A Vacuum Pump cycloidal reducer is a kind of gear reducer. The basic operation is that an input shaft connects to and drives an eccentric bearing. This bearing further drives a cycloidal disk (sometimes known as a cam) that connects to an output shaft.
cycloidal reducer
Usual cycloidal speed reducers, such as for example these Dojen series reducers from Onvio, offer zero backlash by combining a compound reduction cam with preloaded, complete compliment needle bearing cam followers.
The cycloidal disk (or cam) has lobes or teeth that engage with some type of cam follower, typically a pin or needle bearings. The eccentric rotation of the cam is definitely changed into rotation of an output shaft at a reduced speed and an increase in torque.
The main benefit of cycloidal reducers 
is their property of zero or near-zero backlash, which results in high precision and high accuracy. That is especially in demand where highly precise and accurate positioning is required, for instance in robotic applications, machine tools, and comparable applications. Cycloidal reducers also feature rolling as opposed to sliding contact, therefore experiencing less overall wear.