1,721,008 research outputs found
Repetitive control of nonlinear systems via feedback linearization: An application to robotics
Full text linkIn this paper, a novel Repetitive Control (RC) scheme for a class of nonlinear systems is presented and discussed. This work generalizes the approach proposed in Biagiotti et al. (2015) where a RC scheme based on the modification of a B-spline reference trajectory has been presented. Also in this case, the generation of the B-splines based on dynamic filters plays a crucial role in the control scheme since it allows to implement a feedforward action that, coupled with an exact feedback linearization and a stabilizing state feedback, makes the RC robustly asymptotically stable. In this manner, the tracking error at the via-points defining the reference trajectory is nullified even if parametric uncertainties on the system model or exogenous (cyclic) disturbances are present. The application to a two-dof robot manipulator shows the effectiveness of the proposed method and its inherent robustness
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
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
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
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
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
Optimal Trajectories for Vibration Reduction Based on Exponential Filters
Full text linkIn this paper, a new type of trajectory, based
on an exponential jerk, is presented along with filters for
their online generation. The goal is to generalize constant jerk
trajectories, widely used in industrial applications, in order to
reduce vibrations of motion systems. As a matter of fact, constant
jerk trajectories do not assure a complete vibration suppression
when the damping of the resonant modes is not negligible. The
values of the parameters (decay rate and duration) of the jerk
impulses that allow residual vibration cancellation are derived
in an analytical way as a function of the dynamic characteristics
of the plant. Comparisons with the well-known input shaping
techniques and with system-inversion-based filters show the
advantages of the proposed method in terms of robustness with
respect to modeling errors, smoothness of the resulting trajectory,
and time duration of the motion under velocity and acceleration
constraints
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
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