Claudio Melchiorri

Modeling, Identification, and Control of Tendon-Based Actuation Systems

In this paper, we deal with several aspects related to the control of tendon-based actuation systems for robotic devices. In particular, the problems that are considered in this paper are related to the modeling, identification, and control of tendons sliding on curved pathways, subject to friction and viscoelastic effects. Tendons made in polymeric materials are considered, and therefore, hysteresis in the transmission system characteristic must be taken into account as an additional nonlinear effect because of the plasticity and creep phenomena typical of these materials. With the aim of reproducing these behaviors, a viscoelastic model is used to model the tendon compliance. Particular attention has been given to the friction effects arising from the interaction between the tendon pathway and the tendon itself. This phenomenon has been characterized by means of a LuGre-like dynamic friction model to consider the effects that cannot be reproduced by employing a static friction model. A specific setup able to measure the tendons tension in different points along its path has been designed in order to verify the tension distribution and identify the proper parameters. Finally, a simple control strategy for the compensation of these nonlinear effects and the control of the force that is applied by the tendon to the load is proposed and experimentally verified.

The SHERPA project: Smart collaboration between humans and ground-aerial robots for improving rescuing activities in alpine environments

The goal of the paper is to present the foreseen research activity of the European project “SHERPA” whose activities will start officially on February 1th 2013. The goal of SHERPA is to develop a mixed ground and aerial robotic platform to support search and rescue activities in a real-world hostile environment, like the alpine scenario that is specifically targeted in the project. Looking into the technological platform and the alpine rescuing scenario, we plan to address a number of research topics about cognition and control. What makes the project potentially very rich from a scientific viewpoint is the heterogeneity and the capabilities to be owned by the different actors of the SHERPA system: the human rescuer is the “busy genius”, working in team with the ground vehicle, as the “intelligent donkey”, and with the aerial platforms, i.e. the “trained wasps” and “patrolling hawks”. Indeed, the research activity focuses on how the “busy genius” and the “SHERPA animals” interact and collaborate with each other, with their own features and capabilities, toward the achievement of a common goal.

Experimental evaluation of postural synergies during reach to grasp with the UB hand IV

In this paper, the postural synergies configuration subspace given by the fundamental eigengrasps of the UB Hand IV (University of Bologna Hand, version IV) is derived through experiments. This study is based on the kinematic structure of the robotic hand and on the taxonomy of the grasps of common objects. Experimental results show that it is possible to obtain grasp synthesis for a large set of objects both in the case of precision or power grasps by using only a very limited set of dominant eigengrasps. The tasks here presented are planned with an initial hold of the hand followed by reach and grasp phases, that are unique for each object/grasp combination, during which the robotic hand posture evolves continuously within a subset of the hand configuration space given by the two predominant eigenpostures. The paper reports the method adopted to define from experiments the postural synergies for the UB Hand IV and the results of the grasp tasks performed adopting the defined synergies.

Innovative Technologies for the Next Generation of Robotic Hands

With the aim of reproducing the grasping and manipulation capabilities of humans, many robotic devices have been developed all over the world in more than 50 years of research, starting from very simple grippers, normally used in industrial activities, to very complex anthropomorphic robotic hands. Unfortunately, the reduced functionality and/or reliability of the devices developed so far prevent, together with the cost, their usability in unstructured environments, and in particular in human everyday activities. The adoption of design solutions inherited from conventional mechanics and the lack of purposely developed sensors and actuators are among the main causes of the partial fail in achieving the final goal of reproducing human manipulation capabilities. Our research activity aims at developing innovative solutions concerning the mechanical design, the sensory equipment and the actuation system for the implementation of anthropomorphic robotic hands with improved reliability, functionality and reduced complexity and cost, considering also aspects related to safety during human–robot interaction, paving the way toward the next generation of robotic hands.

Design of a Variable Stiffness Actuator Based on Flexures

Variable stiffness actuators can be used in order to achieve a suitable trade-off between performance and safety in robotic devices for physical human―robot interaction. With the aim of improving the compactness and the flexibility of existing mechanical solutions, a variable stiffness actuator based on the use of flexures is investigated. The proposed concept allows the implementation of a desired stiffness profile and range. In particular, this paper reports a procedure for the synthesis of a fully compliant mechanism used as a nonlinear transmission element, together with its experimental characterization. Finally, a preliminary prototype of the overall joint is depicted.

Planning and control during reach to grasp using the three predominant UB hand IV postural synergies

In this paper, a method to derive the three predominant synergies and their temporal weights for planning grasps of the UB Hand IV (University of Bologna Hand, version IV) is proposed. The method adopted to define the postural synergies from experiments is based on the kinematic structure of the robotic hand and on the taxonomy of the grasps of common objects. The control strategy, exploiting postural synergies, that drives the hand during reach to grasp is further described. During prehension the hand moves continuously in a configuration space of highly reduced dimensionality with respect to its degrees of freedom. The experiments confirm that the UB Hand IV works efficiently in a synergy based framework for grasp planning and prehension control. It is shown that the introduction of the third predominant synergy significantly improves the grasping synthesis and performance, especially for the adduction/abduction motion of the thumb.

TRIDENT: Recent Improvements about Autonomous Underwater Intervention Missions

Abstract The need for intervention in underwater environments is significantly increasing in the last years. Possible applications include maintenance intervention in permanent observatories and offshore scenarios, and search & recovery for collecting objects of interest for different application domains like biology, fishery, or marine rescue just to name a few. Nowadays, these kind of tasks are usually solved with “work class” ROVs (i.e. Remote Operated Vehicles) that are launched from support vessels, and remotely operated by expert pilots through an umbilical communications cable and complex control interfaces. These solutions present several drawbacks. Firstly, ROVs are normally large and heavy vehicles that need significant logistics for its transportation and handling. Secondly, the complex user interfaces and control methods require skilled pilots for their use. These two facts significantly increase the cost of the applications. Moreover, the need of an umbilical cable introduces additional problems of control, or range limitation. The fatigue and high stress that users of remotely operated systems normally suffer supposes another serious drawback. All the pointed questions justify the need of more autonomous, cheap and easyto-use solutions for underwater intervention missions, and this is the aim of the current FP7-TRIDENT project. So, in this paper an overview concerning the main research ongoing under this project will be presented and discussed.

Friction compensation and virtual force sensing for robotic hands

This paper presents the latest results in the development of the low-level controller of the robotic hand UBH-IV (University of Bologna Hand, version IV). In particular, the friction effects acting at joint level have been rendered by means of a LuGre-like model and a procedure for the identification of the friction model parameters is described. With the aim of providing an online estimation of the effects due to the interaction of the robotic hand with the environment, a controller able to evaluate the overall external torque acting on the finger joints and to discern between friction and torques generated by the external interaction force without using direct measures of the contact forces is proposed. The identification and control tests are carried over on an experimental setup composed by a single finger phalanx, manufactured with the same material and techniques of the hand itself.

A Graph–Based Collision–Free Distributed Formation Control Strategy

Abstract In this paper we describe a consensus based control strategy to obtain a formation of groups of mobile robots. Weighted graphs are used to obtain the desired formation–shape while avoiding collisions among the robots. Since mobile robots usually move in unknown and unstructured environments, we show how to extend our control strategy to make the robots avoid collision with obstacles as well. To validate our control strategy, we provide both analytical proofs and simulative and experimental results.

A Performance and Stability Analysis for Cooperative Teleoperation Systems

Abstract In this paper the performance, in terms of transparency and stability, of two control architectures for cooperative teleoperation systems are presented and discussed. The cooperative control schemes consider two pairs of teleoperation systems collaborating to carry out operations in a shared remote environment. The information exchange occurs only between the corresponding pairs, and the slave robots may physically interact among themselves either through a common tool or the manipulated object.