Stacking on conveyor

I have attached a model in which flowitems pass through the conveyor and reach the queue.
What is needed is, 3 flowitems has to be stacked one above other on the top of the conveyor and only after the content of flowitems reaching 3 they have to be conveyed over the conveyor.
Stacking has to be carried on conveyor(without using combiner) since flowitems has to be processed on various work station. Help is appreciated.

Hello Manoj,

you can use a queue before the conveyor. Its capacity is the amount of items, which are stacked conveyed. On entry move the second and third item to the first in the queue. If it is important for you, you can change location and size of the stacked items.
If the maximum stack height is reached, close the input of the queue and open its output. After the conveyor use another queue and move each stacked item in that queue.

Jörg

or use a combiner, that is what is was designed for