Category: Publications

Analysis of Principle and Performance of a New 4DOF Hybrid Magnetic Bearing

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Abstract

To satisfy the requirement of magnetically suspended control moment gyroscope (MSCMG) that magnetic bearing can provide torque, a novel 4DOF hybrid magnetic bearing (HMB) with integrated structure was designed. Mathematical models of forces and torques are established by using equivalent magnetic circuit method. The current stiffness, displacement stiffness, tilting current stiffness and angular stiffness of the 4DOF hybrid magnetic bearing are derived by the mathematical models. Equivalent magnetic circuit method and finite element method (FEM) simulation results indicate that the force has a good linear relationship with both displacement and current, and the torque has a good linear relationship with angular displacement and current. The novel 4DOF HMB is capable of achieving control in both two radial translational degrees of freedom (DOF) and also two radial rotational DOFs. The 4DOF HMB is well adapted to MSCMG system, exhibiting advantages in the controllable DOF, light weight and easy to control.

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Investigation of a Stiffness Varying Mechanism for Flexible Robotic System

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Abstract

With the advent of automation and robotic systems, robotic manipulators are becoming increasingly popular in various industries. This project aims to investigate stiffness varying technology for a class of flexible manipulators with the aim of online changing manipulator stiffness. We propose and develop a stiffness varying mechanism based on Polycaprolactone (PCL), characterize it and test out together with extensive experiments. This mainly involves design improvement, modeling, characterization and hands-on experiments.

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Reduction of Power Consumption for Fluidic Soft Robots Using Energy Recovery Technique

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Power-efficient fluidic driven system is beneficial to extending the working time of autonomous and wearable soft robots supplied by independent power sources such as batteries. In this paper, an energy recovery scheme is proposed to reutilize the pressurized air released by retracting pneumatic soft actuators instead of venting to atmosphere. The scheme’s novelty lies in an air accumulator employed to store the recovered energy and boost the inlet pressure of air pumps when there is requirement. Then the energy-saving principle is described based on the comparison of energy flow between the systems with and without energy recovery. Residual pressure, recoverable energy and parametric effect are also presented analytically according to the ideal gas law. Finally, simulation models are developed to evaluate the system performance and the results show that about 20% reduction of power consumption and acceptable residual pressure can be achieved simultaneously when the accumulator volume is three times of the actuator volume, which provides reference to further prototype development. Index Terms – Soft robotics, fluidic driven system, energy recovery, parameter design, air accumulator.

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Development of a Multi-Channel Concentric Tube Robotic System With Active Vision for Transnasal Nasopharyngeal Carcinoma Procedures

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Abstract

Minimally invasive surgery-based nasopharyngeal cancer treatment is promising, but currently, it is not a common treatment choice because of the absence of suitable tools. In this paper, a multi-channel concentric tube robot is proposed for the treatment of nasopharyngeal cancer based on natural orifice translumenal endoscopic surgery. The proposed system has three channels, i.e. two manipulation channels and one vision channel, and all the three channels are confined by a 10 mm active sheath. The robot is controlled by human-in-the-loop bimanual teleoperation under active endoscopic guidance. The reduced sheath diameter and the steerable vision channel improve the functionality of the system and distinguish our design from the prior art. The feasibility of the system has been evaluated through a series of simulations and experiments. Results show that the proposed system is capable to conduct cooperative tasks in a confined space and the miniaturized manipulator is suitable for transnasal procedures. Besides, comparisons with other types of flexible surgical robots are discussed to further demonstrate the superiority of the proposed system in the target clinical applications.

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A Miniature Soft Robotic Manipulator Based on Novel Fabrication Methods

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Flexible robotic manipulators have been widely used in minimally invasive surgery (MIS) and many other applications requiring closer inspection and operation. Although a variety of manipulators enabled by different mechanism have been developed, few of them can preserve softness, thinness, and decent bending capability simultaneously. In this letter, we present a miniature soft robotic manipulator made of hyper-elastic silicone rubber. Along with the manipulator design, two novel fabrication methods are proposed and elaborated. Detailed characterizations are specified to show the bending capability of the manipulator given different air pressure. Specifically, our manipulator, as thin as 6 mm, is able to achieve 360° directional bending, and, when given pressure over 70 kPa, it can reach 180° bending angle and around 5 mm bending radius easily. Due to its innate compliance and small dimension, this type of robotic manipulator can deliver safe and comfortable interactions with the subjects. More significantly, the novel fabrications in this letter diversify the fabrication methods for soft pneumatic robots and actuators (SPRA) and further scale down their sizes.

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A Magnetically actuated guide-wire steering system towards arteriovenous fistula angioplasty procedures

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Working towards remote steering of distal guide-wire in arteriovenous fistula angioplasty procedures, we develop a magnetically actuated robotic guide-wire manipulation system involving electromagnetic coils and a flexible guide-wire with a magneto-responsive attachment. By varying the coil voltages, we show the controlled deflections of the distal guide-wire. Specifically we are investigating the guidewire actuation mechanism under controlled electromagnetic field, the transfer function of the system, and the steering experiments in a custom phantom. The studied phenomenon has importance for guide-wire placement in minimally invasive cardio-vascular surgeries. A video demonstration is available at: http://bioeng.nus.edu.sg/mm/magnetically-actuated-guide-wire-steering.

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Soft haptics using soft actuator and soft sensor

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In this paper, we presented fabric-based soft tactile actuator and soft sensor. The force characterization result indicates that the actuator is able to produce force up to about 2.20(±0.017)N, when it is supplied with 80kPa of pressurized air. Hence it is capable of producing sufficient amount of force, which surpasses the human’s haptic perception threshold. The thin, sheet nature of the material creates lightweight actuator, which improves the payload-to-weight ratio. The pneumatic-based operation principle creates a safer human-machine interface. Thus, it eliminates possible occurrence of safety issues such as the danger of applying high voltages to user’s skin in case of malfunction. Direct force coupling of the soft actuator with the sensor is established to enable transmission of force information from the sensor to the actuator. The test profile indicates that the actuator is able to produce similar force profile as that of the sensor. This opens up possibility of developing soft tactile sensors and actuators based gloves, which can be paired and applied in virtual-reality based training and rehabilitation programs. Superimposition of multiple soft actuators would create an array that provides shape and size specific haptic feedback.

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FPGA implementation of a FA-1 mechanoreceptor model for efficient representation of tactile features

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Spatiotemporal spike patterns from a population of mechanoreceptors provide a concise representation of tactile stimuli that facilitates rapid sensory processing in the brain. Efficient models of mechanoreceptors are needed for the adoption of spike-based processing for robotic tactile sensing applications. This paper presents a biomimetic model of the fast-adapting type 1 (FA-1) mechanoreceptor, implemented on a field-programmable-gate-array (FPGA). The simplicity of this model enables its realization on large arrays of sensing elements while operating with sub-millisecond temporal precision required to capture deformation patterns. We illustrate this capability by interfacing with a 4096 element tactile sensor array with a 5.2 kHz sampling rate. Through physical experiments, we demonstrate the discrimination of force magnitude and local curvature during transient mechanical contact, using spike patterns obtained from the model. The approach has the potential to deliver responsive full-body tactile sensing in robotic and prosthetic applications.

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Design, kinematics, simulation of omni-directional bending reachability for a parallel structure forceps manipulator

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This paper presents a 5-DOF manipulator which consists of three parts, 1-DOF translational joint, a bendable skeleton (2-DOF for Omni-directional bending motion), and a rotatable forceps gripper (1-DOF for rotation, 1-DOF for opening/closing). The bendable segment in the manipulator achieves two orthogonal bending DOFs by pulling or pushing three parallel universal-joint-based shaft chains. Forward and inverse kinematics of the bendable skeleton is analyzed. The workspace calculation illustrates that the structure of the three parallel shaft chains can reach a bending angle of 90 degree in arbitrarily direction. The reachability of the manipulator is simulated in Adams®. According to the surgical requirements, the manipulator is actuated to draw circle during the tests while the end effector is kept bending at 60 degree. The results show that the end effector can precisely track the planning trajectory (precision within 1 mm).

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Delicate manipulations with compliant mechanism and electrostatic adhesion

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Traditional rigid robotic hand manipulator has been used in many field nowadays due to its advantages of large gripping force and stable performance. However, this kind of rigid manipulator is not suitable for gripping fragile objects since it is motorized and force control can be a problem. It is also not suitable to grip object with different shapes since the manipulator is rigid and not compliant. In this study, a novel manipulator with gripping capability is designed and fabricated. The manipulator combines electrostatic adhesion actuation with soft manipulators. The manipulator has high flexibility and can be compliant to different shapes due to the property of the materials. It is very promising to do delicate manipulations in industry field and biomedical field.

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