Length-adjustable clutches are essential for some applications. However, previous models have either been backlash-free or quickly adjustable - clutches that combine both properties have not been available until now. KBK Antriebstechnik has now developed a version that transmits the torque backlash-free and can be adjusted in length to the application within a very short time.

The impetus for the new development came from a printing machine manufacturer. He was looking for a coupling for his machines that could be adapted to the length of the application, was backlash-free and easy to adjust. As such a coupling could not be found on the market, the company's engineers quickly designed a prototype themselves. They became aware of KBK via the internet and asked the company at the end of 2016 whether it would produce this coupling as a contract manufacturer. "We told them that we would be happy to do this, but that we didn't think it made sense," recalls KBK Managing Director Sven Karpstein. "The clutch had a high level of wear and did not perform consistently."

New development as a better solution

Instead, KBK made the customer an offer to design a coupling that exactly matched their application. The order was placed promptly, especially as KBK's engineers and technicians were able to demonstrate the necessary industry knowledge. The Klingenberg coupling specialists have been supplying all well-known printing press manufacturers with couplings for years. Karpstein and his team therefore knew exactly what requirements their solution had to meet. Clutches for printing presses should have a high torsional stiffness and be able to compensate for all types of misalignment. This is necessary to ensure high-quality printing in register. Register-accurate printing means that the print lines on the front and back of a book, newspaper or magazine page lie exactly on top of each other. This is particularly important if the paper to be printed on has a low opacity, so that the print lines on the front or reverse side show through and make reading difficult.

The coupling also had to be shock and vibration resistant, as printing presses generate strong vibrations during operation, which they pass on to the installed components. However, the most important point was simple handling: the clutch had to be used for automatic decoupling of the printing rollers and therefore be able to be quickly adjusted in length. As the print runs of daily newspapers continue to fall and the general trend is towards smaller print jobs, it must be possible to replace the rollers at ever shorter intervals. This is also the reason why conventional backlash-free length-adjustable couplings are not very suitable for use in printing presses: Their length can only be adjusted with difficulty.

Simple operating principle

When designing the new length-adjustable clutch, two seemingly contradictory properties had to be combined: absolute freedom from play and ease of use. Adjusting the length with a locking mechanism was therefore out of the question. KBK chose a different approach and developed a functional principle that is as simple as it is effective: "To take the play out of the system, we run plain bearing bushes on cylindrical pins," explains Karpstein. "In this way, axial movements can be realized with little effort." The coupling is also compatible with other coupling systems, which means that any radial or angular misalignment can be compensated for - this is a very important aspect, especially for printing machines.

After the order was placed, the KBK team got to work at the beginning of 2017 and created the first drafts of the new clutch within three months. These served as the basis for the development of a prototype, which was completed around nine months after the order was placed. The developers discussed the prototype with the customer, made a few minor changes and finally assembled the first pilot series on test machines in spring 2018. It ran flawlessly for six months, allowing KBK to start series production in late summer without having to make any further changes to the coupling.

Applications beyond the printing press

KBK has developed the first backlash-free length-adjustable coupling that can be adapted to the application in a very short time. © KBK

For KBK, the market launch of the new coupling goes hand in hand with the development of a new customer base, as the coupling is not only integrated into the manufacturer's new printing presses, but is also retrofitted to all "old machines". With 12 to 16 printing rollers per machine, each of which is connected to the corresponding servo drive via a coupling, a considerable order volume is generated.

The new coupling is suitable for many other areas of application in addition to the printing industry. "It is ideal for all applications in which the installation space is so limited that the length of the coupling cannot be adjusted with a key," says Karpstein. It is also possible to integrate the length-adjustable coupling into spacer couplings. This eliminates the previously common use of half-shells, and machine operators no longer have to walk long distances to release the coupling from the shaft.

KBK not only offers its customers high-quality couplings, but also manufactures them very cost-effectively thanks to its modular system. And if a customer's coupling should ever fail, the company can provide almost all elastomer and metal bellows couplings from its product range with customer-specific bores within two hours and send them by direct courier.

Thomas Walzel, Sales KBK Antriebstechnik / am