NURBS扫描体的逼近算法研究

提供了一种NURBS扫描体的逼近方法。该方法主要步骤：(1)通过系列平面切割,把NURBS曲面(实体)进行降维处理,变成平面曲线;(2)为曲线设置局部标架;(3)在局部标架下求出每一曲线在每一时刻的极值点后将其转换成原曲线的奇异点;(4)使用marching cubes算法剔除扫描体内部点,保留扫描体边界上的奇异点;(5)由所有保留点拟合成奇异曲面。本算法能较好地逼近NURBS扫描体,其逼近精度可通过控制切割精度和扫描过程中时间间隔的选取而得到有效控制。     

Passivity-based target manipulation inside a deformable object by a robotic system with noncollocated feedback

Target manipulation inside a deformable object by a robotic system is necessary in many medical and industrial applications. However, this is a challenging problem because of the difficulty of imposing the motion of the internal target point by a finite number actuation points located at the boundary of the deformable object. In this work, an optimal contact formulation and a control action are presented, in which a deformable object is externally manipulated with multiple robotic fingers such that an internal target point is positioned to a desired location. First, we formulate an optimization technique that minimizes the total force applied to the object to determine the location of actuation points to affect the desired motion. Then, a passivity-based control approach, based on energy monitoring and dissipation, is developed to improve stability of the whole system. The simulation results demonstrate the efficacy of the proposed method.     

Cooperative manipulation of a floating object by some space robots: application of a tracking control method using the transpose of the generalized Jacobian matrix

In future space missions, it is considered that many tasks will be achieved by cooperative motions of space robots. For free-floating space robots with manipulators, we have proposed a digital tracking control method using the transpose of the generalized Jacobian matrix (GJM). In this paper, the tracking control method using the transpose of the GJM is applied to cooperative manipulations of a floating object by space robots. Simulation results show the effectiveness of the control method. This work was presented in part at the 12th International Symposium on Artificial Life and Robotics, Oita, Japan, January 25–27, 2007     

Dexterous manipulation of an object by means of multi‐DOF robotic fingers with soft tips

This article analyzes the dynamics of motion of various setups of two multiple degree‐of‐freedom (DOF) fingers that have soft tips, in fine manipulation of an object, and shows performances of their motions via computer simulation. A mathematical model of these dynamics is described as a system of nonlinear differential equations expressing motion of the overall fingers‐object system together with algebraic constraints due to tight area contacts between the finger‐tips and surfaces of the object. First, problems of (1) dynamic, stable grasping and (2) regulation of the object rotational angle by means of a setup of dual two‐DOF fingers, are treated. Second, the problem of regulating the position of the object mass center by means of a pair of two‐DOF and three‐DOF fingers is considered. Third, a set of dual three‐DOF fingers is treated, in order to let it perform a sophisticated task, which is specified by a periodic pattern of the object posture and a constant internal force. In any case, there exist sensory‐motor coordinations, which are described by analytic feedback connections from sensing to actions at finger joints. In the cases of setpoint control problems, convergences of motion to secure grasping together with the specified object rotational angle and/or the specified object mass center position, are proved theoretically. A constraint stabilization method (CSM) is used for solving numerically the differential algebraic equations to show performances of the proposed sensory‐feedback schemes. © 2002 Wiley Periodicals, Inc.     

On-line exploration of an unknown surface by a robotic probe

A control strategy is developed for a robotic probe with tactile sensing to explore an unknown surface without losing contact. Digital computer simulations are performed of a three-link, planar manipulator exploring an ellipsoidal surface in order to test the control strategy. The equations of motion are written and linear, time-varying, state-variable feedback is applied to stabilize and decouple the system. A tactile sensor is simulated to supply the normal force between the robot and the surface. From the magnitude and direction of this force, the desired trajectory is determined. An inverse plant and force feedback are implemented to provide the required input torques to the robot's actuators.     

Model-based and neural-network-based adaptive control of two robotic arms manipulating an object with relative motion

In the study of constrained multiple robot control, the relative motion between the constraint object and the end effectors of manipulators are usually neglected in the literature. However, in many industrial applications, such as assembly and machining, the constraint object is required to move with respect to not only the world coordinates but also the end effectors of the robotic arms. In this paper, dynamic modelling of two robotic arms manipulating an object with relative motion is presented first, then a model-based adaptive controller and a model-free neural network controller are developed. Both controllers guarantee the asymptotic tracking of the constraint object and the boundedness of the constraint force. Asymptotic convergence of the constraint force can also be achieved under certain conditions. Simulation studies are conducted to verify the effectiveness of the approaches.     

Robust nonlinear control schemes for finite-time tracking objective of a 5-DOF robotic exoskeleton

This paper investigates the finite-time robust tracking problem for a 5-DOF (degrees of freedom) upper-limb exoskeleton robot subjected to parametric uncertainties, unmodelled dynamics, and unknown human efforts. By developing the non-singular terminal sliding mode control approach, three innovative schemes of robust torques are proposed to steer configuration variables (angular displacements of joints) of the 5-DOF robotic exoskeleton to the reference trajectories within adjustable finite times. Based on mathematical analysis, it is proven that all suggested schemes of control inputs (input torques) accomplish and provide the mentioned tracking objective accurately. In addition, several new formulas (in the form of inequalities) are derived to determine and tune the needed finite times for achieving the tracking objective. Finally, three numerical examples are given to show the appropriate performance and the acceptable effectiveness of the proposed finite-time robust control schemes.     

Control of an object with parallel surfaces by a pair of finger robots without object sensing

This paper proposes a method for controlling an object with parallel surfaces in a horizontal plane by a pair of finger robots. The control method can achieve stable grasping, relative orientation control, and relative position control of the grasped object. The control inputs require neither any object parameters nor any object sensing, such as tactile sensors, force sensors, or visual sensors. The control inputs are also quite simple and do not need to solve either inverse kinematics or inverse dynamics. The stability of the closed-loop system is proved, and simulation and experimental results validate the control method.     

Boundary of the volume swept by a free-form solid in screw motion

The swept volume of a moving solid is a powerful computational and visualization concept. It provides an excellent aid for path and accessibility planning in robotics and for simulating various manufacturing operations. It has proven difficult to evaluate the boundary of the volume swept by a solid bounded by trimmed parametric surfaces undergoing an arbitrary analytic motion. Hence, prior solutions use one or several of the following simplifications: (1) approximate the volume by the union of a finite set of solid instances sampled along the motion; (2) approximate the curved solid by a polyhedron; and (3) approximate the motion by a sequence of simpler motions. The approach proposed here is based on the third type of simplification: it uses a polyscrew (continuous, piecewise-helical) approximation of the motion. This approach leads to a simple algorithm that generates candidate faces, computes the two-cells of their arrangement, and uses a new point-in-sweep test to select the correct cells whose union forms the boundary of the swept volume.     

Real-space investigation of a transverse wave in a liquid system generated by a molecular-dynamics simulation

We have invented a simple intuitive method for describing the existence of microscopic transverse wave in a liquid system produced by molecular-dynamics simulations. The method is based on an idea of using a velocity field which is determined by the velocity of atoms in liquids. One of the significant advantages of our method over a conventional method is that the waves are investigated in real space rather than in wavenumber space. This will help to visualize microscopic waves by computer graphics. We have applied the method to liquid tin at three thermodynamic states generated by ab initio molecular-dynamics simulations and found that it can distinguish whether the liquids have transverse waves or not in the same way as the conventional method. We have also shown that the velocity autocorrelation function consists of the transverse and longitudinal parts.     

Guaranteed search of a target object by an electromechanical system with minimal light power inputs

An optimal guaranteed control problem for electromechanical manipulator with the goal of finding an immovable or mobile target objects is considered. Unlike [1–6], as the optimality criterion, a functional taking into account power inputs of the light source on the gripper of the manipulator is taken. The sought object is assumed to be detected if it falls into the light circle with given illumination. The control algorithms of the gripper motion and corresponding laws of electric current variation in the light source circuit providing the detection of both immovable and mobile sought object in a guaranteed time for minimal light power inputs during the search are developed. The gain in light power inputs achieved for the proposed search algorithms is estimated.     

Kinematic analysis and optimal design of a novel 1T3R parallel manipulator with an articulated travelling plate

Driven by the requirements of the large-scale component assemblage for the docking platform, this paper proposes a novel one-translational-three-rotational (1T3R) parallel manipulator with an articulated travelling plate, which can provide high stiffness and good accuracy performances in the assemblage. The underlying architecture of this manipulator is briefly addressed with emphasis on the practical realization of the articulated travelling plate. On the basis of the kinematic analysis of the 1T3R parallel manipulator, its optimal design considering the force and motion transmissibility is carried out, in which the generalized virtual power transmissibility of this manipulator is defined. This paper aims at laying a solid theoretical and technical foundation for the prototype design and manufacture of the 1T3R parallel manipulator.     

Range identification of features on an object using a single camera

In this paper, an adaptive nonlinear estimator is developed to identify the range and the 3D Euclidean coordinates of feature points on a moving object using a single fixed camera. No explicit model is used to describe the movement of the object. Homography-based techniques are used in the development of the object kinematics, while an adaptive nonlinear estimator is designed by employing signal filters. Lyapunov design methods are utilized to facilitate the design of the estimator and filters as well as the convergence and stability analysis. The performance of the estimator is demonstrated by simulation results.     

Evaluation of a surgical interface for robotic cryoablation task using an eye-tracking system

Computer-assisted navigation systems coupled with surgical interfaces (SIs) are providing doctors with tools that are safer for patients compared to traditional methods. Usability analysis of the SIs that guides their development is hence important. In this study, we record the eye movements of doctors and other people with no medical expertise during interaction with an SI that directs a simulated cryoablation task. There are two different arrangements for the layout of the same SI, and the goal is to evaluate whether one of these arrangements is ergonomically better than the other. We use several gaze related statistics some of which are employed in an SI design context for the first time. Even though the performance and gaze related analysis reveals that the two arrangements are comparable in many respects, there are also differences. Specifically, one arrangement leads to more saccades along the vertical and horizontal directions, lower saccade amplitudes in the crucial phase of the task, more locally clustered and yet globally spread viewing. Accordingly, that arrangement is selected for future use. The present study provides a proof of concept for the integration of novel gaze analysis tools developed for scene perception studies into the interface development process.     

Online construction of the manipulation model of an unknown object by a robot hand using the regrasping primitives

This paper presents a planner which explores an unknown polyhedral object with a multifingered hand in a systematic way by constructing the manipulation-model of the object. The manipulation-model of an object we proposed previously is a database which consists of landmark orientations of the object, the applicability of manipulation primitives to them and intertransformations among them. In this paper, two regrasping primitives, rotation and pivoting, are employed. A multifingered hand probes a given unknown object for pivot/rotation axes. If a new axis is found, the planner recursively performs pivoting or rotation-test (which is similar to rotation but does not actually rotate the object) about the found axis and searches the object for more axes. The manipulation-model of the object is constructed based on the found axes. An experiment for constructing a manipulation-model of a non-convex polyhedral object is conducted using a fourfingered hand. Force/torque sensors mounted on the fingertips collect the data of the object. A geometrical model of the object is also constructed.     

Transfer control of a large object by a group of mobile robots

In this paper, the authors propose a practical cooperative planning architecture of multiple mobile robots by means of a layered architecture consisting of a physical layer, a geometrical layer, and an informational layer. A “Virtual Impedance Model” is used in order to integrate the three layers. The effectiveness of the proposed architecture is verified by experiments and simulations on the task of transferring a large object by multiple mobile robots.     

A dynamic model of an underwater vehicle with a robotic manipulator using Kane's method

Development of a robust autonomous Underwater Robotic Vehicle (URV) is a key element to the exploitation of marine resources. An accurate dynamic model is important for both controller design and mission simulation, regardless of the control strategy employed. In this paper, a dynamic model for an underwater vehicle with an n-axis robot arm is developed based on Kane's method. The technique provides a direct method for incorporating external environmental forces into the model. The model developed in this paper includes four major hydrodynamic forces: added mass, profile drag, fluid acceleration, and buoyancy. The model derived is a closed form solution which can be utilized in modern model-based control schemes.