervention tasks.

Design and Locomotion Control of a Biomimetic Underwater Vehicle With Fin Propulsion

Abstract: As a novel biologically inspired underwater vehicle, a robotic manta ray (RoMan-II) has been developed for potential marine applications. Manta ray can perform diversified locomotion patterns in water by manipulating two wide tins. These motion patterns have been implemented on the developed fish robot, including swimming by flapping fins, turning by modulating phase relations of fins, and online transition of different motion patterns. The movements are achieved by using a model of artificial central pattern generators (CPGs) constructed with coupled nonlinear oscillators. This paper focuses on the analytical formulation of coupling terms in the CPG model and the implementation issues of the CPG-based control on the fish robot. The control method demonstrated on the manta ray robot is expected to be a frame- work that can tackle locomotion control problems in other types of multifin-actuated fish robots or more general robots with rhythmic movement patterns.

Mechatronic Design and Characterization of the Index Finger Module of a Hand Exoskeleton for Post-Stroke Rehabilitation

Abstract: This paper presents HANDEXOS, a novel wearable multiphalanges device for post-stroke rehabilitation. It was designed in order to allow for a functional and safe interaction with the user's hand by means of an anthropomorphic kinematics and the minimization of the human/exoskeleton rotational axes misalignment. This paper describes the mechatronic design of the exoskeleton's index finger module, simulation, modeling, and development of the actuation unit and sensory system. Experimental results on the validation of the dynamic model and experimental characterization of the index finger module with healthy subjects are reported, showing promising results that encourage further clinical trials.

Development of a Hand-Assist Robot With Multi-Degrees-of-Freedom for Rehabilitation Therapy

Abstract: This paper presents a virtual reality (VR)-enhanced new hand rehabilitation support system that enables patients to exercise alone. This system features a multi-degrees-of-freedom (DOF) motion assistance robot, a VR interface for patients, and a symmetrical master-slave motion assistance training strategy called "self-motion control," in which the stroke patient's healthy hand on the master side creates the assistance motion for the impaired hand on the slave side. To assist in performing the fine exercise motions needed for functional recovery of the impaired hand, the robot was constructed in an exoskeleton with 18 DOFs, to assist finger and thumb independent motions such as flexion/extension and abduction/adduction, thumb opposability, and hand-wrist co- ordinated motions. To enhance the effectiveness of the exercises, audio-visual instructions of each training motion using VR technology were designed with the input of clinician researchers. Experimental results from healthy subjects and patients show sufficient performance in the range of motion of the robot as well as sufficient assistance forces.

Miniature 3-Axis Distal Force Sensor for Minimally Invasive Surgical Palpation

Abstract: Minimally invasive surgery (MIS) is a surgical technique that offers distinct advantages in reducing pain and patients' recovery time. However, the drawback due to the lack of force and tactile feedback presents a great deal of limitations in MIS procedures. Tissue palpation, which is easily conducted during traditional open surgery to examine tissue properties and abnormalities, is not possible when performing surgery in a minimally invasive manner. This paper proposes a specially designed miniature 3-axis distal force sensor that can be used to perform tissue palpation, measuring tissue interaction forces at the tip of a surgical instrument. Relying on an optical sensing scheme, the sensor can measure forces within measurement ranges of ±3 N in axial direction and ±1.5 N in radial direction. The resolution is 0.02 N. It is compatible with laparoscopic operations and can be used to localize tissue lesions or relatively hard nodules buried under an organ's surface, which are not detectable by visual means.

Impedance Modeling and Analysis for Piezoelectric Energy Harvesting Systems

Abstract: In a piezoelectric energy harvesting (PEH) system, the dynamics and harvested power vary with different interface circuits connected. The impedance matching theory was regarded as the theoretical base for the harvested power optimization in the harmonically excited PEH systems. The previous literature started the impedance analyses based on the proposition that the harvested power is maximized when the output impedance of the piezoelectric transducer is matched by the input impedance of the harvesting circuit. Yet, retrospecting to the origin of the impedance matching theory, a philosophical problem is found with this proposition. Moreover, the definition, constraint, and composition of the equivalent impedance in the real (nonlinear) harvesting circuits were not clear as well. This paper clarifies these concepts and provides the impedance modeling and analysis for the PEH systems with different interface circuits, including standard energy harvesting, parallel synchronized switch harvesting on inductor, and series synchronized switch harvesting on inductor. The equivalent impedance network and corresponding mechanical schematics of a general PEH system are proposed. The difference between the PEH equivalent impedance network and the conventional impedance network is discussed. The harvested power is investigated based on this impedance analysis. The analytical results show good agreement with the experiments carried out on a base excited PEH device.

A Novel Kinematic Coupling-Based Trajectory Planning Method for Overhead Cranes

Abstract: Motivated by the desire to achieve smooth trolley transportation and small payload swing, a kinematic coupling-based off-line trajectory planning method is proposed for 2-D overhead cranes. Specifically, to damp out unexpected payload swing, an antiswing mechanism is first introduced into an S-shape reference trajectory based on rigorous analysis for the coupling behavior between the payload and the trolley. After that, the combined trajectory is further tuned through a novel iterative learning strategy, which guarantees accurate trolley positioning. The performance of the proposed trajectory is proven by Lyapunov techniques and Barbalat's lemmas. Finally, some simulation and experiment results are provided to demonstrate the superior performance of the planned trajectory.

Investigation of Attitude Tracking Using an Integrated Inertial and Magnetic Navigation System for Hand-Held Surgical Instruments

Abstract: Due to the need for accurate navigation in minimally invasive surgery, many methods have been introduced to the operating room for tracking the position and orientation of instruments. This paper considers the subproblem of using integrated inertial and magnetic sensing to track the attitude (orientation) of surgical instruments. In this scenario, it is usually assumed that the sensor is quasi-static and the surrounding magnetic field is steady. For practical hand-held surgical instruments, perturbations exist due to intended and unintended (e.g., tremor) motion and due to distortion of the surrounding magnetic field. We consider the problem of estimating the gravity and magnetic field in the inertial sensor frame with small perturbations. The dynamics of the gravity and magnetic field is studied under perturbations, their relationships to gyroscope measurements are analyzed, and Kalman filters (KFs) are formulated to reduce these perturbations. The estimated gravity and magnetic values (outputs of the KFs) are subsequently used in an extended KF for attitude estimation. In this filter, the prediction model is given by the system dynamics, formulated using quaternions, and the observation model is given by vector analysis of the estimated gravity and magnetic field. Experiments are performed to validate the algorithms under clinically realistic motions. The complete system demonstrates an improvement in the accuracy of the attitude estimate in the presence of small perturbations, and satisfies the specified accuracy requirement of 1°.

Semiactive Control Methodologies for Suspension Control With Magnetorheological Dampers

Abstract: Suspension systems are one of the most critical components of transportation vehicles. They are designed to provide comfort to the passengers to protect the chassis and the freight. Suspension systems are normally provided with dampers that mitigate these harmful and uncomfortable vibrations. In this paper, we explore two control methodologies (in time and frequency domain) used to design semiactive controllers for suspension systems that make use of magnetorheological dampers. These dampers are known because of their nonlinear dynamics, which requires the use of nonlinear control methodologies for an appropriate performance. The first methodology is based on the backstepping technique, which is applied with adaptation terms and H∞ constraints. The other methodology to be studied is the quantitative feedback theory (QFT). Despite QFT is intended for linear systems, it can still be applied to nonlinear systems. This can be achieved by representing the nonlinear dynamics as a linear system with uncertainties that approximately represents the true behavior of the plant to be controlled. The semiactive controllers are simulated in MATLAB/Simulink for performance evaluation.

A Negative Imaginary Approach to Modeling and Control of a Collocated Structure

Abstract: A transfer-function is said to be negative imaginary if the corresponding frequency response function has a negative definite imaginary part (on the positively increasing imaginary axis). Negative imaginary transfer-functions can be stabilized using negative imaginary feedback controllers. Flexible structures with compatible collocated sensor/actuator pairs have transfer-functions that are negative imaginary. In this paper a model structure that typically represents a collocated structure is considered. An identification algorithm which enforces the negative imaginary constraint is proposed for estimating the model parameters. A feedback control technique, known as integral resonant control (IRC), is proposed for damping vibrations in collocated flexible structures. Conditions for the stability of the proposed controller are derived, and shown that the set of stabilizing IRCs is convex. Finally, a flexible beam with two pairs of collocated piezoelectric actuators/sensors is considered. The proposed identification scheme is used determining the transfer-function and an IRC is designed for damping the vibrations. The experimental results obtained are reported.

On a Bio-inspired Amphibious Robot Capable of Multimodal Motion

Abstract: This paper addresses the system design and locomotion control for a versatile amphibious robot, AmphiRobot-II, inspired by various amphibian principles in the animal kingdom. In terms of the propulsion features of existing amphibians, a novel hybrid propulsive mechanism coupled with wheel-propeller-fin movements is proposed that integrates fish- or dolphin-like swimming and wheel-based crawling. The robot is able not only to implement flexible wheel-based movements on land, but also to perform steady and efficient fish- or dolphin-like swimming under water and can further switch between these two patterns via a specialized swivel device. To achieve multimodal motions, a body deformation steering approach is proposed for the turning locomotion on land with minimum turning radius obtained accordingly. A central pattern generator inspired underwater locomotion control is also implemented and tested on the physical robot. Based on the aforementioned design, the AmphiRobot-II prototype has been built and has successfully demonstrated to confirm the effectiveness of the hybrid propulsive scheme and the amphibious control approaches.

Design, Construction, and Modeling of a Flexible Rotor Active Magnetic Bearing Test Rig

Abstract: A successful industrial application of flexible rotors supported on active magnetic bearings (AMBs) requires careful attention not only to rotordynamic design aspects but also to electromagnetic and feedback control design aspects. Model-based control design provides the framework to ensure efficient, reliable, and safe operation of turbomachinery on AMBs. This paper describes in detail the design, construction, and modeling process for a high performance AMB test rig which typifies a small industrial super-critical centrifugal compressor. A unique aspect of the design are the two additional radial AMBs to allow the application of simulated destabilizing fluid or electromagnetic forces to the rotor. These forces are difficult to predict and can lead to rotordynamic instability of industrial machinery if not properly accounted for. This test rig provides a realistic platform to evaluate stabilizing control algorithms for high performance turbomachinery. A complete model of rotor, AMB actuators and accompanying electronics, is constructed from individually verified component models. Model validation is confirmed through the successful design and implementation of a μ-synthesis controller.

Design and Robust Repetitive Control of a New Parallel-Kinematic XY Piezostage for Micro/Nanomanipulation

Abstract: This paper presents mechanism and controller design procedures of a new piezoactuated flexure XY stage for micro-/nanomanipulation applications. The uniqueness of the proposed stage lies in that it possesses an integrated parallel, decoupled, and stacked kinematical structure, which owns such properties as identical dynamic behaviors in X and Y axes, decoupled input and output motion, single-input-single-output (SISO) control, high accuracy, and compact size. Finite element analysis (FEA) was conducted to predict static performance of the stage. An XY stage prototype was fabricated by wire electrical discharge machining (EDM) process from the alloy material Al7075. Based on the identified plant transfer function of the micropositioning system, an H∞ robust control combined with a repetitive control (RC) was adopted to compensate for the unmodeled piezoelectric nonlinearity. The necessity of using such a combined control is also investigated. Experimental results demonstrate that the H∞ plus RC scheme improves the tracking response by 67% and 28% compared to the stand-alone H∞ for 1-D and 2-D periodic positioning tasks, respectively. Thus, the results illustrate the effectiveness of the proposed mechanism design and control approach.

An Orthogonal Global Task Coordinate Frame for Contouring Control of Biaxial Systems

Abstract: Recent research on the coordinated control of biaxial machines for precise contour following has been using various locally defined task coordinate frames (LTCF) “attached” to the desired contour to approximately calculate the contour error for feedback controller designs. Contour error, by definition, is a geometrical quantity depending on the shape of the desired contour only and has nothing to do with the desired motion on the contour. As such, all those moving LTCF-based algorithms have to make the assumptions that the position tracking errors are much smaller than the radius of curvature of the desired contour and the calculated contour error is only an approximation of actual contour error. In contrast, this paper presents an orthogonal global task coordinate frame (GTCF) in which the calculation of contour error is exact to the first-order approximation of the actual contour error, no matter how large the position tracking errors would be. A systematic way to construct curvilinear coordinates of the proposed GTCF using any description of the geometry of the desired contour in a two-dimensional space is also given. Contouring control of a linear motor driven biaxial high-speed industrial gantry is then used as a case study. A simplistic direct adaptive robust controller (ARC) is constructed to deal with the effect of strong coupling of the system dynamics in the task space in addition to modeling uncertainties. The proposed GTCF-based ARC algorithm, along with the traditional LTCF-based ARC ones, are implemented and comparative experimental results are presented. The results validate the effectiveness of the proposed GTCF approach for free-form contouring control with large curvatures and arbitrary position tracking errors and confirm the excellent contouring performance of the proposed approach in general.

Servo Control of Magnetic Gears

Abstract: This paper considers the analysis and application of magnetic gearbox and magnetic coupling technologies and issues surrounding their use in high performance servo control systems. An analysis of a prototype magnetic coupling is used as a basis for demonstrating the underlying nonlinear torque transfer characteristics, nonlinear damping, and “pole-slipping” features when subjected to overtorque (overload) conditions. It is also shown how pole-slipping results in a consequential loss of control. A theoretical investigation into the suppression of mechanical torsional resonances in transmission systems encompassing these highly compliant magnetically coupled components is included along with experimental results from a demonstrator drive train. Automatic detection of pole slipping and a reconfigurable controller are also investigated. By addressing these issues, the proposed techniques extend the application scope of magnetic gear/coupling technologies to more demanding applications than those hitherto considered possible-specifically, for use in servo control systems and high-bandwidth mechanical drive trains.

Decoupling Control of Magnetically Suspended Rotor System in Control Moment Gyros Based on an Inverse System Method

Abstract: To radically eliminate the influence of gyroscopic effects on system stability and to improve the performances of high-precision, fast-response for the high-speed magnetically suspended rotor system in a control moment gyro, this paper proposes a control strategy that combines inverse system method and internal model control. The stability and robustness problems induced by current-mode linearization have been successfully solved by introducing phase-lead compensation and internal model controller. The effectiveness and superiority of the proposed strategy have been demonstrated by both simulation and experimental results.

Pressure-Based Clutch Control for Automotive Transmissions Using a Sliding-Mode Controller

Abstract: Clutch shift control is critical for efficient and high-performance transmission designs, including automatic, dual clutch, and hybrid transmissions. To ensure a smooth clutch to clutch shift, appropriate controls for two consecutive processes are critical. One is the precise coordination between the on-coming and off-going clutches, which requires the on-coming clutch to be filled and ready for engagement at the predetermined time (clutch fill). The other is the proper torque control during clutch engagement. In this paper, we will investigate the closed-loop “wet” clutch control enabled by a pressure sensor in the clutch chamber. The main challenges of the pressure-based “wet” clutch control lie in the complex nonlinear dynamics due to the interactions between the fluid and the mechanical systems, the ON/OFF behavior of the clutch assembly, the time-varying clutch loading condition, the required short time duration for a precise and robust clutch shift, and the lack of the displacement information. To enable precise and robust pressure-based control, this paper focuses on the following three aspects. First, a clutch dynamic model is constructed and validated, which precisely captures the system dynamics in a wide pressure range. Second, a sliding-mode controller is designed to achieve robust pressure control while avoiding the chattering effect. Finally, an observer is constructed to estimate the clutch piston motion, which is not only a necessary term in the nonlinear controller design but also a diagnosis tool for the clutch fill process. To validate the proposed methods, a transmission clutch fixture has been designed and built in the laboratory. The experimental results demonstrate the effectiveness and robustness of the proposed controller and observer.

Dual-User Teleoperation Systems: New Multilateral Shared Control Architecture and Kinesthetic Performance Measures

Abstract: This paper proposes a novel six-channel multilateral shared control architecture for dual-user teleoperation systems. The proposed controller allows interaction between two users as well as the slave and environment through a dominance factor. The dominance factor adjusts the authority of the users over the slave robot and environment. The proposed controller is implemented on a haptic simulation test bed consisting of two planar twin pantograph haptic devices and a simulated pantograph as the slave robot. To analyze the kinesthetic performance of the proposed multilateral shared controller, a number of performance measures are extended or proposed. These measures are evaluated analytically and experimentally for various types of environments, users’ grasps, and levels of dominance of the users over the task.

A New Approach for Modeling Piezoresistive Force Sensors Based on Semiconductive Polymer Composites

Abstract: Semiconductive polymer composites are used in a wide range of sensors and measurement devices. This paper discusses the development of a model and a new theoretical formulation for predicting piezoresistive behavior in semiconductive polymer composites, including their creep behavior and contact resistance. The relationship between electrical resistance and force applied to the piezoresistive force sensor can be predicted by using the proposed theoretical formulation. In order to verify the proposed formulation, the piezoresistive behavior of Linqstat, a carbon-filled polyethylene, was modeled mathematically. In addition, some experimental tests, such as thermo gravitational analysis and SEM, have been performed on Linqstat to find the volume fraction and size of carbon particles, which are essential for modeling. In addition, on a fabricated force sensor using Linqstat, a force versus resistance curve was obtained experimentally, which verified the validity and reliability of the proposed formulation.

Haptic Teleoperation for 3-D Microassembly of Spherical Objects

Abstract: In this paper, teleoperated 3-D microassembly of spherical objects with haptic feedback is presented. A dual-tip gripper controlled through a haptic interface is used to pick-and-place microspheres (diameter: 4-6 μm). The proposed approach to align the gripper with the spheres is based on a user-driven exploration of the object to be manipulated. The haptic feedback is based on amplitude measurements from cantilevers in dynamic mode. That is, the operator perceives the contact while freely exploring the manipulation area. The data recorded during this exploration are processed online and generate a virtual guide to pull the user to the optimum contact point, allowing correct positioning of the dual tips. A preliminary scan is not necessary to compute the haptic feedback, which increases the intuitiveness of our system. For the pick-and-place operation, two haptic feedback schemes are proposed to either provide users with information about microscale interactions occurring during the operation, or to assist them while performing the task. As experimental validation, a two-layer pyramid composed of four microspheres is built in ambient conditions.

Laser-Based Kinematic Calibration of Robot Manipulator Using Differential Kinematics

Abstract: This paper proposes a novel systematic technique to estimate entire kinematic parameter errors of robot manipulator. Small errors always exist in link length and link twist for physical manipulators, which affect the precision in kinematic equations leading to calculate wrong joint angle values in inverse kinematic equations. In order to solve these problems, the proposed technique employs a structured laser module (SLM), a stationary camera, the Jacobian matrices, and an extended Kalman filter (EKF). The SLM is attached to the end-effector of the manipulator arm and the stationary camera is used to determine an accurate position where the laser comes out. Variances between actual and measured positions of laser beams are represented by the Jacobian matrices formulated from differential kinematics. Then, the EKF is used to estimate kinematic parameters. Effectiveness of the proposed technique is verified with 7 DOF humanoid manipulator arm by computer simulation and 4 DOF manipulator by actual experiment.

Speed Control of a Hydraulic Pressure Coupling Drive Using an Adaptive Fuzzy Sliding-Mode Control

Abstract: In this paper, an adaptive fuzzy sliding-mode control (AFSMC) was proposed for speed control of a hydraulic pressure coupling drive. The AFSMC combined a direct adaptive fuzzy scheme and a fuzzy sliding scheme in a new structure to reduce the tracking error and the chattering of the control effort. The input nonlinearity of the secondary unit, the input dead zone, was taken into account during the speed controller synthesis and analysis of the stability of the closed-loop system. The stability of a system was proven from Lyapunov's sense. Experiments were performed with different controllers, the AFSMC, the traditional sliding-mode control, and the PID controllers, and under different operating conditions. Then, the experimental results were brought into comparison to evaluate the effectiveness of the AFSMC controller from the viewpoints of stability, performance, and robustness of the closed-loop system.

A Wireless Sensory Feedback Device for Real-Time Gait Feedback and Training

Abstract: This paper presents a new sensing and feedback system for a personal gait rehabilitation device based on wireless transmission of ambulation data for real-time sensory feedback for assistive healthcare. An integrated force-sensing insole was designed, using embedded force sensitive resistors that were sampled using a microprocessor, which then transmitted the data to an Android smartphone for presentation to the user. Experiments were performed to verify that the device captured accurate gait data, and was able to influence the gait of the subject. In addition, different sensory methods of feedback were tested to determine their individual efficacy at modulating the gait of study subject. The results show that the feedback system is capable of influencing the gait of the user, without the need for direct supervision by a rehabilitation specialist. In addition, a statistical analysis was performed to establish the reliability and repeatability of the system. From these results, this feedback system is established as a novel, inexpensive, and effective candidate for use in clinical rehabilitation of persons with gait abnormalities.

Dynamic Electromechanical Modeling of Dielectric Elastomer Actuators With Metallic Electrodes

Abstract: In this paper, a nonlinear electromechanical model for a PolyPower dielectric elastomer actuator is proposed based on an electric circuit model coupled with a viscoelastic mechanical model. The parameters of the model are found by fitting to an electrical step impulse for the mechanical part and by standard methods for the electric circuit. The resulting model is compared with experiments for a range of sinusoidal stimuli. The comparison shows good agreement between experiments and model results.

An Antisaturating Adaptive Preaction and a Slide Surface to Achieve Soft Landing Control for Electromagnetic Actuators

Abstract: Real-control applications of any nature can be affected by saturation limits that generate windup. When saturation occurs in a device its performance deteriorates. Electromagnetic actuators for industrial applications are being utilized ever more frequently for positioning and tracking control problems. One of the most important requirements in tracking trajectories is to achieve a soft landing, which guarantees reliable functionality and a longer component life. This paper presents an application of a typical electromagnetic actuator through a hardware-in-the-loop structure in which a soft landing is required in the tracking trajectory. To avoid saturation, which prevents soft landings, a specific new control law is developed. The proposed technique is based on a cyclic adaptive current preaction combined with a sliding surface. The technique consists of building a control law so that the position of the valve at which its velocity assumes its minimum is as close as possible to the landing point. At this time point, the magnetic force compensates for the elastic force and the preaction component is switched off. An experimental setup using a hardware-in-the-loop to allow a pilot investigation, model validation, and testing before implementation is considered. Real measurements of the proposed method are shown.

Bistable Antagonistic Dielectric Elastomer Actuators for Binary Robotics and Mechatronics

Abstract: Binary systems can lead to simple and efficient robotic and mechatronic systems since such systems use a large number of simple bistable actuators to affect its state. Dielectric elastomer actuators (DEAs) are prime candidates for use in binary systems since they are simple, low cost, and lightweight. However, previously proposed bistable DEAs (flip-flop) have relatively low volumetric energy density that limits their use in practical devices. This paper investigates the potential of improving the energy density of bistable designs by employing DEAs in compact antagonistic configurations. To do so, two antagonistic configurations (linear and rotating) are designed and studied using an experimentally validated Bergstrom–Boyce viscoelastic material model. The proposed antagonistic configurations show up to ∼10× higher volumetric energy densities than flip-flop designs. This represents a significant advantage for DEA reliability, since, based on volumetric energy density, antagonist actuators require the manufacturing of significantly less film layers than flip-flop designs. This study also reveals that, in the design of antagonistic DEAs, limiting the polymer film's actuation stretch minimizes viscoelastic losses and allows higher actuation speeds and power outputs for a given actuator stroke and size.