Closed-loop Control Applications Research Articles

Dual-anode magnetron sputtering

Reactive sputtering of dielectrics suffers from an anode problem, which appears when the anode becomes coated with a dielectric layer. A solution to the anode problem is a self-cleaning anode system. It can consist of two anodes and a single magnetron driven by a mid-frequency AC power supply via a center-taped transformer. The anodes are connected to the ends of the secondary coil of the transformer, while the magnetron to its center tap. Such a novel configuration is called dual-anode sputtering system, and has been developed in this work. This configuration creates a self-cleaning regime for both anodes, and provides dynamically cleaned and sustainable anodes. To provide biasing, the substrate holder is connected to the magnetron through a resistor and/or additional floating power supply. Introducing dual anodes does not restrict application of closed-loop control for high rate deposition of transparent and scratch-resistant Al2O3 films. High-rate deposition of dielectrics, using biased dual-anode reactive sputtering, has been proved to be a reliable technology for making dense Al2O3 and other films.

Closed-loop identification and control application for dissolved oxygen concentration in a full-scale coke wastewater treatment plant

The objective of this paper is to apply a closed-loop identification to actual dissolved oxygen control system in the coke wastewater treatment plant. It approximates the dissolved oxygen dynamics to a high order model using the integral transform method and reduces it to the first-order plus time delay (FOPTD) or second-order plus time delay (SOPTD) for the PID controller tuning. To experiment the process identification on the real plant, a simple set-point change of the speed of surface aerator under the closed-loop control without any mode change was used as an activation signal of the identification. The full-scale experimental results show a good identification performance and a good tracking ability for set-point change. As a result of improved control performance, the fluctuation of dissolved oxygen concentration variation has been decreased and the electric power saving has been accomplished.

Web-interfaced, force-reflecting teleoperation systems

An ever-growing number of Internet-connected devices is now accessible to a multitude of users. Being a ubiquitous communication means, the Internet could allow any user to reach and command any device connected to the network. This paper reports the successful application of real-time closed-loop control over the Internet in the Java Based Interface for Telerobotics (JBIT) system, in which Internet users can access and command a two-degrees-of-freedom robot in real time, receiving both visual and force feedback. When the closed-loop control of a remote system comes into play, careful evaluation of the performance and limits of the communication system in use is mandatory. The analysis reported shows that the main limits of the Internet are the unknown available throughput, the variable delay, and the loss of some data packets, in particular, when the network is congested. Once the limits of the communication system are known, it is shown that it is possible to use the Internet for the remote closed-loop control of a slave robot, provided that suitable strategies to guarantee operability and safety of the controlled system have been implemented. The strategies implemented in order to overcome the limits posed by the present Internet characteristics are described, along with an improved coordinating force control scheme, which enhances the transparency of the teleoperator.

In situ combustion measurements of CO, CO 2, H 2O and temperature using diode laser absorption sensors

A diode-laser sensor system based on absorption spectroscopy techniques has been developed to measure CO, CO 2 , and H 2 O concentrations and gas temperature non-intrusively in the combustion and exhaust regions above a C 2 H 4 -air burner operating at atmospheric pressure. In situ measurements of CO concentration in the combustion region (1.5 cm above the burner) and in the exhaust (79 cm above the burner) were determined from absorption lineshapes of the R(30) and R(15) transitions (2ν band) near 2.3 μ m, respectively, using new research-grade GaSb-based diode lasers. A minimum detectivity of less than 10 ppm was demonstrated in the exhaust region. In situ measurements of H 2 O concentration and gas temperature were determined from absorption lineshapes near 1.343 μ m (ν 1 +ν 3 band), 1.392 μ m (2ν 1 , ν 1 +ν 3 bands), and 1.799 μ m (2ν 2 +ν 3 ←ν 2 band) using distributed feedback (DFB) diode lasers. In situ measurements of CO 2 were recorded using a DFB laser near 1.997 μ m (R [50]) transition, ν 1 +2ν 2 +ν 3 band). Gas temperature and H 2 O and CO 2 concentrations were monitored simultaneously along a single path in the combustion region (1.5 cm above the burner surface) using a wavelength-multiplexing arrangement. The CO, CO 2 , and H 2 O concentration measurements in the combustion region agreed with calculated equilibrium populations to within the experimental uncertainty (10% for CO 2 and H 2 O, 5% for CO), and the measured temperatures were in agreement with radiation-corrected type-S thermocouple values to within 4%. These results demonstrate the utility of diode laser sensors for fast in situ measurements of multiple important combustion parameters for emissions-monitoring and closed-loop control applications.

Closed‐loop control of gas pressure in the gas‐assisted injection molding process

This paper is concerned with the practical application of closed-loop control on the gas pressure during the gas-assisted injection molding process. In principle, the gas-injection process can be treated as a valve-controlled tank charging. One of the critical factors for the successful application of the process is the obtaining and maintaining of a desired gas injection pressure within the polymer melt in the mold cavity. Most of the currently available commercial gas-injection machines operate either in an open-loop manner or with closed-loop control, relying upon manual tuning of the associated controllers. This is not only time consuming but also lacking in measurable performance. To improve the controller tuning problem while retaining the currently used controller structure, this study implements a control method which combines system identification and optimal linear quadratic regulator theory into an analytic approach. To demonstrate and verify the proposed method, several experiments were conducted. The results of these experiments show that the approach has excellent potential for designing a control system for regulating gas pressure variation during the gas-assisted injection molding process. © 1999 John Wiley & Sons, Inc. Adv Polym Techn 18: 137–145, 1999

Muscle fatigue from intermittent stimulation with low and high frequency electrical pulses

Objective: To evaluate muscle fatigue resulting from intermittent low frequency and high frequency stimulation for the application of closed-loop control in functional electrical stimulation (FES). Design: Nonrandomized trial. Setting: General community, a referral center, institutional practice, and ambulatory care. Patients: Twenty healthy nondisabled men volunteered for the normal muscle group. Four paraplegic men with implanted percutaneous intramuscular electrodes for FES volunteered for the paralyzed muscle group. Intervention: The stimulation frequency was set at low (20Hz) or high (100Hz). Stimulation was administered in 4-second bursts at the start of 60-second, 120-second, and 240-second periods (duty cycles of 1 15 , 1 30 , and 1 60 , respectively). Main Outcome Measurements: Knee extensor torques were measured during intermittent electrical stimulation. A strength decrement index (SDI) was used to assess muscle fatigue. Actual knee extensor torques in the paraplegic men were also measured with an isokinetic dynamometer. Results: Muscle fatigue was significantly greater at 20Hz than at 100Hz for both the nondisabled and the paraplegic subjects ( p < .0001). Muscle fatigue at the 1 15 cycle was significantly reduced ( p < .01). Conclusions: Muscle fatigue was greater at the lower frequency (20Hz) than at the higher frequency (100Hz) during intermittent electrical stimulation, suggesting that intermittent high frequency stimulation may be valuable in the development of closed-loop control strategies for FES.

Closed-loop control of gas pressure in the gas-assisted injection molding process

This paper is concerned with the practical application of closed-loop control on the gas pressure during the gas-assisted injection molding process. In principle, the gas-injection process can be treated as a valve-controlled tank charging. One of the critical factors for the successful application of the process is the obtaining and maintaining of a desired gas injection pressure within the polymer melt in the mold cavity. Most of the currently available commercial gas-injection machines operate either in an open-loop manner or with closed-loop control, relying upon manual tuning of the associated controllers. This is not only time consuming but also lacking in measurable performance. To improve the controller tuning problem while retaining the currently used controller structure, this study implements a control method which combines system identification and optimal linear quadratic regulator theory into an analytic approach. To demonstrate and verify the proposed method, several experiments were conducted. The results of these experiments show that the approach has excellent potential for designing a control system for regulating gas pressure variation during the gas-assisted injection molding process. © 1999 John Wiley & Sons, Inc. Adv Polym Techn 18: 137–145, 1999

CMAC neural networks for control of nonlinear dynamical systems: Structure, stability and passivity

The cerebellar model articulation computer (CMAC) neural network (NN) has advantages over fully connected NNs due to its increased structure. While its advantages over conventional control techniques have been recognized in the literature, it has primarily been used in system identification and pattern recognition, but not in control applications. This paper attempts to provide a comprehensive treatment of CMAC NNs in closed-loop control applications. Novel weight-update laws are derived that guarantee the stability of the closed-loop system. The passivity properties of the CMAC under the specified tuning laws are examined and the relationship between passivity and closed-loop stability is derived.

Digital controller design — Alternative emulation approaches

The emulation approach to digital controller design involves two steps: (1) the design of a continuous controller to satisfy performance and robustness objectives, and (2) the conversion of the continuous controller into a digital controller with the objective of obtaining comparable closed-loop system properties. This paper addresses the second step of the emulation approach. Previously developed methods are discussed, and several new methods are shown to be effective in accounting for computational delay and for sample-and-hold delay in closed-loop control applications. When the step response of the digitally controlled system is required to be closed to that of the corresponding continuous system, the selection of the sampling period T and the emulation performance are related in a fundamental way. This is illustrated in a closed-loop example.

Closed-loop control for anesthesia breathing systems

Numerous medical applications of closed-loop control have been developed over the past 40 years. For the patient breathing system, appropriate sensors are available. Feedback controllers have been developed and tested. Gas and vapor delivery devices seem ready for use. With the sensors, controllers, and delivery devices developed and tested, it seems likely that closed-loop control will be an integral part of future anesthesia workstations. The convenience and improved stability and response time will be important advantages in future anesthesia delivery systems.

A reduced-delay sampled-data hold

A data holding scheme whose phase delay is significantly less than that of the usual zero-order-hold is presented. Lower sampling rates may thus be used in closed-loop control applications. The improvement is achieved by means of simple additional software. A standard ZOH device is employed. Graphs of the resulting frequency response are presented. An example is included.

A Three Phase Sine Wave Reference Generator For Thyrisitorised Motor Controllers

A variable frequency, variable amplitude three-phase low frequency sine wave reference generator is discussed in this paper. The frequency and amplitude are independently capable of being varied by means of two independent dc control voltages. This reference generator is well suited for closed loop control applications such as constant frequency power supplies, constant amplitude power supplies, induction motor control requiring a finite ratio between amplitude and frequency, etc. The reversal of polarity of the dc voltage controlling the frequency reverses the phase sequence. The reference generator has been very satisfactorily used in the control of a three-phase ``subharmonic'' pulse width modulated inverter. The reference generator is also suitable for cycloconverter control.

On-line computer applications in the electric power industry

In two areas of major importance to the electric power industry-interconnected system operation and steam-electric energy conversion--on-line computer use has expanded during the past five years to applications of increasing complexity and importance. In systems operation, direct digital control is now in successful operation, and many aspects of system security are now monitored by centralized computers. In generating plants on-line computer use has progressed beyond simple data logging; it currently includes some closed-loop control applications, and will be applied to complete boiler control with assemblies now being installed. Simulation and analysis have played an important role in these advances in the application of on-line digital computers.