Autonomous GPR Surveys using the Polar Rover Yeti

The National Science Foundation operates stations on the ice sheets of Antarctica and Greenland to investigate Earth's climate history, life in extreme environments, and the evolution of the cosmos. Understandably, logistics costs predominate budgets due to the remote locations and harsh environments involved. Currently, manual ground‐penetrating radar (GPR) surveys must preceed vehicle travel across polar ice sheets to detect subsurface crevasses or other voids. This exposes the crew to the risks of undetected hazards. We have developed an autonomous rover, Yeti, specifically to conduct GPR surveys across polar ice sheets. It is a simple four‐wheel‐drive, battery‐powered vehicle that executes autonomous surveys via GPS waypoint following. We describe here three recent Yeti deployments, two in Antarctica and one in Greenland. Our key objective was to demonstrate the operational value of a rover to locate subsurface hazards. Yeti operated reliably at ?30 °C, and it has has good oversnow mobility and adequate GPS accuracy for waypoint‐following and hazard georeferencing. It has acquired data on hundreds of crevasse encounters to improve our understanding of heavily crevassed traverse routes and to develop automated crevasse‐detection algorithms. Importantly, it helped to locate a previously undetected buried building at the South Pole. Yeti can improve safety by decoupling survey personnel from the consequences of undetected hazards. It also enables higher‐quality systematic surveys to improve hazard‐detection probabilities, increase assessment confidence, and build datasets to understand the evolution of these regions. Yeti has demonstrated that autonomous vehicles have great potential to improve the safety and efficiency of polar logistics. © 2012 Wiley Periodicals, Inc.     

Design of small hand‐launched solar‐powered UAVs: From concept study to a multi‐day world endurance record flight

We present the development process behind AtlantikSolar, a small 6.9 kg hand‐launchable low‐altitude solar‐powered unmanned aerial vehicle (UAV) that recently completed an 81‐hour continuous flight and thereby established a new flight endurance world record for all aircraft below 50 kg mass. The goal of our work is to increase the usability of such solar‐powered robotic aircraft by maximizing their perpetual flight robustness to meteorological deteriorations such as clouds or winds. We present energetic system models and a design methodology, implement them in our publicly available conceptual design framework for perpetual flight‐capable solar‐powered UAVs, and finally apply the framework to the AtlantikSolar UAV. We present the detailed AtlantikSolar characteristics as a practical design example. Airframe, avionics, hardware, state estimation, and control method development for autonomous flight operations are described. Flight data are used to validate the conceptual design framework. Flight results from the continuous 81‐hour and 2,338 km covered ground distance flight show that AtlantikSolar achieves 39% minimum state‐of‐charge, 6.8 h excess time and 6.2 h charge margin. These performance metrics are a significant improvement over previous solar‐powered UAVs. A performance outlook shows that AtlantikSolar allows perpetual flight in a 6‐month window around June 21 at mid‐European latitudes, and that multi‐day flights with small optical‐ or infrared‐camera payloads are possible for the first time. The demonstrated performance represents the current state‐of‐the‐art in solar‐powered low‐altitude perpetual flight performance. We conclude with lessons learned from the three‐year AtlantikSolar UAV development process and with a sensitivity analysis that identifies the most promising technological areas for future solar‐powered UAV performance improvements.     

Design and analysis of a wall-climbing robot for water wall inspection of thermal power plants

Boiler water wall in thermal power plants is characterized by high-altitude detection requirements. Moreover, the existing water wall-climbing robots are characterized by low obstacle-crossing performance, deviations, and a lack of autonomous crossing pipeline function. In view of this feature, a wall-climbing robot with permanent magnet and electromagnetic hybrid adsorption wheels is proposed. The robot has the function of independent traverse according to its own structural characteristics. Furthermore, transverse movement is proposed by comparing different adsorption modes, moving and driving modes. Robot statics in upward, downward, and transverse crawling are carried out, and nonsliding mechanical and nonoverturning mechanical models are obtained. Robot's dynamics are analyzed by considering the wall movement. The finite element simulation analysis of its main stressed parts is carried out by employing ANSYS, and an optimal structural model is obtained. The gap adsorption permanent magnet model is constructed, and its parametric simulation analysis is carried out using the Ansoft Maxwell module. The influence curve of the gap on the magnetic force is then obtained. Finally, the prototype is developed according to the design model and calculation analysis, and the experimental test is carried out. The experimental results show that the robot meets the expected functions and indexes, providing a basis for the intelligent development of thermal power plants.     

A hardware proof of concept for a remote‐controlled glacier‐surveying boat

The design of a prototype remote‐controlled glacier‐surveying robot, capable of taking accurate above‐ and below‐water measurements of calving glacier fronts, using swath bathymetry and laser scanning hardware is presented. Data captured using the remote control system during field trials on the Lille Gletscher in western Greenland are informally compared with data captured using the same sensors from the same glacier using a much larger manned vessel during the same time period. The potential use of such a device during extended repeat survey missions is discussed and the implications in terms of both the improvement in data quality and the logistics in the field are also outlined. Future improvements to the robot and in particular the control system are described, as well as mechanical and electrical design considerations that became apparent during trials. The transition to a more autonomous system and the possibility of full autonomy are considered. © 2012 Wiley Periodicals, Inc.     

Design and optimization of a tunable W‐band subharmonic cavity based Gunn diode oscillator using computer‐aided design technique

In this work, a systematic computer‐aided design technique is proposed to minimize the fabrication iteration for the design and development of W‐band subharmonic Gunn diode oscillator with wideband tunable bandwidth at W‐band. Gunn diode based single diode oscillator structure was divided into passive and active parts to facilitate the modeling of the component on appropriate simulation environment. Resonating structure and package of Gunn diode are modeled as passive circuit in high frequency structure simulator (HFSS). To satisfy the oscillator design equation, disc‐post resonating structure is tuned in HFSS and its S‐parameters are collaborated with the model of Gunn diode in advanced design system. Magnitude and phase of reflection coefficient (S11) is observed to ascertain the desired frequency of oscillation. Proper tuning of disc‐post structure is done on simulation platform, which reduces the fabrication complexity and cost as well. The measurement results validate the models designed using EM and circuit simulator. The measured maximum stable RF power without any fabrication iteration is 14.2 dBm. A tunable bandwidth of 4 GHz with power output ripple of ±1 dB is measured by using a movable backshort.     

Robotic technologies for solar‐powered UAVs: Fully autonomous updraft‐aware aerial sensing for multiday search‐and‐rescue missions

Large‐scale aerial sensing missions can greatly benefit from the perpetual endurance capability provided by high‐performance low‐altitude solar‐powered unmanned aerial vehicles (UAVs). However, today these UAVs suffer from small payload capacity, low energetic margins, and high operational complexity. To tackle these problems, this paper presents four individual technical contributions and integrates them into an existing solar‐powered UAV system: First, a lightweight and power‐efficient day/night‐capable sensing system is discussed. Second, means to optimize the UAV platform to the specific payload and to thereby achieve sufficient energetic margins for day/night flight with payload are presented. Third, existing autonomous launch and landing functionality is extended for solar‐powered UAVs. Fourth, as a main contribution an extended Kalman filter (EKF)‐based autonomous thermal updraft tracking framework is developed. Its novelty is that it allows the end‐to‐end integration of the thermal‐induced roll moment into the estimation process. It is assessed against unscented Kalman filter and particle filter methods in simulation and implemented on the aircraft's low‐power autopilot. The complete system is verified during a 26 h search‐and‐rescue aerial sensing mock‐up mission that represents the first‐ever fully autonomous perpetual endurance flight of a small solar‐powered UAV with a day/night‐capable sensing payload. It also represents the first time that solar‐electric propulsion and autonomous thermal updraft tracking are combined in flight. In contrast to previous work that has focused on the energetic feasibility of perpetual flight, the individual technical contributions of this paper are considered core functionality to guarantee ease‐of‐use, effectivity, and reliability in future multiday aerial sensing operations with small solar‐powered UAVs.     

A cross‐coupling controller using an H∞ scheme and its application to a two‐axis direct‐drive robot

A cross‐coupling controller (CCC) using an H_∞ control scheme has been proposed to reduce the contouring error for a two‐axis, direct‐drive robot in tracking linear and circular contours effectively. Under the consideration that contour‐tracking performance is a primary target over point‐to‐point tracking performance in a trajectory‐tracking task, a CCC has been associated with joint controllers to reduce the contouring error by coordinating the motion of a two‐axis robot arm. Contouring performance can thus be improved significantly. Furthermore, the proposed CCC design, which is a typical Multi‐Input Multi‐Output (MIMO) system with linear time varying (LTV) characteristics, has been verified as being internally stable. A USM (ultrasonic motor)‐driven, two‐axis, direct‐drive robot is utilized to demonstrate the feasibility of the proposed scheme. Several experiments under various operating conditions are performed to validate its efficacy, and the results showed that the proposed scheme can reduce the contouring error significantly. © 2002 Wiley Periodicals, Inc.     

基于群体智能的自主机器人设计

该文结合群体智能对研究平台的需求,介绍了自主式机器人的设计和实现。机器人的整体结构由主控板和功能板组成,主控板是机器人的控制中心,主要是CPU及其外围电路,以及一些调试用LED灯和按键。功能板是主控板控制信号的执行者,主要包括电源模块、红外测距、电机及驱动和串口等功能块。主控板通过两个接口与功能板相连接。该设计既可以作为一款通用性机器人进行推广应用,在批量生产运用的过程中不需要做较大规模的修改,也可以作为实验室研究的硬件平台。     

Under canopy light detection and ranging‐based autonomous navigation

This paper describes a light detection and ranging (LiDAR)‐based autonomous navigation system for an ultralightweight ground robot in agricultural fields. The system is designed for reliable navigation under cluttered canopies using only a 2D Hokuyo UTM‐30LX LiDAR sensor as the single source for perception. Its purpose is to ensure that the robot can navigate through rows of crops without damaging the plants in narrow row‐based and high‐leaf‐cover semistructured crop plantations, such as corn (Zea mays) and sorghum ( Sorghum bicolor). The key contribution of our work is a LiDAR‐based navigation algorithm capable of rejecting outlying measurements in the point cloud due to plants in adjacent rows, low‐hanging leaf cover or weeds. The algorithm addresses this challenge using a set of heuristics that are designed to filter out outlying measurements in a computationally efficient manner, and linear least squares are applied to estimate within‐row distance using the filtered data. Moreover, a crucial step is the estimate validation, which is achieved through a heuristic that grades and validates the fitted row‐lines based on current and previous information. The proposed LiDAR‐based perception subsystem has been extensively tested in production/breeding corn and sorghum fields. In such variety of highly cluttered real field environments, the robot logged more than 6 km of autonomous run in straight rows. These results demonstrate highly promising advances to LiDAR‐based navigation in realistic field environments for small under‐canopy robots.     

Energy‐efficient Path Planning for Solar‐powered Mobile Robots*

We explore the problem of energy‐efficient, time‐constrained path planning of a solar‐powered robot embedded in a terrestrial environment. Because of the effects of changing weather conditions, as well as sensing concerns in complex environments, a new method for solar power prediction is desirable. We present a method that uses Gaussian Process regression to build a solar map in a data‐driven fashion. Using this map and an empirical model for energy consumption, we perform dynamic programming to find energy‐minimal paths. We validate our map construction and path‐planning algorithms with outdoor experiments, and we perform simulations on our solar maps to further determine the limits of our approach. Our results show that we can effectively construct a solar map using only a simple current measurement circuit and basic GPS localization, and this solar map can be used for energy‐efficient navigation. This establishes informed solar harvesting as a viable option for extending system lifetime even in complex environments with low‐cost commercial solar panels.     

Design, control, and energetics of an electrically actuated leggedrobot

To study the design, control and energetics of autonomous dynamically stable legged machines we have built a planar one-legged robot, the ARL Monopod. Its top running speed of 4.3 km/h (1.2 m/s) makes it the fastest electrically actuated legged robot to date. We adapted Raibert's control laws for the low power electric actuation necessary for autonomous locomotion and performed a detailed energetic analysis of our experiments. A comparison shows that the ARL Monopod with its 125 W average power consumption is more energy efficient than previously built robots.     

Component design and testing for a miniaturised autonomous sensor based on a nanowire materials platform

We present the design considerations of an autonomous wireless sensor and discuss the fabrication and testing of the various components including the energy harvester, the active sensing devices and the power management and sensor interface circuits. A common materials platform, namely, nanowires, enables us to fabricate state-of-the-art components at reduced volume and show chemical sensing within the available energy budget. We demonstrate a photovoltaic mini-module made of silicon nanowire solar cells, each of 0.5 mm² area, which delivers a power of 260 μW and an open circuit voltage of 2 V at one sun illumination. Using nanowire platforms two sensing applications are presented. Combining functionalised suspended Si nanowires with a novel microfluidic fluid delivery system, fully integrated microfluidic–sensor devices are examined as sensors for streptavidin and pH, whereas, using a microchip modified with Pd nanowires provides a power efficient and fast early hydrogen gas detection method. Finally, an ultra-low power, efficient solar energy harvesting and sensing microsystem augmented with a 6 mAh rechargeable battery allows for less than 20 μW power consumption and 425 h sensor operation even without energy harvesting.     

Distributed stereo vision‐based 6D localization and mapping for multi‐robot teams

Joint simultaneous localization and mapping (SLAM) constitutes the basis for cooperative action in multi‐robot teams. We designed a stereo vision‐based 6D SLAM system combining local and global methods to benefit from their particular advantages: (1) Decoupled local reference filters on each robot for real‐time, long‐term stable state estimation required for stabilization, control and fast obstacle avoidance; (2) Online graph optimization with a novel graph topology and intra‐ as well as inter‐robot loop closures through an improved submap matching method to provide global multi‐robot pose and map estimates; (3) Distribution of the processing of high‐frequency and high‐bandwidth measurements enabling the exchange of aggregated and thus compacted map data. As a result, we gain robustness with respect to communication losses between robots. We evaluated our improved map matcher on simulated and real‐world datasets and present our full system in five real‐world multi‐robot experiments in areas of up 3,000 m² (bounding box), including visual robot detections and submap matches as loop‐closure constraints. Further, we demonstrate its application to autonomous multi‐robot exploration in a challenging rough‐terrain environment at a Moon‐analogue site located on a volcano.     

基于视觉伺服控制的光伏板清洗系统设计

光伏板上的鸟粪、枯叶等污渍若不及时清理会导致光伏板热斑现象的发生,严重影响光伏板的使用寿命和安全。现有光伏板清理方法存在清洗效果不好、浪费水资源、清洗效率低等问题,为此,及时清理维护光伏板成为光伏发电企业亟待解决的首要问题。基于以上问题,该文提出光伏板清洗视觉伺服控制系统和一种改进型模糊PID控制算法,利用从实时视频图像中提取的反馈信息控制机械臂对准污渍点,实现定点喷射清洗污渍点,达到节水高效的目的。实验结果表明,基于改进型模糊PID控制算法的光伏板清洗视觉伺服控制系统能够准确地定位到光伏板污渍位置并精准喷射清洗污渍,最大限度地节约水资源。     

Power quality improvement of solar power plants in grid connected system using novel Resilient Direct Unbalanced Control (RDUC) technique

Distributed Generation systems (DGs) using solar power is one of the new trends in power generation. These distributed generating units are integrated to form a micro grid to serve the loads among the locality, which is in connection with the utility grid for power transmission. The elimination of the harmonics in the grid and the usage of solar energy resources in the power electronics applications become famous worldwide. In this work, a Resilient Direct Unbalanced Control (RDUC) algorithm is used to improve the performance of the controller by achieving optimal numerical parameters for photovoltaic power generation - Unified Power Quality Conditioner (PV-UPQC). Then the voltage sag, swell and elimination of current harmonics are used to study the effects of proposed RDUC algorithm for photovoltaic feed UPQC system. According to the evaluations, the proposed unified power quality conditioner eliminates both the supply current distortion caused by a non-linear load and the load voltage distortion introduced after adding fifth and seventh harmonics to the Alternating Current (AC) mains voltage. To validate the simulation results of Resilient Direct Unbalanced Control scheme, tests are performed under various operating conditions. Test results show the satisfactory behavior under steady state, and dynamic conditions such as load unbalance, insolation variation, voltage sag and swell. Finally, Total Harmonic Distortions (THDs) of proposed optimization-based grid current and grid voltages found within limits of the IEEE standard.     

In-flight calibration of NOAA AVHRR visible and near-IR bands over Greenland and Antarctica

A new method for in-flight calibration of NOAA AVHRR visible and near-IR bands is presented. The approach involves using calibrated NOAA-9 near-nadir reflectances over spatially and temporally uniform ice-surfaces from Greenland and Antarctica to produce reflectance calibration curves for AVHRR instruments in all orbits. The reflectance calibration curves consist of second order polynomial regressions of reflectance on solar zenith angle, derived from observations that are spatially uniform in all AVHRR channels over sub-regions of area 68 km by 68 km. By comparing reflectances from uncalibrated AVHRR instruments with these calibration curves, new channel 1 and 2 calibration coefficients are obtained with an accuracy of 5 per cent. The main advantages of this calibration method are: (1) calibration targets are large; (2) it can be applied over multiple years; (3) it is applicable for a wide range of solar zenith angles, and can therefore be used year-round. When calibration coefficients inferred from NOAA-11 (1994) and NOAA-14 (1995) observations over Greenland and Antarctica are compared with those from the formulae of Rao and Chen (1995, 1996), the two methods are in excellent agreement in channel 1 (within 3 per cent). In channel 2, they agree to within 4 per cent for NOAA-14, but are significantly different for NOAA-11 ( 9 per cent). When applied to NOAA-12 AVHRR observations for 1994-95, channel 1 and 2 calibration coefficients are 20 per cent and 35 per cent larger than prelaunch values, respectively.     

A systematic design of 1.5–9 GHz high power–high efficiency two‐stage GaAs PHEMT power amplifier

In this article, a systematic design approach for a Class‐A operated wideband power amplifier is presented. The power amplifier structure comprises of two transistors in the cascaded single stage traveling wave amplifier topology. A power amplifier was designed by using the systematic approach and fabricated with 0.25 μm GaAs PHEMT MMIC process. The amplifier has an area of 3.4 × 1.4 mm². Measurement results show that almost flat gain performance is obtained around 15 dB over 1.5–9 GHz operating bandwidth. In most of the band, with the help of a wideband load‐pull matching technique, the amplifier delivers P_o,sat and P_o,1dB of around 30 dBm and 28 dBm where the corresponding power added efficiencies are >50% and >36%, respectively. It is shown that the proposed design approach has the advantage of simple and systematic design flow and it helps to realize step‐by‐step design for the designers. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:615–622, 2014.     

Visual control of autonomous mobile robot based on self-organizing model for pattern learning

This article proposes a self-organizing model for pattern learning together with an application to an autonomous mobile robot system. The self-organizing model consists of a processing rule prescribed and a memory part being blank at the initial stage. To an input signal, the model searches for a similar signal in the memory, and recalls its related information. If the information accompanied with the input signal differs from the recalled information, the model adds the new information to the memory. It influences the subsequent operations. Thus, the model constructs successively a data-base in a self-organizing way. This model can universally learn and reproduce any pattern of input-output response desired. Two principal functions in autonomous movement, i.e., position identification and obstacle avoiding movement were realized based on the self-organizing model. Furthermore, a camera type autonomous mobile robot system for indoor was made up. The size of the robot is about 0.7 × 0.7 × 0.7 m, and the weight is about 30 kg. The speed of movement is less than 3 km/h. A small computer that has a 16 bit microprocessor and a 1 Mbyte RAM controls the motion of the robot with an extended C language.     

Dual‐tracked mobile robot for motion in challenging terrains

In this paper we present a novel design for a dual‐tracked mobile robot. The robot is designed for safe, stable, and reliable motion in challenging terrains, tunnels, and confined spaces. It consists of two tracked platforms connected with a semipassive mechanism. Sensors attached to the connecting mechanism provide redundant localization data that improve the vehicle's autonomous dead reckoning. Each tracked platform mechanically backs up the other platform, resulting in a more robust and reliable operation. The load share between the platforms enables a high payload‐to‐weight ratio even on soft and slippery terrains. The robot's configurations make it suitable for motion in confined spaces such as underground tunnels, collapsed structures, pipes, and caves. The paper presents the mechanical design of the robot, its kinematic model, stability analysis, and a motion planner. Experimental results conducted on prototype models in various types of environments verify the robot capabilities to operate successfully on challenging terrains. The dual‐tracked robot is capable of climbing slopes 50% steeper than a single robot can. Moreover, the improved odometry system shows high accuracy with 2% error of the total travel distance. © 2011 Wiley Periodicals, Inc.     

Filtering balanced‐to‐single‐ended power dividing network

In this article, the filtering balanced‐to‐single‐ended power dividing networks are proposed. Except the fundamental functions of differential‐mode transmission, common‐mode suppression, and out‐of‐phase single‐ended output ports with isolation, the proposed designs show the advantages of wide controllable range of differential‐mode bandwidth, multiple transmission zeros (TZs), and wide bandwidth for high out‐of‐band suppression. The frequencies of TZs, bandwidth, isolation, and common‐mode suppression can be controlled by the parameters. For demonstration, three prototypes (Deigns I, II, and III) with two, four, or six TZs are implemented. The measured results show that design I (II and III) has an insertion loss of 0.38 dB (0.7 dB and 0.8 dB), an operating bandwidth of 12.5% (7.5% and 6.9%), and a bandwidth for 30‐dB out‐of‐band suppression of 0.06f₀ (0.09f₀ and 0.14f₀). The isolation and common‐mode suppression inside the passbands of the three prototypes are all larger than 17 and 38 dB, respectively.