Actuator saturation

While one of the most critical factors that determines the performance of a servo system is the closed-loop bandwidth (Skogestad and Postlethwaite 2005) (i.e., active frequency range, within which disturbance inputs are successfully rejected and reference inputs are accurately followed), there are also important limitations that determine the achievable bandwidth in a servo system arising typically from the dynamics of the plant and controller such as unstable zeros and delays, umnodeled dynamics, vibration modes, actuator saturations, and... 

The Limitations Due to Actuator Constraints. Disturbance directions for which the steady-state DC exceeds the actuator constraints are those in which offset is incurred because of actuator saturation. Assuming that the process model has been scaled such that inputs are constrained to lie within m 1, steady-state DC values above unity indicate that the actuator constraints are exceeded, and hence, such flowsheets should be avoided or modified to ensure adequate regulation. 

Butler [27] formulated a LFR for smart structures based on measurement errors during the identification process. Based on this uncertainty model, mixed H l /Hoo controllers [29] were designed incorporating actuator saturation. 

Butler, R. Rao, V.S. Sana, S. Design of Robust Controllers for Smart Structural Systems with Actuator Saturation. J. of Intelligent Material Systems and Structures, 8, no. 9 (1997), pp. 721 811... 

Most of the integrated plant and control system design studies have used linear control systems such as multi-loop PI control, and do not accommodate actuator saturation discontinuities. However, promising recent approaches include strategies for incorporating actuator saturation into a simultaneous optimization framework [33], and controller parametrization that accommodates saturation behavior [34]. Application of these techniques to more complex problems within an integrated design and control framework, as well as the consideration of other more complex control systems, would be useful. 

Viscosity measurements were made with two Cannon-Ubbelohde viscometers, and timing was by an optical device actuating an electronic timer (Wescan Instruments, Inc.). An air thermostat was used. The viscometers were calibrated with redistilled air-saturated water over the range 10°-50°C. The kinetic-energy correction was used in the form ... 

Since actuators are subject to saturation, the phenomenon of integral windup must be properly tackled namely, if the controller outputs a command beyond the... 

Sample preparation 2 mL Whole blood or plasma -l- 2 mL buffer -I- 5 mL chloroform isopropanol n-heptane 60 14 26, shake gently horizontally for 10 min, centrifuge at 2800 g for 10 min. Remove the lower organic layer and evaporate it to dryness under vacuum at 45°, reconstitute the residue in 100 pL mobile phase, centrifuge at 2800 g for 5 min, inject a 50 xL aliquot of the supernatant. (Buffer was saturated ammonium chloride solution 25% diluted with water, actuated to pH 9.5 with 25% ammonia solution.)... 

Thus, the influence of the medium DO concentration in the fermentation was investigated. Fermentations were carried out with DO concentration set points at 1.0, 4.0, and 6.0 mg/1. Those values correspond, respectively, to 14, 57, and 86% of the saturation concentration of oxygen that was equal to 7.0 mg/1 in the defined fermentation conditions. This value was calculated using an expression stated by Blanch and Clark [20] for the temperature and medium composition used in the experiments. The control system (with the PLC) actuated in the oxygenation device to raise the oxygenation rate (for example, raising the oxygen gas pressure) any time that the DO concentration in the medium got below the set point. 

In (c) and (d) the response AVto saturated hydrocarbons at 600°C as a function of equivalence ratio a is given, as well as the response to unsaturated hydrocarbons at temperatures of 100-400°C and concentrations well below the equivalence ratio. The equivalence ratio is defined as the ratio of the actual fuel-to-oxidizer ratio to the stoichiometric fuel-to-oxidizer ratio. Panels (a) and (b) are reprinted with permission from the Journal of Applied Physics 98 3 (2005), 034903. 2012 American Institute of Physics (Eriksson eta ., 2005). Panel (c) is reprinted with permission from Sensors and Actuators B43 (1997), 52-5. 1997 Elsevier (Baranzahi ef a/., 1997). Panel (d) is reprinted with permission from the Proceedings of the IEEE International Conference on Sensors, Atlanta, Georgia, USA, October 2007, 493-4. 2007 IEEE (Andersson etal., 2007)... 

The actuation properties of IPMC are presented in. [6—10] By applying a voltage of 0.2-3 V on an IPMC film, bending towards the anode occurred. An increase in voltage level (up to 6 or 7 V) causes larger bending displacement along with nonlinear saturation in displacement. IPMCs also work very well in water or blood environments. 

PPy layers that forms the outside layers on either side of a polymer electrol5de layer in the middle. The pol5mier electrolyte layer could be solid state electrolyte or electrol5de saturated media (i.e., porous PVDF film). Once a voltage is applied, one PPy layer performs as cathode and the other performs as the anode. Since oxidation and reduction occur separately at both sides, expansion and contraction on each side will cause bending actuation (Fig 4.9). 

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