According to the Federal Environmental Agency, electrical drives in industrial and commercial applications consume almost two-fifths of all electricity in Germany. Optimised solutions offer users enormous potential for reducing operating costs and conserving resources.
Following the BEUMER Group’s introduction of the new OptiDrive technology back in 2010 for the smaller BS7 high-performance sorter, the intralogistics specialist has now also implemented this for the larger models from the BS25 to the BS60, with mechanically or electrically operated load-bearing elements.
“So far we’ve used double comb asynchronous linear motor drives in these systems,” explains Heino Heitplatz, Team Leader Research & Development and Deputy Head of Development at BEUMER.
“We wanted to increase the efficiency while at the same time reducing procurement costs. In addition, our goal was to ensure high availability with minimum maintenance and repair costs.” BEUMER high-performance sorters are used for sorting and picking a variety of items such as mail, textiles, mail order products, foods or baggage.
For the BEUMER OptiDrive, the contact pressure with which the drive wheel is pressed against the movable friction blade of the circulating carriage assembly is automatically adjusted proportionally to the required driving power. Thus, the drive always automatically operates at the optimal operating point. On one hand, this allows for safe and slip-free starting up of the sorter from a standstill. On the other hand, the efficiency is improved in the predominant partial load range, while at the same time prolonging the service life of the drive wheels.
“Without this innovative proportional contact pressure, we would have had to design the contact pressure of the friction wheel for the worst case, that is, for starting up a stationary, cold machine,” says Heitplatz.”We call this the Monday morning effect.” However, the contact pressure for normal operating conditions would then be much higher than actually required and this would clearly impact efficiency and the service life of the drive wheels. The energy consumption has been reduced by up to 80 percent compared to the previously used asynchronous linear motor drive. “With the new OptiDrive BS25/55, we can achieve effective efficiencies of up to 85 percent,” Heitplatz reports.
More efficiency, less wear
What is genuinely innovative about the new drive system is its double-acting proportional contact pressure. This works in both directions of action – when accelerating and braking. This means that the new OptiDrive can act as a holding brake. Compared with single sided linear motor drives, this solution does not cause attraction forces between the drive and the carriage, which reduces the load on the carriage and reduces wear. The drive also lines itself up with the carriage. This means that the user does not need to adjust the system.
With this drive method, each carriage has a blade on the underside that acts as a friction blade. The blade is clamped between the friction wheel and an opposite pressure roller and pushed forward. The drive power transitions to the carriage system via this blade. The drive unit is connected to the sorter frame by means of a centre of rotation. This “floating” bearing prevents transverse forces from the drive unit transferring to the carriage at all times.
Patented functional principle
The patented functional principle of the OptiDrive can be explained as follows: the drive motor with directly attached drive wheel is pushed against the blade by a slight spring force. The traction and the applied driving power generate a reaction torque in the motor bracket, which is pivotally borne, and to which the two contract press rolls are attached. These two press rolls, in turn, act on a pivotally borne press arm, on which the pressure roller is mounted. Thus, a contact force is built up on the blade between the drive wheel and the press roll. The force automatically adjusts proportionally to the driving power. The arrangement with two press rolls ensures this function in both directions of action, that is, for driving and braking.
The OptiDrive is equipped with an automatic tolerance compensation system. It compensates for things such as wear and tear on the drive wheel, or component tolerances. To this end, a spring-loaded wedge is integrated between the press arm and the press rolls. Assembly tolerances are compensated for by the pivotal connection of the drive unit. “The drive permanently lines up with the blades and not vice versa,” Heitplatz explains. “This means we can allow larger tolerances in assembly and in the components without functional restrictions or transverse forces acting on the carriage system.
Specially adapted for optimal operation
The blades on the BEUMER OptiDrive act like friction blades. To keep the gaps between the carriages as small as possible, thus enabling smooth and silent transitions between each carriage, the blades feature a special contour and arc-shaped ends. BEUMER has been able to reduce gap between the blades to a minimum — and without impairing the mobility of the carriage system in horizontal or vertical curves.
The friction blades are made of extremely light aluminium profiles. This helps to keep the moving mass of the carriages and the motion resistance as low as possible. “In comparison with other systems that need secondary parts on the carriage, for example, for synchronous linear motor drives, where the carriages are additionally weighed down by the permanent magnets, you definitely can reduce the energy consumption. The fact that the moving mass is lower, is independent of the actual drive efficiency,” Heitplatz explains.
The OptiDrive is powered by a modern, highly-efficient gearless synchronous servomotor. The drive wheel is mounted directly on the motor shaft. “Because we consistently do without transmission parts such as gears or belt drives, we leverage the maximum efficiency of the drive. In addition, noise sources and potential maintenance points are consistently avoided,” says Heino Heitplatz.
The direct drive also allows for a very compact design. “Unlike the central converters of the asynchronous linear motor drives, the OptiDrive concept means that each drive has its own controller which is installed locally in the field,” says Heitplatz. The controllers are in close proximity to the drive. The individual drive controllers use Profinet to communicate with the sorter controller. The Profinet installation is daisy-chained, as is the power supply to the drives. This reduces the required cable length and the installation overhead. A special control algorithm ensures that all the drives apply the same propulsion power to the carriage system at any given time. This has the advantage that all drives are equally loaded and the force profile is optimised in the carriage system.
The BEUMER OptiDrive BS25/55 is designed for a permanent propulsion power of 600 Newton, and a short-term propulsion power of 1,000 Newton (for acceleration and braking processes) as well as for sorter speeds of up to 3.2 metres per second. The system is monitored by numerous diagnostics systems. Any malfunctions are indicated to the operator in good time. The user can also maintain the drive system remotely. “Thanks to remote access, our experts in Beckum have the ability to remotely access every single drive worldwide, and thus give the customer the best possible support on site”, Heitplatz explains.