A magnetic suspension system with linear actuators and permanent magnets (instead of electromagnets) has been developed. In this system the bearing forces are controlled by adjusting the air gaps between permanent mag...
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A magnetic suspension system with linear actuators and permanent magnets (instead of electromagnets) has been developed. In this system the bearing forces are controlled by adjusting the air gaps between permanent magnets and the levitated object (a circular disk). This system uses less energy and exhibits none of the over-heating of coils typical of systems employing electro-magnets. This paper describes a disk suspension system with three degrees of freedom. The system can operate either with a decentralized (distributed) feedback control system or with a centralized (lumped) one. Feedback gain matrices are calculated for each type of control system. The performances of the two types of control systems are compared by numerical simulations and experiment. This work is part of an effort to develop a magnetic levitation conveyer system.
Prototype based methods are commonly used in cluster analysis and the results may be highly dependent on the prototype used. In this paper, we propose a fuzzy clustering method that involves adaptively expanding conve...
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Prototype based methods are commonly used in cluster analysis and the results may be highly dependent on the prototype used. In this paper, we propose a fuzzy clustering method that involves adaptively expanding convex polytopes. Thus, the dependency on the use of prototypes can be eliminated. Also, the proposed method makes it possible to effectively represent an arbitrarily distributed data set without a priori knowledge of the number of clusters in the data set. Specifically, nonlinear membership functions are utilized to determine whether a new cluster is created or which vertex of the cluster should be expanded. For this, the membership function of a new vertex is assigned according to not only a distance measure between an incoming pattern vector and a current vertex, but also the amount of how much the current vertex has been modified. Therefore, cluster expansion can be only allowed for one cluster per incoming pattern. Several experimental results are given to show the validity of our method.
This paper presents a design experience of a supervisory control system for coordination of multiple robotic devices. To effectively program job commands, a Petri net-type graphical robot language(PGRL) is proposed, w...
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This paper presents a design experience of a supervisory control system for coordination of multiple robotic devices. To effectively program job commands, a Petri net-type graphical robot language(PGRL) is proposed, where some functions for coordination among tasks such as concurrency and synchronization, can be easily programmed. Each task of PGRL is described by employing formal model languages, which are composed of three modules, sensory, data handling, and action module. It is expected that by using our proposed PGRL and formal model languages, one can efficiently describe a job or task, and hence can easily operate a complex real-time concurrent system. The proposed control system has been implemented by using VME-based 32-bit microprocessor boards and a real-time multitasking operating system (VxWorks), and is shown to successfully work for robotic jobs.
A robust internal force-based impedance control scheme for coordinating manipulators is introduced. Internal force-based impedance control enforces a relationship between the velocity of each manipulator and the inter...
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A robust internal force-based impedance control scheme for coordinating manipulators is introduced. Internal force-based impedance control enforces a relationship between the velocity of each manipulator and the internal force on the manipulated objects and requires no knowledge of the object dynamic model. Each manipulator's nonlinear dynamics is compensated by a robust auxiliary controller which is insensitive to robot-model uncertainty and payload variation. The controller is only weakly-dependent on each manipulator's inertia matrix. Stability of the system is analyzed. The scheme is computationally inexpensive and suitable for general-purpose microcomputer implementation. Rigorous experimental investigations are performed and the results presented which validate the proposed concepts.
A common approach to control multi-fingered grippers during stable grasping is the stiffness control scheme. "Internal" stiffness parameters and suitable references for internal grasping forces-often determi...
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A common approach to control multi-fingered grippers during stable grasping is the stiffness control scheme. "Internal" stiffness parameters and suitable references for internal grasping forces-often determined heuristically-ensure a stable grasp. In this paper, optimal internal forces are obtained in real-time by linearly constrained gradient flows on the smooth manifold of positive definite matrices. This optimization approach is a generic one for any number of fingers in contact with the object. Experiments with the 3-fingered Darmstadt hand show the simplicity and efficiency of the approach.
This paper proposes a decentralised compensation scheme for unstructured uncertainties and modelling errors of robotic manipulators. The scheme employs a central decoupler and independent joint neural network compensa...
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This paper proposes a decentralised compensation scheme for unstructured uncertainties and modelling errors of robotic manipulators. The scheme employs a central decoupler and independent joint neural network compensators. Recursive Newton Euler formulas are used to decouple robot dynamics to obtain a set of equations in terms of input and output of each joint. Each joint sub-system is then controlled separately by neural network controllers which suppress the effects of uncertainties associated with the model. Multi-layered perceptrons using back-propagation learning algorithm are employed as the adaptive elements in the control scheme. The effectiveness of the proposed scheme is demonstrated by a simulation experiment on PUMA 560. Simulation results show that this control scheme achieves fast and precise robot motion control under substantial model inaccuracies. Properties of the neural compensation technique are compared with those of a globally stable adaptive controller.
The search for minimum-time motion of an articulated mechanical arm by tessellating the joint space involves heavy computational burden. In this work, Genetic Algorithms (GAs) are used to tackle this problem while con...
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The search for minimum-time motion of an articulated mechanical arm by tessellating the joint space involves heavy computational burden. In this work, Genetic Algorithms (GAs) are used to tackle this problem while considering different optimisation criteria, namely, minimum motion time, constraints on torque commands and constraints on end-point velocities. In addition, the search algorithm considers all constraints imposed on the manipulator design, including bounds on motor torque values. Several case studies are simulated for a two joint planner arm as well as for the PUMA 560 industrial manipulator, with results showing much better performance than those reported in the literature.
The design of structured mathematical models of processes in a certain level of abstraction defined by the given task appears to be difficult and time consuming even for experienced experts. This paper reports on a ne...
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作者:
R.G. BonitzT.C. HsiaSystems
Control and Robotics Laboratory Department of Electrical and Computer Engineering University of California Los Angeles Davis CA USA
An internal force-based impedance control scheme for two coordinating robots manipulating a rigid object via palm grasping is introduced. The minimal internal force required to maintain the grasp on the object is comp...
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An internal force-based impedance control scheme for two coordinating robots manipulating a rigid object via palm grasping is introduced. The minimal internal force required to maintain the grasp on the object is computed from the frictional constraints and sensed forces. A closed-form solution to the minimization problem is developed which makes the algorithm suitable for real-time control. The controller uses sensed moments at the palm interface to maintain proper orientation of the palms to achieve maximum surface contact. Each manipulator's nonlinear dynamics is compensated by a robust auxiliary controller which is insensitive to robot-model uncertainty and payload variation. The controller is only weakly-dependent on each manipulator's inertia matrix. Stability of the system is analyzed. Rigorous experimental investigations are are performed and the results presented which validate the proposed concepts.
An intelligent coordinated control system is designed for the active steering and the left/right traction force distribution control of 2-wheel-drive and 2-wheel-steering (2WD/2WS) electric vehicles, where input-outpu...
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An intelligent coordinated control system is designed for the active steering and the left/right traction force distribution control of 2-wheel-drive and 2-wheel-steering (2WD/2WS) electric vehicles, where input-output linearization is employed. Also, a fuzzy-rule-based cornering force estimator is suggested to avoid using an uncertain highly nonlinear expression, and a neural network compensator is additionally utilized for the estimator to correctly find cornering force. With these techniques, the proposed control system is shown by simulation results to be robust against drastic change of the external environments such as road conditions.
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