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

Decentralised Compliant Control for Hexapod Robots: A Stick Insect Based Walking Model

Institute of Perception, Action and BehaviourThis thesis aims to transfer knowledge from insect biology into a hexapod walking robot. The similarity of the robot model to the biological target allows the testing of hypotheses regarding control and behavioural strategies in the insect. Therefore, this thesis supports biorobotic research by demonstrating that robotic implementations are improved by using biological strategies and these models can be used to understand biological systems. Specifically, this thesis addresses two central problems in hexapod walking control: the single leg control mechanism and its control variables; and the different roles of the front, middle and hind legs that allow a decentralised architecture to co-ordinate complex behavioural tasks. To investigate these problems, behavioural studies on insect curve walking were combined with quantitative simulations. Behavioural experiments were designed to explore the control of turns of freely walking stick insects, Carausius morosus, toward a visual target. A program for insect tracking and kinematic analysis of observed motion was developed. The results demonstrate that the front legs are responsible for most of the body trajectory. Nonetheless, to replicate insect walking behaviour it is necessary for all legs to contribute with specific roles. Additionally, statistics on leg stepping show that middle and hind legs continuously influence each other. This cannot be explained by previous models that heavily depend on positive feedback controllers. After careful analysis, it was found that the hind legs could actively rotate the body while the middle legs move to the inside of the curve, tangentially to the body axis. The single leg controller is known to be independent from other legs but still capable of mechanical synchronisation. To explain this behaviour positive feedback controllers have been proposed. This mechanism works for the closed kinematic chain problem, but has complications when implemented in a dynamic model. Furthermore, neurophysiological data indicate that legs always respond to disturbances as a negative feedback controller. Additional experimental data presented herein indicates that legs continuously oppose forces created by other legs. This thesis proposes a model that has a velocity positive feedback control modulated via a subordination variable in cascade with a position negative feedback mechanism as the core controller. This allows legs to oppose external and internal forces without compromising inter-leg collaboration for walking. The single leg controller is implemented using a distributed artificial neural network. This network was trained with a wider range of movement to that so far found in the simulation model. The controller implemented with a plausible biologica

Kinematics of cricket phonotaxis

Male crickets produce a species specific song to attract females which in response move towards the sound source. This behaviour, termed phonotaxis, has been the subject of many morphological, neurophysiological and behavioural studies making it one of the most well studied examples of acoustic communication in the animal kingdom. Despite this fact, the precise leg movements during this behaviour is unknown. This is of specific interest as the cricket’s ears are located on their front legs, meaning that the perception of the sound input might change as the insect moves. This dissertation describes a methodology and an analysis that fills this knowledge gap. I developed a semi-automated tracking system for insect motion based on commercially available high-speed video cameras and freely available software. I used it to collect detailed three dimensional kinematic information from female crickets performing free walking phonotaxis towards a calling song stimulus. I marked the insect’s joints with small dots of paint and recorded the movements from underneath with a pair of cameras following the insect as it walks on the transparent floor of an arena. Tracking is done offline, utilizing a kinematic model to constrain the processing. I obtained, for the first time, the positions and angles of all joints of all legs and six additional body joints, synchronised with stance-swing transitions and the sound pattern, at a 300 Hz frame rate. I then analysed this data based on four categories: The single leg motion analysis revealed the importance of the thoraco-coxal (ThC) and body joints in the movement of the insect. Furthermore the inside middle leg’s tibio-tarsal (TiTa) joint was the centre of the rotation during turning. Certain joints appear to be the most crucial ones for the transition from straight walking to turning. The leg coordination analysis revealed the patterns followed during straight walking and turning. Furthermore, some leg combinations cannot be explained by current coordination rules. The angles relative to the active speaker revealed the deviation of the crickets as they followed a meandering course towards it. The estimation of ears’ input revealed the differences between the two sides as the insect performed phonotaxis by using a simple algorithm. In general, the results reveal both similarities and differences with other cricket studies and other insects such as cockroaches and stick insects. The work presented herein advances the current knowledge on cricket phonotactic behaviour and will be used in the further development of models of neural control of phonotaxis

A biologically Inspired active compliant joint using local positive velocity feedback (LPVF)

Schneider A, Cruse H, Schmitz J. A biologically Inspired active compliant joint using local positive velocity feedback (LPVF). IEEE Trans. Systems Man Cybern. Part B: Cybernetics. 2005;35(6):1120-1130.Starting from studies which revealed that positive feedback is found in the control system for walking in arthropods, we have constructed a new positive feedback driven joint that can be used for solving compliant motion tasks. We propose two different joint constructions each of which shows passive compliance. Based on these joints we introduce three different local positive velocity feedback (LPVF) controllers and discuss their properties in the context of motion generation in closed kinematic chains. The third circuit named undelayed dLPVF is used for the control of a compliant planar manipulator which turns a crank. Our concept is of highly decentralized nature and follows the idea of embodiment. In our case this means that a process which is controlled by LPVF controllers reveals its nature when the controllers interact with this process

Understanding standing

Research objectives. Psychophysical acceleration threshold is a tool for detecting deficits in dynamic postural control. Our lab has shown differences in the acceleration threshold among young adults, elderly adults, and elderly adults with diabetes. Electromyography, Semmes-Weinstein monofilaments, and hearing tests investigate the underlying physiological mechanisms for the detriments in postural control. Due to peri-sway perturbations, the motion of a person\u27s sway affects the signal to noise ratio for perturbed stance. Since increases in sway range accompany postural instabilities, sway entrainment will allow us to investigate changes in acceleration threshold at different points in sway. The center of pressure, observed for entrainment, only changes due to rotations about joints, specifically the ankle. The current method to model rotation about the ankle is a single orthogonal joint, and therefore inaccurate. Methods. The SLIP-FALLS-STEPm Platform has lead to the ability to accurately measure and observe interactions in the range of postural sway. The combination of the platform with other testing modalities such as camera tracking systems, force mats, and accelerometers will allow for a comprehensive testing scheme. The new scheme can be combined with the induced sway produced by a sub-threshold sinusoidal entrainment process. The nonorthogonal modelling is programmed in Matlab®. Results. For constant displacements, anterior accelerations thresholds via two-alternate forced choice (2AFC) showed differences in postural stability in mature, diabetic individuals with peripheral neuropathy (DPN) and those who are neurally intact (DNI) compared to healthy mature adults (HMA), which corresponded with previous results of lateral perturbations. Both DNI and DPN had significantly higher thresholds for acceleration via 2AFC than HMA at 1 and 4 mm displacements (p \u3c 0.01 and p Conclusion. The anterior acceleration thresholds show that peripheral neuropathy is not the sole cause for postural instability with diabetes. The ability to control the motion of sway will allow us to describe acceleration threshold throughout the range of sway. With a realistic ankle model, we will be able to better simulate postural dynamics