Hugh H. T. Liu

Decentralized Localization of Sparsely-Communicating Robot Networks: A Centralized-Equivalent Approach

Finite-range sensing and communication are factors in the connectivity of a dynamic mobile-robot network. State estimation becomes a difficult problem when communication connections allowing information exchange between all robots are not guaranteed. This paper presents a decentralized state-estimation algorithm guaranteed to work in dynamic robot networks without connectivity requirements. We prove that a robot only needs to consider its own knowledge of network topology in order to produce an estimate equivalent to the centralized state estimate whenever possible while ensuring that the same can be performed by all other robots in the network. We prove certain properties of our technique and then it is validated through simulations. We present a comprehensive set of results, indicating the performance benefit in different network connectivity settings, as well as the scalability of our approach.

Aeroservoelastic Design Optimization of a Flexible Wing

In this paper a multidisciplinary design optimization framework is developed that integrates control system design with aerostructural design. The equations of motion are derived for a flexible aircraft and used to perform aeroservoelastic analysis. The objective of this framework is to go beyond the current limits of aircraft performance through simultaneous design optimization of aerodynamic shape, structural sizing and control system. The control system uses load alleviation to reduce the critical structural loads. Time-domain analysis of the aircraft performing an altitude change maneuver and encountering an atmospheric gust is included in the design process. The optimal trade-off between aerodynamics, structures and control system is found by maximizing the endurance subjected to stress and maneuverability constraints. Two cases — with and without load alleviation system — are considered. Due to the proposed MDO framework, the inclusion of load alleviation system in design leads to a significant increase in endurance performance.

Formation UAV flight control using virtual structure and motion synchronization

In this paper, the synchronized position tracking controller is incorporated in formation flight control for multiple flying wings. With this technology, the performance and effectiveness of the formation controller are improved when the virtual structure approach is utilized to maintain formation geometry. Simulations are conducted on the nonlinear model of two flying wings to verify the proposed controller.

Model-Predictive Gust Load Alleviation Controller for a Highly Flexible Aircraft

In this paper, a gust load alleviation system based on model-predictive control is developed for a very flexible aircraft. Two main contributions presented in this work are as follows. First, a unified dynamics framework is developed to represent the full six-degrees-of-freedom rigid body alongwith the structural dynamics. This allows for an integrated control design to account for maneuverability (flying qualities) and aeroelasticity simultaneously, leading to a new and improved configuration for a very flexible aircraft. Second, an improved model-predictive control formulation is proposed for stabilization and gust load alleviation. The performance of the model-predictive control is further improved by introducing an additional feedback loop to increase the prediction accuracy. To demonstrate the effectiveness of the proposed approach, the integrated formulation is compared with existing approaches. Further, the load alleviation performance is evaluated for various discrete and continuous gusts.

Multidisciplinary optimization framework for control-configuration integration in aircraft conceptual design

The emerging flight-by-wire and flight-by-light technologies increase the possibility of enabling and improving aircraft design with excellent handling qualities and performance across the flight envelope. As a result, it is desired to take into account the dynamic characteristics and automatic control capabilities at the early conceptual stage. In this paper, an integrated control-configured aircraft design sizing framework is presented. It makes use of multidisciplinary design optimization to overcome the challenges which the flight dynamics and control integration present when included with the traditional disciplines in an aircraft sizing process. A commercial aircraft design example demonstrates the capability of the proposed methodology. The approach brings higher freedom in design, leading to aircraft that exploit the benefits of control configuration. It also helps to reduce time and cost in the engineering development cycle.

A cooperative UAV/UGV platform for wildfire detection and fighting

Unmanned aerial vehicles (UAVs) and unmanned ground vehicles (UGVs) have received much attention in the research and development community due to their strong potential in certain high-risk missions. In applications that involve multiple vehicles, the inter-vehicle communication and cooperation becomes a critical challenge to a successful mission. An effective co-operative control framework is required to co-ordinate the system-level decision making process and information flow among the multiple agents such that the collective mission is optimally achieved. In this paper, a cooperative control framework for a hierarchical UAV/UGV platform is proposed. A top-level mobile mission controller provides effective mission planning and system-level decision making such that mission completion time and resource expenditure are optimized. The mobile mission controller can monitor the dynamic environment with its own sensing capabilities and coordinate UAVs/UGVs in their actions. This paper discusses the potential application of the proposed hierarchical vehicle platform to high-risk missions, specifically in the context of wildfire fighting. The task generation and allocation problems and proposed approaches are presented under the given control framework.

The UTIAS multi-robot cooperative localization and mapping dataset

This paper presents a two-dimensional multi-robot cooperative localization and mapping dataset collection for research and educational purposes. The dataset consists of nine sub-datasets, which can be used for studying problems such as robot-only cooperative localization, cooperative localization with a known map, and cooperative simultaneous localization and mapping (SLAM) . The data collection process is discussed in detail, including the equipment we used, how measurements were made and logged, and how we obtained groundtruth data for all robots and landmarks. The format of each file in each sub-dataset is also provided. The dataset is available for download at http://asrl.utias.utoronto.ca/datasets/mrclam/.

Hybrid control of a rotational flexible beam using enhanced PD feedback with a nonlinear differentiator and PZT actuators

In this paper, a hybrid control algorithm is proposed to control the rotation of a flexible beam while suppressing the beams vibration. The control law combines an enhanced PD feedback with a nonlinear differentiator to derive a high-quality velocity signal to control the gross motion of the beam, and a vibration control by PZT actuators bonded on the surface of the beam. There are three advantages of the proposed method: (i) the enhanced PD control is model free, and appears to be more robust against the noise; (ii) the linear velocity rather than the angular velocity is used in the PZT actuator control, a signal which is easily available; (iii) a unique solution is provided for examination of the actuator placement, based on the analysis of mode shape functions. Experimental results validate these theoretical analyses.

Fault tolerance of cooperative interception using multiple flight vehicles

Abstract Cooperative interception of a moving target by multiple vehicles is studied. The main contributions of research work presented in this paper include: (1) cooperative interception is achieved for multiple vehicles to reach the target simultaneously at a finite time, by proposing and solving for a novel finite-time consensus problem and (2) in addition, the cooperative interception is investigated with tolerance of actuator or network failures, where novel fault tolerant consensus protocols are proposed to address actuator failures (or loss of effectiveness) and network failures, respectively. The maximum fault tolerance against network failures can be estimated. Simulations of a three-against-one interception case are presented to demonstrate the effectiveness of the proposed design approaches.

Three-Dimensional Integrated Thermodynamic Simulation for Wing Anti-Icing System

Thermal flow in an aircraft wing leading-edge anti-icing system is a complicated physical phenomenon and remains a challenging research topic of modeling and analysis. We present a complete three-dimensional simulation of a wing segment including the piccolo-type thermal anti-icing bays inside the leading edge is presented. The Navier-Stokes analysis has been conducted for the integrated internal/external thermal flows with heat conductivity through the solid skin. The fully structured zones and boundary-layer meshing have reduced the total cell number and enhanced the near-wall impingement and the heat transfer analysis. Simulation results visually reveal the hot/cold flow interactions and heat conductivity through the fluid and solid zones. The calculated leading-edge surface temperature is compared with flight-test data of a similar configuration. The computational fluid dynamics model and its analysis under different flight conditions and configuration modifications provide a valuable assessment for wing anti-icing system research and development