Robust actuator

In order to control the air supply of what is known as an atmospheric appliance, the main challenge lies in finding a low-cost and robust actuator to achieve an optimal air ratio. Numerous methods are mentioned in the relevant literature and in patent specifications. Unfortunately, most of these concepts are far too costly and elaborate to be used in serial production. Despite these difficulties there have been some promising approaches. 

Prom an engineering practice point of view, the actuators for civil structures are most interesting. Simple and robust actuators are necessary. There are only few practical examples of actuators for civil structures. Figure 8.56 shows an example of an actuator with variable damping showed by Kawa-shima and Unjoh in [188]. 

A. Friedberger, R. Kreisl, E. Rose, G. Muller, G. Kuhner, J. Wdllenstein, and H. Bottner. Micromechanical fabrication of robust low-power metal oxide gas sensors . Sensors and Actuators B 93 (2003), 345-349. 

The outline of this paper is as follows. First, a theoretical model of unsteady motions in a combustion chamber with feedback control is constructed. The formulation is based on a generalized wave equation which accommodates all influences of acoustic wave motions and combustion responses. Control actions are achieved by injecting secondary fuel into the chamber, with its instantaneous mass flow rate determined by a robust controller. Physically, the reaction of the injected fuel with the primary combustion flow produces a modulated distribution of external forcing to the oscillatory flowfield, and it can be modeled conveniently by an assembly of point actuators. After a procedure equivalent to the Galerkin method, the governing wave equation reduces to a system of ordinary differential equations with time-delayed inputs for the amplitude of each acoustic mode, serving as the basis for the controller design. 

An extensive series of studies is conducted to investigate the effects of various weighting factors associated with the mechanical energy of the oscillatory field ((/), actuation energy (r), plant disturbance (a), and sensor noise (/ ) on the robustness and performance of the controller. Also included in the parametric investigation are the affordable bound of system dynamics uncertainty (I/7) and the maximum time delay of the distributed combustion of control fuel 5t). Results indicate that... 

MEMS technology also allows embedding of actuators and sensors in single reactor channels. Despite problems with temperature robustness, a solution must be found to transport the signals from the micro channels to the central process control system. To avoid a confusing cable set-up ( spaghetti conditions ), it is desirable to process the sensor data on-site, for example in an A/D converter, and to feed the digital data in a common bus system [13]. 

The literature focused on model-based FD presents a few applications of observers to chemical plants. In [10] an unknown input observer is adopted for a CSTR, while in [7] and [21] an Extended Kalman Filter is used in [9] and [28] Extended Kalman Filters are used for a distillation column and a CSTR, respectively in [45] a generalized Luenberger observer is presented in [24] a geometric approach for a class of nonlinear systems is presented and applied to a polymerization process in [38] a robust observer is used for sensor faults detection and isolation in chemical batch reactors, while in [37] the robust approach is compared with an adaptive observer for actuator fault diagnosis. 

Despite the optimistic overtones, robust control is not a solved problem. Some difficult theoretical questions remain in the synthesis area. The available software is, at best, experimental the controller is complex and its structure is not obvious. It generally uses all the measurements and all the manipulated variables in a centralized fashion. On-line tuning is difficult except when the IMC structure is employed [8], Fault tolerance, that is, continued satisfactory or at least stable performance in the event of an actuator or sensor failure, cannot be guaranteed. 

The optimal robust controller designed with one of the new synthesis techniques is generally not of a form that can be readily implemented. The main benefit of the new synthesis procedure is that it allows the designer to establish performance bounds that can be reached under ideal conditions. In practice, a decentralized (multiloop) control structure is preferred for ease of start-up, bumpless automatic to manual transfer, and fault tolerance in the event of actuator or sensor failures. Indeed, a practical design does not start with controller synthesis but with the selection of the variables that are to be manipulated and measured. It is well known that this choice can have more profound effects on the achievable control performance than the design of the controller itself. This was demonstrated in a distillation example [17, 18] in which a switch from reflux to distillate flow as the manipulated variable removes all robustness problems and makes the controller design trivial. 

The ability to fill a device with many different fluids in different channels and chambers allows for the implementation of a simple and robust geometric method of metering solutions. The principle behind this scheme is to set up a geometry in which two microfluidic chambers may be primed with different solutions and connected via a fluidic interface that is controlled by a microfabricated valve (Fig. 11.4). With a central interface valve closed, the two chambers are first deadend filled with two different solutions using the POP technique. Once both chambers have been completely filled, containment valves are actuated, isolating the chambers from the rest of the chip. The interface valve is then opened, creating a... 

Each pair of chambers is connected to the protein sample and one of 48 crystallization solution reservoirs. The chip has 480 integrated valves that are actuated through three separately addressable control lines. As a precaution, 48 safety valves are included at the solution inlets to avoid the unwanted loss of protein sample in the unlikely event of an interface valve failure. The remaining two lines simultaneously control all interface and containment valves. By virtue of this parallel architecture and the robustness of the BIM scheme, solutions of varying viscosity, surface tension, pH and ionic strength may be simultaneously metered and mixed at three different mixing ratios using only two hydraulic control lines. 

Mortimer, A.G. and Reed, G.R, Development of a robust electrochemical oxygen sensor, Sens. Actuators B Chem. 24 (1995) 328-335. 

Horizontal vibrating screens require less headroom than the inclined type, but, because they do not utilise gravity, require higher levels of vibration and need to be more robustly built. The mats also need to be more resistant to abrasion. They are generally actuated by linear vibration inclined at 45° towards the discharge of the screen to help transport the material. 

Modeling the actuation response of IPMC for robust control of IPMC actuators is described in references 12 and 13. [12—13] Step response of actuators can be used for identification of actuator dynamics to derive a second order transfer... 

Robust ionic electroactive materials have been synthesized, where the strength and electroactivity can be tailored by controlling the extent of crosshnking and other synthetic strategies. These EAP based materials and actuators can undergo rapid... 

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