1,720,997 research outputs found
Damped Harmonic Smoother for Trajectory Planning and Vibration Suppression
Full text linkIn this brief, a novel filter for online trajectory generation is presented. The filter can be categorized as an input smoother since it acts on the input signal by increasing its continuity level. When fed with simple signals, as, e.g., a step input, it behaves like a trajectory generator that produces harmonic motions. Moreover, it can be combined with other filters, and in particular, with smoothers having a rectangular impulse response, in order to generate (online) more complex trajectories compliant with several kinematic constraints. On the other hand, being a filter, it possesses the capability of shaping the frequency spectrum of the output signal. This possibility can be profitably exploited to suppress residual vibration by imposing that the zeros of the filter cancel the oscillatory dynamics of the plant. For this purpose, the standard harmonic filter has been generalized in order to consider not only the natural frequency but also the damping coefficient of the plant. In this manner, the so-called ``damped harmonic filter" and the related ``damped harmonic trajectory" have been defined. By means of theoretical considerations, supported by experimental tests, the novel approach has been compared with the existing methods, and the advantages of its use have been proved
Performance and sealing material evaluation in 6-axis force-torque sensors for underwater robotics
No full textIn this paper, the effects of two different materials for the sealing on the performance of an innovative optoelectronic force/torque sensor for underwater robotic applications are investigated. The sensor has been designed to exhibit a considerable compliance in comparison with commercial F/T sensors for industrial applications, and optoelectronic components have been used as sensible elements for the development of the sensor, allowing a relatively simple and reliable implementation. These properties allow dealing with uncertain environments and an easy sensor integration in complex robotic systems, such as in robotic grippers for underwater applications. The paper presents the basic working principle and the design of the sensor together with experimental data to illustrate its main features. Finally, the use of the sensor as an intrinsic tactile sensor is investigated and experimentally validated, and the comparison of different materials for the rubber sealing in terms of their effects on the sensor performance is executed
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
Optimal Trajectories for Vibration Reduction Based on Exponential Filters
No full textIn 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
A Repetitive Control Scheme Based on B-Spline Trajectories Modification
No full textIn many applications of interest in industrial robotics, tasks are cyclic and must be repeated over and over. In this context, it seems natural to exploit the intrinsic properties of repetitive control schemes, where the cyclic nature of "disturbances" and/or unmodeled dynamic effects can be exploited to reduce the tracking errors. In this paper, we propose a new repetitive control scheme, where the main idea consists in the modification of the reference trajectory in order to compensate for the periodic undesired effects. By exploiting the dynamic filters for the B-spline generation, it is possible to integrate the trajectory planning within a repetitive control scheme able to modify in real-time the reference signal with the aims of nullify interpolation errors. By means of an extensive experimental activity on a servo mechanism pros and cons of the proposed approach are analyzed
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
Toward the Next Generation of Robotic Waiters
Full text linkThe gap between human waiters and state-of-the-art robot systems that try to serve something to drink is
often embarrassing, with the former able to manipulate glasses and trays or glasses on trays with incredible
dexterity and the latter that move at incredible slowness.
In this video, we want to show that robots can do it better by moving a bottle or a tankard full of beer that are
simply placed on a flat steel plate connected the flange of a robot manipulator.
The robot tracks the trajectory defined by a human operator that moves its hand in the 3D space, with a motion
capture system that acquires in real time the position. A feed-forward controller, placed between the user and the
robot and based on the combination of a smoother and proper orientation compensation, counteracts the lateral
accelerations and suppress sloshing phenomena of the liquids. Eventually a camera mounted on the robot arm
provides a visual feedback to the operator with monitoring purposes.
The challenge for the operator was to drop the carried object. will the feed-forward control be robust enough to
avoid this event, even at high speed? Watch the video and find out
Multidimensional Trajectories Generation with Vibration Suppression Capabilities: the Role of Exponential B-splines
No full textIn this paper, exponential B-spline trajectories are presented and discussed. They are generated by means of a chain of filters characterized by a truncated exponential impulse response. If properly tuned, the filters applied to a vibrating plant are able to cancel the oscillations and in this sense the resulting splines are optimized with respect to the problem of vibrations suppression. Different types of exponential B-spline are illustrated, with one or more exponential filters in the chain, and the procedure for the interpolation of a given set of desired via-points, with a proper choice of the control points, is shown. As a matter of fact, exponential B-splines, generated by means of dynamic filters, combine the vibration suppression capability of input shapers and smoothing filters with the possibility of exactly interpolating some via-points. The advantages of these curves are experimental proved by considering the motion of a spherical pendulum connected to the flange of an industrial robot
Feedforward control of Variable Stiffness Joints robots for vibrations suppression
No full textThis paper presents a new feedforward controller based on a continuous-time finite impulse response filter, designed to minimize the vibrations that usually affect robot manipulators with elastic joints. In particular, Variable Stiffness Joints (VSJ) robots are considered, since they are usually characterized by a very low level of damping which makes the problem of the oscillations quite important. The proposed approach allows to simplify the overall control structure of VSJ robots, which is based on a decentralized control of each servomotor, imposing the desired position and the desired stiffness at each joint, and on a novel feedforward control, filtering the reference signals. After analyzing some of the filter properties and the method for the parameters choice, experimental results on a VSJ robot demonstrate the importance of the proposed filtering action for minimizing vibrations and oscillations
A repetitive control scheme for industrial robots based on b-spline trajectories
No full textIn this paper, a novel repetitive control 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 unmodelled dynamics that cyclically affect it. By exploiting the dynamic filters for the B-spline trajectory planning, it has been possible to integrate the trajectory generation within a repetitive control scheme able to modify in real-time the reference signal with the aims of nullify interpolation errors. Experimental results obtained controlling two joints of a standard industrial manipulator are reported, showing the effectiveness of the proposed method
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