José E. Simó

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.

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.

Video Sensor Architecture for Surveillance Applications

This paper introduces a flexible hardware and software architecture for a smart video sensor. This sensor has been applied in a video surveillance application where some of these video sensors are deployed, constituting the sensory nodes of a distributed surveillance system. In this system, a video sensor node processes images locally in order to extract objects of interest, and classify them. The sensor node reports the processing results to other nodes in the cloud (a user or higher level software) in the form of an XML description. The hardware architecture of each sensor node has been developed using two DSP processors and an FPGA that controls, in a flexible way, the interconnection among processors and the image data flow. The developed node software is based on pluggable components and runs on a provided execution run-time. Some basic and application-specific software components have been developed, in particular: acquisition, segmentation, labeling, tracking, classification and feature extraction. Preliminary results demonstrate that the system can achieve up to 7.5 frames per second in the worst case, and the true positive rates in the classification of objects are better than 80%.

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.

Control kernel: A key concept in embedded control systems

Abstract Embedded control systems are becoming ubiquitous in control applications. They combine the properties of computer embedded system with newly designed complex controllers where flexible, safe and reconfigurable operations are required. Some common and general features are always required in any control system, independently of the hardware implementing platform. The new concept of the control kernel of an application is introduced, making easier the design of general purpose applications.

Flexible real-time mobile robotic architecture based on behavioural models

Abstract Behaviour-based models have been widely used to represent mobile robotic systems, which operate in uncertain dynamic environments and combine information from several sensory sources. The specification of complex mobile robotic applications is performed in such models by combining deliberative goal-oriented planning with reactive sensor driven operations. Consequently, the design of mobile robotic architectures requires the combination of time-constrained activities with deliberate time-consuming components. Furthermore, the temporal requirements of the reactive activities are variable and dependent on the environment (i.e. recognition processes) and/or on application parameters (i.e. process frequencies depend on robot speed). In this paper, a real-time mobile robotic architecture to cope with the functional and variable temporal characteristics of behaviour-based mobile robotic applications is proposed. Run-time flexibility is a main feature of the architecture that supports the variability of the temporal characteristics of the workload. The system has to be adapted to the environmental conditions, by adjusting robot control parameters (i.e. speed) or the system load (i.e. computational time), and take actions depending on it. This influence is focused on the ability of the system to select the appropriate activity to be executed depending on the available time, and, to change its behaviour depending on the environmental information. The flexibility of the system is allowed thanks to the definition of a real-time task model and the design of adaptation mechanisms for the regulation of the reactive load. The improvement of the robot quality of service (QoS) is another important aspect discussed in the paper. The architecture incorporates a quality of service manager (QoSM) that allows dynamically monitor analyse and improve the robot performances. Depending on the internal state, on the environment and on the objectives, the robot performance requirements vary (i.e. when the environment is overloaded, global map processes generating high-quality maps are required). The QoSM receives the performance requirements of the robot, and by adjusting the reactive load, the system enables the necessary slack time to schedule the more suitable deliberative processes and hence fulfilling the robot QoS. Moreover, the deliberative load can be scheduled by different heuristic strategies that provide answers of varying quality.

A Multisensor Robot Distributed Architecture

Abstract In this work the distributed sensory system and the architecture intended for data fusion, planning and supervision of an experimental, multi-sensor prototype of autonomous robot is described. The robot is currently being developed to serve as a platform to experiment with different real time issues, as distributed sensor systems, data fusion algorithms, operating systems, and field buses. The robot has a distributed architecture composed by several intelligent actuator and sensory modules that are interconnected by a CAN bus, a standard bus that has been elected by its real-time features. Also, a reactive robotic control system architecture is proposed for the robot. The architecture for distributed behaviour selection is based on the concept of “motivation”. The distributed selection is performed by a set of objects whose access is controlled by an uniform protocol that allows the selection of sets of behaviours in a opportunistic game level of motivation processes.

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.