Abstract
Future machines will require distributed actuation integrated with load-bearing structures, so that they are lighter, move faster, use less energy, and are more adaptable. Good examples are shape-changing aircraft wings which can adapt precisely to the ideal aerodynamic form for current flying conditions, and light but powerful robotic manipulators which can interact safely with human co-workers. A 'tensegrity structure' is a good candidate for this application due to its potentially excellent stiffness and strength-to-weight ratio and a multi-element structure into which actuators could be embedded. This paper presents results of an analysis of an example practical actuated tensegrity structure consisting of 3 ‘unit cells’. A numerical method is used to determine the stability of the structure with varying actuator length, showing how four actuators can be used to control movement in three degrees of freedom as well as simultaneously maintaining the structural pre-load. An experimental prototype has been built, in which 4 pneumatic artificial muscles (PAMs) are embedded in one unit cell. The PAMs are controlled antagonistically, by high speed switching of on-off valves, to achieve control of position and structure pre-load. Experimental and simulation results are presented, and future prospects for the approach are discussed.
Highlights
Efficient aircraft are desirable for both environmental and economic reasons
4.3 Simulation results Two sets of simulation were carried out to investigate the dynamic behaviours of the unit cell according to the model and the controller given in Subsections 4.1 and 4.2
The results demonstrate that position control of the unit cell can be successfully achieved
Summary
Efficient aircraft are desirable for both environmental and economic reasons. A possible solution to further improve efficiency is to allow an aircraft to adapt its aerodynamic shape for different flight regimes. The unit cell prototype is equivalent to the middle cell of the example structure in Figure 2 and is sized according to the mid-stroke position of the PAM, i.e. the length when the muscle contracts 12.5%. The changes in pressure and volume of the PAM are dictated by the mass flow rate of the compressed air resulting in the change of tensile force and displacement of the muscle.
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