Category: Publications

A compliant modular robotic hand with fabric force sensor for multiple versatile grasping modes

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Abstract

This paper presents the development of a compliant, modular, reconfigurable, and sensorized robotic hand with multiple grasping capabilities. Each finger consists of a soft pneumatic actuator with embedded fabric force sensor and a detachable casing. The casing has a through hole for housing the actuator and special connectors for attachment to other casings. One casing each from the thumb and finger parts has a protrusion for connecting both parts together via a screw tightening system. The through-hole design allows different grasping length to be achieved and the inflated pneumatic channel of the actuator locks it in place. The modular robotic hand is capable of various versatile grasping tasks by simply changing the bending direction of the actuator, the distance between the thumb and finger parts, the grasping length of the actuator, or attaching/detaching additional fingers to the hand. (1) Hook grasping with single finger, (2) pinching with pad opposition, (3) reverse grasping for holding a pipe-like object, (4) wrap grasping with palm opposition, as well as (5) picking up an object through its handle with one thumb and two or more fingers were illustrated. These studies show the capability of the compliant modular robotic hand in performing various types of grasping by simply using different configurations of the casings. The excellent payload-to-weight ratio of the robotic hand was demonstrated. Also, the fabric force sensor that was embedded in the soft actuator indicated the difference in grasping forces that were applied to different objects during hook grasping. The modular robotic hand has the potential to broaden or substitute the usage of existing robotic hands, especially in applications where soft versatile configurable grasping is desired.

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Human-Compliant Body-Attached Soft Robots Towards Automatic Cooperative Ultrasound Imaging

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Ultrasound imaging procedures are deemed as one of the most convenient and least invasive medical diagnostic imaging modalities and have been widely utilized in health care providers, which are expecting semiautomatic or fully-automatic imaging systems to reduce the current clinical workloads. This paper presents a portable and wearable soft robotic system which has been designed with the purpose of replacing the manual operation to cooperatively steer the ultrasound probe. This human-compliant soft robotic system, which is equipped with four separated parallel soft pneumatic actuators and is able to achieve movements in three directions. Vacuum suction force is introduced to attach the robot onto the intended body location. The design and fabrication of this soft robotic system are illustrated. To our knowledge, this is the first body-attached soft robot for compliant ultrasound imaging. The feasibility of the system is demonstrated through proof-of-concept experiments.

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Simultaneous Temperature Compensation and Synchronous Error Elimination for Axial Displacement Sensors Using an Auxiliary Probe

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The output stability of the displacement sensors is an important issue for safe operations in magnetic bearing supported high-speed rotor system. This paper proposes an effective postprocessing solution to the problems of temperature drift and synchronous measuring error for the axial displacement sensor in a 10-kW magnetically suspended motor. The proposed configuration of the axial displacement sensor consists of three probes: one pair is used to eliminate the synchronous measuring error, and the third probe is employed for the consideration of temperature drift. First, the generating mechanism of the synchronous measuring error caused by the improper assemble is presented, and an operational amplifier is proposed to obtain an accurate position of the axial center by adjusting the weights of sensing signals from one pair of probes. Then the scheme of temperature compensation using an auxiliary probe is presented. In order to obtain accurately the characteristics of temperature drift at the operating point, the detailed procedure is given to determine the temperature-drift ratio. Finally, the terms related to temperature drift and synchronous error in the final output of the displacement sensor are both eliminated. Experimental results on a magnetically suspended motor test rig show the effectiveness of the proposed solution.

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Development of a compact continuum tubular robotic system for nasopharyngeal biopsy

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Abstract

Traditional posterior nasopharyngeal biopsy using a flexible nasal endoscope has the risks of abrasion and injury to the nasal mucosa and thus causing trauma to the patient. Recently, a new class of robots known as continuum tubular robots (CTRs) provide a novel solution to the challenge with miniaturized size, curvilinear maneuverability, and capability of avoiding collision within the nasal environment. This paper presents a compact CTR which is 35 cm in total length, 10 cm in diameter, 2.15 kg in weight, and easy to be integrated with a robotic arm to perform more complicated operations. Structural design, end-effector design, and workspace analysis are described in detail. In addition, teleoperation of the CTR using a haptic input device is developed for position control in 3D space. Moreover, by integrating the robot with three electromagnetic tracking sensors, a navigation system together with a shape reconstruction algorithm is developed. Comprehensive experiments are conducted to test the functionality of the proposed prototype; experiment results show that under teleoperation, the system has an accuracy of 2.20 mm in following a linear path, an accuracy of 2.01 mm in following a circular path, and a latency time of 0.1 s. It is also found that the proposed shape reconstruction algorithm has a mean error of around 1 mm along the length of the tubes. Besides, the feasibility and effectiveness of the proposed robotic system being applied to posterior nasopharyngeal biopsy are demonstrated by a cadaver experiment. The proposed robotic system holds promise to enhance clinical operation in transnasal procedures.

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Active Balancing Control of AMB-Rotor Systems Using a Phase-Shift Notch Filter Connected in Parallel Mode

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The vibration controllability is an important feature in the applications of active magnetic bearings (AMBs). This paper addresses the two key challenges on the active balancing control of AMB-rotor systems: presenting a parallel-mode scheme to enhance the notch performance at high speeds, and proposing a phase-shift notch filter to ensure stable operations over the entire speed ranges. First, both the frequency characteristics of the simplified notch filter in series and in parallel mode are discussed. The analysis shows that the closed-loop system with a parallel-mode notch filter has a deeper notch depth and faster convergence. The capacities of the synchronous current elimination are also improved at high speeds. Then, an improved phase-shift notch filter connected in parallel with the controller is modeled and analyzed. In order to understand the sensibility of the proposed solution to phase-shift variations, the stability analysis of the closed-loop system in the entire operational speed range is performed using the frequency response method. Experimental results on a high-speed centrifugal air blower test rig show the effectiveness of the proposed solution.

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Robust Fault-Tolerant Control for a Class of Second-Order Nonlinear Systems Using an Adaptive Third-Order Sliding Mode Control

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Due to the robustness against the uncertainties, conventional sliding mode control (SMC) has been extensively developed for fault-tolerant control (FTC) system. However, the FTCs based on conventional SMC provide several disadvantages such as large transient state error, less robustness, and large chattering , that limit its application for real application. In order to enhance the performance, a novel adaptive third-order SMC, which combines a novel third-order sliding mode surface, a continuous strategy and an adaptation law, is proposed. Compared with other innovation approaches, the proposed controller has an excellent capability to tackle several types of actuator faults with an enhancing on robustness, precision, chattering reduction, and time of convergence. The proposed method is then applied for an attitude control of a spacecraft and the results demonstrate the superior performance. Index Terms—Fault diagnosis, fault-tolerant control (FTC), high-order sliding mode (HOSM) control, nonlinear systems, observer-controller system.
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Fault-Tolerant Inverter for High-Speed Low-Inductance BLDC Drives in Aerospace Applications

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Abstract
Due to the simplicity and high reliability, brushless dc (BLDC) motors are widely used in space application. High-reliability levels are the vital aspect for ensuring the long-term stable operation of the BLDC motor system, which is used in aerospace applications. The fault-tolerant control of the BLDC motor is of great importance for its continuous operating capacity even under the faulty situation. This paper proposes a fault-tolerant topology composed of an additional phase leg and a fault-protective circuit for the high-speed low-inductance BLDC motor. Based on the analysis of the overcurrent and overvoltage phenomenon after the switch faults, a novel fault isolation and system reconfiguration method is presented. The method can achieve safe isolation and reconfiguration to avoid the secondary fault caused by direct switch of the redundant switch and the faulty switch after the fault-diagnosis process. Both simulation and experimental results confirm the feasibility and effectiveness of the proposed method.
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Preliminary development of a soft robotic ultrasound steering system

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Abstract:
Intravascular ultrasound (IVUS) imaging provides
two-dimensional (2D) real-time luminal and transmural
cross-sectional images of intravascular vessels with detailed
pathological information. It has offered significant advantages
in terms of diagnosis and guidance and has been increasingly
introduced from coronary interventions into more generalized
endovascular surgery. However, IVUS itself does not provide
spatial pose information for its generated images, making it
difficult to construct a 3D intravascular visualization. To
address this limitation, IVUS imaging-driven 3D intravascular
reconstruction techniques have been developed. These
techniques enable accuratediagnosis andquantitative
measurements of intravascular diseases to facilitate optimal
treatment determination. Such reconstruction extends the IVUS
imaging modality from pure diagnostic assistance to
intraoperative navigation and guidance and supports both
therapeutic options and interventional operations. This paper
presents a comprehensive survey of technological advances and
recent progress on IVUS imaging-based 3D intravascular
reconstruction and its state-of-the-art applications. Limitations
of existing technologies and prospects of new technologies are
also discussed.
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Self-correction of Commutation Point for High-speed Sensorless BLDC Motor With Low Inductance and Nonideal Back EMF

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This paper presents a novel self-correction method of commutation point for high-speed sensorless brushless dc motors with low inductance and nonideal back electromotive force (EMF) in order to achieve low steady-state loss of magnetically suspended control moment gyro. The commutation point before correction is obtained by detecting the phase of EMF zero-crossing point and then delaying 30 electrical degrees. Since the speed variation is small between adjacent commutation points, the difference of the nonenergized phase’s terminal voltage between the beginning and the end of commutation is mainly related to the commutation error. A novel control method based on model-free adaptive control is proposed, and the delay degree is corrected by the controller in real time. Both the simulation and experimental results show that the proposed correction method can achieve ideal commutation effect within the entire operating speed range
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Motion Planning based on Learning from Demonstration for Multiple-Segment Flexible Robots Actuated by Electroactive Polymers

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Abstract
Multiple-segment flexible and soft robotic arms composed by ionic polymer – metal composite (IPMC) flexible actuators exhibit compliance but suffer from the difficulty of path planning due to their redundant degrees of freedom, although they are promising in complex tasks such as crossing body cavities to grasp objects. We propose a learning from demonstration method to plan the motion paths of IPMC-based manipulators, by statistics machine-learning algorithms. To encode demonstrated trajectories and estimate suitable paths for the manipulators to reproduce the task, models are built based on Gaussian mixture model and Gaussian mixture regression, respectively. The forward and inverse kinematic models of IPMC-based soft robotic arm are derived for the motion control. A flexible and soft robotic manipulator is implemented with six IPMC segments, and it verifies the learned paths by successfully completing a representative task of navigating through a narrow keyhole.
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