The 4-axis palletizer is a common robot type, employed mostly for pallet­izing tasks. It has 4 controlled rotary axes (drawn in red in the figure aside) and a fifth rotary mechanical axis (drawn in grey). The fifth axis mechanically keeps the gripper horizontally aligned.

The coordinate system at the bottom of the robot is the machine coordi­nate system. The Z axis points vertically upwards, the X axis points "forward", i.e. that direction the robot arm points to if it is in zero position. The coordinate system origin is the intersection point of the joint axis 1 and the bottom side of the robot. The picture aside shows the rotation direction of the 4 axes. The black arrows run along the joint axis. The direction of rotation is defined according to the "right-hand rule": If the thumb of the right hand is along with the arrow, then the positive direction of rotation is along with the slightly curved fingers of the hand. For example, seen from the top, the positive direction of rotation of axis 0 is counterclockwise, axis 1 and axis 2 tilt forward.

The picture aside shows the kinematics in zero position of all axes: The names of the parameters are according to the Denavit-Hartenberg convention.