Cycloidal gears offer unbeatable advantages
The two-stage reduction of cycloidal gears makes solutions from Nabtesco so successful. The reason is that the speed is reduced by the double cams. In addition, vibration is reduced by the two-stage reduction principle and low inertia. The force is also distributed very evenly, thanks to the roller cam design, and this contributes to the minimum hysteresis loss and enormous resistance to shock loading. Consequently, cycloidal gears are as versatile as they are resilient.
The drive or servomotor is connected to the spur gear stage of the gearbox via a pinion. The rotating speed reduces at this point relative to the reduction ratio between the pinion and planetary gear. The planetary gears are connected to crankshafts which drive the cams using needle bearings. These cams rotate inside the case which is lined with pins.
The cycloidal design of the precision reducer ensures extremely precise operation throughout the entire life cycle, with a hysteresis loss of less than one arcminute. The gear systems with zero backlash* are designed for high repeatability, positioning and rotational accuracy to allow exact positioning even at high speeds and accelerations, which makes them ideal for use as servo gearboxes.
*in the cycloidal gear stage
Nabtesco gears are extremely robust, durable and low-wear. They feature high overload capability and extreme rigidity, and are insensitive to vibrations. This is likewise an advantage for the servo gearboxes of the RH-N and RD series. The integrated angular ball bearings absorb axial and radial loads, as well as bending moments, which makes the gears highly resistant to impacts and overloads.
The high torque density of the low-backlash precision gears enables an extremely compact design. The precision reducer are lightweight, space-saving, and efficient – ideal for all applications requiring high performance and a compact design. Nabtesco offers a large selection of compact servo gearboxes for highly dynamic applications.
High shock resistance in emergency stop situations
The cam has exactly one eccentric section less than the pin ring has pins. A 360° revolution of the crankshafts therefore causes the cams to rotate one pin farther, whereby practically all the gear teeth are in continuous contact with the pins. The rotating movement is then transmitted from the input shaft to the crankshafts via the spur gear stage, and these then shift the cams in the pin ring and, consequently, generate a reduced speed with high precision. This technology enables the RV gears to absorb 5 times the rated torque in emergency-stop situations without suffering any damage. The resulting overall reduction is the same as the product of the two reduction ratios (spur gear stage and eccentric stage).
"RV" stands for our gear's "rotor vector" type of construction, and thus also for their extremely high resilience and precision.
- High rated torque of up to 28.000 Nm
- Minimum space required
- High shock load (5 times the rated torque)
- High rigidity
- Extreme precision (hysteresis loss < 1 arcmin)
- Low inertia
- Insensitive to vibrations
- Extremely low wear
- Long service life
State-of-the-art bearing concept
All cycloidal gears made by Nabtesco come with a strong, integrated main bearing that boasts large angular ball bearings and a multitude of rolling elements. This allows them to absorb bending moments that are 250% greater than the ones that can be absorbed by conventional planetary gears of comparable size. What is more, their robust bearing lets cycloidal gears also serve as a supporting element in a robot / machine or plant, eliminating the need for an additional external bearing. This makes it possible to manufacture more compact designs, reduce the engineering and installation expense and bring down cost. All bearings are assembled and preloaded by Nabtesco themselves.
Integrated main bearing:
- Absorption of great bending moments
- A supporting machine element
- No additional external bearing required
- Handling of heavy loads
- Manufacture of more compact robots, machines and plants
- Reduced costs of engineering and installation
History of the cycloidal gear
In the late 1920s the German design engineer and entrepreneur Lorenz Braren developed an entirely new technology: the cyclo gear. It used pins and rollers for power transmission instead of the usual gear wheels – the cycloidal gear was born. Originally, the invention was intended for use in cameras, but due to their outstanding properties the gears are used today primarily in robotics and other high-tech industries.
The first cycloidal gear from Nabtesco was produced in the year 1980. It was used in the power drives of excavators and was yet not designed as a precision gear. With the emergence and progress of robotic technology, one started using the Nabtesco gears in industrial robots – which marked the start of a successful “career” for these precision gears.
The first precision gear with a cycloidal design from Nabtesco was the RV gear. It was introduced in 1985. At that time the gears already featured the typical two-stage reduction principle, as well as three crankshafts. The gear also set standards with respect to standardisation: The cycloid stage is consistent within a gear size, while the different reduction ratios are achieved by means of the spur gear stage.