The full cans are transported from the 
drawframe to the rotor spinning machine and the empty cans in the reverse direction by process-controlled, unmanned transport vehicles (see Fig. 64). These vehicles are also responsible for automatic can change on the rotor spinning machine. The transport vehicles are steered either inductively via wires embedded in the floor or optically via colored strips. The control effort required for complex travel concepts of this kind is high, but they enable highly flexible systems to be implemented that are ideally adapted to changes in loading. By contrast, vehicles running on rails are confined to fixed routes. These systems are considerably less complex, but are also much less flexible.
A working cycle commences with the unmanned transport vehicle collecting an appropriate number of filled cans from the can trolley at the drawframe and thus starting its monitoring run. One space always remains free in the transport vehicle in order to accept the empty can at the first can change, which is then replaced by a full can. The next empty can then takes the place of the full can, and so on.
The machine control of the spinning machine calculates the can running time on the basis of the delivery speed of the sliver, the downtimes and the sliver length. When the can has run empty a new (full) feed can is requested via the central machine control.
The empty can is pulled out of its position under the machine onto the empty space in the transport vehicle by means of a suction device on the transport vehicle. The transport vehicle then positions itself, offset by one spinning position gauge, in front of the gap and pushes a full can under the machine. The end of the sliver, already positioned precisely on the lip of the can in the drawframe, is taken manually or by the suction arm of the operating robot and introduced into the spinning position. After all full cans have been placed in position the transport vehicle travels back to the can trolley on the drawframe with the empty cans, where the empty cans are again replaced with full cans. An operating cycle is thus completed and the transport vehicle prepared for the next monitoring run.
The number of transport vehicles depends not only on the size of the mill, i.e. the number of machines, but also on the material throughput (coarse or fine count yarns) and the variety of products. Transport volume per transport vehicle, taking the above factors into account, amounts to between 500 and 1 100 kg/h. Experience in practice shows that 3 - 5 different assortments can be run simultaneously.
It is also possible to divide the spinning mill into different zones, e.g. a cotton and a man-made fiber zone, and to allocate the transport vehicles accordingly. The control software of the transport system then ensures that both zones remain strictly separated in the use of the cans, transport vehicles and can stores on the drawframe. This reliably prevents contamination of either raw material by extraneous fibers.
Although rectangular cans have been developed primarily for fully automated transport systems, they can also be conveyed manually by means of special transport trolleys. The advantage over round cans is that operating personnel on the spinning machine can check the filling level of rectangular cans much better (since all cans are visible) and can ensure timely replacement of the cans. Manual utilization of rectangular cans offers the possibility of integrating these in an automated transport system at any time.
Fig. 64 – Concept for automatic can transport between drawframe and rotor spinning machine
