Distributed actuation system

The adaptronic approach would be one that would borrow directly from the biological world. Materials that behave more or less like muscles can be used in adaptronic structures and are called induced strain actuators. When energy is applied to the actuators, they attempt to expand/contract and work against any load that is applied to them. The actuators are typically bonded to the surface of a structure, or embedded within the material. This means that the artificial muscles must now work against the inherent structural impedance of the component, just as hmnan muscles are parallel to the skeletal structure or bone. However, whereas the arm has discrete joints about which rotation occurs, the adaptronic structure may be a continuum, thereby necessitating a distributed actuation system. For example, the tip motion of a beam will not occur by rotating the beam about a joint but by inducing its deformation by means of induced strain actuators placed on the beam. 

Prahlad, H., Kombluh, R., Pelrine, R., Stanford, S., Eckerle, J., and Oh, S. Polymer power Dielectric elastomers and their applications in distributed actuation and power generation. Proceedings of ISSS International Conference on Smart Materials, Structures and Systems, Bangalore, India, July 28-30, 2005, SA-13, pp. 100-107. 

Figure 22.1 Schematic of feedback control system with distributed actuators...

The ISA symbology provides different symbols for different types of actuators. Furthermore, variations for the controller symbol distinguish control algorithms implemented in distributed control systems from those in panel-mounted single-loop controllers. 

Prahlad H, Kombluh R, Pelrine R, Stanford S, Eckerle J, Oh S (2005) Polymer power dielectric elastomers and their applications in distributed actuation and power generation. In Proceedings of ISSS 2005 international conference on smart materials structures and systems, pp SA-lOO-SA-107... 

Brignell, J.E. Sensors in distributed instrumentation systems. Sens. Actuators, 10 (1986), pp. 249-261... 

The pilot plant has a Distributed Control System by ABB Automation, model Sattline. All the sensors and actuators are connected to the DCS. The DCS program has to be developed taking into account the integration architecture framework described in Section 5. Therefore it was necessary to describe the plant following the S88 terminology. Description of the Control Module (only reactor R1 is shown). Equipment Module (only reactor R1 is shown). Master Recipe (full recipe for the two products) and Control Recipes (only product PI and Equipment Eql is shown) are given next. 

Figure 22.11b shows the distribution of system stiffness in the radial direction (perpendicular to the needle) at the needle entry point (z = 500 mm). The figure shows that system stiffness is quite uniform although absolute values are low. Recall that, for this prototype, system stiffness is limited by the low forces of the handmade DBAs. Developing higher stiffness requires actuators with higher force output. To meet the clinical requirements on needle insertion forces, it is estimated that the number of active layers must increase from 2 to 30, which is technically feasible with proper actuator manufacturing techniques [24]. 

APC, MPC and RTO require modem instrumentation, which includes actuator valves, distributed control systems (DCS), high-flux data highways, analyzers, and dedicated computers. They also require trained support staff, which at this writing is in short supply. 

Single-loop controllers with auxiliary power use compressed air or, more commonly now, electrical power to receive and transmit signals. These devices are much more accurate than those without the auxiliary power also they are not integrated in the measurement apparatus or the actuator. Distributed control systems are rapidly replacing the single-loop controller panel boards unless only a small number of control loops are involved. 

The functionality of the PLC has evolved over the years to include sequential relay control, motion control, process control, distributed control systems, and networking. The data handling, storage, processing power, and communication capabilities of some modem PLCs are approximately equivalent to desktop computers. A major advantage of PLCs is that it is typically armored for severe conditions, such as dust, moisture, heat, cold. Also, PLCs have the facility for extensive input/output (I/O) arrangements for connecting the PLC to sensors and actuators. 

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