Keywords: adaptive tensegrity module, octahedral cell, actuator, sensors, test equipment, tests, control commands, closed-form solution, finite-element analysis.

Lightweight self-stressed tensegrity systems, that are composed of tensioned members (cables) and compressed members (struts), offer an economical and efficient alternative to many classical civil-engineering and aerospace structures [1]. Their use is very promising in projects that require active or deployable systems [2]. Tensegrity structures have been intensively studied since they appeared in the 1950s and their applications have been extended from art and architecture to other areas including aerospace structures, robotics and cell mechanics.

A newly developed adaptive tensegrity module which has the ability to alter its geometrical form and pre-stress properties in order to adapt its behaviour in response to the current loading conditions is presented in this paper. This tensegrity system contains sensors and an actuator that sense a force from the environment and adjust the shape, making the structure more rigid or more flexible depending upon the load. The elementary shape of the tensegrity module is an octahedral cell in the form of a double symmetrical pyramid. The system consists of eight pre-stressed cables, four circumferential compressed rods and the central compressed rod designed as an actuator. The special test equipment has been designed. Three types of the tests were carried out: a pre-stressing test, a static loading test and an adaptation test. Tests confirmed the required functionality of the developed adaptive tensegrity system and the correctness of the proposed electronic equipment, software, and control commands.

In this paper the closed-form and discrete computational models for the geometrically non-linear and linear static analysis of the adaptive tensegrity module are presented. As a result of the symmetry of the spatial tensegrity module the closed-form analysis is based on the two-dimensional solution of the equivalent pre-stressed triangular cable truss under a vertical point load. The concrete forms of the cable equations are derived and presented. The model serves to determine the horizontal components of cable forces and deflection as the basis for control commands. A three-dimensional discrete geometrically non-linear solution is based on the non-linear finite element method. The predicted responses from the finite element analysis of the adaptive tensegrity module are compared with those obtained from the tests. The results confirmed a physical relevance and logical correctness of the applied theoretical approaches. This approach is useful to increase the reliability and enhance the performance of tensegrity structures.

1

R. Motro, "Tensegrity: Structural systems for the future", Hermes, ed., Penton Science, U.K., 2003.

2

E. Fest, K. Shea, I.F.C. Smith, "Active tensegrity structure", Journal of Structural Engineering, 130(10), 1454-1465, 2004. doi:10.1061/(ASCE)0733-9445(2004)130:10(1454)

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