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
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50 results found

Abad Guaman S-A, Herzig N, Sadati SMH, Nanayakkara DPTet al., Significance of the compliance of the joints on the dynamic slip resistance of a bio-inspired hoof, IEEE Transactions on Robotics, 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

Akhond S, Herzig N, Wegiriya H, Nanayakkara DPTet al., A Method to Guide Local Physical Adaptations in a Robot Based on Phase Portraits, IEEE Access, ISSN: 2169-3536

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

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

Variousmethodsbased on hyperelastic assumptions have been developedto address the mathematical complexities ofmodellingmotion and deformation of continuum manipulators. Here, wepropose a quasi-static approach for 3D modelling and real-time simulation of a pneumatically actuated soft continuum robotic appendage to estimate the contact forces and the overall pose.Our model can incorporate external load at any arbitrary point on the body anddeliver positional and force propagation information along the entire backbone. In line with the proposed model, theeffectiveness ofelasticity vs.hyperelasticity assumptions(Neo-Hookean and Gent) are investigated and compared.Experiments are carried out with and without external load,andsimulations are validated across a range of Young’s moduli. Results show best conformity with Hooke’smodel for limited strains with about6% average normalized error of position;and a mean absolute error of less than 0.08N for force applied at the tip and on the body; demonstrating high accuracy in estimating the positionand the contact forces.

Journal article

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

He L, Herzig N, Lusignan SD, Nanayakkara Det al., Granular jamming based controllable organ design for abdominal palpation, 40th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, Publisher: IEEE, ISSN: 1557-170X

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

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

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

Rijanto E, Sugiharto A, Utomo S, Rahmayanti R, Afrisal H, Nanayakkara Tet al., 2017, Trends in robot assisted endovascular catheterization technology: A review, Pages: 34-41

© 2017 IEEE. Thirty-Three years has passed since the first utilization of laparoscopic technology in surgery, yet the deployment of robots in endovascular catheterization process is currently still in its infancy. Following up some reviews by other researchers, this paper elaborates trends in robotic-Assisted endovascular catheterization through literature study of published articles since the last 4 years, direct observation of on going minimally invasive endovascular intervention surgery, and discussions with an interventional cardiologist. Some important facts have been identified such as, some commercial robots have been used In Vitro, and magnetic resonance compatible slave robots as well as methods for physician skill evaluation are under development. The existing issues include miniaturization of flexible robots, side contact force sensing device for catheters, and stable haptic feedback in master robot. Some examples of interesting topics for future research are more stable and robust haptic feedback, structure and mechanism of catheter, intra-cardiac sensors, estimation methods of catheter tip states (position, angle and contact force), modeling and control methods, image sensing technology which does not yield radiation exposure yet more economically affordable, and simulator with skill assessment algorithm.

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 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

Abad S-A, Sornkarn N, Nanayakkara T, 2016, The role of morphological computation of the goat hoof in slip reduction, IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), Publisher: IEEE, Pages: 5599-5605, ISSN: 2153-0866

The remarkable ability of goats to maintain stability during climbing cliffs or trees provides a valuable opportunity to understand some of the secrets of stable legged locomotion on unstructured terrains. This paper, for the first time, presents analytical and experimental explanations as to how the morphological computation at the goat hoof makes a significant contribution to slip reduction on both smooth and rough surfaces. We conducted experiments using a laboratory made hoof and compared its dynamic behavior against a rounded foot. We recorded forces and position of the hoof to analyze the effect of its shape and the individual contributions from 3-joints in the hoof on the work required to slip. Results state that the work required to move the hoof is more than 3 times that required to move a rounded foot. Additionally, the variables in the transient state are affected not only by the number and type of joints but also by the interaction with the environment. These findings promote the development of new types of feet for robots for all terrain conditions with greater stability and less control complexity.

Conference paper

Sornkarn N, Nanayakkara T, 2016, Can a Soft Robotic Probe Use Stiffness Control Like a Human Finger to Improve Efficacy of Haptic Perception?, IEEE TRANSACTIONS ON HAPTICS, Vol: 10, Pages: 183-195, ISSN: 1939-1412

When humans are asked to palpate a soft tissue to locate a hard nodule, they regulate the stiffness, speed, and force of the finger during examination. If we understand the relationship between these behavioral variables and haptic information gain (transfer entropy) during manual probing, we can improve the efficacy of soft robotic probes for soft tissue palpation, such as in tumor localization in minimally invasive surgery. Here, we recorded the muscle co-contraction activity of the finger using EMG sensors to address the question as to whether joint stiffness control during manual palpation plays an important role in the haptic information gain. To address this question, we used a soft robotic probe with a controllable stiffness joint and a force sensor mounted at the base to represent the function of the tendon in a biological finger. Then, we trained a Markov chain using muscle co-contraction patterns of human subjects, and used it to control the stiffness of the soft robotic probe in the same soft tissue palpation task. The soft robotic experiments showed that haptic information gain about the depth of the hard nodule can be maximized by varying the internal stiffness of the soft probe.

Journal article

Konstantinova J, Cotugno G, Dasgupta P, Althoefer K, Nanayakkara Tet al., 2016, Autonomous robotic palpation of soft tissue using the modulation of applied force, IEEE RAS and EMBS International Conference on Biomedical Robotics and Biomechatronics 2016, Publisher: IEEE, Pages: 323-328, ISSN: 2155-1774

Palpation or perception of tactile information from soft tissue organs during minimally invasive surgery is required to improve clinical outcomes. One of the methods of palpation includes examination using the modulation of applied force on the localized area. This paper presents a method of soft tissue autonomous palpation based on the mathematical model obtained from human tactile examination data using modulations of palpation force. Using a second order reactive auto-regressive model of applied force, a robotic probe with spherical indenter was controlled to examine silicone tissue phantoms containing artificial nodules. The results show that the autonomous palpation using the model abstracted from human demonstration can be used not only to detect embedded nodules, but also to enhance the stiffness perception compared to the static indentation of the probe.

Conference paper

Nanayakkara V, Ataka A, Venetsanos D, Duran O, Vitzilaios N, Nanayakkara T, Sahinkaya MNet al., 2016, Kinematic analysis of the human thumb with foldable palm, TAROS 2016, Publisher: Springer, Pages: 226-238, ISSN: 0302-9743

There have been numerous attempts to develop anthropomorphic robotic hands with varying levels of dexterous capabilities. However, these robotic hands often suffer from a lack of comprehensive understanding of the musculoskeletal behavior of the human thumb with integrated foldable palm. This paper proposes a novel kinematic model to analyze the importance of thumb-palm embodiment in grasping objects. The model is validated using human demonstrations for five precision grasp types across five human subjects. The model is used to find whether there are any co-activations among the thumb joint angles and muskuloskeletal parameters of the palm. In this paper we show that there are certain pairs of joints that show stronger linear relationships in the torque space than in joint angle space. These observations provide useful design guidelines to reduce control complexity in anthropomorphic robotic thumbs.

Conference paper

Sornkarn N, Nanayakkara T, 2016, The efficacy of interaction behavior and internal stiffness control for embodied information gain in haptic perception, IEEE International Conference on Robotics and Automation (ICRA) 2016, Publisher: IEEE, Pages: 2657-2662, ISSN: 1050-4729

Haptic perception in biological systems not only depends on the environmental conditions, but also on the behavioral state and the internal impedance of the embodiment because proprioceptive sensors are embedded in the muscle and tendons used for actuation. A simple example of such a phenomenon can be found when people are asked to palpate a soft tissue to identify a stiff-inclusion. People tend to perform a variety of palpation strategies depending on their previous knowledge and the desired information. Does this mean that the probing behavioral variables and internal muscle impedance parameters and their interaction with given environmental conditions play a role in the perception information gain during the estimation of soft tissue's properties? In this paper, we use a two-degree of freedom laboratory-made variable stiffness and indentation probe to investigate how the modulation of probing behavioral and internal stiffness variables can affect the accuracy of the depth estimation of stiff inclusions in artificial silicon phantom tissue using information gain metrics based on prior knowledge in form of memory primitives.

Conference paper

Sadati SMH, Shiva A, Ataka A, Naghibi SE, Walker ID, Althoefer K, Nanayakkara Tet al., 2016, A geometry deformation model for compound continuum manipulators with external loading, Proceedings - IEEE International Conference on Robotics and Automation, Vol: 2016-June, Pages: 4957-4962, ISSN: 1050-4729

© 2016 IEEE. The complexity of soft continuum manipulators with hybrid and tuneable structures poses a challenging task to achieve an inverse kinematics model which is both precise and computationally efficient for control and optimization purposes. In this paper, a new method based on the principle of virtual work and a geometry deformation approach is presented for the inverse kinematics model of the STIFF-FLOP arm which is a pneumatically actuated continuum manipulator. We propose a novel simplified and computationally efficient yet accurate analytical solution to analyse the static behaviour of a compound soft manipulator in the presence of external and body forces which is verified against experimental data, showing promising agreement with 10% mean error for planar movements. In the process, we present a new modelling approach for braided soft extensor actuators with no braid-surface relative slip constraint. For the first time, our model predicts a simple analytical solution for the cross section deformation which is essential to control soft manipulators with regional tunable stiffness structure.

Journal article

Sornkarn N, Dasgupta P, Nanayakkara T, 2016, Morphological computation of haptic perception of a controllable stiffness probe, PLOS One, Vol: 11, ISSN: 1932-6203

When people are asked to palpate a novel soft object to discern its physical properties such as texture, elasticity, and even non-homogeneity, they not only regulate probing behaviors, but also the co-contraction level of antagonistic muscles to control the mechanical impedance of fingers. It is suspected that such behavior tries to enhance haptic perception by regulating the function of mechanoreceptors at different depths of the fingertips and proprioceptive sensors such as tendon and spindle sensors located in muscles. In this paper, we designed and fabricated a novel two-degree of freedom variable stiffness indentation probe to investigate whether the regulation of internal stiffness, indentation, and probe sweeping velocity (PSV) variables affect the accuracy of the depth estimation of stiff inclusions in an artificial silicon phantom using information gain metrics. Our experimental results provide new insights into not only the biological phenomena of haptic perception but also new opportunities to design and control soft robotic probes.

Journal article

Nanayakkara T, Jiang A, Del Rocío Armas Fernández M, Liu H, Althoefer K, Bimbo Jet al., 2016, Stable grip control on soft objects with time-varying stiffness, IEEE Transactions on Robotics, Vol: 32, Pages: 626-637, ISSN: 1552-3098

Humans can hold a live animal like a hamster without overly squeezing despite the fact that its soft body undergoes impedance and size variations due to breathing and wiggling. Although the exact nature of such biological motor controllers is not known, existing literature suggests that they maintain metastable interactions with dynamic objects based on prediction rather than reaction. Most robotic gripper controllers find such tasks very challenging mainly due to hard constraints imposed on the stability of closed-loop control and inadequate rates of convergence of adaptive controller parameters. This paper presents experimental and numerical simulation results of a control law based on a relaxed stability criterion of reducing the probability of failure to maintain a stable grip on a soft object that undergoes temporal variations in its internal impedance. The proposed controller uses only three parameters to interpret the probability of failure estimated using a history of grip forces to adjust the grip on the dynamic object. Here, we demonstrate that the proposed controller can maintain smooth and stable grip tightening and relaxing when the object undergoes random impedance variations, compared with a reactive controller that involves a similar number of controller parameters.

Journal article

Cotugno G, Althoefer K, Nanayakkara T, 2016, The Role of the Thumb: Study of Finger Motion in Grasping and Reachability Space in Human and Robotic Hands, IEEE TRANSACTIONS ON SYSTEMS MAN CYBERNETICS-SYSTEMS, Vol: 47, Pages: 1061-1070, ISSN: 2168-2216

It is well acknowledged that the opposing thumb granted humans advanced manipulation capabilities. However, such a feature is not statistically quantified, and its representation is not formally addressed in robotics yet. This paper studies whether the displacement of the opposing thumb in humans is a determining factor for shaping the grip. Using statistical analysis of the variability of motion capture data from the GRASP database, we found that the displacement of the thumb plays a leading role on the shaping of the grip, independently from the specific object being grasped. Furthermore, we map and compare the reachability spaces of the human thumb and two state-of-the-art robotic thumbs: (1) the shadow and (2) the iCub hands. We conclude that the kinematics of robotic thumbs does not evenly span the reachability space of the human thumb, favoring precision grasping motions. Hence, our findings contribute to the discussion of the optimal modeling of robotic hands.

Journal article

Li M, Konstantinova J, Secco EL, Jiang A, Liu H, Nanayakkara T, Seneviratne LD, Dasgupta P, Althoefer K, Wurdemann HAet al., 2015, Using visual cues to enhance haptic feedback for palpation on virtual model of soft tissue., Med Biol Eng Comput, Vol: 53, Pages: 1177-1186

This paper explores methods that make use of visual cues aimed at generating actual haptic sensation to the user, namely pseudo-haptics. We propose a new pseudo-haptic feedback-based method capable of conveying 3D haptic information and combining visual haptics with force feedback to enhance the user's haptic experience. We focused on an application related to tumor identification during palpation and evaluated the proposed method in an experimental study where users interacted with a haptic device and graphical interface while exploring a virtual model of soft tissue, which represented stiffness distribution of a silicone phantom tissue with embedded hard inclusions. The performance of hard inclusion detection using force feedback only, pseudo-haptic feedback only, and the combination of the two feedbacks was compared with the direct hand touch. The combination method and direct hand touch had no significant difference in the detection results. Compared with the force feedback alone, our method increased the sensitivity by 5%, the positive predictive value by 4%, and decreased detection time by 48.7%. The proposed methodology has great potential for robot-assisted minimally invasive surgery and in all applications where remote haptic feedback is needed.

Journal article

Ranasinghe A, Sornkarn N, Dasgupta P, Althoefer K, Penders J, Nanayakkara Tet al., 2015, Salient feature of haptic-ased guidance of people in low visibility environments using hard reins., IEEE Transactions on Cybernetics, Vol: 46, Pages: 568-579, ISSN: 2168-2267

This paper presents salient features of human-human interaction where one person with limited auditory and visual perception of the environment (a follower) is guided by an agent with full perceptual capabilities (a guider) via a hard rein along a given path. We investigate several salient features of the interaction between the guider and follower such as: 1) the order of an autoregressive (AR) control policy that maps states of the follower to actions of the guider; 2) how the guider may modulate the pulling force in response to the trust level of the follower; and 3) how learning may successively apportion the responsibility of control across different muscles of the guider. Based on experimental systems identification on human demonstrations from ten pairs of naive subjects, we show that guiders tend to adopt a third-order AR predictive control policy and followers tend to adopt second-order reactive control policy. Moreover, the extracted guider's control policy was implemented and validated by human-robot interaction experiments. By modeling the follower's dynamics with a time varying virtual damped inertial system, we found that it is the coefficient of virtual damping which is most sensitive to the trust level of the follower. We used these experimental insights to derive a novel controller that integrates an optimal order control policy with a push/pull force modulator in response to the trust level of the follower monitored using a time varying virtual damped inertial model.

Journal article

Sadati SMH, Noh Y, Naghibi SE, Kaspar A, Nanayakkara Tet al., 2015, Stiffness Control of Soft Robotic Manipulator for Minimally Invasive Surgery (MIS) Using Scale Jamming, 8th International Conference on Intelligent Robotics and Applications (ICIRA), Publisher: SPRINGER-VERLAG BERLIN, Pages: 141-151, ISSN: 0302-9743

Conference paper

Morland MFE, Althoefer K, Nanayakkara T, 2015, Novel method to form adaptive internal impedance profiles in walkers, 2015 37TH ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY (EMBC), Pages: 7764-7767, ISSN: 1557-170X

Journal article

Ranasinghe A, Dasgupta P, Althoefer K, Nanayakkara Tet al., 2015, Identification of Haptic Based Guiding Using Hard Reins., PLoS One, Vol: 10

This paper presents identifications of human-human interaction in which one person with limited auditory and visual perception of the environment (a follower) is guided by an agent with full perceptual capabilities (a guider) via a hard rein along a given path. We investigate several identifications of the interaction between the guider and the follower such as computational models that map states of the follower to actions of the guider and the computational basis of the guider to modulate the force on the rein in response to the trust level of the follower. Based on experimental identification systems on human demonstrations show that the guider and the follower experience learning for an optimal stable state-dependent novel 3rd and 2nd order auto-regressive predictive and reactive control policies respectively. By modeling the follower's dynamics using a time varying virtual damped inertial system, we found that the coefficient of virtual damping is most appropriate to explain the trust level of the follower at any given time. Moreover, we present the stability of the extracted guiding policy when it was implemented on a planar 1-DoF robotic arm. Our findings provide a theoretical basis to design advanced human-robot interaction algorithms applicable to a variety of situations where a human requires the assistance of a robot to perceive the environment.

Journal article

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