Adaptive closed-loop control

Prior to some adaptive close-loop control schemes, we revealed some key factors, which control molecule dissociative ionization by limiting the laser pulse... 

All of this can be controlled using computer software, which should also include an adaptive learning algorithm, capable of computing the next step towards producing the optimum product yield and then tailoring the laser pulse in an appropriate way (this is termed adaptive closed-loop control). After each laser pulse,... 

The general concept for adaptive closed-loop control is shown in the lower panel of Figure 19.1. The sequence of events for adaptive closed-loop control is as follows ... 

Because the initial emphasis of this study was on extending ACC to liquid-fueled combustors, a simple closed-loop controller, which had been well tested in the previous studies involving gaseous fuel, was utilized. Such a controller, however, may not be effective in a combustor where the oscillation frequencies drift significantly with the control. The main problem was the frequency-dependent phase shift associated with the frequency filter. For such a case, it would be more useful to employ an adaptive controller that can rapidly modify the phase setting depending on the shift in the dominant oscillation frequencies. 

The outputs of the sensors were used in two closed-loop control strategies developed for combustor performance optimization [7]. The objective of the first strategy, based on an adaptive least-mean squares (LMS) algorithm, was to maximize the magnitude and coherence of temperature oscillations at the forcing frequency /o in the measured region. The LMS algorithm was used to determine... 

We have also performed experiments using an open-plus-closed-loop control technique [156] and adaptive control algorithm [157] to steer the system from... 

There are adaptive PCs. They are control system that changes the settings in response to changes in machine performance to bring the product back into its preset requirements or specification. The shift is maintained so that the control has adapted to changing conditions. It is a technique typically used to modify a closed loop control system. The process control comparator is the portion of the control elements that determines the feedback error on which a controller acts. 

Another fundamental state variable that can be regulated during the cycle is cavity pressure. Closed loop control of cavity pressure could automatically compensate for variations in melt viscosity and injection pressure to achieve a consistent process and consistency of molded products. Adaptive control methods have been developed to track the cavity pressure profile at one location in the mold. In these earlier works, cavity pressure control was handicapped by the absence of actuators for distributed pressure control, as conventional molding machines are equipped with only one actuator (the screw), which prevents the simultaneous cavity pressure control at multiple points in the mold. This problem has been solved with the development of dynamic melt flow regulators that allow control of the flow and pressure of the polymer melt at multiple points in the mold.[ °l... 

Contrary to this closed-loop control adapts the measured material properties and process parameters (current values) to the required values (set values). This is done by converting the signals supplied by the sensors into a controller output which influences final control elements such as control valves. A characteristic of the closed-loop control is the comparison between the current process signals and their respective setpoints. The controlled parameter permanently influences itself via the closed loop. 

Only a machine with independent closed-loop control on each station would (attempt to) prevent this effect, resulting in double the complexity and cost of the simulator machine itself. Some modem and advanced simulators featme the so-called adaptive control in their driver software. In those simulators, adaptation is made automatically during running tests. 

The lime feeding system may be controlled by an instrumentation system integrating both plant flow and pH of the wastewater after lime addition. However, it should be recognized that pH probes require daily maintenance in this application to monitor the pH accurately. Deposits tend to build up on the probe and necessitate frequent maintenance. The low pH lime treatment systems (pH 9.5 to 10.0) can be more readily adapted to this method of control than high-lime treatment systems (pH 11.0 or greater) because less maintenance of the pH equipment is required. In a close-loop pH-flow control system, milk of lime is prepared on a batch basis and... 

Pattern recognition self-adaptive controllers exist that do not explicitly require the modeling or estimation of discrete time models. These controllers adjust their tuning based on the evaluation of the system s closed-loop response characteristics (i.e., rise time, overshoot, settling time, loop damp-... 

Other recent developments in the field of adaptive control of interest to the processing industries include the use of pattern recognition in lieu of explicit models (Bristol (66)), parameter estimation with closed-loop operating data (67), model algorithmic control (68), and dynamic matrix control (69). It is clear that discrete-time adaptive control (vs. continuous time systems) offers many exciting possibilities for new theoretical and practical contributions to system identification and control. 

To evaluate the proposed adaptive control performance, opening of production choke and flow rate of injected gas at the well-head are random pulses as command signals, as shown in figure 5. The opening value of the production choke Upc also is the manipulated variable of the control strategy. Figure 6 shows noisy measurements and filtering outputs of closed-loop system, where variable variances of measurement noises are apparent. Note that Wpc illustrated the stabilized behavior of closed-loop system. 

An adaptive posi-cast controller has been developed for dynamic systems with large time-delays [17]. Recently, the authors evaluated its performance in the context of a 4-megawatt combustor mod >1 that mimics many of the dynamic characteristics of an actual engine includi g a significant time-delay [18]. Using closed-loop input-output data and syste.n identification (SI), a model of the test-rig was derived. The resulting expression of the SI model is... 

Using this model, adaptive posi-cast controllers were designed, and detailed numerical simulation studies were carried out. These studies consisted of (i) the closed-loop performance of the adaptive controller, (ii) comparison of the adaptive controller with an empirical phase-shift controller, (iii) robustness with respect to parametric uncertainties, (w) robustness with respect to unmodeled dynamics and uncertain delays, (i/) performance in the presence of noise. 

Figure 19.5 Pressure response of the closed-loop system using an adaptive low-order posi-cast controller with changes in frequency of a combustor model (a) changes of a resonant frequency and (6) pressure-time responses.

Figure 31.3 dramatizes the effect of the on-line adaptation on the quality of the closed-loop response versus the case of controlling without controller adaptation. 

Figure 31.4 shows the improved quality of the closed-loop response when the adapted control policy [eq. (31.14)] is used in comparison with the closed-loop response using the old process parameters. 

In general, it is difficult to make online measurement of product quality it is often an inferred entity based on experience. The moisture content can be a measured variable if a suitable moisture sensor is used in the process. Analyzers are available for moisture analysis, which can be adapted for automatic, closed-loop dryer control. The most successful of these units rely on infrared, microwave, or capacitance detection [1]. Care must be exercised in the selection to allow for changes in bulk density or for void spaces, which will... 

C. elegans being manipulated to travel along a closed loop by turning the acoustic field on and off with proper timing control (Image is adapted from Ref. [7] with permission)... 

Figure 19.1 Diagram showing the arrangement for closed-loop learning control. Following a femtosecond laser pulse, the products of the photochemical process are detected and compared with the user-defined objectives stored on the computer. A learning algorithm then calculates the modified electric fields required to shape the laser pulse and further optimize the yield of the desired product. Cycling through the loop many times gives the optimum pulse shape and best product yield. Adapted from Brixner et o/, Chem. Phys. Chem., 2003, 4 418, with permission of John Wiley Sons Ltd...

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