Discrete Control Logic Research Articles

A formal refinement-based analysis of the hybrid ERTMS/ETCS level 3 standard

This paper presents a formal model of the case study proposed for the ABZ2018 conference, which concerns the Hybrid ERTMS/ETCS Level 3 Standard. This standard allows trains to communicate with a train supervisor to report their integrity and positions, thanks to an onboard train integrity monitoring system. The supervisor assigns trains a movement authority to control traffic and to avoid collisions. The standard also provides for trains that cannot communicate with the supervisor; these trains are detected by sensors on tracks and obey traffic signals set by the supervisor along the trackside. Using communication allows for a finer grain control of the tracks. Our model is derived using stepwise refinement with the Event-B method. We take into account the main features of the case study (VSS management, timers, ERTMS and non-ERTMS trains). Our model is decomposed into four refinements. All proof obligations have been discharged using the Rodin provers, except those related to the computation of the VSS state machine, which was found to be ambiguous (nondeterministic). Our model has been validated using ProB. The main safety property, which is that ERTMS trains do not collide, is proved. Our model focuses on the discrete control logic aspects of the case study.

A low-cost PackML-based control solution for a modular production line

The contribution deals with an implementation of discrete control logic for a modular production line, with two main objectives pursued. Firstly, the basic ideas of PackML standard should be implemented, in particular the behaviour of the machine from the operational state viewpoint, and secondly, the implementation should be based on low-end programmable logic controllers, with limitations on the available memory and processing speed. The paper presents a general idea of the implementation with discussion of its relation to PackML standard, and provides relevant details of the implementation case study on a laboratory scale modular production system.

Towards Synthesizing Energy-efficient Controllers for Modern Production Systems from Scenario-based Specifications

Abstract Due to continuously rising electricity prices, the energy efficiency of production systems is an increasingly important factor in industrial manufacturing. One goal is therefore to reuse the braking energy of manipulator axes. The acceleration and deceleration phases of axes must be synchronized such that, ideally, the braking energy can be reused immediately within the system. In our current technique for the energy-efficient motion planning of concurrent movements of axes, we do not yet consider changing the discrete control logic to reorder movement sequences. This is difficult, since this reordering must not violate critical system requirements. In this paper, we outline a new technique for automatically synthesizing energy-efficient discrete controllers from a scenario-based specification of a production system, which we enrich with information about consumed and generated energy. Last, we provide an outlook on challenging open research problems.

Smart Power Module Molding Advances: Evaluating high temperature suitability of Molding Compounds

During the last years within power electronics packaging a trend towards compact power electronics modules for automotive and industrial applications could be observed, where a smart integrated control unit for motor drives is replacing bulky substrates with discrete control logic and power electronics. Most recent modules combine control and power electronics yielding maximum miniaturization. Transfer molding is the method of choice for cost effective encapsulation of such modules due to robustness of the molded modules and moderate cost of packaging. But there are challenges with this type of package: Typically those packages are asymmetric, a substrate with single sided assembly is overmolded on the component side and the substrate backside is exposed providing a heat path for optimized cooling. This asymmetric geometry is prone to yield warped substrates, preventing optimum thermal contact to the heatsink and also putting thermo-mechanical stress on the encapsulated components, possibly reducing reliability. Such packages being truly heterogeneous, combining powerICs, wire bonds, SMDs, controlICs, substrate and leadframe surfaces, the encapsulant used needs to adhere sufficiently to all surfaces present. Additionally those packages need to operate at elevated temperatures for long time, e.g. operate at 200 °C for 1000 h and more, so high thermal stability is of ample importance. Within this paper the main goal is to identify transfer molding compounds suitable for the encapsulation of smart power modules, ready to be used at 200 °C and determine the actual maximum temperature of use of such high performance molding compounds currently available in the market. Summarized a detailed description of the high temperature suitability of high performance molding compounds is provided – additionally an extended test methodology is described to facilitate future material evaluation for HT or harsh environment use of polymeric materials as encapsulants or base materials.

Transfer Molding Technology for Smart Power Electronics Modules: Materials and Processes

In recent years, within power electronics packaging, there has been a trend toward compact power electronics modules for automotive and industrial applications, where a smart integrated control unit for motor drives is replacing bulky substrates with discrete control logic and power electronics. Most recent modules combine control and power electronics, yielding maximum miniaturization. Transfer molding is the method of choice for cost-effective encapsulation of such modules due to robustness of the molded modules and moderate cost of packaging. But there are challenges with this type of package. Typically, these packages are asymmetric, and thus a substrate with single sided assembly is overmolded on the component side and the substrate backside is exposed, providing a heat path for optimized cooling. This asymmetric geometry is prone to yielding warped substrates, preventing optimum thermal contact to the heat sink and also putting thermomechanical stress on the encapsulated components, possibly reducing reliability. Such packages are truly heterogeneous, combining power ICs, wire bonds, SMDs, control ICs, substrate, and lead frame surfaces. As a result, the encapsulant used needs to adhere sufficiently to all surfaces present. Additionally, those packages need to operate at elevated temperatures for extended time periods, for example, at 150°C for 2000 h and more, so high thermal stability is of prime importance. Within this paper, a reference application is described integrating power and control logic inside a lead frame based molded package. Taking into account the challenges mentioned above, a detailed description of material selection for this module will be given, including material analysis, such as rheology, reactivity, and change in εr; and thermomechanical properties, in initial stage as f(t,T) and after media storage. Process development tools for module molding are used to ensure manufacturability and usability. Concluding rules for encapsulant material selection and package setup are provided.

On an LAS-integrated soft PLC system based on WorldFIP fieldbus

Communication efficiency is lowered and real-time performance is not good enough in discrete control based on traditional WorldFIP field intelligent nodes in case that the scale of control in field is large. A soft PLC system based on WorldFIP fieldbus was designed and implemented. Link Activity Scheduler (LAS) was integrated into the system and field intelligent I/O modules acted as networked basic nodes. Discrete control logic was implemented with the LAS-integrated soft PLC system. The proposed system was composed of configuration and supervisory sub-systems and running sub-systems. The configuration and supervisory sub-system was implemented with a personal computer or an industrial personal computer; running subsystems were designed and implemented based on embedded hardware and software systems. Communication and schedule in the running subsystem was implemented with an embedded sub-module; discrete control and system self-diagnosis were implemented with another embedded sub-module. Structure of the proposed system was presented. Methodology for the design of the sub-systems was expounded. Experiments were carried out to evaluate the performance of the proposed system both in discrete and process control by investigating the effect of network data transmission delay induced by the soft PLC in WorldFIP network and CPU workload on resulting control performances. The experimental observations indicated that the proposed system is practically applicable.

Transfer molding technology for smart power electronics modules - materials and processes

During the last years within power electronics packaging a trend towards compact power electronics modules for automotive and industrial applications could be observed, where a smart integrated control unit for motor drives is replacing bulky substrates with discrete control logic and power electronics. Most recent modules combine control and power electronics yielding maximum miniaturization. Transfer molding is the method of choice for cost effective encapsulation of such modules due to robustness of the molded modules and moderate cost of packaging. But there are challenges with this type of package: Typically those packages are asymmetric, a substrate with single sided assembly is overmolded on the component side and the substrate backside is exposed providing a heat path for optimized cooling. This asymmetric geometry is prone to yield warped substrates, preventing optimum thermal contact to the heatsink and also putting thermomechanical stress on the encapsulated components, possibly reducing reliability. Such packages being truly heterogeneous, combining powerICs, wire bonds, SMDs, controlICs, substrate and leadframe surfaces, the encapsulant used needs to adhere sufficiently to all surfaces present. Additionally those packages need to operate at elevated temperatures for increased times, e.g. operate at 150 °C for 2000 h and more, so high thermal stability is of ample importance. Within this paper a reference application is described, integrating power and control logic inside a leadframe based molded package. Taking into account the challenges mentioned above, a detailed description of material selection for this module will be given, including material analysis as rheology, reactivity, change in ɛr and thermomechanical properties as f(t,T) and of media storage. Process development tools for module molding are used to ensure manufacturability and useability. Concluding rules for encapsulant material selection and package setup are provided.

An admissible-behaviour-based analysis of the deadlock in Petri-net controllers

This paper addresses the problem of verifying the discrete control logic that is typically implemented by programmable controllers. Not only are the logical properties of the controller studied during verification, the behaviour of the overall controlled system is also examined. An approach that combines the calculation of the safety-oriented interlock controllers in terms of supervisory control theory (SCT), the corresponding calculation of the admissible behaviour of the system, and the specification of the desired system operation by Petri nets is proposed. A potential deadlock in the controlled system is then verified by taking the admissible-behaviour model as a process model. The analysis of the simultaneously operated supervisory-control-based interlock controller and the Petri-net-based sequential controller is performed with a C-reachability graph. The paper focuses on the calculation of the graph, and the approach is illustrated with an example of a simple manufacturing cell.

Design recovery for relay ladder logic

An algorithm for converting relay ladder logic (RLL) programs for programmable logic controllers (PLCs) into sequential function chart (SFC) programs is introduced. Since an SFC (a standardization of Grafcet) better represents the sequential flow of control logic, it is considerably easier to understand and modify SFC programs. The practical motivation for this study is to provide a tool for converting existing RLL programs into SFC programs by recovering the underlying sequential control logic. A basic design recovery algorithm is presented and applied to a simple RLL program for one stage of a batch chemical process. Several fundamental issues in discrete control logic representation and analysis are identified as fertile areas for future research. >

Microprocessor/ASIC to total ASIC design for cycloconverter drives

The paper examines the logic and control strategy used in a microprocessor-controlled cycloconverter drive. The design and development of two ASICs used to replace the discrete control logic is described. The paper then illustrates how the digital control circuit was developed to produce a total ASIC cycloconverter control, by producing ASICs which replaced the microprocessor in the system. A comparison of the microprocessor solution is made with the total digital ASIC cycloconverter control method. In each case the two ASICs were produced using Mentor Graphics electronic design automation (EDA) packages for design, simulation and layout, prior to fabrication by Micro Circuit Engineering (MCE). This has allowed a considerable reduction in the size of the control equipment used to control the induction motor: a reduction of 16-to-1 has been achieved by using ASICs and PCB design techniques.