Vanni Zanotto

Model Predictive Control of a Flexible Links Mechanism

Vibration suppression in flexible link manipulator is a recurring problem in most robotic applications. Solving this problem would allow to increase many times both the operative speed and the accuracy of manipulators. In this paper an innovative controller for flexible-links mechanism based on MPC (Model Predictive Control) with constraints is proposed. So far this kind of controller has been employed almost exclusively for controlling slow processes, like chemical plants, but the authors’ aim is to show that this approach can be successfully adapted to plants whose dynamical behavior is both nonlinear and fast changing. The effectiveness of this control system will be compared to the performance obtained with a classical industrial control. The reference mechanism chosen to evaluate the effectiveness of this control strategy is a four-link closed loop planar mechanism laying on the horizontal plane driven by a torque-controlled electric actuator.

Experimental Validation of Minimum Time-jerk Algorithms for Industrial Robots

In this paper, we present a minimum-time/jerk algorithm for trajectory planning and its experimental validation. The algorithm search for a trade-off between the need for a short execution time and the requirement of a sufficiently smooth trajectory, which is the well known necessary condition to limit the vibration during fast movements. The trade-off is achieved by adjusting the weight of two suitable functions, able to consider both the execution time and the squared-jerk integral along the whole trajectory. The main feature of this algorithm is its ability to smooth the trajectory’s profile by adjusting the intervals between two consecutive via-points so that the overall time is minimally delayed. The practical importance of this technique lies in the fact that it can be implemented in any industrial manipulator without a hardware upgrade. The algorithm does not need for a dynamic model of the robot: only the mechanical constraints on the position, velocity and acceleration ranges have to be set a priori. The experimental proof is provided in this paper by comparing the results of the proposed algorithm with those obtained by adopting some classical algorithms.

Active Position and Vibration Control of a Flexible Links Mechanism Using Model-Based Predictive Control

In order to develop an efficient and,fast position control for robotic manipulators, vibration phenomena have to be taken into account. Vibrations are mainly caused by the flexibility of manipulator linkages, especially when dealing with high-speed and lightweight robots. In this paper, a constrained model-based predictive control is employed for controlling both position and vibrations in a mechanism with high link flexibility. This kind of controller has so far been used mainly to control slow processes, but here simulation results that show its effectiveness in dealing with high-speed and nonlinear processes are presented. The mechanism chosen to evaluate the performances is a four-link closed chain mechanism laying on the horizontal plane and driven by a single torque-controlled electric motor.

Design of a controller for trajectory tracking for compliant mechanisms with effective vibration suppression

In this paper, a numerical investigation of the Model Predictive Control strategy applied to flexible-link mechanisms is presented. The mechanisms used for all the tests are a planar five-link mechanisms. The tests are aimed at showing how the proposed control system can be used for the trajectory tracking and the vibration suppression. An analysis of the effects of the choice of tuning parameters is presented as well. The design of the predictive controller is based on a linearized version of an accurate nonlinear dynamic model. The effectiveness of the proposed approach is confirmed by extensive numerical results.

Validation of Minimum Time-Jerk Algorithms for Trajectory Planning of Industrial Robots

In this paper, an experimental analysis and validation of a minimum time-jerk trajectory planning algorithm is presented. The technique considers both the execution time and the integral of the squared jerk along the whole trajectory, so as to take into account the need for fast execution and the need for a smooth trajectory, by adjusting the values of two weights. The experimental tests have been carried out by using an accelerometer mounted on a Cartesian robot. The algorithm does not require a dynamic model of the robot, but just its mechanical constraints, and can be implemented in any industrial robot. The outcomes of the tests have been compared with both simulation and experimental results yielded by two trajectory planning algorithms taken from the literature.

Toward an optimal performance index for neurosurgical robot's design

In the past years a large number of new surgical devices have been developed to improve the operation outcomes and reduce the patients trauma. Nevertheless, the dexterity and accuracy required in positioning the surgical tools are often unreachable if the surgeons are not assisted by a suitable system. Since a medical robot works in an operating room, close to the patient and the medical staff, it has to satisfy much stricter requirements with respect to an industrial one. From a kinematic point of view, the robot must reach any target position in the patients body, being as less invasive as possible for the surgeons workspace. In order to meet such requirements, the right robot structure has to be chosen by means of the definition of suitable kinematic performance indices. In this paper some task-based indices based on the robot workspace and stiffness are presented and discussed. The indices will be used in a multiobjective optimization problem to evaluate best robot kinematic structure for a given neurosurgical task.

Vibration reduction in a flexible link mechanism through the synthesis of an MPC controller

The modeling and the control of flexible link robots have received a great deal of attention in the last decades due to the wide prospective industrial and space applications of ultra-light and high-speed mechanisms. This paper introduces a general and practical procedure for the design of effective control schemes for the position and vibration control of flexible links mechanisms. In particular, an innovative controller based on MPC (Model-based Predictive Control) is proposed. So far the MPC controllers have been employed almost exclusively in slow industrial processes. Nevertheless, this work shows that the MPC approach can be successfully adapted to plants whose dynamics are both nonlinear and fast changing as well. The performances of this approach will be evaluated for a single link mechanism and compared to those obtained with a standard PID position controller.

A delayed force-reflecting haptic controller for master–slave neurosurgical robots

This paper presents a new force-reflecting control system for master–slave haptic devices. This controller has been implemented and tested on the robotic systems for minimally invasive neurosurgery developed by our Research Group. Robot-assisted surgery is a very valuable treatment, since it allows benefits of high precision, accuracy, and repeatability of robotic devices. The proposed controller is meant to be used for master–slave haptic robotic surgery, but it can be used for any device that provides haptic feedback. The new controller merges the paradigms of force reflection (FR) control and delayed reference control. Unlike the FR control, the proposed solution enhances the safety since it does not allow an unwanted motion of the slave device once the operator releases the haptic controller. Experimental tests are provided to show the capabilities and the performance of the controller. Closed-loop stability is investigated both theoretically and experimentally. The analytic results on stability impose a limit on the ratio between the measured contact force and the sampling frequency of the closed-loop controller. Graphical Abstract

Trajectory Planning for Manufacturing Robots: Algorithm Definition and Experimental Results

In this paper an analysis of the experimental results yielded by a minimum time-jerk trajectory planning algorithm is presented. The technique considers both the execution time and the integral of the squared jerk along the trajectory, and the kinematic constraints of the robot manipulator under test. The need for a fast execution and the need for a smooth trajectory are taken into account by adjusting the values of two weights, whose suitable values are set with an “automatic” choice algorithm. The outcomes of the tests are compared with both simulations and experimental results obtained by using a “classic” spline trajectory planning algorithm. The experimental tests are carried out by using an accelerometer mounted on a Cartesian robot.© 2010 ASME

A Robotic Approach to Stereotactic Radio-Surgery

The aim of this paper is to present a new robotic system for minimally invasive radio surgery. The system is called DAANS and is used to move a new miniaturized x-ray source called PRS with great precision and repeatability. By means of the DAANS the PRS dose delivery center can be moved linearly along the emission axis and rotated about the same axis. Moreover the DAANS is provided with a load cell which measures the force, along the emission axis, exerted by the PRS on a patient’s tissues, and which allows generating an appropriate force feedback on a specifically developed haptic console. The system is now being manufactured and will soon be employed in clinical tests.Copyright