Application of distributed control on smart structures

The proposed project aims at bridging the gap between industry and academia in the field of smart structures. The motivation comes from the aerospace and automotive industries where the growing popularity of light composite structures introduces demand to attenuate very tightly packed weakly damped flexible modes. For a while now, in aerospace, lightweight is one of the key words. A few kilograms more on a satellite have a dramatic impact on the cost. Manufacturing equipment like robots need to be light to guarantee quick response and to reduce energy cost. Lightweight agricultural machines are preferred to avoid soil compaction and degradation. Architects seek light materials to create artistic buildings. In ground transportation, vehicle manufacturers also try to minimise the weight to reduce fuel consumption. With the emergence of electric vehicles, lightweight became even more important. In all cases, it is not just a matter of decreasing the weight but also preserving or increasing stiffness and dynamic properties of the construction. Therefore, new materials, which often happen to be composites, are increasingly used. Aerospace uses for a long time composite materials and sports equipment e.g. bike parts, sticks, rackets, cars, sleds, contain these materials too. In automotive, body parts are constructed from new materials. The passenger cell of the LifeDrive concept of BMW’s new electric vehicles will consist of carbon-fibre reinforced plastic (CFRP). One of the major issues of such materials is their extremely low material damping, similar to steel or aluminium. To solve this problem, in actual cars, trim material is used and additional masses are added to attenuate vibrations and improve acoustic comfort in the passengers’ compartment. To further reduce the weight of the vehicle, one must get rid of the trim material. Additionally, to reduce low frequency noise and vibrations it is favourable to have a greater mass which is conflicting with the lightweight requirement. Therefore, instead of using passive means, the active damping concept has been introduced, realised by adding actuators and sensors to the system and counteracting the vibrations of the structure by means of a controller. This active structure or smart structure concept is actually very multi-disciplinary in which control, structural modelling, actuating and sensing, and new materials are combined, covering different sectors ranging from aerospace, automotive, civil and manufacturing applications to the domain of leisure sports and health-care.

The project objectives are to be achieved by a tandem between a high level academic, well established partner in the control community: CTU in Prague, and the industrial partner LMS, well embedded in aforementioned industrial sectors. Scientifically, the novelty is in introducing distributed control concepts in the world of flexible structures and vibrations. Through a dedicated training program, the potentials of the modern paradigm of spatially distributed control using arrays of actuators and sensors for smart (mechanical) structures will be investigated. Recent advances in sensors and actuators make the concept of large and dense arrays of sensors and actuators a feasible and attractive option for large flexible structures. Rather than controlling the mechanical structure through a small set of isolated points, a dense array will be considered which approaches the behaviour of a spatially continuous distributed actuator. This invokes spatially distributed control, whether the actual controller will be centralized or also distributed. The key focus of the project is on providing a multi-disciplinary training in mathematical modelling, involving the structures, actuators and sensors, and on the control design to two ESRs. To develop entrepreneur skills, the ESRs will be building a demonstrator that shall serve for experimental verification and facilitate dissemination of the project results to a larger audience, other than purely scientific one.

The primary objective of this Marie Curie EID is to provide a training program to two young researchers on active structures, to familiarize them with engineering tools commonly used in industry and to bring them in contact with working in industrial development.

An important ingredient of any active damping scheme is the control law. Relatively simple control laws, like direct velocity feedback, acceleration feedback, integral force feedback, etc. have been applied successfully. Preferably, collocated control is used in which sensing and actuation is performed at the same location. In this way a fairly good performance and robustness can be achieved. By such kind of control though, one is always restricted to the control of just one or a few modes by actuating at a few locations of the structure. Industrial structures however are very often characterized by a high modal density. Applying the aforementioned control strategies to industrial problems gives disappointing results. Therefore there is a need to use another type of control methodologies, and recent advances in MEMS sensors and (micro)actuators, and progress in computational power pave way to massive development of distributed control.

The secondary objective of the proposed project is to explore potentials of distributed control for vibration dampening in lightweight structures. The controller itself (not just actuation and sensing) could be also distributed (in the form of an array), which remains to be determined within the project.

From a technological point of view the piezo-materials, which are commonly used in this context, present a feasible approach. A useful feature of piezo-materials is that they are normally available in different forms e.g. stacks or films.  In this way, they can be easily integrated in structures as trusses in framework structures or a patch or even a layer in a composite material. Therefore, they are extremely useful in lightweight structures as they are not an ‘add-on’, introducing extra mass, but can be made an integral part of the structure. When they are applied as a film in a lot of small patches, spatially distributed actuator can be considered which assumes a form of an array. For certain spatially large systems, an advantage can be seen in avoiding the need for centralized controller.