RV reducers for industrial robot joints

How an RV reducer works

An RV reducer has two reduction stages in one compact housing. In the first stage, a sun gear on the input shaft drives two or three spur gears. Each spur gear turns a crankshaft with two eccentric journals. In the second stage, those eccentrics push two cycloid discs, mounted 180° apart for balance, around a ring of pins in the housing. Each disc has one lobe fewer than there are pins, so it advances one pin pitch per crank revolution. The crankshafts are held by the output carrier, which turns slowly with high torque.

Multiplying the two stages gives ratios from about 30:1 to over 180:1. Because many pins and lobes carry load at once, and the discs roll rather than slide, the reducer is extremely stiff and survives shock loads that would damage a gear tooth.

Why robot makers choose RV reducers

In a six-axis robot, joints 1 to 3 carry the arm, the payload and the tilting moments of fast motion. RV reducers integrate large angular-contact bearings, so they carry these moments directly and the joint needs no extra support bearing. Their stiffness keeps the arm accurate at the tool point, and their low lost motion (≤ 1 arcmin) gives repeatable positioning. The same qualities suit welding positioners, turntables, ATC magazines and heavy indexing tables.

Specifications that matter

• Rated torque at a given output speed, and the allowable acceleration and deceleration torque, which usually governs sizing for robot joints.
• Momentary maximum torque for emergency stops and collisions.
• Allowable moment of the main bearing, which must exceed the tilting moment from the arm.
• Lost motion and torsional rigidity, which set how accurately the joint holds position under changing load.

Sizing an RV reducer

Build a load cycle for the joint: acceleration, constant speed, deceleration and dwell, with torque and speed for each segment. Calculate the average load torque and average output speed, compare them with the rated values, and check that the peak torque stays below the allowable acceleration torque. Then check the tilting moment against the bearing rating. Our engineers will do this check for free if you send the joint's load cycle.