On state and inertial parameter estimation of free-falling planar rigid bodies subject to unsche dule d frictional impacts

This paper addresses the problem of simultaneous state estimation and inertial and frictional parameter identification for planar rigid-bodies subject to unscheduled frictional impacts. The aim is to evaluate to what level of accuracy, given noisy captured poses of an object free-falling under gravity and impacting the surrounding environment, it is conceivable to reconstruct its states, the sequence of normal and tangential impulses and, concurrently, estimate its inertial properties along with Coulomb’s coefficient of friction at contacts. To this aim we set up a constrained nonlinear optimization problem, where the unscheduled impacts are handled via a complementarity formulation. To assess the validity of the proposed approach we test the identification results both (i) with respect to ground truth values produced with a simulator, and (ii) with respect to real experimental data. In both cases, we are able to provide accurate/realistic estimates of the inertia-to-mass ratio and friction coefficient along with a satisfactory reconstruction of systems states and contact impulses

Optimal Contact Force Distribution for Compliant Humanoid Robots in Whole-Body Loco-Manipulation Tasks

The stiffness ellipsoid, i.e. the locus of task-space forces obtained corresponding to a deformation of unit norm in different directions, has been extensively used as a powerful representation of robot interaction capabilities. The size and shape of the stiffness ellipsoid at a given end-effector posture are influenced by both joint control parameters and - for redundant manipulators - by the chosen redundancy resolution configuration. As is well known, impedance control techniques ideally provide control parameters which realize any desired shape of the Cartesian stiffness ellipsoid at the end-effector in an arbitrary non-singular configuration, so that arm geometry selection could appear secondary. This definitely contrasts with observations on how humans control their arm stiffness, who in fact appear to predominantly use arm configurations to shape the stiffness ellipsoid. To understand this discrepancy, we provide a more complete analysis of the task-space force/deformation behavior of redundant arms, which explains why arm geometry also plays a fundamental role in interaction capabilities of a torque controlled robot. We show that stiffness control of realistic robot models with bounds on joint torques can't indeed achieve arbitrary stiffness ellipsoids at any given arm configuration. We first introduce the notion of maximum allowable Cartesian force/displacement (“stiffness feasibility”) regions for a compliant robot. We show that different robot configurations modify such regions, and explore the role of different configurations in defining the performance limits of Cartesian stiffness controllers. On these bases, we design a stiffness control method that suitably exploits both joint control parameters and redundancy resolution to achieve desired task-space interaction behavior

On the Identification of Machine Settings for Gear Surface Topography Corrections

In this paper we set out to investigate the performances of some algorithms proposed in the gear literature for identifying the machine-tool settings required to obtain predesigned gear tooth surface topographies, or needed to compensate for flank form deviations of real teeth. For ease of comparison, the problem is formulated as a nonlinear least squares problem, and the most widely employed algorithms are derived as special cases. The algorithms included in the analysis are: (i) one-step methods, (ii) iterative methods, (iii) iterative methods with step control. The performance index is devised in their ability of returning practical solutions in the presence of: (i) strong model nonlinearities, (ii) ill-conditioning of the sensitivity matrix, (iii) demanding topographic shapes. Instrumental here is an original classification of topographic modifications as either “simple” or “complex”, based on the SVD analysis of the sensitivity matrix. Some selected numerical examples demonstrate that iterative techniques with step control are the most convenient in terms of reliability and robustness of the obtained solutions. The generation process considered here is face-milling of hypoid gears, although the methodology is general enough to cope with any gear cutting/grinding method

Ease-off based compensation of tooth surface deviations for spiral bevel and hypoid gears: only the pinion needs corrections

This paper presents a novel methodology to restore the designed functional properties of hypoid gear sets whose teeth deviate from their theoretical models due to inevitable imperfections in the machining process. Corrective actions are applied to one member only: the pinion. The concept of ease-off is profitably employed as the true means to evaluate the contact properties of a gear set as a whole. It is indeed the sameness of the designed and the real ease-off that ultimately renders two gear sets equivalent in terms of contact pattern, transmission error and vibrational properties. On this basis, gear deviations can be mapped into equivalent pinion deviations, added to those of the pinion itself, and cumulatively compensated for by applying corrective machine-tool settings to the pinion. The gear member is perfect “as is”. The ensuing advantages are highlighted in the paper. The method is illustrated with a real-life numerical example. It demonstrates that, applying corrective (i) machine-tool settings and (ii) machine settings only to the pinion grinding process, the originally designed transmission properties can be restored with a high level of accuracy

A Two-Stage Trajectory Optimization Strategy for Articulated Bodies with Unscheduled Contact Sequences

In this letter, we propose a two-stage strategy for optimal control problems of robotic mechanical systems that proves to be more robust, and yet more efficient, than straightforward solution strategies. Specifically, we focus on a simplified humanoid model, represented as a two-dimensional articulated serial chain of rigid bodies, in the tasks of getting up (sitting down) from (to) the supine and prone postures. Interactions with the environment are integral parts of these motions, and a priori unscheduled contact sequences are discovered by the solver itself, opportunistically making or breaking contacts with the ground through feet, knees, hips, elbows, and hands. The present investigation analyzes the effects on the computational performance of: 1) the explicit introduction of contact forces among the optimization variables, 2) the substitution of undesired contact forces with geometric constraints that prevent interpenetrations, and 3) the splitting of the planning problem into two consecutive phases of increasing complexity. To the best of our knowledge, these tests represent the only quantitative analysis of the performances achievable with different solution strategies for optimization-based, whole-body dynamic motion planning in the presence of contacts

Grasp planning with soft hands using Bounding Box object decomposition

In this paper, we present a method to plan grasps for soft hands. Considering that soft hands can easily conform to the shape an the object, with preference to certain types of basic geometries and dimensions, we decompose the object into one type of these geometries, particularly into Minimal Volume Bounding Boxes (MVBBs), which are proved to be efficiently graspable by the hand we use. A set of hand poses are then generated using geometric information extracted from such MVBBs. All hand postures are used in a dynamic simulator of the PISA/IIT Soft Hand and put on a test to evaluate if a proposed hand posture leads to a successful grasp. We show, through a set of numerical simulations, that the probability of success of the hand poses generated with the proposed algorithm is very good and represents an evident improvement with respect to our previous results published in [1]

Complessi dinucleari di ferro con leganti a ponte per la produzione elettrocatalitica di idrogeno

Il forte incremento della popolazione mondiale, la continua crescita del tenore di vita e del livello di consumi hanno portato negli ultimi decenni ad un enorme aumento della richiesta mondiale di energia. Diviene pertanto fondamentale ricercare nuovi metodi altamente efficienti di produzione, trasporto ed utilizzo di energia, che migliorino la qualità della vita dell’uomo e nello stesso tempo salvaguardino il clima e l’ambiente. Proprio a questo proposito, in questi ultimi anni, vi è un crescente interesse nei riguardi della molecola di idrogeno, H2. Ad oggi è impossibile sostituire i combustibili fossili con l’idrogeno, per motivi prettamente tecnologici (difficoltà nello stoccaggio e nel trasporto) e per motivi legati alla sua produzione. Infatti, l’idrogeno è sì uno degli elementi più presenti in natura, ma non come sostanza gassosa pura bensì in forma combinata, generalmente acqua, quindi per produrlo è necessario rompere il legame con l’elemento con cui è combinato, consumando energia; questo spiega il motivo per cui l’idrogeno viene considerato un vettore di energia e non una fonte di energia. La produzione di idrogeno, o meglio del suo equivalente costituito da un flusso di elettroni e protoni, dall’acqua è un processo che avviene in natura, precisamente nelle cellule vegetali durante la prima fase della fotosintesi clorofilliana. Tale processo mostra l’importanza dei complessi bio-inorganici che vi partecipano, ai quali si ispira la ricerca di nuovi efficienti catalizzatori per la produzione di idrogeno mediante scissione catalitica dell’acqua (water splitting). Una classe di enzimi particolarmente studiata, in quest’ambito, è costituita dalle idrogenasi; la maggior parte di questi enzimi contengono un frame dinucleare Ni-Fe o Fe-Fe. Numerosi gruppi di ricerca sono fortemente impegnati nell’obiettivo di sintetizzare complessi simili a questi enzimi (enzyme mimics), e con prestazioni paragonabili, in modo da produrre idrogeno in modo efficiente e rispettando i principi di sostenibilità ambientale ed economica. Il gruppo di ricerca presso il quale è stato svolto il tirocinio oggetto del presente elaborato si occupa dello studio di complessi metallorganici caratterizzati dalla presenza di un “core” metallico costituito da due atomi di Ferro adiacenti coordinati tra loro mediante leganti a ponte diversamente funzionalizzati. Obiettivo del tirocinio è stato quello di verificare l’efficienza catalitica di alcuni di questi complessi nel promuovere il processo di interconversione H+/H2; per fare ciò, si è fatto ricorso ad un approccio elettrochimico, sfruttando la tecnica della voltammetria ciclica

Grasp compliance regulation in synergistically controlled robotic hands with VSA

In this paper, we propose a general method to achieve a desired grasp compliance acting both on the joint stiffness values and on the hand configuration, also in the presence of restrictions caused by synergistic underactuation. The approach is based on the iterative exploration of the equilibrium manifold of the system and the quasi-static analysis of the governing equations. As a result, the method can cope with large commanded variations of the grasp stiffness with respect to an initial configuration. Two numerical examples are illustrated. In the first one, a simple 2D hand is analyzed so that the obtained results can be easily verified and discussed. In the second one, to show the method at work in a more realistic scenario, we model grasp compliance regulation for a DLR/HIT hand II grasping a ball

Human-Like Impedance and Minimum Effort Control for Natural and Efficient Manipulation

Humans incorporate and switch between learnt neuromotor strategies while performing complex tasks. Towards this purpose, kinematic redundancy is exploited in order to achieve optimized performance. Inspired by the superior motor skills of humans, in this paper, we investigate a combined free motion and interaction controller in a certain class of robotic manipulation. In this bimodal controller, kinematic degrees of redundancy are adapted according to task-suitable dynamic costs. The proposed algorithm attributes high priority to minimum-effort controller while performing point to point free space movements. Once the robot comes in contact with the environment, the Tele-Impedance, common mode and configuration dependent stiffness (CMS-CDS) controller will replicate the human’s estimated endpoint stiffness and measured equilibrium position profiles in the slave robotic arm, in real-time. Results of the proposed controller in contact with the environment are compared with the ones derived from Tele-Impedance implemented using torque based classical Cartesian stiffness control. The minimum-effort and interaction performance achieved highlights the possibility of adopting human-like and sophisticated strategies in humanoid robots or the ones with adequate degrees of redundancy, in order to accomplish tasks in a certain class of robotic manipulatio

On the integration of singularity-free representations of SO(3) for direct optimal control

In this paper we analyze the performance of different combinations of: (1) parameterization of the rotational degrees of freedom (DOF) of multibody systems, and (2) choice of the integration scheme, in the context of direct optimal control discretized according to the direct multiple-shooting method. The considered representations include quaternions and Direction Cosine Matrices, both having the peculiarity of being non-singular and requiring more than three parameters to describe an element of the Special Orthogonal group SO(3). These representations yield invariants in the dynamics of the system, i.e., algebraic conditions which have to be satisfied in order for the model to be representative of physical reality. The investigated integration schemes include the classical explicit Rungeâ\u80\u93Kutta method, its stabilized version based on Baumgarteâ\u80\u99s technique, which tends to reduce the drift from the underlying manifold, and a structure-preserving alternative, namely the Rungeâ\u80\u93Kutta Munthe-Kaas method, which preserves the invariants by construction. The performances of the combined choice of representation and integrator are assessed by solving thousands of planning tasks for a nonholonomic, underactuated cart-pendulum system, where the pendulum can experience arbitrarily large 3D rotations. The aspects analyzed include success rate, average number of iterations and CPU time to convergence, and quality of the solution. The results reveal how structure-preserving integrators are the only choice for lower accuracies, whereas higher-order, non-stabilized standard integrators seem to be the computationally most competitive solution when higher levels of accuracy are pursued. Overall, the quaternion-based representation is the most efficient in terms of both iterations and CPU time to convergence, albeit at the cost of lower success rates and increased probability of being trapped by higher local minima