KTR ROTEX GS Backlash-Free Servo Coupling

Backlash-free jaw coupling for positioning drives

The KTR ROTEX GS is a three-part servo coupling, backlash-free under prestress. Two hubs and a flexible spider form an elastomer coupling that stays torsionally stiff enough for precise positioning while still damping vibration. KTR offers it with different hub versions and five Shore hardnesses of spider, so the same size can be tuned toward damping or toward stiffness. It is applied where drives must position precisely, for example on servo axes, feed drives and automation equipment.

The values below come from KTR operating and assembly instructions KTR-N 45510 EN (edition 26) for ROTEX GS shaft couplings, clamping hubs, Compact, clamping ring hubs, DKM and combinations.

Technical specifications

Choosing hub version and spider

For motor and encoder shafts without keyways the clamping hubs (types 2.0 and 2.5, Compact types 2.8 and 2.9, and the clamping ring hub 6.0) avoid a key connection and fit directly onto smooth servo shafts. Standard hub 1.0 with keyway and setscrew is the general-purpose alternative. The spider hardness decides the compromise: the softer 80 and 92 Shore A spiders damp more and carry less rated torque, while the 64 and 72 Shore D spiders are the stiffest and carry the highest torque but allow the smallest displacement. KTR recommends steel hubs when the 72 Shore D spider is used.

As for other KTR elastomer couplings, the torque data refer to the spider only. The transmittable torque of the clamping or keyed shaft connection depends on bore, tolerance and tightening torque and must be checked separately. KTR gives the displacement figures as standard values for loads up to the rated torque and an ambient temperature of +30 °C. In drives with torsional vibration the coupling must be selected with a torsional vibration calculation.

Assembly notes

Hubs with no keyway and no setscrew, such as type 1.2, are not approved for explosive atmospheres, and hubs without a feather keyway may be used in category 3 only. Hubs can be heated lightly, to about 80 °C, to ease fitting. Clamping screws are tightened to the torque listed for each size; for example the size 14 clamping screw M3 takes 1.34 Nm, and the size 19 clamping hub takes M4 screws at 2.9 Nm on bores of 22 to 24 mm. Alignment must stay inside the displacement tables for the spider hardness chosen.

Documents and quotation

The attached PDF is the KTR operating and assembly instruction for ROTEX GS and contains dimension tables per hub type. For a quotation send the shaft diameters, tolerance and keyway if any, peak and rated torque, speed, accuracy requirement, ambient temperature and hub version. Matching amplifiers are listed under Servo Drives.