The boxes arriving from the production line are taken by the conveyor belt that passes through the buffer: in case of stops of the upstream machine, this latter sends a signal to advice that the machine is not ready that activates the buffering system PST, which provides to stop the arriving boxes to create a line of 10 pieces that is taken from the belt by lifting up step by step, allowing the arrival of other boxes. In this way the production line does not reduce the speed and this cycle can be repeated many times up to the maximum buffer capacity or until a signal of “machine ready” coming from the upstream machine. In this way the emptying cycle begins during the normal production. This means that the program is able to calculate the arriving boxes flow and provides to stop it temporarly to insert a line of 10 boxes coming from the buffer without overloading the downstream machine.