Monica Reggiani

Leveraging on a virtual environment for robot programming by demonstration

Abstract The Programming by Demonstration paradigm promises to reduce the complexity of robot programming. Its aim is to let robot systems learn new behaviors from a human operator demonstration. In this paper, we argue that while providing demonstrations in the real environment enables teaching of general tasks, for tasks whose essential features are known a priori demonstrating in a virtual environment may improve efficiency and reduce trainer’s fatigue. We next describe a prototype system supporting Programming by Demonstration in a virtual environment and we report results obtained exploiting simple virtual tactile fixtures in pick-and-place tasks.

Rate modulation of soft real-time tasks in autonomous robot control systems

Due to the high number of sensors managed and need to perform complex reasoning activities, real-time control systems of autonomous robots exhibit a high potential for overload, i.e., real-time tasks missing their deadlines. In these systems overload should be regarded as a likely occurrence and hence managed accordingly. In this paper we illustrate a novel scheduling technique for adaptation of soft real-time load to available computational capacity in the context of autonomous robot control architectures. The technique is based on rate modulation of a set of periodic tasks in a range of admissible rates. The technique is shown to be easily computable and several variations in implementation are reviewed within the paper.

A software framework based on real-time CORBA for telerobotic systems

The technological developments in distributed systems have led to new telerobotic applications, such as virtual laboratories and remote maintenance of complex equipment. These applications must satisfy both the general requirements of distributed computing, e.g. location transparency and interoperability, and the domain-specific requirements of reconfigurability, guaranteed performance, real-time operation, and cooperation among robots and sensory systems. In this paper, we describe a software framework for distributed telerobotic systems exploiting advanced CORBA features, including Asynchronous Method Invocation and real-time priorities. The framework allows development of portable multithreaded client-server applications supporting concurrent and preemptable actions in the target robot system, and has been evaluated in a laboratory setup including a robot manipulator and two cameras accessible by multiple clients.

An experimental evaluation of collision detection packages for robot motion planning

Randomized motion planners are greatly affected by the efficiency and robustness of algorithms for collision checking of robot configurations. A number of powerful collision detection algorithms are currently available to the research community although their relative capabilities and performance cannot be easily compared due to the many factors involved. We have experimentally evaluated collision detection packages within the context of motion planning for rigid and articulated robots in 3D workspaces. Artificial and realistic problems have been chosen as benchmarks to assess package behavior with different object models. Reported experimental results should help the user in choosing the appropriate collision detection package. In this paper we also present the framework we exploited in our planner to allow pluggable distance computation functions and keep the code simple and easy to maintain.

ERPP: An experience-based randomized path planner

This paper presents a motion planning algorithm capable of exploiting the experience gained in previous path computations in the same static workspace. The algorithm takes advantage of a parallel approach to speed up computation and compile a graph retaining useful knowledge about the environment. Experimental results assess the performance improvement of the experience-based planner over the parallel implementation of a well-known probabilistic motion planning algorithm.

Toward programming of assembly tasks by demonstration in virtual environments

Service robots require simple programming techniques allowing users with little or no technical expertise to integrate new tasks in a robotic platform. A promising solution for automatic acquisition of robot behaviours is the programming by demonstration (PbD) paradigm. Its aim is to let robot systems learn new behaviours from a human operator demonstration. This paper describes a PbD system able to deal with assembly operation in a 3D block world. The main objective of the research is to investigate the benefits of a virtual demonstration environment. Overcoming some difficulties of real world demonstrations, a virtual environment can improve the effectiveness of the instruction phase. Moreover, the user can also supervise and validate the learned task by means of a simulation module, thereby reducing errors in the generation process. Some experiments involving the whole set of system components demonstrate the viability and effectiveness of the approach.

Architectural paradigms for robotics applications

In recent years, several technical architectural paradigms have been proposed to support the development of distributed and concurrent systems. Object-oriented, component-based, service-oriented approaches are among the most recent paradigms for the implementation of heterogeneous software products that require complex interprocess communications and event synchronization. Despite the sharing of common objectives with distributed systems research, the robotics community is still late in applying these research results in the development of its architectures, often relying only on the most basic concepts. In this paper, we shortly illustrate these paradigms, their characteristics, and the successful stories about their application within the robotic domain. We discuss benefits and tradeoffs of the different solutions with the goal of deriving some practical principles and strategies to be exploited in robotics practice. Understanding the characteristics, features, advantages, and drawbacks of the different paradigms is, indeed, crucial for the successful design, implementation, and use of robotic architectures.

Heuristic methods for randomized path planning in potential fields

Randomized path planning driven by a potential field is a well established technique for solving complex, many degrees of freedom motion planning problems. In this technique a suitable potential field shapes the search of the path toward the goal. However, randomized path planning can become relatively inefficient when deep local minima are present in the potential field. Indeed, the algorithm usually spends most its running time trying to escape from local minima by means of uninformed random motions. In this paper we present simple yet effective heuristics for escaping local minima, with the goal of improving overall planning performance. We integrate these heuristics into a path planner without sacrificing the overall probabilistic completeness of the algorithm. Experimental results on several test cases show a remarkable performance improvement, up to a factor of 4 for complex problem instances.

Evaluation of virtual fixtures for a robot programming by demonstration interface

We investigate the effectiveness of several types of virtual fixtures in a robot programming by demonstration interface. We show that while all types of virtual fixtures examined yield a significant reduction in the number of errors in tight tolerance peg-in-hole tasks, color and sound fixtures generally outperform a tactile fixture in terms of both execution time of successful trials and error rate. We have found also that when users perceive that the task is very difficult but the system is providing some help by means of a virtual fixture, they tend to spend more time trying to achieve a successful task execution. Thus, for difficult tasks the benefits of virtual fixturing are better reflected in a reduction of the error rate than in a decreased execution time. We conjecture that these trends are related to the limitations of currently available interfaces for human-robot interaction through virtual environments and to the different strategies adopted by the users to cope with such limitations in high-accuracy tasks.

Design of a VIA based communication protocol for LAM/MPI suite

The increasing use of System Area Network (SAN) demands efficient communication to benefit SAN features through a direct access to network resources and avoiding kernel intervention in communication path. Recently, a consortium composed by Microsoft, Compaq and Intel authored a new standard, the Virtual Interface Architecture (VIA), designed to reduce software overhead in data transfers. This paper describes the communication protocol proposed in order to allow a complete implementation of MPI based on VIA. This protocol is needed because the plain use of the two VIA data transfer models does not allow the implementation of MPI based on VIA, due to the large number of MPI communication flavors. To validate the goodness of the proposed protocol, a new communication layer based on VIA has been introduced in the LAM/MPI suite. The reported results, referring to a software VIA implementation for fast Ethernet networks, exhibits a significant reduction in latency time of LAM/MPI based on VIA with respect to the same library based on the TCP/IP protocol.