Lean Six Sigma 4.0 in an empirical application: a case of digital measurement for thickness deviation on a galvanizing line in a steel industry

The insertion of communication networks in closed-loop of digital control systems makes the system synthesis and analysis complex. In this paper, we consider the combination of classical reliability, risk and safety evaluation with typical control system through digital networked control systems. The main purpose is to study the influence of transmission delays and packet dropouts on the reliability of digital networked control systems by using a modified statistical method-Monte Carlo simulation. The behaviors of two types of fault are modelled by different statistical distribution. The control strategies we apply for digital control systems are Proportion Integration Differentiation control strategies, generated by Genetic Algorithm. In terms of a realistic system model, we evaluate and compare the influences on the reliability of digital networked control systems with different control strategies from quantitative aspect. Numerical examples are presented to illustrate the effectiveness and correctness of the approach.

Experimental studies of using the digital control system in power conversion equipment of high-voltage power supply systems in spacecrafts with a hydrogen energy accumulator

Safety-critical, real-time applications make use of fault-tolerant digital control systems to achieve their performance goals. Even though these digital control systems are fault-tolerant, they are susceptible to errors induced by common-mode faults, since these errors cannot be masked by standard redundancy provisions. Such errors can be handled by special error correction mechanisms, which could require stopping the control law computations while the errors are removed. Thus, the effect of these special error recovery mechanisms on digital control systems needs to be understood. This paper presents a comprehensive study of the effect of three error recovery mechanisms–rollback, reset and cold restart–on the stability of digital closed-loop control systems. The effect of the faults, detected and handled by these error recovery mechanisms, on the digital control system is modelled by a set of interference maps. It is assumed that the arrival and departure of common-mode faults can be represented by a Markov process. The overall system behaviour is then described by a Markov jump linear model, whose stability is explored using standard techniques from the literature. The result of this analysis is a new metric, the minimum average interarrival spacing (MAIS), which is useful for comparing the performance of different error recovery mechanisms and for designing new fault-tolerant controllers. The theoretical results are illustrated via Monte Carlo simulations that show the effects of common-mode faults on the closed-loop stability of the longitudinal dynamics of an AFTI/F-16 aircraft.

A helicopter auxiliary power unit (APU) is initially equipped with a hydro-mechanical control system (HMC). Because HMC's complex structure is difficult to be modified to realize sophisticated control algorithms and the APU is faced with the need for performance improvement, it is urgently necessary to carry out digital control modification of HMC. Based on the analysis of control laws of the original HMC and differences between HMC and digital control system, key techniques involved in the digital control system are studied, such as overall structure, control laws and fuel system based on electric fuel pump, and finally a full authority digital electronic control system (FADEC) is developed for APU. Functions, performances and key techniques of the FADEC system are evaluated on test rig, and the test results show functions of original control system are enhanced and performances of APU are improved more effectively under the control of the designed FADEC compared with the original HMC.

The United States (U.S.) nuclear industry, like similar process control industries, has moved toward upgrading its control rooms. The upgraded control rooms typically feature digital control system (DCS) displays embedded in the panels. These displays gather information from the system and represent that information on a single display surface. In this manner, the DCS combines many previously separate analog indicators and controls into a single digital display, whereby the operators can toggle between multiple windows to monitor and control different aspects of the plant. The design of the DCS depends on the function of the system it monitors, but revolves around presenting the information most germane to an operator at any point in time. DCSs require a carefully designed human system interface. This report centers on redesigning existing DCS displays for an example chemical volume control system (CVCS) at a U.S. nuclear power plant. The crucial nature of the CVCS, which controls coolant levels and boration in the primary system, requires a thorough human factors evaluation of its supporting DCS. The initial digital controls being developed for the DCSs tend to directly mimic the former analog controls. There are, however, unique operator interactions with a digital vs. analog interface, and the differences have not always been carefully factored in the translation of an analog interface to a replacement DCS. To ensure safety, efficiency, and usability of the emerging DCSs, a human factors usability evaluation was conducted on a CVCS DCS currently being used and refined at an existing U.S. nuclear power plant. Subject matter experts from process control engineering, software development, and human factors evaluated the DCS displays to document potential usability issues and propose design recommendations. The evaluation yielded 167 potential usability issues with the DCS. These issues should not be considered operator performance problems but rather opportunities identified by experts to improve upon the design of the DCS. A set of nine design recommendations was developed to address these potential issues. The design principles addressed the following areas: (1) color, (2) pop-up window structure, (3) navigation, (4) alarms, (5) process control diagram, (6) gestalt grouping, (7) typography, (8) terminology, and (9) data entry. Visuals illustrating the improved DCS displays accompany the design recommendations. These nine design principles serve as the starting point to a planned general DCS style guide that can be used across the U.S. nuclear industry to aid in the future design of effective DCS interfaces.

In the development of technological systems with pneumatic or hydraulic drive, the use of automated means for their control is required. At present, automated control tools built with the help of logic controllers are widely used. The logical controller allows to solve a wide variety of tasks with minimal costs, both in terms of cost and time spent for developing the system. So the logic controller ensures the speed of systems with pneumatic or hydraulic drive up to 1 ms or less. With the use of digital automated controls, questions related to the synthesis of PID regulators and the stability of systems with pneumatic / hydraulic drive in the time domain arise. The purpose of this work was the creation and practical implementation of a digital PID controller for controlling the pneumatic / hydraulic system to provide practical recommendations for its use in engineering. The article presents a block diagram of analog and digital control systems with a proportional pneumatic distributor. The implementation of analog and digital PID-controller and optimization of its parameters by an integral criterion is presented. Comparison of analog and digital systems with the PID controller introduced into their composition is made. The quality of these systems is suggested to be estimated in the time domain by the time of the transient process and the maximum dynamic error. Practical recommendations for determining the sampling time of digital systems with a PID controller are given. An example of the developed digital automatic control system for tracking pneumatic drive is shown, its structural diagram, the general view of the control device with the logic controller and the graphic operator interface, which makes it easy to configure the automated control tool and monitor its state. The scientific novelty of the results presented in the article was that the task of investigating the dynamics of a pneumatic / hydraulic distributor with an electric control in the time domain was solved using a mathematical model that included a digital PID controller and a comparison of the results of modeling a digital system with analogue was made, and practical recommendations for determining the sampling time were given.

Quantitative evaluation of common cause failures in high safety-significant safety-related digital instrumentation and control systems in nuclear power plants

With a rapid development of the digital signal processor in recent years, a full digital control system for the superconducting section of APT is designed and implemented by using TI's C6x processor. A digital control system is first modeled and simulated using Matlab/Simulink. Simulation results confirmed the feasibility and flexibility of the digital control system for LLRF feedback system. Due to flexibility of DSP, different control algorithms are implemented and compared in the system. Particular attention is paid to the inherent pipeline delay problem associated with a digital control system and its effect and limitation on the overall system performance.

In spite of wide expansion of digital systems for NPP control, information about realistic operating reliability measures of these systems is still lacking. The paper is a continuation of report [1] and contains results of analysis of operating reliability of digital control systems used in Ukrainian nuclear power plants. This paper contains: - reliability measures of digital instrumentation and control systems of first generation (designed in 1979–1983); - reliability measures of digital reactor control systems of second generation (designed after 2000) including reasons of failures; - analysis of the reasons of NPP violations due to digital instrumentation and control systems.

Recently, the Plant Input Mapping (PIM) method was proposed as a digital-redesign (or an emulation) approach in digital control system design. This method guarantees stability of a redesigned digital control system for a wide range of sampling periods. In this paper the PIM method is applied to the design of a digital model-matching flight control system. In the model-matching control system design a plant must have no unstable zeros. However, unstable zeros appear for small sampling periods in a step invariance model of a continuous-time (CT) plant with the relative degree greater than two, even if the CT plant has no unstable zeros. Hence, in such a case, the direct-digital approach cannot be applied to the design of a digital model-matching control system. By contrast, the digital-redesign approach such as the Tustin's method or the PIM method is free from the problem. Simulation results for an unstable VTOL aircraft show that the proposed method gives better performance than the conventional design methods.

A key feature of the new digital plasma control system installed on the TCV (Tokamak à Configuration Variable) tokamak is its possibility to rapidly design, test and deploy real-time algorithms. It accommodates hundreds of diagnostic inputs and actuator outputs, and offers the possibility to design advanced control algorithms with better knowledge of the plasma state and to coherently control all TCV actuators, including poloidal field coils, gas valves, the gyrotron powers and launcher angles of the electron cyclotron heating and current drive system together with diagnostic triggering signals. It encompasses plasma control applications ranging from basic experiments of coil current and density control to advanced experiments of magnetohydrodynamics (MHD) and plasma profile control. The system consists of multiple nodes, each of which may have a local analog to digital (ADC) and/or digital to analog (DAC) card; all nodes are connected to a reflective memory (RFM), providing a deterministic method of sharing memory between them. Recently, a generalized plasma position and shape controller based on the real-time (RT) Grad-Shafranov solver RTLIUQE was developed and implemented, providing the basis for future high performance plasma operation with advanced plasma configurations. The controller design is based on an isoflux control scheme and utilizes singular value decomposition (SVD), to respect the limits on poloidal field coils currents by limiting the controlled parameters to the set that can be more easily controlled. The controller is capable in principle of providing improved equilibrium control especially for unconventional plasma scenarios, for e.g. reliable control of ‘snowflake’ equilibria with closely spaced x-points, i.e. the ‘exact’ snowflake, and the development of negative triangularity plasmas in H-mode. An addition of a new node on the digital control system has enhanced the real time computational capacity and hosts the real-time transport code RAPTOR (rapid plasma transport simulator), an advanced density profile reconstruction algorithm including real-time fringe jump correction, as well as a plasma state monitoring, supervision and actuator management algorithm. In future, more signals from existing TCV diagnostics, including multiview pinhole x-ray diagnostics, Thomson scattering, visible image processing and magnetic signals for MHD mode analysis will be added to expand the capabilities of the digital control system.

Abstract: In the current domestic control system of submerged arc welding machine, most walking DC motor speed control uses the method of analog control pulse width modulation (PWM), which has a complex circuit, high failure rate and is inconvenient to use. For this phenomenon, DSP (TMS320F2812) disc is used to build a digital control system, and replace the traditional analog controller, allowing the weld control system more simple and practical. The main content of this paper is the hardware circuit design and software algorithms programming of digital control DC speed control system. Tested by experiment, this digital control system can replace the weld analog control system, enabling the motor to have good control performance at low speed thereby enhancing the welding effect of submerged arc welding machine.

Managing the aging of digital control systems ensures that nuclear power plant systems are in adequate safety margins during their life cycles. Software is a core component in the execution of control logic and differs between digital and analog control systems. The hardware aging management for the digital control system is similar to that for the analog system, which has matured over decades of study. However, software aging management is still in the exploratory stage. Software aging evaluation is critical given the higher reliability and safety requirements of nuclear power plants. To ensure effective inputs for reliability assessment, this paper provides the required software aging information during the life cycle. Moreover, the software aging management scheme for safety digital control system is proposed on the basis of collected aging information.

The design of a combined topography-adhesion-stiffness imaging mode in a scanning force microscope (SFM) based on a digital control system is presented. The digital control system provides for the flexibility in designing the shape of the loading-unloading force waveform and enables a fast rate (up to 1 kHz) of applying the loading-unloading waveform with a pre-defined maximum loading force. Furthermore, flexibility in optimizing the imaging conditions and analyzing the resulting force-displacement data is achieved. The limiting factor for the data acquisition speed appears to be the viscous drag of the working medium exerted onto the SFM cantilever. It is shown that subtracting a no-contact, zero-deflection baseline can compensate for the effects of the viscous drag. The performance of the digital adhesion mapping control system is illustrated by analyzing several different samples: a rigid silicon grid; a molecularly thin block copolymer film; and a thin, heterogeneous polymer film. The remaining problems are related to the cross-talk between the topography and stiffness-related slope.

Distributed digital real-time control system for TCV tokamak