Gianni Borghesan

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.

Bridging the gap between discrete symbolic planning and optimization-based robot control

Symbolic reasoners generate plans which are often not exploiting the robot capabilities and are sensitive to runtime disturbances. This work proposes a scheduler as an interface between a discrete, symbolic plan and a motion control based on constraint optimization. Acting as a local reasoner, the scheduler valuates a set of predicates to decide when an action will be executed. Given a task specification which describes how the action should be realized, the scheduler configures the controller at runtime. A demonstration will be provided considering an “open drawer” scenario.

A constraint-based programming approach to physical human-robot interaction

This work aims to extend the constraint-based formalism iTaSC for scenarios where physical human-robot interaction plays a central role, which is the case for e.g. surgical robotics, rehabilitation robotics and household robotics. To really exploit the potential of robots in these scenarios, it should be possible to enforce force and geometrical constraints in an easy and flexible way. iTaSC allows to express such constraints in different frames expressed in arbitrary spaces and to obtain control setpoints in a systematic way. In previous implementations of iTaSC, industrial velocity-controlled robots were considered. This work presents an extension of the iTaSC-framework that allows to take advantage of the back-drivability of a robot thus avoiding the use of force sensors. Then, as a casestudy, the iTaSC-framework is used to formulate a (positionposition) teleoperation scheme. The theoretical findings are experimentally validated using a PR2 robot.

Constraint-based specification of hybrid position-impedance-force tasks.

This work aims to extend the application field of the constraint-based control framework called iTaSC (instantaneous task specification using constraints) toward tasks where physical interaction between the robot and the environment, or a human, is contemplated. iTaSC, in its original formulation, allows for a systematic derivation of control schemes from task descriptions; tasks are defined as constraints enforced on outputs (e.g. distances, angles), and the iTaSC control takes care to fulfil such constraints by computing desired velocities to be commanded to the robot(s) joints. This approach, being based on a velocity resolution scheme, principally addresses tasks where positioning is the main issue. However, tasks that involve contacts with the environment or with the user, either desired or accidental, can be considered as well, taking advantage of impedance control, when position is controlled, or with force control. This paper describes the implementation of force tasks, and, by the combination of conflicting force and position tasks, impedance control, within the iTaSC formalism. This result is achieved by taking advantage of an approximate physical modelling of the robotic system and the environment. The proposed control scheme is tested by means of experiments where constraints on forces and/or positions described in cylindrical coordinates are imposed on a Kuka LWR arm.

Constraint-Based Interaction Control of Robots Featuring Large Compliance and Deformation

This paper introduces a framework for constraint-based force/position control of robots that exhibit large nonlinear structural compliance and that undergo large deformations. Controller synthesis follows hereto the principles of the Task Frame and instantaneous Task Specification using Constraints (iTaSC) formalisms. iTaSC is found particularly suitable due to its ability to express and combine control tasks in a natural way. Control tasks can be formulated as combinations of target positions, velocities, or forces expressed in an arbitrary number and type of coordinate frames. The proposed framework is applied to a mixed mechatronic system composed of a traditional rigid-link robot whose end-effector is a continuum (flexible) link. A selection of different position/force control tasks is prepared to demonstrate the validity and general nature of the proposed framework.

Control of a hybrid robotic system for computer-assisted interventions in dynamic environments.

PurposeMinimally invasive surgery is becoming the standard treatment of care for a variety of procedures. Surgeons need to display a high level of proficiency to overcome the challenges imposed by the minimal access. Especially when operating on a dynamic organ, it becomes very difficult to align instruments reliably and precisely. In this paper, a hybrid rigid/continuum robotic system and a dedicated robotic control approach are proposed to assist the surgeon performing complex surgical gestures in a dynamic environment.MethodsThe proposed robotic system consists of a rigid robot arm on top of which a continuum robot is mounted in series. The continuum robot is locally actuated with McKibben muscles. A control scheme based on quadratic programming framework is adopted. It is shown that the framework allows enforcing a set of constraints on the pose of the tip, as well as of the instrument shaft, which is commanded to slide in and out through the entry point.ResultsThrough simulation and experiments, it is shown how the robot tool tip is able to follow sinusoidal trajectories of 0.37 and 2xa0Hz, while maintaining the instrument shaft pivoting along the entry point. The positioning and tracking accuracy of such system are shown to lie below 4.7xa0mm in position and

A framework for formal specification of robotic constraint-based tasks and their concurrent execution with online qos monitoring

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Introducing Geometric Constraint Expressions Into Robot Constrained Motion Specification and Control

5.4∘ in angle.ConclusionThe results suggest a good potential for applying the proposed technology to assist the surgeon during complex robot-assisted interventions. It is also illustrated that even when using flexible hence relatively safe end-effectors, it is possible to reach acceptable tracking behaviour at relatively high frequencies.