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Soft Robotics and Applied Control

Soft and flexible robotic systems for affordable healthcare.

Head of Group

B414B Bessemer Building
South Kensington Campus

What we do

Our research investigates fundamental aspects of control of soft and flexible robots for surgery. These include harnessing the intrinsic compliance of soft robots, rejecting disturbances that characterise the surgical environment, and complying with stringent safety requirements. Our ambition is to provide affordable robotic solutions for a range of surgical applications, including endoscopy, percutaneous intervention, and multi-handed surgery.

Why it is important?

Robotics for healthcare is one of the fastest growing segments in the global robotics market. However, conventional surgical robots are unaffordable in low-resource settings. Harnessing the potential of soft and flexible robots can contribute to making surgery safter, more accurate, and more accessible in low-middle income countries. These are pressing needs due to the aging population, and to the growing workforce crisis in the healthcare market.

How can it benefit patients?

Our work aims to improve accuracy, reduce the risk of injury, and reduce discomfort in percutaneous interventions such as biopsy, in diagnostic and interventional endoscopy, and in multi-handed surgery.

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Journal article
Franco E, Garriga Casanovas A, 2021,
Energy shaping control of soft continuum manipulators with in-plane disturbances
, International Journal of Robotics Research, Vol: 40, Pages: 236-255, ISSN: 0278-3649
Soft continuum manipulators offer levels of compliance and inherent safety that can render thema superior alternative to conventional rigid robotsfor a variety of tasks, such as medical interventions or human-robot interaction. However, the ability of soft continuum manipulators to compensate external disturbances need to be further enhanced to meet the stringent requirements of many practical applications.In this paper, we investigate the control problem forsoft continuum manipulators that consist of one inextensible segmentof constant section, which bends under the effect of the internal pressure and is subject to unknown disturbances acting in the plane of bending. A rigid-link model of the manipulatorwith a single input pressureis employed for control purposes and an energy-shaping approach isproposedto derive thecontrol law. A method for the adaptive estimation of disturbances is detailed and a disturbance compensation strategy is proposed.Finally, the effectiveness of the controlleris demonstrated with simulations and with experiments on an inextensible soft continuum manipulator that employs pneumatic actuation.
Journal article
Franco E, Rodriguez y Baena F, Astolfi A, 2020,
Robust dynamic state feedback for underactuated systems with linearly parameterized disturbances
, International Journal of Robust and Nonlinear Control, Vol: 30, Pages: 4112-4128, ISSN: 1049-8923
This article investigates the control problem for underactuated port‐controlled Hamiltonian systems with multiple linearly parameterized additive disturbances including matched, unmatched, constant, and state‐dependent components. The notion of algebraic solution of the matching equations is employed to design an extension of the interconnection and damping assignment passivity‐based control methodology that does not rely on the solution of partial differential equations. The result is a dynamic state‐feedback that includes a disturbance compensation term, where the unknown parameters are estimated adaptively. A simplified implementation of the proposed approach for underactuated mechanical systems is detailed. The effectiveness of the controller is demonstrated with numerical simulations for the magnetic‐levitated‐ball system and for the ball‐on‐beam system.
Journal article
Meagher C, Franco E, Turk R, Wilson S, Steadman N, McNicholas L, Vaidyanathan R, Burridge J, Stokes Met al., 2020,
New advances in mechanomyography sensor technology and signal processing: validity and intrarater reliability of recordings from muscle
, Journal of Rehabilitation and Assistive Technologies Engineering, Vol: 7, ISSN: 2055-6683
IntroductionThe Mechanical Muscle Activity with Real-time Kinematics project aims to develop a device incorporating wearable sensors for arm rehabilitation following stroke. These will record kinematic activity using inertial measurement units and mechanical muscle activity. The gold standard for measuring muscle activity is electromyography; however, mechanomyography offers an appropriate alterative for our home-based rehabilitation device. We have patent filed a new laboratory-tested device that combines an inertial measurement unit with mechanomyography. We report on the validity and reliability of the mechanomyography against electromyography sensors.MethodsIn 18 healthy adults (27–82 years), mechanomyography and electromyography recordings were taken from the forearm flexor and extensor muscles during voluntary contractions. Isometric contractions were performed at different percentages of maximal force to examine the validity of mechanomyography. Root-mean-square of mechanomyography and electromyography was measured during 1 s epocs of isometric flexion and extension. Dynamic contractions were recorded during a tracking task on two days, one week apart, to examine reliability of muscle onset timing.ResultsReliability of mechanomyography onset was high (intraclass correlation coefficient = 0.78) and was comparable with electromyography (intraclass correlation coefficient = 0.79). The correlation between force and mechanomyography was high (R2 = 0.94).ConclusionThe mechanomyography device records valid and reliable signals of mechanical muscle activity on different days.
Conference paper
Franco E, Garriga Casanovas A, Rodriguez y Baena F, Astolfi Aet al., 2020,
Model based adaptive control for a soft robotic manipulator
, 58th IEEE Conference on Decision and Control, Publisher: IEEE, Pages: 1019-1024
The application of model based adaptive control to an underactuated system representative of a class of soft continuummanipulators is investigated. To this end, a rigid-linkmodel with elastic joints is employed and an energy shaping controller is designed. Additionally, model uncertainties and external disturbances, both matched and unmatched, are compensated with an adaptive algorithm. This results in a control law that only depends on the orientation and on the angular velocity of the distal link and it is therefore independent of the number of links. Finally, stability conditions are discussed and the effectiveness of the controller is verified via simulations.
Conference paper
Franco E, Brown T, 2019,
Energy shaping control for robotic needle insertion
, 23rd International Conference on System Theory, Control and Computing (ICSTCC), Publisher: IEEE, Pages: 1-6
This work investigates the use of energy shaping control to reduce deflection in slender beams with tip load and actuation at the base. The ultimate goal of this research is a buckling avoidance strategy for robotic-assisted needle insertion. To this end, the rigid-link model of a flexible beam actuated at the base and subject to tip load is proposed, and an energy shaping approach is employed to construct a nonlinear controller that accounts for external forces. A comparative simulation study highlights the benefits of the proposed approach over a linear control baseline and a simplified nonlinear control.
Conference paper
Franco E, 2019,
Energy-based design of elastic joints for inverted pendulum systems with input saturation
, 27th Mediterranean Conference on Control and Automation, Publisher: IEEE
This work investigates the balancing control of underactuated inverted pendulum systems with input saturation. To this end, the design of elastic joints according to potential-energy shaping principles is combined with energy-shaping control. As a result, analytical design guidelines are synthesized and implemented fortwo classical examples: the inertia-wheel pendulum and the Acrobot system.Asimulation study demonstrates the effectiveness of the proposed approach in reducing control effort while preserving transient performance.
Journal article
Franco E, 2019,
IDA-PBC with adaptive friction compensation for underactuated mechanical systems
, International Journal of Control, Vol: 94, Pages: 860-870, ISSN: 0020-7179
In this work the control of underactuated mechanical systems with dry friction on actuated and unactuated joints is investigated. A new interconnection-and-damping-assignment passivity-based-control (IDA-PBC) design is presented, which includes the adaptive estimation of the friction forces and the introduction of a nonlinear dissipative term in the closed-loop system dynamics. As a result, the traditional IDA-PBC is complemented with an additional matching condition and the control law is augmented with a new term that accounts for the Coulomb friction forces on all joints. Two adaptive control paradigms are considered for comparison purposes and stability conditions are discussed. The control design is detailed for two demonstrative examples: the disk-on-disk system; the Acrobot system. The effectiveness of the proposed design is demonstrated with numerical simulations.
Journal article
Franco E, 2019,
Adaptive IDA-PBC for underactuated mechanical systems with constant disturbances
, International Journal of Adaptive Control and Signal Processing, Vol: 33, Pages: 1-15, ISSN: 0890-6327
This work investigates the control of nonlinear underactuated mechanical systems with matched and unmatched constant disturbances. To this end, a new control strategy is proposed, which builds upon the interconnection‐and‐damping‐assignment passivity‐based control, augmenting it with an additional term for the purpose of disturbance compensation. In particular, the disturbances are estimated adaptively and then accounted for in the control law employing a new matching condition of algebraic nature. Stability conditions are discussed, and for comparison purposes, an alternative controller based on partial feedback linearization is presented. The effectiveness of the proposed approach is demonstrated with numerical simulations for three motivating examples: the inertia wheel pendulum, the disk‐on‐disk system, and the pendulum‐on‐cart system.
Journal article
Franco E, Rodriguez y Baena F, Astolfi A, 2018,
Robust balancing control of flexible inverted-pendulum systems
, Mechanism and Machine Theory, Vol: 130, Pages: 539-551, ISSN: 0094-114X
This work studies the balancing control problem for flexible inverted-pendulum systems and investigates the relationship between system parameters and robustness to disturbances. To this end, a new energy-shaping controller with adaptive disturbance-compensation for a class of underactuated mechanical systems is presented. Additionally, a method for the identification of key system parameters that affect the robustness of the closed-loop system is outlined. The proposed approach is applied to the flexible pendulum-on-cart system and a simulation study is conducted to demonstrate its effectiveness. Finally, the control problem for a classical pendulum-on-cart system with elastic joint is discussed to highlight the similarities with its flexible-link counterpart.
Conference paper
Franco E, 2018,
Discrete-time IDA-PBC for underactuated mechanical systems with input-delay and matched disturbances
, 2018 26th Mediterranean Conference on Control and Automation (MED), Publisher: IEEE, ISSN: 2473-3504
This work investigates the control problem of discrete-time underactuated mechanical systems with fixed input-delay and matched disturbances. A new control strategy is proposed, which builds upon a discrete-time implementation of the interconnection-and-damping-assignment passivity-based control (IDA-PBC) and extends it in two ways: the disturbances are estimated adaptively; the input-delay is compensated with a recursive algorithm. The resulting control law is constructed from IDA-PBC without solving any additional partial-differential-equation (PDE). Stability conditions are discussed and compared to alternative designs. Numerical simulations for the ball-on-beam system and for the Acrobot system demonstrate the effectiveness of the proposed approach.

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