Real-time Control Applications Research Articles

A Variable Curvature Continuum Kinematics for Kinematic Control of the Bionic Handling Assistant

We present a new variable curvature continuum kinematics for multisection continuum robots with arbitrarily shaped backbone curves assembled from sections with three degrees of freedom (DoFs) (spatial bending and extension, no torsion). For these robots, the forward kinematics and the differential forward kinematics are derived. The proposed model approach is capable of reproducing both the constant and variable backbone curvature in a closed form. It describes the deformation of a single section with a finite number of serially connected circular arcs. This yields a section model with piecewise constant and, thus, a variable section curvature. Model accuracy and its suitability for kinematic real-time control applications are demonstrated with simulations and experimental data. To solve the redundant inverse kinematics problem, a local resolution of redundancy at the velocity level through the use of the robot's Jacobian matrix is presented. The Jacobian is derived analytically, including a concept for regularization in singular configurations. Experimental data are recorded with Festo's Bionic Handling Assistant. This continuum robot is chosen for experimental validation, as it consists of a variable backbone curvature because of its conically tapering shape.

Comparative analysis of algorithms and models for train running simulation

In order to find an algorithm applicable for train running time simulation in timetabling and real-time control applications (conflict detection and resolution, driver advisory system), three state-of-the-art algorithms for running time computation are compared concerning calculation imprecisions and computation times which are the main requirements in those computations. Therefore the exact solution of the differential equation of movement of the infinitesimal calculus is compared with those of the numeric approximations by Euler’s method and Gauss quadrature. A case study on German real-world tracks using three modern train configurations is performed. Additionally, the influences of mass modelling as mass strap or mass point and the possibility to emulate the mass strap behaviour by using a pre-computed slope profile is examined. Furthermore the influence of the detailedness of slope profiles on computation times and accuracy is analysed and a method which can be used for reducing the grade of detailedness of pre-computed slope profiles is shown. It is illustrated that high precision computations can only be carried out, when it is acceptable to use more computation time. In this context, the results reveal that this conflict of objectives can be solved by using a correctly parameterised Euler’s method, which can be used for all applications under examination as it offers a good trade-off between calculation time and preciseness.

Instrumentation for a multichord motional Stark effect diagnostic in KSTAR.

The motional Stark effect (MSE) diagnostic is used to measure the radial magnetic pitch angle profile in neutral beam heated plasmas. This information is used to calculate the safety factor, q, with magnetic equilibrium reconstruction codes such as EFIT. The MSE diagnostic is important during active shaping of the q profile to optimize confinement and stability, and it has become a key diagnostic in high performance tokamaks. A multichord photo-elastic modulator (PEM) based MSE system is being developed for a real-time plasma current profile control in Korea Superconducting Tokamak Advanced Research (KSTAR). The PEM-based approach is a standard method that measures the polarization direction of a single Stark line with narrow tunable bandpass filters. A tangential view of the heating beam provides good spatial resolution of 1-3 cm, which provides an opportunity to install 25 spatial channels spanning the major radius from 1.74 m to 2.84 m. Application of real-time control is a long-term technical goal after commissioning the diagnostic in KSTAR, which is expected in 2015. In this paper, we describe the design of this newly-constructed multichord MSE diagnostic in KSTAR.

Precise relative clock synchronization for distributed control using TSC registers

Precise clock synchronization is essential in emerging time-critical distributed control systems operating over computer networks where the clock synchronization requirements are mostly focused on relative clock synchronization and high synchronization precision. Existing clock synchronization techniques such as the Network Time Protocol (NTP) and the IEEE 1588 standard can be difficult to apply to such systems because of the highly precise hardware clocks required, due to network congestion caused by a high frequency of synchronization message transmissions, and high overheads. In response, we present a Time Stamp Counter based precise Relative Clock Synchronization Protocol (TSC-RCSP) for distributed control applications operating over local-area networks (LANs). In our protocol a software clock based on the TSC register, counting CPU cycles, is adopted in the time clients and server. TSC-based clocks offer clients a precise, stable and low-cost clock synchronization solution. Experimental results show that clock precision in the order of 10 microseconds can be achieved in small-scale LAN systems. Such clock precision is much higher than that of a processor׳s Time-Of-Day clock and is easily sufficient for most distributed real-time control applications over LANs.

Gray-Box Modeling for Performance Control of an HCCI Engine With Blended Fuels

High fidelity models that balance accuracy and computation load are essential for real-time model-based control of homogeneous charge compression ignition (HCCI) engines. Gray-box modeling offers an effective technique to obtain desirable HCCI control models. In this paper, a physical HCCI engine model is combined with two feed-forward artificial neural network models to form a serial architecture gray-box model. The resulting model can predict three major HCCI engine control outputs, including combustion phasing, indicated mean effective pressure (IMEP), and exhaust gas temperature (Texh). The gray-box model is trained and validated with the steady-state and transient experimental data for a large range of HCCI operating conditions. The results indicate that the gray-box model significantly improves the predictions from the physical model. For 234 HCCI conditions tested, the gray-box model predicts combustion phasing, IMEP, and Texh with an average error of less than 1 crank angle degree, 0.2 bar, and 6 °C, respectively. The gray-box model is computationally efficient and it can be used for real-time control application of HCCI engines.

A Practical Method for Implementing an Attitude and Heading Reference System

This paper describes a practical and reliable algorithm for implementing an Attitude and Heading Reference System (AHRS). This kind of system is essential for real time vehicle navigation, guidance and control applications. When low cost sensors are used, efficient and robust algorithms are required for performance to be acceptable. The proposed method is based on an Extended Kalman Filter (EKF) in a direct configuration. In this case, the filter is explicitly derived from both the kinematic and error models. The selection of this kind of EKF configuration can help in ensuring a tight integration of the method for its use in filter-based localization and mapping systems in autonomous vehicles. Experiments with real data show that the proposed method is able to maintain an accurate and drift-free attitude and heading estimation. An additional result is to show that there is no ostensible reason for preferring that the filter have an indirect configuration over a direct configuration for implementing an AHRS system.

A Fast Algorithm to Compute Precise Type-2 Centroids for Real-Time Control Applications

An interval type-2 fuzzy set (IT2 FS) is characterized by its upper and lower membership functions containing all possible embedded fuzzy sets, which together is referred to as the footprint of uncertainty (FOU). The FOU results in a span of uncertainty measured in the defuzzified space and is determined by the positional difference of the centroids of all the embedded fuzzy sets taken together. This paper provides a closed-form formula to evaluate the span of uncertainty of an IT2 FS. The closed-form formula offers a precise measurement of the degree of uncertainty in an IT2 FS with a runtime complexity less than that of the classical iterative Karnik-Mendel algorithm and other formulations employing the iterative Newton-Raphson algorithm. This paper also demonstrates a real-time control application using the proposed closed-form formula of centroids with reduced root mean square error and computational overhead than those of the existing methods. Computer simulations for this real-time control application indicate that parallel realization of the IT2 defuzzification outperforms its competitors with respect to maximum overshoot even at high sampling rates. Furthermore, in the presence of measurement noise in system (plant) states, the proposed IT2 FS based scheme outperforms its type-1 counterpart with respect to peak overshoot and root mean square error in plant response.

The Development and Empirical Evaluation of the Korean Smart Distribution Management System

This paper introduces the development and actual test results of the Korean Smart Distribution Management System (KSDMS). The KSDMS has been designed and developed to cope with the lack of interconnection capability of the Dispersed Energy Resource (DER), to provide standardization and compatibility, and to implement automatic processing of service restoration, in the existing Distribution Automation System (DAS) in Korea. First, real-time system analysis and control application programs were developed, to solve the problems of the existing DAS; and the Distribution Management System (DMS) platform was developed, to run the developed application programs. Second, international standard-based communication, platform, and database structures were adopted, for standardization and compatibility. Third, a platform and application program functions were developed to process faults automatically; and a communication device and an intelligent electronic device (IED) were developed to automate fault restoration, through communication between devices. The KSDMS was evaluated by three tests: unit function test, platform and application program integration test, and empirical test. The first two were conducted on both small and large demonstration systems. The empirical test was performed at the Power Testing Center (PTC) in Gochang, and on a real system, at the Korea Electric Power Corporation (KEPCO), on Jeju Island. The test results verified that the KSDMS can actively resolve the problems of the existing DAS.

Online Algebraic Identification of the Payload Changes in a Single-Link Flexible Manipulator Moving under Gravity

This paper presents a method for the on-line identification of the payload carried by a single-link flexible manipulator whose movement is constrained to the vertical plane. The vertical movement of the robot makes the effect of gravity not negligible, and determines therefore, the non-linear behaviour of the analysed system. The proposed estimator is based on the algebraic derivative approach in the frequency domain. The short period of time it takes for the algorithm to make an estimate, and its low computational burden make it suitable for real-time and adaptive control applications. The proposed estimator is experimentally tested in several situations carefully chosen to reproduce routine operations of the flexible manipulator.

Performance Analysis of Distributed Control Systems Using the FlexRay Protocol

Spatially distributed systems which share communication resources have advantages such as lower implementation cost, better flexibility and reliability. When real-time distributed control applications make use of such architecture, the drawbacks are the networked-induced effects, which may severely degrade the controlled system performance. Efforts have been made by both communication and control communities to assess this problem: new control design techniques now consider explicitly the effects of these constraints, and some new communication protocols offer services to support the requirements from this kind of application. FlexRay is a protocol developed to support real-time safety-critical applications. In this study, a FlexRay network is built and an active suspension control is implemented in a distributed environment. The main goal is to analyse the impact the network-induced effects may bring to system performance.

Scheduling imprecise task graphs for real-time applications

Many of the real-time tasks within embedded real-time control applications fall into the imprecise category. Such tasks are iterative in nature, with output precision improving as execution time increases (up to a point). These tasks can be terminated early at the cost of poorer quality output. Many imprecise tasks in CPS are dependent, with one task feeding other tasks in a task precedence graph (TPG). A task output quality depends on the quality of its input data as well as on the execution time that is allotted to it. In this paper, we study the allocation/scheduling of imprecise TPGs on multiprocessors to maximise output quality where resources (time and energy) are limited. Our heuristic algorithms can effectively reclaim resources when tasks finish earlier than their estimated worst-case execution time. Dynamic voltage scaling is used to manage energy consumption and keep it under a specified bound.

Dynamic Formulation and Simplified Model of a Novel 3-DOF Parallel Mechanism with Actuation Redundancy

Dynamics plays an important role in the application of parallel mechanism, which is the key to analyze the dynamic characteristics and achieve high-precision operation. The inverse dynamic model for a novel redundantly actuated parallel mechanism is formulated in the task space using Lagrangian formalism and the driving force is optimized by utilizing the minimal 2-norm method. By investigating the contribution of each term in the dynamic model to the driving force, a simplified strategy of the dynamic model for real-time control application is presented, and the subsequent model error is compensated by adopting RBF neural network. Simulation results verify the correctness and effectiveness of the proposed dynamic model and simplified strategy.

Distributed Computation Particle Filters on GPU Architectures for Real-Time Control Applications

We present the design, analysis, and real-time implementation of a distributed computation particle filter on a graphic processing unit (GPU) architecture that is especially suited for fast real-time control applications. The proposed filter architecture is composed of a number of local subfilters that can share limited information among each other via an arbitrarily chosen abstract connected communication topology. We develop a detailed implementation procedure for GPU architectures focusing on distributed resampling as a crucial step in our approach, and describe alternative methods in the literature. We analyze the role of the most important parameters such as the number of exchanged particles and the effect of the particle exchange topology. The significant speedup and increase in performance obtained with our framework with respect to both available GPU solutions and standard sequential CPU methods enable particle filter implementations in fast real-time feedback control systems. This is illustrated via experimental and simulation results using a real-time visual servoing problem of a robotic arm capable of running in closed loop with an update rate of 100 Hz, while performing particle filter calculations that involve over one million particles.

하수도 시스템의 실시간 제어시스템 구축 방안

Real time control (RTC) can be broadly defined as a system that dynamically adjusts the operation of facilities in response to online measurements in the field to maintain and meet the operational objectives, both during dry and wet weather conditions. RTC adds a dynamic component that is actively adjusted in real time based on system conditions. In terms of reducing or eliminating sewer flooding, CSOs and/or managing flows, implementation of RTC has various benefits to sewer system operation. It has been emerging as an attractive approach, but related elements (such as framework for the application, its components and equipments, aspects to be considered) towards its application on sewer systems have not been throughly introduced so far. The main goal of this study is to review several applications of RTC and firm guidelines published abroad, and finally to provide a framework for the proper application of RTC on sewer systems.

Real time control (RTC) of urban drainage systems – A discussion of the additional efforts compared to conventionally operated systems†

Application of real time control (RTC) in urban drainage systems is discussed in this paper as a potential solution for water management tasks. Though, in engineering practice, often the opinion prevails that to perform RTC requires far more effort than to use conventionally operated systems. Depending on the objectives and the boundary conditions of the entire urban drainage system under review, the additional effort (and extra cost) needed may well be limited. This concerns measurement and control devices as well as the planning process involved and the adaptation of daily operations. Due to the increased flexibility of controlled systems, their degree of utilisation can be essentially improved. With that, it is not only possible to reduce environmental impacts, but also to achieve operational objectives more easily.

Control of leader–follower formation and path planning of mobile robots using Asexual Reproduction Optimization (ARO)

This paper presents the optimal path of nonholonomic multi robots with coherent formation in a leader–follower structure in the presence of obstacles using Asexual Reproduction Optimization (ARO). The robots path planning based on potential field method are accomplished and a novel formation controller for mobile robots based on potential field method is proposed. The efficiency of the proposed method is verified through simulation and experimental studies by applying them to control the formation of four e-Pucks robots (low-cost mobile robot platform). Also the proposed method is compared with Simulated Annealing, Improved Harmony Search and Cuckoo Optimization Algorithm methods and the experimental results, higher performance and fast convergence time to the best solution of the ARO demonstrated that this optimization method is appropriate for real time control application.

A highly adjustable magnetorheological elastomer base isolator for applications of real-time adaptive control

Inspired by its controllable and field-dependent stiffness/damping properties, there has been increasing research and development of magnetorheological elastomer (MRE) for mitigation of unwanted structural or machinery vibrations using MRE isolators or absorbers. Recently, a breakthrough pilot research on the development of a highly innovative prototype adaptive MRE base isolator, with the ability for real-time adaptive control of base isolated structures against various types of earthquakes including near- or far-fault earthquakes, has been reported by the authors. As a further effort to improve the proposed MRE adaptive base isolator and to address some of the shortcomings and challenges, this paper presents systematic investigations on the development of a new highly adjustable MRE base isolator, including experimental testing and characterization of the new isolator. A soft MR elastomer has been designed, fabricated and incorporated in the laminated structure of the new MRE base isolator, which aims to obtain a highly adjustable shear modulus under a medium level of magnetic field. Comprehensive static and dynamic testing was conducted on this new adaptive MRE base isolator to examine its characteristics and evaluate its performance. The experimental results show that this new MRE base isolator can remarkably change the lateral stiffness of the isolator up to 1630% under a medium level of magnetic field. Such highly adjustable MRE base isolator makes the design and implementation of truly real-time adaptive (e.g. semi-active or smart passive) seismic isolation systems become feasible.

A fully adaptive forecasting model for short-term drinking water demand

For the optimal control of a water supply system, a short-term water demand forecast is necessary. We developed a model that forecasts the water demand for the next 48 h with 15-min time steps. The model uses measured water demands and static calendar data as single input. Based on this input, the model fully adaptively derives day factors and daily demand patterns for the seven days of the week, and for a configurable number of deviant day types. Although not using weather data as input, the model is able to identify occasional extra water demand in the evening during fair weather periods, and to adjust the forecast accordingly.The model was tested on datasets containing six years of water demand data in six different areas in the central and Southern part of Netherlands. The areas have all the same moderate weather conditions, and vary in size from very large (950,000 inhabitants) to small (2400 inhabitants). The mean absolute percentage error (MAPE) for the 24-h forecasts varied between 1.44 and 5.12%, and for the 15-min time step forecasts between 3.35 and 10.44%. The model is easy to implement, fully adaptive and accurate, which makes it suitable for application in real time control.

D-MSR: A Distributed Network Management Scheme for Real-Time Monitoring and Process Control Applications in Wireless Industrial Automation

Current wireless technologies for industrial applications, such as WirelessHART and ISA100.11a, use a centralized management approach where a central network manager handles the requirements of the static network. However, such a centralized approach has several drawbacks. For example, it cannot cope with dynamicity/disturbance in large-scale networks in a real-time manner and it incurs a high communication overhead and latency for exchanging management traffic. In this paper, we therefore propose a distributed network management scheme, D-MSR. It enables the network devices to join the network, schedule their communications, establish end-to-end connections by reserving the communication resources for addressing real-time requirements, and cope with network dynamicity (e.g., node/edge failures) in a distributed manner. According to our knowledge, this is the first distributed management scheme based on IEEE 802.15.4e standard, which guides the nodes in different phases from joining until publishing their sensor data in the network. We demonstrate via simulation that D-MSR can address real-time and reliable communication as well as the high throughput requirements of industrial automation wireless networks, while also achieving higher efficiency in network management than WirelessHART, in terms of delay and overhead.

System-Management-Mode in Real-Time PC-Based Control Applications

There is a tendency toward the use of personal computers in real-time control applications. These computers have high processing capacity and reduced costs when compared to software and hardware development for dedicated platforms. However, some control systems require latency predictability and the processors of the x86 architecture have a special protection and correction mode known as system management mode (SMM). This mode is not traceable by the operating system, and it can cause unpredictability in the system. This article describes the SMM, presents tools and methods for its detection and an analysis of its impact on real-time systems.