A gear rate reducer is a representative example of velocity changers, and presently used models could be categorized by the kind of gears, shaft positions and arrangement of gears into (1) equipment reducer with parallel axes, (2) gear reducer with orthogonal axes, (3) equipment reducer with perpendicular non-intersecting axes, and (4) gear reducer with coaxial axes.

Types and mechanisms of equipment planetary gearbox reducers with parallel axes
The gear reducers with parallel axes use spur gears, helical gears, or herringbone gears. Their input and output 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 a lot more than three-stage shafts are commercially available. The overall characteristics of equipment reducers with parallel axes are as follows :

For high precision gears, the transmitting efficiency is very high. (98 to 95% for one-stage equipment reducer)
When correctly lubricated, it can be utilized for a long period.
Can be produced relatively cheaply because standardized gears are used.
Gear reducers with spur gears are used for increasing velocity.
The sizes of gear reducers with spur gears are is normally large. Compared to worm equipment reducers with the same quickness ratio, their outer shapes are large, and the number of parts increases resulting in constructional disadvantages. As a result, it can be used for devices with high rotation on the strain side, or which need higher output rotation than the prime movers (for increasing speed). The apparatus types are shown in Table 2.1.

The apparatus reducers with parallel axes usually use helical gears. They are found in steel services, ships, cranes, elevators, and conveyors. For automation machines, these gear reducers are also known for geared motors which are equipment reducers with directly connected motors.