This article challenges Bernstein's problem of redundant degrees of freedom (DOF) that remains unsolved from the control-theoretic point of view as well as from the standpoint of both neuro-physiology and robotics...
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ISBN:
(纸本)9783540738893
This article challenges Bernstein's problem of redundant degrees of freedom (DOF) that remains unsolved from the control-theoretic point of view as well as from the standpoint of both neuro-physiology and robotics. Firstly, a rather simpler but mysterious control problem of movements of human-like multi-joint reaching with excess DOFs is analyzed from Newtonian mechanics and differential geometry. Secondly, another illustrative control problem that seems to be sophisticated and complicated is tackled, which is to find a sensory coordinated control signal for 3-Dimensional stable grasping and object manipulation by a pair of robot fingers with multiple joints under the effect of gravity and nonholonomic constraints. In each illustrative control problem, it is possible to find a simple control signal that renders each corresponding closed-loop dynamics stable on its corresponding equilibrium-point manifold. It is claimed, however, that convergences of solutions of closed-loop dynamics to an equilibrium-point manifold can not be analyzed by using Lyapunov's direct method, because a Lyapunov-like energy form can not be positive definite due to redundancy of DOFs. Instead, a novel definition called "stability on a manifold" based upon the concept of Riemannian distance on the constraint manifold is introduced in both illustrative problems and used in the analysis of convergence of solution trajectories. It is also shown that finiteness of Riemannian metrics plays an important role in evaluation of the performance of control in both problems.
In short-circuit CO2 arc welding, the transfer behavior, process stability and weld quality are strongly affected by the molten droplet shape just before short-circuit and the electromagnetic pinch action on the liqui...
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ISBN:
(纸本)9783540733737
In short-circuit CO2 arc welding, the transfer behavior, process stability and weld quality are strongly affected by the molten droplet shape just before short-circuit and the electromagnetic pinch action on the liquid bridge during short-circuit phase. By using Static Force Balance Model, the effects of electromagnetic force, surface tension and gravity on the molten droplet shape during arc phase are simulated, the electromagnetic force being the dominant factor. To obtain a appropriate molten droplet shape in favor of arc stability and metal transfer, it is preferable to adopt a certain large pulse current in arc prophase and a small arc-keeping current in arc anaphase The numerical analysis to the effects of electromagnetic pinch action on the liquid bridge during short-circuit phase shows that a large current at initial stage will block the molten droplet from well spreading into the weld pool, but a large pulse current at metaphase will facilitate the formation of a neck in the liquid bridge. The simulation results are validated experimentally in waveform-controlled short-circuit CO2 arc welding, the welding process being improved to be much stable and gentle.
An algorithm is presented for the computation of the most powerful unfalsified model associated with an observed vector time series in the class of dynamical systems described by linear constant coefficient difference...
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ISBN:
(纸本)9783540735694
An algorithm is presented for the computation of the most powerful unfalsified model associated with an observed vector time series in the class of dynamical systems described by linear constant coefficient difference equations. This algorithm computes a module basis of the left kernel the Hankel matrix of the data, and is recursive in the elements of the basis. It is readily combined with subspace identification ideas, in which a state trajectory is computed first, directly from the data, and the parameters of the identified model are derived from the state trajectory.
A novel manipulator trajectory planning approach using geodesic is proposed in this paper. Geodesic is the necessary condition of the shortest length between two points on the Riemannian surface in which the covariant...
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ISBN:
(纸本)9783540733737
A novel manipulator trajectory planning approach using geodesic is proposed in this paper. Geodesic is the necessary condition of the shortest length between two points on the Riemannian surface in which the covariant derivative of the geodesic's tangent vector is zero. The geometric characteristic of geodesic is discussed and used to implement trajectory planning of the manipulator. First, the Riemannian metric is constructed according to the planning task, e.g. to establish a distance metric by arc length of the trajectory to achieve shortest path. Once the Riemannian metric is obtained, the corresponding Riemannian surface is solely determined. Then the geodesic equations on this surface can be attained. For the given initial conditions of the trajectory, the geodesic equations can be solved and the results are the optimal trajectory of the manipulator in the joint space for the given metric. The planned trajectories in the joint space can also be mapped into the workspace. To demonstrate the effectiveness of the proposed approach, simulation experiments are conducted using some typical manipulators, e.g. spatial 3R, 3-PSS parallel and planar 3R manipulators.
Mobile manipulation is a key capability to many robotic applications in construction, space, underwater, nuclear plant and home services. Dynamic modeling and trajectory control for a holonomic omnidirectional mobile ...
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ISBN:
(纸本)9783540733737
Mobile manipulation is a key capability to many robotic applications in construction, space, underwater, nuclear plant and home services. Dynamic modeling and trajectory control for a holonomic omnidirectional mobile manipulator are principle problems for mobile manipulation, and are presented in this paper. Considered the redundantly-actuated property of omnidirectional mobile platform, the kinematic model of the whole mobile manipulator is presented. Then, an integrated dynamic model for the system is developed by the kinematic model and Lagrangian formalism. According to the dynamic model, a modified inverse dynamic control is addressed to track the trajectories of the mobile platform and end-effector simultaneously. Then, the simulations results show the effectiveness of the proposed modeling and control approach.
In this chapter we look at a geometric target assignment problem consisting of an equal number of mobile robotic agents and distinct target locations. Each agent has a fixed communication range, a maximum speed, and k...
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ISBN:
(纸本)9783540735694
In this chapter we look at a geometric target assignment problem consisting of an equal number of mobile robotic agents and distinct target locations. Each agent has a fixed communication range, a maximum speed, and knowledge of every target's position. The problem is to devise a distributed algorithm that allows the agents to divide the target locations among themselves and, simultaneously, leads each agent to its unique target. We summarize two algorithms for this problem;one designed for "sparse" environments, in which communication between robots is sparse, and one for "dense" environments, where communication is more prevalent. We characterize the asymptotic performance of these algorithms as the number of agents increases and the environment grows to accommodate them.
Resistance spot welding quality is always one of key subject matters for study to which many welding scholars at home and abroad in the world devote *** has not been solved satisfactorily at present. The complexity of...
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ISBN:
(纸本)9783540733737
Resistance spot welding quality is always one of key subject matters for study to which many welding scholars at home and abroad in the world devote *** has not been solved satisfactorily at present. The complexity of spot welding process, invisibleness of nugget formation and singleness of control method decide that stabilizing quality is a rather difficult task. The limitations of describing how the nugget grows up based on single-sensor information source is analyzed. A control method of multi-parameter comprehensive decision making for spot welding is put forward. The multi-sensor information fusion is adopted for real time monitoring four parameters which are closely concerned with the weld nugget size(welding current, electrode displacement, dynamic resistance, welding time). information fusion algorithm includes sensor-based weighted average fusion algorithm and knowledge-based production rule fusion algorithm. The spot welding experiments indicate that nugget size fluctuations are within 8%similar to 22% under constant current control, and are within 6%similar to 12.5% under information fusion control. It conforms that the new quality control method can compensate for various factors of influence in the welding process such as shunt, loop inductive reactance variation and electrode wear, etc, and assure the spot welding quality to be stable.
When applying autonomous industrial robotic systems in an unknown/partially known or cluttered environment, mapping and representation of the environment as well as collision detection becomes crucial. Existing techni...
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ISBN:
(纸本)9783540733737
When applying autonomous industrial robotic systems in an unknown/partially known or cluttered environment, mapping and representation of the environment as well as collision detection becomes crucial. Existing techniques in these areas are generally complex and computationally expensive to implement. In this paper an efficient sphere representation method is introduced for environment representation, collision detection and distance queries. In particular, this method is designed for the application in an autonomous bridge maintenance system. Simulation results show that this method is effective in environment representation and collision detection. Furthermore, the proposed method is also computationally efficient for real-time implementation.
We begin with an interpretation of the L(1)-distance between two power spectral densities and then, following an analogous rationale, we develop a natural metric for quantifying distance between respective covariance ...
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ISBN:
(纸本)9783540735694
We begin with an interpretation of the L(1)-distance between two power spectral densities and then, following an analogous rationale, we develop a natural metric for quantifying distance between respective covariance matrices.
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