A review of friction models in interacting joints for durability design.

This paper presents a comprehensive review of friction modelling to provide an understanding of design for durability within interacting systems. Friction is a complex phenomenon and occurs at the interface of two components in relative motion. Over the last several decades, the effects of friction and its modelling techniques have been of significant interests in terms of industrial applications. There is however a need to develop a unified mathematical model for friction to inform design for durability within the context of varying operational conditions. Classical dynamic mechanisms model for the design of control systems has not incorporated friction phenomena due to non-linearity behaviour. Therefore, the tribological performance concurrently with the joint dynamics of a manipulator joint applied in hazardous environments needs to be fully analysed. Previously the dynamics and impact models used in mechanical joints with clearance have also been examined. The inclusion of reliability and durability during the design phase is very important for manipulators which are deployed in harsh environmental and operational conditions. The revolute joint is susceptible to failures such as in heavy manipulators these revolute joints can be represented by lubricated conformal sliding surfaces. The presence of pollutants such as debris and corrosive constituents has the potential to alter the contacting surfaces, would in turn affect the performance of revolute joints, and puts both reliability and durability of the systems at greater risks of failure. Key literature is identified and a review on the latest developments of the science of friction modelling is presented here. This review is based on a large volume of knowledge. Gaps in the relevant field have been identified to capitalise on for future developments. Therefore, this review will bring significant benefits to researchers, academics and industrial professionals

Monitoring bioinspired fibrillar grippers by contact observation and machine learning

The remarkable properties of bio-inspired microstructures make them extensively accessible for various applications, including industrial, medical, and space applications. However, their implementation especially as grippers for pick-and-place robotics can be compromised by multiple factors. The most common ones are alignment imperfections with the target object, unbalanced stress distribution, contamination, defects, and roughness at the gripping interface. In the present work, three different approaches to assess the contact phenomena between patterned structures and the target object are presented. First, in-situ observation and machine learning are combined to realize accurate real-time predictions of adhesion performance. The trained supervised learning models successfully predict the adhesion performance from the contact signature. Second, two newly developed optical systems are compared to observe the correct grasping of various target objects (rough or transparent) by looking through the microstructures. And last, model experiments are provided for a direct comparison with simulation efforts aiming at a prediction of the contact signature and an analysis of the rate and preload-dependency of the adhesion strength of a soft polymer film in contact with roughness-like surface topography. The results of this thesis open new perspectives for improving the reliability of handling systems using bioinspired microstructures.Durch die besonderen Eigenschaften bioinspirierter Mikrostrukturen können diese für verschiedene Anwendungen genutzt werden, einschließlich industrieller, medizinischer und Weltraumanwendungen. Ihre Implementierung, insbesondere als Greifer für Pick-and-Place-Robotiker, kann jedoch durch mehrere Faktoren beeinträchtigt werden. Am häufigsten sind Ausrichtungsmängel an das Zielobjekt, unausgeglichene Spannungsverteilungen, Defekte und Rauheit an der Greifschnittstelle. Die vorliegende Arbeit zeigt drei verschiedene Ansätze, um den Kontakt zwischen strukturierten Adhäsiven und Zielobjekten zu untersuchen. Zunächst werden in-situ Beobachtungen und maschinelles Lernen kombiniert, um Echtzeitvorhersagen der Adhäsionsleistung zu ermöglichen. Die trainierten Modelle werden verwendet, um die Haftungsleistung anhand der Kontaktsignatur des Pads erfolgreich zu prognostizieren. Anschließend werden zwei neu entwickelte, optische Systeme verglichen, mit denen das korrekte ” Greifen“ von verschiedenen Objekten (mit rauen oder undurchsichtigen Oberflächen) durch die Mikrostrukturen live verfolgt werden kann. Zuletzt werden Modellexperimente durchgeführt, die mit Simulationen der Signatur des Kontakts einer weichen Polymerschicht mit einer idealisierten rauen Gegenfläche direkt verglichen werden können. Die Ergebnisse dieser Arbeit eröffnen neue Perspektiven zur zuverlässigeren Verwendung von Handhabungssystemen mit bioinspirierten Mikrostrukturen.Leibniz Competition Grant MUSIGAND (No. K279/2019) awarded to Eduard Arz

Functional surface microstructures inspired by nature – From adhesion and wetting principles to sustainable new devices

In the course of evolution nature has arrived at startling materials solutions to ensure survival. Investigations into biological surfaces, ranging from plants, insects and geckos to aquatic animals, have inspired the design of intricate surface patterns to create useful functionalities. This paper reviews the fundamental interaction mechanisms of such micropatterns with liquids, solids, and soft matter such as skin for control of wetting, self-cleaning, anti-fouling, adhesion, skin adherence, and sensing. Compared to conventional chemical strategies, the paradigm of micropatterning enables solutions with superior resource efficiency and sustainability. Associated applications range from water management and robotics to future health monitoring devices. We finally provide an overview of the relevant patterning methods as an appendix

Functional surface microstructures inspired by nature : From adhesion and wetting principles to sustainable new devices

In the course of evolution nature has arrived at startling materials solutions to ensure survival. Investigations into biological surfaces, ranging from plants, insects and geckos to aquatic animals, have inspired the design of intricate surface patterns to create useful functionalities. This paper reviews the fundamental interaction mechanisms of such micropatterns with liquids, solids, and soft matter such as skin for control of wetting, self-cleaning, anti-fouling, adhesion, skin adherence, and sensing. Compared to conventional chemical strategies, the paradigm of micropatterning enables solutions with superior resource efficiency and sustainability. Associated applications range from water management and robotics to future health monitoring devices. We finally provide an overview of the relevant patterning methods as an appendix

Compliant contact force models in multibody dynamics : evolution of the Hertz contact theory

Over the last decades, several compliant contact force models have been proposed. However, no complete and systematic comparison has been done on these models, which provides information on their range of application and accuracy for use in different contact scenarios. Thus, the selection of an appropriate model for a given contact problem is still an important and challenging issue to be addressed. The Hertzian contact theory remains the foundation for almost all of the available force models, but by itself, it is not appropriate for most impacts in practice, due to the amount of energy dissipated during the impact. A good number of contact force models have been offered that augment the Hertzian law with a damping term to accommodate the energy loss during the impact process for small or moderate impact velocities. In this work, the main issues associated with the most common compliant contact force models of this type are analyzed. Results in terms of the dynamic simulations of multibody systems are presented, which allow for the comparison of the similarities and differences among the models considered.Fundação para a Ciência e a Tecnologia (FCT) - DACHOR - Multibody Dynamics and Control of Hybrid Active Orthoses (MIT-Pt/BSHHMS/0042/2008), BIOJOINTS - Development of advanced biological joint models for human locomotion biomechanics (PTDC/EMEPME/ 099764/2008), SFRH/BD/40164/2007, SFRH/BD/64477/200

Modeling and simulation in tribology across scales: An overview

This review summarizes recent advances in the area of tribology based on the outcome of a Lorentz Center workshop surveying various physical, chemical and mechanical phenomena across scales. Among the main themes discussed were those of rough surface representations, the breakdown of continuum theories at the nano- and micro-scales, as well as multiscale and multiphysics aspects for analytical and computational models relevant to applications spanning a variety of sectors, from automotive to biotribology and nanotechnology. Significant effort is still required to account for complementary nonlinear effects of plasticity, adhesion, friction, wear, lubrication and surface chemistry in tribological models. For each topic, we propose some research directions

Adhesive Wear Phenomena in High Performance Polyaryletherketones (PAEK) Polymers

Adhesive wear is one of the most difficult types to study and is especially challenging for polymers. Such wear processes involve the mutual sticking of surface asperities followed by removal of debris from the bulk. This differs from abrasive wear in which debris is formed due to the penetration of hard rough asperities into the softer surface. Such descriptions have served the polymer tribology community for decades and are well suited for post-mortem analysis of wear surfaces. For instance, the presence of rippled features on the wear surface and large flake shaped debris are typical indicators of adhesive wear. However, this approach offers little insight into the underlying physics that occur at the interface. The overall objective of this research is to gain fundamental knowledge of adhesive wear phenomena in polyaryletherketone (PAEK) polymers. Ultimately, the hope is to correlate the observed surface damage and friction response with material science based explanations. Since no true adhesive wear test configuration exists, a top down approach was used in designing a set of experimental conditions. This was done with a multi-axis tribometer capable of being programmed to a wide array of displacements and trajectories. A catastrophic form of adhesive wear is termed fretting and results from the repeated slip of mutually loaded contacts. Using the multi axis tribometer PAEK polymers were studied in both multi directional sliding and fretting configurations with varied environmental conditions. An important aspect of PEEK tribology is the surface temperature reached during sliding. Infrared thermography was used to observe the full field temperature map of PEEK during ball-on-disc sliding. Additionally, friction studies were performed with steel and sapphire counterfaces. The results of this study illustrate the important role transfer films play in determining both the friction and temperature response of the PEEK wear interface. The formation of transfer films resembles a unidirectional drawing process. Polarized FTIR-ATR measurements were used to assess chain orientation in the friction formed PEEK on steel transfer films. The results of these studies serve to better elucidate underlying mechanisms involved in adhesive wear of PAEK polymers

Working together: a review on safe human-robot collaboration in industrial environments

After many years of rigid conventional procedures of production, industrial manufacturing is going through a process of change toward flexible and intelligent manufacturing, the so-called Industry 4.0. In this paper, human-robot collaboration has an important role in smart factories since it contributes to the achievement of higher productivity and greater efficiency. However, this evolution means breaking with the established safety procedures as the separation of workspaces between robot and human is removed. These changes are reflected in safety standards related to industrial robotics since the last decade, and have led to the development of a wide field of research focusing on the prevention of human-robot impacts and/or the minimization of related risks or their consequences. This paper presents a review of the main safety systems that have been proposed and applied in industrial robotic environments that contribute to the achievement of safe collaborative human-robot work. Additionally, a review is provided of the current regulations along with new concepts that have been introduced in them. The discussion presented in this paper includes multidisciplinary approaches, such as techniques for estimation and the evaluation of injuries in human-robot collisions, mechanical and software devices designed to minimize the consequences of human-robot impact, impact detection systems, and strategies to prevent collisions or minimize their consequences when they occur

Interfacial Dissipative Phenomena in Tribomechanical Systems

The book is a collection of articles on the themes of contact mechanics and non-linear dynamics. In particular, the contribution focus on the mechanisms that lead to interfacial energy dissipation, which is a crucial quantity to determine in order to correctly predict the non-linear dynamic response of mechanical systems. The book is a collection of nine journal papers, among those one editorial, one review paper, and seven articles. The papers consider different dissipative mechanisms, such as Coulomb friction, interfacial adhesion, and viscoelasticity, and study how the system response and stability is influenced by the interfacial interactions. The review paper describes old and recent test rigs for friction and wear measurements, focusing on their performance and range of operability