A gear speed reducer is a representative example of quickness changers, and presently used devices 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) 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 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 used for a long period.
Can be produced relatively cheaply as standardized gears are used.
Gear reducers with spur gears are used for increasing rate.
The sizes of gear reducers with spur gears are is usually large. In planetary gearbox comparison to worm gear reducers with the same acceleration ratio, their outer designs are large, and the amount of parts increases resulting in constructional disadvantages. Consequently, it is utilized for machines with high rotation on the strain side, or which need higher output rotation compared to the primary movers (for increasing acceleration). The gear types are demonstrated 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. As for automation machines, these gear reducers 
are also known for geared motors which are gear reducers with directly connected motors.
