PC-based Control Research Articles

Experiments in Active Control of Stall on an Aeroengine Gas Turbine

This paper describes work carried out between 1989 and 1994 to investigate the application of “Active Stall Control” to a Rolls-Royce Viper turbojet. The results demonstrate that stall control is feasible and can increase the stable operating range by up to 25 percent of pressure rise. Stall disturbances were detected using rings of high response pressure transducers positioned at different axial planes along the compressor, and processed using a PC-based data acquisition and control system. Actuation was provided by six hydraulically operated sleeve valves positioned to recirculate air over all or part of the compressor. Stall was artificially induced using combinations of in-bleed into the combustor outer casing, fuel spiking, hot gas ingestion, and inlet pressure spoiling, thus replicating many of the transient conditions commonly observed to make a compressor prone to stall. Results are compared from a number of stall control strategies including those demonstrated at low speed by Paduano et al. (1993) and Day (1993). Best results were obtained with detection of nonaxisymmetric disturbances coupled with axisymmetric control action. A control system of this type is demonstrated to be capable of extending the stable engine operating range at all speeds and with each method of inducing stall.

The white-radiation dynamic topography experimental system at the BSRF.

A white-radiation dynamic topography experimental system has been established at the BSRF (Beijing Synchrotron Radiation Facility) and is now in operation. Each part of this system is described in this paper, with particular emphasis given to the PC-based online control system, the X-ray video-imaging system and the image-treatment system. Moreover, some of the experimental results, such as the phase transition of KNbO(3) nonlinear optical crystals and of blue bronze charge-density-wave material, are briefly presented.

New developments in multi-point die-cushion technology

An important and developing topic in sheet metal forming is the improvement of reproducibility of the deep drawing process. One key factor is the control of material flow by the corresponding control of the blankholder pressure. Conventional single or double-action press systems do not offer the means of adjusting a pressure profile that suits a specific part geometry in an optimal way. This causes increased tool run-in times, extended tool change times and high scrap rates for critical forming tasks. This paper describes a new generation of the multi-point-control system consisting of a hydraulic press, a multiple cylinder unit for the blankholding function and flexible forming elements as punch drive. Based on the principles of separating the blankholder function from the slide operation, a part-geometry related blankholder cylinder pattern and providing of centric loading of the forming elements, an improved process stability is achieved. The introduction of a PC-based control system using MS-Windows for the operator interface and a PLC as a software emulation ensures an easy handling of the complex parameter adjustments. An application in the field of stainless steel forming verifies the improvement of process control.

Fast PC-based data acquisition system for gas-filled position sensitive detectors

The high flux of the new generation of synchrotron radiation sources requires fast position sensitive detectors with high count rate data acquisition systems capability. Though the local count rate in a gas-filled position-sensitive detector is limited by the space charge effect, the integral rate will increase with the area of the detector. Thus, more than several 10 6 events per second can be achieved. Therefore, we developed a new PC-based histogramming and control interface (HCl) with an intrinsic dead time lower than 200 ns for linear and area X-ray detectors for time-resolved measurement applications. An overview of the complete acquisition system including a fast time-to-digital converter and image processing software will be given. The design principles and operating characteristics including experimental results obtained with a 100 mm linear delay-line detector at the SAXS beamline 5.2 in Elettra (Trieste) will be presented.

Vision-guided tripod material transport system for the packaging industry

A new lightweight parallel kinematic serves as the basis for a material transport system designated for the automated supply of packaging machines with the necessary paper and foil material. The manipulator, a modified Stewart platform, resembles an overhead tripod and is equipped with an air compressor and a PC-based control with a multitasking real-time operating system. It travels on a gantry railway, using on-board visual sensors for the location of the bobbins with packaging material that are to be transported. The intelligent sensors enable the manipulator to locate the proper bobbin in the quasi-disordered arrangement, depalletize it and transfer it to the requesting machine.

A synthetic medium for continuous culture of the S‐layer carrying Bacillus stearothermophilus PV 72 and studies on the influence of growth conditions on cell wall properties

Bacterial cell surface layers (S-layers) which show a crystalline structure, defined pores, and a regular arrangement of functional groups can be used for production of isoporous ultrafiltration membranes and as a matrix for immobilization of macromolecules. S-layer-carrying cell wall fragments from thermophilic Bacillaceae possess an extremely thin peptidoglycan-containing layer with pores larger than those in the S-layer lattice. Thus, they can directly be used for biotechnological applications, when an S-layer protein pool is stored in the rigid cell wall layer which is released during cell wall preparation, forming an inner S-layer. In the present study, a synthetic medium for Bacillus stearothermophilus PV 72 was developed by applying the pulse and shift technique with the aim to produce cell wall fragments with before-mentioned properties by varying the growth conditions in continuous culture. The organism was grown at 57 degrees C in a bioreactor with 1 L working volume equipped with exhaust gas analysis and connected to a PC-based process control system. Biomass concentration was 2.2 g/L out of 8 g/L glucose at a dilution rate of 0.3 h(-1), giving a biomass productivity of 0.66 g/L h. Although the organism was grown under different conditions, no change in peptidoglycan composition, extent of peptidoglycan crosslinking, and content of secondary cell wall polymers was observed. The amount of S-layer protein pool stored in the rigid cell wall layer and the autolytic activity depended mainly on the specific growth rate. Cell wall fragments with properties required for ultrafiltration membrane production could be produced by parameter settings in continuous culture.

Modeling and control of cnc machines using a PC-based open architecture controller

A PC-based open architecture computer numerical controller (CNC) is introduced to control milling machines. The controller is implemented on two systems: (1) a single-axis high speed milling machine using analog control signals where the PC-based controller assumes all CNC functions and (2) a three-axis milling machine controlled by digital signals where the existing CNC continues to monitor peripheral functions but the PC-based system generates the reference commands for the axes and spindle. System models are developed using sinusoidal inputs to build the frequency response functions of each axis drive. An experimental controller is implemented with the open architecture controller to maintain constant peak cutting force in the presence of uncertain machining conditions in end milling. An adaptive cross-coupling controller is also introduced to reduce tracking and contour error for a two-dimensional contour via the open architecture controller.

Practical Automation for Mature Producing Areas

Summary Successful installation and operation of supervisory control and data acquisition (SCADA) systems on two U.S. gulf coast platforms, prompted the installation of the first SCADA, or automation, system in Oklahoma in 1989. The initial installation consisted of four remote terminal units (RTU's) at four beam-pumped leases and a PC-based control system communicating by means of a 900-MHz data repeater. This first installation was a building block for additional wells tobe automated, and then additional systems, consisting of RTU's, a PC, and a data repeater, were installed. By the end of 1992 there were 98 RTU's operating on five separate systems (Fig. 1), and additional RTU's are being installed on a regular basis. The tangible and intangible savings generated by these automation systems have exceeded expectations in all cases. Downtime has been reduced by up to 83%, surface maintenance costs on beam- pumped wells have been reduced by an average of 40%, and the cost of well workovers for rod, tubing, and/or pump repairs has been reduced by 17% to 44%, depending on field conditions. These improvements have led to production increases of up to 30%. Additionally, spills have been significantly reduced and early detection of leaks, when they occur, has reduced the impact of these spills, enhancing the environmental compatibility of operations. This paper outlines the logical development of automation systems on properties in Oklahoma operated by Phillips Petroleum Co. Those factors critical to the success of the effort are (1) designing data-gathering and control capability in conjunction with the field operations staff to meet and not exceed their needs; (2) selection of a computer operating system and automation software package; (3) selection of computer, RTU, and end-device hardware; and (4) continuous involvement of the field operations staff in the installation, operation, and maintenance of the systems. Additionally, specific tangible and intangible results are discussed.

95/02158 PC-based instrumentation and control. Second edition

95/02158 PC-based instrumentation and control. Second edition

A PC-based water level controller for nuclear steam generators

An adaptive control was proposed early by Na and No (1990) for the control of the water level of steam generators. In this work the algorithm of the controller is changed a little. In order to know if this controller is robust in modeling errors and in high frequency measurement noises in controlling the water level of steam generators, a scaled-down steam generator is made which has the dimension of nearly one-tenth of the reference height and pressure, and 1/10,000 of its power. The controller is studied experimentally by implementing it to the mock-up of a nuclear steam generator. It is known that the controller is robust in unmodelled dynamics.

A modular integrated robot control system

The Modular Integrated Robot Control System (MIRCS) is a PC-based distributed control system for industrial robots. This system possesses expansibility and flexibility for the strict requirements of computation power and the complicated robot control. A host computer and several server computers constitute the hardware architecture of MIRCS. The host computer communicates with the other server computers in two ways: tight coupling by dual-port RAM and loose coupling by an Ethernet network. The hierarchical software architecture in MIRCS has several modules to make the system flexible and portable.

PC-Based Monitoring and Control System for Microwave Curing of Polymer Composites

Abstract Microwave, curing is increasingly being considered as an economically viable process in the production of polymer composite parts. Nevertheless, the improper control of microwave energy for industrial production, especially for the processing of thick laminates, can lead to quality problems such as the formation of voids, non-uniform heating, and over curing. In this paper, the design and development of Cure-Control for the monitoring and control of the microwave curing of polymer composite components is discussed. In particular, this paper discusses some of the quality and production issues, as well as the control of the process parameters such as pressure, temperature and the rate of power intensity. Preliminary experiments confirm the viability of the Cure-Control system in the monitoring and controlling the curing of polymer composite components. The work has the potential of being commercialised on a large-scale, on-line basis.

Implementation of a PC-based integrated control system for children

Children with severe physical disabilities often require a range of technological devices to and them with the fundamental tasks carried out in everyday life. These task areas may include mobility, communication, environment control and computer access for education. The most efficient, and often the most cost-effective, way of providing for these requirements is by the provision of a single, integrated system tailored to the individual's needs and abilities. BASIS, the Barnsley And Sheffield Integrated System, is an integrated control system based on a wheelchair-mounted personal computer (PC) and currently implements the following modules: wheelchair control; a spoken communication package; control of home equipment via infra-red; and a facility to run third-party software. The system presents a consistent and uniform environment to the user for selection and activation of these modules and can be controlled by one to four switches (scanning or directed access), a touch screen, a head pointer or a mouse. Safety considerations have played a central part in the design of the system. BASIS can be tailored to the user's requirements by editing a text file in software and by connecting the appropriate hardware modules to the serial and parallel ports. The graphical user interface has been designed for use by children and employs pictorial representation (icons) of available functions on a colour screen. These icons can be chosen from clip-art or drawn on computer drawing package. It is also possible to scan in and utilize drawings or photographs. The computer-based integrated system offers significant advantages over systems previously reported, which were based on logic-gate circuitry with feedback to the user via a LED array.

164 PC-based hierarchical manufacturing cell control

164 PC-based hierarchical manufacturing cell control

Nonlinear model predictive control of a fixed-bed water-gas shift reactor: An experimental study

This paper describes new results on the experimental application of nonlinear model-predictive control (NMPC) to a fixed-bed water-gas shift (WGS) reactor. The development and experimental validation of an appropriate first-principles WGS reactor model, and how it impacts controller performance is discussed. The implementation of NMPC is computationally intense, requiring that a large nonlinear program (NLP) be solved at each sampling period. The significant computational burden dictates that a relatively slow sampling rate be used. Infrequent sampling, however, diminishes disturbance rejection capabilities. To combat this problem, NMPC was implemented in a master- slave cascade configuration where a low-level liner controller, having a significantly faster sampling rate, was employed. The control study was performed using a PC-based distributed control system (DCS) . One of the three processors was dedicated to NMPC calculations. A complete and rigorous implementation strategy is described in the paper, and the performance of NMPC for set-point tracking of this nonlinear process is shown to be superior to adaptive or linear control. We also illustrate the ease with which NMPC accommodated feedforward control.

PC-based hierarchical manufacturing cell control

Robots in the industrial factory plant build the backbone for CIM, which is outlined to be the factory automation strategy of the future. In this paper a hierarchical manufacturing cell control system for robotic work cells is described. This approach is based on low-cost personal computer hardware and consists of two different control systems, one for the robot control tasks and another for the work cell control tasks. The underlying concept is based on a strategic architectural model for hierarchical manufacturing control, where it focuses on the process sequence coordination and the process control in the bottom hierarchical layers.

Computer-controlled float zone crystal growth

A PC-based computer control system to automate a high-temperature float zone growth of titanium carbide is reported. The control strategy of the computer control system relies on the relations derived from a combination of empirical relations and results from detailed mathematical analysis of the physical transports of the entire float zone assembly. A system control computer program was written to establish real-time determination of the size of the molten zone from a thermal image, control parameters from established relationships, and collected processed data to achieve control objectives. We found that the developed computer control allows the growth process to be operated nearer the stability limit. Any slight variations in growth conditions can be corrected in time to avoid any instability growth, which otherwise cannot be adjusted via manual control.

Adaptive mould level control for continuous steel slab casting

An adaptive controller was applied to mould level control for continuous steel slab casting. The controller is embedded within a PC-based real-time control program, named RTS. The work is the outgrowth of adaptive LQ designs which have been applied since 1981; a multivariable version of the adaptive controller is embedded within Connoisseur, a larger control system. Control of mould level for continuous steel slab casting involves a process whose model contains an integrator and oscillatory terms, noise and non-linearities, while the excitation of the actuation is poor. The combination is potentially devastating for adaptive controllers. The RTS controller incorporates filters, noise models and other techniques to deal with these problems. The on-line experiments offered insights into appropriate methodologies requiring interesting techniques for non-invasive monitoring and changeover from one controller to another so as not to affect normal production.

Microcomputer-based multi-tasking on a SCADA system using interrupts in MS-DOS

This paper describes a multi-tasking operation using interrupts in MS-DOS for PC-based supervisory control and data acquisition (SCADA) systems. The structure of a generalized interface circuitry is formulated to serve as a standard interface for SCADA application programs to be independent from the types of hardware interface. Communication between processes is implemented through a set of common memory areas declared in one process. A prototype SCADA system employing five different types of hardware interface has been implemented through one main process for SCADA applications, a clock-based interrupted process to handle the scanning and the transformation of different types of hardware interface, and a serial port interrupted process for the communication to the RTUs and another PC.

Flexible pneumatic actuators for horticultural robots—A feasibility study

A novel form of rotary pneumatic actuator, incorporating flexible, inflatable elements, has been investigated with a view to its use in closed loop position control applications. The characteristics of the patented actuator (registered trade name ‘Flexator’) have been analysed and a model predicting static torque produced, which is consistent with experimentally-derived data. Hysteresis is a significant feature of the characteristic and suggestions are made as to how this effect can be minimized. Modifications that allow the production of constant torque over full stroke, which can be a maximum of just under 360°, are also described. A PC-based digital controller, based on techniques already in use for more conventional pneumatic actuators, has been implemented on a one degree of freedom test rig. The dynamic performance achieved with steady state errors of ± 0.2° indicate it would be feasible to satisfy the specifications for a horticultural robotic manipulator using flexible rotary actuators.