Francisco Blanes

Agent-based distributed architecture for mobile robot control

Mobile robots are physical agents that move and interact continuously while embedded in a dynamic environment. Communications can be one of the most difficult parts of building robot architecture because of the increasing complexity of sensor and actuator hardware, and the interaction between intelligent features and real-time constraints. Currently, hybrid architectures offer the most widespread solutions for controlling intelligent mobile robots. This paper deals with the communications framework necessary to design and implement these architectures. The main goal of this work is to design a modular and portable architecture that allows the development of robot control systems. A multi-level and distributed architecture based on the reactive/deliberative paradigm is presented. Its main components are mobile software agents that interact through a distributed blackboard communications framework. These agents can be run on onboard processors, as well as on fixed workstations depending on their real-time restrictions. The presented control architecture has been tested in a real mobile robot and results demonstrate the effectiveness of distributing software agents to guarantee hard real-time execution.

A CAN Architecture for an Intelligent Mobile Robot

Abstract Yet Another Intelligent Robot (YAIR) is a multisensor prototype of autonomous robot that is currently being developed. The main purpose of this experimental robot is to provide a general platform to research about different real time issues such as distributed sensor systems, data fusion algorithms, operating systems and field buses. This paper describes the robot architecture developed around the CAN (Controller Area Network) bus standard. The paper also analyzes the operational modes that can be found in the robot. Seven basic modes have been defined. Each mode is related with its different movement types and the specific tasks than can be programmed. A preliminar study of the real time characteristics for the different message sets used in each operational mode is also presented.

Differentiating walls from corners using the amplitude of ultrasonic echoes

Abstract This paper analyzes the use of ultrasonic echo amplitudes to evaluate the characteristics of the detected surfaces (such as distinguishing between walls and corners). The shape and surface characteristics of the environment, such as roughness or absorption coefficient, as well as the distance and the angle of incidence, have high influence on the amplitude of the echoes. As a consequence, the amplitude of the received echoes has received little attention from robotic researchers. Instead, time-of-flight (ToF) has been used as the main source of information of the environment. It is also well known that the shape of the echoes of a corner is the same as that of a wall [IEEE Trans. Pattern Anal. Mach. Intell. (PAMI), 12 (1990) 560]. Several authors have proposed special multi-transducer configurations to avoid this problem. This paper studies the amplitude of received echoes and presents a simple model to predict the shape and amplitude of echoes received from different materials in environments composed of walls and corners. Using this model, and analysing the amplitude of the echoes it is possible to distinguish between walls and corners in a single scan of a single ultrasonic transducer pair. The parameters of the model were obtained from tests performed on different materials and surfaces. The last section of the paper shows the experimental results of the wall–corner classifications obtained in real tests during the walk of a mobile robot. The results suggest that the method proposed can be of great interest for map building in robotics.

Communications structure for sensory data in mobile robots

Abstract Mobile robotics development provides an excellent opportunity to experiment with various architectural solutions for distributed real-time systems. This is because of the increasing complexity of sensor and actuator hardware, and the interaction between intelligent features and real-time constraints. Currently, hybrid control structures seem to be the most widespread method of control. This paper describes a communications scenario resulting from hybrid structures. The YAIR robot and its communication infrastructure is described by addressing the control problems found and the solutions adopted. This paper presents a case study of implementing a hybrid communications system using the CAN bus. The worst-case message delay analysis for this bus is also presented, as well as the structure of identifiers defining its semantic possibilities. The deliberative part of the communication system is a developed object bus on TCP/IP protocol networks. The programming interface at this level takes the form of a distributed blackboard with extended properties such as a bind-notification mechanism and a temporal register recording the temporal firewall of information supplied. The overlap between both communication systems is a gateway service performing bi-directional mirroring over a set of CAN identifiers. Finally, a system test is presented. The test emphasises the intra-level gateway for validating performance and time expressiveness.

Behaviour Selection in the YAIR Architecture

Abstract In this paper, a new architecture for vehicle guidance based on behavioural composition is proposed. The behaviour selection is distributed and based on the concept of motivation. The operation under real time constraints is obtained avoiding the deliberative cycle sense-plan-act and taking into account a behavioural description of basic tasks. The system is based on a blackboard architecture where objects and processes are located. The motivation processes allow us to modify the expected behavior of the system changing the action priorities. The described architecture is part of the YAIR project developed in the department. the project is focused on developing an embedded hardware and software architecture far autonomous robots.

Formal Specification and Design Techniques for Wireless Sensor and Actuator Networks

A current trend in the development and implementation of industrial applications is to use wireless networks to communicate the system nodes, mainly to increase application flexibility, reliability and portability, as well as to reduce the implementation cost. However, the nondeterministic and concurrent behavior of distributed systems makes their analysis and design complex, often resulting in less than satisfactory performance in simulation and test bed scenarios, which is caused by using imprecise models to analyze, validate and design these systems. Moreover, there are some simulation platforms that do not support these models. This paper presents a design and validation method for Wireless Sensor and Actuator Networks (WSAN) which is supported on a minimal set of wireless components represented in Colored Petri Nets (CPN). In summary, the model presented allows users to verify the design properties and structural behavior of the system.

Communication jitter influence on control loops using protocols for distributedreal-time systems on can bus

Abstract The paper focuses on the behaviour of distributed control loops affected by the jitter derived from the communication latencies of CAN. The work uses a hybrid communication protocol between a pure TTP (Time Triggered Protocol) and ETP (Event Triggered Protocol), a reasonable choice for distributed real-time systems, as a reactive mobile robot. This hybrid protocol shares the time-slots to reduce the jitter effects. This guarantees fixed transmissions latencies for periodic messages, allowing also sporadic messages transmission, as is the case of alarms, or in long data blocks, by means of using shared TTP slots. The protocol assigns private time slots for realtime messages, and shared time slots for non real-time messages. Also, the protocol uses only a simple and static table. The implementation is validated by means of a quantitative comparison, using the data obtained from a simulation of a typical distributed control system consisting of an industrial process and a remote controller forming a closed control loop that uses CAN as its communication channel. In the simulation, the effect of the jitter introduced into the control loop is measured for the above mentioned communication protocols, and the obtained results from this simulation are also discussed.

Wireless Sensor and Actuator Networks: Charecterization and case study for confined spaces healthcare applications

Nowadays developments in wireless sensor and actuators networks (WSAN) applications are determined by the fulfillment of constraints imposed by the application. For this reason, in this work a characterization of WSAN applications in health, environmental, agricultural and industrial sectors are presented. A case study for detecting heart arrhythmias in non-critical patients during rehabilitation sessions in confined spaces is presented, and finally an architecture for the network and nodes in these applications is proposed.

Line-based incremental map building using infrared sensor ring

Geometric representation of the environment, known as mapping, plays an important role in mobile robotics as it support various tasks such as localization, path planning and motion control. Line models represent a popular approach to represent the geometric features of the environment. The mapping problem gives rise to a variety of solutions for using different exteroceptive sensors (sonar, infrared, laser, vision, etc.). One of the possible choices is to use an infrared sensor (IR sensor). These devices are inexpensive, practical and widely available. Infrared sensors are largely used in obstacle avoiding processes because they are fast and cheap, and require only simple signal processing. Although the collision avoidance routine has received good attention for many years, the infrared feature mapping has been neglected. A problem with this kind of sensor is its short range (about one meter). This problem forces to an incremental mapping approach, so the robot has to move and concurrently model the environment. In this paper we present an IR sensor able to measure distances based on the light that is back-scattered from objects. This IR sensor is used for line-based map building purposes, so we also present a methodology for line extraction, range data clustering and line segmentation. The experimental test has been carried out in a long corridor, and results show the usefulness of the IR sensor and the methodology we propose for feature extraction and line-based mapping processes.

Distributed real time architecture for small biped robot YABIRO

In this paper, we present a real time architecture for embedded control systems to be used in a mobile biped robot called YABIRO. The robot has a total of 14 degrees of freedom (DOF). This number of joints enables YABIRO to produce many different gait configurations, and is also suitable to test and validate the proposed real time control architecture. A new embedded intelligent motor controller (IMCD) has been also designed and implemented in each joint node of the distributed architecture, to work inside the real time network.