On the Control of Complementary-Slackness Juggling Mechanical Systems Bernard Brogliato, Arturo Zavala Rio
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On the control of complementary-slackness juggling mechanical systems Bernard Brogliato, Arturo Zavala Rio To cite this version: Bernard Brogliato, Arturo Zavala Rio. On the control of complementary-slackness juggling mechanical systems. IEEE Transactions on Automatic Control, Institute of Electrical and Electronics Engineers, 2000, 45 (2), pp.235-246. 10.1109/9.839946. hal-02303804 HAL Id: hal-02303804 https://hal.archives-ouvertes.fr/hal-02303804 Submitted on 2 Oct 2019 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. On the Control of Complementary-Slackness Juggling Mechanical Systems Bernard Brogliato and Arturo Zavala Río Abstract—This paper studies the feedback control of a class (2) of complementary-slackness hybrid mechanical systems. Roughly, (3) the systems we study are composed of an uncontrollable part (the “object”) and a controlled one (the “robot”), linked by a unilateral where the classical dynamics of Lagrangian systems is in (1), constraint and an impact rule. A systematic and general control de- sign method for this class of systems is proposed. The approach is the set of unilateral constraints is in (2) with , a nontrivial extension of the one degree-of-freedom (DOF) juggler and the so-called complementarity conditions [14] are in (3), control design. In addition to the robot control, it is also useful to where is the Lagrange multiplier vector. We assume study some intermediate controllability properties of the object’s frictionless constraints. , , impact Poincaré mapping, which generally takes the form of a non- , , and are the generalized coordinate linear discrete-time system. The force input mainly consists of a family of dead-beat feedback control laws, introduced via a recur- vector, the inertia matrix, the Coriolis and centrifugal terms, the sive procedure, and exploiting the underlying discrete-time struc- gravity forces and torques, and the control input, respectively, ture of the system. The main goal of this paper is to highlight the and . In order to render the dynamical system com- role of various physical and control properties characteristic of the plete, we must add to (1)–(3) a so-called restitution law that re- system on its stabilizability properties and to propose solutions in lates postimpact and preimpact velocities. Such physical rules certain cases. are necessary [30], [40]. The most widely used restitution rule Index Terms—Complementary slackness, feedback, hybrid, im- is known as Newton’s conjecture [4]. It is based on the knowl- pact Poincaré mappings, nonsmooth, underactuated, viabililty. edge of restitution coefficients . When ,itis represented in its generalized form as follows: I. INTRODUCTION (4) A. General Introduction where , , and generically denote ECENT researches in the robotics and the systems and the impact times (the superindices and stand, respectively, R control communities on mechanical systems subject to for the instants just after and just before the collisions), with unilateral constraints have focused on stabilization of manipu- . In case of a codimension 1 con- lators during complete robotic tasks [10], [39], well-posedness straint ( ), from energetical arguments. The and system theoretic issues [9], [30]–[32], walking and hopping system in (1)–(4) is complete, in the sense that, given preimpact machines [1], [5], [7], [8], [12], control of juggling and catching velocities , we are able to calculate the postimpact veloci- robots [6], [26], [27], [33], [37], systems with dynamic backlash ties and continue the integration after the collision has occurred. [2], [16], stabilization of polyhedral objects in some manipula- Notice that the system in (1)–(4) is a complex hybrid dynamical tion tasks [35], and nonprehensile manipulation [11], [19], [24]; system [32]. This class of dynamical systems can be divided fur- see [19] for a more complete bibliography on this last topic. ther into subclasses. In particular, the case in which the free-mo- The work presented in this paper focuses essentially on the last tion dynamics are controllable has recently received attention five listed topics. The open-loop models used are basically rigid [31], [39]. This class does not, however, cover some impacting body dynamics with a set of unilateral constraints on the gener- robotic systems. Indeed, write the dynamical equations of a two alized position. Such hybrid dynamical systems may be repre- degree-of-freedom (DOF) juggler; i.e., a system composed of sented as follows: an object (a point mass) subject to gravity, which rebounds on a (1) controlled table, as shown in Fig. 1: (5) (6) (7) B. Brogliato is with the Laboratoire d’Automatique de Grenoble (UMR 5528 (8) CNRS-INPG), ENSIEG, BP 46, 38402 St. Martin d’Hères, France (e-mail: [email protected]). A. Zavala Río was with the Mechanical Engineering Laboratory (MITI), Tsukuba, Ibaraki 305-8564, Japan. He is now with the University de Queretaro, Facultad de Ingenieria, DEPFI, 76010 Queretaro, Qro., Mexico (e-mail: (9) [email protected]). Restitution rule in (4) (10) Fig. 1. One and two DOF jugglers. Notice that the ball dynamics in (5) and (6) are not controlled like the impact damper [2], [16], we may consider that (11) cre- because only gravity acts on the ball. Hence, the only way to ates disturbances in the dynamics of (12), or on the contrary, we influence the trajectory of the ball is through impacts. This is may desire to control (11) using the impacts. In this paper, we a strong motivation for considering the feedback control of a will mainly focus on the control of from the input in (12), two DOF juggler, as in (5)–(10), because it represents a sim- via sequences of impacts. In other words, we shall restrict our- plified model of manipulation of objects through “controlled” selves to control tasks with zero-measure contact phases. The collisions with a robotic device [35]. We may suppose that the controllability and stabilizability properties of such hybrid sys- length of the surface is infinite. Hence, the impacts always occur tems, which depend on the vector fields in (11) and (12) and on with the same side of the table. In this paper, we shall use this in (13), have not yet been fully understood. It is advocated here example as an illustration of the influence of the physical and that impact Poincaré mappings [40] provide a suitable frame- control parameters on the control design. work for such analysis. Let us introduce the following defini- tion. B. A Class of Complementary-Slackness Hybrid Systems Definition 1: A viable controller is a function Juggling robots may also be considered as a particular case such that 1) or and of a class of complementary-slackness systems between programmed impact times, and 2) and are right-continuous of local bounded (11) variation (LBV) in time. (12) Here, programmed impacts are defined as those shock in- (13) stants planned in the control design (contrary to accidental im- pacts that may be caused by various model uncertainties or dis- where , , ( and turbances in the control loop). As we shall see, the sequence may have the same or different values), and a restitution rule depends on the controller design that in turn must in- has to be added to complete the model. Notice that if , corporate the object ballistic constraints. Let us recall that an such a system may a priori evolve in different modes [32]: LBV function possesses a countable set of discontinuity points its hybridness is therefore intrinsic. As indicated in the title and [21]; hence, a viable input ensures the well-posedness of the the abstract, we choose to generically name such systems jug- closed-loop system. glers, even though, as we shall see later, other types of sys- Definition 2: The “object” in (11) is controllable if given tems may fall into this class. In this setting, (11) plays the role , , satisfying the object’s ballistic constraints, of the “object,” and (12) is the “robot.” may repre- and , such that , and , a viable sent the “distance” between the object and the robot, but this is control law that drives from to exists, with not always the case, as some examples will prove. A necessary . condition to transform (1) into (11) and (12) is that a general- The study of such notions, however, requires some interme- ized coordinate transformation exists and ful- diate steps, for which some basic properties are important (in- fills for all , terestingly enough, some of them are similar to those done in . Also consider , and notice that the [17] for the control of a class of cascaded nonlinear systems system in (11) and (12) corresponds to (1) written in a non- that model some nonholonomic mechanical systems). Among controllable canonical form. Such systems are therefore quite those: different from so-called triangular systems [15]. In particular, 1) the properties of the object’s flow setting , (11) and (12) are not in general locally feedback on [explicit knowledge of the trajecto- stabilizable because the uncontrollable modes are not nec- ries, or controllability with state and input ]; essarily stable. The control problem for (11)–(13) may change 2) the controllability of (12); depending on our goal: for instance, in a system with clearance, 3) the controllability of (11) through impacts; 4) the relative degree1 of with respect to and the capsulate the whole essence of the general problem. It provides relative degrees of with respect to ; us, however, with a nice starting point.