移动机器人视觉定位方法的研究与实现

针对移动机器人的局部视觉定位问题进行了研究。首先通过移动机器人视觉定位与目标跟踪系统求出目标质心特征点的位置时间序列，然后在分析二次成像法获取目标深度信息的缺陷的基础上，提出了一种获取目标的空间位置和运动信息的方法。该方法利用序列图像和推广卡尔曼滤波，目标获取采用了HIS模型。在移动机器人满足一定机动的条件下，较精确地得到了目标的空间位置和运动信息。仿真结果验证了该方法的有效性和可行性。     

Invariant surface and motion estimation from sparse range data

In this paper, we present a system for the estimation of the surface structure and the motion parameters of a free-flying object in a tele-robotics experiment. The system consists of two main components: (i) a vision-based invariant-surface and motion estimator and (ii) a Kalman filter state estimator. We present a new algorithm for motion estimation from sparse multi-sensor range data. The motion estimates from the vision-based estimator are input to a Kalman filter state estimator for continuously tracking a free-flying object in space under zero-gravity conditions. The predicted position and orientation parameters are then fed back to the vision module of the system and serve as an initial guess in the search for optimal motion parameters. The task of the vision module is two-fold: (i) estimating a piecewise-smooth surface from a single frame of multi-sensor data and (ii) determining the most likely (in the Bayesian sense) object motion that makes data in subsequent time frames to have been sampled from the same piecewise-smooth surface. With each incoming data frame, the piecewise-smooth surface is incrementally refined. The problem is formulated as an energy minimization and solved numerically resulting in a surface estimate invariant to 3D rigid motion and the vector of motion parameters. Performance of the system is depicted on simulated and real range data.     

Understanding people motion in video sequences using Voronoi diagrams

This work describes a model for understanding people motion in video sequences using Voronoi diagrams, focusing on group detection and classification. We use the position of each individual as a site for the Voronoi diagram at each frame, and determine the temporal evolution of some sociological and psychological parameters, such as distance to neighbors and personal spaces. These parameters are used to compute individual characteristics (such as perceived personal space and comfort levels), that are analyzed to detect the formation of groups and their classification as voluntary or involuntary. Experimental results based on videos obtained from real life as well as from a crowd simulator were analyzed and discussed.     

Motion parameter estimation from global flow field data

Presented are two methods for the determination of the parameters of motion of a sensor, given the vector flow field induced by an imaging system governed by a perspective transformation of a rigid scene. Both algorithms integrate global data to determine motion parameters. The first (the flow circulation algorithm) determines the rotational parameters. The second (the FOE search algorithm) determines the translational parameters of the motion independently of the first algorithm. Several methods for determining when the function has the appropriate form are suggested. One method involves filtering the function by a collection of circular-surround zero-mean receptive fields. The other methods project the function onto a linear space of quadratic polynomials and measures the distance between the two functions. The error function for the first two methods is a quadratic polynomial of the candidate position, yielding a very rapid search strategy     

由特征点的空间位置估计运动参数

确定被观察物体和摄像机之间的三维相对运动是计算机视觉领域的一个重要课题.假定 物体上有若干特征点,它们在空间的位置已由双目视觉求得.在此假定下,本文讨论如何由特 征点空间位置的观察值来估计运动参数.现有文献中所用的目标函数导致的是一个非线性最 优化问题.本文利用凯莱(Cayley)定理提出一种新的目标函数,它导致的是一个十分简单的 线性最小二乘问题.文中还讨论了这两种目标函数之间的关系.     

On the problem of optimal spacecraft attitude control

The problem of the optimal control of a spacecraft reorientation from an arbitrary initial position into a prescribed final angular position is studied. For optimization, we use a generalized integral index characterizing the complexity of the rotation trajectory from the viewpoint of the “distance covered,” which is the generalized rotation angle that takes into account the different weights of the spacecraft axes in the sense of expenditures (of fuel, time, or another irreplaceable resource) needed to rotate the spacecraft by the same angle. An analytical solution of this problem is obtained. Two versions of the optimal spacecraft slew maneuver problem (using the shortest trajectory) are considered—the quickest maneuver and a maneuver in the prescribed time. The optimal control problem is solved for several types of constraints on the control variables. The time of starting the deceleration is determined based on the actual motion parameters (mismatch angle and angular velocity) using the terminal control principles (based on the angular position and angular velocity measurements). An example and simulation results of the spacecraft dynamics under the optimal control are presented, which demonstrate the practical usefulness of the proposed control algorithms.     

Contextual motion field-based distance for video analysis

In this work, we propose a general method for computing distance between video frames or sequences. Unlike conventional appearance-based methods, we first extract motion fields from original videos. To avoid the huge memory requirement demanded by the previous approaches, we utilize the “bag of motion vectors” model, and select Gaussian mixture model as compact representation. Thus, estimating distance between two frames is equivalent to calculating the distance between their corresponding Gaussian mixture models, which is solved via earth mover distance (EMD) in this paper. On the basis of the inter-frame distance, we further develop the distance measures for both full video sequences. Our main contribution is four-fold. Firstly, we operate on a tangent vector field of spatio-temporal 2D surface manifold generated by video motions, rather than the intensity gradient space. Here we argue that the former space is more fundamental. Secondly, the correlations between frames are explicitly exploited using a generative model named dynamic conditional random fields (DCRF). Under this framework, motion fields are estimated by Markov volumetric regression, which is more robust and may avoid the rank deficiency problem. Thirdly, our definition for video distance is in accord with human intuition and makes a better tradeoff between frame dissimilarity and chronological ordering. Lastly, our definition for frame distance allows for partial distance.     

Qualitative egomotion

Due to the aperture problem, the only motion measurement in images, whose computation does not require any assumptions about the scene in view, is normal flow—the projection of image motion on the gradient direction. In this paper we show how a monocular observer can estimate its 3D motion relative to the scene by using normal flow measurements in a global and qualitative way. The problem is addressed through a search technique. By checking constraints imposed by 3D motion parameters on the normal flow field, the possible space of solutions is gradually reduced. In the four modules that comprise the solution, constraints of increasing restriction are considered, culminating in testing every single normal flow value for its consistency with a set of motion parameters. The fact that motion is rigid defines geometric relations between certain values of the normal flow field. The selected values form patterns in the image plane that are dependent on only some of the motion parameters. These patterns, which are determined by the signs of the normal flow values, are searched for in order to find the axes of translation and rotation. The third rotational component is computed from normal flow vectors that are only due to rotational motion. Finally, by looking at the complete data set, all solutions that cannot give rise to the given normal flow field are discarded from the solution space.Research supported in part by NSF (Grant IRI-90-57934), ONR (Contract N00014-93-1-0257) and ARPA (Order No. 8459).     

Pontryagin’s maximum principle in optimal control problems of orientation of a spacecraft

Pontryagin’s maximum principle is used for solution of topical problems of spacecraft motion control. The dynamic optimal control problem of space orientation of a spacecraft from an arbitrary initial to a given final angular position with minimization of the turning time is studied in detail. The solution to the formulated problem is obtained and numerical expressions for synthesis of optimal control program are given. Results of mathematical simulation of the dynamics of motion of a spacecraft at optimal control are presented; these results demonstrate practical feasibility of the developed control algorithm.     

Study of observability of motion of an orbital group of navigation space system using intersatellite range measurements. I

The problem of specification of reference ephemeris (reference motion) using intersatellite range measurements on a given interval between spacecrafts of the space navigation system is formulated; observability for this problem is analyzed. Observability is the possibility of unambiguous determination of motion parameters of the orbital group of the space navigation system using known inter-satellite measurements on a given measurement interval. Linear approximate model describing the dependence between measurements and specified parameters are obtained for investigation of observability properties. In the framework of linear model problems of observability of motion of two any spacecrafts of the navigation system are studied using intersatellite range measurements.     

基于PH曲线的Delta机器人轨迹规划方法

针对Delta并联机器人高速作业时笛卡儿空间轨迹不平滑的问题,提出一种基于毕达哥拉斯速端曲线（PH曲线）的轨迹规划方法．首先,利用PH曲线平滑竖直运动与水平运动间的直角过渡部分,确定拾放操作轨迹;然后,利用多项式运动规律对轨迹的1维曲线位移进行规划,确定运动轨迹插补点的位置;最后,以最小化拾放操作周期为目标优化PH曲线参数,得到平滑的运动轨迹．仿真分析表明,基于该方法的拾放操作具有较短的运动周期,轨迹平滑且有较平稳的运动特性;实验结果表明,Delta机器人能够以90次/分钟的速度进行抓取操作,实现了并联机器人的高速作业．     

Orthogonal distance fitting of implicit curves and surfaces

Dimensional model fitting finds its applications in various fields of science and engineering and is a relevant subject in computer/machine vision and coordinate metrology. In this paper, we present two new fitting algorithms, distance-based and coordinate-based algorithm, for implicit surfaces and plane curves, which minimize the square sum of the orthogonal error distances between the model feature and the given data points. Each of the two algorithms has its own advantages and is to be purposefully applied to a specific fitting task, considering the implementation and memory space cost, and possibilities of observation weighting. By the new algorithms, the model feature parameters are grouped and simultaneously estimated in terms of form, position, and rotation parameters. The form parameters determine the shape of the model feature and the position/rotation parameters describe the rigid body motion of the model feature. The proposed algorithms are applicable to any kind of implicit surface and plane curve. In this paper, we also describe algorithm implementation and show various examples of orthogonal distance fit     

Optimization-based posture reconstruction for digital human models

Digital human modeling provides a valuable tool for designers when implemented early in the design process. Motion capture experiments offer a means of validation of the digital human simulation models. However, there is a gap between the motion capture experiments and the simulation models, as the motion capture results are marker positions in Cartesian space and the simulation model is based on joint space. Therefore, it is necessary to map the motion capture data to simulation models by employing a posture reconstruction algorithm. Posture reconstruction is an inherently redundant problem where the collective distance error between experimental joint centers and simulation joint centers is minimized. This paper presents an optimization-based method for determining an accurate and efficient solution to the posture reconstruction problem. The procedure is used to recreate 120 experimental postures. For each posture, the algorithm minimizes the distance between the simulation model joint centers and the corresponding experimental subject joint centers which is called the mean measurement error.     

Manipulator-actuated Adaptive Integrated Translational and Rotational Stabilization for Spacecraft in Proximity Operations with Control Constraint

This paper tackles the problem of integrated translation and rotation stabilization of the spacecraft in proximity operations by proposing a novel manipulator actuation strategy. To do so, by theoretically integrating the attitude/position motion of the spacecraft and the joint motion of the manipulator, a coupled translational and rotational kinematics of the spacecraft with a single space manipulator mounted is formulated, where system unknown parameters and residual system momentum are taken into account and analyzed. Taking the joint motion as the control input, a projection-based adaptive control scheme is then developed such that the translation and rotation of the spacecraft can be robustly stabilized with the manipulator-based actuation. The closed-loop asymptotic stability is guaranteed within Lyapunov framework. Meanwhile, considering the constrained joint motion of the manipulator, the resulting control constraint issue is handled by developing an optimization based bound analysis method, which also facilitates the determination of control parameters. Two scenario numerical simulations demonstrate the effect of the designed control scheme.     

单目序列图像的运动目标参数估算新方法

可疑运动目标的检测和参数估算是智能视频监控的关键。为克服传统计算机双目技术系统复杂等缺点,提出一种单目运动目标识别技术并估算目标运动参数的方法。利用几何成像原理,推导出运动目标与固定摄像机的实际水平距离和目标在二维图像中的位置之间数学模型,结合摄像机参数,估算出目标实际位置及运动速度。通过搭建的硬件平台和编写的测试软件,在实际码头对海面目标的参数估计进行了实验,结果显示了该方法简单、有效和可行。     

Efficient complete coverage of a known arbitrary environment with applications to aerial operations

The problem of coverage of known space arises in a multitude of domains, including search and rescue, mapping, and surveillance. In many of these applications, it is desirable or even necessary for the solution to guarantee both the complete coverage of the free space, as well as the efficiency of the generated trajectory in terms of distance traveled. A novel algorithm is introduced, based on the boustrophedon cellular decomposition technique, for computing an efficient complete coverage path for a known environment populated with arbitrary obstacles. This hierarchical approach first partitions the space to be covered into non-overlapping cells, then solves the Chinese postman problem to compute an Eulerian circuit traversing through these cells, and finally concatenates per-cell seed spreader motion patterns into a complete coverage path. Practical considerations of the coverage system are also explored for operations with a non-holonomic aerial vehicle. The effects of various system parameters are evaluated in controlled environments using a high-fidelity flight simulator, in addition to over 200 km of in-field flight sessions with a fixed-wing unmanned aerial vehicle.     

A Pseudo-Distance Algorithm for Collision Detection of Manipulators Using Convex-Plane-Polygons-based Representation

Robots have become indispensable parts for the industrial automated workshop. The distance calculation between the industrial robot and obstacles is a fundamental problem for the robotic collision-free motion control. But existing methods for this problem have the disadvantage that the accuracy and execution efficiency cannot be guaranteed at the same time. In this paper, a pseudo-distance algorithm is presented based on the convex-plane-polygons-based representation to solve this problem. In this algorithm, convex plane polygons (CPPs) and cylinders are utilized to represent obstacles and the manipulator, respectively. The spatial relationship between each CPP and each cylinder is discussed through defining condition parameters, and is divided into six conditions including three special conditions when the contact happens, and the other three conditions when there exists a certain distance between the CPP and the cylinder. The distance is modelled under different relations based on the theory of mathematics and geometry. The pseudo distance is determined through selecting the smallest value from distances between CPPs and cylinders. The numerical experiment is performed based on the proposed and two previous algorithms to estimate the shortest distance between an industrial robot and a groove-shape obstacle. And an application example is performed to show the significance of this work on the robotic motion control. Results indicate that the proposed algorithm is more efficient than previous algorithms under a certain precision requirement, and can be effectively applied in the robotic motion control.     

Numerical control optimization methods in one pursuit-evasion problem

This paper is devoted to the construction and study of different numerical suboptimal strategies of the pursuing player in a nonlinear three-dimensional pursuit-evasion game problem. The dynamics of the objects correspond to the known game of two cars [1]. The distinction of this problem from those considered before is the cost function structure, which contains the angular position of the velocity vectors with respect to the line of sight in addition to the distance between the players. In order to construct the numerical strategies of the pursuing player, we use the results of [2–6], where the elements of optimal control for simplified problems are obtained by using the Pontryagin maximum principle and the basic Isaacs-Bellman equation. On the basis of the strategies presented, we propose the algorithm for numerical construction of a suboptimal synthesis in the entire phase space of the initial problem. This algorithm follows an idea formulated in [7]. The numerical results of the suboptimal synthesis in a certain subdomain of the phase space are performed for some specified values of the parameters.     

Structure and motion estimation from apparent contours under circular motion

In this paper, we address the problem of recovering structure and motion from the apparent contours of a smooth surface. Fixed image features under circular motion and their relationships with the intrinsic parameters of the camera are exploited to provide a simple parameterization of the fundamental matrix relating any pair of views in the sequence. Such a parameterization allows a trivial initialization of the motion parameters, which all bear physical meaning. It also greatly reduces the dimension of the search space for the optimization problem, which can now be solved using only two epipolar tangents. In contrast to previous methods, the motion estimation algorithm introduced here can cope with incomplete circular motion and more widely spaced images. Existing techniques for model reconstruction from apparent contours are then reviewed and compared. Experiment on real data has been carried out and the 3D model reconstructed from the estimated motion is presented.