TETROBOT is a modular system for the design, implementation, and control of a class of highly redundant parallel robotic mechanisms. This paper describes new experimental results based on evaluation of prototype confi...
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TETROBOT is a modular system for the design, implementation, and control of a class of highly redundant parallel robotic mechanisms. This paper describes new experimental results based on evaluation of prototype configurations with up to 18 nodes, 48 links and 15 actuators. TETROBOT is an actuated robotic structure which may be reassembled into many different configurations while still being controlled by the same hardware and software architecture. Implementations of a double octahedral platform, a tetrahedral arm and a six-legged walker, constructed from the same set of parts, are described. The TETROBOT system addresses the needs of application domains, such as space, undersea, mining, and construction, where adaptation to unstructured and changing environments and custom design for rapid implementation are required.
Parallel robots can be built by linking together unit cells in configurations which retain the static determinacy of the overall structure. In the Tetrobot system, the kinematics of these concatenated structures can b...
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Parallel robots can be built by linking together unit cells in configurations which retain the static determinacy of the overall structure. In the Tetrobot system, the kinematics of these concatenated structures can be solved by propagation of solutions through connected graphs of linked modules. In this paper, we examine the synthesis of unit cells which could be used in creating these structures and retain the ability to compute the kinematics for control of the actuated system. Admissible unit cells are shown to form families in two- and three-dimensions, and a set of synthesis rules is described which generates the members of these families recursively for each generations. The resulting set of modules comprises a broad set of useful cells which can be used to design parallel robots and guarantee the computability of their kinematics on a cell-by-cell basis.
This paper presents an application of feature-based visual servoing to achieve accurate and robust 3D filament alignment. Two orthogonal cameras are used to localize the five degrees of freedom of an axi-symmetric fil...
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This paper presents an application of feature-based visual servoing to achieve accurate and robust 3D filament alignment. Two orthogonal cameras are used to localize the five degrees of freedom of an axi-symmetric filament. An algorithm for precisely estimating the center and orientation features of a filament in a camera view is described. The use of feature-based servoing overcomes the difficulty of 3D camera calibration in a factory environment. These features drive a PID control loop for each view. The two views are coupled in one degree of freedom, and the multiple-view controller switches between two single-view controllers to achieve 3D servoing. The overall accuracy achieved is in thousandths of an inch. Experimental results on the performance of the control algorithm are discussed. Models explaining the system behavior are presented. The use of visual servoing in this application far exceeds the positioning accuracy and the repeatability of human operators.
This paper introduces a new feedback algorithm for steering a point robot through an obstacle field. The key innovation is the use of a circulatory field to rotate the robot path around the obstacles instead of the co...
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This paper introduces a new feedback algorithm for steering a point robot through an obstacle field. The key innovation is the use of a circulatory field to rotate the robot path around the obstacles instead of the common potential field which repels the robot. This idea is motivated by a charged particle in a magnetic field generated by a current flowing around the obstacle. In constrast, the potential field approach is associated with a repulsive static electric field generated by charges of the same polarity as the robot, on the obstacle. The circulatory field does not generate any spurious local minimum as it does not change the total energy of the system. By combining with an attractive potential field associated with the desired destination, this method achieves global convergence while avoiding collisions with obstacles.
An object-oriented modular approach to the engineering of complex robotic systems emphasizes reliability, reusability, ease of development, and user and network interfaces. This modular approach integrates many archit...
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An object-oriented modular approach to the engineering of complex robotic systems emphasizes reliability, reusability, ease of development, and user and network interfaces. This modular approach integrates many architectural principles and computational techniques which support adaptive and learning capability at the local, modular level. The TETROBOT is a modular and reconfigurable robotic system which was developed to demonstrate the reliable performance in a wide variety of task domains through reconfiguration of the same fundamental hardware and software components. Such a modular approach emphasizes the synthesis and integration of engineering modules and takes advantage of object-oriented engineering principles to design for a family of tasks. This paper provides an overview of the TETROBOT modular system and describes three modular systems in other applications domains.
This paper defines a new approach and investigates a fundamental problem in route planners. This capability is important for robotic vehicles(Martian Rovers, etc.) and for planning off-road military maneuvers. The emp...
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This paper defines a new approach and investigates a fundamental problem in route planners. This capability is important for robotic vehicles(Martian Rovers, etc.) and for planning off-road military maneuvers. The emphasis throughout this paper will be on the design and analysis and hieiaichical implementation of our route planner. This work was motivated by anticipation of the need to search a grid of a trillion points for optimum routes. This cannot be done simply by scaling upward from the algorithms used to search a grid of 10,000 points. Algorithms sufficient for the small grid are totally inadequate for the large grid. Soon, the challenge will be to compute off-road routes more than 100 km long and with a one or two-meter grid. Previous efforts are reviewed and the data structures, decomposition methods and search algorithms are analyzed and limitations are discussed. A detailed discussion of a hieraichical implementation is provided and the experimental results are analyzed.
This paper presents a new approach to reactive control utilizing the output of an explicit path planner which considers terrain preferences. To demonstrate the concept, a wavefront propagation, type of planner algorit...
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This paper presents a new approach to reactive control utilizing the output of an explicit path planner which considers terrain preferences. To demonstrate the concept, a wavefront propagation, type of planner algorithm, Trulla, is integrated into a reactive framework and used as part of the overall architecture. Terrain preferences are represented as weights or costs which are considered in generating a near optimal path. The algorithm is demonstrated on the CSM Denning-Branch MRV4 mobile robot for three scenarios: navigation out of a box canyon, planning with terrain preferences, and opportunistic path improvement.
Recovering depth and 3D position using known camera motion is useful for solving many problems in robotics such as object manipulation, navigation, and localization. Most existing techniques attempt to solve the gener...
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Recovering depth and 3D position using known camera motion is useful for solving many problems in robotics such as object manipulation, navigation, and localization. Most existing techniques attempt to solve the general problem by recovering depth across the entire image. They oftentimes make linear dynamics assumptions or use poorly recoverable metrics such as optical flow. An estimation technique is presented that retains the nonlinear camera dynamics and provides an accurate 3D position estimate of selected targets within the environment. In practice, the technique is accurate enough to fully specify the placement of a gripper for object manipulation after forward (as opposed to lateral) movement of a single camera. The technique also provides probabilistic information regarding the estimate, which can be used to make intelligent, informed decisions. We employed this technique at the 1995 AAai robot competition where our robot, Lola, placed 1st in Office Clean-up where it was able to pick up trash and recyclables and deposit them in the appropriate receptacles with great success. Results of our implementation on Lola are also presented.
One method of detecting closed loops in surface intersections requires the computation of collinear normal vectors. Such collinear normal vectors form a subset of critical points of the plane vector field defined by t...
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One method of detecting closed loops in surface intersections requires the computation of collinear normal vectors. Such collinear normal vectors form a subset of critical points of the plane vector field defined by the gradient of an oriented distance function from one surface to the other. The Poincare index theorem detects the existence of a critical point in a region of the vector field, but fails when two critical points having different signs of the index are in the same region. This paper presents a method for a conclusive test by extending the Poincare index theorem to three-dimensional vector fields. The idea of solid angle is introduced to compute the rotation of vector fields in three dimensions. The Poincare index gives the total number of critical points enclosed by a three-dimensional boundary.
The recent surge of interest in connectionist models arose through the availability of high speed parallel supercomputers and the advent of new leaning algorithms. The computations performed on concurrent architecture...
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The recent surge of interest in connectionist models arose through the availability of high speed parallel supercomputers and the advent of new leaning algorithms. The computations performed on concurrent architectures are less costly than similar ones performed on sequential machines. In this paper, the design and implementation of a parallel version of fuzzy ARTMAP (Carpenter et al. 1992), which encompasses both neural and fuzzy logic, is discussed. Fuzzy ARTMAP is a supervised leaning algorithm utilising two fuzzy ART modules and an associated mapping network. A simplified version of fuzzy ARTMAP (SFAM) was designed by incorporating a simplification of the match tracking concept on unsupervised fuzzy ART paradigms. The proposed simplified version consists of only one fuzzy ART module and an associated mapping network. A parallel fuzzy ARTMAP (PFAM) algorithm is then designed and implemented on a hypercube simulator (iPSC). The algorithm is parallelised for any architecture and, with the exception of issues related to communications, the implementation remains the same on any type of parallel machine. PFAM enjoys the advantage of reduced training time that makes the algorithm a successful candidate for applications that require both online testing and training. Such applications can range from underwater sonar detection and chemical plant processing control to nuclear reactor process control, flexible manufacturing and systems analysis.
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