Traditional robots have rigid underlying structures that limit their ability to interact with their environment. For example, conventional robot manipulators have rigid links and can manipulate objects using only their specialised end effectors. These robots often encounter difficulties operating in unstructured and highly congested environments. A variety of animals and plants exhibit complex movement with soft structures devoid of rigid components. Muscular hydrostats e.g. octopus arms and elephant trunks are almost entirely composed of muscle and connective tissue and plant cells can change shape when pressurised by osmosis. Researchers have been inspired by biology to design and build soft robots. With a soft structure and redundant degrees of freedom, these robots can be used for delicate tasks in cluttered and/or unstructured environments. This paper discusses the novel capabilities of soft robots, describes examples from nature that provide biological inspiration, surveys the state of the art and outlines existing challenges in soft robot design, modelling, fabrication and control.

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Soft robotics: Biological inspiration, state of the art, and future research

Flies are among the most agile flying creatures on Earth To mimic this aerial prowess in a similarly sized robot requires tiny, high-efficiency mechanical components that pose miniaturization challenges governed by force-scaling laws, suggesting unconventional solutions for propulsion, actuation, and manufacturing To this end, we developed high-power-density piezoelectric flight muscles and a manufacturing methodology capable of rapidly prototyping articulated, flexure-based sub-millimeter mechanisms We built an 80-milligram, insect-scale, flapping-wing robot modeled loosely on the morphology of flies Using a modular approach to flight control that relies on limited information about the robot's dynamics, we demonstrated tethered but unconstrained stable hovering and basic controlled flight maneuvers The result validates a sufficient suite of innovations for achieving artificial, insect-like flight

http://science.sciencemag.org/content/sci/340/6132/603.full.pdf

Controlled Flight of a Biologically Inspired, Insect-Scale Robot

Recent progress in flapping wing aerodynamics and aeroelasticity

Nonlinear Oscillations: Exact Solutions and their Approximations

Progresses in sensor technology, data processing and integrated actuators has made the development of miniature flying robots fully possible. Micro VTOL systems represent a useful class of flying robots because of their strong capabilities for small-area monitoring and building exploration. In this paper we describe the approach that our lab has taken to micro VTOL evolving towards full autonomy, and present the mechanical design, dynamic modelling, sensing, and control of our indoor VTOL autonomous robot OS4.

/pdf/design-and-control-of-an-indoor-micro-quadrotor-2bdaw3cv4v.pdf

Design and control of an indoor micro quadrotor

Describes results on the design and simulation of a flight control system for the micromechanical flying insect (MFI), a 10-25 mm (wingtip-to-wingtip) device eventually capable of sustained autonomous flight. The biologically inspired system architecture results in a hierarchical structure of different control methodologies, which give the possibility to plan complex missions from a sequence of simple flight modes and maneuvers. As a case study, a stabilizing hovering control scheme is presented and simulated with VIFS, a software simulator for insect flight.

Flight control system for a micromechanical flying insect: architecture and implementation

Flapping wings continuously create and send vortices into their wake, while imparting downward momentum into the surrounding fluid. However, experimental studies concerning the details of the three-dimensional vorticity distribution and evolution in the far wake are limited. In this study, the three-dimensional vortex wake structure in both the near and far field of a dynamically scaled flapping wing was investigated experimentally, using volumetric three-component velocimetry. A single wing, with shape and kinematics similar to those of a fruitfly, was examined. The overall result of the wing action is to create an integrated vortex structure consisting of a tip vortex (TV), trailing-edge shear layer (TESL) and leading-edge vortex. The TESL rolls up into a root vortex (RV) as it is shed from the wing, and together with the TV, contracts radially and stretches tangentially in the downstream wake. The downwash is distributed in an arc-shaped region enclosed by the stretched tangential vorticity of the TVs and the RVs. A closed vortex ring structure is not observed in the current study owing to the lack of well-established starting and stopping vortex structures that smoothly connect the TV and RV. An evaluation of the vorticity transport equation shows that both the TV and the RV undergo vortex stretching while convecting downwards: a three-dimensional phenomenon in rotating flows. It also confirms that convection and secondary tilting and stretching effects dominate the evolution of vorticity.

https://royalsocietypublishing.org/doi/pdf/10.1098/rsif.2013.0984

Three-dimensional vortex wake structure of flapping wings in hovering flight

Designing a hummingbird-inspired, at-scale, tail-less flapping-wing micro aerial vehicle (FWMAV) is a challenging task in order to achieve animallike flight performance under the constraints of size, weight, power, and actuation limitations. It is even more challenging to design such a vehicle with a pair of independently controlled wings equipped with a total of only two actuators. This article details a systematic solution for the design optimization and prototyping of such FWMAVs. The proposed solution covers the complete system models and analysis of wing-actuation dynamics, control authorities, body dynamics, mechanical limitations, and electrical constraints. Each subsystem, as well as the overall system, is experimentally validated. This comprehensive approach can facilitate the design of such FWMAVs with different optimization goals. To demonstrate the effectiveness of the proposed approach, in this article, we conduct three different design optimization tasks, which yield three different prototype systems: optimizing the lift-to-weight ratio, optimizing control bandwidth, and optimizing control authority. We first construct a vehicle with an optimized lift-to-weight ratio. Based on it, the other two platforms with different design optimization goals are presented for better flight performance. Flight tests were performed on each prototype to validate their flight performance and design goals. Compared to optimized control bandwidth, we demonstrate that the vehicle with optimized control authorities is significantly more capable in terms of flight performance. It shows sustained stable flight in both hovering and heavy load carrying (more than 60% of the vehicle's total weight), which is hard for the other two platforms to achieve.

An At-Scale Tailless Flapping-Wing Hummingbird Robot. I. Design, Optimization, and Experimental Validation

Controlled hovering of motor driven flapping wing micro aerial vehicles (FWMAVs) is challenging due to its limited control authority, large inertia, vibration produced by wing strokes, and limited components accuracy due to fabrication methods. In this work, we present a hummingbird inspired FWMAV with 12 grams of weight and 20 grams of maximum lift. We present its full non-linear dynamic model including the full inertia tensor, non-linear input mapping, and damping effect from flapping counter torques (FCTs) and flapping counter forces (FCFs). We also present a geometric flight controller to ensure exponentially stable and globally exponential attractive properties. We experimentally demonstrated the vehicle lifting off and hover with attitude stabilization.

Geometric flight control of a hovering robotic hummingbird

Robotic vehicles (RVs) are being adopted in a variety of application domains. Despite their increasing deployment, many security issues with RVs have emerged, limiting their wider deployment. In this paper, we address a new type of vulnerability in RV control programs, called input validation bugs, which involve missing or incorrect validation checks on control parameter inputs. Such bugs can be exploited to cause physical disruptions to RVs which may result in mission failures and vehicle damages or crashes. Furthermore, attacks exploiting such bugs have a very small footprint: just one innocent-looking ground control command, requiring no code injection, control flow hijacking or sensor spoofing. To prevent such attacks, we propose RVFUZZER, a vetting system for finding input validation bugs in RV control programs through control-guided input mutation. The key insight behind RVFUZZER is that the RV control model, which is the generic theoretical model for a broad range of RVs, provides helpful semantic guidance to improve bug-discovery accuracy and efficiency. Specifically, RVFUZZER involves a control instability detector that detects control program misbehavior, by observing (simulated) physical operations of the RV based on the control model. In addition, RVFUZZER steers the input generation for finding input validation bugs more efficiently, by leveraging results from the control instability detector as feedback. In our evaluation of RVFUZZER on two popular RV control programs, a total of 89 input validation bugs are found, with 87 of them being zero-day bugs.

/pdf/rvfuzzer-finding-input-validation-bugs-in-robotic-vehicles-4kvsqm3290.pdf

Xinyan Deng

Papers

Flight control system for a micromechanical flying insect: architecture and implementation

Three-dimensional vortex wake structure of flapping wings in hovering flight

An At-Scale Tailless Flapping-Wing Hummingbird Robot. I. Design, Optimization, and Experimental Validation

Geometric flight control of a hovering robotic hummingbird

RVFuzzer: Finding Input Validation Bugs in Robotic Vehicles through Control-Guided Testing