Showing papers in "IEEE-ASME Transactions on Mechatronics in 2006"

Biomechanical design of the Berkeley lower extremity exoskeleton (BLEEX)

Abstract: Wheeled vehicles are often incapable of transporting heavy materials over rough terrain or up staircases. Lower extremity exoskeletons supplement human intelligence with the strength and endurance of a pair of wearable robotic legs that support a payload. This paper summarizes the design and analysis of the Berkeley lower extremity exoskeleton (BLEEX). The anthropomorphically based BLEEX has 7 DOF per leg, four of which are powered by linear hydraulic actuators. The selection of the DOF, critical hardware design aspects, and initial performance measurements of BLEEX are discussed.

Design and control of an exoskeleton for the elderly and patients

Abstract: Recently, the exoskeletal power assistive equipment, which is a kind of wearable robot, has been widely developed to help human body motion. The exoskeleton for elderly people and patients, however, has some limitations due to the weight and volume of the equipment. In this paper, a tendon-driven exoskeletal power assistive device, exoskeleton for patients and the old by the Sogang University (EXPOS), is proposed as a feasible solution. In case of EXPOS, the caster walker carries heavy items such as motors, drivers, controllers, and batteries so that the weight and volume of the wearable exoskeleton are minimized. The tendon-connecting motors and pulleys of hip and knee generate the assistive power according to the requirement of the users. In this paper, the design concepts of the EXPOS, sensing techniques, and control methods are discussed

Design of a haptic arm exoskeleton for training and rehabilitation

Abstract: A high-quality haptic interface is typically characterized by low apparent inertia and damping, high structural stiffness, minimal backlash, and absence of mechanical singularities in the workspace. In addition to these specifications, exoskeleton haptic interface design involves consideration of space and weight limitations, workspace requirements, and the kinematic constraints placed on the device by the human arm. These constraints impose conflicting design requirements on the engineer attempting to design an arm exoskeleton. In this paper, the authors present a detailed review of the requirements and constraints that are involved in the design of a high-quality haptic arm exoskeleton. In this context, the design of a five-degree-of-freedom haptic arm exoskeleton for training and rehabilitation in virtual environments is presented. The device is capable of providing kinesthetic feedback to the joints of the lower arm and wrist of the operator, and will be used in future work for robot-assisted rehabilitation and training. Motivation for such applications is based on findings that show robot-assisted physical therapy aids in the rehabilitation process following neurological injuries. As a training tool, the device provides a means to implement flexible, repeatable, and safe training methodologies.

A robust compliant grasper via shape deposition manufacturing

Abstract: Joint compliance can enable successful robot grasping despite uncertainties in target object location. Compliance also enhances manipulator robustness by minimizing contact forces in the event of unintended contacts or impacts. In this paper, we describe the design, fabrication, and evaluation of a novel compliant robotic grasper constructed using polymer-based shape deposition manufacturing. Joints are formed by elastomeric flexures, and actuator and sensor components are embedded in tough rigid polymers. The result is a robot gripper with the functionality of conventional metal prototypes for grasping in unstructured environments but with robustness properties that allow for large forces due to inadvertent contact.

Gearshift control for automated manual transmissions

Abstract: A gearshift control strategy for modern automated manual transmissions (AMTs) with dry clutches is proposed. The controller is designed through a hierarchical approach by discriminating among five different AMT operating phases: engaged, slipping-opening, synchronization, go-to-slipping, and slipping-closing. The control schemes consist of decoupled and cascaded feedback loops based on measurements of engine speed, clutch speed, and throwout bearing position, and on estimation of the transmitted torque. Models of driveline, dry clutch, and controlled actuator are estimated on experimental data of a medium size gasoline car and used to check through simulations the effectiveness of the proposed controller.

MRI/fMRI-compatible robotic system with force feedback for interaction with human motion

Abstract: This paper presents a robotic system that is compatible with anatomical magnetic resonance imaging (MRI) as well as with the more sensitive functional MRI (fMRI), and can safely and smoothly interact with human motion during the imaging. The system takes advantage of the electromagnetic shield that encloses the MR room by placing the interfering or sensitive components outside the shield, in the control room. This eliminates the need for extensive compatibility testing before each use. The concept is based on a conventional actuator placed outside the scanner room and a hydrostatic connection to transmit force and motion to an MR-compatible slave placed next to or inside the MR scanner. A force sensor, based on reflected light intensity measurement over optical fibers, measures interaction forces with the human subject. A robotic interface for wrist motion demonstrates the MR compatibility of this concept and the possibility to interact with various dynamic environments during functional imaging. This technology provides a basis for applications such as assistive devices for interventional MRI and haptic interfaces for neuroscience investigations.

Analytical and experimental investigation on the magnetic field and torque of a permanent magnet spherical actuator

Abstract: This paper presents the torque model of a ball-joint-like three-degree-of-freedom (3-DOF) permanent magnet (PM) spherical actuator. This actuator features a ball-shaped rotor with multiple PM poles and a spherical stator with circumferential air-core coils. An analytical expression of the magnetic field of the rotor is obtained based on Laplace's equation. Based on this expression and properties of air-core stator coils, Lorentz force law is employed for the study of the relationship between the rotor torque and coil input currents. By using linear superposition, the expression of the actuator torque in terms of current input to the stator coils can be obtained in a matrix form. The linear expression of the actuator torque will facilitate real-time motion control of the actuator as a servo system. Experimental works are carried out to measure the actual magnetic field distribution of the PM rotor in three-dimensional (3-D) space as well as to measure the actual 3-D motor torque generated by the actuator coils. The measurement results were coincident with analytical study on the rotor magnetic field distribution and actuator torque expressions. The linearity and superposition of the actuator torque were also verified through the experiments

Model-based fault diagnosis in electric drives using machine learning

Abstract: Electric motor and power electronics-based inverter are the major components in industrial and automotive electric drives. In this paper, we present a model-based fault diagnostics system developed using a machine learning technology for detecting and locating multiple classes of faults in an electric drive. Power electronics inverter can be considered to be the weakest link in such a system from hardware failure point of view; hence, this work is focused on detecting faults and finding which switches in the inverter cause the faults. A simulation model has been developed based on the theoretical foundations of electric drives to simulate the normal condition, all single-switch and post-short-circuit faults. A machine learning algorithm has been developed to automatically select a set of representative operating points in the (torque, speed) domain, which in turn is sent to the simulated electric drive model to generate signals for the training of a diagnostic neural network, fault diagnostic neural network (FDNN). We validated the capability of the FDNN on data generated by an experimental bench setup. Our research demonstrates that with a robust machine learning approach, a diagnostic system can be trained based on a simulated electric drive model, which can lead to a correct classification of faults over a wide operating domain.

On the design of large degree-of-freedom digital mechatronic devices based on bistable dielectric elastomer actuators

Abstract: Binary actuation has been proposed to reduce complexity in robotic and mechatronic systems. However, a relatively large number of binary actuators are required to achieve the accuracy necessary for practical applications. Conventional actuators are not practical for such large degree-of-freedom (DoF) devices. Here, a dielectric elastomer (DE) actuator is developed for these applications. It is shown that DE actuators have high energy densities, light weight, low cost, and large displacements. Hence they could potentially make large DoF binary systems practical. DE actuators proposed here consist of thin electrically sensitive elastomer films that are mounted in a flexible frame that incorporates a passive bistable element. The frame prestrains the film and provides a restoring force that allows the actuator to operate bidirectionally. A simple experimental prototype 6-DoF binary manipulator demonstrates the concept

Wheel slippage and sinkage detection for planetary rovers

Abstract: Mobile robots are increasingly being used in high-risk rough terrain situations, such as planetary exploration and military applications. Current control and localization algorithms are not well suited to rough terrain, since they generally do not consider the physical characteristics of the vehicle and its environment. Little attention has been devoted to the study of the dynamic effects occurring at the wheel-terrain interface, such as slip and sinkage. These effects compromise odometry accuracy, traction performance, and may even result in entrapment and consequent mission failure. This paper describes methods for wheel slippage and sinkage detection aiming at improving vehicle mobility on soft sandy terrain. Novel measures for wheel slip detection are presented based on observing different onboard sensor modalities and defining deterministic conditions that indicate vehicle slippage. An innovative vision-based algorithm for wheel sinkage estimation is discussed based on edge detection strategy. Experimental results, obtained with a Mars rover-type robot operating in high-slippage sandy environments and with a wheel sinkage testbed, are presented to validate our approach. It is shown that these techniques are effective in detecting wheel slip and sinkage.

Localization and follow-the-leader control of a heterogeneous group of mobile robots

Abstract: This paper investigates the control and localization of a heterogeneous (e.g., different sensing, mechanical, computational capabilities) group of mobile robots. The group considered here has several inexpensive sensor-limited and computationally limited robots, which follow a leader robot in a desired formation over long distances. This situation is similar to a search, demining, or planetary exploration situation where there are several deployable/disposable robots led by a more sophisticated leader. Specifically, the robots in this paper are designed for highway safety applications where they automatically deploy and maneuver safety barrels commonly used to control traffic in highway work zones. Complex sensing and computation are performed by the leader, while the followers perform simple operations under the leader's guidance. This architecture allows followers to be simple, inexpensive, and have minimal sensors. Theoretical and statistical analysis of a tracking-based localization method is provided. A simple follow-the-leader control method is also presented, including a method for changing follower's configuration. Experimental results of localization and follow-the-leader formation-motion are included.

A Low-Order DGPS-Based Vehicle Positioning System Under Urban Environment

Abstract: The vehicle positioning system is a key component in functions such as vehicle guidance, driver alert and assistance, and vehicle automation. Since installing a low-cost global positioning system (GPS) or inertial navigation system (INS) unit is becoming a common practice in vehicle applications, its involvement in vehicle guidance and vehicle safety deserves a closer investigation. Typical vehicle applications require high reliability, low cost, and sufficient accuracy under all operational conditions. For GPS-based positioning, urban driving with its complicated maneuvers, frequent GPS blockage, and multipath, are some of the most difficult driving environments. This paper explores the feasibility of a low-order vehicle positioning system functioning under an urban environment. The equipped vehicle has a midrange differential GPS (DGPS) unit and few relatively simple in-vehicle sensors. A low-order integration is explored by utilizing a vehicle model-based extended Kalman filter (EKF) to incorporate in-vehicle motion sensors and to largely avoid direct integration of INS signals. Further, the characteristics of DGPS measurements under urban environments are investigated, and novel DGPS noise processing techniques are proposed to reduce the chances of exposing the EKF to undesirable DGPS measurements due to common DGPS problems such as blockage and multipath. A resulting fourth order EKF based positioning system is successfully implemented in the test vehicle to demonstrate the feasibility of the proposed design. Experimental results illustrate the ability of the system to meet the accuracy and robustness requirements in the presence of blockage and multipath under a typical urban driving environment

Design of learning input shaping technique for residual vibration suppression in an industrial robot

Abstract: In this paper, a practical method is proposed to suppress residual vibrations of industrial robots without a real-time estimation of vibration frequencies. Through theoretical analysis and experiments, we designed an input shaping technique (IST) for the first three axes of a six-degrees-of-freedom industrial robot. Iterative learning IST (LIST) is applied to the first axis to suppress its time-varying nonlinear residual vibration, while conventional IST is applied to the second and third axes. Experimental results show that LIST can suppress residual vibrations to a level similar to that of a time-varying IST which requires complicated real-time estimation of a dynamic model. The LIST is an attractive method for suppression of nonlinear and time-varying residual vibrations in industrial robots which perform repetitive tasks because most industrial robots have limited computing power and memory space in their controllers.

Hybrid Model Predictive Control of Direct Injection Stratified Charge Engines

Abstract: This paper illustrates the application of hybrid modeling and model predictive control techniques to the management of air-to-fuel ratio and torque in advanced technology gasoline direct-injection stratified-charge (DISC) engines. A DISC engine is an example of a constrained hybrid dynamical system, because it can operate in two distinct modes (stratified and homogeneous) and because the mode-dependent constraints on the air-to-fuel ratio and on the spark timing need to be enforced during its operation to avoid misfire, knock, and high combustion variability. In this paper, we approximate the DISC engine dynamics as a two-mode discrete-time switched affine system. Using this approximation, we tune a hybrid model predictive controller with integral action based on online mixed-integer quadratic optimization, and show the effectiveness of the approach through simulations. Then, using an offline multiparametric optimization procedure, we convert the controller into an equivalent explicit piecewise affine form that is easily implementable in an automotive microcontroller through a lookup table of linear gains

Precise Speed Estimation From a Low-Resolution Encoder by Dual-Sampling-Rate Observer

Abstract: This paper describes an effective way to estimate state variables, such as motor speed and disturbance from a low-resolution encoder at low speed by using the dual-sampling-rate observer. The dual-sampling-rate observer estimates the state variables at every DSP control period and correct the estimation error at the instant that the measurement signal is detected. A novel pole assignment method, which considers the relation of the estimation and error correction periods, is proposed to maintain the stability for long error correcting period. Moreover, the dual-sampling-rate observer can be applied for higher order systems since it is generalized in state space. The effectiveness of the observer is verified through various simulations and experiments

Simple Derivative-Free Nonlinear State Observer for Sensorless AC Drives

Abstract: In this paper, a new Kalman filtering technique, unscented Kalman filter (UKF), is utilized both experimentally and theoretically as a state estimation tool in field-oriented control (FOC) of sensorless ac drives. Using the advantages of this recent derivative-free nonlinear estimation tool, rotor speed and dq-axis fluxes of an induction motor are estimated only with the sensed stator currents and voltages information. In order to compare the estimation performances of the extended Kalman filter (EKF) and UKF explicitly, both observers are designed for the same motor model and run with the same covariance matrices under the same conditions. In the simulation results, it is shown that UKF, whose several intrinsic properties suggest its use over EKF in highly nonlinear systems, has more satisfactory rotor speed and flux estimates, which are the most critical states for FOC. These simulation results are supported with experimental results

Development of a three-axis active vibration isolator using zero-power control

Abstract: This paper presents the development of an active 3-degree-of-freedom (DoF) vibration isolation system using zero-power magnetic suspension. The developed system is capable to suppress direct disturbances and isolate ground vibrations of the 3-DoF motions, associated with vertical translational and rotational modes. Two categories of control strategy for the actuators are proposed, i.e., local control and mode control. The latter method allows to overcome limitations of the poor performances for rotational modes exhibited by the former. A mathematical model of the system is derived and each DoF motion is treated separately for the control system. It is demonstrated analytically that the infinite stiffness to static direct disturbances can be generated and the resonance peak due to floor vibration can effectively be suppressed for the system. Moreover, the experiments have been carried out to measure the static and dynamic responses of the isolation table to direct disturbances, and transmissibility characteristic of the isolator from the floor. The results indicate good vibration isolation and attenuation performances, and show the efficacy of the developed isolator for industrialization

High-frequency acceleration feedback in wave variable telerobotics

Abstract: The human hand is very sensitive to the high-frequency accelerations produced by tool contact with a hard object, yet most time delayed telerobots neglect this feedback band entirely in order to achieve stability. We present a control architecture that both incorporates this important information and provides the ability to scale and shape it independently of the low-frequency force feedback. Leveraging the clean power flows afforded by wave variables, this augmented controller preserves the passivity of any environment that it renders to the user, but is not subject to the limitations of being passive itself. This architecture guarantees stability in the presence of communication delay while achieving a level of feedback not possible with a passive controller. We show experimentally that this feedback augmentation and shaping can present a high-frequency acceleration profile to the user's hand that is similar to that experienced by the slave end effector. Two simple user studies also show that the feedback augmentation improves the user's perception, performance, and confidence with the given tasks. We anticipate that these natural haptic cues will make teleoperative systems easier to use and thus more widely applicable.

Energetics-based design of small flapping-wing micro air vehicles

Abstract: In this paper, the energetics of a flapping-wing micro air vehicle (MAV) is analyzed with the objective of designing it. The salient features of this paper are as follows: 1) designing an energy storage mechanism in the air vehicle similar to an insect thorax that stores part of the kinetic energy of the wing as elastic potential energy during a flapping cycle; 2) inclusion of simplified aerodynamic wing models and inertia of the mechanism using rigid-body modeling techniques; 3) optimization of parameters of the energy storage mechanism using the dynamic models, so that energy input from the external actuators is minimized during a flapping cycle. A series of engineering prototypes based on these studies have been planned which will justify the use of these mathematical techniques

HIFE-haptic interface for finger exercise

Abstract: A haptic device with two active degrees of freedom and a tendon-driven transmission system was designed, built, and tested. It was constructed as a mechanism with a small workspace that envelops a finger workspace and can generate forces up to 10 N, suitable for finger exercise. Kinematic and dynamic model equations of the haptic device are presented in the paper. The control strategies, the implementation of the application on a PC, the real-time millisecond-class control environment, running under the MS Widows operating system, and safety mechanisms are described. Also, the duration test for the maximum sustained output force, and validations of accuracy of the output force and the consistency of the followed path, were performed. The performance, accuracy, and safety of the device were found to be very good, which makes the device suitable for rehabilitation purposes.

Design of a mechanism for biaxial rotation of a wing for a hovering vehicle

Abstract: This paper presents a novel mechanism to actuate the wings of a hovering micro air vehicle (MAV). The mechanism uses a single actuator, but each wing can rotate about two orthogonal axes. The goal of this work is to design a light-weight compact mechanism that flaps the wings, inspired from the wing motion of hummingbird and hovering insects, to generate enough lift for the vehicle to hover. This paper explains in detail the proposed mechanism and its working prototypes. Also, the paper presents a dynamic simulation of the mechanism. The proposed dynamic simulation is used to predict the theoretical lift of the ornithopter. Further, the theoretical model is supported by actual experimental data collected from the prototype. The experimental data shows that the vehicle has the potential to develop enough lift to hover.

Rapid Prototyping of a Model-Based Control With Friction Compensation for a Direct-Drive Robot

Abstract: The development and application of the most recent model-based control schemes for robots require the investigation and solution of problems concerning various aspects, from the real-time (RT) simulation and control issues, to the necessity of determining a robot model suitable for control, and of experimentally testing the control performances. In this paper, different aspects are investigated for a planar, two-link direct-drive manipulator, with particular attention to the joint friction compensation within the control loop. A real-time architecture, based on the RT-Lab software by Opal-RT, is developed and used to carry out all the design phases, from the identification of the robot model, including joint friction torques, to the application of the inverse dynamics control schemes, with different solutions for the robot dynamics and friction compensation. The performances of such schemes are investigated executing various trajectories, suitable to check the effectiveness of the friction compensation

High bandwidth tilt measurement using low-cost sensors

Abstract: In this paper, a state estimation technique is developed for sensing inclination angles using low-cost sensors. A low-bandwidth tilt sensor is used along with an inaccurate rate gyro and a low-cost accelerometer to obtain the measurement. The rate gyro has an inherent bias along with sensor noise. The tilt sensor uses an internal pendulum and therefore has its own slow dynamics. These sensor dynamics were identified experimentally and combined to achieve high-bandwidth measurements using an optimal linear state estimator. Potential uses of the measurement technique range from robotics, to rehabilitation, to vehicle control.

Self-sensing actuation for nanopositioning and active-mode damping in dual-stage HDDs

Abstract: Position sensors other than the R/W heads are not embedded into current hard-disk drives (HDDs) due to cost, resolution, and signal-to-noise ratio (SNR) issues. Moreover, the "optimal" location for placing these sensors is still unknown. In this paper, the Pb-Zr-Ti (PZT) elements in the PZT suspension-based microactuator are used as a secondary actuator and a displacement sensor simultaneously with self-sensing actuation. The proposed displacement estimation circuit produces an estimated PZT microactuator's displacement with high SNR and nanometer resolution comparable to that measured from the laser doppler vibrometer (LDV). A robust active mode damping controller is then designed to damp the PZT microactuator suspension's torsion modes and sway mode, as well as decoupling the HDD dual-stage servo into two distinct loops for individual sensitivity optimization. Our results show attenuation of PZT microactuator's suspension modes by 5 dB and sway mode by 30 dB with low sensitivity. A reduction of up to 20% in 3/spl sigma/ position error signal is also observed.

Extremum-seeking nonlinear controllers for a human exercise machine

Abstract: In this paper, a next generation exercise machine controller is developed for a single degree of freedom (DOF) system to maximize the user's power output and ensure passivity with the user. In an effort to optimize the user's power expenditure, a desired velocity trajectory is developed that seeks the unknown user-dependent optimal velocity setpoint. Two extremum-seeking algorithms are presented (e.g., Kristic and Deng, and Tuekosky et al.) that seek the optimal velocity setpoint while ensuring the trajectory is sufficiently differentiable. To track the reference trajectory and to ensure passivity, two controllers are developed. The first controller is developed based on the assumption that the user's torque input can be measured. A second controller is designed that estimates the user's torque input. Both controllers are proven to ensure that the exercise machine remains passive with respect to the user's power output. The controllers are proven to yield semiglobal tracking through Lyapunov-based analyses. Proof-of-concept experimental results are provided that illustrate the performance of the torque estimation controller.

Optimum Vehicle Trajectory Control for Obstacle Avoidance Problem

Abstract: This paper discusses an obstacle avoidance problem. A new control algorithm for obstacle avoidance within the shortest possible distance is proposed. The algorithm is composed of two steps. In the first step, optimal trajectory and a corresponding force and moment are determined based on a second-order cone programming. In the second step, the computed force and moment are realized through the controlling brake and steering systems while using a sequential quadratic programming with pseudo-inverse matrix for the derivation

Stable identification of nonlinear systems using neural networks: theory and experiments

Abstract: This paper presents an approach for stable identification of multivariable nonlinear system dynamics using a multilayer feedforward neural network. Unlike most of the previous neural network identifiers, the proposed identifier is based on a nonlinear-in-parameters neural network (NLPNN). Therefore, it is applicable to systems with higher degrees of nonlinearities. Both parallel and series-parallel models are used with no a priori knowledge about the system dynamics. The method can be considered both as an online identifier that can be used as a basis for designing a neural network controller as well as an offline learning scheme for monitoring the system states. A novel approach is proposed for the weight updating mechanism based on the modification of the backpropagation (BP) algorithm. The stability of the overall system is shown using Lyapunov's direct method. To demonstrate the performance of the proposed algorithm, an experimental setup consisting of a three-link macro-micro manipulator (M3) is considered. The proposed approach is applied to identify the dynamics of the experimental robot. Experimental and simulation results are given to show the effectiveness of the proposed learning scheme

Design considerations for complementary inchworm actuators

Abstract: An inchworm actuator is described, which uses complementary configurations for the two clamping sections. In one configuration, clamping and release are achieved using high and low voltages, respectively, while for the other, clamping and release are achieved using low and high voltages, respectively. The resulting inchworm actuator can be driven by a two-channel controller with the two clamps sharing the first channel and the extender piezoelectric actuator using the second channel. The paper also describes a diode-shunted delay circuit that causes unclamping to occur more slowly than clamping. It is shown that by using the delay circuit in series with each clamp, the overall force drive capability of the actuator is increased. The paper presents simulated and experimental results of clamp force versus time during the switching transient. An analysis of a generalized delay circuit having both resistive and reactive elements shows that a purely resistive design provides the better tradeoff between increased force drive capability and power loss in the delay circuit.

Design and energetic characterization of a proportional-injector monopropellant-powered actuator

Abstract: This paper describes the design and energetic characterization of an actuator designed to provide enhanced system energy and power density for self-powered robots. The proposed actuator is similar to a typical compressible gas fluid-powered actuator, but pressurizes the respective cylinder chambers via a pair of proportional injector valves, which control the flow of a liquid monopropellant through a pair of catalyst packs and into the respective sides of the double-acting cylinder. This paper describes the design of the proportional injection valves and describes the structure of a force controller for the actuator. Finally, an energetic characterization of the actuator shows improvement relative to prior configurations and marked improvement relative to state-of-the-art batteries and motors.

Symbolic time-series analysis for anomaly detection in mechanical systems

Abstract: This paper examines the efficacy of a novel method for anomaly detection in mechanical systems, which makes use of a hidden Markov model, derived from the time-series data of pertinent measurement(s). The core concept of the anomaly detection method is symbolic time-series analysis that is built upon the principles of Automata Theory, Information Theory, and Pattern Recognition. The performance of this method is compared with that of other existing pattern-recognition techniques from the perspective of early detection of small fatigue cracks in ductile alloy structures. The experimental apparatus, on which the anomaly detection method is tested, is a multi-degree-of-freedom mass-beam structure excited by oscillatory motion of two electromagnetic shakers. The evolution of fatigue crack damage at one or more failure sites are detected from symbolic time-series analysis of displacement sensor signals