Dr Sajeeva Abeywardena


My qualifications

Doctor of Philosophy in Mechanical Engineering
Monash University, Australia
Bachelor of Mechatronic Engineering (First Class Hons.)
University of Adelaide, Australia
Bachelor of Mathematical and Computer Sciences
University of Adelaide, Australia


Sajeeva Abeywardena, Eisa Anwar, Stuart Charles Miller, Ildar Farkhatdinov (2024)Mechanical Characterization of Supernumerary Robotic Tails for Human Balance Augmentation, In: ASME Journal of Mechanisms and Robotics16(6)061007 ASME

Humans are intrinsically unstable in quiet stance from a rigid body system viewpoint; however, they maintain balance, thanks to neuro-muscular sensory control properties. With increasing levels of balance related incidents in industrial and ageing populations globally each year, the development of assistive mechanisms to augment human balance is paramount. This work investigates the mechanical characteristics of kinematically dissimilar one and two degrees-of-freedom (DoF) supernumerary robotic tails for balance augmentation. Through dynamic simulations and manipulability assessments, the importance of variable coupling inertia in creating a sufficient reaction torque is highlighted. It is shown that two-DoF tails with solely revolute joints are best suited to address the balance augmentation issue. Within the two-DoF options, the characteristics of open versus closed loop tails are investigated, with the ultimate design selection requiring trade-offs between environmental workspace, biomechanical factors, and manufacturing ease to be made.

Chao Chen, Thibault Gayral, Stephane Caro, Damien Chablat, Guillaume Moroz, Sajeeva Abeywardena (2012)A Six Degree of Freedom Epicyclic-Parallel Manipulator, In: ASME Journal of Mechanisms and Robotics4(4) Asme

A new six-dof epicyclic-parallel manipulator with all actuators allocated on the ground is introduced. It is shown that the system has a considerably simple kinematics relationship, with the complete direct and inverse kinematics analysis provided. Further, the first and second links of each leg can be driven independently by two motors. The serial and parallel singularities of the system are determined, with an interesting feature of the system being that the parallel singularity is independent of the position of the end-effector. The workspace of the manipulator is also analyzed with future applications in haptics in mind. [DOI: 10.1115/1.4007489]

Sajeeva Abeywardena, Chao Chen (2017)Implementation and Evaluation of a Three-Legged Six-Degrees-of-Freedom Parallel Mechanism as an Impedance-Type Haptic Device, In: IEEE/ASME Transactions on Mechatronics22(3)pp. 1412-1422 IEEE

The Monash Epicyclic Parallel Manipulator (MEPaM) is a three-legged six-degrees-of-freedom (dof) parallel mechanism with base mounted actuators. Due to the architecture of MEPaM, a closed form solution to the direct geometric problem was obtained. The concepts of Z-Width and transparency were used to analyze the performance of MEPaM as a haptic device. It was found that the Z-Width is superior to two out of three commercially available six-dof haptic devices. Closed-loop control was found to provide the most transparent interaction.

Sajeeva Abeywardena, Chao Chen (2017)Inverse dynamic modelling of a three-legged six-degree-of-freedom parallel mechanism, In: Multibody System Dynamics41(1)pp. 1-24 Springer Nature

The Monash Epicyclic Parallel Manipulator (MEPaM) is a novel six-degree-offreedom (dof) parallel mechanism with base mounted actuators. Closed form equations of the inverse dynamic model of MEPaM are obtained through two different methods, with simulation showing these models to be equivalent. The base inertial parameters for the dynamic model of MEPaM are determined, reducing the number of inertial parameters from 100 to 28. This significantly simplifies the dynamic calibration model and thus the number of computations required.

Efi Psomopoulou, Raj Persad, Anthony Koupparis, Sajeeva Abeywardena, Mohammad Fattahi Sani, Chris Melhuish, Sanja Dogramadzi (2019)Evaluation of Force Feedback for Palpation and Application of Active Constraints on a Teleoperated System

A desktop haptic device is used to teleoperate an industrial redundant and compliant robotic arm with a surgical instrument mounted on its end-effector. The master and slave devices are coupled in a bilateral position-position architecture. Force feedback is provided by the master haptic device to the user, from the position of the slave's wrist. A surgical task (palpation) that involves force feedback is presented and tested in a user study with surgeons and non-medical participants. Results show that users easily discern between three different materials during palpation given minimal familiarisation time. Active constraint enforcement is also integrated with the system as a sensitive area around the palpation samples which the slave instrument is prohibited to enter.

Mohammad Fattahi Sani, Sajeeva Abeywardena, Efi Psomopoulou, Raimondo Ascione, Sanja Dogramadzi (2019)Towards Finger Motion Tracking and Analyses for Cardiac Surgery

Robot Assisted Surgery is attracting increasing amount of attention as it offers numerous benefits to patients as well as surgeons. Heart surgery requires a high level of precision and dexterity, in contrast to other surgical specialties. Robot assisted heart surgery is not as widely performed due to numerous reasons including a lack of appropriate and intuitive surgical interfaces to control minimally invasive surgical tools. In this paper, finger motion of the surgeon is analyzed during cardiac surgery tasks on an ex-vivo animal model with the purpose of designing a more intuitive master console. First, a custom finger tracking system is developed using IMU sensors, which is lightweight and comfortable enough to allow free movement of the surgeon's fingers/hands while using instruments. The proposed system tracks finger joint angles and fingertip positions for three involved fingers (thumb, index, middle). Accuracy of the IMU sensors has been evaluated using an optical tracking system (Polaris, NDI). Finger motion of the cardiac surgeon while using a Castroviejo instrument is studied in suturing and knotting scenarios. The results show that PIP and MCP joints have larger Range Of Motion (ROM), and faster rate of change compared to other finger/thumb joints, while thumb has the largest Fingertip WorkSpace (FWS) of all three digits.

Sajeeva Abeywardena, Qiaodi Yuan, Antonia Tzemanaki, Efi Psomopoulou, Leonidas Droukas, Chris Melhuish, Sanja Dogramadzi (2019)Estimation of Tool-Tissue Forces in Robot-Assisted Minimally Invasive Surgery Using Neural Networks, In: Frontiers in robotics and AI656 Frontiers Media S.A

A new algorithm is proposed to estimate the tool-tissue force interaction in robot-assisted minimally invasive surgery which does not require the use of external force sensing. The proposed method utilizes the current of the motors of the surgical instrument and neural network methods to estimate the force interaction. Offline and online testing is conducted to assess the feasibility of the developed algorithm. Results showed that the developed method has promise in allowing online estimation of tool-tissue force and could thus enable haptic feedback in robotic surgery to be provided.

Sajeeva Abeywardena, Ildar Farkhatdinov (2023)Towards Enhanced Stability of Human Stance With a Supernumerary Robotic Tail, In: IEEE Robotics and Automation Letters8(9)pp. 5743-5750 IEEE

Neural control is paramount in maintaining upright stance of a human; however, the associated time delay affects stability. In the design and control of wearable robots to augment human stance, the neural delay dynamics are often overly simplified or ignored leading to over specified systems. In this letter, the neural delay dynamics of human stance are modelled and embedded in the control of a supernumerary robotic tail to augment human balance. The actuation, geometric and inertial parameters of the tail are examined. Through simulations it was shown that by incorporating the delay dynamics, the tail specification can be greatly reduced. Further, it is shown that robustness of stance is significantly enhanced with a supernumerary tail and that there is positive impact on muscle fatigue.

Sajeeva Abeywardena, Efi Psomopoulou, Mohammad Fattahi Sani, Antonia Tzemanaki, Sanja Dogramadzi (2019)Control of a da Vinci EndoWrist Surgical Instrument Using a Novel Master Controller

A novel master controller for robot-assisted minimally invasive surgery (RAMIS) is introduced and used to control a da Vinci EndoWrist instrument. The geometric model of the master mechanism and its mapping to the geometry of the EndoWrist tool are derived. Experimental results are conducted to open and close the jaws of an EndoWrist tool, and show that the developed mapping algorithm is accurate with a root mean square error of 0.7463 mm.

Sajeeva Abeywardena, Eisa Anwar, Stuart Miller, Ildar Farkhatdinov (2022)Human balance augmentation via a supernumerary robotic tail

Humans are intrinsically unstable in quiet stance from a rigid body system viewpoint; however, they maintain balance thanks to neuro-muscular sensory properties whilst still exhibiting postural sway characteristics. This work intro-duces a one-degree-of-freedom supernumerary tail for balance augmentation in the sagittal plane to negate anterior-posterior postural sway. Simulations showed that the tail could success-fully balance a human with impaired ankle stiffness and neural control. Insights into tail design and control were made; namely, to minimise muscular load the tail must have a significant component in the direction of the muscle, mounting location of the tail is significant in maximising inertial properties for balance augmentation and that adaptive control of the tail will be best suited for different loads held by a wearer.