As the compact Galaxie D is completely inaccessible in the swivel axis, Hekuma attached great importance to a permanently service- and maintenance-free solution. With high backlash stability and a motor feedback system whose multi-turn functionality does not require battery buffering, the Galaxie D drive system also meets these important requirements from the end customer's point of view - in contrast to the previously used tension shaft gearbox, which had also proven to be too soft for this precision application, i.e. not sufficiently torsionally rigid and low backlash.

Hekuma - based in Hallbergmoos near Munich - is a leading manufacturer of high-performance automation systems for plastic injection molding machines. The core business of the company, which is part of the Elexis Group, includes high-performance removal systems for injection molding production, the integration of injection molding machines and molds as well as complete turnkey solutions for the removal, processing, assembly, marking, testing and packaging operations. "Our customers are primarily interested in the high-availability automation of upstream and downstream manufacturing steps in injection molding production," says Alexander Kappes, team-leading mechanical designer at Hekuma.

This also applies to the transfer unit, which will combine a two-stage injection molding process with thermoset and thermoplastic substrates at a consumer goods manufacturer. "High sales figures require a high number of cavities in production with a short cycle time," explains Reinhard Steinhoff from Mechanical Design when describing the system. "Each insertion and removal element has 32 cavities. The cycle time is 20 seconds and the machine runs in three-shift operation 340 days a year. The swivel unit with the Galaxie D therefore moves more than 47 million injection molded articles per year."

In addition to the dynamics, however, there was another argument: "The swivel arm of the transfer unit rotates 180 degrees in the y-direction and has a moving mass of around 270 kilograms. In order to position the cavities in front of the injection molding machines with millimeter precision for smooth handling of the molded parts, the drive had to be extremely rigid with minimal torsional backlash," explains Alexander Kappes. However, only limited installation space was available for the servo technology implementation. "The switch to a new motor-gear unit was not allowed to result in any design changes to the swivel unit," confirms Reinhard Steinhoff.

Dynamized single shear teeth, multi-tooth engagement and synchronization

The Galaxie D drive system is a compact mechatronic unit consisting of a specially developed, permanently excited high-performance synchronous motor and a Galaxie® gearbox. (Image: Wittenstein)

Galaxie is scientifically proven and recognized on the market as an independent and fundamentally superior type of gearbox. The decisive features - dynamized individual thrust teeth instead of rigid gears, full-surface multi-tooth meshing with hydrodynamic contact and mathematically exact synchronization as well as a segmented outer ring as a bearing - mean that the Galaxie gearbox kinematics are superior to known planetary, cycloidal, eccentric and tension shaft gearboxes in all important technical disciplines in relation to the market standard. The gearbox kinematics guarantee top performance in terms of backlash-free operation, synchronization, rigidity, torque density and overload protection without having to "play off" these features against each other.

The decisive requirement for Hekuma from an application perspective was to guarantee outstanding and permanently consistent positioning accuracy. The GalaxieD fulfills this performance feature thanks to its high torsional rigidity and torsional backlash reduced to less than one angular minute. The single thrust tooth kinematics mean that almost all individual teeth are involved in tooth engagement at the same time - and therefore in torque transmission and rigidity formation. In addition, the tooth flanks of the individual teeth and the ring gear are designed as a logarithmic spiral for the first time, which means that contact in multi-tooth meshing is no longer linear as in gearboxes with gearwheels, but instead occurs as surface contact with Galaxie - with a higher contact ratio. This ensures a very high level of rigidity, even with alternating loads in the zero passage.

The second aspect of positioning accuracy, as required by Hekuma, concerns torsional backlash. "In principle, it would have been possible to design the Galaxie D as a zero backlash variant," says Alexander Kappes, looking back. "However, we then opted for a reduced backlash of less than one minute of angle. Together with the torsional rigidity, it optimally reflects our accuracy requirements and at the same time makes it possible to absorb any locking forces that occur during positioning." His colleague Reinhard Steinhoff adds: "As the transfer systems are designed for years of continuous operation, it is particularly important that the torsional backlash remains constant once it has been set."

This is ensured by the Galaxie D's design principle, as a hydrodynamic lubricating film with a large, stable pressure cushion builds up when the polygon and individual teeth mesh even at low speeds. This reduces wear in the gearing to a minimum - as microscope images of loaded contact areas on individual teeth after endurance tests and high practical loads on the gears prove. Furthermore, as the fit between the round tooth bodies and the tooth carrier bores does not wear measurably, once a backlash has been set, it remains absolutely constant over the service life of Galaxie - even with the zero backlash variant.