Patent ID: 8622685

Claim:
A method of stacking a first layer of two or more objects from a collection platform having parallel grooves onto at least two objects forming a second layer of objects wherein upper surfaces of said at least two objects of the second layer have two different heights, the method comprising: locating a gripper proximate the collection platform, the gripper having a support frame which is provided with a row of forks, each fork comprising an upright joined to the support frame and a horizontal beam joined to the upright a distance beneath the support frame, wherein each beam comprises a drive unit for individually moving the beam backward and forward in a longitudinal direction thereof, and wherein each upright comprises a drive unit for individually moving the upright in a vertical direction during operation, and wherein each fork is individually adjustable relative to the support frame; moving at least some of the beams longitudinally, wherein each beam is moved into a groove using the drive unit for the beam, wherein a vertical distance of each of said at least some of the beams to the support frame is substantially the same; displacing the gripper upwardly so as to lift and carry the first layer of the objects with said at least some beams, wherein a beam carries two objects of the first layer of objects; and operating individual drive units of the uprights while the first layer of objects are being carried so as to adjust a relative vertical distance of each of the corresponding beams relative to the support frame so as to adjust relative heights of lower surfaces of the first layer of objects to correspond to the two different heights of the upper surfaces of said at least two objects of the second layer; and positioning the objects of the first layer onto the second layer of objects, wherein positioning comprises retracting the beam in consecutive steps to position each object of said two objects at different respective heights on the second layer of objects.