Backlash and hysteresis loss largely characterise the precision of a gearbox. A lower value corresponds to higher gear precision. Hysteresis loss is measured by scanning the hysteresis. In a standardised test procedure the gear output shaft is fixed and then subjected first to an increasing torque, followed by decreasing and then increasing torque again. The angular tolerance between the gear input and output shaft at a torque of 0 Nm is referred to as hysteresis loss. Backlash and hysteresis loss are specified in arc.min (= minutes of arc). One arcminute is defined as one 60th of a degree.
Minimal backlash
The hysteresis loss in Nabtesco cycloidal gears is less than one arcminute. The majority of the loss results from friction, which occurs in every gearbox in normal operation. The purely mechanical backlash is between 0.1 and 0.3 arc.min, which means there is no perceptible backlash at the gear output shaft.
Another important characteristic is the lost motion value. Measured at 3 % of the rated torque, it specifies how the gear behaves when subjected to low torques. This characteristic is also negligible in Nabtesco gears, on average between 0.3 and 0.6 arc.min. The result is extremely good positioning precision and repeatability – also at high acceleration torques and under heavy loads.
For maximum precision such as that required in medical technology, gears with values below 0.25 arc.min are also available.
Precision through rigidity
Minimal hysteresis loss in cycloidal gears is the result of their special design principle. This design ensures virtually full contact and even distribution of forces within the gearbox, which produces high rigidity. Another decisive factor here is the robust main bearing. As a result, it is possible to transmit very high torques with maximum precision and smooth operation.
Cycloidal gears require no readjustment, since they maintain their minimal circumferential backlash throughout the entire service life. For the user, this means utmost reliability, a long life and higher machine or robot availability.
Zero backlash gears
Wherever there is contact between components, friction is inevitable. Gears with minimal backlash of less than 1 arc.min are considered to be almost backlash-free. Backlash-free gears without any backlash are only used in extremely few applications.
Hysteresis loss, backlash and lost motion are specific to each individual gear.
The most important data at a glance:
- Hysteresis loss = 0.2 to max. 1 arc.min
- Values < 0.25 arc.min are technically feasible
- Backlash/purely mechanical backlash = 0.1 to 0.3 arc.min
- Lost motion = 0.3 to 0.6 arc.min