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Luigi BIAGIOTTI

Professore Associato presso: Dipartimento di Ingegneria "Enzo Ferrari"


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Pubblicazioni

- Bioreattore per la stimolazione di cellule staminali [Brevetto]
Biagiotti, Luigi; S., Cavalcanti; E., Giordano; F., Lotti; C., Muscari; C. M., Caldarera; M., Govoni
abstract

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2020 - Damped Harmonic Smoother for Trajectory Planning and Vibration Suppression [Articolo su rivista]
Biagiotti, Luigi; Melchiorri, Claudio; Moriello, Lorenzo
abstract

In 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.


2020 - Fondamenti di controlli automatici. Ediz. MyLab. Con Contenuto digitale per accesso on line [Monografia/Trattato scientifico]
Katsuhiko, Ogata; Biagiotti, Luigi
abstract


2020 - Grasp-Oriented Myoelectric Interfaces for Robotic Hands: A Minimal-Training Synergy-Based Framework for Intent Detection, Control and Perception [Capitolo/Saggio]
Meattini, Roberto; Biagiotti, Luigi; Palli, Gianluca; Melchiorri, Claudio
abstract


2020 - Improving the Accuracy of Industrial Robots via Iterative Reference Trajectory Modification [Articolo su rivista]
Biagiotti, Luigi; Moriello, Lorenzo; Melchiorri, Claudio
abstract

In 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.


2020 - Optimization of Generalized S-curve Trajectories for Residual Vibration Suppression and Compliance with Kinematic Bounds [Articolo su rivista]
Biagiotti, L.; Melchiorri, C.
abstract

This 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.


2020 - Repetitive Control Meets Continuous Zero Phase Error Tracking Controller for Precise Tracking of B-spline Trajectories [Articolo su rivista]
Biagiotti, Luigi; Califano, Federico; Melchiorri, Claudio
abstract

In 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 non-minimum 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 non-ideal conditions, provided that the desired reference trajectory and the disturbances are periodic. Asymptotic stability of the overall control scheme is proved mathematically and experimental validation based on a non-minimum phase system is performed. 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.


2019 - A Control Architecture for Grasp Strength Regulation in Myocontrolled Robotic Hands Using Vibrotactile Feedback: Preliminary Results [Relazione in Atti di Convegno]
Meattini, Roberto; Biagiotti, Luigi; Palli, Gianluca; De Gregorio, Daniele; Melchiorri, Claudio
abstract

Nowadays, electric-powered hand prostheses do not provide adequate sensory instrumentation and artificial feedback to allow users voluntarily and finely modulate the grasp strength applied to the objects. In this work, the design of a control architecture for a myocontrol-based regulation of the grasp strength for a robotic hand equipped with contact force sensors is presented. The goal of the study was to provide the user with the capability of modulating the grasping force according to target required levels by exploiting a vibrotactile feedback. In particular, the whole human-robot control system is concerned (i.e. myocontrol, robotic hand controller, vibrotactile feedback.) In order to evaluate the intuitiveness and force tracking performance provided by the proposed control architecture, an experiment was carried out involving four naïve able-bodied subjects in a grasping strength regulation task with a myocontrolled robotic hand (the University of Bologna Hand), requiring for grasping different objects with specific target force levels. The reported results show that the control architecture successfully allowed all subjects to achieve all grasping strength levels exploiting the vibrotactile feedback information. This preliminary demonstrates that, potentially, the proposed control interface can be profitably exploited in upper-limb prosthetic applications, as well as for non-rehabilitation uses, e.g. in ultra-light teleoperation for grasping devices.


2019 - Trajectory generation via FIR filters: A procedure for time-optimization under kinematic and frequency constraints [Articolo su rivista]
Biagiotti, Luigi; Melchiorri, Claudio
abstract

This 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.


2019 - Zero-phase velocity tracking of vibratory systems with actuation constraints [Articolo su rivista]
Biagiotti, Luigi; Melchiorri, Claudio
abstract

In 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.


2018 - A Plug-In Feed-Forward Control for Sloshing Suppression in Robotic Teleoperation Tasks [Relazione in Atti di Convegno]
Biagiotti, Luigi; Chiaravalli, Davide; Moriello, Lorenzo; Melchiorri, Claudio
abstract

In this paper, the problem of suppressing sloshing dynamics in liquid handling robotic systems has been faced by designing a dynamic filter that starting from the desired motion of the liquid container calculates the complete position/orientation trajectory for the robot end-effector. Specifically, a design philosophy mixing a filtering technique that suppresses the frequency contributions of the reference motion that may cause liquid oscillations and an active compensation of lateral accelerations by a proper container re-orientation has been adopted. In principle, the latter contribution requires the knowledge of acceleration of the reference trajectory, but because of the use of an harmonic smoother that performs a shaping of the original motion, it is possible to obtain the value of the acceleration in runtime. In this way, the proposed methods can be applied also to reference motions that are not known in advance, e.g. commands directly provided by a human operator. This possibility has been demonstrated by means of a number of experimental tests in which the user teleoperates the robot carrying the container with the liquid by simply moving in the free space its hand, whose 3D position is detected by a motion capture system.


2018 - Manipulating liquids with robots: A sloshing-free solution [Articolo su rivista]
Moriello, Lorenzo; Biagiotti, Luigi; Melchiorri, Claudio; Paoli, Andrea
abstract

This paper addresses the problem of suppressing sloshing dynamics in liquid handling robotic systems by an appropriate design of position/orientation trajectories. Specifically, a dynamic system, i.e. the exponential filter, is used to filter the desired trajectory for the liquid-filled vessel moved by the robot and counteract the sloshing effect. To this aim, the vessel has been modelled as a spherical pendulum of proper mass/length subject to the accelerations imposed by the robot and the problem has been approached in terms of vibration suppression to cancel the residual oscillations of the pendulum, i.e. the pendulum swing at the end of the reference rest-to-rest motion. In addition, in order to reduce the relative motion between liquid and vessel, an orientation compensation mechanism has been devised aiming to maintain the vessel aligned with the pendulum during the motion. The effectiveness of the proposed approach, both in simple point-to-point motions and complex multi-point trajectories, has been proved by means of an exhaustive set of experimental tests on an industrial manipulator that moves a cylindrical vessel filled with water. This innovative solution effectively uses all the degrees of freedom of the robotic manipulator to successfully suppress sloshing, thus significantly improving the performances of the robotic system. Furthermore, the proposed solution, showing a high degree of robustness as well as intrinsic design simplicity, is very promising for designing novel industrial robotics applications with a short time-to-market across key manufacturing sectors (e.g., food and beverage, among others).


2018 - Physical-consistent behavior embodied in B-spline curves for robot path planning [Relazione in Atti di Convegno]
Chiaravalli, Davide; Califano, Federico; Biagiotti, Luigi; De Gregorio, Daniele; Melchiorri, Claudio
abstract

In this paper, a path planning algorithm for smooth obstacle avoidance of mobile robots is presented and discussed. The idea is based on B-splines, which are trajectories defined by a linear combination of basis functions weighted by constants called control points. Since the overall curve depends locally only on the position of a limited set of control points, B-splines are ideal tools for generating online reference trajectories able to react to local changes of the environment (e.g. mobile or spawning obstacles). The via-points of the reference B-spline are treated as dynamic agents with customized dynamic properties. These agents interact with each other and with the environment in such a way to generate the correct reference for the B-spline generator and thus for the robot. The high flexibility and the low computational burden of the proposed algorithm allow to develop applications in partially unknown or dynamically changing environments since a local modification of the trajectory does not require an entire re-computation. Experimental results performed with a KUKA Youboot mobile robot within a ROS based set-up are reported.


2018 - Toward the Next Generation of Robotic Waiters [Relazione in Atti di Convegno]
Moriello, Lorenzo; Chiaravalli, Davide; Biagiotti, Luigi; Melchiorri, Claudio
abstract

The 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!


2017 - Control of liquid handling robotic systems: A feed-forward approach to suppress sloshing [Relazione in Atti di Convegno]
Moriello, Lorenzo; Biagiotti, Luigi; Melchiorri, Claudio; Paoli, Andrea
abstract

This paper presents a feed-forward approach to reduce sloshing dynamics in liquid handling robotic systems. According to our solution, the dynamics of a liquid into an open vessel manipulated by a robot can be described by means of a spherical pendulum mechanical model. By doing this, the sloshing problem can be addressed as a vibration suppression problem for a second order system. More in details, the pendulum model is utilized to tune an exponential filter which shapes the reference trajectory for the robot, thus achieving a sloshing-free motion of the liquid inside the vessel.


2017 - Feedforward control of Variable Stiffness Joints robots for vibrations suppression [Relazione in Atti di Convegno]
Biagiotti, Luigi; Moriello, Lorenzo; Melchiorri, Claudio
abstract

This 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.


2017 - Multidimensional Trajectories Generation with Vibration Suppression Capabilities: the Role of Exponential B-splines [Relazione in Atti di Convegno]
Moriello, Lorenzo; Biagiotti, Luigi; Melchiorri, Claudio
abstract

In 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.


2016 - Optimal Trajectories for Vibration Reduction Based on Exponential Filters [Articolo su rivista]
Biagiotti, Luigi; Melchiorri, Claudio; Moriello, Lorenzo
abstract

In 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.


2016 - Repetitive control of non-minimum phase systems along B-spline trajectories [Relazione in Atti di Convegno]
Biagiotti, Luigi; Califano, Federico; Melchiorri, Claudio
abstract

In this paper, a novel repetitive control scheme is presented and discussed, based on the so called B-spline filters. This type of dynamic filters are able to provide a Bspline trajectory if they are fed with the sequence of proper control points that define the trajectory itself. Therefore, they are ideal tools for generating online the reference signal with the prescribed level of smoothness for driving dynamic systems, e.g. with a feedforward compensator. In particular, the so-called Continuous Zero Phase Error Tracking Controller (ZPETC) can be used for tracking control of non-minimum phase systems but because of its open-loop nature cannot guarantee robustness with respect to modelling 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 non-ideal conditions, provided that the desired reference trajectory and the disturbances are periodic. The asymptotic stability of the overall control scheme has been proved and its performances have been demonstrated by considering a well-known non-minimum phase plant, i.e. a flexible link arm.


2015 - A Repetitive Control Scheme Based on B-Spline Trajectories Modification [Relazione in Atti di Convegno]
Biagiotti, Luigi; Moriello, Lorenzo; Melchiorri, Claudio
abstract

In 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.


2015 - A repetitive control scheme for industrial robots based on b-spline trajectories [Relazione in Atti di Convegno]
Biagiotti, Luigi; Moriello, Lorenzo; Melchiorri, Claudio
abstract

In 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.


2015 - Qualitative graphical representation of Nyquist plots [Articolo su rivista]
Zanasi, Roberto; Grossi, Federica; Biagiotti, Luigi
abstract

In this paper, the procedure for manually drawing the Nyquist plot of a generic transfer function is revised and, in particular, two novel parameters (ΔτΔτ, ΔpΔp), which allow to simplify this process, are presented. Thanks to these parameters, the analysis of the frequency response at low and high frequencies is considerably enhanced, with a very little effort. These parameters allow to predict initial and final directions of the polar curve in the vicinity of initial and final points and consequently the sectors of the complex plane where the plot starts/ends. In many cases it is possible to obtain a qualitative Nyquist plot, able to correctly predict the stability properties of the closed-loop system, by simply joining the initial and final tracts found with the proposed procedure. Moreover, the analysis based on these parameters can aid to correctly interpret the plots obtained with computer programs which often, in particular when poles at the origin are present, hide the behavior of the frequency response in the area close to the origin of the complex plane.


2014 - An innovative stand-alone bioreactor for the highly reproducible transfer of cyclic mechanical stretch to stem cells cultured in a 3D scaffold [Articolo su rivista]
Marco, Govoni; Fabrizio, Lotti; Biagiotti, Luigi; Maurizio, Lannocca; Gianandrea, Pasquinelli; Sabrina, Valente; Claudio, Muscari; Francesca, Bonafè; Claudio M., Caldarera; Carlo, Guarnieri; Silvio, Cavalcanti; Emanuele, Giordano
abstract

Much evidence in the literature demonstrates the effect of cyclic mechanical stretch in maintaining, or addressing, a muscle phenotype. Such results were obtained using several technical approaches, useful for the experimental collection of proofs of principle but probably unsuitable for application in clinical regenerative medicine. Here we aimed to design a reliable innovative bioreactor, acting as a stand-alone cell culture incubator, easy to operate and effective in addressing mesenchymal stem cells (MSCs) seeded onto a 3D bioreabsorbable scaffold, towards a muscle phenotype via the transfer of a controlled and highly-reproducible cyclic deformation. Electron microscopy, immunohistochemistry and biochemical analysis of the obtained pseudotissue constructs showed that cells 'trained' over 1 week: (a) displayed multilayer organization and invaded the 3D mesh of the scaffold; and (b) expressed typical markers of muscle cells. This effect was due only to physical stimulation of the cells, without the need of any other chemical or genetic manipulation. This device is thus proposed as a prototypal instrument to obtain pseudotissue constructs to test in cardiovascular regenerative medicine, using good manufacturing procedures.


2013 - Integration of robotic systems in a packaging machine: A tool for design and simulation of efficient motion trajectories [Relazione in Atti di Convegno]
Biagiotti, Luigi; C., Melchiorri; M., Pilati; G., Mazzuchetti; G., Collepalumbo; P., Ragazzini
abstract

In this paper, the advantages of CACSD (Computer Aided Control System Design) tools for integrating a robotic system in a packaging machine are illustrated. Beside the mechanical integration of the robot into the machine architecture, it is necessary a functional integration, that requires a precise synchronization with the other parts of the system. In the proposed application, a robot with a parallel kinematics is used for pick-and-place tasks between two conveyor belts. It is therefore necessary a proper motion planning which allows to synchronize the grasp and release phases with the conveyor belts, avoiding obstacles and guaranteeing the compliance with bounds on velocity, acceleration and limits in the workspace. A trajectory composed by quintic polynomials has been considered and a specific tool has been designed in the Matlab environment, which allows to modify the parameters of the trajectory and to analyze the obtained motion profiles from both the kinematic and dynamic point of view.


2013 - Online trajectory planning and filtering for robotic applications via B-spline smoothing filters [Relazione in Atti di Convegno]
Biagiotti, L.; Melchiorri, C.
abstract

In 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. © 2013 IEEE.


2013 - Online trajectory planning and filtering for robotic applications via B-spline smoothing filters2013 IEEE/RSJ International Conference on Intelligent Robots and Systems [Relazione in Atti di Convegno]
Biagiotti, Luigi; Melchiorri, Claudio
abstract

In 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.


2012 - FIR filters for online trajectory planning with time- and frequency-domain specifications [Articolo su rivista]
Biagiotti, Luigi; Melchiorri, Claudio
abstract

In this paper, the use of FIR (Finite Impulse Response) filters for planning minimum-time trajectories for robots or automatic machines under constraints of velocity, acceleration, etc. is presented and discussed. In particular, the relationship between multi-segment polynomial trajectories, i.e. trajectories composed of several polynomial segments, each one possibly characterized by constraints on one or more specific derivatives (i.e. velocity, acceleration, jerk, etc.), and FIR filters disposed in a cascade configuration is demonstrated and exploited in order to design a digital filter for online trajectory planning. The connection between analytic functions and dynamic filters allows a generalization of these trajectories, usually obtained by second- or third-order polynomial functions (e.g. trapezoidal velocity and double S velocity trajectories), to a generic order with only a modest increase of the complexity. As a matter of fact, the computation of trajectories with higher degree of continuity simply requires additional FIR filters in the chain. Moreover, the modular structure of the planner provides a direct frequency characterization of the motion law. In this way, it is possible to define the trajectories by considering constraints expressed in the frequency-domain besides the classical time-domain specifications, such as bounds on velocity, acceleration, and so on. Two examples illustrate the main features of the proposed trajectory planner, in particular with respect to the problems of multi-point trajectories generation and residual vibrations suppression.


2012 - Open-loop and Closed-loop Filters for Optimal Trajectory Planning under Time and Frequency Constraints [Relazione in Atti di Convegno]
Biagiotti, Luigi; Zanasi, Roberto
abstract

Dynamic filters for real-time trajectory generation can be designed in different ways with quite different levels of performances and complexity. However, one can observe that the configurations of such filters are based on two main schemes: systems composed of a chain of integrators with a feedback control and systems formed of a sequence of linear filters disposed in a cascade configuration. According to these schemes, it is possible to obtain minimum-time trajectories under constraints of velocity, acceleration, jerk and even higher derivatives. In both cases, the degree of continuity of the resulting trajectory depends on the order n of the filter, which can be designed according to a modular approach. After a short overview of the structure of the trajectory generators, pro and cons of the two approaches are analyzed. In particular, the attention is focussed on linear filters, since their structure allows a straightforward characterization of the trajectory from a frequency point of view. As a consequence, the generator can be designed by taking into account frequency constraints, besides more standard time constraints (i.e. limits on velocity, acceleration, etc.). The proposed method combines the advantages of minimum-time trajectories with those of input shaping techniques. Moreover, it is possible to prove that, under additional hypotheses, the same chain of linear filters proposed for minimum-time trajectories generation can be used for obtaining uniform B-spline curves, that are widespread in the robotic field when the interpolation of a set of given via-points is required. In this case, the additional constraints do not allow to impose limits on the velocity or acceleration, but only to properly shape the trajectory in the frequency domain. It is therefore possible to select the trajectory/filter parameters with the purpose of suppressing residual vibrations, that may be present because elastic phenomena affecting the robotic system.


2011 - Efficient Simulation of Static and Dynamic Friction for Automotive Applications [Relazione in Atti di Convegno]
Biagiotti, Luigi; Zanasi, Roberto
abstract

In this paper, a technique for modeling frictional phenomena among several bodies that move relatively is proposed with the purpose of optimizing the dynamic simulation of a complex system such as the driveline of a vehicle based on a dual clutch transmission. The proposed method considers together the inertial and frictional properties of the different subsystems, but decouples a main dynamics, that describes their average motion and does not depend on friction, from a proper number of relative dynamics. In this way, for each of these dynamics a standard static friction models can be used, leading to a very efficient numerical simulation. In this sense, the method adopted can be considered an enhancement of Karnopp model.


2011 - Input Shaping Via B-Spline Filters for 3-D Trajectory Planning [Relazione in Atti di Convegno]
Biagiotti, Luigi; Melchiorri, Claudio
abstract

In 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.


2011 - Online Planning of Multi-Segment Trajectories with Trigonometric Blends [Relazione in Atti di Convegno]
Biagiotti, Luigi; Melchiorri, Claudio
abstract

In this paper, the approach based on FIR (Finite Impulse Response) filters, that has been shown to be very efficient for planning time-optimal trajectories composed by polynomial segments, is extended to the design of trajectories characterized by profiles of velocity, acceleration, jerk or even higher derivatives composed by trigonometric functions.A simple discrete-time filter, able to provide as output this kind of trajectories when a rough input signal composed by step functions is applied, is proposed, with two main consequences: 1) the generation of the trajectory results very efficient, even with high degree of continuity and the planning can be performed online; 2) the equivalence between the considered class of trajectories and linear filters allows an immediate frequency characterization of the motion law. In this way, it is possible to define the trajectories by considering constraints expressed in the frequency-domain besides the classical time-domain specifications, such as bounds on velocity, acceleration, and so on. Two examples illustrates the main features of the proposed trajectory planner, in particular with respect to the problems of multi-point trajectory generation and residual vibrations suppression by proper reference inputs application.


2010 - B-Spline Based Filters for Multi-Point Trajectories Planning [Relazione in Atti di Convegno]
Biagiotti, Luigi; Melchiorri, Claudio
abstract

In this paper, the relation between B-splines and FIR (Finite Impulse Response) filters is demonstrated and exploited to design a digital filter for trajectory planning, combining the very simple structure and computational efficiency of FIR filters withthe flexibility of splines. In particular, the trajectorygenerator consists of two main elements. The former is devoted to the solution of an optimization problem that, given a set of points to be interpolated (or approximated), provides the control points defining the spline. The latter, a cascade of moving average filters, gives the trajectory profile at each sampling time on the basis of such points. The proposed method has been applied to several robotic and industrial applications, and inthis paper two case studies are reported as examples: an industrial robot performing a welding operation and a mobile robot moving in an environment with obstacles. With respect to these tasks, the main features of the trajectory generator are shown: the possibility of planning trajectories with high degree of smoothness (continuity of the derivatives), the possibility of easily changing the duration of the trajectory (and therefore thevelocity, acceleration, jerk, etc. of the trajectory) maintaining the same geometric path, the possibility of locally modifying the pre-planned path.


2010 - Dynamic Filters for Online Planning Optimal Trajectories [Relazione in Atti di Convegno]
Biagiotti, Luigi; Melchiorri, Claudio; Zanasi, Roberto
abstract

Filters 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 $n$ 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 $n$-th order filter from that of $n-1$ 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 ($n=4$ or $5$). 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.


2010 - Online trajectory planner with constraints on velocity, acceleration and torque [Relazione in Atti di Convegno]
Biagiotti, Luigi; Zanasi, Roberto
abstract

A filter for trajectories smoothing is presented. The filter provides an output reproducing the input trajectory if this is compliant with given constraints on the velocity, the acceleration and the torque required for tracking it. Otherwise, the filter approximates the input profile guaranteeing that the output trajectory satisfies all the kinematic and dynamic limits. The tracking of the input signal is optimal in the sense that at each time instant the limit value of one among velocity, acceleration and torque is reached. The filter, based on a variable structure controller, is designed in the continuous-time domain but can be implemented by discretization as a sampled system. It can therefore used in mechatronic and robotic applications driven by digital controllers in order to filter trajectories planned without considering the above mentioned constraints or to generate realtime smooth trajectories by simply providing basic inputs such as step or ramp functions.


2010 - Time-Optimal Regulation of a Chain of Integrators with Saturated Input and Internal Variables: An Application to Trajectory Planning [Relazione in Atti di Convegno]
Biagiotti, Luigi; Zanasi, Roberto
abstract

The design of a planner for time-optimal trajectories with constraints on velocity, acceleration, jerk, . . . , is translated into a regulation problem for a chain of integrators with saturations not only in the input but also in all the internal (state) variables. Then the problem is solved by designing a regulator, based on the variable structure control, able to steer the state vector to the origin in minimum time, being compliant with all the constraints. For this purpose, a modular structure with a cascade of controllers, each one devoted to the regulation to the origin of a specific component of the state vector, is demonstrated to be effective and ideally suitable to cope with systems of any order. Analytical examples are provided for filters of first, second and third order.


2009 - Trajectory Planning for Automatic Machines and Robots [Monografia/Trattato scientifico]
BIAGIOTTI, Luigi; MELCHIORRI, CLAUDIO
abstract

This 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.


2007 - An Open Source Distributed Platform for the Control of the PUMA 560 Manipulator [Relazione in Atti di Convegno]
Palli, Gianluca; Biagiotti, Luigi; Melchiorri, Claudio
abstract

[RELAZIONE]


2007 - Bioreactor for electromechanical stress of cells to address towards cardiac phenotype [Abstract in Rivista]
F., Lotti; G., Vassura; Melchiorri, Claudio; Biagiotti, Luigi; C., Muscari; E., Giordano; M., Govoni; C. M., Caldarera; C., Guarnieri; S., Cavalcanti
abstract

-


2007 - Environment Estimation in Teleoperation Systems [Capitolo/Saggio]
Biagiotti, Luigi; Melchiorri, Claudio
abstract

One of the main objectives of control algorithms for teleoperation systems is to have a master device mimicking the response of the remote environment, while the slave device is requested to behave as the human operator. In general, the remote environment is compliant, with a quite different behavior with respect to perfectly rigid surfaces (e.g. in surgery or humancentered applications). In these cases, the knowledge of the dynamical properties of the remote environment can be used in order to improve the transparency of the overall system. A number of analytical and computational models have been proposed in literature in order to describe the behavior of compliant materials but, for sake of simplicity, design and simulation of controllers for robotic telemanipulation are still tied to classical linear spring-damper models. On the other hand, previous experimental activities with soft materials and human tissues have demonstrated that they are characterized by dynamical effects (relaxation and creep phenomena), which cannot be taken into account by means of linear, low-order models. In this Chapter, we study the suitability of a class of nonlinear contact models to describe and emulate compliant visco-elastic environments. Their parameters, estimated on-line, can then be used to command a suitable behavior to the master device in order to render a better contact sensation to the user. © 2007 Springer-Verlag Berlin Heidelberg.


2007 - Traiettorie per azionamenti elettrici [Relazione in Atti di Convegno]
Melchiorri, Claudio; Biagiotti, Luigi
abstract

[Relazione]


2006 - Roboticad: a Matlab Toolbox for Robot Manipulator [Relazione in Atti di Convegno]
R., Falconi; Melchiorri, Claudio; Macchelli, Alessandro; Biagiotti, Luigi
abstract

[RELAZIONE]


2006 - Smooth Trajectories for High-Performance Multi-Axes Automatic Machines [Relazione in Atti di Convegno]
Biagiotti, Luigi; Melchiorri, Claudio
abstract

[RELAZIONE]


2005 - Development of UB Hand 3: Early results [Relazione in Atti di Convegno]
Lotti, F.; Tiezzi, P.; Vassura, G.; Biagiotti, L.; Palli, G.; Melchiorri, C.
abstract

The first part of this paper describes the development of a humanoid robot hand based on an endoskeleton made of rigid links connected with elastic hinges, actuated by sheath routed tendons and covered by continuous compliant pulps. The project is called UB Hand 3 (University of Bologna Hand, 3rd version) and aims to reduce the mechanical complexity of robotic end effectors yet maintaining full anthropomorphic aspect and a good level of dexterity. In the second part this paper focuses on the early experiences of the UB Hand 3 in performing manipulation tasks. ©2005 IEEE.


2005 - Modelling and Controlling the Compliance of a Robotic Hand with Soft Finger-pads [Relazione in Atti di Convegno]
Biagiotti, Luigi; P., Tiezzi; G., Vassura; Melchiorri, Claudio
abstract

[CAPITOLO DI LIBRO]


2005 - Modelling and identification of soft pads for robotic hands [Relazione in Atti di Convegno]
Biagiotti, L.; Melchiorri, C.; Tiezzi, P.; Vassura, G.
abstract

In this work the static and dynamic characterization of viscoelastic pads for robotic hands is performed. A quasi-linear model, developed to describe the behavior of human hand pads and, more generally, of biological tissues, is adopted in order to overcome the problems tied to classical (linear) models, often used in the robotic field. Through experimental tests, the values of the parameters of this model have been found for two different materials (a polyurethane gel and a silicon rubber) which show a behavior similar to that of human pads and seems very suitable for robotic applications. Finally, the model has been extended with the use of digital filters, making the identification process very straightforward. © 2005 IEEE.


2005 - Nonlinear modeling and experimental identification of hemispherical soft pads for robotic manipulators [Relazione in Atti di Convegno]
Tiezzi, P.; Vassura, G.; Biagiotti, L.; Melchiorri, C.
abstract

In this work the dynamic contact of hemispherical indenter covered by a thick viscoelastic layer and pressed against a flat rigid surface is modelled. The goal is to investigate the dynamic behavior of robotic fingertips composed by an inner rigid structure covered by a soft layer, mimicking the human biological model. A quasi-linear model, frequently used to describe the behavior of soft and pulpy biological tissues, is adopted in order to achieve a compromise between the simplicity of classical linear models and the difficulty of nonlinear approaches. Two different materials (a polyurethane gel and a silicon rubber) have been experimentally tested in order to find the parameters of the model and to validate it. Finally, the advantage of the use of digital filters method in identification process is exploited, so that the identification becomes suitable for online process. Copyright © 2005 by ASME.


2005 - Robotic Interaction Through Compliant Interfaces: Modelling and Identification [Relazione in Atti di Convegno]
Biagiotti, Luigi; C., Melchiorri
abstract

In this work, a new model, able to emulate theinteraction of a robot with the environment when viscoelasticphenomena occur, is presented. The starting point of thisresearch activity has been the study of soft pads for dexterousmanipulation but the results obtained are applicable to allsituations which foresee the interaction of a robotic manipulatorthrough/with a viscoelastic medium (e.g. robotic surgery).Based on the so called quasi-linear model, adopted to describethe behavior of human hand pads and, more generally, ofbiological tissues, this model allows to overcome the problemstied to classical (linear) models, often used in the robotic field.A procedure aiming to obtain the parameters of this nonlinearmodel is developed on the basis of classical identificationmethods and of physical insights. Finally, through experimentaltests on some viscoelastic materials (a polyurethane gel and asilicon rubber) the model is validated.


2003 - A dexterous robotic gripper for autonomous grasping [Articolo su rivista]
Biagiotti, L.; Melchiorri, C.; Vassura, G.
abstract

In 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.


2003 - Cartesian Impedance Control for Dexterous Manipulation [Relazione in Atti di Convegno]
Biagiotti, L.; Liu, H.; Hirzinger, G.; Melchiorri, C.
abstract

In this work, a cartesian impedance controller purposely designed for dexterous manipulation is described. Based on the main features of the DLR Hand II, concerning kinematic structure and sensory equipment of fingers, this control strategy allows to overcome the main problems encountered in fine manipulation, namely: effects of the friction (and unmodeled dynamics) on robot performances and occurrence of singularity conditions. The achieved control scheme has been experimentally validated by testing it on a finger of the DLR Hand.