Not only precision and throughput are important for capsule fillers, but also reliability and production flexibility. Exactly synchronous operations and precise positioning are essential for this. In addition, the Italian manufacturer MG2 also wants its machines to meet customer requirements for standardised, easy-to-maintain, and cost-effective automation components.
Paolo Norse, Elmar Lippert
Capsule fillers from MG2 are designed for dosing pharmaceutical products into capsules made of hard gelatine. During operation, they carry out a continuous rotating movement. The main components of the machines are a capsule feeding and orientation unit, a capsule transfer system, a dosing unit and a filled-capsule exit unit.
The first unit consists of a funnel for the empty capsules, which are then transported vertically downwards in boat-shaped feeding containers. An orientation drum aligns the capsules in the right position. The second unit is a horizontal ring which rotates in phase with the other units. The cylindrical exterior contains seats for the capsules and drilled holes for removing them with a suction system. The capsules are thus opened, dosed and closed. The finished capsules are extracted from the machine by centrifugal force. The colour of the capsules is verified between the orientation and dosing phases. Precise positioning is particularly important here. If a capsule is not properly positioned under the colour recognition device, then a reliable and rapid detection process of this kind, taking only 1 millisecond to complete, is impossible.
MG2 capsule fillers have a production output of up to 140,000 capsules/h in the case of the classic G70 and G140 models, while the high-speed G250 machine achieves a throughput of up to 200,000 capsules/h.
Use of standardised automation solutions
In order to meet practical requirements for standardised components, the Electronics department at MG2 decided to use standard asynchronous motors. Although the movement needs to be very precise, it is still entrusted to these simple, robust motors, which are controlled by Danfoss frequency inverters in the VLT 5000 series. The decision by MG2 was also influenced by the integration flexibility of these inverters. They can accommodate a SyncPos card for synchronisation and positioning, thus enabling real control of the axes without stressing the PLC. It should be emphasised once again that these machines require dynamically synchronised movements as well as precise positioning when stopping.
Benefits of three-phase technology
The standard asynchronous motor can be mounted on a low-backlash and standardised gear. This means that, in the event of maintenance, it can be replaced with any standard motor without having to exchange the complete system. The discharged PLC carries out the numerous control and monitoring operations rapidly.
The Danfoss SyncPos shaft control needs no motor or position feedback (slow shaft of the gear). A single encoder on the outgoing shaft of the gear is sufficient to control the movement with the required precision. Moreover, the controller already has a programming platform of its own, which can be customised in a few easy steps. All closed-loop control parameters such as heights, speed ratios, phase angles and PID values are accessible from the liquid crystal panel of the VLT 5000. By using the internal SyncPos controller, the reaction time of the complete drive is significantly reduced, since the cycle time of the PLC has no effect on control performance.
The “total integration” philosophy of these inverters also proved to be of interest to MG2 because it guarantees that the capsule fillers meet EMC requirements thanks to the built-in RFI filters. Since the Bologna-based company exports more than 90% of its production, it additionally appreciates the multiple supply voltages (380 to 500 V three-phase current) of the VLT 5000.
SyncPos motion controller plays a key role
In order to facilitate the high production performance of the G250 capsule filler, MG2 developed modern mechanical technologies and tested an electrical system for synchronisation between certain key components. This system consists of two VLT 5000 frequency inverters with a SyncPos card, one in the master for the position and one in the slave for interlinking the phases with the master. The resulting precision is high and similar to that of brushless servo drive technology. Position synchronisation begins immediately. The machine allows the transmission ratio between the master and the slave to be altered and thus adapted to any format or product.
The G250, which is equipped with an industrial PC with a graphics monitor and runs under Windows NT, controls all the machine functions. Just like the other models in the MG2 series, it can be adjusted for unattended operation. The machine can be equipped with a weight control system for the capsules, automatic dosing control and even a 100 percent check of the net weight of all capsules dosed during the process.
All operations require perfectly synchronised positions, including during the stop and restart phases. The Danfoss VLT 5000 inverter with SyncPos plays a central role here. The impressive automation results are, of course, also the achievement of the engineers responsible for continuous further development at MG2.
The available distributed intelligence is extremely useful for plant manufacturers and operators alike, since the space saving enables a more compact equipment design and simplifies installation by reducing the amount of wiring. Moreover, there are fewer sources of error, leading to greater reliability. The higher flexibility allows complex motion processes to be implemented. If a field-bus option is used, installation costs are even further reduced.