The increasing complexity of real time software has led to a recent trend in the use of high level modeling languages for development of real time software. One representative example is the modeling language ROOM (real time object oriented modeling), which provides features such as object orientation, state machine description of behaviors, formal semantics for executability of models, and possibility of automated code generation. However these modeling languages largely ignore the timeliness aspect of real time systems, and fail to provide any guidance for a designer to a priori predict and analyze temporal behavior. We consider schedulability analysis for automated implementations of ROOM models, based on the ObjecTime toolset. This work builds on results presented by M. Saksena (1997), where we developed some guidelines for the design and implementation of real time object oriented models. Using the guidelines, we have modified the run time system library provided by the ObjecTime toolset to make it amenable to schedulability analysis. Based on the modified toolset, we show how a ROOM model can be analyzed for schedulability, taking into account the implementation overheads and structure. The analysis is validated experimentally, first using simple periodic models, and then using a large case study of a train tilting system.

Forestry machines are essentially four degree of freedom electrohydraulic telemanipulators equipped with specialised end-effectors for harvesting trees. In this paper, we describe forestry telemanipulation and then review the development of a computer-based training aid based on graphical simulation. To the best of our knowledge, our work here represents the first concentrated attempt at developing a system intended to become an integral part of forestry machine operator training.

We present our experiences in applying real time scheduling theory to embedded control systems designed using ROOM (Real time Object Oriented Modeling) methodology. ROOM has originated from the telecommunications community and has been successfully applied to many commercial systems through the supporting case tool ObjecTime. It is particularly suitable for modeling reactive real time behavior. Furthermore, it provides many other advantages through the use of object orientation, and the use of executable models from which code may be generated quickly and efficiently. Since many real time embedded control systems have significant reactive, event driven behavior, it is attractive to use ROOM methodology to develop such systems. However, the ROOM methodology does not provide tools to specify and analyze the temporal behavior as is required for the hard real time components of embedded systems, and for which the real time scheduling theory provides an analytical basis. We show how real time scheduling theory may be applied to ROOM models using a cruise control example to illustrate. The biggest challenge comes from minimizing the adverse effects of priority inversions. Our results are very encouraging, and we show that not only is it possible to apply real time scheduling theory, but that it can be done very efficiently provided certain guidelines are followed in the design and implementation of the ROOM model.

While the two solitudes of our title, computerized control and telecommunications, are both concerned with computerized solutions to real world problems, we suggest that they are really addressing different needs and are therefore naturally preoccupied by slightly different concerns. We present a taxonomy of key elements intended to make such differences explicit in order to promote more mutual understanding and more collaborative work where concerns are shared. In particular, we suggest that one key difference lies in the nature of the timing requirements associated with reactivity, and whether they are considered as extensions to logical correctness or performance.

This paper describes an approach to combining range data from both a set of sonar sensors as well as from a directional laser range finder to efficiently take advantage of the characteristics of both types of devices when exploring and mapping unknown worlds. The authors call their approach "just in time sensing" because it uses the more accurate but constrained laser range sensor only as needed, based upon a preliminary interpretation of sonar data. In this respect, it resembles "just in time" inventory control which attempts to judiciously obtain materials for industrial manufacturing only when and as needed. Experiments with a mobile robot equipped with sonar and a laser rangefinder demonstrate that by judiciously using the more accurate but more complex laser rangefinder to deal with the well-known ambiguity which arises in sonar data, the authors are able to obtain a much better map of an interior space at little additional cost (in terms of time and computational expense).

Mobile robot navigation and localization is frequently aided by, or even dependent upon, a good estimate of the rate of dead-reckoning error accumulation. Sensor data can be used for position estimation, but this often involves overheads in acquiring and processing the data. By sensing and then classifying the surface type, an estimate of the rate of error accumulation for dead-reckoning allows one to estimate accurately how often localization, including sensor data acquisition, must be performed. The authors describe experiments in which a boom-mounted microphone is tapped on different floor materials, much as a blind man might tap his cane. The acoustic signature arising from the contact is then used to classify the floor type by comparing a windowed power spectrum of the acoustic signature with one of a family of prototypical signatures generated statistically from the same material. The technique is low-cost, involves limited computational expense, and performs very well.

ORCCAD (Open Robot Controller Computer Aided Design), is a development environment for robotic controllers which provides verification and simulation tools along with a graphical human-machine interface, in order to bridge the gap between control laws as understood by the control systems community, and real-time computing as understood by the computer science community. In this paper, we introduce some recent extensions to ORCCAD which make it possible to perform certain kinds of temporal verification of real-time closed loop robotic tasks.>

Reviews the inadequacies of models of robot actions, proposed in the literature for intervention tasks. The STRIPS-inspired model of robot actions defined in terms of pre-conditions and post-conditions is extended by defining conditions which qualify the execution contexts of the actions. It is demonstrated that when all of the conditions are defined in terms of state variables and their possible values it becomes possible to study the soundness of the specifications of the possible actions to be performed, and the soundness of the interrelationships between these specifications. To this end, a particular kind of Petri net is proposed. An example of a mobile robot is also presented.>

Based on the Petri net (PN) theory a particular class of condition/event nets called Omega , suitable for modeling repetitive workcell tasks, is defined. Nets in Omega are either deterministic or exhibit a restricted kind of conflict called choice among alternatives. It is shown how the repetitive behavior of such a net may be studied by decomposing this conflict into deterministic components associated with mutually exclusive alternatives. A unified description of the important temporal extensions of PN theory is presented, with emphasis on formal analysis. The PN notion of coverability is extended in the temporal sense and it is demonstrated that, for nets in Omega , the period of repetition (cycle time) can be directly computed from the durations associated with the individual operations, once the decomposition into components is performed. When the durations are specified in the form of minimum and maximum values, this period of repetition may be described by optimistic and pessimistic bounds. A typical assembly example adapted from work with a multirobot workcell testbed is also presented to illustrate two forms of temporal analysis.>

Given a workcell program defined as a set of repetitive tasks to be concurrently performed, one can associate with each workcell element (robots, vision systems, etc.) a repetitive partial order of operations; together, they define a workcell cycle. An evaluation of such cycles in terms of cycle time, task throughput, and machine utilization is proposed. To automate the sequencing analysis, a Prolog-based decision-support system, SAGE (sequence analysis by generalized enumeration), is presented. Given the specification of the work-cell program in terms of the operations to be performed by each workcell element, SAGE constructs all feasible cycles for exploring the space for all possible time evolutions of workcell behavior. Three variations on the same multirobot assembly example are used to illustrate the approach.>

The authors introduce a classification of sequencing problems according to the presence of nondeterminism, whether due to the structure of the problem itself (internal) or to online events (external). They develop a theory, in the context of timed Petri nets, of how repetition can be described and predicted. They conclude with a description of a PROLOG-based decision-support system which manages this nondeterminism by exploring the consequences of alternate orderings of workcell operations, and ultimately constructs the time-optimal sequence. The analysis and optimization are illustrated with an example.>

Robot tasks have come to demand flexible sensory-based "intelligent" behavior. The single robot has given way to multiple robots cooperating in three-dimensional dynamic environments which allow them to accomplish complex and intricate tasks. Because of the complex nature of the tasks performed, centralized control is no longer practical; workcells have become centers of distributed computing. This motivates the need for an interprocess communication (IPC) facility which would integrate the individual elements both within and between workcells. A survey of IPC is presented in the context of distributed robotics. To make the survey more meaningful, it is introduced by some remarks about general approaches to communication within a distributed computing environment. A discussion of the main IPC design issues for distributed robotics is included.