(57) The extendable arm comprises two structures (2,3) whose mutual distance can vary,
each structure (2,3) being constituted by at least three corner elements (4,5), each
of which has two angled pivoting elements (6,7) for pivoting the corresponding ends
(10) of at least three pairs of mutually articulated linkage members (11,12) which
substantially constitute at least three pantograph-type couplings which are mutually
connected in space, the approach or spacing of two of the corner elements (4,5) arranged
on one of the diagonals of one of the structures (2,3) being adapted to determine
the spacing or approach of the other structure and the simultaneous extension or retraction
of the arm (1).
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