Straight line mechanism

A linkage mechanism for an industrial manipulator comprising at least a first conchoid-type straight-line mechanism associated with a second conchoid-type straight-line mechanism in each of which straight-line mechanisms a rotatable member (31, 32), rotatable about a pivot axis which passes through the rotatable member, is pivotally attached to a second member (19) at an attachment, and the second member is oriented by orienting means (24, 28) located at a fixed distance from the said axis, the said members and orienting means being mounted and the distance of the attachment from the axis, the said fixed distance, and the length of the second member (19) being chosen such that on rotary movement of the rotatable member (31, 32) through an angle the said attachment describes an arc of a circle with respect to the said axis and the said axis and orienting means move in first and second straight lines respectively or a geometric point on the second member moves in a third straight line which straight line movement occurs in a plane perpendicular to the axis and may be resolved into two mutually perpendicular components in the said plane to provide a minor component on a line passing through the axis and the said geometric point, the said straight line mechanisms having a common second member (19) and being arranged with the said plane of the second straight-line mechanism such that rotary movement of the said rotatable members is effected by or effects a movement of the orienting means of the first straight line mechanisms in a plane parallel to a plane through the orienting means of the second straight line mechanism.