ABSTRACT
The conventional scissor-like element alone cannot be used to build a mobile planar closed chain which has mobility, the mobile assembly always takes a spatial form. This only becomes possible with the utilisation of the Sarrus linkage for connection of planar chains of conventional scissor-like elements. The Sarrus linkage was the first reported spatial overconstrained linkage. The conventional scissor-like elements can also be used to form spatial rings. Selection of the rings depends on the actual applications. For example, when the ring is for a support structure of a deployable reflector, the beams are likely to carry compressive forces. At the corners of either a ring or a dome, corner joint pieces are used where beams from the scissor-like elements in a loop and tie meet. The derivations for both rings and domes are based on an implicit assumption that the links and the joints have no physical size.
