1,721,301 research outputs found
Control by Interconnection of Mixed Port Hamiltonian Systems
No full textIn this note, the regulation problem for mixed finite and infinite dimensional port Hamiltonian systems (m-pH systems) is discussed. A m-pH system results from the power conserving interconnection of finite and infinite dimensional systems in port Hamiltonian form. In particular, the system given by the interconnection of two finite dimensional systems, one of which is the controller, by means of an infinite dimensional connection is studied. The proposed control methodology is a generalization to the infinite dimensional case of a well-established passivity-based control technique for finite-dimensional port Hamiltonian systems, the control by interconnection and energy shaping, according to which the open-loop energy function is shaped so that a minimum in the desired configuration is introduced. This procedure is possible once the state variable of the controller is related to the state variable of the plant by constraining the state of the closed-loop system on a structural invariant (defined by a set of Casimir functions). In this way, the energy function of the controller, which is freely assignable, becomes a function of the configuration of the plant and, then, it can be easily shaped in order to solve the regulation problem
Trajectory generation via FIR filters: A procedure for time-optimization under kinematic and frequency constraints
Full text linkThis paper starts from the results reported in the article “FIR Filters for Online Trajectory Planning with Time- and Frequency-Domain Specifications”, where the use of a cascade of FIR (Finite Impulse Response) filters for planning minimum-time multi-segment polynomial trajectories, i.e. trajectories composed of several polynomial segments, under constraints of velocity, acceleration, etc. is proposed. In particular, in that paper the relationship between the limits acting on the trajectory derivatives (i.e. velocity, acceleration, jerk, etc.), and the parameters of the filters is deduced, along with a set of constraints among these parameters that guarantees the time-optimality of the trajectory in the rest-to-rest case, that is with null boundary conditions on the trajectory derivatives. However, the choice of the parameters, when these conditions are not satisfied, was still an open problem, at least for high order trajectories. In this paper, we show that in case the conditions are not met by the filters parameters, the optimality of the trajectory under the given kinematic bounds can be assured in any case. An algorithm for the selection of the optimal parameters for a generic th order trajectory planner subject to kinematic limits is provided. Additionally, the optimal combination of kinematic and frequency constraints is considered. In fact, the compliance with these two types of constraints may lead to a planner composed by a redundant number of filters and, therefore, a procedure for the selection of the minimum number of FIR filters is devised. The effectiveness of the time-optimal trajectory planner is proved by means of numerical simulations and experimental tests
Zero-phase velocity tracking of vibratory systems with actuation constraints
Full text linkIn this paper, a novel filter for precise tracking of constant velocity signals is presented, which allows the reduction of residual vibrations along with the compliance with kinematic constraints that affect the actuation system. A technique achieving both these two objectives at the same time is the main contribution of the work. The filter is based on a cascade of smoothers, i.e. dynamic filters that act on the input signal by increasing its continuity level. Unfortunately, when applied to a generic input composed by ramp (and step) functions, the filter introduces a phase delay not acceptable in many applications where moving parts have to be mated, such as high-speed automatic machines. In order to guarantee a perfect synchronization between the original and the filtered reference signal, once the transient is terminated, a proper compensation scheme has been designed. Moreover, the expressions of the smoothers parameters which assure vibration cancellation at specific frequencies and compliance with given bounds on velocity and acceleration have been analytically deduced. By means of an extensive experimental activity, the effectiveness of the proposed approach has been demonstrated, by comparing its performances with the results of well established approaches for vibrations suppression or signal derivatives limitation
Trajectory Planning for Automatic Machines and Robots
No full textThis book deals with the problems related to planning motion laws and trajectories for the actuation system of automatic machines, in particular for those based on electric drives, and robots. The problem of planning suitable trajectories is relevant not only for the proper use of these machines, in order to avoid undesired effects such as vibrations or even damages on the mechanical structure, but also in some phases of their design and in the choice and sizing of the actuators. This is particularly true now that the concept of 'electronic cams' has replaced, in the design of automatic machines, the classical approach based on 'mechanical cams'. The choice of a particular trajectory has direct and relevant implications on several aspects of the design and use of an automatic machine, like the dimensioning of the actuators and of the reduction gears, the vibrations and efforts generated on the machine and on the load, the tracking errors during the motion execution. For these reasons, in order to understand and appreciate the peculiarities of the different techniques available for trajectory planning, besides the mathematical aspects of their implementation also a detailed analysis in the time and frequency domains, a comparison of their main properties under different points of view, and general considerations related to their practical use are reported
Online trajectory planning and filtering for robotic applications via B-spline smoothing filters2013 IEEE/RSJ International Conference on Intelligent Robots and Systems
Full text linkIn this paper, a novel technique for online generating trajectories in the 3-D space is presented. The trajectory planner is based on cubic B-splines. However, while the definition of B-splines requires the solution of a global problem that involves the entire set of via-points to be interpolated/approximated, and therefore it is not suitable for online implementation, the proposed generator is able to approximate spline functions with the prescribed precision on the basis of local computations, which only need the knowledge of a very limited number of via-points. FIR filters are the foundation of this result. As a matter of fact the planner is composed by a first FIR filter for the computation of the control points from the sequence of desired via-points, followed by a chain of moving average filters. Therefore, the generator combines the characteristics of B-spline trajectories (smoothness and minimum curvature) and those of FIR filters (simple structure and computational efficiency). Moreover, besides standard cubic curves, the so-called smoothing B-splines have been considered for online trajectory generation. This allows to find a tradeoff between the possibility of exactly crossing the given via-points and the smoothness of the resulting trajectory. A simple teleoperation task with a Puma 560 industrial manipulator has been arranged for experimentally validating the proposed method
Input Shaping Via B-Spline Filters for 3-D Trajectory Planning
No full textIn this paper, the equivalence between uniform B-splines of degree p and the output of a chain composed by p average filters is exploited for optimizing the trajectories used in robotic applications. In particular, the spline trajectories obtained with the proposed generator are characterized from a frequency point of view. Their frequency content is completely determined by the degree p and by the time period T between the equally-spaced knots. It is therefore possible to select these parameters with the purpose of suppressing residual vibrations, that may be present because elastic phenomena affecting the robotic system. In this sense, the proposed approach is very similar to input shaping methods and allows to find a trade-off between two different problems: on one side the requirement of exactly interpolating a set of given points by means of a complex trajectory such as a spline, on the other hand the need of suppressing mechanical vibrations. The effectiveness of the proposed approach is shown by applying it to the generation of a 3D trajectory for a cartesian robot with elastic joints
Experimental Evaluation of Guided Twisted Actuation
No full textIn this paper, an ongoing work for verifying the behavior of a twisted string actuator in contact with a sliding surface or guided through a sheath is presented. After the presentation of the basic properties of the twisted string actuation system, the model of the twisted string in contact with a sliding surface is discussed. The behavior of the system has been then experimentally verified and discussed. A preliminary evaluation of control strategies for compensating the side effects generated by the contact of the twisted string with the sliding surface is also presented
Dynamic Filters for Online Planning Optimal Trajectories
No full textFilters for time-optimal trajectory generation can be obtained in different ways with quite different performances and complexity levels. However, one can easily observe that the configurations of such filters are based on two main schemes: systems composed by a chain of integrators with a feedback control and systems formed by a sequence of Finite Impulse Response (FIR) filters disposed in a cascade configuration. Both trajectory generators are characterized by the order that defines the degree of continuity of the resulting trajectory and both can be designed according to a modular approach that allows to obtain the -th order filter from that of order. In this paper, after having presented the structure and the analytical expression of the two types of trajectory filters, their common features (possibility of generating online time-optimal trajectories under constraints of velocity, acceleration, jerk, etc.) but especially the main differences are analyzed. In particular, the possible applications of the two systems are considered. Trajectory filters with a feedback loop are able to track generic input signals (and not only step functions) guaranteing the compliance of the output with the given constraints but are characterized by a complexity that limits their use to the third order. Conversely, the simple structure and the low computational cost make open-loop filters desirable for point-to point motions, even with an high degree of smoothness ( or ). Moreover, the low-pass response of this type of filters allows to characterize (and to design) the output trajectory from a frequency point of view, but, on the other hand, it may cause large delays and distortions between input and the output signals
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