Roche has developed the Cobas Plasma Separation Card (PSC), a new technology that simplifies and improves the examination and monitoring of HIV patients, particularly in remote areas. For the first time, blood plasma samples no longer need to be cooled during transport to the laboratory. The prerequisite for this breakthrough was a flexible, compact and dynamic production technology that allowed the PSC to be produced cost effectively. This was realised with the eXtended Transport System (XTS) from Beckhoff, which increases efficiency with its high flexibility.
The credit card sized Cobas PSC requires only a small amount of blood from a patient’s fingertip and greatly simplifies sample transport. For people in rural areas of sub-Saharan Africa, HIV testing is now more accessible as it eliminates the need to cool blood samples during transport to the lab. The special feature of this innovative product is that the plasma only needs to dry up a little for safe transport and can then be easily liquefied again in the laboratory to be analysed like normal blood plasma.
The PSC is manufactured in a compact machine measuring 3,5 x 3 m, in which the eXtended Transport System (XTS) from Beckhoff played a central role as a highly flexible transport system, as it allowed the production unit to be adapted to changing requirements during the development process.
The complex structure of the PSC requires a sophisticated production process. The special nonwoven fabric for the plasma-separating membrane is very sensitive and requires exact adherence to the desired geometry in order to minimise waste. Furthermore, the forces acting on the nonwoven fabric must not exceed 7 N in order avoid altering its structure to ensure that the permeability of the structure is maintained.
A laser cuts out the membrane very gently, using a special measuring procedure. When the unit starts up, the processing table from which the membrane is collected is measured. The system then checks the workpiece carriers on all 10 XTS movers. In this way, all component tolerances are compensated. To exert as little process force as possible, the membrane is applied to the adhesive layer with vacuum grippers. In this demanding product handling environment, XTS offers the great advantage that the component tolerances determined can easily be stored in the software and be assigned to each mover individually for the entire production process.
The benefits of precision and software functionality are evident in the motion axes of the workstations implemented using EL7211 servomotor terminals and AX5000 servo drives, such as cutting units, rotary tables and transfer arms. A good example is the measuring probe function of the AX5000 servo drive, which can be used to store the actual position of the controller without time offset, depending on an event.
XTS enables highly flexible product transport with minimum space requirements. Roche was able to design an extremely compact system and accommodate it in the limited space available in the production environment. An XTS with 10 movers and a 3 m track length is used, around which the individual workstations are set up. This results in a symmetrical machine layout in which the first preliminary product – the carrier layer – is processed on one side and the second preliminary product – the upper layer – is processed and optically inspected on the other side. The membrane is cut out in the centre of the unit, so that the complete card can be produced in a single XTS cycle.
XTS offers additional benefits through its dynamic cycle and easy synchronisation of fast workstations with slow process sequences. The slowest processes in the line are laser cutting of the nonwoven fabric and the associated pick-and-place. With XTS, it is now very easy to prepare six cards at a time, transfer them to the laser cutting unit and then glue them individually to the corresponding card tops. In addition, the highly flexible product transport with XTS simplifies early ejection of defective sub-components.
In addition to the collision avoidance and synchronisation functions provided by the TwinCAT 3 XTS Extension software, Roche also benefits from the option of limiting the controller current. This simplifies the mechanical referencing without losing the position control via the XTS encoder system that is advantageous elsewhere in the system. The EtherCAT communication system offers further advantages through its high performance, simple commissioning and widespread use as a global standard.
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