Local Positive Velocity Feedback for the movement control of elastic joints in closed kinematic chains : a modelling and simulation study of a 2DoF arm and a 3DoF insect leg

Schneider A. Local Positive Velocity Feedback for the movement control of elastic joints in closed kinematic chains : a modelling and simulation study of a 2DoF arm and a 3DoF insect leg. Bielefeld (Germany): Bielefeld University; 2006.In der Beinbewegungssteuerung von laufenden Tieren (z.B. in unserem Modellsystem, der indischen Stabheuschrecke Carausius morosus) unterscheidet man Stemm- und Schwingbewegungen. Während einer Schwingbewegung hat das schwingende Bein keinerlei Objektkontakt, da es vom Boden abgehoben duch die Luft nach vorne geführt wird. Das Bein kann als offene kinematische Kette betrachtet und jedes Gelenk der Kette frei bewegt werden. Während der Stemmbewegung haben alle beteiligten Beine Bodenkontakt und bilden somit geschlossene kinematische Ketten. Die Gelenkwinkel derjenigen Beine, die an diesen geschlossenen kinematischen Ketten beteiligt sind, sind nicht mehr frei wählbar. Eine beliebige Einzelbewegung eines Gelenks führt zu Verspannungen in den kinematischen Ketten, die nur durch die aktive (entspannende) Bewegung anderer Gelenke aufgelöst werden können. Ähnliche Probleme treten auch bei Bewegungen mit Armen und Händen auf, wenn diese Manipulationsaufgaben mit Objektkontakt ausführen (z.B. beim Öffnen einer Tür durch einen Menschen). Aufgabenstellungen dieser Art werden in der Robotik unter dem Begriff "compliant motion tasks" zusammengefasst. Beispiele hierfür sind Kontaktschweißen, kooperative Manipulation von Objekten durch mehrere Roboter, Pick-and-Place Aufgaben bei Montagerobotern und, wie erwähnt, auch Stemmbewegungen bei Laufmaschinen. Klassische Lösungsansätze für diese Art von Problemen basieren auf dem "hybrid control" Ansatz von Raibert und Craig (Raibert and Craig, 1981, Trans. of the ASME, 102: 126-133) oder auf dem "impedance control" Ansatz von Hogan (Hogan, 1985, ASME J. Dynam. Syst., Meas., Contr., 107: 1-23). Für die Ansteuerung einer sechsbeinigen Laufmaschine mit insgesamt 18 Gelenken müssen dafür die entsprechenden kinematischen und dynamischen Gleichungen bekannt sein und in jedem Regleraufruf neu berechnet werden. Es scheint unwahrscheinlich, dass Tiere diese Berechnungen explizit durchführen. Cruse und Mitarbeiter (Cruse et al., 1995, Advances in Artificial Life, 668-678) schlugen vor, dass Insekten diese Aufgabe unter Ausnutzung der in der Literatur vielfach beschriebenen Reflexumkehr (auch Unterstützungsreflex) bewältigen (siehe z.B. Bässler, 1976, Biol. Cybernetics, 24: 47-49). Bei der Reflexumkehr unterstützt ein Regelmechanismus, der im ruhenden Tier für die Beibehaltung einer Gelenksposition bei äußeren Störungen sorgt, im aktiven Tier eine passive Bewegung und verstärkt diese aktiv. Nimmt man nun im stemmenden Tier eine aktive Bewegung eines Gelenks an, so wirkt sich diese mechanisch vermittelt über die geschlossenen Ketten auf alle anderen Gelenke aus. Der Unterstützungsreflex in den anderen Gelenken führt dazu, dass diese die angeregte Bewegung mitmachen und verstärken. Das Ergebnis ist eine koordinierte Stemmbewegung, die von den lokal geregelten Gelenken gemeinsam ausgeführt wird, obwohl diese nicht neuronal miteinander kommunizieren und keine zentrale Instanz einen vorausberechneten Bewegungsplan ausgibt. In der vorliegenden Arbeit wird diese Hypothese aufgegriffen und quantitativ überprüft. Es werden verschiedene elastische Gelenkmodelle entwickelt, die als Grundlage für die Implementierung eines Unterstützungsreflex dienen. Der Unterstützungsreflex als solcher wird in Form von Lokaler Positiver Geschwindigkeitsrückkopplung (Local Positive Velocity Feedback, LPVF) hergeleitet und seine Funktionsfähigkeit mit einem Standardtest, dem einarmigen Kurbeln, getestet. Die wichtigste Eigenschaft, nämlich die Fähigkeit, verschiedene Gelenke ohne direkte Kommunikation zu koordinieren, wird damit nachgewiesen. In einem weiteren Schritt wird gezeigt, dass eine Erweiterung des Ansatzes durch Einführung einer Leistungssteuerung dazu führt, dass die Koordinationsfähigkeit selbst dann erhalten bleibt, wenn eine stemmende Gliedmaße große Kräfte, z.B. gegen eine äußere Trägheitskraft, aufbringen muss. Das Regelungskonzept wird auf einer dynamischen Einbeinsimulation getestet, die Funktionsfähigkeit demonstriert und mit den biologischen Daten von aktivierten Tieren verglichen. In einem letzten Schritt wird der LPVF-Regler mit einem Stehregler kombiniert. Der entstandene Gesamtregler erklärt biologische Befunde aus der Lauf- und aus der Stehdomäne

Mechanisms of deformation and energy dissipation in antler and arthropod cuticle with bio-inspired investigations

PhDBio-composite hierarchical materials have attracted the interest of the academic community operating in the field of bio-inspired materials for their outstanding mechanical properties achieved via lightweight structural designs. Antler and mantis shrimp’s cuticle are extreme examples of materials naturally optimised to resist impacts and bear dynamic loading. Firstly, a class of finite-element fibril models was developed to explain the origin of heterogeneous fibrillar deformation and hysteresis from the nanostructure of antler. Results were compared to synchrotron X-ray data and demonstrated that the key structural motif enabling a match to experimental data is an axially staggered arrangement of stiff mineralised collagen fibrils coupled with weak, damageable interfibrillar interfaces. Secondly, the cuticle of the crustacean Odontodactylus scyllarus, known as peacock mantis shrimp, was investigated. At the nanoscale it consists of mineralised chitin fibres and calcified protein matrix, which form plywood layers at the microscale. Lamination theory was used to calculate fibrillar deformation and reorientation and, in addition, an analytical formulation was used to decouple in-plane fibre reorientation from diffraction intensity changes induced by 3D lamellae tilting. This animal also attracted my attention for using its hammer-like appendages to attack and destroy the shells of prey with a sequence of two strikes. Inspired by this double impact strategy, I performed a set of parametric finite-element simulations of single, double and triple mechanical hits, to compute the damage energy of the target. My results reveal that the crustacean attack strategy has the most damaging effect among the double impact cases, and lead me to hypothesise, that optimal damaging dynamics exists, depending on the sequence of consecutive impacts and on their time separation values. These new insights may provide useful indications for the design of bio-inspired materials for high load-bearing applications

Sensor based pre-symptomatic detection of pests and pathogens for precision scheduling of crop protection products

Providing global food security requires a better understanding of how plants function and how their products, including important crops are influenced by environmental factors. Prominent biological factors influencing food security are pests and pathogens of plants and crops. Traditional pest control, however, has involved chemicals that are harmful to the environment and human health, leading to a focus on sustainability and prevention with regards to modern crop protection. A variety of physical and chemical analytical tools is available to study the structure and function of plants at the whole-plant, organ, tissue, cellular, and biochemical levels, while acting as sensors for decision making in the applied crop sciences. Vibrational spectroscopy, among them mid-infrared and Raman spectroscopy in biology, known as biospectroscopy are well-established label-free, nondestructive, and environmentally friendly analytical methods that generate a spectral “signature” of samples using mid-infrared radiation. The generated wavenumber spectrum containing hundreds of variables as unique as a biochemical “fingerprint”, and represents biomolecules (proteins, lipids, carbohydrates, nucleic acids) within biological samples. Spectral “biomarkers” generated by biospectroscopy is useful for the discrimination of distinct as well as closely related biomaterials, for various applications. Applications within the plant and crop sciences has been limited to date, especially for the investigation of dynamic biological processes in intact plant tissues. Even more scarce is the application of biospectroscopy to plant interactions with pests and pathogens. To adequately probe in vivo plant-environment interactions, surface structures of intact plant tissues such as leaves, and fruit need to be characterized. Infrared light energy can measure plant epidermal structures including the cuticle and cell wall for chemical profiling of different varieties and cultivars, as well as physiological applications such as plant health monitoring and disease detection. A review of the application of biospectroscopy to study plant and crop biology reveals the potential of biospectroscopy as a prominent technology for fundamental plant research and applied crop science. The application of biospectroscopy for in vivo plant analysis, to elucidate spectral alterations indicative of pest and pathogen effects, may therefore be highly beneficial to crop protection. Highlighting the in vivo analysis capability and portability of modern biospectroscopy, ATR-FTIR provided an invaluable tool for a thorough spectrochemical investigation of intact tomato fruit during development and ripening. This contributes novel spectral biomarkers, distinct for each development and ripening stage to indicate healthy development. Concurrently, this approach demonstrates the effectiveness of using spectral data for machine learning, indicated by classifier results, which may be applied to crop biology. Complementary to monitoring healthy growth and development of plants and crops, is the detection of threats to plant products that compromise yield or quality. This includes physical damage and accelerated decay caused by pests and pathogens. Biochemical changes detected by ATR-FTIR using principal component analysis and linear discriminant analysis (PCA–LDA), for damage-induced pathogen infection of cherry tomato (cv. Piccolo), showed subtle biochemical changes distinguishing healthy tomato from damaged, early or late sour rot-infected tomato. Sour rot fungus Geotrichum candidum was detected in vivo and characterized based on spectral features distinct from tomato fruit providing biochemical insight and detection potential for intact plant–pathogen systems. Pre-harvest detection of pests and pathogens in growing plants is paramount for crop protection and for effective use of crop protection products. Established previously as an exceptionally versatile bioanalytical sensor, for post-harvest applications, biospectroscopy was applied for the pre-harvest detection of microscopic pathogen Botrytis cinerea fungus infecting developing tomato plants. Compact MIR spectroscopy using ATR mode was adapted for the biochemical investigation of the plant-microbe interaction S. lycopersicum and B. cinerea, on the whole-plant level. Chemometric modeling including principal component analysis, and linear discriminant analysis were applied. Fingerprint spectra (1800-900 cm-1) were excellent discriminators of plant disease in pre-symptomatic as well as symptomatic plants. Spectral alterations in leaf tissue caused by infection are discussed. Potential for automatic decision-making is shown by high accuracy rates of 100% for detecting plant disease at various stages of progression. Similar accuracy rates using similar chemometric models are obtained for fruit development and ripening also. Overall, this research showcases the biospectroscopy potential for development monitoring and ripening of fruit crops, damage and infection induced decay of fruit in horticultural systems post-harvest, complemented by pre-harvest detection of microscopic pathogens. Based on the results from experiments performed under semi-controlled conditions, biospectroscopy is ready for field applications directed at pest and pathogen detection for improved crop production through the mitigation of crop loss

Recent Developments in Atomic Force Microscopy and Raman Spectroscopy for Materials Characterization

This book contains chapters that describe advanced atomic force microscopy (AFM) modes and Raman spectroscopy. It also provides an in-depth understanding of advanced AFM modes and Raman spectroscopy for characterizing various materials. This volume is a useful resource for a wide range of readers, including scientists, engineers, graduate students, postdoctoral fellows, and scientific professionals working in specialized fields such as AFM, photovoltaics, 2D materials, carbon nanotubes, nanomaterials, and Raman spectroscopy