A gear rate reducer is a representative example of acceleration changers, and presently used models can be categorized by the type of gears, shaft positions and set up of gears into (1) gear reducer with planetary gearbox 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 equipment 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. For reduction 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 gear reducers with parallel axes are as follows :

For high precision gears, the transmission efficiency is quite high. (98 to 95% for one-stage gear reducer)
When correctly lubricated, it can be used for a long period.
Could be produced relatively cheaply since standardized gears are used.
Gear reducers with spur gears are used for increasing speed.
The sizes of gear reducers with spur gears are is usually 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. For that reason, it is utilized for devices with high rotation on the load side, or which require higher output rotation compared to the prime movers (for increasing acceleration). The apparatus types are demonstrated in Table 2.1.

The apparatus 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 gear reducers with directly connected motors.