fig2 there is a number of empty places between the orientation station so and the filling station sr the optimal number for these places can be deduced with reference to the configuration in fig5 in this figure the first battery 11 is queued behind the third battery 21 at rest at the station sr and the last gripping organ of the first battery 11 is upstream of the inlet station si consequently the number of empty places between the first battery 11 and the third battery 21 as in fig2 is equal to n n with n equal to four that is the places relative to the gripping organs reaching the inlet station si the cleaning station sp the orientation station so and the gripping organ upstream of the station si substantially in the illustrated example the maximum number of empty places fig2 between the station so and the station sr is eight and there are obviously also eight empty places between the station su and the fourth battery 22 see fig2 in total there are therefore sixteen empty places in fig5 the first battery 11 is queued behind the third battery 21 correspondingly the second battery 12 is queued behind the fourth battery 22 in the embodiment illustrated the time required to complete one step of the first battery 11 and of.