Enric X. Martín

One-step finite horizon boundary with varying control gain for event-driven Networked Control Systems

Recent research has shown that event-driven control requires less samples than time-driven (periodic) control. Consequently, event-driven control applied to Networked Control Systems (NCS) is a good approach for alleviating controllers bandwidth demands and reducing overall network traffic. Following this trend, this paper presents an execution rule for event-driven networked controllers that at each job execution aims at postponing the next job execution while applying an appropriated controller gain considering each varying sampling interval that applies at run time. This method permits to dynamically lower the generated traffic for each networked control loop while ensuring the same or better control performance than the achieved by the periodic case. In addition, an implementation strategy capable of dealing with network induced time delays is also presented. Simulation results illustrate the operation and benefits of the presented approach.

Effect of Heat Treatments in the Silicon Eutectic Crystal Evolution in Al-Si Alloys

This paper describes the heat treatment effect on the eutectic silicon evolution in the A357 alloy, obtained by semisolid forming process (SSM). The coarsening rate of the silicon was determined by Image Analysis Technique in specimens from rheocasting ingots and thixocasting components. The study was realized in the temperature range from 450 to 550°C by applying heating times between 1 and 24 hours. The results show that during the heat treatment the coarsening and sphereodization of the silicon particles is produced and the fragmentation stages, which are observed in conventional alloys, do not appear. Kinetic silicon growth has been adjusted to the Oswald’s ripening equation.

Networked sliding mode control of the double integrator system using the event-driven self-triggered approach

Sliding mode control (SMC) methods rely on applying a high-frequency switching control. In networked control systems (NCS), high-frequency operations/transactions are not desirable because communication bandwidth consumption increases dramatically. This paper studies the application of event-driven self-triggered techniques to sliding mode control over networks as a means for reducing the bandwidth utilization. To this end, sliding mode control with hysteresis is adopted and control updates are forced to only occur at the hysteresis band boundary. This paper elaborates on the conditions that must be fulfilled in order to ensure such operation for the case of the double integrator system. Simulation results illustrate the presented concepts.

Experimental Bilateral Control Telemanipulation Using a Virtual Exoskeleton

The introduction of less invasive interfaces in control usually carry with them new drawbacks such as less perception, less dexterity, etc. This work tackles the experimentation of new means of perceptual feedback in teleoperation, when the operator guides the task by means of a virtual exoskeleton, and consequently without any mechanical device that can be provided with haptic devices. The work describes the evaluation of augmented images and sound feedback as alternative means for the bilateral control.

Performance Evaluation of Secondary Control Policies With Respect to Digital Communications Properties in Inverter-Based Islanded Microgrids

A key challenge for inverted-based microgrids working in islanded mode is to maintain their own frequency and voltage to a certain reference values while regulating the active and reactive power among distributed generators and loads. The implementation of frequency and voltage restoration control policies often requires the use of a digital communication network for real-time data exchange (tertiary control covers the coordinated operation of the microgrid and the host grid). Whenever a digital network is placed within the loop, the operation of the secondary control may be affected by the inherent properties of the communication technology. This paper analyzes the effect that properties like transmission intervals and message dropouts have for four existing representative approaches to secondary control in a scalable islanded microgrid. The simulated results reveals pros and cons for each approach, and identifies threats that properly avoided or handled in advance can prevent failures that otherwise would occur. Selected experimental results on a low-scale laboratory microgrid corroborate the conclusions extracted from the simulation study.

Sub Liquidus Casting Technology for the Production of High Integrity Component

This work is a contribution to improve the knowledge of components behavior produced by semi-solid processes particularly the Sub-Liquidus-Casting process. Die design was supported by using the Procast simulation program. The effect of the different variables of the process in structural integrity of the product has been described and analyzed. The components were produced using A356 alloy formed on a pilot plant with a 400 Ton THT press. The components study was made by RX, metallographic analysis and mechanical tests. The effects of T5 and T6 heat treatments were also studied.

Refining 3D Recovering by Carving through View Interpolation and Stereovision

In this paper, we present a method for obtaining accurate 3D models by merging the carving and stereo-matching algorithms. Multiple views of an object are taken from known camera poses. Object images, when segmented, are used to carve a rough 3D model of the object. View synthesis results are compared with real object views in order to validate the recovered model. When errors are detected, commonly due to occlusions and/or concavities, a fine stereo-matching algorithm is applied. Obtained depth map updates the inconsistent areas of the object model. Performed tests show the reached improvements in the accuracy of the model.

Communication-aware consensus for frequency restoration in islanded MicroGrids

MicroGrids (MGs) include spatially distributed generation (DG) systems and loads that may require operating autonomously in islanded mode. The operation of islanded MGs can benefit from consensus theory and practice, which are the foundations of distributed control. One of the main features of consensus strategies is that they rely on a cooperative scheme where inverters are required to communicate with their neighbors. Therefore properties of the communication network become fundamental. The contribution of this paper is twofold. First, it analyses the impact that communication properties such as transmission interval and message dropouts have in a given consensus-based frequency restoration strategy. Second, new design guidelines for the consensus policy are derived considering the communication dynamics as an opportunity for performance improvement.

Smart reconfigurable miniature vision system for mobile robots

The robot vision system presented consists of a PCB with a hardware-reconfigurable image processor, and a PCB with a standard commercial microprocessor. The microprocessor board interfaces with the host robot, configures the hardware of the image processor and runs the high-level image algorithms. Both boards occupy a volume of 10/spl times/10/spl times/3 cm/sup 3/ and consume less than 1A.

Internet-based control of a ball-and-plate system: A case study of modeling and automatic code generation for networked control systems

The evolution of technology and application needs leads to design complex systems both at hardware and software levels. Modeling approaches and automatic code generation are mature techniques in several application areas to shorten development times even in complex applications. This paper introduces the application of these techniques to critical embedded systems such as networked control systems (NCS). In particular, the case of an Internet-based control of a ball&plate system is presented. The first part of the paper is devoted to the plant modeling and control design strategy taking into account the distributed layout. The second part covers the automatic code generation process: from ScicosLab diagrams, C code is automatically generated onto multiple and physically distributed threads, with the automatic synthesis of thread scheduling, communication and access to the I/O primitives for sampling and actuation. The case study corroborates that model-based design tools mastering NCS complexity can contribute to the success of future industrial projects.