Soft Robotics and Applied Control

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• Conference paper
  Runciman M, Franco E, Avery J, Rodriguez y Baena F, Mylonas Get al., 2023,

  Model based position control of soft hydraulic actuators

  , IEEE International Conference on Robotics and Automation, Publisher: IEEE, Pages: 1-7

  In this article, we investigate the model based position control of soft hydraulic actuators arranged in an an-tagonistic pair. A dynamical model of the system is constructed by employing the port-Hamiltonian formulation. A control algorithm is designed with an energy shaping approach, which accounts for the pressure dynamics of the fluid. A nonlinear observer is included to compensate the effect of unknown external forces. Simulations demonstrate the effectiveness of the proposed approach, and experiments achieve positioning accuracy of 0.043 mm with a standard deviation of 0.033 mm in the presence of constant external forces up to 1 N.

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• Journal article
  Franco E, Astolfi A, 2023,

  Energy shaping control of a class of underactuated mechanical systems with high-order actuator dynamics

  , European Journal of Control, Vol: 72, Pages: 1-13, ISSN: 0947-3580

  In this work we present some new results on energy shaping control for underactuated mechanical systems with high-order actuator dynamics. To this end, we propose an extension of the Interconnection and damping assignment Passivity based control methodology to account for actuator dynamics. This brings the following new results: i) a potential and kinetic energy shaping and damping assignment procedure that yields two alternative controllers; ii) a potential energy shaping and damping assignment procedure for a narrower class of underactuated mechanical systems. The proposed approach is illustrated with numerical simulations on three examples: an Acrobot system with a series elastic actuator; a soft continuum manipulator actuated by electroactive polymers; a two-mass-spring system actuated by a DC motor.

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• Conference paper
  Treratanakulchai S, Franco E, Rodriguez y Baena F, 2023,

  Model-free position control of a soft continuum manipulator in cartesian space

  , International Conference on Control, Automation and Diagnosis, Publisher: IEEE, Pages: 1-6

  This work investigates the position control in Cartesian space of a soft continuum manipulator with pneumatic actuation. To this end, we employ a feedback integral action initialized using an optimized mapping between pressure and tip position. This approach is detailed for a manipulator consisting of either a single actuated segment or of two actuated segments connected in series. Experiments are conducted on individual prototypes and with a teleoperation setup including a master unit from our track record.

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• Conference paper
  Virdyawan V, Ayatullah T, Sugiharto A, Franco E, Garriga Casanovas A, Mahyuddin AI, Rodriguez y Baena F, Indrawantoet al., 2023,

  Design and manufacturing of an affordable soft robotic manipulator for minimally invasive diagnosis

  , International Conference on Robotics and Automation Engineering (ICRAE), Publisher: IEEE

  Soft robotic manipulators are inherently compliant thus they are ideally suited for minimally invasive diagnosis and intervention. In addition, soft robotics allows for affordable manufacturing, thus it could be adopted in low and middle-income countries where conventional robotics is prohibitively expensive. In this work, the design, manufacturing, and actuation strategy of an affordable soft robotic manipulator is presented. The manufacturing process does not rely on sophisticated technologies, and the pneumatic actuation does not require digital pressure regulators. Instead, a low-cost solution consisting of a needle valve operated by a servo motor is employed. The prototype is assessed with experiments that demonstrate its functionality.

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• Journal article
  Alian A, Zari E, Wang Z, Franco E, Avery JP, Runciman M, Lo B, Rodriguez y Baena F, Mylonas Get al., 2023,

  Current engineering developments for robotic systems in flexible endoscopy

  , Techniques and Innovations in Gastrointestinal Endoscopy, Vol: 25, Pages: 67-81, ISSN: 2590-0307

  The past four decades have seen an increase in the incidence of early-onset gastrointestinal cancer. Because early-stage cancer detection is vital to reduce mortality rate, mass screening colonoscopy provides the most effective prevention strategy. However, conventional endoscopy is a painful and technically challenging procedure that requires sedation and experienced endoscopists to be performed. To overcome the current limitations, technological innovation is needed in colonoscopy. In recent years, researchers worldwide have worked to enhance the diagnostic and therapeutic capabilities of endoscopes. The new frontier of endoscopic interventions is represented by robotic flexible endoscopy. Among all options, self-propelling soft endoscopes are particularly promising thanks to their dexterity and adaptability to the curvilinear gastrointestinal anatomy. For these devices to replace the standard endoscopes, integration with embedded sensors and advanced surgical navigation technologies must be investigated. In this review, the progress in robotic endoscopy was divided into the fundamental areas of design, sensing, and imaging. The article offers an overview of the most promising advancements on these three topics since 2018. Continuum endoscopes, capsule endoscopes, and add-on endoscopic devices were included, with a focus on fluid-driven, tendon-driven, and magnetic actuation. Sensing methods employed for the shape and force estimation of flexible endoscopes were classified into model- and sensor-based approaches. Finally, some key contributions in molecular imaging technologies, artificial neural networks, and software algorithms are described. Open challenges are discussed to outline a path toward clinical practice for the next generation of endoscopic devices.

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• Journal article
  Bastos G, Franco E, 2023,

  Dynamic tube model predictive control for a class of soft manipulators with fluidic actuation

  , International Journal of Robust and Nonlinear Control, ISSN: 1049-8923

  Controlling soft continuum manipulators is a challenging task due to the structural compliance of these systems which results in underactuation. While a variety of control approaches have been proposed for regulation tasks, tracking control requires further investigation. To this end, a new dynamic tube-Model Predictive Control formulation is presented, which includes an ancillary control law constructed analytically with an energy-shaping approach. Two different models are considered: (i) a rigid-link model with direct-torque actuation, which is representative of miniature soft continuum manipulators supplied by digital pressure regulators; (ii) an extended model that includes the pressure dynamics of the fluid, which is representative of fluidic actuation by means of a variable flow rate. The effectiveness of the proposed algorithm is demonstrated with numerical simulations considering bounded external disturbances, either constant or time-varying.

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• Conference paper
  Treratanakulchai S, Franco E, Garriga Casanovas A, Hu M, Kassanos P, Rodriguez y Baena Fet al., 2022,

  Development of a 6 DOF soft robotic manipulator with integrated sensing Skin

  , International Conference on Intelligent Robots and Systems (IROS 2022), Publisher: IEEE, Pages: 6944-6951

  This paper presents a new 6 DOF soft roboticmanipulator intended for colorectal surgery. The manipulator,based on a novel design that employs an inextensible tube tolimit axial extension, is shown to maximize the force exertedat its tip and the bending angle, the latter being measuredwith a soft sensing skin. Manufacturing of the prototypeis achieved with a lost-wax silicone-casting technique. Thekinematic model of the manipulator, its workspace, and itsmanipulability are discussed. The prototype is evaluated withextensive experiments, including pressure-deflection measure-ment with and without tip load, and lateral force measurementswith and without the soft sensing skin to assess hysteresis. Theexperimental results indicate that the prototype fulfils the keydesign requirements for colorectal surgery: (i) it can generatesufficient force to perform a range of laparoscopic tasks; (ii) theworkspace is commensurate with the dimensions of the largeintestine; (iii) the soft sensing skin only results in a marginalreduction of the maximum tip rotation within the range ofpressures and external loads relevant for the chosen application.

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• Journal article
  Franco E, Astolfi A, 2022,

  Energy shaping control of underactuated mechanical systems with fluidic actuation

  , International Journal of Robust and Nonlinear Control, Vol: 32, Pages: 10011-10028, ISSN: 1049-8923

  Energy shaping is a remarkably effective control strategy which can be applied to a wide range of systems, including underactuated mechanical systems. However, research in this area has generally neglected actuator dynamics. While this is often appropriate, it might result in degraded performance in the case of fluidic actuation. In this work we present some new results on energy shaping control for underactuated mechanical systems for which the control action is mediated by a pressurized ideal fluid. In particular, we introduce an extended multi-step energy shaping and damping-assignment controller design procedure that builds upon the Interconnection-and-damping-assignment Passivity-based-control methodology in a modular fashion to account for the pressure dynamics of the fluid. Stability conditions are assessed with a Lyapunov approach, the effect of disturbances is discussed, and the case of redundant actuators is illustrated. The proposed approach is demonstrated with numerical simulations for a modified version of the classical ball-on-beam example, which employs two identical cylinders, either hydraulic or pneumatic, to actuate the beam.

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• Journal article
  Franco E, Donaire A, 2022,

  Energy shaping nonlinear control of underactuated needle insertion

  , Control Engineering Practice, Vol: 128, ISSN: 0967-0661

  This work investigates the position control of an underactuated mechatronic system for straight needle insertions in soft tissues. The system consists of a pneumatic cylinder pushing a slender needle supported at the base and subject to external forces at the tip due to interactions with soft tissues. The system dynamics is described by a rigid-link underactuated model for controller design purposes. The main contribution of this work is a new energy shaping control law that: (i) does not rely on the analytical solution of partial differential equations, which is a major hurdle in energy shaping techniques, and does not require partial feedback linearization, which is known to be sensitive to model uncertainties; (ii) accounts for the work of the friction forces on the pneumatic cylinder and of the lateral forces acting on the needle tip, which are estimated adaptively with nonlinear observers. For comparison purposes, an alternative controller that employs feedback linearization is also presented. Simulations and experiments on silicone rubber phantoms using a needle with axial-symmetric tip indicate that the proposed controller can reduce the needle tip rotation and the corresponding deflection compared to a PID algorithm. In case of larger insertion forces, the controller can limit the insertion depth to prevent large needle deflections: this behavior can be influenced by acting on a specific tuning parameter, thus providing additional flexibility compared to previous implementations. Finally, the proposed solution is less sensitive to parameter uncertainties than the alternative controller.

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• Journal article
  Franco E, 2022,

  Model based eversion control of soft growing robots with pneumatic actuation

  , IEEE Control Systems Letters, Vol: 6, Pages: 2689-2694, ISSN: 2475-1456

  This letter investigates the model based position control of soft growing robots with pneumatic actuation that extend according to the principle known as eversion. A dynamical model of the system which accounts for the energy of the ideal gas is presented by employing the port-Hamiltonian formulation. A new control law is constructed with an energy shaping approach. An adaptive observer is employed to compensate the effect of external forces, including that of gravity. Numerical simulations indicate that the proposed controller is superior to simpler energy shaping algorithms.

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