Showing papers in "IEEE-ASME Transactions on Mechatronics in 2014"
TL;DR: In this article, a robust integral of the sign of the error controller and an adaptive controller are synthesized via backstepping method for motion control of a hydraulic rotary actuator.
Abstract: Structured and unstructured uncertainties are the main obstacles in the development of advanced controllers for high-accuracy tracking control of hydraulic servo systems. For the structured uncertainties, nonlinear adaptive control can be employed to achieve asymptotic tracking performance. But modeling errors, such as nonlinear frictions, always exist in physical hydraulic systems and degrade the tracking accuracy. In this paper, a robust integral of the sign of the error controller and an adaptive controller are synthesized via backstepping method for motion control of a hydraulic rotary actuator. In addition, an experimental internal leakage model of the actuator is built for precise model compensation. The proposed controller accounts for not only the structured uncertainties (i.e., parametric uncertainties), but also the unstructured uncertainties (i.e., nonlinear frictions). Furthermore, the controller theoretically guarantees asymptotic tracking performance in the presence of various uncertainties, which is very important for high-accuracy tracking control of hydraulic servo systems. Extensive comparative experimental results are obtained to verify the high-accuracy tracking performance of the proposed control strategy.
443 citations
TL;DR: In this paper, the design and control of a prismatic series elastic actuator with high mechanical power output in a small and lightweight form factor is discussed. And the actuator's performance is demonstrated through a series of experiments designed to operate at the limits of its mechanical and control capability.
Abstract: This paper discusses design and control of a prismatic series elastic actuator with high mechanical power output in a small and lightweight form factor. A design is introduced that pushes the performance boundary of electric series elastic actuators by using high motor voltage coupled with an efficient drivetrain to enable large continuous actuator force while retaining speed. Compact size is achieved through the use of a novel piston-style ball screw support mechanism and a concentric compliant element. Generic models for two common series elastic actuator configurations are introduced and compared. These models are then used to develop controllers for force and position tracking based on combinations of PID, model-based, and disturbance observer control structures. Finally, our actuator's performance is demonstrated through a series of experiments designed to operate the actuator at the limits of its mechanical and control capability.
332 citations
TL;DR: The medical motivation for an endonasal surgical robot featuring concentric tube manipulators is provided, and the model-based design and teleoperation methods, as well as a complete system incorporating image guidance are described.
Abstract: Mechanics-based models of concentric tube continuum robots have recently achieved a level of sophistication that makes it possible to begin to apply these robots to a variety of real-world clinical scenarios. Endonasal skull base surgery is one such application, where their small diameter and tentacle-like dexterity are particularly advantageous. In this paper, we provide the medical motivation for an endonasal surgical robot featuring concentric tube manipulators, and describe our model-based design and teleoperation methods, as well as a complete system incorporating image guidance. Experimental demonstrations using a laparoscopic training task, a cadaver reachability study, and a phantom tumor resection experiment illustrate that both novice and expert users can effectively teleoperate the system, and that skull base surgeons can use the robot to achieve their objectives in a realistic surgical scenario.
252 citations
TL;DR: In this article, an adaptive position control for a pump-controlled electrohydraulic actuator (EHA) based on an adaptive backstepping control scheme is presented, which combines a modified back-stepping algorithm with a special adaptation law to compensate all nonlinearities and uncertainties in EHA system.
Abstract: This paper presents an adaptive position control for a pump- controlled electrohydraulic actuator (EHA) based on an adaptive backstepping control scheme. The core feature of this paper is the combination of a modified backstepping algorithm with a special adaptation law to compensate all nonlinearities and uncertainties in EHA system. First of all, the mathematical model of the EHA is developed. The position control is then formulated using a modified backstepping technique and the uncertainties in hydraulic system are adapted by employing a special Lyapunov function. The control signal consists of an adaptive control signal to compensate the uncertainties and a simple robust structure to ensure the robustness corresponding to a bounded disturbance. Experimental results proved strongly the ability of the proposed control method.
246 citations
TL;DR: In this article, an adaptive impedance control is proposed for a robot collaborating with a human partner, in the presence of unknown motion intention of the human partner and unknown robot dynamics, which makes the robot follow a given target impedance model.
Abstract: In this paper, adaptive impedance control is proposed for a robot collaborating with a human partner, in the presence of unknown motion intention of the human partner and unknown robot dynamics. Human motion intention is defined as the desired trajectory in the limb model of the human partner, which is extremely difficult to obtain considering the nonlinear and time-varying property of the limb model. Neural networks are employed to cope with this problem, based on which an online estimation method is developed. The estimated motion intention is integrated into the developed adaptive impedance control, which makes the robot follow a given target impedance model. Under the proposed method, the robot is able to actively collaborate with its human partner, which is verified through experiment studies.
235 citations
TL;DR: In this article, a flexible nitinol needle with 12 fiber bragg grating (FBG) sensors was used to estimate axial strain and reconstruct the 3D needle shape from the curvature.
Abstract: We present a prototype of a flexible nitinol needle (φ 1.0 mm and length 172 mm) integrated with an array of 12 Fiber Bragg Grating (FBG) sensors. These sensors measure the axial strain, which enables the computation of the needle curvature. We reconstruct the three-dimensional (3-D) needle shape from the curvature. Experiments are performed where the needle is deflected in free space. The maximum errors between the experiments and beam theory-based model are 0.20 mm (in-plane deflection with single bend), 0.51 mm (in-plane deflection with double bend), and 1.66 mm (out-of-plane). We also describe kinematics-based and mechanics-based models for predicting the 3-D needle shape during insertion into soft tissue. We perform experiments where the needle is inserted into a soft-tissue simulant, and the 3-D needle shape is reconstructed using the FBG sensors. We compare the reconstructed needle shape to deflection obtained from camera images and our models. The maximum error between the experiments and the camera images is 0.74 mm. The maximum errors between the kinematics-based and mechanics-based models and the camera images are 3.77 mm and 2.20 mm, respectively. This study demonstrates that deflection models and needles integrated with FBG sensors have the potential to be used in combination with clinical imaging modalities in order to enable accurate needle steering.
226 citations
TL;DR: In this paper, a novel adaptive wearable ankle robot for the treatments of ankle sprain through physical rehabilitation is presented, which employs lightweight but powerful pneumatic muscle actuators which mimics skeletal muscles in actuation.
Abstract: This paper presents the development of a novel adaptive wearable ankle robot for the treatments of ankle sprain through physical rehabilitation. The ankle robot has a bioinspired design, devised after a careful study of the improvement opportunities in the existing ankle robots. Robot design is adaptable to subjects of varying physiological abilities and age groups. Ankle robot employs lightweight but powerful pneumatic muscle actuators (PMA) which mimics skeletal muscles in actuation. To address nonlinear characteristics of PMA, a fuzzy-based disturbance observer (FBDO) has been developed. Another instance of an adaptive fuzzy logic controller based on Mamdani inference has been developed and appended with the FBDO to compensate for the transient nature of the PMA. With the proposed control scheme, it is possible to simultaneously control four parallel actuators of the ankle robot and achieve three rotational degrees of freedom. To evaluate the robot design, the disturbance observer, and the adaptive fuzzy logic controller, experiments were performed. The ankle robot was used by a neurologically intact subject. The robot-human interaction was kept as active-passive while the robot was operated on predefined trajectories commonly adopted by the therapists. Trajectory tracking results are reported in the presence of an unpredicted human user intervention, use of compliant and nonlinear actuators, and parallel kinematic structure of the ankle robot.
176 citations
TL;DR: In this article, a novel four-leg/four-wheel transformable mobile robot, Quattroped, is implemented with a unique transformation mechanism that directly switches the morphology of the driving mechanism between the wheels and 2 degrees of freedom leg (i.e., a full circle) so that the same system of actuation power can be efficiently utilized in both wheel and legged modes.
Abstract: This paper reports on the design, integration, and performance evaluation of a novel four-leg/four-wheel transformable mobile robot, Quattroped. In contrast to most hybrid platforms that have separate mechanisms and actuators for wheels and legs, this robot is implemented with a unique transformation mechanism that directly switches the morphology of the driving mechanism between the wheels (i.e., a full circle) and 2 degrees of freedom leg (i.e., combining two half circles as a leg), so that the same system of actuation power can be efficiently utilized in both wheeled and legged modes. The design process, mechatronics, software infrastructure, behavioral development, and leg-wheel dynamic characteristics are described. The performance of the robot is evaluated in various scenarios, including driving and turning in wheeled mode, driving, step and bar crossing, irregular terrain passing, and stair climbing in legged mode. Taking advantage of the leg-wheel combination on a single platform, the comparison of the wheeled and legged locomotion is also discussed.
162 citations
TL;DR: The actuator with adjustable stiffness (AwAS-II) as discussed by the authors is an enhanced version of the original realization AwAS, which can change the stiffness in a much broader range even by using softer springs and shorter lever arm.
Abstract: This paper presents the actuator with adjustable stiffness (AwAS-II), an enhanced version of the original realization AwAS. This new variable stiffness actuator significantly differs from its predecessor on the mechanism used for the stiffness regulation. While AwAS tunes the stiffness by regulating the position of the compliant elements along the lever arm, AwAS-II changes the position of the lever's pivot point. As a result of the new principle, AwAS-II can change the stiffness in a much broader range (from zero to infinity) even by using softer springs and shorter lever arm, compared to AwAS. This makes the setup of AwAS-II more compact and lighter and improves the stiffness regulation response. To evaluate the aptitude of the fast stiffness adjustment, experiments on reproducing the stiffness profile of the human ankle during the stance phase of a normal walking gait are conducted. Results indicate that AwAS-II is capable of reproducing an interpolated stiffness profile of the ankle while providing a net positive work and thus a sufficient amount of energy as required for the toe-off.
149 citations
TL;DR: In this paper, a tubular linear electromagnetic transducers (LET) for large-scale vibration energy harvesting from vehicle suspensions, tall buildings, or long-span bridges is presented.
Abstract: This paper presents the design and optimization of tubular linear electromagnetic transducers (LETs) for the applications of large-scale vibration energy harvesting from vehicle suspensions, tall buildings, or long-span bridges. The LETs are composed of magnet and coil assemblies, which convert the vibration energy into electricity when moving relatively with each other. The parameters of the LETs, such as the thickness of the magnets in the axial direction and the thickness of the coils in the radial direction, are optimized using finite-element method to achieve high power density and damping density. Four LETs with different configurations namely, single-layer axial magnets and steel spacers, double-layer axial magnets and steel spacers, single-layer axial and radial magnets, double-layer axial and radial magnets are investigated for further improvement. It is found that the parameter optimization can increase the power density [W/m 3] of LETs to 3.8 times compared with the initial design by Zuo and coworkers, and the double-layer configuration with both radial and axial magnets can improve the power density up to 5.6 times, approaching to the energy dissipation rate of traditional oil dampers. A prototype using off-shelf axial NdFeB magnet is built and tested on a vibration shaker. The experiment results show that the prototype of 63.5 mm ( 2.5'') outer diameter and 305 mm (12 in) compressed length can harvest 2.8 W power at 0.11 m/s relative velocity and provide a damping coefficient of 940 N·s/m. It is estimated that average 26-33 W electrical power and 1680-2142 N·s/m damping coefficient can be achieved at 0.25 m/s root-mean-square velocity for different LETs of 3'' outer diameter and 12'' compressed length.
144 citations
TL;DR: In this article, a robust adaptive feedback linearizing dynamic controller (RAFLDC) is proposed to control the system using estimated upper-bounds of uncertainties, and the stability of the control algorithm is verified using the Lyapunov method.
Abstract: A tractor-trailer wheeled robot (TTWR) is a kind of modular robotic system that consists of a tractor template attached with a single or multiple trailers, and hence it is a nonlinear and underactuated system subjected to nonholonomic constraints. Tracking control of such a complicated system is a challenging problem, and that is the focus of this paper. To this end, first dynamics model of a TTWR is developed. Next, feasible reference trajectories are generated to define a trajectory tracking problem. Then, a Lyapunov kinematic control law is elaborated to stabilize tracking errors. Subsequently, a feedback linearizing dynamic controller (FLDC) is designed to generate actuator torques. In a wheeled mobile robot (WMR), like most of real engineering applications, it is impossible to obtain an exact dynamics model due to various unknown, or unpredictable and irregular features. Therefore, the robustness of controllers to overcome uncertainties and external disturbances is necessary. So, a robust adaptive feedback linearizing dynamic controller (RAFLDC) is proposed to control the system using estimated upper-bounds of uncertainties. The stability of the control algorithm is verified using the Lyapunov method. Robustness and effectiveness of the proposed controller, and comparison of results for RAFLDC and FLDC algorithms, is investigated using both simulation studies and experimental implementations, and obtained results will be discussed.
TL;DR: This work considers the problem of source seeking using a group of mobile robots equipped with sensors for source concentration measurement, and presents two control algorithms with all-to-all and limited communications, respectively.
Abstract: We consider the problem of source seeking using a group of mobile robots equipped with sensors for source concentration measurement. In the formulation, the robot team cooperatively estimates the gradient of the source field, moves to the source by tracing the gradient-ascending direction, and keeps a predefined formation in movement. We present two control algorithms with all-to-all and limited communications, respectively. For the case of all-to-all communication, rigorous analytic analysis proves that the formation center of the robots converges to the source in the presence of estimation errors with a bounded error, the upper bound of which is explicitly given. In the case of limited communication where centralized quantities are not available, distributed consensus filters are used to distributively estimate the centralized quantities, and then embedded in the distributed control laws. Numerical simulations are given to validate the effectiveness of the proposed approaches. Experimental results on the E-puck robot platform demonstrate satisfactory performances in a light source seeking application.
TL;DR: In this article, a new optimal motion planning aiming to minimize the energy consumption of a wheeled mobile robot in robot applications is presented. But this method is not suitable for wheeled vehicles.
Abstract: This paper presents a new optimal motion planning aiming to minimize the energy consumption of a wheeled mobile robot in robot applications. A model that can be used to formulate the energy consumption for kinetic energy transformation and for overcoming traction resistance is developed first. This model will provide a base for minimizing the robot energy consumption through a proper motion planning. To design the robot path, the A* algorithm is employed to generate an energy-efficient path where a new energy-related criterion is utilized in the cost function. To achieve a smooth trajectory along the generated path, the appropriate arrival time and velocity at the defined waypoints are selected for minimum energy consumption. Simulations and experiments are performed to demonstrate the energy-saving efficiency of the proposed motion planning approach.
TL;DR: In this article, the Hilbert-Huang transform of vibration data and power spectral density of current and acoustic signals are used as the features in a hierarchical classifier to distinguish a faulty motor from a healthy motor.
Abstract: This paper presents a stand-alone multisensor wireless system for continuous condition monitoring of induction motors. The proposed wireless system provides a low-cost alternative to expensive condition monitoring technology available through dedicated current signature analysis or vibration monitoring equipment. The system employs multiple sensors (acoustic, vibration, and current) mounted on a common wireless platform. The faults of interest are static and dynamic air-gap eccentricity, bearing damage, and their combinations. The Hilbert-Huang transform of vibration data and power spectral density of current and acoustic signals are used as the features in a hierarchical classifier. The proposed wireless system can distinguish a faulty motor from a healthy motor with a probability of 99.9% of correct detection and less than 0.1% likelihood of false alarm. It can also discriminate between different fault categories and severity with an average accuracy of 95%.
TL;DR: In this paper, the rotational variable stiffness actuator vsaUT-II is presented, which is characterized by the property that the apparent stiffness at the actuator output can be varied independently from its position.
Abstract: In this paper, the rotational variable stiffness actuator vsaUT-II is presented. This actuation system is characterized by the property that the apparent stiffness at the actuator output can be varied independently from its position. This behavior is realized by implementing a variable transmission ratio between the internal elastic elements and the actuator output, i.e., a lever arm with variable pivot point position. The pivot point is moved by a planetary gears mechanism, which acquires a straight motion from only rotations, thereby providing a low-friction transmission. The working principle details of the vsaUT-II are elaborated and the design is presented. The actuator dynamics are described by means of a lumped parameter model. The relevant parameters of the actuator are estimated and identified in the physical setup and measurements are used to validate both the design and the derived model.
TL;DR: This paper presents the design and development of the CAFE, a three-degree-of-freedom robotic exoskeleton for the index finger, with performance testing results.
Abstract: Finger impairment following stroke results in significant deficits in hand manipulation and the performance of everyday tasks. While recent advances in rehabilitation robotics have shown promise for facilitating functional improvement, it remains unclear how best to employ these devices to maximize benefits. Current devices for the hand, however, lack the capacity to fully explore the space of possible training paradigms. Particularly, they cannot provide the independent joint control and levels of velocity and torque required. To fill this need, we have developed a prototype for one digit, the cable actuated finger exoskeleton (CAFE), a three-degree-of-freedom robotic exoskeleton for the index finger. This paper presents the design and development of the CAFE, with performance testing results.
TL;DR: In this paper, a quaternion-based complementary observer (CO) was designed for rigid body attitude estimation without resorting to GPS data, which is an alternative one to overcome the limitations of the extended Kalman filter.
Abstract: This paper presents a viable quaternion-based complementary observer (CO) that is designed for rigid body attitude estimation. We claim that this approach is an alternative one to overcome the limitations of the extended Kalman filter. The CO processes data from a small inertial/magnetic sensor module containing triaxial angular rate sensors, accelerometers, and magnetometers, without resorting to GPS data. The proposed algorithm incorporates a motion kinematic model and adopts a two-layer filter architecture. In the latter, the Levenberg Marquardt algorithm preprocesses acceleration and local magnetic field measurements, to produce what will be called the system's output. The system's output together with the angular rate measurements will become measurement signals for the CO. In this way, the overall CO design is greatly simplified. The efficiency of the CO is experimentally investigated through an industrial robot and a commercial IMU during human segment motion exercises. These results are promising for human motion applications, in particular future ambulatory monitoring.
TL;DR: In this article, the authors present the mechanical design, computational optimization, and experimentation of a decoupled 2-DOF monolithic mechanism, where statically indeterminate leaf parallelograms provide the decoupling effect, and the displacement of the piezoelectric actuator (PEA) is amplified with a statically unknown lever mechanism.
Abstract: This paper presents the mechanical design, computational optimization, and experimentation of a decoupled 2-DOF monolithic mechanism. In the mechanical design, statically indeterminate leaf parallelograms provide the decoupling effect, and the displacement of the piezoelectric actuator (PEA) is amplified with a statically indeterminate lever mechanism. In a piezo-driven mechanism, the contact interface between the PEA and the mechanism is a major cause of the discrepancies between the estimated and measured characteristics. However, no explicit and reliable model is available to estimate the contact stiffness. In this paper, a computational optimization based on the response surface methodology is performed and the influence of the contact interface is taken into consideration by adding adequate safety margin to the design objectives. Ultimately, a prototype is manufactured and experimentally investigated for its characteristics and performances. Experimental results show that the developed mechanism has a workspace range in excess of 82 μm × 82 μm with a first natural frequency of 423 Hz (with a 53.4-g load mass). The cross-axis coupling ratio is experimentally measured to be below 1%, indicating excellent decoupling performances.
TL;DR: In this article, three different real-time EECA schemes, namely adaptive EECA (A-EECA), KKT-based, and rule-based EECA, are proposed and compared for longitudinal speed tracking control of an electric ground vehicle (EGV) with two pairs of in-wheel motors.
Abstract: The energy-efficient control allocation (EECA) scheme was previously proposed to distribute control efforts for overactuated systems by explicitly incorporating efficiency functions and working modes of redundant actuators. In this paper, three different real-time EECA schemes, namely adaptive EECA (A-EECA), KKT-based, and rule-based EECA, are proposed and compared for longitudinal speed tracking control of an electric ground vehicle (EGV) with two pairs of in-wheel motors. Two additional power resistor packs inserted in the dc circuits are applied to modify the operating efficiencies of two rear in-wheel motors, which are calibrated for experimental validations of the three EECA designs on a prototype EGV. In terms of the vehicle speed tracking performances, actuator dynamic responses, and total energy consumptions, both simulation and experimental results are evaluated and compared for the three distinct EECA methods. For the same EGV speed tracking effects, both simulation and experimental results indicate different power consumption savings are achieved by three EECA designs with different dynamic responses.
TL;DR: In this article, a cascade structure is used with an inverse kinematics block to generate the velocity references given to the predictive controller, allowing the use of efficient algorithms for linear MPC with constraints.
Abstract: This paper presents and discusses the implementation results of a model-predictive control (MPC) scheme with friction compensation applied to trajectory following of an omnidirectional three-wheeled robot. A cascade structure is used with an inverse kinematics block to generate the velocity references given to the predictive controller. Part of the control effort is used to compensate for the effects of static friction, allowing the use of efficient algorithms for linear MPC with constraints. Experimental results show that the proposed strategy is efficient in compensating for frictional effects as well as for tracking predefined trajectories.
TL;DR: In this paper, a new motion control method based on robust lateral tire force control (LTFC) is presented to improve vehicle stability or maneuverability during cornering, vehicle motion is totally governed by lateral forces acting on tires.
Abstract: This paper presents a new motion control method based on robust lateral tire force control (LTFC) to improve vehicle stability or maneuverability During cornering, vehicle motion is totally governed by lateral forces acting on tires Thus, the real-time information on tire forces provides advantages in vehicle motion control Since the lateral tire force measurements are available by using multisensing hub (MSHub) units which were invented by NSK Ltd, the direct LTFC is realizable via active front steering In control design, a robust control method, eg, two degree-of-freedom control (2-DOF) with a disturbance observer, is used for improving the reference tracking performance Moreover, the stability of the proposed control system is discussed by using small gain theorem The proposed motion controller is implemented on an experimental in-wheel-motor-driven electric vehicle and its performance and effectiveness are verified by field tests Finally, practical applications of lateral tire force sensors to vehicle motion control systems are discussed
TL;DR: The proposed framework integrating the state-of-the-art sensor technology with the developed algorithms provides researchers a versatile and adaptable platform for human hand motion analysis and has potential applications especially in robotic hand or prosthetic hand control and human-computer interaction.
Abstract: In order to study and analyze human hand motions that contain multimodal information, a generalized framework integrating multiple sensors is proposed and consists of modules of sensor integration, signal preprocessing, correlation study of sensory information, and motion identification. Three types of sensors are integrated to simultaneously capture the finger angle trajectories, the hand contact forces, and the forearm electromyography (EMG) signals. To facilitate the rapid acquisition of human hand tasks, methods to automatically synchronize and segment manipulation primitives are developed in the signal preprocessing module. Correlations of the sensory information are studied by using Empirical Copula and demonstrate that there exist significant relationships between muscle signals and finger trajectories and between muscle signals and contact forces. In addition, recognizing different hand grasps and manipulations based on the EMG signals is investigated by using Fuzzy Gaussian Mixture Models (FGMMs) and results of comparative experiments show FGMMs outperform Gaussian Mixture Models and support vector machine with a higher recognition rate. The proposed framework integrating the state-of-the-art sensor technology with the developed algorithms provides researchers a versatile and adaptable platform for human hand motion analysis and has potential applications especially in robotic hand or prosthetic hand control and human-computer interaction.
TL;DR: In this paper, the performance of fuzzy and PID controller-based BLDC servomotor drives is investigated under different operating conditions such as change in reference speed, parameter variations, load disturbance, etc.
Abstract: This paper presents design and digital implementation of a fuzzy controller for achieving improved performance of Brushless dc (BLDC) servomotor drive. The performance of fuzzy and PID controller-based BLDC servomotor drives is investigated under different operating conditions such as change in reference speed, parameter variations, load disturbance, etc. BLDC servomotors are used in aerospace, instrumentation systems, space vehicles, electric vehicles, robotics, and industrial control applications. In such applications, conventional controllers like P, PI, and PID are being used with the BLDC servomotor drive control systems to achieve satisfactory transient and steady-state responses. However, the major problem associated with the conventional PID controller is that the tuned gain parameters obtained for such BLDC servomotor drive control systems do not yield better transient and steady-state responses under different operating conditions such as parameter variations, load disturbances, etc. In this paper, design and implementation of fuzzy controller is presented and its performance is compared with PID controller to show its capability to track the error and usefulness of fuzzy controller in control applications.
TL;DR: In this paper, an improved mathematical model of a twisted string transmission system is presented, which has been validated experimentally and provided a better match with the practical data in comparison with the conventional model.
Abstract: This paper presents an improved mathematical model of a twisted string transmission system. The proposed mathematical model has been validated experimentally and provided a better match with the practical data in comparison with the conventional model. Translational transmission systems based on twisted strings coupled with electric motors can compose light-weight, compact, and mechanically simple actuators that can be used in various robotic applications. An extensive experimental study on the performance of different types of strings during twisting is presented. The drawbacks and advantages of each type of strings, along with some of their properties, are discussed.
TL;DR: The development of an MRI-Safe robot for direct (interventional) MRI-guided endorectal prostate biopsy is reported, and a comprehensive set of preclinical tests for MRI compatibility and needle targeting accuracy are presented.
Abstract: This paper reports the development of an MRI-Safe robot for direct (interventional) MRI-guided endorectal prostate biopsy. The robot is constructed of nonmagnetic and electrically nonconductive materials, and is electricity free, using pneumatic actuation and optical sensors. Targeting biopsy lesions of MRI abnormality presents substantial clinical potential for the management of prostate cancer. This paper describes MRI-Safe requirements and presents the kinematic architecture, design, and construction of the robot, and a comprehensive set of preclinical tests for MRI compatibility and needle targeting accuracy. The robot has a compact and simple three degree-of-freedom (DoF) structure, two for orienting a needle-guide and one to preset the depth of needle insertion. The actual insertion is performed manually through the guide and up to the preset depth. To reduce the complexity and size of the robot next to the patient, the depth setting DoF is remote. Experimental results show that the robot is safe to use in any MRI environment (MRI-Safe). Comprehensive MRI tests show that the presence and motion of the robot in the MRI scanner cause virtually no image deterioration or signal-to-noise ratio change. Robot's accuracy in bench test, CT-guided in-vitro, MRI-guided in-vitro , and animal tests are 0.37, 1.10, 2.09, and 2.58 mm, respectively. These values are acceptable for clinical use.
TL;DR: In this article, an adaptive fault tolerant attitude controller, based on variable structure control, is proposed to address tracking control problem of spacecraft in the presence of unknown actuator failure, control input saturation and external disturbances.
Abstract: This paper proposes an adaptive fault tolerant attitude controller, based on variable structure control, to address tracking control problem of spacecraft in the presence of unknown actuator failure, control input saturation and external disturbances In contrast to traditional robust fault tolerant attitude controllers, the proposed controller is capable of controlling the transient response of the closed loop system by means of a dedicated parameter Also this method does not require exact knowledge of the actuator faults and is implemented with uncertain value of fault information By adjusting a simple parameter dynamically and using Lyapunov direct method and the properties of quaternion representation, the ultimate boundedness of attitude and angular velocity errors in presence of external disturbances is proven Numerical simulations used to prove the success of proposed controller in achieving high attitude performance in the presence of external disturbances, inexact knowledge of fault information, actuator failures and control input saturation
TL;DR: A camera-based assistive text reading framework to help blind persons read text labels and product packaging from hand-held objects in their daily lives and a novel text localization algorithm by learning gradient features of stroke orientations and distributions of edge pixels in an Adaboost model.
Abstract: We propose a camera-based assistive text reading framework to help blind persons read text labels and product packaging from hand-held objects in their daily lives. To isolate the object from cluttered backgrounds or other surrounding objects in the camera view, we first propose an efficient and effective motion-based method to define a region of interest (ROI) in the video by asking the user to shake the object. This method extracts moving object region by a mixture-of-Gaussians-based background subtraction method. In the extracted ROI, text localization and recognition are conducted to acquire text information. To automatically localize the text regions from the object ROI, we propose a novel text localization algorithm by learning gradient features of stroke orientations and distributions of edge pixels in an Adaboost model. Text characters in the localized text regions are then binarized and recognized by off-the-shelf optical character recognition software. The recognized text codes are output to blind users in speech. Performance of the proposed text localization algorithm is quantitatively evaluated on ICDAR-2003 and ICDAR-2011 Robust Reading Datasets. Experimental results demonstrate that our algorithm achieves the state of the arts. The proof-of-concept prototype is also evaluated on a dataset collected using ten blind persons to evaluate the effectiveness of the system's hardware. We explore user interface issues and assess robustness of the algorithm in extracting and reading text from different objects with complex backgrounds.
TL;DR: In this paper, a PID-based sliding mode observer (PIDSMO) is proposed to relax the observer matching condition as required in the use of unknown-input observers, which can accurately estimate the PEA states and achieve better tracking control performance compared to the PIDSMC with α-β filter control scheme.
Abstract: Tracking control of piezoelectric actuators (PEAs) has stimulated the development of various advanced control schemes that utilize the feedback of PEA system states for improved control performance. Among them, the one based on the concept of sliding mode has been shown promising due to its robustness to matched uncertainties, but leaving the required state estimation to be desired. Previous studies show that the PEA can be modeled as a linear dynamic system with matched uncertainties. On this basis, this paper presents the development of a novel observer based on the concept of proportional-integral-derivative-based (PID-based) sliding mode, in which the switching function is replaced by a PID regulator. The novel observer, referred to as the PID-based sliding mode observer (PIDSMO), relaxes the observer matching condition as required in the use of the unknown-input observers. The PIDSMO is then integrated with the PID-based sliding mode controller (PIDSMC) to form a novel integrated PID-based sliding mode observer-controller (PIDSMOC) for PEA tracking control. Experiments performed on a PEA showed that the PIDSMO can accurately estimate the PEA states and that the integrated PIDSMOC can achieve better tracking control performances as compared to the PIDSMC with α-β filter control scheme.
TL;DR: In this article, the compensator is designed as a regeneration device consisting of a hydraulic motor and an electric generator, where hydraulic energy can be regenerated and pressure compensation function is realized by adapting the electromagnetic torque of the generator to the load as well.
Abstract: Mobile hydraulic systems are developed toward better control performance and higher energy efficiency. Pressure compensators, which govern the pressure drops over the control orifices, are widely used in multiactuator systems to improve their operability. However, additional energy is also dissipated in the compensators especially under the overrunning load conditions. This paper presents a novel energy-saving system, where the compensator is designed as a regeneration device consisting of a hydraulic motor and an electric generator. Then, hydraulic energy can be regenerated and pressure compensation function is realized by adapting the electromagnetic torque of the generator to the load as well. The close-loop control of the generator is designed by effective pressure drop estimation. The proposed energy-saving system and controller are implemented on an experimental platform of hybrid excavators which is equipped with an electric energy storage device. The experimental results show both good control performance and significant energy-saving effect.
TL;DR: In this article, the authors proposed a new mechanism for targeted drug release based on active locomotion, which is a magnetic torque control based on a rotating magnetic field using a three-axis Helmholtz coil system.
Abstract: In this paper, we propose a new mechanism for targeted drug release based on active locomotion. The manipulating method is a magnetic torque control based on a rotating magnetic field using a three-axis Helmholtz coil system. The applied magnetic field creates two rolling (radial and longitudinal directions) and a rotating motion for active locomotion according to variations in the working space and robot posture. Two spiral components in the robot mechanism and the rotating motion completely conduct and control the drug release. Magnetic attractive force between the two spiral components prevents drug leakage during the movement for targeting. When the robot arrives at the destination, the robot switches the direction of the thrust force of the two spiral components to separate the robot body for the drug release. The thrust force for the drug release is higher than the magnetic attractive force. We verified the rapid active locomotion and targeted drug release using precise control through various experiments. In our assessment, the proposed robot mechanism can realize the role of a functional medical robot for therapy and diagnosis.