Fast approximate clearance evaluation for rovers with articulated suspension systems

We present a light‐weight body‐terrain clearance evaluation algorithm for the automated path planning of NASA's Mars 2020 rover. Extraterrestrial path planning is challenging due to the combination of terrain roughness and severe limitation in computational resources. Path planning on cluttered and/or uneven terrains requires repeated safety checks on all the candidate paths at a small interval. Predicting the future rover state requires simulating the vehicle settling on the terrain, which involves an inverse‐kinematics problem with iterative nonlinear optimization under geometric constraints. However, such expensive computation is intractable for slow spacecraft computers, such as RAD750, which is used by the Curiosity Mars rover and upcoming Mars 2020 rover. We propose the approximate clearance evaluation (ACE) algorithm, which obtains conservative bounds on vehicle clearance, attitude, and suspension angles without iterative computation. It obtains those bounds by estimating the lowest and highest heights that each wheel may reach given the underlying terrain, and calculating the worst‐case vehicle configuration associated with those extreme wheel heights. The bounds are guaranteed to be conservative, hence ensuring vehicle safety during autonomous navigation. ACE is planned to be used as part of the new onboard path planner of the Mars 2020 rover. This paper describes the algorithm in detail and validates our claim of conservatism and fast computation through experiments.     

基于地面力学的月球车爬坡轮—地相互作用模型

月球车爬坡地面力学模型在月球车的设计、越障性能评价、控制和仿真等方面具有极其重要作用．利 用月球车轮地相互作用测试系统进行车轮爬坡性能实验,结合实验数据在传统车轮—土壤相互作用应力分布模型之 上推导出爬坡轮—地相互作用模型,同时考虑爬坡角度对浅层月壤应力分布的影响,提出了随滑转率变化的沉陷 因数经验公式,来反映月壤压实、刮带、侧向流动等引起的滑转沉陷．通过对应力分布公式进行积分转化得到集中 力／力矩计算模型,利用ADAMS 二次开发的柔性爬坡仿真环境并结合实验数据进行模型验证．在斜坡角度为16±, 载荷为100 N,当滑转率从0 增加到0.6 时,将模型的车轮斜坡法向载荷、挂钩牵引力和驱动力矩的计算值与实验数 据相对比,结果相对误差不超过10%,因而该爬坡模型可以有效地用于月球车轮地相互作用的力学计算．     

湿吸附机理及其在仿生爬壁机器人中的应用

提出一种新的基于湿吸附机理的仿生爬壁机器人．首先讨论湿吸附模型及吸附力的控制方法,对一种 基于硫化硅橡胶（聚合物）的仿生足垫的湿吸附力进行测试,由此验证足垫与壁面间的液体薄膜对吸附力的积极影 响．然后设计一种实验研究用的轮爪式仿生爬壁机器人,并对其进行静力学分析．最后对所设计的机器人进行爬壁 试验．结果表明,液体薄膜可以有效提高足垫吸附力,所研制的湿吸附机器人可吸附于约85度的壁面,可成功爬行 于坡度约65度的玻璃壁面,一定程度上验证了湿吸附机理爬壁机器人的可行性．     

Efficient autonomous navigation for planetary rovers with limited resources

Rovers operating on Mars require more and more autonomous features to fulfill their challenging mission requirements. However, the inherent constraints of space systems render the implementation of complex algorithms an expensive and difficult task. In this paper, we propose an architecture for autonomous navigation. Efficient implementations of autonomous features are built on top of the ExoMars path following navigation approach to enhance the safety and traversing capabilities of the rover. These features allow the rover to detect and avoid hazards and perform significantly longer traverses planned by operators on the ground. The efficient navigation approach has been implemented and tested during field test campaigns on a planetary analogue terrain. The experiments evaluated the proposed architecture by autonomously completing several traverses of variable lengths while avoiding hazards. The approach relies only on the optical Localization Cameras stereo bench, a sensor that is found in all current rovers, and potentially allows for computationally inexpensive long‐range autonomous navigation in terrains of medium difficulty.     

Environment adaptation of a new staircase-climbing wheelchair

This paper describes the mechanical devices conforming a novel wheelchair prototype capable of climbing staircases. The key feature of the mechanical design is the use of two decoupled mechanisms in each axle, one to negotiate steps, and the other to position the axle with respect to the chair to accommodate the overall slope. This design simplifies the control task substantially. Kinematic models are necessary to describe the behavior of the system and to control the actuated degrees of freedom of the wheelchair to ensure the passenger’s comfort. The choice of a good climbing strategy simplifies the control and decreases the power consumption of the wheelchair. In particular, we demonstrate that if the movement of the wheelchair has the same slope as the racks or the same slope as the terrain that supports the wheel axles (depending on the configuration mechanism), control is easier and power consumption is less. Experimental results are reported which show the behavior of the prototype as it moves over different situations: (a) ascending a single step of different heights using different climbing strategies; and (b) climbing a staircase using an appropriate climbing strategy that simplifies the control and reduces the power consumption of the wheelchair.

Mars Science Laboratory Curiosity Rover Megaripple Crossings up to Sol 710 in Gale Crater

After landing in Gale Crater on August 6, 2012, the Mars Science Laboratory Curiosity rover traveled across regolith‐covered, rock‐strewn plains that transitioned into terrains that have been variably eroded, with valleys partially filled with windblown sands, and intervening plateaus capped by well‐cemented sandstones that have been fractured and shaped by wind into outcrops with numerous sharp rock surfaces. Wheel punctures and tears caused by sharp rocks while traversing the plateaus led to directing the rover to traverse in valleys where sands would cushion wheel loads. This required driving across a megaripple (windblown, sand‐sized deposit covered by coarser grains) that straddles a narrow gap and several extensive megaripple deposits that accumulated in low portions of valleys. Traverses across megaripple deposits led to mobility difficulties, with sinkage values up to approximately 30% of the 0.50 m wheel diameter, resultant high compaction resistances, and rover‐based slip up to 77%. Analysis of imaging and engineering data collected during traverses across megaripples for the first 710 sols (Mars days) of the mission, laboratory‐based single‐wheel soil experiments, full‐scale rover tests at the Dumont Dunes, Mojave Desert, California, and numerical simulations show that a combination of material properties and megaripple geometries explain the high wheel sinkage and slip events. Extensive megaripple deposits have subsequently been avoided and instead traverses have been implemented across terrains covered with regolith or thin windblown sand covers and megaripples separated by bedrock exposures.     

Mars microrover navigation: Performance evaluation and enhancement

In 1996, NASA will launch the Mars Pathfinder spacecraft, which will carry an 11 kg rover to explore the immediate vicinity of the lander. To assess the capabilities of the rover, as well as to set priorities for future rover research, it is essential to evaluate the performance of its autonomous navigation system as a function of terrain characteristics. Unfortunately, very little of this kind of evaluation has been done, for either planetary rovers or terrestrial applications. To fill this gap, we have constructed a new microrover testbed consisting of the Rocky 3.2 vehicle and an indoor test arena with overhead cameras for automatic, real-time tracking of the true rover position and heading. We create Mars analog terrains in this arena by randomly distributing rocks according to an exponential model of Mars rock size frequency created from Viking lander imagery. To date, we have recorded detailed logs from over 85 navigation trials in this testbed. In this paper, we outline current plans for Mars exploration over the next decade, summarize the design of the lander and rover for the 1996 Pathfinder mission, and introduce a decomposition of rover navigation into four major functions: goal designation, rover localization, hazard detection, and path selection. We then describe the Pathfinder approach to each function, present results to date of evaluating the performance of each function, and outline our approach to enhancing performance for future missions. The results show key limitations in the quality of rover localization, the speed of hazard detection, and the ability of behavior control algorithms for path selection to negotiate the rock frequencies likely to be encountered on Mars. We believe that the facilities, methodologies, and to some extent the specific performance results presented here will provide valuable examples for efforts to evaluate robotic vehicle performance in other applications.     

Perception‐aware autonomous mast motion planning for planetary exploration rovers

Highly accurate real‐time localization is of fundamental importance for the safety and efficiency of planetary rovers exploring the surface of Mars. Mars rover operations rely on vision‐based systems to avoid hazards as well as plan safe routes. However, vision‐based systems operate on the assumption that sufficient visual texture is visible in the scene. This poses a challenge for vision‐based navigation on Mars where regions lacking visual texture are prevalent. To overcome this, we make use of the ability of the rover to actively steer the visual sensor to improve fault tolerance and maximize the perception performance. This paper answers the question of where and when to look by presenting a method for predicting the sensor trajectory that maximizes the localization performance of the rover. This is accomplished by an online assessment of possible trajectories using synthetic, future camera views created from previous observations of the scene. The proposed trajectories are quantified and chosen based on the expected localization performance. In this study, we validate the proposed method in field experiments at the Jet Propulsion Laboratory (JPL) Mars Yard. Furthermore, multiple performance metrics are identified and evaluated for reducing the overall runtime of the algorithm. We show how actively steering the perception system increases the localization accuracy compared with traditional fixed‐sensor configurations.     

Planetary Rover Developments Supporting Mars Exploration, Sample Return and Future Human-Robotic Colonization

We overview our recent research on planetary mobility. Products of this effort include the Field Integrated Design & Operations rover (FIDO), Sample Return Rover (SRR), reconfigurable rover units that function as an All Terrain Explorer (ATE), and a multi-Robot Work Crew of closely cooperating rovers (RWC). FIDO rover is an advanced technology prototype; its design and field testing support NASA's development of long range, in situ Mars surface science missions. Complementing this, SRR implements autonomous visual recognition, navigation, rendezvous, and manipulation functions enabling small object pick-up, handling, and precision terminal docking to a Mars ascent vehicle for future Mars Sample Return. ATE implements on-board reconfiguration of rover geometry and control for adaptive response to adverse and changing terrain, e.g., traversal of steep, sandy slopes. RWC implements coordinated control of two rovers under closed loop kinematics and force constraints, e.g., transport of large payloads, as would occur in robotic colonies at future Mars outposts. RWC is based in a new extensible architecture for decentralized control of, and collective state estimation by multiple heterogeneous robotic platforms—CAMPOUT; we overview the key architectural features. We have conducted experiments with all these new rover system concepts over variable natural terrain. For each of the above developments, we summarize our approach, some of our key experimental results to date, and our future directions of planned development.     

Visual terrain mapping for Mars exploration

One goal for future Mars missions is for a rover to be able to navigate autonomously to science targets not visible to the rover, but seen in orbital or descent images. This can be accomplished if accurate maps of the terrain are available for the rover to use in planning and localization. We describe techniques to generate such terrain maps using images with a variety of resolutions and scales, including surface images from the lander and rover, descent images captured by the lander as it approaches the planetary surface, and orbital images from current and future Mars orbiters. At the highest resolution, we process surface images captured by rovers and landers using bundle adjustment. At the next lower resolution (and larger scale), we use wide-baseline stereo vision to map terrain distant from a rover with surface images. Mapping the lander descent images using a structure-from-motion algorithm generates data at a hierarchy of resolutions. These provide a link between the high-resolution surface images and the low-resolution orbital images. Orbital images are mapped using similar techniques, although with the added complication that the images may be captured with a variety of sensors. Robust multi-modal matching techniques are applied to these images. The terrain maps are combined using a system for unifying multi-resolution models and integrating three-dimensional terrains. The result is a multi-resolution map that can be used to generate fixed-resolution maps at any desired scale.     

Kinematics Modeling and Analyses of Articulated Rovers

This paper describes a general approach to the kinematics modeling and analyses of articulated rovers traversing uneven terrain. The model is derived for full 6-degree-of-freedom motion, enabling movements in the$x$,$y$, and$z$directions, as well as pitch, roll, and yaw rotations. Differential kinematics is derived for the individual wheel motions in contact with the terrain. The resulting equations of the individual wheel motions are then combined to form the composite equation for the rover motion. Three types of kinematics, i.e., navigation, actuation, and slip kinematics are identified, and the equations and application of each are discussed. The derivations are specialized to Rocky 7, a highly articulated prototype Mars rover, to illustrate the developed methods. Simulation results are provided for the motion of the Rocky 7 over several terrains, and various motion profiles are provided to explain the behavior of the rover.     

月球车驱动轮爬坡性能的影响因素研究

研究了驱动轮的滑转率、结构参数和载荷对月球车爬坡性能的影响。针对月表复杂路况下车辆通过性较差问题,为提高月球车爬坡性能,基于车辆地面力学中土壤的承压和剪切特性理论,建立了刚性驱动轮与月面斜坡松软月壤间的相互作用模型。通过车轮实例对月球车爬坡性能进行预测和分析。实验结果表明,增大驱动轮的滑转率、半径、宽度、轮刺高度和减小载荷能够增强月球车爬坡能力和提高车轮驱动效率,但随着爬坡能力的增强,车轮驱动效率呈现先增大后减小的趋势。研究结果为月球车轮结构设计以及控制策略的研究提供了参考。     

Perfect r-domination in the Kronecker product of two cycles, with an application to diagonal/toroidal mesh

If r?1, and m and n are each a multiple of (r+1)²+r², then each isomorphic component of C_m×C_n admits of a vertex partition into (r+1)²+r² perfect r-dominating sets. The result induces a dense packing of C_m×C_n by means of vertex-disjoint subgraphs, each isomorphic to a diagonal array. Areas of applications include efficient resource placement in a diagonal mesh and error-correcting codes.     

火星车沉陷机理与脱困策略研究

以“祝融号”火星车为研究对象,基于车辆地面力学理论分析了火星车发生沉陷的机理,基于滑转率、电流、沉陷深度等给出沉陷判别方法,制定了不同条件下“祝融号”火星车的沉陷判别准则及脱困策略。验证试验结果表明：临界沉陷时滑转率为61.25%、驱动电流为1.90 A,达到沉陷临界值后“祝融号”火星车将无法直接驶离,而“祝融号”火星车主动悬架的蠕动是实现脱困的有效方法。研究成果可为“祝融号”火星车在轨使用策略提供试验数据和参考。     

Estimating Siberian timber volume using MODIS and ICESat/GLAS

Geosciences Laser Altimeter System (GLAS) space LiDAR data are used to attribute a MODerate resolution Imaging Spectrometer (MODIS) 500 m land cover classification of a 10° latitude by 12° longitude study area in south-central Siberia. Timber volume estimates are generated for 16 forest classes, i.e., four forest cover types × four canopy density classes, across this 811,414 km² area and compared with a ground-based regional volume estimate. Two regional GLAS/MODIS timber volume products, one considering only those pulses falling on slopes ≤ 10° and one utilizing all GLAS pulses regardless of slope, are generated. Using a two-phase(GLAS-ground plot) sampling design, GLAS/MODIS volumes average 163.4 ± 11.8 m³/ha across all 16 forest classes based on GLAS pulses on slopes ≤ 10° and 171.9 ± 12.4 m³/ha considering GLAS shots on all slopes. The increase in regional GLAS volume per-hectare estimates as a function of increasing slope most likely illustrate the effects of vertical waveform expansion due to the convolution of topography with the forest canopy response. A comparable, independent, ground-based estimate is 146 m³/ha [Shepashenko, D., Shvidenko, A., and Nilsson, S. (1998). Phytomass (live biomass) and carbon of Siberian forests. Biomass and Bioenergy, 14, 21-31], a difference of 11.9% and 17.7% for GLAS shots on slopes ≤ 10° and all GLAS shots regardless of slope, respectively. A ground-based estimate of total volume for the entire study area, 7.46 × 10⁹ m³, is derived using Shepashenko et al.'s per-hectare volume estimate in conjunction with forest area derived from a 1990 forest map [Grasia, M.G. (ed.). (1990). Forest Map of USSR. Soyuzgiproleskhoz, Moscow, RU. Scale: 1:2,500,000]. The comparable GLAS/MODIS estimate is 7.38 × 10⁹ m³, a difference of less than 1.1%. Results indicate that GLAS data can be used to attribute digital land cover maps to estimate forest resources over subcontinental areas encompassing hundreds of thousands of square kilometers.     

An enlarged family of packing polynomials on multidimensional lattices

HereN = {0, 1, 2, ...}, while a functionf onN ^m or a larger domain is apacking function if its restrictionf|N ^m is a bijection ontoN. (Packing functions generalize Cantor's [1]pairing polynomials, and yield multidimensional-array storage schemes.) We call two functionsequivalent if permuting arguments makes them equal. Alsos(x) =x ₁ + ... +x _m when x = (x ₁,...,x _m); and such anf is adiagonal mapping iff(x) <f(y) whenever x, y εN ^m ands(x) <s(y). Lew [7] composed Skolem's [14], [15] diagonal packing polynomials (essentially one for eachm) to constructc(m) inequivalent nondiagonal packing polynomials on eachN ^m. For eachm > 1 we now construct 2^m−2 inequivalent diagonal packing polynomials. Then, extending the tree arguments of the prior work, we obtaind(m) inequivalent nondiagonal packing polynomials, whered(m)/c(m) → ∞ asm → ∞. Among these we count the polynomials of extremal degree.     

一种蛇形机器人的结构设计与研制

蛇形机器人(以下简称机器蛇)因其身体细长和环境适应能力强的优点被广泛应用于不适宜人类工作的领域.介绍了一种仿生机器蛇的设计与制作.设计时选用体积小、动力足的P0090舵机作为机器蛇驱动,Atmega128和Atmega8单片机作为控制器.HPD8506A作为无线数据发射模块,完成PC与机器蛇的数据传输.根据舵机尺寸逆向设计关节、蛇头和蛇尾,采用正交关节连接方式装配,实现机器蛇蜿蜒、蠕动等多步态的移动,加载的红外避障传感器保障了机器蛇能安全躲避障碍物.此系统的研究为今后机器蛇在狭小管道或高空缆绳上攀爬并完成检测任务奠定基础.     

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.     

Improved Rover State Estimation in Challenging Terrain

Given ambitious mission objectives and long delay times between command-uplink/data-downlink sessions, increased autonomy is required for planetary rovers. Specifically, NASA's planned 2003 and 2005 Mars rover missions must incorporate increased autonomy if their desired mission goals are to be realized. Increased autonomy, including autonomous path planning and navigation to user designated goals, relies on good quality estimates of the rover's state, e.g., its position and orientation relative to some initial reference frame. The challenging terrain over which the rover will necessarily traverse tends to seriously degrade a dead-reckoned state estimate, given severe wheel slip and/or interaction with obstacles. In this paper, we present the implementation of a complete rover navigation system. First, the system is able to adaptively construct semi-sparse terrain maps based on the current ground texture and distances to possible nearby obstacles. Second, the rover is able to match successively constructed terrain maps to obtain a vision-based state estimate which can then be fused with wheel odometry to obtain a much improved state estimate. Finally the rover makes use of this state estimate to perform autonomous real-time path planning and navigation to user designated goals. Reactive obstacle avoidance is also implemented for roaming in an environment in the absence of a user designated goal. The system is demonstrated in soft soil and relatively dense rock fields, achieving state estimates that are significantly improved with respect to dead reckoning alone (e.g., 0.38 m mean absolute error vs. 1.34 m), and successfully navigating in multiple trials to user designated goals.     

Effects of foot placement,hand positioning,age and climbing biodynamics on ladder slip outcomes

Ladder falls frequently cause severe injuries; yet the factors that influence ladder slips/falls are not well understood. This study aimed to quantify (1) the effects of restricted foot placement, hand positioning, climbing direction and age on slip outcomes, and (2) differences in climbing styles leading to slips versus styles leading to non-slips. Thirty-two occupational ladder users from three age groups (18–24, 25–44 and 45–64 years) were unexpectedly slipped climbing a vertical ladder, while being assigned to different foot placement conditions (unrestricted vs. restricted toe clearance) and different hand positions (rails vs. rungs). Constraining foot placement increased the climber's likelihood of slipping (p < 0.01), while younger and older participants slipped more than the middle-aged group (p < 0.01). Longer double stance time, dissimilar and more variable foot and body positioning were found in styles leading to a slip. Maintaining sufficient toe clearance and targeting ladder safety training to younger and older workers may reduce ladder falls.

Practitioner Summary: Ladder falls frequently cause severe occupational fall injuries. This study aims to identify safer ladder climbing techniques and individuals at risk of falling. The results suggest that ladders with unrestricted toe clearance and ladder climbing training programmes, particularly for younger and older workers, may reduce ladder slipping risk.