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SLIDING MODE CONTROL FOR GRADIENT TRACKING AND ROBOT NAVIGATION USING ARTIFICIAL POTENTIAL FIELDS

IEEE TRANSACTIONS ON robotics AND AUTOMATION 1995年第2期11卷 247-254页

作者： GULDNER, J UTKIN, VI DLR Institute for Robotics and System Dynamics Wessling Germany

This paper introduces a sliding mode control strategy for tracking the gradient of an artificial potential field, The control methodology is applicable to fully actuated holonomic robotic systems with n-degrees of freedom, The controller yields exact tracking of the gradient lines and is invariant with respect to parametric uncertainty and disturbances in system dynamics, A detailed case study for mobile robots introduces the equilibrium point placement method for designing harmonic planar potential fields for circular obstacle security zones. Diffeomorph mappings can be utilized for more complex obstacle security zones, The gradient of the harmonic potential field is shown to always lead away from the obstacle security zone and to continuously approach the goal point.

关键词： Sliding mode control Navigation Control systems Mobile robots Mechanical systems Force control Security Motion control Torque control Actuators

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Real-time visual servoing for laparoscopic surgery

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IEEE ENGINEERING IN MEDICINE AND BIOLOGY MAGAZINE 1997年第1期16卷 40-45页

作者： Wei, GQ ARbter, K Hirzinger, G German AeroSpace Research Establishment Institute of Robotics and System Dynamics DLR Germany

The authors propose a visual tracking method for stereo laparoscopes, which is robust, simple, and operates at a maximum rate of 17 Hz. The use of a stereo laparoscope enables the robot to track the instrument in both lateral and longitudinal motions. Due to the multiplicity of problems with shape analysis, the authors do not check for the presence of any particular shape or structure. Instead, they use color information alone for instrument segmentation. The non-uniqueness of the instrument color inspires the authors to distinguish it by use of an artificial color mark. They analyzed the color distribution of typical laparoscopic images and chose a color that did not appear to mark the instrument. With color image segmentation, the mark can be correctly located in the image and used to control the robot motion. Thus, even if only a very small part of the instrument is visible, reliable data can still be obtained for robot control. The image processing component is implemented on a commercially available image processing system MaxVideo MV200 (Datacube, Inc., Danvers, MA). The robot the authors use is the AESOP 1000 (Automated Endoscope system for Optimal Positioning) (Computer Motion, Inc., Goleta, CA).

关键词： Visual servoing Minimally invasive surgery Motion control Robot control Robot motion Image segmentation Instruments Laparoscopes Image color analysis Tracking

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SENSOR-BASED SPACE robotics - ROTEX AND ITS TELEROBOTIC FEATURES

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IEEE TRANSACTIONS ON robotics AND AUTOMATION 1993年第5期9卷 649-663页

作者： HIRZINGER, G BRUNNER, B DIETRICH, J HEINDL, J Institute for Robotics and System Dynamics German Aerospace Research Establishment Wessling Germany

In early 1993 the space robot technology experiment ROTEX has flown with space-shuttle COLUMBIA (spacelab mission D2 on flight STS-55 from April 26 to May 6). A multisensory robot on board the space-craft successfully worked in autonomous modes, teleoperated by astronauts, as well as in different telerobotic ground control modes. These include on-line teleoperation and telesensor-programming, a task-level oriented programming technique involving ''learning by showing'' concepts in a virtual environment. The robot's key features were its multisensory gripper and the local sensory feedback schemes that are the basis for shared autonomy. The corresponding man-machine interface concepts using a 6-DOF nonforce-reflecting control ball and visual feedback to the human operator are explained. Stereographic simulation on ground was used to predict not only the robot's free motion but even the sensor based path refinement on board;prototype tasks performed by this space robot were the assembly of a truss structure, connecting/disconnecting an electrical plug (orbit replaceable unit exchange ORU), and grasping free-floating objects.

关键词： Robot sensing systems Orbital robotics Telerobotics Space technology Feedback Robotic assembly Space vehicles Robot programming Virtual environment Grippers

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Parametric shape-from-shading by radial basis functions

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IEEE TRANSACTIONS ON PATTERN ANALYSIS AND MACHINE INTELLIGENCE 1997年第4期19卷 353-365页

作者： Wei, GQ Hirzinger, G Institute of Robotics and System Dynamics German Aerospace Research Establishment Oberpfaffenhofen Germany

In this paper, we present a new method of shape from shading by using radial basis functions to parameterize the object depth. The radial basis functions are deformed by adjusting their centers, widths, and weights such that the intensity errors are minimized. The initial centers and widths are arranged hierarchically to speed up convergence and to stabilize the solution. Although the smoothness constraint is used, ii can be eventually dropped out without causing instabilities in the solution. An important feature of our parametric shape-from-shading method is that it offers a unified framework for integration of multiple sensory information. We show that knowledge about surface depth and/or surface normals anywhere in the image can be easily incorporated into the shape from shading process. It is further demonstrated that even qualitative knowledge can be used in shape from shading to improve 3D reconstruction. Experimental comparisons of our method with several existing ones are made by using both synthetic and real images. Results show that our solution is more accurate than the others.

关键词： shape from shading radial basis functions hierarchical structure depth constraints normals constraints qualitative knowledge stochastic gradient method

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Learning shape from shading by a multilayer network

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IEEE TRANSACTIONS ON NEURAL NETWORKS 1996年第4期7卷 985-995页

作者： Wei, GQ Hirzinger, G Institute of Robotics and System Dynamics German Aerospace Research Establishment Oberpfaffenhofen Germany

The multilayer feedforward network has been usually used for learning a nonlinear mapping based on a set of examples of the input-output data, In this paper, we present a novel use of the network, in which the example data are not explicitly given, We consider the problem of shape from shading in computer vision, where the input (image coordinates) and the output (surface depth) satisfy only a known differential equation, We use the feedforward network as a parametric representation of the object surface and reformulate the shape from shading problem as the minimization of an error function over the network weights, The stochastic gradient and conjugate gradient methods are used for the minimization, Boundary conditions for either surface depth or surface normals (or both) can be imposed by adjusting the same network at different levels, It is further shown that the light source direction can be estimated, based on an initial guess, by integrating the source estimation with the surface estimation, Extensions of the method to a wider class of problems are discussed, The efficiency of the method is verified by examples of both synthetic and real images.

关键词： Shape Nonhomogeneous media Computer vision Differential equations Computer errors Stochastic processes Gradient methods Minimization methods Boundary conditions Light sources

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TRANSPUTER-BASED MULTIBODY system, DYNAMIC SIMULATION .2. PARALLEL IMPLEMENTATION - RESULTS

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MECHANICS OF STRUCTURES AND MACHINES 1994年第2期22卷 239-261页

作者： EICHBERGER, A [a]DLR—GERMAN AEROSPACE RESEARCH ESTABLISMENT INSTITUTE FOR ROBOTICS AND SYSTEM DYNAMICS WESSLING GERMANY

This paper continues demonstration of the benefits of parallel multibody simulation. In Part I implicit integration schemes combined with a modified inverse dynamic formulation were proposed for parallel multibody simulation. In Part II the modified inverse dynamics algorithm and computation of the integrator's Jacobian are split up into independent work packages for parallelization on medium-and coarse-grain levels, respectively. The farming concept, which organizes the flow of work and result packages through a network of processors, is presented. Transputers are used to build a distributed memory multiprocessor system, where both the medium- and coarse-grain approaches are implemented, resulting in the PARSIM-package for parallel multibody dynamics. The simulation of an off-road vehicle and a multibody model for a cable demonstrate the considerable savings in simulation times achieved by the new software package.

关键词： systems analysis

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TRANSPUTER-BASED MULTIBODY system DYNAMIC SIMULATION .1. THE RESIDUAL ALGORITHM - A MODIFIED INVERSE DYNAMIC FORMULATION

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MECHANICS OF STRUCTURES AND MACHINES 1994年第2期22卷 211-237页

作者： EICHBERGER, A [a]DLR—GERMAN AEROSPACE RESEARCH ESTABLISHMENT INSTITUTE FOR ROBOTICS AND SYSTEM DYNAMICS WESSLING GERMANY

The benefits of parallel multibody simulation are demonstrated in this paper. In Part I an extensive analysis of the options available in parallel multibody system simulation is given. As a result of this analysis, implicit integration schemes are proposed for simulation and a modified inverse dynamic formulation is presented, which generates the equations of motion directly, in an implicit differential-algebraic form. In Part II medium-and coarse-grain levels will be exploited for the parallelization of the modified inverse dynamic formulation and the integrator's Jacobian, respectively. Both approaches are implemented on a Transputer network, resulting in the PARSIM-package for parallel multibody simulation. Computational efficiences of the package are demonstrated.

关键词： systems analysis

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ROBUST LOW-ORDER CONTROL DESIGN OF A GENERIC FLEXIBLE TEST STRUCTURE

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IEE PROCEEDINGS-D CONTROL THEORY AND APPLICATIONS 1993年第3期140卷 167-175页

作者： GOH, CH Institute for Robotics and System Dynamics DLR German Aerospace Research Establishment Wessling Germany

The design of robust low-order controllers based on a high-order model of a generic flexible test structure with collocated sensors/actuators is considered. A new synthesis technique which combines the projective and the positive-real control concepts is developed and used for control design. The proposed method alleviates the known difficulty of the projective approach where the residual (nonretained) closed-loop modes can become unstable, and guarantees the strictly positive realness of the controller. Two approaches for selecting the free design parameters of the design technique are provided. Based on the new technique, two global controllers and one decentralised controller are designed with their performance evaluated and compared.

关键词： CONTROL THEORY CLOSED-LOOP CONTROL FLEXIBLE SPACE STRUCTURES PROJECTIVE CONTROL POSITIVE REAL CONTROL

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ROBUSTIZATION OF A LEARNING-METHOD FOR RBF NETWORKS

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NEUROCOMPUTING 1995年第1期9卷 85-94页

作者： SANCHEZ, VD German Aerospace Research Establishment DLR Oberpfaffenhofen Institute for Robotics and System Dynamics D-82230 Wessling Germany

Outliers in a given training data set can cause substantial deterioration of the approximation realized by a neural network architecture. Robustization refers to the process of enhancing a learning method to deal with data containing outliers. The robustization of a learning method for training RBF networks for function approximation is presented leading to a novel efficient robust learning method for this architecture class. Its experimental evaluation confirms the expectations created from its theoretical foundations.

关键词： FUNCTION APPROXIMATION LEARNING FROM EXAMPLES NETWORK SYNTHESIS RADIAL BASIS FUNCTIONS REGRESSION ROBUST LEARNING METHODS

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ROBUST DECOUPLING, IDEAL STEERING dynamics AND YAW STABILIZATION OF 4WS CARS

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AUTOMATICA 1994年第11期30卷 1761-1768页

作者： ACKERMANN, J [a]German Aerospace Research Establishment (DLR) Institute for Robotics and System Dynamics Oberpfaffenhofen D-82230 Wessling Germany

Four-wheel car steering is modeled by a single-track model with nonlinear tire characteristics. A generic control law for robust decoupling of lateral and yaw motion by yaw-rate feedback to front-wheel steering is derived. Ideal steering dynamics are achieved by velocity-scheduled lateral acceleration feedback to front-wheel steering. For robust yaw stabilization a velocity-scheduled yaw-rate feedback to rear-wheel steering is given, by which the linearized system gets velocity-independent yaw eigenvalues.

关键词： AUTOMOBILES ROBUST CONTROL DECOUPLING NONLINEAR systemS

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