Continuous damping control

Liu et al. also studied LIPN systems for damping control in coating applications [Liu et al, 1995]. A polystyrene (PS)/polyacrylate (PAcr) latex IPN was synthesized in a two-stage emulsion polymerization. Crosslinked PS was synthesized first as the seed polymer by a semi-continuous process,... 

FIG 5 19. The proportional characteristic of a continuous nonlinear controller displays variable damping. 

If the reactor is stable, based on its heat transfer characteristics, as discussed earlier with regard to continuous reactors, control of temperature will be simplified. The reactor will respond rapidly, with a period of perhaps 20 min, and 10 percent proportional band may be sufficient for effective damping. All three control modes should be adjusted while at the operating temperature. 

Hence, our first step is to use root locus to find the closed-loop poles of a PI control system with a damping ratio of 0.8. The MATLAB statements to continue with Example 4.7B are ... 

With continuous systems we made root locus plots in the s plane. Controller gain was varied from zero to infinity, and the roots of the closedloop characteristic equation were plotted. Time constants, damping coefficients, and stability could be easily determined from the positions of the roots in the s plane. The limit of stability was the imaginary axis. Lines of constant closedloop damping coefficient were radial straight lines from the origin. The closedloop time constant was the reciprocal of the distance from the origin. 

So we can design sampled-data controllers for a desired closedloop damping coefficient by adjusting the controller gain to position the roots on the desired damping line. Some examples will illustrate the method and will point out the differences and the similarities between continuous systems and sampled-data systems. 

Up to this point we have dealt with processes which give worse control performance when sampled-data control is used than when continuous control is used. We have demonstrated this effect quantitatively by showing that ultimate gains and gains that give a desired closedloop damping coefficient decrease as T, is increased. 

Electrorheological (ER) fluids are materials whose rheological properties (viscosity, yield stress, shear modulus, etc.) can be readily controlled using an external electric field. For example, in some cases, they can switch from a liquid-like material to a solid-like material within a millisecond with the aid of an electric field, by means of the so-called ER effect.1617 The unique feature of the ER effect is that ER fluids can reversibly and continuously change from a liquid state to a solid state. ER fluid research is focused mainly on the automotive and robotics industry as electrical and mechanical interfaces for applications such as clutches, brakes, damping devices, fuel injection, and hydraulic valves. However, more recently, there is growing... 

A more robust method involves preheating the air 10-20°C above ambient. This increases the low adsorptive capacity of the air and ensures that drying continues throughout winter. Less basic versions recycle the heated air within an enclosed space and in effect function as a uninsulated, low-temperature kiln. Such an operation has attractions where damp winters make air-drying very slow. They are cheap, and capital is often limited for small companies. Low-temperature, low-cost driers provide some control over the drying elements that is lacking in air-drying. 

For some processes no cycling of the controlled variable is desirable, for example, because the oscillations might be amplified in process units downstream. In other processes, continuous cycling is not objectionable so long as the controlled variable always lies within a specified range. In still other processes a temporary oscillation which damps out quickly may be required. 

Oscillatory States in the CSTR limit Cycles.— The nature of the diemically open system makes it an ideal vehicle for studying reactions which odiibit chemical oscillations. The continuous supply of reactants diminates damping from reactant depletion inevitable in closed systems and permits the experimental establishment of true limit-cycle behaviour. However, not all oscillations in the CSTR need be kinetically interesting in their origin (e.g. the periodic variations in temperature and concentrations in reactors run with feedback control More importantly from the combustion researcher s viewpoint, oscillations may arise between multiple stable steady states of any normal exothermic reaction because of restric-... 

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