A gear speed reducer is a representative exemplory case of velocity changers, and presently used products can be categorized by the type of gears, shaft planetary gearbox positions and set up of gears into (1) equipment reducer with parallel axes, (2) equipment reducer with orthogonal axes, (3) gear reducer with perpendicular non-intersecting axes, and (4) gear reducer with coaxial axes.
Types and mechanisms of gear reducers with parallel axes
The gear reducers with 
parallel axes use spur gears, helical gears, or herringbone gears. Their input and result shafts are parallel. 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 gear reducers with parallel axes are as follows :
For high precision gears, the transmission efficiency is very high. (98 to 95% for one-stage equipment reducer)
When properly lubricated, it can be utilized for a long time.
Can be produced relatively cheaply as standardized gears are used.
Gear reducers with spur gears are used for increasing acceleration.
The sizes of gear reducers with spur gears are is usually large. Compared to worm gear reducers with the same acceleration ratio, their outer designs are large, and the number of parts increases resulting in constructional disadvantages. Consequently, it can be used for devices with high rotation on the load side, or which require higher output rotation than the primary movers (for increasing speed). The apparatus types are shown 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 gear reducers with directly linked motors.