A linkage assembly includes a first link (40) connected at a first point (a) to a translation mechanism (56) attached to a support structure (16). The translation mechanism (56) is arranged to allow the first point (a) of the first link (40) to translate along a substantially straight axis (59, 86). A second link (64, 66) is pivotally connected at a first point (d) to the support structure (16), and at a second point (b) to the first link (40). A second point (b) of the first link travels on or near an arc (94) of substantially constant finite radius when the first link (40) pivots with respect to the second link (64, 66).
