Attachments for power assisted lifting devices capable of rigidly positioning an object in three-dimensional space, for example pneumatically assisted manually operated mechanical arm manipulators, wherein the attachment is capable of securing an object for remote positioning thereof. More particularly, an end effector for a pneumatic manipulator that is capable of both passively following the motion of a secured object and actively adjusting the position of the secured object in an arcuate direction relative to the attachment of the end effector to the manipulator. The end effector is able to rotate the object about an axis passing through the end effector that also moves arcuately with the end effector. The end effector is particularly useful in the bending of metallic sheets or plates using a conventional sheet metal brake, as the end effector is capable of both positioning heavy sheets in the brake and following the movement of the sheet as it is being bent. The end effector may be used in conjunction with the manipulator to remove the sheet from the brake, flip the sheet using the rotation feature, then re-position the sheet within the brake for making successive bends on the same sheet without necessitating release by the end effector.