On a Directed Tree Problem Motivated by a Newly Introduced Graph Product

In this paper we introduce and study a directed tree problem motivated by a new graph product that we have recently introduced and analysed in two conference contributions in the context of periodic real-time processes. While the two conference papers were focussing more on the applications, here we mainly deal with the graph theoretical and computational complexity issues. We show that the directed tree problem is NP-complete and present and compare several heuristics for this problem

Communicating Process Architectures

Abstract. Most motion control systems for mechatronic systems are implemented on digital computers. In this paper we present an FPGA based solution implemented on a low cost Xilinx Spartan III FPGA. A Production Cell setup with multiple parallel operating units is chosen as a test case. The embedded control software for this system is designed in gCSP using a reusable layered CSP based software structure. gCSP is extended with automatic Handel-C code generation for configuring the FPGA. Many motion control systems use floating point calculations for the loop controllers. Low cost general purpose FPGAs do not implement hardware-based floating point units. The loop controllers for this system are converted from floating point to integer based calculations using a stepwise refinement approach. The result is a complete FPGA based motion control system with better performance figures than previous CPU based implementations

Modeling Mechatronic Systems Using The Sidops+ Language

Automated modeling is a field of research that is subject to considerable evolution. Both the increase in available computer power and better insight in the modeling and design process lead to a stream of new opportunities for automated modeling support. To make this support possible, a language is needed that forms the medium for the exchange of information between the computer and the user. In this paper, we propose the SIDOPS+ model description language that not only covers state of the art automated modeling techniques, but that also provides openness towards future developments. Keywords: model description languages, model reusability, bond graphs, mechatronics 1 INTRODUCTION Modeling and simulation are frequently used in the design and analysis of engineering systems. The computer plays an important role in these activities, since it can provide the numerical results for a given simulation model, and because it can assist the engineer in composing models out of existing model f..

Constitutive Hybrid Processes: a Process-Algebraic Semantics for Hybrid Bond Graphs

Models of physical systems have to be based on physical principles such as conservation of energy and continuity of power. These principles are inherently enforced by the bond graph modeling formalism. Often, however, physical components may be best modeled as piecewise continuous with discrete mode changes, which leads to a violation of continuity principles. To support such hybrid models, bond graphs can be extended by facilitating a dynamic model structure, resulting in hybrid bond graphs. Behavior generation then requires computing continuous-time evolution, detecting the occurrence of events, executing the discrete state changes and re-initializing the continuous-time state. This paper presents a comprehensive representation of these different aspects of behavior using hybrid process algebra. The behavior of a hybrid bond graph can then be studied using a uniform representation while a direct correspondence with the elements of the bond graph is maintained. Additionally, non-determinism can be included in hybrid bond graph semantics which may alleviate the modeling task without being detrimental to the required analyses. \ud \u

Model-Driven Robot-Software Design using integrated Models and Co-Simulation

The work presented here is on a methodology for design of hard real-time embedded control software for robots, i.e. mechatronic products. The behavior of the total robot system (machine, control, software and I/O) is relevant, because the dynamics of the machine influences the robot software. Therefore, we use two appropriate Models of Computation, which represent continuous-time equations for the machine / robot part, and discrete event / discrete time equations for the control software part. To compute (simulate) such combined models, co-simulation of these models is used. The design work can be done as a stepwise refinement process, whereby each step is verified via co-simulation. This in general yields a shorter design time, and a better quality product. The tools pass model-specific information between each other via parametrized tokens in the generated, high-level code to get a better separation of design steps. This allows for better quality of the models and more reuse, thus enhancing the efficiency of model-driven design for the (industrial) end user. The method is illustrated with a case study using the tools, some of which are at the prototype level. Especially the structuring of the models and regularly doing simulations (of which some can be ’repeated’ as real experiments), is beneficial, shortening the development time and producing better models. Future work is to test the method on more complex cases, and to extend the method by detailing out the electronics and mechanics sub design flows

Model semantics and simulation of time scale abstractions in collision models

E ective design of models requires simpli cation of di erent components of the system. For example, interactions of the system under scrutiny with its environment are modeled as idealized sources and sinks, and system behavior is derived from idealized interactions among constituent components. Some of the more detailed behavior is governed by small parameters, that produce continuous but complex nonlinear behaviors. These nonlinear continuous behaviors are often simpli ed to piecewise continuous forms, which then results in discontinuities at the temporal or spatial scale of interest. The resulting models are of a mixed continuous/discrete, or hybrid, nature. Physical systems theory based on continuity of power and conservation of energy is well understood. However, once discontinuous e ects are included, these laws may be violated at the macroscopic level. The challenge is to endow hybrid models with semantics that do not violate the underlying physical nature of the system. This paper studies the e ects and semantics of time scale abstraction, suchasembodied by Newton's collision rule. The results show that hybrid modeling of physical systems can be systematic without the need for ad hoc hysteresis e ects. Keywords|hybrid systems, bond graphs, modeling, simulation Pieter J. Mosterman is supported by a grant from the DFG Schwerpunktprogramm KONDISK.