A gear rate reducer is a representative exemplory 
case of acceleration changers, and presently used devices could be categorized by the type of gears, shaft positions and arrangement of gears into (1) equipment reducer with parallel axes, (2) gear reducer with orthogonal axes, (3) gear reducer with perpendicular nonintersecting axes, and (4) gear reducer with coaxial axes.
Types and mechanisms of gear reducers with parallel axes
The apparatus reducers with parallel axes use spur gears, helical gears, or herringbone gears. Their input and result shafts are parallel. As for decrease ratios, 1/1 – 1/7 for one-stage shafts, 1/10 – 1/30 for two-stage shafts, and 1/5 – 1/200 for more than three-stage shafts are commercially available. The overall characteristics of gear reducers with parallel axes are as follows :
For high precision gears, the tranny efficiency is very high. (98 to 95% for one-stage equipment reducer)
When properly lubricated, it can be used for a long period.
Can be produced relatively cheaply because standardized gears are used.
Gear reducers with spur gears are used for planetary gearbox increasing rate.
The sizes of gear reducers with spur gears are is normally large. In comparison to worm gear reducers with the same acceleration ratio, their outer shapes are huge, and the amount of parts increases leading to constructional disadvantages. Consequently, it can be used for machines with high rotation on the strain side, or which need higher output rotation than the prime movers (for increasing quickness). The apparatus types are demonstrated in Table 2.1.
The gear reducers with parallel axes usually use helical gears. They are used in steel facilities, ships, cranes, elevators, and conveyors. As for automation machines, these equipment reducers are also known for geared motors which are equipment reducers with directly linked motors.