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National Research Project supported by MURST 1998


Robotica Articolata e Mobile per i SErvizi e le TEcnologie
(Articulated and Mobile Robots for Services and Technology)

Scientific Responsible:
Prof. Salvatore NICOSIA
Universita` degli Studi di Roma "TOR VERGATA"
Dipartimento di Informatica, Sistemi e Produzione
tel: ++39-06-7259.7434
fax: ++39-06-2020519

List of tasks and involved R.U.:
(for descriptions of the tasks, see in the following)

Task MA3:
Impact analysis: modeling and control of robotic links subject to impacts with the external environment. (Politecnico di Torino)

Task TA1:
Advanced Sensors and Control Techniques for Robotic Manipulation (University of Bologna)

Task 1:

Task 2:

Task 3:

Task 4:

Task 5:

Task 6:

Task 7:

Task 8:

Task 9:

Task 10:

Task TA1:
Advanced Sensors and Control Techniques for Robotic Manipulation (University of Bologna)

Task MA3:
Impact analysis: modeling and control of robotic links subject to impacts with the external environment (Politecnico di Torino)

State of the art

Robot manipulators force control has motivated a lot of research studies during the last years, but while in the most classical works (see e.g. [1]-[3]) the manipulators were considered directly in constrained motion, only recently interesting attempts  have been made to model and control the transition phase between free motion and constrained motion, typically in the case of impacts between the end-effector of a robot and an external surface.

The study and the control of the impact phenomena are especially important in robotics for different reasons: i) as a prevention of the mechanical structure of the robot, since all the highest and greatest stresses arise as a consequence of impact, and many serious failures can be generated when impact forces are not properly recognized and taken under control; ii) as a control goal, for the execution of tasks requiring the interaction of the manipulator with an external environment, or with another robot, with which it must cooperate, or in the case of walking robots.

The basic physical phenomena involved in bodies impact are quite well-known (see e.g. [4], [5], and the numerous references therein), whereas the problem of controlling the impact is still open, mainly due to the sudden change of the equations of motion that happens when the bodies involved in the impact swish sharply from a condition of non contact to a condition of contact. In particular, the manipulator may leave the contact surface after impact, due to some unexpected disturbances, resulting in changes of the robot dynamics, and limit cycle response or instability may be excited. Besides, it is fundamental to take into account the practical limitations, which can reduce the effectiveness of some impact analysis and control schemes. These limitations arise from the difficulty to a priori establish the approximation level to be used for the study of the various phenomena involved in the impact, and to correctly describe how different parameters, such as masses, geometric dimensions, stiffness, duration of the impact, affect the collision. Finally, for the practical application of many impact control schemes quite powerful tools are required, e.g. for precise data storing and/or for the impact detection, thus limiting the actual control performances. Among the most recent papers devoted to such a problem, see e.g. [6]-[12]. A general classification of the solutions proposed in literature may be made with reference to the existence or not of a “switching condition” in the definition of the control scheme, i.e., a unique control law can be applied during free-motion, contact  mode and in the impact transition phase between them (e.g., as in [7], where the proposed impact controller uses a simplified impedance control scheme to reduce impulsive forces as well as rebound effects), or different controllers are employed in the three situations, by switching from a control law to another one detecting the impact by means of force measurements (e.g., as in [8]-[10], [12]). In particular, various switching control strategies are discussed in [6], with reference to the problem of the control of a class of mechanical systems with a finite number of degrees of freedom, subject to  unilateral constraints on the position, whereas in [10] a sensor-referenced control method using a positive acceleration feedback, together with a switching control strategy, is developed for robot impact control and force regulation. All the control schemes in the cited references consider the impact between  the robot end-effector and an external surface or an object, and require the use of force sensors and the entire or partial knowledge of the robot kinematics and dynamics.

More recently, the equations of motion of mechanical systems subject to inequality constraints have been considered in [13], by using two different methods: the method of the valentine variables (introducing the concept of “nonsmooth impacts”, in the case of very stiff impacting parts), and the method of the penalty functions (introducing the concept of  “smooth impacts”, in the case of flexible impacting parts). Control laws are proposed, and experimentally tested, to solve regulation problems in the presence of possible contacts and impacts among parts of a mechanical systems or with the external environment.


[1] M.H. Raibert, J.J. Craig, “Hybrid position/force control of manipulators”, Trans. ASME J. Dynam. Syst. Meas. Control, 102, 126-133, 1981.
[2] H. Kazerooni, “Robust nonlinear impedance control for robot manipulators”, IEEE Int. Conf. Robotics and Autom., 741-750, 1991.
[3] T. Yoshikawa, T. Surgie, and M. Tanaka, “Dynamic hybrid position/force control of robot manipulators – controller design and experiment”, IEEE J. Of Robotics and Automation, 4, 699-705, 1988.
[4] J.A. Zukas, Impact Dynamics, New York: John Wiley and Sons, Inc., 1982.
[5] B. Brogliato, Nonsmooth Impact Mechanics, London: Springer-Verlag, 1996.
[6] B. Brogliato, S.-I. Niculescu, and P. Orhant, "On the Control of Finite-Dimensional Mechanical Systems with Unilateral Constraints", IEEE Trans. on Automatic Control, 42, 2, 200-215, 1997.
[7] Z.C. Lin, R.V. Patel, and C.A. Balafoutis, “Impact Reduction for Redundant Manipulators Using Augmented Impedance Control”, J. of Robotic Systems, 12, 1, 67-92, 1995.
[8] N. Mandal and S. Payandeh, "Control Strategies for Robotic Contact Tasks: An Experimental Study", J. of Robotic Systems, 12, 1, 67-92, 1995.
[9] J.K. Mills and D.M. Lokhorst, "Control of Robotic Manipulators During General Task Execution: A Discontinuous Control Approach", Int. J. of Robotics Research, 12, 2, 146-163, 1993.
[10] T.-J. Tarn, Y. Wu, N. Xi, and A. Isidori, "Force Regulation and Contact Transition Control", IEEE Control Systems, 16, 1, 32-40, 1996.
[11] A. Tornambè, "Global regulation of a planar robot arm striking a surface", IEEE Trans. on Automatic Control, 41, 10, 1517-1521, 1996.
[12] R. Volpe and P. Khosla, "A theoretical and experimental investigation of impact control for manipulators", Int. J. of Robotics Research, 13, 4, 351-365, 1993.
[13] B. Bona, M. Indri, A. Tornambè, “Flexible Piezoelectric Structures: Approximate Motion Equations and Control Algorithms”, IEEE Trans. on Automatic Control, 42, 1, 94-101, 1997.
[14] M. Indri, A. Tornambè, “Robust regulation and trajectory tracking for flexible robots by using piezoelectric actuators”, Advanced Robotics, 10, 3, 265-282, 1996.
[15] M. Indri, A. Tornambè, “Robust trajectory tracking for flexible piezoelectric structures”, IEE Proceedings, Control Theory and Applications, 141, 5, 289-294, 1994.
[16] B. Bona, E. Brusa, P. Canestrelli, G. Genta, A. Tonoli, “Finite Element Modeling and Experimental Validation of an Elastic Beam with Surface Bonded Piezoelectric Devices”, 1994 IEEE Int. Conf. on Robotics and Automation, 2659-2664, 1994.

Task description

Goal of the present task is the study of methodologies for modeling, analysis, and control of robotic links, subject to impacts with the external environment.
In particular, mathematical models will be proposed to represent and analyse the transition phase from the robot free-motion state to the contact condition with external bodies, taking into account the discontinuity of the equations of motion of the systems involved (the manipulator and the external environment) at the impact time. Different models will be considered to analyse different "elasticity conditions" of the robotic links and of the external contact surfaces (basically, rigid links  with elasticity located only on the end-effector or flexible links, quasi-rigid external bodies or flexible, compliant surfaces).
On the basis of such models, control schemes will be developed to achieve a stable, steady-state contact, with the assignment of desired contact forces. Another control goal, when flexible links are concerned, will be the reduction of impact-induced vibrations. The design of the control strategy will take into account some fundamental matters, as:

The proposed impact models and control schemes will be validated by experimental tests, which will be carried out in the laboratories of the Unit of Torino (see the list of the available equipments), or in those of one of the other interested Units (Roma Tor Vergata and Napoli). The available equipments will constitute the starting point for the realization of experimental setups, which allow the testing of both the concentrated elasticity case (by considering a rigid manipulator, as the two-link planar robot or the six dof COMAU SMART-3S one, with a flexible tool mounted on the end-effector) and flexible structures (suitably sensored and actuated). With this regard, particular efforts will be devoted to study the possibility to attain, together with the contact force control, achieved by the joint actuators, a simultaneous active reduction of the structure vibrations induced by the impact, by means of piezoelectric transducers. Such devices could be used also as force sensors, but only if the contact forces are always kept small, for example by means of an accurate motion planning that brings the robotic link in contact with the external environment with almost zero velocity (such result is achievable only with a nearly perfect knowledge of the physical and geometrical characteristics of the impact and of the external environment itself). Previous studies about piezoelectric transducers will be used (see e.g. references [11] - [14]).

The implementation of the experimental setup will require the solution of some hardware and software problems, as:

Final outputs of the research will be: Current research

According to the project scheduling, the main topics of this task (developed by the Units of Torino and Roma Tor Vergata) in the first six-months phase are given by:

The main results already obtained can be summarized as follows:

Universita` degli Studi di Roma "TOR VERGATA"
Dipartimento di Informatica, Sistemi e Produzione
Prof. Salvatore NICOSIA
tel: ++39-06-7259.7434
fax: ++39-06-2020519

Universita` degli Studi di Bologna
DEIS - Dipartimento di Elettronica Informatica Sistemistica
Via Risorgimento 2, 40136 Bologna, Italy
Prof. Claudio MELCHIORRI

Universita` di Roma La Sapienza
Prof. Alessandro DE LUCA
Via Eudossiana 18, 00184 Roma
Tel. +39-6-44585371
Fax +39-6-44585367

Politecnico di Milano
Prof. Gianantonio MAGNANI
Dipartimento di Elettronica e Informazione
Piazza Leonardo da Vinci, 32 - 20133 Milano
tel: +39-02-2399-3400

Universita` degli Studi di Napoli Federico II
Dipartimento di Informatica e Sistemistica
Via Claudio 21, 80125 Napoli
Tel: +39 081 768-3179

Universita` di Genova
Prof. Giuseppe CASALINO
Via all'Opera Pia 13 - 16145 Genova, Italia
Tel. +39 10 3532727
Fax +39 10 3532948/2154

Universita` di Pisa
Prof. Antonio BICCHI
DSEA, Universita` di Pisa
Facolta` di Ingegneria
via Diotisalvi, 2 56100 PISA, ITALY
Phone: +39-50-553639 [565328]
Fax: +39-50-550650 [565333]
E-mail:, []

Universita` di Perugia
Prof. Michele LA CAVA
Dipartimento di Ingegneria Elettronica e dell'Informazione
Via G.Duranti 93 I-06125 Perugia - Italy
Phone: +39-075-585-2683

Politecnico di Torino
Prof. Basilio BONA
Dipartimento di Automatica e Informatica
Corso Duca degli Abruzzi, 24
10129 Torino, ITALY
Phone: +39-11-564 7023
Fax: +39-11-564 7099

Universita' di Roma Tre
Prof. Lorenzo SCIAVICCO
Dipartimento di Informatica e Automazione
Via della Vasca Navale 79
00146 Roma
phone (+39) 06 55173242
fax (+39) 06 5573030

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