Growing Structures

Eversion Robots for Extreme Environments

A Technology Readiness Level (TRL) 4 Project

This work is done in collaboration with the National Centre for Nuclear Robotics (NCNR) to develop soft manipulators, so-called eversion robots, made from fabrics, and capable of growing from their tip to tens of metres in length in a fashion similar to growing vine. I have developed innovative approaches so that these structures can elongate from the tip as well as to precisely control the motion of these robotic manipulators achieving multiple degrees of freedom in bending. They are compliant and therefore are capable of safely interacting with the environment around them as they grow through narrow pipelines and tight openings. These pneumatic and tendon driven robots will greatly enhance the capabilities of conducting complex sensing and manipulation tasks in remote, constrained and otherwise inaccessible areas.

Complementing these actuation techniques, we are developing low cost bending sensors based on optical fibres that can be embedded into such soft eversion robots as well as fabric-based grippers to provide sensory feedback. The low transmission losses in the optical fibres will enable placing the readout electronics far from the working areas which are potentially radioactive, achieving a greatly improved sensor lifetime when compared to standard sensors relying on sensitive electronics.

EPAM: Eversive Pneumatic Artificial Muscle

Pneumatic Artificial Muscles, which are lightweight actuators with inherently compliant behavior, are broadly recognized as safe actuators for devices that assist or interact with humans. This paper presents the design and implementation of a soft pneumatic muscle based on the eversion principle - Eversive Pneumatic Artificial Muscle (EPAM). The proposed pneumatic muscle exerts a pulling force when elongating based on the eversion (growing) principle. It is capable of extending its length by a minimum of 100% when fully inflated. In contrast to other soft pneumatic actuators, such as the McKibben's muscle, which contract when pressurized, our EPAM extends when pressure is increased. Additionally, important advantages of employing the eversion principle are the capability to achieve high pulling forces and an efficient force to pressure ratio. In a pivoting joint/link mechanism configuration the proposed muscle provides motion comparable to human arm flexion and extension. In this work, we present the design of the proposed EPAM, study its behavior, and evaluate its displacement capability and generated forces in an agonistic and antagonistic joint/link arrangement. The developed EPAM prototype with a diameter of 25 mm and a length of 250 mm shows promising results, capable of exerting 10 N force when pressurized up to 62 KPa.

Eversion Robots in the Voids under the Houses and Incavity Walls

A Technology Readiness Level (TRL) 4 Project

In this project, in collaboration with Q-bot, a London-based robotic company. The aim is to design, manufacture and validate robust, soft robots to remotely inspect insulation below the ground floor of domestic dwellings, especially in areas of restricted access, such as in the void under the house and incavity walls.

Extensions of the projects will explore the development of robots in extreme and challenging environments of inaccessible areas of buildings (initially), infrastructure networks (including sewers) as well as nuclear site inspection The project will deliver a stiffness-controllable and flexible robot prototype that will be validated in demanding environments.

At the end of the project, a proof of concept prototype is developed that validates in demanding environments as well as developing further the service robotics business model (and validating it in various industrial segments using the Lean Start-up principles).

Publications

A Suite of Robotic Solutions for Nuclear Waste Decommissioning

Dealing safely with nuclear waste is an imperative for the nuclear industry. Increasingly, robots are being developed to carry out complex tasks such as perceiving, grasping, cutting, and manipulating waste. Radioactive material can be sorted, and either stored safely or disposed of appropriately, entirely through the actions of remotely controlled robots. Radiological characterisation is also critical during the decommissioning of nuclear facilities. It involves the detection and labelling of radiation levels, waste materials, and contaminants, as well as determining other related parameters (e.g., thermal and chemical), with the data visualised as 3D scene models. This paper overviews work by researchers at the QMUL Centre for Advanced Robotics (ARQ), a partner in the UK EPSRC National Centre for Nuclear Robotics (NCNR), a consortium working on the development of radiation-hardened robots fit to handle nuclear waste. Three areas of nuclear-related research are covered here: human–robot interfaces for remote operations, sensor delivery, and intelligent robotic manipulation.

Highly Manoeuvrable Eversion Robot Based on Fusion of Function with Structure

Despite their soft and compliant bodies, most of today’s soft robots have limitations when it comes to elongation or extension of their main structure. In contrast to this, a new type of soft robot called the eversion robot can grow longitudinally, exploiting the principle of eversion. Eversion robots can squeeze through narrow openings, giving the possibility to access places that are inaccessible by conventional robots. The main drawback of these types of robots is their limited bending capability due to the tendency to move along a straight line. In this paper, we propose a novel way to fuse bending actuation with the robot’s structure. We devise an eversion robot whose body forms both the central chamber that acts as the backbone as well as the actuators that cause bending and manoeuvre the manipulator. The proposed technique shows a significantly improved bending capability compared to externally attaching actuators to an eversion robot showing a 133% improvement in bending angle. Due to the increased manoeuvrability, the proposed solution is a step towards the employment of eversion robots in remote and difficult-to-access environments.

An Inhomogeneous Structured Eversion Actuator

Soft actuators are free from any rigid, bulky, and hard components. This is greatly beneficial towards achieving compliant actuation and safe interactions in robots. Inspired by the eversion principle, we develop a novel soft actuator of the inhomogeneous cross-section that can linearly extend and achieve a large payload capability. The proposed soft actuator is a hollow sleeve, made from an airtight fabric, and features a top part of cylindrical shape and a bottom part of a conical shape. Unlike conventional eversion robots that extend unilaterally from the tip, in this proposed actuator the top cylindrical part and the bottom conical part are partially folded inwards so that the two tips are attached together. When pneumatic pressure is applied, the cylindrical part everts increasing in length while the conical section reduces in length folding inwards. The actuator achieves linear strains of 120% and can generate a force 84 N at a low pressure of 62 kPa. We develop a theoretical model to describe the force and strain characteristics of the actuator during eversion from conical shape to cylindrical shape. The results showcase a step towards large strain, high force actuators for safe and compliant robots.

Model-Based Pose Control of Inflatable Eversion Robot With Variable Stiffness

Plant-inspired inflatable eversion robots with their tip growing behaviour have recently emerged. Because they extend from the tip, eversion robots are particularly suitable for applications that require reaching into remote places through narrow openings. Besides, they can vary their structural stiffness. Despite these essential properties which make the eversion robot a promising candidate for applications involving cluttered environments and tight spaces, controlling their motion especially laterally has not been investigated in depth. In this letter, we present a new approach based on model-based kinematics to control the eversion robot's tip position and orientation. Our control approach is based on Euler-Bernoulli beam theory which takes into account the effect of the internal inflation pressure to model each robot bending segment for various conditions of structural stiffness. We determined the parameters of our bending model by performing a least-square technique based on the pressure-bending data acquired from an experimental study. The model is then used to develop a pose controller for the tip of our eversion robot. Experimental results show that the proposed control strategy is capable of guiding the tip of the eversion robot to reach a desired position and orientation whilst varying its structural stiffness.

Observer-based Control of Inflatable Robot with Variable Stiffness

In the last decade, soft robots have been at the forefront of a robotic revolution. Due to the flexibility of the soft materials employed, soft robots are equipped with a capability to execute new tasks in new application areas -beyond what can be achieved using classical rigid-link robots. Despite these promising properties, many soft robots nowadays lack the capability to exert sufficient force to perform various real-life tasks. This has led to the development of stiffness-controllable inflatable robots instilled with the ability to modify their stiffness during motion. This new capability, however, poses an even greater challenge for robot control. In this paper, we propose a model-based kinematic control strategy to guide the tip of an inflatable robot arm in its environment. The bending of the robot is modelled using an Euler-Bernoulli beam theory which takes into account the variation of the robot's structural stiffness. The parameters of the model are estimated online using an observer based on the Extended Kalman Filter (EKF). The parameters' estimates are used to approximate the Jacobian matrix online and used to control the robot's tip considering also variations in the robot's stiffness. Simulation results and experiments using a fabric-based planar 3-degree-of-freedom (DOF) inflatable manipulators demonstrate the promising performance of the proposed control algorithm.

Payload Capabilities and Operational Limits of Eversion Robots

Recent progress in soft robotics has seen new types of actuation mechanisms based on apical extension which allows robots to grow to unprecedented lengths. Eversion robots are a type of robots based on the principle of apical extension offering excellent maneuverability and ease of control allowing users to conduct tasks from a distance. Mechanical modelling of these robotic structures is very important for understanding their operational capabilities. In this paper, we model the eversion robot as a thin-walled cylindrical beam inflated with air pressure, using Timoshenko beam theory considering rotational and shear effects. We examine the various failure modes of the eversion robots such as yielding, buckling instability and lateral collapse, and study the payloads and operational limits of these robots in axial and lateral loading conditions. Surface maps showing the operational boundaries for different combinations of the geometrical parameters are presented. This work provides insights into the design of eversion robots and can pave the way towards eversion robots with high payload capabilities that can act from long distances.

EPAM: Eversive Pneumatic Artificial Muscle

Pneumatic Artificial Muscles, which are lightweight actuators with inherently compliant behavior, are broadly recognized as safe actuators for devices that assist or interact with humans. This paper presents the design and implementation of a soft pneumatic muscle based on the eversion principle - Eversive Pneumatic Artificial Muscle (EPAM). The proposed pneumatic muscle exerts a pulling force when elongating based on the eversion (growing) principle. It is capable of extending its length by a minimum of 100% when fully inflated. In contrast to other soft pneumatic actuators, such as the McKibben's muscle, which contract when pressurized, our EPAM extends when pressure is increased. Additionally, important advantages of employing the eversion principle are the capability to achieve high pulling forces and an efficient force to pressure ratio. In a pivoting joint/link mechanism configuration the proposed muscle provides motion comparable to human arm flexion and extension. In this work, we present the design of the proposed EPAM, study its behavior, and evaluate its displacement capability and generated forces in an agonistic and antagonistic joint/link arrangement. The developed EPAM prototype with a diameter of 25 mm and a length of 250 mm shows promising results, capable of exerting 10 N force when pressurized up to 62 KPa.

Plant-Inspired Soft Pneumatic Eversion Robot

Due to safety concerns in human-robot interaction, researchers are moving from rigid-component robotics to soft robotics. This paper presents the design of a novel linear pneumatic robot structure based on the eversion principle. Experiments are carried out to investigate the forces that this robot can exert. This robot was successfully able to exert pushing force from its distal end and pulling force from its stationary end while extending along the longitudinal direction.