1,721,156 research outputs found
Optimization of Generalized S-curve Trajectories for Residual Vibration Suppression and Compliance with Kinematic Bounds
Full text linkThis paper proposes a new optimization algorithm that assures the minimum possible duration of generalized S-curve trajectories compliant with kinematic limitations and capable of suppressing residual vibrations when tracked by a resonant plant. Thanks to the possibility of generating such kind of trajectories with a chain of filters, called smoothers, each one characterized by a single parameter, i.e. the duration Ti of its impulse response, the optimization process aims at minimizing the order of the trajectory, and accordingly the number of smoothers in the chain, and leads to rest-to-rest trajectories that, under the given specifications, cannot be made shorter in time. Therefore, the structure of the trajectory is not predetermined but is the outcome of the proposed algorithm together with the optimal parameters defining it. The effectiveness of the proposed approach is proven by applying the designed trajectories to an experimental setup based on a flexible link
Mobility and kinematic analysis of general cooperating robot systems
No full textThe coordinator of the movements of multiple robot arms manipulating a common object is considered. In order to provide a general framework for the study of such cooperating systems as common industrial arms, multifingered hands, and legged vehicles, the analysis does not rely on the assumption of full mobility for each cooperating arm, which is otherwise common in related literature. The aim of the present work is to provide a systematic method to characterize the mobility and differential kinematics of general cooperating systems. The proposed analysis and algorithms provide an insight into the structure of the input (joint)-output (task) relationship of such system
Geometric Grasping and Telemanipulation
No full textIn this paper, an extension of the so-called intrinsic passive control (IPC) is illustrated, showing that an improvement of performances can be achieved by considering different types of energy-storing elements, i.e. "springs", in the IPC. In particular, two new "springs" are introduced: a 'variable rest length' spring and a 'variable stiffness' spring, that are properly defined in order to maintain the passivity of the IPC and to improve its performances in given situations. Simulations of the resulting control, applied to a defective system and to a simple telemanipulation device, are presented and discusse
A dexterous robotic gripper for autonomous grasping
No full textIn advanced robotics applications in unstructured environments (e.g. those foreseen in space) some degree of dexterity and autonomy is necessary in order to safely and successfully execute the required tasks. With this respect, besides the kinematic configuration, important aspects to be considered in the design of robotic end-effectors are the sensorial equipment and proper control strategies. In this paper, an activity for designing and experimenting a gripper for this operation in unstructured environments is reported, and laboratory results are presented and discussed
Repetitive Control Meets Continuous Zero Phase Error Tracking Controller for Precise Tracking of B-Spline Trajectories
No full textIn this paper, a novel repetitive control scheme is presented and discussed, based on the so-called B-spline filters. These dynamic filters are able to generate a B-spline trajectory if they are fed with the sequence of control points defining the curve. Therefore, they are ideal tools for generating online reference signals with the prescribed level of smoothness for driving dynamic systems, possibly together with a feedforward compensator. In particular, a continuous zero phase error tracking controller (ZPETC) can be used for tracking control of nonminimum phase systems but because of its open-loop nature it cannot guarantee the robustness with respect to modeling errors and exogenous disturbances. For this reason, ZPETC and trajectory generator have been embedded in a repetitive control scheme that allows to nullify interpolation errors even in nonideal conditions, provided that the desired reference trajectory and the disturbances are periodic. This paper is based on the results presented in the conference paper [L. Biagiotti, F. Califano, and C. Melchiorri, 'Repetitive control of non-minimum phase systems along b-spline trajectories,' in Proc. IEEE 55th Conf. Decis. Control, 2016, pp. 5496-5501.], where asymptotic stability of the overall control scheme has been proved mathematically, but extends such results with an experimental validation based on a nonminimum phase system. Different models of the same physical system have been identified and used in the implementation of this model-based control scheme, allowing a real evaluation of the relationship between control system performance and model accuracy
Combining Hybrid Genetic Algorithms and Feedforward Neural Networks for Pallet Loading in Real-World Applications
No full textThe “Distributor’s Pallet Packing Problem” in a real industrial scenario is addressed in this paper. The main goal is to develop a two-stage algorithm capable to provide the spatial coordinates of the placed boxes vertices and also the optimal boxes input sequence, while guaranteeing geometric, stability, fragility constraints and a reduced computational time. Due to NP-hard complexity of the problem, a hybrid genetic algorithm coupled with a feedforward neural network is used. In the first stage, the hybrid genetic algorithm is run several times on each order within a large set of packing instances, using a different fitness weight vector at each iteration, and storing the best chromosomes to form a rich solution set. After its generation, the best solution is chosen for each order, optimizing a new global weighted function. The global optimal weight vector is tuned by hand, relying on a graphical user interface that allows to show, in real-time, the best solution as a function of the global weights. The dataset is then created, keeping track of both local and global weight vectors related to the optimal solution. Hence, the dataset is used to train, validate and test the neural network. In the second stage, the trained neural network is used to provide the optimal pair of fitness weight vectors, allowing to run the hybrid genetic algorithm only one time and to select directly the optimal solution in the set. The proposed algorithm has been tested and validated on several packing instances provided by an industrial company
Position/force control of an arm/gripper system for space manipulation
No full textIn advanced robotics applications, as those foreseen in space, some degree of dexterity and autonomy is necessary in order execute tasks in unstructured environments. For this purpose besides the kinematic configuration of the device other basic issues are the sensorial equipment and proper control strategies. This paper presents an experimental activity for the validation of a robotic gripper for space applications. In particular the project foresees the compatibility of the gripper with the EUROPA arm, developed by ASI and Tecnospazio. Main Key points of the gripper design are the wide working space compared with its physical dimensions and the capability to deal with free-flying objects in no-gravity conditions. This capability is achieved by using proximity and force/torque sensor and by properly controlling and coordinating the gripper and the carrying arm. After a brief illustration on the main features of the gripper, the experimental activity is presented and the results achieved so far are discu ssed
Improving the accuracy of industrial robots via iterative reference trajectory modification
Full text linkIn this paper, a novel repetitive control (RC) scheme is presented and discussed. The general framework is the control of repetitive tasks of robotic systems or, more in general, of automatic machines. The key idea of the proposed scheme consists in modifying the reference trajectory provided to the plant in order to compensate for external loads or unmodeled dynamics that cyclically affect it. By exploiting the fact that uniform B-spline trajectories can be generated by means of dynamic filters, the trajectory planning phase has been integrated within an RC scheme that is able to modify in real time the reference signal in order to nullify the tracking errors occurring at the desired via-points. Because of this mechanism, the control scheme is very suitable for the application to industrial plants with off-the-shelf, unmodifiable controllers. Experimental results obtained with a standard industrial manipulator both in joint space and in workspace show the effectiveness of the proposed method
A hybrid genetic algorithm for pallet loading in real-world applications
Full text linkThis paper addresses the so called "Distributor's Pallet Packing Problem"in a real industrial scenario. The main goal is to develop an algorithm for loading heterogeneous rectangular boxes on a bin, minimizing some objective functions and also satisfying geometric, stability and fragility constraints. The algorithm must be able to provide, in a reasonable time, the spatial coordinates of the vertices of the placed boxes and also the optimal boxes input sequence. Since this type of combinatorial problem is classified as NP-hard, classical optimization techniques are not suitable. For these reasons, a metaheuristic approach has been developed in order to reduce burden complexity. In particular, a genetic algorithm hybridized with an innovative heuristic technique has been used. The validity and the performance of this algorithm have been tested on several packing instances (orders) provided by an industrial company. The paper is intended as a preliminary study for future developments in the area of industrial container loading problems
Control of a robotic gripper for grasping objects in no-gravity conditions
No full textIn space applications, it is conceivable that part of the robotic activities could involve the grasp and/or manipulation of free-floating objects in absence of gravity. In this case, synchronous application of contacts seems to represent a basic feature in order to efficiently grasp the floating items. In this sense, an additional difficulty is that objects may have irregular shape and/or be non well positioned in the gripper workspace. These difficulties cannot be handled in a simple way with standard 2-jaw grippers, with one (or two) degrees of freedom. In this paper, an activity for designing and experimenting a gripper for this type of operations is reported, and the first laboratory results are presented and discussed. Main features of the gripper are its kinematic configuration (3 fingers with 3 dof) and its sensorial equipment, features that improve the dexterity of this device if compared to more classical devices
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