Actuating element

So far, we know that the secondary loop helps to reduce disturbance in the manipulated variable. If we design the control loop properly, we should also accomplish a faster response in the actuating element the regulating valve. To go one step further, cascade control can even help to make the entire system more stable. These points may not be intuitive. We ll use a simple example to illustrate these features. 

Here, we use L to denote the major load variable and its corresponding transfer function is GL. We measure the load variable with a sensor, Gnu., which transmits its signal to the feedforward controller GFF. The feedforward controller then sends its decision to manipulate the actuating element, or valve, Gv. In the block diagram, the actuator transfer function is denoted by G v. The idea is that cascade control may be implemented with the actuator, Gv, as we have derived in Eq. (10-1). We simply use G v to reduce clutter in the diagram. 

The piezoelectric stepper, nicknamed the louse, was the first successful stepper used in UHV STM (Binnig and Rohrer, 1982). A schematic of the louse is shown in Fig. 12.1. As shown, the actuating element of the louse is a piezoelectric plate (PP), which can be expanded or contracted by applying a voltage (100 to 1000 V). It is resting on three metal feet (MF), separated by high-dielectric-constant insulators (I) from the metal ground plate (GP). 

There are many different types of valve fitted with actuators to form control valves. Valves may be single- or double-ported (Fig. 7.123). With single-ported valves the valve plug is subjected to the total differential force across the valve. Such valves are sensitive to pressure fluctuations and powerful actuator elements are required for large pressure drops. Double-ported valves balance out the pressure differential but it is difficult to obtain complete shut-off. 

Ogure K., Kawami Y., Takanama H., An actuator element of polymer electrolyte gel-membrane-electrode composite Bull. Government Industrial Research Institute Osaka, 43 (1992) 21. 

The hydrodynamic transistors shown in Table 2 can be classified in two types distinguished by the function of the gel actuator. The actuator of type B acts as servo drive actuating the valve seat. The actuator of type B is directly placed within the flow channel. Therefore, the stimulant, which is typically a component of the process medium, directly controls the sensor-actuator element. The hydrogel swells or shrinks by absorption or release of the process medium and regulates the channel cross-section. Figure 1 shows two examples of such hydrodynamic transistors. 

It was established that the performance of smart structures depends on the quality of the bonding along the interface between the main structure and the attached sensing and actuating elements [295]. 

Thermal Activation. Most of the application examples of SM actuators presented so far rely on a thermal activation of the shape memory effect, i. e. the actuator element reacts according to the ambient temperature. Here is a short list of various application areas ... 

The two-way effect will be stabihzed after 20... 100 thermal and mechanical cycles. Due to the ability of the martensite (low-temperature phase) to form a twinned crystalline structure, different areas of the actuator element may be strained in different ways extension, compression, or shear are deformations that will be reverted to by heating. This variety offers the interesting opportunity to adapt the actuators shape change to the special needs of the actuating task. By this means, transmission links or gears may be eliminated, which helps reduce the size and price of a system. 

Tadokoro, S., Fuji, S., Fushimi, M., Kanno, R., Kimura, T., Takamori, T., Oguro, K. Development of a distributed actuation device consisting of soft gel actuator elements. In Proceedings of IEEE International Conference on Robotics and Automation, pp. 2155-2160 (1998)... 

Solar car Ma-Tech-Mentoring, 2010 Design and development of a remote-controlled model car with solar-powered drive power engineering (focus on photovoltaics), mechatronics, actuating elements... 

The operation of a regulator with an actuator element with phase control under production conditions (at a given temperature of 250 °C and a cycle time of 15 seconds) (see Figure 5.22) will now be considered. During plastic injection friction heat is generated in the nozzle gate, which causes a temperature rise by some 10 °C above the set level. It may be... 

Actuator elements necessary if the smart structure is designed to influence either its own behavior or the surrounding,... 

Actuators govern the flow of energy and mass streams in the process [25]. Through the actuators the controller output results in changes to the controlled variable (temperature, pressure, flow, level, and so on) and thus the control loop is closed. Actuators consist of the control positioner (for example, a valve positioner) and the actuator element. The control positioner transfers the signal output of the controller in a controlled movement to bring the actuator element into a new position. 

This chapter describes how to start experiments with ionic polymer-metal composite (IPMC) actuators. In the first part, a fabrication of IPMC actuator element is summarized. In the next part, how to setup a measurement system of IPMC actuator and test the actuator performance is described. In the last part, a control method of IPMC actuator is discussed. From the information in this chapter, experiments with IPMC actuators can be started. 

Abstract. A high redundancy actuator (HRA) is composed of a high number of actuation elements, increasing both the travel and the force above the capability of an individual element. This provides inherent fault tolerance if one of the elements fails, the capabihties of the actuator may be reduced, but it does not become dysfunctional. This paper analyses the likelihood of reductions in capabihties. The actuator is considered as a multi-state system, and the approach for fc-out-of-n G systems can be extended to cover the case of the HRA. The result is a probability distribution that quantifies the capability of the HRA. By comparing the distribution for different configurations, it is possible to identify the optimal configuration of an HRA for a given situation. 

The most general way to improve reliability in an efficient way is to use a greater number of smaller actuation elements. For example, a S3 tem with ten elements may still work with only eight of them operational. The reliability improves because two faults can be accommodated. At the same time, the overall capacity is only over-dimensioned by 25 %, making the system more efficient. This is the central idea of the high redundancy actuator (HRA). 

In an HRA, actuation elements are used both in parallel and in series (see Fig. 1). This increases the available travel and force over the capability of an individual element, and it makes the actuator resilient to faults where an element becomes loose or locked up. These faults will reduce the overall capability, but they do not render the assembly functionless. 

Section 2 deals with the basic terms and concepts used for the reliability assessment, and it defines the behaviour of individual actuation elements. In Section 3, the effect of series or parallel arrangement of elements on reliability is investigated. In Section 4, the special cases of series-in-parallel and parallel-in-series configuration is analysed for a simple 2x2 system. In Section 5, this concept is extended to configuration with multiple layers, and an exhaustive study of 4 x 4 systems is presented. The paper finishes with some conclusions in Section 6. 

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