Robust hybrid global asymptotic stabilization of rigid body dynamics using dual quaternions

A hybrid feedback control scheme is proposed for stabilization of rigid body dynamics (pose and velocities) using unit dual quaternions, in which the dual quaternions and veloc- ities are used for feedback. It is well-known that rigid body attitude control is subject to topological constraints which often result in discontinuous control to avoid the unwinding phenomenon. In contrast, the hybrid scheme allows the controlled system to be robust in the presence of uncertainties, which would otherwise cause chattering about the point of discontinuous control while also ensuring acceptable closed-loop response characteristics. The stability of the closed-loop system is guaranteed through a Lyapunov analysis and the use of invariance principles for hybrid systems. Simulation results for a rigid body model are presented to illustrate the performance of the proposed hybrid dual quaternion feedback control scheme

Space station structural dynamics/reaction control system interaction study

The performance of the Reaction Control System is impacted by the extreme flexibility of the space station structure. The method used to analyze the periodic thrust profile of a simple form of phase plane logic is presented. The results illustrate the effect on flexible body response of the type of phase plane logic utilized and the choice of control parameters: cycle period and attitude deadband

MCC level C formulation requirements. Shuttle TAEM targeting

The level C requirements for the shuttle orbiter terminal area energy management (TAEM) guidance and flight control functions to be incorporated into the Mission Control Center entry profile planning processor are described. This processor is used for preentry evaluation of the entry through landing maneuvers, and includes a simplified three degree-of-freedom model of the body rotational dynamics that is necessary to account for the effects of attitude response on the trajectory dynamics. This simulation terminates at TAEM-autoland interface

Food provisioning and growth in the Atlantic puffin fratercular Arctica: an experimental approach

This study provided Puffin chicks with an additional 25g of food per day during the period of maximum growth rate to determine whether: 1) adult puffins can evaluate and respond to the nutritional requirements of their chicks, and 2) whether growth parameters (rate and elevation) of structural body components are flexible in response to variable levels of nutrition. Adult provisioning rates were significantly reduced in response to supplementary feeding, with experimental chicks receiving a mean of 2.1 feeds/d(^-1) compared to control chicks which received 4.7 feeds/d(^-1). There was no difference in the mean weight or energy content of the loads delivered to both groups, suggesting that the adult response to supplementary feeding took the form of a decrease in feeding frequency rather than a decrease m the size or nutritional quality of the load. No significant differences were found between the experimental and control groups in both the growth rate of overall body size and body weight. Neither was there a difference between groups in body mass elevation (mass corrected for age). However, chicks provided with supplementary food grew significantly larger for their age than control chicks. The fact that control birds were smaller but body masses were identical between the two groups suggests that control birds were not energy limited but nutrient limited; supplementary food may have provided the additional nutrients allowing structural tissues of experimental birds to grow larger. Differences in body tissue composition, and thus differences in metabolic energy requirements, may have been indirectly responsible for the similarities in body mass between the two groups. Identical growth rates between the two groups may have been a result of constraints acting at the physiological level, which prevented any further increase in rate once maximum size was reached for a given nutrient intake. In conclusion, variation in the quality or quantity of Puffin nestling diets does effect growth patterns of structural body components. Environmental sources of morphological variation should not be neglected in studies of phenotypic variation in birds

Interoceptive robustness through environment-mediated morphological development

Typically, AI researchers and roboticists try to realize intelligent behavior in machines by tuning parameters of a predefined structure (body plan and/or neural network architecture) using evolutionary or learning algorithms. Another but not unrelated longstanding property of these systems is their brittleness to slight aberrations, as highlighted by the growing deep learning literature on adversarial examples. Here we show robustness can be achieved by evolving the geometry of soft robots, their control systems, and how their material properties develop in response to one particular interoceptive stimulus (engineering stress) during their lifetimes. By doing so we realized robots that were equally fit but more robust to extreme material defects (such as might occur during fabrication or by damage thereafter) than robots that did not develop during their lifetimes, or developed in response to a different interoceptive stimulus (pressure). This suggests that the interplay between changes in the containing systems of agents (body plan and/or neural architecture) at different temporal scales (evolutionary and developmental) along different modalities (geometry, material properties, synaptic weights) and in response to different signals (interoceptive and external perception) all dictate those agents' abilities to evolve or learn capable and robust strategies

Practical approaches to exploiting body dynamics in robot motor control

Motor control systems in the brain of humans and mammals are hierarchically organised, with each level controlling increasingly complex motor actions. Each level is controlled by the higher levels and also receives sensory and/or proprioceptive feedback. Through learning, this hierarchical structure adapts to its body, its sensors and the way these interact with the environment. An even more integrated view is taken in morphological or embodied computation. On the one hand, there is both biological and mechanical (robotics) evidence that a properly chosen body morphology can drastically facilitate control when the body dynamics naturally generate low level motion primitives. On the other hand, several papers have used robot bodies as reservoirs in a reservoir computing setup. In some cases, reservoir computing was used as an easy way to obtain robust linear feedback controllers for locomotion. In other cases, the body dynamics of soft robots were shown to perform general computations in response to some input stimulation. In general, very specific highly compliant bodies were used. At Ghent University’s Reservoir Lab, we have previously used reservoir computing to generate locomotion on quite different robot platforms: the highly compliant tensegrity robot Recter and the far less compliant quadruped robot Oncilla and a new low cost modular quadruped puppy robot. In all cases, we succeeded in generating stable gaits. However, not surprisingly, not all robot bodies are equally suitable to help generating their own motor actuations. As a result, the reservoir computing principle alone was not always sufficient. We present an overview of our experience with these different robot platforms and give practical guidelines for applying physical reservoir computing to new robots. We finally discuss some perspectives on a more systematic evaluation between body morphology, compliance and the complexity of generating stable gaits for locomotion

Corticosterone selectively decreases humoral immunity in female eiders during incubation

Immunity is hypothesized to share limited resources with other physiological functions and this may partly account for the fitness costs of reproduction. Previous studies have shown that the acquired immunity of female common eider ducks (Somateria mollissima) is suppressed during their incubation, during which they entirely fast. Corticosterone was proposed to be an underlying physiological mechanism for such immunosuppression. Therefore, the current study aimed to assess the effects of exogenous corticosterone on acquired immunity in captive eiders. To this end, females were implanted with corticosterone pellets at different stages of their incubation fast. We measured total immunoglobulin levels, T-cell-mediated immune response, body mass and corticosterone levels in these females and compared them with those of control females prior to and after manipulation (i.e. corticosterone pellet implantation). To mimic corticosterone effects on body mass, we experimentally extended fasting duration in a group of females termed ;late fasters'..