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Positioners normally are equipped with multiple axes, both for turning and for swivelling and tilting. Traditionally, these motions are performed by planetary or worm gears. Compared to cycloidal gears, however, there are decisive disadvantages to using such gears. Planetary gears, for example, are lacking in terms of positioning accuracy in the case of transmission ratios greater than 30:1. Another disadvantage is the elongated design. In applications with higher transmission ratios the length of planetary gears increases substantially. As a result, they take up much more space lengthwise than cycloidal gears with the same transmission ratio. Worm gear drives, on the other hand, are less efficient and, due to their design, show signs of wear after a while. As self-locking gears, their friction has a negative effect on the dynamics of the positioner. Also, in the case of high moments and dynamic cycles, bearing stress occurs, which has a detrimental effect on the material. When ultra-precise placing and positioning is required, such deficits can definitely become a problem. Cycloidal gears, on the other hand, allow precisely executed motions also at high acceleration torques and under heavy loads – which makes them ideal for high-precision positioners.

Positioners with cycloidal gears achieve high-precision positioning

With their high repeatability, positioning and rotational speed accuracy, cycloidal gears achieve pin-point positioning. The design ensures very even distribution of force inside the gearbox, which minimises hysteresis loss (0.5 to max. 1 arcmin) and greatly increases resistance to impacts. Even after long-term use the increase in backlash is minimal – a significant advantage over normal planetary gears, which often suffer from increased backlash during the course of their service life. This ensures precise positioning in a very compact design. Cycloidal gears are also more robust than planetary gears, and their two-stage reduction principle makes them less prone to wear. They therefore have an extremely long life and generally “outlive” both worm gears and conventional planetary gears. Positioners equipped with cycloidal gears are superior in terms of precision, dynamics and reliability. The advantages in production: shorter processing times, improved product quality, higher productivity and more stable processes.

The RS series from Nabtesco: hollow shaft gears for positioners

Ideal for use in positioners are the gears of the RS series. These robust precision gears with a hollow shaft were specially developed for rotational positioning, and deliver high positioning accuracy and exceptional performance in a compact design. The cast iron base is easy to mount on the floor and provides for high stability. The hollow middle axis allows the feedthrough of supply lines, cables and drive shafts, while simultaneously improving the load-bearing capacity.

The RS series at a glance:

• Five sizes for loads up to 9 t
• High torsional rigidity for exact positioning in dynamic cycles
• Sturdy, durable and compact construction
• Large hollow shaft
• Compatible with all standard servo motors
• Uncomplicated mounting and convenient handling

Variable 2-axis positioner for welding applications

The best example for the outstanding performance of cycloidal gears is the variable 2-axis positioner RSX-40K for welding applications. Designed for fast and easy integration in welding cells, the positioner allows spot welds with pin-point accuracy down to hundredths of a millimetre without having to unclamp and reclamp the workpiece. The swivel axis can be tilted by ±16°. This allows exact positioning to achieve the ideal height for loading.

The 2-axis positioner RSX-40K:

• 2 axes for turning and swivelling
• Load-bearing capacity up to 4 t
• Positioning accuracy of <1 arcmin
• User-friendly cable routing 
• Individually adaptable

Would you like to learn more about the advantages of cycloidal gears in positioners? Click here for more information.