Multilevel control of an anthropomorphic prosthetic hand for grasp and slip prevention

The success of grasping and manipulation tasks of commercial prosthetic hands is mainly related to amputee visual feedback since they are not provided either with tactile sensors or with sophisticated control. As a consequence, slippage and object falls often occur. This article wants to address the specific issue of enhancing grasping and manipulation capabilities of existing prosthetic hands, by changing the control strategy. For this purpose, it proposes a multilevel control based on two distinct levels consisting of (1) a policy search learning algorithm combined with central pattern generators in the higher level and (2) a parallel force/position control managing slippage events in the lower level. The control has been tested on an anthropomorphic robotic hand with prosthetic features (the IH2 hand) equipped with force sensors. Bi-digital and tri-digital grasping tasks with and without slip information have been carried out. The KUKA-LWR has been employed to perturb the grasp stability inducing controlled slip events. The acquired data demonstrate that the proposed control has the potential to adapt to changes in the environment and guarantees grasp stability, by avoiding object fall thanks to prompt slippage event detection

Sensors for Robotic Hands: A Survey of State of the Art

Recent decades have seen significant progress in the field of artificial hands. Most of the surveys, which try to capture the latest developments in this field, focused on actuation and control systems of these devices. In this paper, our goal is to provide a comprehensive survey of the sensors for artificial hands. In order to present the evolution of the field, we cover five year periods starting at the turn of the millennium. At each period, we present the robot hands with a focus on their sensor systems dividing them into categories, such as prosthetics, research devices, and industrial end-effectors.We also cover the sensors developed for robot hand usage in each era. Finally, the period between 2010 and 2015 introduces the reader to the state of the art and also hints to the future directions in the sensor development for artificial hands

Design, fabrication and stiffening of soft pneumatic robots

Although compliance allows the soft robot to be under-actuated and generalise its control, it also impacts the ability of the robot to exert forces on the environment. There is a trade-off between robots being compliant or precise and strong. Many mechanisms that change robots' stiffness on demand have been proposed, but none are perfect, usually compromising the device's compliance and restricting its motion capabilities. Keeping the above issues in mind, this thesis focuses on creating robust and reliable pneumatic actuators, that are designed to be easily manufactured with simple tools. They are optimised towards linear behaviour, which simplifies modelling and improve control strategies. The principle idea in relation to linearisation is a reinforcement strategy designed to amplify the desired, and limit the unwanted, deformation of the device. Such reinforcement can be achieved using fibres or 3D printed structures. I have shown that the linearity of the actuation is, among others, a function of the reinforcement density and shape, in that the response of dense fibre-reinforced actuators with a circular cross-section is significantly more linear than that of non-reinforced or non-circular actuators. I have explored moulding manufacturing techniques and a mixture of 3D printing and moulding. Many aspects of these techniques have been optimised for reliability, repeatability, and process simplification. I have proposed and implemented a novel moulding technique that uses disposable moulds and can easily be used by an inexperienced operator. I also tried to address the compliance-stiffness trade-off issue. As a result, I have proposed an intelligent structure that behaves differently depending on the conditions. Thanks to its properties, such a structure could be used in applications that require flexibility, but also the ability to resist external disturbances when necessary. Due to its nature, individual cells of the proposed system could be used to implement physical logic elements, resulting in embodied intelligent behaviours. As a proof-of-concept, I have demonstrated use of my actuators in several applications including prosthetic hands, octopus, and fish robots. Each of those devices benefits from a slightly different actuation system but each is based on the same core idea - fibre reinforced actuators. I have shown that the proposed design and manufacturing techniques have several advantages over the methods used so far. The manufacturing methods I developed are more reliable, repeatable, and require less manual work than the various other methods described in the literature. I have also shown that the proposed actuators can be successfully used in real-life applications. Finally, one of the most important outcomes of my research is a contribution to an orthotic device based on soft pneumatic actuators. The device has been successfully deployed, and, at the time of submission of this thesis, has been used for several months, with good results reported, by a patient

Bio-inspired robotic joint and manipulator : from biomechanical experimentation and modeling to human-like compliant finger design and control

textOne of the greatest challenges in controlling robotic hands is grasping and manipulating objects in unstructured and uncertain environments. Robotic hands are typically too rigid to react against unexpected impacts and disturbances in order to prevent damage. The human hands have great versatility and robustness due, in part, to the passive compliance and damping. Designing mechanical elements that are inspired by the nonlinear joint compliance of human hands is a promising solution to achieve human-like grasping and manipulation. However, the exact role of biomechanical elements in realizing joint stiffness is unknown. We conducted a series of experiments to investigate nonlinear stiffness and damping of the metacarpophalangeal (MCP) joint at the index finger. We designed a custom-made mechanism to integrate electromyography sensors (EMGs) and a motion capture system to collect data from 19 subjects. We investigated the relative contributions of muscle-tendon units and the MCP capsule ligament complex to joint stiffness with subject-specific modeling. The results show that the muscle-tendon units provide limited contribution to the passive joint compliance. This findings indicate that the parallel compliance, in the form of the capsule-ligament complex, is significant in defining the passive properties of the hand. To identify the passive damping, we used the hysteresis loops to investigate the energy dissipation function. We used symbolic regression and principal component analysis to derive and interpret the damping models. The results show that the nonlinear viscous damping depends on the cyclic frequency, and fluid and structural types of damping also exist at the MCP joint. Inspired by the nonlinear stiffness of the MCP joint, we developed a miniaturized mechanism that uses pouring liquid plastic to design energy storing elements. The key innovations in this design are: a) a set of nonlinear elasticity of compliant materials, b) variable pulley configurations to tune the stiffness profile, and c) pretension mechanism to scale the stiffness profile. The design exhibits human-like passive compliance. By taking advantage of miniaturized joint size and additive manufacturing, we incorporated the novel joint design in a novel robotic manipulator with six series elastic actuators (SEA). The robotic manipulator has passive joint compliance with the intrinsic property of human hands. To validate the system, we investigated the Cartesian stiffness of grasping with low-level force control. The results show that that the overall system performs a great force tracking with position feedback. The parallel compliance decreases the motor efforts and can stabilize the system.Mechanical Engineerin

Fingerprint-enhanced capacitive-piezoelectric flexible sensing skin to discriminate static and dynamic tactile stimuli

nspired by the structure and functions of the human skin, a highly sensitive capacitive‐piezoelectric flexible sensing skin with fingerprint‐like patterns to detect and discriminate between spatiotemporal tactile stimuli including static and dynamic pressures and textures is presented. The capacitive‐piezoelectric tandem sensing structure is embedded in the phalange of a 3D‐printed robotic hand, and a tempotron classifier system is used for tactile exploration. The dynamic tactile sensor, interfaced with an extended gate configuration to a common source metal oxide semiconductor field effect transistor (MOSFET), exhibits a sensitivity of 2.28 kPa−1. The capacitive sensing structure has nonlinear characteristics with sensitivity varying from 0.25 kPa−1 in the low‐pressure range (<100 Pa) to 0.002 kPa−1 in high pressure (≈2.5 kPa). The output from the presented sensor under a closed‐loop tactile scan, carried out with an industrial robotic arm, is used as latency‐coded spike trains in a spiking neural network (SNN) tempotron classifier system. With the capability of performing a real‐time binary naturalistic texture classification with a maximum accuracy of 99.45%, the presented bioinspired skin finds applications in robotics, prosthesis, wearable sensors, and medical devices

Design and Implement Towards Enhanced Physical Interactive Performance Robot Bodies

In this thesis, it will introduce the design principle and implement details towards enhanced physical interactive performance robot bodies, which are more specically focused on under actuated principle robotic hands and articulated leg robots. Since they both signicantly function as the physical interactive robot bodies against external environment, while their current performance can hardly satisfy the requirement of undertaking missions in real application. Regarding to the enhanced physical interactive performances, my work will emphasis on the three following specific functionalities, high energy efficiency, high strength and physical sturdiness in both robotics actuation and mechanism. For achieving the aforementioned targets, multiple design methods have been applied, rstly the elastic energy storage elements and compliant actuation have been adopted in legged robots as Asymmetrical Compliant Actuation (ACA), implemented for not only single joint but also multiple joints as mono and biarticulation congurations in order to achieve higher energy effciency motion. Secondly the under actuated principle and modular nger design concept have been utilized on the development of robotic hands for enhancing the grasping strength and physical sturdiness meanwhile maintaining the manipulation dexterity. Lastly, a novel high payload active tuning Parallel Elastic Actuation (PEA) and Series Elastic Actuation (SEA) have been adopted on legged robots for augmenting energy eciency and physical sturdiness. My thesis contribution relies on the novel design and implement of robotics bodies for enhancing physical interactive performance and we experimentally veried the design effectiveness in specic designed scenario and practical applications

The "Federica" hand: a simple, very efficient prothesis

Hand prostheses partially restore hand appearance and functionalities. Not everyone can afford expensive prostheses and many low-cost prostheses have been proposed. In particular, 3D printers have provided great opportunities by simplifying the manufacturing process and reducing costs. Generally, active prostheses use multiple motors for fingers movement and are controlled by electromyographic (EMG) signals. The "Federica" hand is a single motor prosthesis, equipped with an adaptive grasp and controlled by a force-myographic signal. The "Federica" hand is 3D printed and has an anthropomorphic morphology with five fingers, each consisting of three phalanges. The movement generated by a single servomotor is transmitted to the fingers by inextensible tendons that form a closed chain; practically, no springs are used for passive hand opening. A differential mechanical system simultaneously distributes the motor force in predefined portions on each finger, regardless of their actual positions. Proportional control of hand closure is achieved by measuring the contraction of residual limb muscles by means of a force sensor, replacing the EMG. The electrical current of the servomotor is monitored to provide the user with a sensory feedback of the grip force, through a small vibration motor. A simple Arduino board was adopted as processing unit. The differential mechanism guarantees an efficient transfer of mechanical energy from the motor to the fingers and a secure grasp of any object, regardless of its shape and deformability. The force sensor, being extremely thin, can be easily embedded into the prosthesis socket and positioned on both muscles and tendons; it offers some advantages over the EMG as it does not require any electrical contact or signal processing to extract information about the muscle contraction intensity. The grip speed is high enough to allow the user to grab objects on the fly: from the muscle trigger until to the complete hand closure, "Federica" takes about half a second. The cost of the device is about 100 US$. Preliminary tests carried out on a patient with transcarpal amputation, showed high performances in controlling the prosthesis, after a very rapid training session. The "Federica" hand turned out to be a lightweight, low-cost and extremely efficient prosthesis. The project is intended to be open-source: all the information needed to produce the prosthesis (e.g. CAD files, circuit schematics, software) can be downloaded from a public repository. Thus, allowing everyone to use the "Federica" hand and customize or improve it

A shape memory alloy-based biomimetic robotic hand : design, modelling and experimental evaluation

Every year more the 400,000 people are subject to an upper limb amputation. Projections foresee that this number may double by the 2050. Infections, trauma, cancer, or complications that arise in blood vessels represent the main causes for amputations. The access to prosthetic care is worldwide extremely limited. This is mainly due to the high cost both of commercially available prostheses and of the rehabilitation procedure which every prostheses user has to endure. Aside from high costs, commercially available hand prostheses have faced high rejection rates, mainly due to the their heavy weight, noisy operation and also to the unnatural feel of the fingers. To overcome these limitations, new materials, such as Shape Memory Alloys (SMAs), have been considered as potential candidate actuators for these kind of devices. In order to provide a contribution in the development of performant and easily affordable hand prostheses, the development of a novel and cost-effective five-fingered hand prototype actuated by Shape Memory Alloy (SMA) wires is presented in this work. The dissertation starts with the description of a first generation of a SMA actuated finger. Structure assemblage and performances in term of force, motion and reactiveness are investigated to highlight advantages and disadvantages of the prototype. In order to improve the achievable performances, a second generation of SMA actuated finger having soft features is introduced. Its structure, a five-fingered hand prosthesis having intrinsically elastic fingers, capable to grasp several types of objects with a considerable force, and an entirely 3D printed structure is then presented. Comparing this prototype with the most important prostheses developed so far, relevant advantages especially in term of noiseless actuation, cost, weight, responsiveness and force can be highlighted. A finite element based framework is then developed, to enable additional structure optimization and further improve the SMA finger performances. On the same time, a concentrated parameters physics-based model is formulated to allow, in the future, an easier control of the device, characterized by strong nonlinearities mainly due to the Shape Memory alloy hysteretic behavior.Jedes Jahr werden weltweit bei mehr als 400.000 Menschen Amputationen der oberen Gliedmaßen durchgeführt. Prognosen gehen davon aus, dass sich diese Zahl bis zum Jahr 2050 verdoppeln wird. Hauptursachen der Amputationen sind Infektionen, Unfälle, Krebs oder Durchblutungsstörungen. Der Zugang zu prothetischer Versorgung ist besonders in den Entwicklungsländern stark eingeschränkt. Dies liegt vor allem an den hohen Kosten sowohl der im Handel erhältlichen Prothesen als auch des Rehabilitationsprozesses, den jeder Prothesenträger durchlaufen muss. Neben den hohen Kosten haben kommerziell erhältliche Handprothesen aufgrund ihres hohen Gewichts, des lauten Betriebes und auch des unnatürlichen Gefühls hohe Ablehnungsraten. Um diese Einschränkungen zu überwinden, wurden neue Materialien, wie z.B. Formgedächtnislegierungen (SMAs), als potenzielle Materialien für den Antrieb von Prothesen untersucht . Um einen Beitrag zur Entwicklung von leistungsfähigen und erschwinglichen Handprothesen zu leisten, wird in dieser Arbeit die Entwicklung eines neuartigen und kostengünstigen Fünf-Finger-Handprototyps vorgestellt, der durch Drähte aus Formgedächtnislegierungen aktiviert wird. Die Doktorarbeit beginnt mit der Beschreibung der ersten Generation eines SMA-aktivierten Fingers. Zuerst wird der Aufbau und das Wirkungsprinzip des SMA Fingers erläutert und die Leistungs- und Bewegungsfähigkeit des Systems untersucht sowie Vor- und Nachteile des Prototyps dargestellt. Anschließend, um die erreichbare Leistungsfähigkeit zu verbessern, wird eine zweite Generation von SMA-gesteuerten Fingern vorgestellt, die eine vollständig in 3D gedruckte Struktur aufweisen. Diese Fünffinger-Handprothese mit inhärent elastischen Fingern ermöglicht nicht nur das Greifen unterschiedlich geformter Objekte sondern auch das Heben und Halten schwerer Gegenstände. Dieser neuartige Prototyp wird mit den wichtigsten bisher entwickelten Prothesen verglichen und die relevanten Vorteile insbesondere in Bezug auf geräuschlose Ansteuerung, Kosten, Gewicht, Reaktionszeit und Kraft hervorgehoben. Abschließend wird ein Finite-Elemente-Modell entwickelt, mit Hilfe dessen die Fingerstruktur weiter optimiert und die Leistungsfähigkeit des SMA-Fingers noch verbessert werden kann. Zusätzlich wird ein Konzentriertes-Parameter-Modell formuliert, um, in der Zukunft, eine leichtere Regelung des Systems zu ermöglichen. Dieses ist notwendig, da der SMA-Finger starke Nichtlinearitäten aufweist, die auf das hysteretische Verhalten der Formgedächtnislegierung zurückzuführen sind