Control of biomimetic locomotion via averaging theory

Based on a recently developed "generalized averaging theory", we present a generic approach for the design of stabilizing feedback controller for biomimetic locomotive systems. The control laws exponentially stabilize in the average, and they apply to a very wide class of systems. Two examples are given: a "kinematic biped" that demonstrates how our theory handles discontinuities, and the snakeboard, which is an underactuated mechanical system with drift

A functional electrical stimulation system for human walking inspired by reflexive control principles

This study presents an innovative multichannel functional electrical stimulation gait-assist system which employs a well-established purely reflexive control algorithm, previously tested in a series of bipedal walking robots. In these robots, ground contact information was used to activate motors in the legs, generating a gait cycle similar to that of humans. Rather than developing a sophisticated closed-loop functional electrical stimulation control strategy for stepping, we have instead utilised our simple reflexive model where muscle activation is induced through transfer functions which translate sensory signals, predominantly ground contact information, into motor actions. The functionality of the functional electrical stimulation system was tested by analysis of the gait function of seven healthy volunteers during functional electrical stimulation–assisted treadmill walking compared to unassisted walking. The results demonstrated that the system was successful in synchronising muscle activation throughout the gait cycle and was able to promote functional hip and ankle movements. Overall, the study demonstrates the potential of human-inspired robotic systems in the design of assistive devices for bipedal walking

Robot Impedance Control and Passivity Analysis with Inner Torque and Velocity Feedback Loops

Impedance control is a well-established technique to control interaction forces in robotics. However, real implementations of impedance control with an inner loop may suffer from several limitations. Although common practice in designing nested control systems is to maximize the bandwidth of the inner loop to improve tracking performance, it may not be the most suitable approach when a certain range of impedance parameters has to be rendered. In particular, it turns out that the viable range of stable stiffness and damping values can be strongly affected by the bandwidth of the inner control loops (e.g. a torque loop) as well as by the filtering and sampling frequency. This paper provides an extensive analysis on how these aspects influence the stability region of impedance parameters as well as the passivity of the system. This will be supported by both simulations and experimental data. Moreover, a methodology for designing joint impedance controllers based on an inner torque loop and a positive velocity feedback loop will be presented. The goal of the velocity feedback is to increase (given the constraints to preserve stability) the bandwidth of the torque loop without the need of a complex controller.Comment: 14 pages in Control Theory and Technology (2016

Averaging of the Nonlinear Dynamics of Flapping Wing Micro Air Vehicles for Symmetrical Flapping

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90719/1/AIAA-2011-1228-201.pd

Biomechanics in batoid fishes

Batoid fishes (e.g., manta rays) are extremely efficient swimmers, combining extreme strength and incredible maneuverability. Replicating these unique properties in synthetic autonomous under-water vehicles would have tremendous implications. Several research groups have been exploring these concepts for the past decade, and a small number of prototypes have been demonstrated. Importantly though, these prototypes match the batoid external motion (in terms of range of motion and actuation force) but do not employ a similar internal mechanics. The configuration of skeletons and muscle structures for a number of different batoid fishes have been recently unveiled, presenting a unique opportunity to analyze the internal mechanics of these complex structures, and ultimately use the acquired understanding to realize truly bio-mimetic underwater vehicles. As a whole wing has hundreds of moving elements, a full finite elements simulation of the entire wing is not feasible. To address this problem, we implemented a numerical model which will represent a part of the entire wing, and we investigated the effects of geometric and materials parameters on its stiffness. The length of each radial and the offset between them are going to be the most relevant variables and hence, the ones tested. Furthermore, to represent efficiently all the wing, we calculated its effective elastic properties using rigorous homogenization theory. These properties could then be used in shell FE models of the entire wing, and capture spatial variation in elastic constants in a numerically efficient way. Within the context of this work, the stiff and compliant direction will be found and that will give us an idea of the ability of the model to capture the experimentally observed deformation patterns. We observe that our 2D homogenized wing model fails to capture the substantial twisting/bending coupling that is observed experimentally. We speculate that the lack of torsional degree of freedom at the joints is responsible for this discrepancy. Once this deformation mechanism is built into a model, future investigations can use the homogenized stiffness approach to extract an effective continuum-based representation of the response of the wing in a continuum shell finite element model. This element can then be used for efficient modeling of entire wings; this will allow efficient modeling of spatially non-uniform wing morphologies in a Finite Elements setting. Once the elastic response of the wing is completely characterized, efforts will need to focus on actuation.Outgoin