Drives with centrally controlled servo motors are commonly used in end-of-line packaging. However, in applications with large inertia or long travel distances – for example palletising, stabilising or handling – they are usually not mandatory. Decentralised drive solutions, such as those with controlled asynchronous motors, are an economical alternative in this context. They achieve similar kinematic properties and, due to their higher internal inertia, ensure better regulation and motion control with heavy loads. The use of decentralised frequency inverters with ‘closed-loop control’ also results in enormous cost savings.
End-of-line packaging defines the final step in the packaging process and thus the end of the production line. Here, the products and goods are packaged ready for sale and prepared for transport to the customer. Heavy pallets with bags, boxes and containers are the primary items being moved.
Electrical drive systems are of essential importance to end-of-line packaging. They bring automated machines and systems into motion and make a major contribution to cost-efficient, precise and reliable processes. Wherever pallets need to be lifted, rotated, positioned, or moved, they need to be transported using electrical drive technology.
End-of-line packaging is highly price-driven, therefore economical aspects are a priority. The drives must be absolutely reliable and guarantee smooth operation with minimal downtime as the primary objective. If a replacement is necessary after inspection or for routine maintenance, inspection and maintenance, it should be possible to carry out the process quickly and easily.
THE ROLE OF SERVO DRIVES
The packaging industry understands a servo drive as a component based on a permanently excited synchronous motor (PMSM). It has a slim design and low inertia that provides high speeds, high torques, high dynamics and high power density. In PMSMs, the rotor is driven synchronously by the rotating field of the stator with applied permanent magnets, which causes a synchronous movement to the applied rotating field frequency and, among other things, ensures good control properties.
Synchronous servo drives are considered the ultimate in the packaging industry due to their low internal inertia (low rotor inertia), good control characteristics with low external inertia, high dynamics and their high torque – however there are other solutions. Due to their specific characteristics, asynchronous motors are an ideal solution for the specific requirements in end-of-line packaging – heavy loads, high forces, long movement distances, slow movements, dynamic load changes – and represent an efficient and economical solution to drives with centrally controlled synchronous servo motors.
DECENTRALISED DRIVE TECHNNOLOGY
Compared to commonly used drives with synchronous servo motors with or without a gear unit with large ratios, asynchronous geared motors offer advantages in end-of-line packaging. Asynchronous motors have higher inertia in the rotor due to their design. When combined with a controlled frequency inverter, they ensure better regulation and motion control with high external inertia, i.e. heavy loads.
Decentrally controlled asynchronous drive solutions are more cost effective to purchase than central synchronous servo drive systems. They also offer economic advantages in terms of installation, maintenance, service life and space requirements. Further cost reductions are realised from operation with decentralised frequency inverter that uses an integrated PLC. These drive systems provide the opportunity to directly connect and control surrounding sensors and actuators, as well as evaluate the signals. This reduces wiring efforts and saves control capacities in the control cabinet.
SERVO AND ASYNCHRONOUS GEARED MOTORS
If you compare the most important characteristics of servo and asynchronous geared motors, it becomes clear: in the specific application of end-of-line packaging, where heavy loads are commonplace, drive systems with asynchronous motors have many advantages. They feature better regulation and motion control with lower gear ratios of heavy masses, are more cost effective to purchase, require less space and are also less complicated in terms of commissioning, installation and maintenance. The lower values regarding precision and dynamics are not a disadvantage, as end-of-line packaging requirements are lower than in primary and secondary packaging. Additionally, the increased inertia of the drive reduces vibrations and increases control.
Asynchronous drive systems are suitable for a range of applications in end-of-line packaging – be it handling, palletising, or transport securing. Overall, they achieve comparable kinematic properties to synchronous servo drives with reduced costs, especially when used in connection with decentralised drive electronics.
REDUCED COSTS WITH MORE EFFICIENCY
For users, decentralisation of drive technology means faster commissioning and simplified maintenance and repair processes. Costs can be reduced considerably on the software side, such as with factory pre-configurations. With a modular concept, the drive also maintains maximum flexibility, as changes to the system architecture can be made at any time without large structural modifications – and additional drives can be added later without changes to the control cabinet. As a result, costs are reduced, drives are more efficient and scalability is increased.
With decentralised solutions, spatial proximity of the motor and inverter reduce the wiring effort and cabling between the cabinet and drive in the field to a minimum. Only short cables are required – if needed at all – and do not require shielding due to their optimal EMC properties. Since the frequency inverters are installed directly on the motor or in its immediate vicinity, commissioning close to the motor is also possible, which can reduce walking distances and improve safety.
The decentralisation of drive technology enables a system design that consists of autonomous production islands that largely regulate their own processes. This scenario reduces load on the higher level control system and decreases system complexity.
As a result, the entire system is much easier to maintain and it also works more efficiently and the modular structure provides maximum flexibility, as changes and extensions can be made at any time.
SUCCESS STORY: PALLETISING MACHINES
A practical example of the palletising machines of a Dutch machine manufacturer shows how the changeover from drives with centrally controlled servo technology to decentrally controlled drive technology can be successful. Palletising machines play a key role in the production and distribution process and they must function smoothly so that product flows do not come to a standstill. They must also be flexible enough to adapt to various goods and applications.
In the past, the company relied entirely on centralised drive systems. This required control boxes to be installed on the top of the machine, which took up a lot of space, increased costs and obstructed access during maintenance work. In the course of modernisation, the centralised servo technology was replaced by decentralised drive technology with asynchronous motors. This resulted in the TCO being reduced.
These palletising machines place each product individually. A specially designed gantry enables precise, gentle handling. The three to four meter high machines are fed via a conveyor belt and the goods are picked up by a gripper. Bags slide against a fixed stop and are aligned by a centring unit so that the gripper can drop them exactly at the programmed position. This layout enables precise, stable overlap stacking with the ability to program different stacking patterns. The pallet deck is lowered layer by layer during the stacking process until a defined final height is reached. The loaded pallet can then be transported via a roller conveyor to a wrapping machine and wrapped with film.
Decentralised asynchronous drive systems have proven their worth in controlling the complex motion sequences of the palletising machine’s gripper. Centring of the unit is more economical than the previous servo technology solution. The new configuration also provides the necessary dynamic performance, opens up new design possibilities for developers, and resulted in cost savings in various areas.
Advantages of the new system are not only lower procurement costs, but also greater choice for machine designers, as asynchronous motors are available everywhere in a range, are easy to maintain – and can be combined with different types of gear units and frequency inverters. Additionally, they are easy to replace, particularly with the push-on version that utilises plugin connectors. The elimination of the control cabinet on these palletising machines also results in lower installation costs. The wiring of sensors and actuators in the machine is carried out with pre-assembled plugs with reduced cable lengths, zero errors, and the shortest possible installation time. M23 plug connectors that are expensive and time consuming to assemble and install have become obsolete; conventional installation work such as stripping, setting ferrules, and clamping are no longer necessary. If you combine all advantages and disadvantages, the palletising machines with decentralised asynchronous drive technology again result in a lower TCO.
In summary, the following can be said: asynchronous motors with decentralised frequency inverters and encoder feedback via absolute or incremental encoders enable economic and precise positioning applications, as well as dynamic movement of large, heavy packaging units. This makes the technology a real solution for application fields such as end-of-line packaging, where heavy loads and high forces are the norm. When used with decentralised frequency inverters, components such as control cabinets and wiring are also eliminated and the setup effort is lower. Furthermore, space saving is an important advantage of this decentralised approach. All in all, cost savings of up to 50% are possible.