Imperial College London

Dr Thrishantha Nanayakkara

Faculty of EngineeringDyson School of Design Engineering

Reader in Design Engineering and Robotics
 
 
 
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Contact

 

+44 (0)20 7594 0965t.nanayakkara Website CV

 
 
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Location

 

RCS1 M229Dyson BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
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117 results found

Wegiriya H, Herzig N, Guaman SAA, Sadati H, Nanayakkara Tet al., A stiffness controllable multimodal whisker sensor follicle for texture comparison, IEEE Sensors Journal, Vol: 20, Pages: 2320-2328, ISSN: 1530-437X

Mammals like rats, who live in dark burrows, heav-ily depend on tactile perception obtained through the vibrissalsystem to move through gaps and to discriminate textures. Theorganization of a mammalian whisker follicle contains multiplesensory receptors and glands strategically organized to capturetactile sensory stimuli of different frequencies. In this paper, weused a controllable stiffness soft robotic follicle to test the hy-pothesis that the multimodal sensory receptors together with thecontrollable stiffness tissues in the whisker follicle form a physicalstructure to maximize tactile information. In our design, the ringsinus and ringwulst of a biological follicle are represented by alinear actuator connected to a stiffness controllable mechanismin-between two different frequency-dependent data capturingmodules. In this paper, we show for the first time the effectof the interplay between the stiffness and the speed of whiskingon maximizing a difference metric for texture classification.

Journal article

Sadati SMH, Maiolino P, Iida F, Nanayakkara T, Hauser Het al., 2020, Editorial: Current Advances in Soft Robotics: Best Papers From RoboSoft 2018, FRONTIERS IN ROBOTICS AND AI, Vol: 7, ISSN: 2296-9144

Journal article

He L, Lu Q, Abad S-A, Rojas N, Nanayakkara DPTet al., 2020, Soft fingertips with tactile sensing and active deformation for robust grasping of delicate objects, IEEE Robotics and Automation Letters, Vol: 5, Pages: 2714-2721, ISSN: 2377-3766

Soft fingertips have shown significant adaptability for grasping a wide range of object shapes, thanks to elasticity. This ability can be enhanced to grasp soft, delicate objects by adding touch sensing. However, in these cases, the complete restraint and robustness of the grasps have proved to be challenging, as the exertion of additional forces on the fragile object can result in damage. This letter presents a novel soft fingertip design for delicate objects based on the concept of embedded air cavities, which allow the dual ability of tactile sensing and active shape-changing. The pressurized air cavities act as soft tactile sensors to control gripper position from internal pressure variation; and active fingertip deformation is achieved by applying positive pressure to these cavities, which then enable a delicate object to be kept securely in position, despite externally applied forces, by form closure. We demonstrate this improved grasping capability by comparing the displacement of grasped delicate objects exposed to high-speed motions. Results show that passive soft fingertips fail to restrain fragile objects at accelerations as low as 0.1 m/s 2 , in contrast, with the proposed fingertips delicate objects are completely secure even at accelerations of more than 5 m/s 2 .

Journal article

Sadati H, Shiva A, Herzig N, Rucker C, Hauser H, Walker I, Bergeles C, Althoefer K, Nanayakkara DPTet al., 2020, Stiffness imaging with a continuum appendage: Real-time shape and tip force estimation from base load readings, IEEE Robotics and Automation Letters, Vol: 5, Pages: 2824-2831, ISSN: 2377-3766

In this letter, we propose benefiting from load readings at the base of a continuum appendage for real-time forward integration of Cosserat rod model with application in configuration and tip load estimation. The application of this method is successfully tested for stiffness imaging of a soft tissue, using a 3-DOF hydraulically actuated braided continuum appendage. Multiple probing runs with different actuation pressures are used for mapping the tissue surface shape and directional linear stiffness, as well as detecting non-homogeneous regions, e.g. a hard nodule embedded in a soft silicon tissue phantom. Readings from a 6-axis force sensor at the tip is used for comparison and verification. As a result, the tip force is estimated with 0.016–0.037 N (7–20%) mean error in the probing and 0.02–0.1 N (6–12%) in the indentation direction, 0.17 mm (14%) mean error is achieved in estimating the surface profile, and 3.4–15 [N/m] (10–16%) mean error is observed in evaluating tissue directional stiffness, depending on the appendage actuation. We observed that if the appendage bends against the slider motion (toward the probing direction), it provides better horizontal stiffness estimation and better estimation in the perpendicular direction is achieved when it bends toward the slider motion (against the probing direction). In comparison with a rigid probe, $\approx \!\!10$ times smaller stiffness and $\approx \!\!7$ times larger mean standard deviation values were observed, suggesting the importance of a probe stiffness in estimation the tissue stiffness.

Journal article

Xinyang T, He L, Cao J, Chen W, Nanayakkara DPTet al., 2020, A soft pressure sensor skin for hand and wrist orthoses, IEEE Robotics and Automation Letters, Vol: 5, Pages: 2192-2199, ISSN: 2377-3766

Side effects caused by excessive contact pressure such as discomfort and pressure sores are commonly complained by patients wearing orthoses. These problems leading to low patient compliance decrease the effectiveness of the device. To mitigate side effects, this study describes the design and fabrication of a soft sensor skin with strategically placed 12 sensor units for static contact pressure measurement beneath a hand and wrist orthosis. A Finite Element Model was built to simulate the pressure on the hand of a subject and sensor specifications were obtained from the result to guide the design. By testing the fabricated soft sensor skin on the subject, contact pressure between 0.012 MPa and 0.046 MPa was detected, revealing the maximum pressure at the thumb metacarpophalangeal joint which was the same location of the highest pressure of simulation. In this letter, a new fabrication method combining etching and multi-material additive manufacture was introduced to produce multiple sensor units as a whole. Furthermore, a novel fish-scale structure as the connection among sensors was introduced to stabilize sensor units and reinforce the soft skin. Experimental analysis reported that the sensor signal is repeatable, and the fish-scale structure facilitates baseline resuming of sensor signal during relaxation.

Journal article

Scimeca L, Iida F, Maiolino P, Nanayakkara Tet al., 2020, Human-robot medical interaction, Pages: 660-661

© 2020 ACM. Advances in Soft Robotics, Haptics, AI and simulation have changed the medical robotics field, allowing robotics technologies to be deployed in medical environments. In this context, the relationship between doctors, robotics devices, and patients is fundamental, as only with the synergetic collaboration of the three parties results in medical robotics can be achieved. This workshop focuses on the use of soft robotics technologies, sensing, AI and Simulation, to further improve medical practitioner training, as well as the creation of new tools for diagnosis and healthcare through the medical interaction of humans and robots. The Robo-patient is more specifically the idea behind the creation of sensorised robotic patient with controllable organs to present a given set of physiological conditions. This is both to investigate the embodied nature of haptic interaction in physical examination, as well as the doctor-patient relationship to further improve medical practice through robotics technologies. The Robo-doctor aspect is also relevant, with robotics prototypes performing, or helping to perform, medical diagnosis. In the workshop, key technologies as well as future views in the field will be discussed both by expert and new upcoming researchers.

Conference paper

Sadati H, Naghib E, Shiva A, Michael B, Renson L, Howard M, Rucker C, Althoefer K, Nanayakkara DPT, Zschaler S, Bergeles C, Hauser H, Walker Iet al., TMTDyn: A Matlab package for modeling and control of hybrid rigid–continuum robots based on discretized lumped system and reduced-order models, International Journal of Robotics Research, ISSN: 0278-3649

A reliable, accurate, and yet simple dynamic model is important to analyze, design and control hybrid rigid-continuumrobots. Such models should be fast, as simple as possible and user-friendly to be widely accepted by the ever-growingrobotics research community. In this study, we introduce two new modeling methods for continuum manipulators: ageneral reduced-order model (ROM) and a discretized model with absolute states and Euler-Bernoulli beam segments(EBA). Additionally, a new formulation is presented for a recently introduced discretized model based on EulerBernoulli beam segments and relative states (EBR). We implement these models to a Matlab software package,named TMT Dyn, to develop a modeling tool for hybrid rigid-continuum systems. The package features a new Highlevel Language (HLL) text-based interface, a CAD-file import module, automatic formation of the system EOM fordifferent modeling and control tasks, implementing Matlab C-mex functionality for improved performance, and modulesfor static and linear modal analysis of a hybrid system. The underlying theory and software package are validated formodeling experimental results for (i) dynamics of a STIFF-FLOP continuum appendage, and (ii) general deformationof a fabric sleeve worn by a rigid link pendulum. A comparison shows higher simulation accuracy (8-14% normalizederror) and numerical robustness of the ROM model, and computational efficiency of the EBA model with near real-timeperformances that makes it suitable for large systems. The challenges and necessary modules to further automate thedesign and analysis of hybrid systems with a large number of states are briefly discussed in the end.

Journal article

Abad S-A, Herzig N, Sadati SMH, Nanayakkara DPTet al., 2019, Significance of the Compliance of the Joints on the Dynamic Slip Resistance of a Bioinspired Hoof, IEEE Transactions on Robotics, Vol: 35, Pages: 1450-1463, ISSN: 1552-3098

Robust mechanisms for slip resistance are an open challenge in legged locomotion. Animals such as goats show impressive ability to resist slippage on cliffs. It is not fully known what attributes in their body determine this ability. Studying the slip resistance dynamics of the goat may offer insight towards the biologically-inspired design of robotic hooves. This paper tests how the embodiment of the hoof contributes to solving the problem of slip resistance. We ran numerical simulations and experiments using a passive robotic goat hoof for different compliance levels of its 3 joints. We established that compliant yaw and pitch and stiff roll can increase the energy required to slide the hoof by ≈ 20% compared to the baseline (stiff hoof). Compliant roll and pitch allow the robotic hoof to adapt to the irregularities of the terrain. This produces an Anti-Lock Braking System-like behavior of the robotic hoof for slip resistance. Therefore, the pastern and coffin joints have a substantial effect on the slip resistance of the robotic hoof while the fetlock joint has the lowest contribution. These shed insights into how robotic hooves can be used to autonomously improve slip resistance.

Journal article

Nanayakkara V, Sornkaran N, Wegiriya H, Vitzilaios N, Venetsanos D, Rojas N, Sahinkaya MN, Nanayakkara Tet al., 2019, A method to estimate the oblique arch folding axis for thumb assistive devices, 20th Towards Autonomous Robotic Systems Conference, Publisher: Springer Verlag, Pages: 28-40, ISSN: 0302-9743

People who use the thumb in repetitive manipulation tasks are likelyto develop thumb related impairments from excessive loading at the base jointsof the thumb. Biologically informed wearable robotic assistive mechanisms canprovide viable solutions to prevent occurring such injuries. This paper tests thehypothesis that an external assistive force at the metacarpophalangeal joint willbe most effective when applied perpendicular to the palm folding axis in termsof maximizing the contribution at the thumb-tip as well as minimizing the pro-jections on the vulnerable base joints of the thumb. Experiments conducted usinghuman subjects validated the predictions made by a simplified kinematic modelof the thumb that includes a foldable palm, showing that: 1) the palm folding an-gle varies from 71.5◦to 75.3◦(from the radial axis in the coronal plane) for thefour thumb-finger pairs and 2) the most effective assistive force direction (fromthe ulnar axis in the coronal plane) at the MCP joint is in the range 0◦<ψ<30◦for the four thumb-finger pairs. These findings provide design guidelines for handassistive mechanisms to maximize the efficacy of thumb external assistance.

Conference paper

Akhond S, Herzig N, Wegiriya H, Nanayakkara DPTet al., 2019, A method to guide local physical adaptations in a robot based on phase portraits, IEEE Access, Vol: 7, Pages: 1-13, ISSN: 2169-3536

In this paper, we propose a method that shows how phase portraits rendered by a controller can inform the development of a physical adaptation at a single degree of freedom (DoF) for a given control task. This approach has the advantage of having physical adaptations sharing the responsibility of control to accomplish a task. We use an inverted pendulum which is reminiscent of the trunk of a biped walker to conduct numerical simulations and hardware experiments to show how our method can innovate a physical adaptation at the pivot joint to reduce the control effort. Our method discovered that a torsional spring at the pivot joint would lead to a lower input effort by the regulator type feedback controller. The method can tune the spring to minimize the total cost of control up to about 32.81%. This physical adaptation framework allows multiple degrees of freedom robotic system to suggest local physical adaptations to accomplish a given control objective.

Journal article

Gow J, Dijxhoorn E, Kerr R, Verdirame Get al., 2019, Routledge Handbook of War, Law and Technology, Publisher: Routledge, ISBN: 9781351619974

HANDBOOK. OF. WAR,. LAW. AND. TECHNOLOGY. This volume provides an authoritative, cutting-edge resource on the characteristics of both technological and social change in warfare in the twentyfirst century, and the challenges such&nbsp;...

Book

Shiva A, Sadati SH, Noh Y, Fras J, Ataka A, Wurdemann H, Hauser H, Walker I, Nanayakkara DPT, Althoefer Ket al., 2019, Elasticity vs hyperelasticity considerations in quasi-static modelling of a soft finger-like robotic appendage for real-time position and force estimation, Soft Robotics, Vol: 6, ISSN: 2169-5172

Various methods based on hyperelastic assumptions have been developed to address the mathematical complexities of modeling motion and deformation of continuum manipulators. In this study, we propose a quasistatic approach for 3D modeling and real-time simulation of a pneumatically actuated soft continuum robotic appendage to estimate the contact force and overall pose. Our model can incorporate external load at any arbitrary point on the body and deliver positional and force propagation information along the entire backbone. In line with the proposed model, the effectiveness of elasticity versus hyperelasticity assumptions (neo-Hookean and Gent) is investigated and compared. Experiments are carried out with and without external load, and simulations are validated across a range of Young's moduli. Results show best conformity with Hooke's model for limited strains with about 6% average normalized error of position; and a mean absolute error of less than 0.08 N for force applied at the tip and on the body, demonstrating high accuracy in estimating the position and the contact force.

Journal article

Cotugno G, Konstantinova J, Althoefer K, Nanayakkara DPTet al., 2018, Modelling the structure of object-independent human affordances of approaching to grasp for robotic hands, PLoS ONE, Vol: 13, ISSN: 1932-6203

Grasp affordances in robotics represent different ways to grasp an object involving a variety of factors from vision to hand control. A model of grasp affordances that is able to scale across different objects, features and domains is needed to provide robots with advanced manipulation skills. The existing frameworks, however, can be difficult to extend towards a more general and domain independent approach. This work is the first step towards a modular implementation of grasp affordances that can be separated into two stages: approach to grasp and grasp execution. In this study, human experiments of approaching to grasp are analysed, and object-independent patterns of motion are defined and modelled analytically from the data. Human subjects performed a specific action (hammering) using objects of different geometry, size and weight. Motion capture data relating the hand-object approach distance was used for the analysis. The results showed that approach to grasp can be structured in four distinct phases that are best represented by non-linear models, independent from the objects being handled. This suggests that approaching to grasp patterns are following an intentionally planned control strategy, rather than implementing a reactive execution.

Journal article

Wijesundera I, Halgamuge M, Nirmalathas A, Nanayakkara DPTet al., 2018, Predicting the Mean First Passage Time (MFPT) to reach any state for a passive dynamic walker with steady state variability, PLoS ONE, Vol: 13, ISSN: 1932-6203

Idealized passive dynamic walkers (PDW) exhibit limit cycle stability at steady state. Yet in reality, uncertainty in ground interaction forces result in variability in limit cycles even for a simple walker known as the Rimless Wheel (RW) on seemingly even slopes. This class of walkers is called metastable walkers in that they usually walk in a stable limit cycle, though guaranteed to eventually fail. Thus, control action is only needed if a failure state (i.e. RW stopping down the ramp) is imminent. Therefore, efficiency of estimating the time to reach a failure state is key to develop a minimal intervention controller to inject just enough energy to overcome a failure state when required. Current methods use what is known as a Mean First Passage Time (MFPT) from current state (rotary speed of RW at the most recent leg collision) to an arbitrary state deemed to be a failure in the future. The frequently used Markov chain based MFPT prediction requires an absorbing state, which in this case is a collision where the RW comes to a stop without an escape. Here, we propose a novel method to estimate an MFPT from current state to an arbitrary state which is not necessarily an absorbing state. This provides freedom to a controller to adaptively take action when deemed necessary. We demonstrate the proposed MFPT predictions in a minimal intervention controller for a RW. Our results show that the proposed method is useful in controllers for walkers showing up to 44.1% increase of time-to-fail compared to a PID based closed-loop controller.

Journal article

He L, Herzig N, Lusignan SD, Nanayakkara Det al., 2018, Granular jamming based controllable organ design for abdominal palpation, 40th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, Publisher: IEEE

Medical manikins play an essential role in the training process of physicians. Currently, most available simulators for abdominal palpation training do not contain controllable organs for dynamic simulations. In this paper, we present a soft robotics controllable liver that can simulate various liver diseases and symptoms for effective and realistic palpation training. The tumors in the liver model are designed based on granular jamming with positive pressure, which converts the fluid-like impalpable particles to a solid-like tumor state by applying low positive pressure on the membrane. Through inflation, the tumor size, liver stiffness, and liver size can be controlled from normal liver state to various abnormalities including enlarged liver, cirrhotic liver, and multiple cancerous and malignant tumors. Mechanical tests have been conducted in the study to evaluate the liver design and the role of positive pressure granular jamming in tumor simulations.

Conference paper

Nanayakkara T, Sahin F, Jamshidi M, 2018, Intelligent Control Systems with an Introduction to System of Systems Engineering, Publisher: CRC Press, ISBN: 9781351834537

Azani, C., “An open systems approach to system of systems engineering” System of Systems Engineering— Innovations for the 21st Century, John Wiley Series on Systems Engineering (M. Jamshidi, Ed.). Wiley, New York, 2008. Sage, A. P.&nbsp;...

Book

Sadati SMH, Naghibi SE, Althoefer K, Nanayakkara Tet al., 2018, Toward a low hysteresis helical scale Jamming interface inspired by teleost fish scale morphology and arrangement, Pages: 455-460

© 2018 IEEE. Inspired by teleost fish scale, this paper investigates the possibility of implementing stiffness control as a new source of robots dexterity and flexibility control. Guessing about the possibility of biological scale jamming in real fish, we try to understand the possible underlying actuation mechanism of such behavior by conducting experiments on a Cyprinus carpio fish skin sample. Bulking tests are carried out on an encapsulated skin sample, in thin latex rubber, for unjammed and vacuum jammed cases. For the first time, we observed biological scale jamming with very small hysteresis due to the unique scale morphology and jammed stacking formation. We call this unique feature 'Geometrical Jamming' where the resisting force is due to the stacking formation rather than the interlocking friction force. Inspiring by this unique morphology and helical arrangement of the scale, in this research, we investigate different possible design and actuation mechanisms for an integrable scale jamming interface for stiffness control of continuum manipulators. A set of curved scales are 3D printed which maintain a helix formation when are kept in place and jammed with two thin fishing steel wires. The non-self locking jagged contact surfaces replicate inclined stacking formation of the jammed fish scale resulting in the same reversible low hysteresis characteristics, in contrast to the available interlocking designs. The effectiveness of the designs are shown for uniaxial elongation experiments and the results are compared with similar research. The contact surfaces, in our design, can be lubricated for further hysteresis reduction to achieve smooth, repeatable and accurate stiffness control in dynamic tasks.

Conference paper

Sadati SH, Sullivan L, Walker ID, Althoefer K, Nanayakkara DPTet al., 2018, 3D-printable thermoactive helical interface with decentralized morphological stiffness control for continuum manipulators, IEEE International Conference on Robotics and Automation, Publisher: Institute of Electrical and Electronics Engineers, Pages: 2283-2290, ISSN: 2377-3766

We present a three-dimensional (3-D)-printable thermoactive scale jamming interface as a new way to control a continuum manipulator dexterity by taking inspiration from the helical arrangement of fish scales. A highly articulated helical interface is 3-D-printed with thermoactive functionally graded joints using a conventional 3-D printing device that utilizes UV curable acrylic plastic and hydroxylated wax as the primary and supporting material. The joint compliance is controlled by regulating wax temperature in phase transition. Empirical feed-forward control relations are identified through comprehensive study of the wax melting profile and actuation scenarios for different shaft designs to achieve desirable repeatability and response time. A decentralized control approach is employed by relating the mathematical terms of the Cosserat beam method to their morphological counterparts in which the manipulator local anisotropic stiffness is controlled based on the local stress and strain information. As a result, a minimalistic central controller is designed in which the joints' thermomechanical states are observed using a morphological observer, an external fully monitored replica of the observed system with the same inputs. Preliminary results for passive shape adaptation, geometrical disturbance rejection, and task space anisotropic stiffness control are reported by integrating the interface on a continuum manipulator.

Conference paper

Ranasinghe A, Dasgupta P, Nagar A, Nanayakkara Det al., 2018, Human behavioral metrics of a predictive model emerging during robot assisted following without visual feedback, IEEE Robotics and Automation Letters, Vol: 3, Pages: 2624-2631, ISSN: 2377-3766

Robot-assisted guiding is gaining increased interest due to many applications involving moving in the noisy and low visibility environments. In such cases, haptic feedback is the most effective medium to communicate. In this letter, we focus on perturbation-based haptic feedback due to applications like guide dogs for visually impaired people and potential robotic counterparts providing haptic feedback via reins to assist indoor fire fighting. Since proprioceptive sensors like spindles and tendons are part of the muscles involved in the perturbation, haptic perception becomes a coupled phenomenon with spontaneous reflex muscle activity. The nature of this interplay and how the model-based sensory-motor integration evolves during haptic-based guiding is not well understood yet. We asked human followers to hold the handle of a hard rein attached to a one-DoF robotic arm that gave perturbations to the hand to correct an angle error of the follower. We found that followers start with a second-order reactive autoregressive following model and changes it to a predictive model with training. The reduction in cocontraction of muscles and leftward/rightward asymmetry of a set of followers behavioral metrics show that the model-based prediction accounts for the internal coupling between proprioception and muscle activity during perturbation responses.

Journal article

Konstantinova J, Cotugno G, Dasgupta P, Althoefer K, Nanayakkara Tet al., 2018, Palpation force modulation strategies to identify hard regions in soft tissue organs (vol 12, e0171706, 2017), PLOS ONE, Vol: 13, ISSN: 1932-6203

Journal article

Herzig N, Maiolino P, Iida F, Nanayakkara Det al., 2018, A Variable Stiffness Robotic Probe for Soft Tissue Palpation, IEEE Robotics and Automation Letters, Vol: 3, Pages: 1168-1175, ISSN: 2377-3766

During abdominal palpation diagnosis, a medical practitioner would change the stiffness of their fingers in order to improve the detection of hard nodules or abnormalities in soft tissue to maximize the haptic information gain via tendons. Our recent experiments using a controllable stiffness robotic probe representing a human finger also confirmed that such stiffness control in the finger can enhance the accuracy of detecting hard nodules in soft tissue. However, the limited range of stiffness achieved by the antagonistic springs variable stiffness joint subject to size constraints made it unsuitable for a wide range of physical examination scenarios spanning from breast to abdominal examination. In this letter, we present a new robotic probe based on a variable lever mechanism able to achieve stiffness ranging from 0.64 to 1.06 N ⋅m/rad that extends the maximum stiffness by around 16 times and the stiffness range by 33 times. This letter presents the mechanical model of the novel probe, the finite element simulation as well as experimental characterization of the stiffness response for lever actuation.

Journal article

Weheliye A, Sornkarn N, Dasgupta P, Nanayakkara Tet al., 2018, Haptic Information Gain in Remote Soft Tissue Examination Using a Controllable Stiffness Robotic Probe, 9th IEEE International Conference on Information and Automation for Sustainability (ICIAfS), Publisher: IEEE, ISSN: 2151-1802

Conference paper

Sadati SMH, Naghibi SE, Walker ID, Althoefer K, Nanayakkara Tet al., 2017, Control Space Reduction and Real-Time Accurate Modeling of Continuum Manipulators Using Ritz and Ritz–Galerkin Methods, IEEE Robotics and Automation Letters, Vol: 3, Pages: 328-335, ISSN: 2377-3766

To address the challenges with real-time accurate modeling of multisegment continuum manipulators in the presence of significant external and body loads, we introduce a novel series solution for variable-curvature Cosserat rod static and Lagrangian dynamic methods. By combining a modified Lagrange polynomial series solution, based on experimental observations, with Ritz and Ritz-Galerkin methods, the infinite modeling state space of a continuum manipulator is minimized to geometrical position of a handful of physical points (in our case two). As a result, a unified easy to implement vector formalism is proposed for the nonlinear impedance and configuration control. We showed that by considering the mechanical effects of highly elastic axial deformation, the model accuracy is increased up to 6%. The proposed model predicts experimental results with 6%-8% (4-6 mm) mean error for the Ritz-Galerkin method in static cases and 16%-20% (12-14 mm) mean error for the Ritz method in dynamic cases, in planar and general three-dimensional motions. Comparing to five different models in the literature, our approximate solution is shown to be more accurate with the smallest possible number of modeling states and suitable for real-time modeling, observation, and control applications.

Journal article

Sadati SM, Naghibi SE, Shiva A, Walker ID, Althoefer K, Nanayakkara Tet al., 2017, Mechanics of continuum manipulators, a comparative study of five methods with experiments, TAROS 2017, Publisher: Springer, Pages: 686-702, ISSN: 0302-9743

Investigations on control and optimization of continuum manipulators have resulted in a number of kinematic and dynamic modeling approaches each having their own advantages and limitations in various applications. In this paper, a comparative study of five main methods in the literature for kinematic, static and dynamic modeling of continuum manipulators is presented in a unified mathematical framework. The five widely used methods of Lumped system dynamic model, Constant curvature, two-step modified constant curvature, variable curvature Cosserat rod and beam theory approach, and series solution identification are re-viewed here with derivation details in order to clarify their methodological differences. A comparison between computer simulations and experimental results using a STIFF-FLOP continuum manipulator is presented to study the advantages of each modeling method.

Conference paper

Afrisal H, Sadati SMH, Nanayakkara T, 2017, A bio-Inspired electro-active velcro mechanism using shape memory alloy for wearable and stiffness controllable layers, 8th IEEE International Conference on Information and Automation for Sustainability (ICIAfS) - Interoperable Sustainable Smart Systems for Next Generation, Publisher: IEEE, ISSN: 2151-1802

Smart attachment mechanisms are believed to contribute significantly in stiffness control of soft robots. This paper presents a working prototype of an active Velcro based stiffness controllable fastening mechanism inspired from micro active hooks found in some species of plants and animals. In contrast to conventional passive Velcro, this active Velcro mechanism can vary the stiffness level of its hooks to adapt to external forces and to maintain the structure of its supported layer. The active hooks are fabricated using Shape Memory Alloy (SMA) wires which can be actuated using Lenz-Joule heating technique via thermo-electric manipulation. In this paper, we show experimental results for the effects of active SMA Velcro temperature, density and number on the attachment resisting force profile in dynamic displacement. We aim to provide new insights into the novel design approach of using active hook systems to support future implementation of active velcro mechanisms for fabrication of wearable stiffness controllable thin layers.

Conference paper

Nanayakkara T, 2017, Message from the Program Chair

Conference paper

Sadati SMH, Naghibi SE, Shiva A, Noh Y, Gupta A, Walker ID, Althoefer K, Nanayakkara Tet al., 2017, A geometry deformation model for braided continuum manipulators, Frontiers Robotics AI, Vol: 4

© 2017 Sadati, Naghibi, Shiva, Noh, Gupta, Walker, Althoefer and Nanayakkara. Continuum manipulators have gained significant attention in the robotic community due to their high dexterity, deformability, and reachability. Modeling of such manipulators has been shown to be very complex and challenging. Despite many research attempts, a general and comprehensive modeling method is yet to be established. In this paper, for the first time, we introduce the bending effect in the model of a braided extensile pneumatic actuator with both stiff and bendable threads. Then, the effect of the manipulator cross-section deformation on the constant curvature and variable curvature models is investigated using simple analytical results from a novel geometry deformation method and is compared to experimental results. We achieve 38% mean reference error simulation accuracy using our constant curvature model for a braided continuum manipulator in presence of body load and 10% using our variable curvature model in presence of extensive external loads. With proper model assumptions and taking to account the cross-section deformation, a 7-13% increase in the simulation mean error accuracy is achieved compared to a fixed cross-section model. The presented models can be used for the exact modeling and design optimization of compound continuum manipulators by providing an analytical tool for the sensitivity analysis of the manipulator performance. Our main aim is the application in minimal invasive manipulation with limited workspaces and manipulators with regional tunable stiffness in their cross section.

Journal article

Nanayakkara DPT, Konstantinova J, Cotugno G, Dasgupta P, Althoefer Ket al., 2017, Palpation force modulation strategies to identify hard regions in soft tissue organs, PLOS One, Vol: 12, ISSN: 1932-6203

This paper presents experimental evidence for the existence of a set of unique force modulation strategies during manual soft tissue palpation to locate hard abnormalities such as tumors. We explore the active probing strategies of defined local areas and outline the role of force control. In addition, we investigate whether the applied force depends on the non-homogeneity of the soft tissue. Experimental results on manual palpation of soft silicone phantoms show that humans have a well defined force control pattern of probing that is used independently of the non-homogeneity of the soft tissue. We observed that the modulations of lateral forces are distributed around the mean frequency of 22.3 Hz. Furthermore, we found that the applied normal pressure during probing can be modeled using a second order reactive autoregressive model. These mathematical abstractions were implemented and validated for the autonomous palpation for different stiffness parameters using a robotic probe with a rigid spherical indentation tip. The results show that the autonomous robotic palpation strategy abstracted from human demonstrations is capable of not only detecting the embedded nodules, but also enhancing the stiffness perception compared to static indentation of the probe.

Journal article

Wegiriya H, Sornkarn N, Bedford H, Nanayakkara Tet al., 2017, A biologically inspired multimodal whisker follicle, 2016 IEEE International Conference on Systems, Man, and Cybernetics, SMC 2016 - Conference Proceedings, Pages: 3847-3852

Mammalian whisker follicle contains multiple sensory receptors strategically organized to capture tactile sensory stimuli of different frequencies via the vibrissal system. There have been a number of attempts to develop robotic whiskers to perform texture classification tasks in the recent past. Inspired by the features of biological whisker follicle, in this paper we design and use a novel soft whisker follicle comprising of two different frequency-dependent data capturing modules to derive deeper insights into the biological basis of tactile perception in the mammalian whisker follicle. In our design, the innervations at the Outer Conical Body (OCB) of a biological follicle are realized by a piezoelectric transducer for capturing high frequency components; whereas the innervations around the hair Papilla are represented by a hall sensor to capture low frequency components during the interaction with the environment. In this paper, we show how low dimensional information such as the principle components of co-variation of these two sensory modalities vary for different speeds and indentations of brushing the whisker against a surface. These new insights into the biological basis of tactile perception using whiskers provides new design guidelines to develop efficient robotic whiskers.

Conference paper

Ranasinghe A, Althoefer K, Dasgupta P, Nagar A, Nanayakkara Tet al., 2017, Wearable Haptic Based Pattern Feedback Sleeve System, 6th International Conference on Soft Computing for Problem Solving (SocProS), Publisher: SPRINGER-VERLAG BERLIN, Pages: 302-312, ISSN: 2194-5357

Conference paper

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