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

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

Adaptive Synergies for the Design and Control of the Pisa/IIT SoftHand

In this paper we introduce the Pisa/IIT SoftHand, a novel robot hand prototype designed with the purpose of being robust and easy to control as an industrial gripper, while exhibiting high grasping versatility and an aspect similar to that of the human hand. In the paper we briefly review the main theoretical tools used to enable such simplification, i.e. the neuroscience-based notion of soft synergies. A discussion of several possible actuation schemes shows that a straightforward implementation of the soft synergy idea in an effective design is not trivial. The approach proposed in this paper, called adaptive synergy, rests on ideas coming from underactuated hand design. A synthesis method to realize a desired set of soft synergies through the principled design of adaptive synergy is discussed. This approach leads to the design of hands accommodating in principle an arbitrary number of soft synergies, as demonstrated in grasping and manipulation simulations and experiments with a prototype. As a particular instance of application of the synthesis method of adaptive synergies, the Pisa/IIT SoftHand is described in detail. The hand has 19 joints, but only uses 1 actuator to activate its adaptive synergy. Of particular relevance in its design is the very soft and safe, yet powerful and extremely robust structure, obtained through the use of innovative articulations and ligaments replacing conventional joint design. The design and implementation of the prototype hand are shown and its effectiveness demonstrated through grasping experiments, reported also in multimedia extensio

Advanced grasping with the Pisa/IIT softHand

This chapter presents the hardware, software and overall strategy used by the team UNIPI-IIT-QB to participate to the Robotic Grasping and Manipulation Competition. It relies on the PISA/IIT SoftHand, which is underactuated soft robotic hand that can adapt to the grasped object shape and is compliant with the environment. It was used for the hand-in-hand and for the simulation tracks, where the team reached first and third places respectively

Sistema per l’identificazione di difetti su una superficie di almeno una porzione di una scocca e relativo metodo

La presente invenzione riguarda un sistema e un metodo per l’identificazione, la classificazione e la successiva rimozione di difetti di fabbricazione presenti sui componenti di veicoli

Kineto-Static Methods for Whole-Robot Interaction Control

In robotic grasping, it is usual the distinction between tip grasp and whole-hand grasp. In the first case, only fingertips interact with the grasped object, as it happens grasping e.g. a strawberry. In the second case, on the contrary, also internal phalanges are in contact with the object, as it happens, for example, grabbing an hummer from the handle. Similarly, it is usual for a humanoid robot to interact with the environment with the feet and the hands. But the interaction can also occur in the internal limbs, as the torso or the knees, as e.g. lifting up a large box. We refer to these cases as whole-body loco-manipulationtasks. In both the cases, collectively referred to as whole-body robot interactions, multiple contacts, can greatly affects the robot capabilities. As a consequence, the presence of a high number of degrees of freedom is not sufficient to ensure the full controllability of the interaction forces and/or of the system displacements. This thesis presents novel thinking and approaches to the kineto-static analysis of whole-body robot interaction, general enough to treat compliant and/or underactuated robots. In the first part, the developed approaches and tools are presented and explained analyzing the problem of grasping with synergistically underactuated robotic hands. The quasi-static model of the whole system is obtained considering the congruence and the equilibrium equations, both for the grasped object and the robotic hand. The constitutive equations of the contact are introduced via a penalty formulation, making the problem of the contact force computation statically determined. Grouping together all the previous equations, the Fundamental Grasp Equation (FGE) is obtained. The FGE is investigated acting both on (i) its coefficient matrix, the Fundamental Grasp Matrix (FGM) and on (ii) the solution space of the system, i.e. the nullspace of the FGM. From the elaboration of the FGM, the canonical form of the Fundamental Grasp Equation (cFGE) is obtained, both in numeric and symbolic form. The cFGE provides some relevant information on the system as the subspace of the controllable internal forces, the subspace of the controllable object displacements, and the grasp compliance matrix. Moreover, some relevant manipulation tasks are defined in terms of nullity or non-nullity of the system variables (joint angles, joint torques, object displacements, etc...), as e.g. the pure squeeze of the object, in which the contact forces change without affecting the object configuration, and the kinematic grasp displacements in which the object is moved without influencing the contact forces. In order to discover the feasibility of such predefined tasks, a method for investigating the solution space of the FGE is presented, based on the computation of the reduced row echelon form (RREF) of suitable matrices. Some of the previous methods have been used to support the design of two prototypes: the Velvet Finger and the Pisa/IIT SoftHand. The Velvet Finger is a smart gripper, equipped with conveyor belts on the surfaces of its phalanges. In this case, the decomposition of the solution space of the FGE was used to extract the necessary information for evaluating the manipulability capabilities of the prototype, showing the convenience of the actuation design with respect to other more conventional solutions. The Pisa/IIT SoftHand is a humanoid robotic hand in which the human inspired principle of the synergistic underactuation is implemented via the adaptive synergy mechanism. The construction of the cFGE for both the cases brings to find the conditions for which the two underactuation methods are equivalent in terms of controllable forces and displacements. The first part of the thesis is completed by the definition of the reduced form of the Fundamental Grasp Equation (rFGE), obtained substituting all the congruence equations into the others. As a consequence, the rFGE can be seen as the first order approximation of a suitable system of nonlinear equations, called the Equilibrium Manifold (EM) of the system. The EM formulation was exploited to approach the problem of regulating the grasp compliance in the non trivial case of a robotic hand equipped with variable stiffness actuators (VSA) and synergistic underactuation. In the second part of the thesis, the previous concepts are usedto study compliant humanoid robots in whole-body loco-manipulation tasks. The introduction of the quasi-static form of the congruence, the equilibrium and the constitutive equations of the system allows to define the Fundamental Loco-Manipulation Equation (FLME). After the canonical form of the Fundamental Loco-Manipulation Equation (cFLME) is found, some relevant information can be extracted as the subspace of the controllable contact forces and the controllable displacements of the center of mass of the robot. Relevant locomanipulation tasks are later defined in terms of (non-)nullity of the system variables. Moreover, the basis of the controllable contact forces is used to show that the contact force distribution problem can be formulated in convex fashion. Finally, a discussion of similarities and differences between grasping and loco-manipulation problems is performed, after which a unified formulation is given by the Fundamental Whole-Body Interaction Equations (FWE). The FWE shows that grasping and locomanipulation problems can share not just analysis methods, but also part of the analysis results, e.g. the symbolic expressions of the blocks composing the respective canonical forms of the Fundamental Equations, for equivalent actuation conditions

Localizzazione acustica in tempo reale per veicoli subacquei autonomi

Cenni di teoria dei raggi per propagazione acustica subacquea, algoritmi utilizzati per la localizzazione real time, simulazioni e risultati ottenut

Toward whole-body loco-manipulation: Experimental results on multi-contact interaction with the Walk-Man robot

In this paper a quasi-static framework for optimally controlling the contact force distribution is experimentally verified with the full-size compliant humanoid robot Walk-Man. The proposed approach is general enough to cope with multi-contact scenarios, i.e. robot-environment interactions occurring on feet and hands, up to the more general case of whote-body toco-manipulation, in which the robot is in contact with the environment also with the internal Iimbs, with a consequent loss of contact force controllability. Experimental tests were conducted with the Walk-Man robot (i) standing on Hat terrain, (ii) standing on uneven terrain and (Hi) interacting with the environment with both feet and a hand touching a vertical wall. Moreover, the in Huence of unmodeled weight on the robot, and the combination with a higher priority Cartesian tasks are shown. Results are presented also in the attached video

Quasi-Static Analysis of Synergistically Underactuated Robotic Hands in Grasping and Manipulation Tasks

As described in Chaps. 2–5, neuroscientific studies showed that the control of the human hand is mainly realized in a synergistic way. Recently, taking inspiration from this observation, with the aim of facing the complications consequent to the high number of degrees of freedom, similar approaches have been used for the control of robotic hands. As Chap. 12 describes SynGrasp, a useful technical tool for grasp analysis of synergy-inspired hands, in this chapter recently developed analysis tools for studying robotic hands equipped with soft synergy underactuation (see Chap. 8) are exhaustively described under a theoretical point of view. After a review of the quasi-static model of the system, the Fundamental Grasp Matrix (FGM) and its canonical form (cFGM) are presented, from which it is possible to extract relevant information as, for example, the subspaces of the controllable internal forces, of the controllable object displacements and the grasp compliance. The definitions of some relevant types of manipulation tasks (e.g. the pure squeeze, realized maintaining the object configuration fixed but changing contact forces, or the kinematic grasp displacements, in which the grasped object can be moved without modifying contact forces) are provided in terms of nullity or non-nullity of the variables describing the system. The feasibility of such predefined tasks can be verified thanks to a decomposition method, based on the search of the row reduced echelon form (RREF) of suitable portions of the solution space. Moreover, a geometric interpretation of the FGM and the possibility to extend the above mentioned methods to the study of robotic hands with different types of underactuation are discussed. Finally, numerical results are presented for a power grasp example, the analysis of which is initially performed for the case of fully-actuated hand, and later verifying, after the introduction of a synergistic underactuation, which capacities of the system are lost, and which other are still present

Sample-Based Motion Planning for Robot Manipulators with Closed Kinematic Chains

Random sampling-based methods for motion planning of constrained robot manipulators have been widely studied in recent years. The main problem to deal with is the lack of an explicit parametrization of the non linear submanifold in the Configuration Space (CS) imposed by the constraints in the system. Most of the proposed planning methods use projections to generate valid configurations of the system slowing the planning process. Recently, new robot mechanism includes compliance either in the structure or in the controllers. In this kind of robot most of the times the planned trajectories are not executed exactly due to uncertainties and interactions with the environment. Indeed, controller references are generated such that the constraint is violated to indirectly generate forces during interactions. With the purpose of avoiding projections, in this paper we take advantage of the compliance of systems to relax the geometric constraints imposed by closed kinematic chains. The relaxed constraint is then used in a state-of-the-art suboptimal random sampling based technique to generate paths for constrained robot manipulators. As a consequence of relaxation, arising contact forces acting on the constraint change from configuration to configuration during the planned path. Those forces can be regulated using a proper controller that takes advantage of the geometric decoupling of the subspaces describing constrained rigid-body motions of the mechanism and the controllable forces