an arm 10 fitted to a powered vertical shaft 11 to rotate about a fixed axis 12 coaxial with shaft 11 and close to the intersection of axes x and y and a further arm 13 hinged at one end to a free end of arm 10 and rotated with respect to arm 10 and by a known transmission not shown about an axis 14 parallel to axis 12 arm 13 is he same length as arm 10 and is fitted on the free end with a powered swivel shaft 15 having an axis 16 parallel to axis 12 and to which is suspended a pickup head 17 of this only portion is shown for the sake of simplicity defined by a detecting device 18 comprising an optical sensor 19 e g a laser sensor for emitting a beam 20 which on encountering a point on a surface is reflected back to cause sensor 19 to emit a signal of an intensity proportional to the distance between the point and sensor 19 pickup head 17 of known type may be fitted to articulated arm 9 at any point within loading region z and can be oriented by shaft 15 to selectively grip stacks 2 in top layer 5 and feed stacks 2 successively to the input not shown of a packing unit not shown of packing machine a as shown in fig2 each blank 3 is positioned on.