Although robotic helicopters have received increasing interest from university, industry, and military research groups, their flight envelope in autonomous operations remains extremely limited. The absence of high-fidelity simulation models has prevented the use of well-established multivariable control techniques for the design of high-bandwidth control systems. Existing controllers are of low bandwidth and cover only small portions of the vehicle's flight envelope. The results of the synergic use of high-fidelity integrated modeling strategies and robust multivariable control techniques for the rapid and reliable design of a high-bandwidth controller for robotic helicopters are presented. The project implemented and flight tested an H ∞ loop shaping controller on the Carnegie Mellon University (CMU) Yamaha R-50 robotic helicopter. During the flight tests, the CMU R-50 flew moderate-speed coordinated maneuvers with a level of tracking performance that exceeds performance reported in the publicly available literature. The authors believe that the results open the road to the implementation on robotic helicopters of full-flight-envelope control systems for complex autonomous missions.

Design and Flight Testing of an H00 Controller for a Robotic Helicopter

Flight Control Law Design: An Industry Perspective

Design and Flight Testing of a High-Bandwidth H-Infinity Loop Shaping Controller for a Robotic Helicopter

New tools are presented for the computation of tight lower bounds on the structured singular value π, for highorder plants subject to purely real parametric uncertainty. The e rst approach uses the π-sensitivity function to systematically reduce the order of the real uncertainty matrix, so that exponential time lower bound algorithms can be applied. The second approach formulates the search for a worst-case real destabilizing perturbation as a constrained nonlinearoptimization problem.Both approachesareapplied to theproblem ofanalyzing thestability robustness properties of an integrated e ight and propulsion control system for an experimental vertical/short takeoff and landing aircraft cone guration. Currently available software tools for calculating lower bounds on real π fail for this problem, whereas both new approaches deliver tight bounds over the frequency range of interest.

New Tools for Computing Tight Bounds on the Real Structured Singular Value

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Design and Evaluation of a Balance Assistance Control Moment Gyroscope

A robust integrated e ight and propulsion controller is designed for an experimental short takeoff and vertical landing aircraftcone guration,using themethod of 1 loop-shaping. Theaircraftmodelused in thestudy isbased on the Harrier airframe with the Pegasus engine replaced by a thermodynamic simulation of a Rolls-Royce Spey power plant, to allow the incorporation of advanced engine control concepts. The controller follows a two-inceptor strategy to command e ight-path angle rate and velocity along the e ight path, whilesimultaneously keeping several airframeandenginevariableswithinspecie edsafetylimits.Thecentralizedintegratede ightandpropulsioncontrol system is evaluated in piloted simulation trials. Results indicate that level 1 or 2 e ying qualities are achieved over the low-speed powered lift region of the e ight envelope.

Design and Piloted Simulation of a Robust Integrated Flight and Propulsion Controller

Balancing the upper body is pivotal for upright and efficient gait. While models have identified potentially useful characteristics of biarticular thigh muscles for postural control of the upper body, experimental evidence for their specific role is lacking. Based on theoretical findings, we hypothesised that biarticular muscle activity would increase strongly in response to upper-body perturbations. To test this hypothesis, we used a novel Angular Momentum Perturbator (AMP) that, in contrast to existing methods, perturbs the upper-body posture with only minimal effect on Centre of Mass (CoM) excursions. The impulse-like AMP torques applied to the trunk of subjects resulted in upper-body pitch deflections of up to 17° with only small CoM excursions below 2 cm. Biarticular thigh muscles (biceps femoris long head and rectus femoris) showed the strongest increase in muscular activity (mid- and long-latency reflexes, starting 100 ms after perturbation onset) of all eight measured leg muscles which highlights the importance of biarticular muscles for restoring upper-body balance. These insights could be used for improving technological aids like rehabilitation or assistive devices, and the effectiveness of physical training for fall prevention e.g. for elderly people.

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Biarticular muscles are most responsive to upper-body pitch perturbations in human standing

Gyroscopic actuation is appealing for wearable applications due to its ability to impart free moments on a body without exoskeletal structures on the joints. We recently proposed an unobtrusive balancing aid consisting of multiple parallel-mounted control moment gyroscopes (CMGs) contained within a backpack-like orthopedic corset. Using conventional CMG control techniques, geometric singularities result in a number of performance issues, including either unintended oscillations or freezing of the gimbals at certain alignments, which are typically mitigated by the addition of redundant actuators or by allowing errors in the generated moment; however, because of the minimalistic design of the proposed device and focus on accurate moment tracking, a new methodology is required. In this paper, a control scheme is proposed for nonredundant CMG systems in which oscillations at saturated states are avoided and all remaining singularities are efficiently escaped by exploiting the system geometry; due to its use of classification-specific singularity proximity measures that account for the command moment orientation, it is named the directional singularity-robust control law. The performance of this control law is assessed in both simulations and hardware testing. The proposed method is suitable for a wide range of CMG systems, including both balancing and aerospace applications.

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Directional Singularity-Robust Torque Control for Gyroscopic Actuators

Despite the long history of studies on the singularity problem inherent to single-gimbal control moment gyroscopes, few existing gimbal steering laws can both accurately track moments and escape or...

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Directional Singularity Escape and Avoidance for Single-Gimbal Control Moment Gyroscopes

Gyroscopic actuators are appealing for wearable applications due to their ability to provide overground balance support without obstructing the legs. Multiple wearable robots using this actuation principle have been proposed, but none has yet been evaluated with humans. Here we use the GyBAR, a backpack-like prototype portable robot, to investigate the hypothesis that the balance of both healthy and chronic stroke subjects can be augmented through moments applied to the upper body. We quantified balance performance in terms of each participant’s ability to walk or remain standing on a narrow support surface oriented to challenge stability in either the frontal or the sagittal plane. By comparing candidate balance controllers, it was found that effective assistance did not require regulation to a reference posture. A rotational viscous field increased the distance healthy participants could walk along a 30mm-wide beam by a factor of 2.0, compared to when the GyBAR was worn but inactive. The same controller enabled individuals with chronic stroke to remain standing for a factor of 2.5 longer on a narrow block. Due to its wearability and versatility of control, the GyBAR could enable new therapy interventions for training and rehabilitation.

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Andrew Berry

Papers

Design and Piloted Simulation of a Robust Integrated Flight and Propulsion Controller

Biarticular muscles are most responsive to upper-body pitch perturbations in human standing

Directional Singularity-Robust Torque Control for Gyroscopic Actuators

Directional Singularity Escape and Avoidance for Single-Gimbal Control Moment Gyroscopes

Controller synthesis and clinical exploration of wearable gyroscopic actuators to support human balance.