Ondrives.US has been designing and manufacturing reliable, high performance gearboxes for more than thirty years. Our FF Series parallel shaft spur gear reducers (FF and FFS models) are designed for high efficiency with low backlash. Manufactured from durable, high quality materials and permanently lubricated for superior performance with minimal maintenance requirements the FF and FFS are lightweight but rugged. Our parallel shaft gearboxes will provide years of reliable service, even in nonstop or high cycle operation ideal for a wide range of power transfer applications ( view catalog ). If youre unsure which parallel shaft gear reducer is right for your specific needs, view our Buyers Guide for ten important points to consider when choosing a gearbox. Another valuable reference, Inertia and the Use of Inertia Figures offers a formula for dealing with inertia in gearbox selection.
Huading Product Page
This article is reproduced with the permission.
Japan Institute of Plant Maintenance, Shinpan Gensokuki No Hon, Tokyo : JMA Consultants Inc. .
The copyrighted work used here was written in Japanese and was translated solely by KHK Co., Ltd.
A gear speed reducer is a representative example of speed changers, and presently used units can be categorized by the type of gears, shaft positions and arrangement of gears into (1) gear reducer with parallel axes, (2) gear reducer with orthogonal axes, (3) gear reducer with perpendicular non-intersecting axes, and (4) gear reducer with coaxial axes.
The gear reducers with parallel axes use spur gears, helical gears, or herringbone gears. Their input and output shafts are parallel. As 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 more than three-stage shafts are commercially available. The general characteristics of gear reducers with parallel axes are as follows :
The sizes of gear reducers with spur gears are is usually large. Compared to worm gear reducers with the same speed ratio, their outer shapes are large, and the number of parts increases leading to constructional disadvantages. Therefore, it is used for machines with high rotation on the load side, or which need higher output rotation than the prime movers (for increasing speed). The gear 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 gear reducers are also known for geared motors which are gear reducers with directly connected motors.
Spur gears :
Tooth traces are straight and teeth are parallel to the axis. Easily manufactured and most frequently used. Often used for increasing speed.
Helical gears :
Tooth traces of spur gear are slanted. Stronger than spur gears and produce less noise because of higher meshing ratios than spur gears. Axial forces are generated. Mainly used for power transmission.
Herringbone gears :
A type of helical gears where a pair of opposite hand helical gears are combined symmetrically. Similar to helical gears, but axial forces are not generated. Mainly used for high load power transmission.
Gear reducers with orthogonal axes are also known as bevel gear reducers, whose input and output shafts are perpendicular. Among the gears used are straight bevel gears, helical bevel gears, spiral bevel gears, Zerol bevel gears, face gears, and crown gears. Gear reducers with orthogonal axes are commonly used as power branching devices on site.
The precision of gear reducers with orthogonal axes are less than gear reducers with parallel axes. Especially, the pinion which is supported only on one side is easy to deflect, leading to a somewhat lower transmission efficiency (98%) due to resulting bad teeth contact. Straight bevel gear reducers are suitable for slow rotation under rpm, and standardized reduction ratios are 1:1 and 1:2.
In addition, the meshing ratio of the spiral bevel gear reducer is large and suitable for high load and high-speed rotation compared to straight bevel gear reducers. Generally, reduction ratio is limited to 1:6 for one stage. Table 2.2 shows the gears for bevel gear reducers.
Gear reducers whose input and output axes are offset and orthogonal to each other generally use hypoid gears or worm gears. Especially, worm gears have been used to reduce speed for a long time, and are still used frequently at present. The characteristics of gears used in them are shown in Table 2.3. The distinctive features of these reducers are as follows :
Figure 2.1 worm gears transmission efficiency
Vertical axis : Transmission efficiency (%)
Horizontal axis : Lead angle (r)
The coaxial type is also known as the planetary gear type, which is grouped into (1) simple planetary gears, (2) differential planetary gears, (3) eccentric planetary gears, and (4) elastic planetary gears.
The gear reducers with parallel axes or orthogonal axes previously discussed all have gears rotating around fixed axes.
As shown in Figure 2.2, planetary gear reducers are made up of the gear which rotates around the fixed axis (called the sun gear) and the meshed gears which rotate around the sun gear (called the planetary gears).
The Input and output gears can be concentrically installed in the planetary gear reducers to obtain high torque and efficiency, but it is said that it is necessary to transmit power equally to three planetary gears to maximize their ability.
Figure 2.3 shows a type of simple planetary gear reducer. In this compact gear reducer, three to five planetary gears mesh with the internal gear and transmit power from the input sun gear into multiple branches.
If load is uniformly distributed as in the ideal picture, a force of one gear times the number of planetary gears can be transmitted compared to a normal gear drive with one small and one large gear. Distributing forces as evenly as possible is the challenge for designers, and various mechanisms for equidistribution have been developed and put into practical use.
Figure 2.4 shows the structure of TRIRED reducer. One small gear is floated and supported at the center of the three large gears to balance the meshing reaction forces, so that the force branches into three directions.
Figure 2.2 Basic structure of planetary gear
1. Fixed axis / 2. Sun gear / 3. Arm (rotation support frame) / 4. Planetary gear
Figure 2.3 Structure example of simple planetary gear reducer
1. Slow axis / 2. Slow axis cover / 3. Case / 4. Internal gear / 5. Planetary gear bearing / 6. Planetary gear / 7. Joint cover / 8. Sun gear / 9. High speed side cover / 10. High speed axis
Figure 2.3 Structure example of simple planetary gear reducer (Equidistribution of load)
Figure 2.4 Structure of TRIRED reducer
Figure 2.4 Structure of TRIRED reducer (Equidistribution of load)
Only one or two teeth of normal external gears transmit force at any moment. The next pair of teeth should start meshing before the previous pair completes its meshing to rotate the gear smoothly. The force transmission capacity can be increased by having more teeth meshing simultaneously. For the same motion transmission, this unit is more compact than others. The Cyclo speed reducer is an example of one such type.
Figure 2.5 Structure of cyclo speed reducer (difference of the number of teeth: 1)
1. Outer pin / 2. Curved plate / 3. Eccentric body / 4. e (eccentric amount) / 5. Inner pin (with inner roller)
For more information, please visit Parallel Shaft Gear Reducer.
As shown in Figure 2.5, this speed reducer is an eccentric differential planetary gear reducer where the fixed internal sun gear with circular arc tooth profile (outer pin) is combined with the planetary gear with trochoidal smooth curved tooth profile (curved plate) with the difference of the numbers of teeth being 1.
The Cyclo speed reducer has a large number of teeth which mesh simultaneously, and resists overload and shock load well for its compact size.
Figure 2.6 shows the mechanism of an internal contact type planetary gear. Suppose that the number of teeth of afixed internal sun gear is S, and the number of teeth of a planetary gear is P. The relation of angular speed ω1 and ω2 is expressed in the following formula according to planetary gear theory :
ω2 / ω1 = 1 - S/P = -(S-P)/P
Suppose that S - P=1 (difference of the number of teeth: 1),
ω2 / ω1 = -1/P
For example, in Figure 2.6, assume that number of the teeth of the fixed internal sun gear is S=51, and the number of teeth of planetary gear is P=50. Then theoretically, it is possible to obtain a very large speed reduction of 1/50 using two spur gears.
However, since the general involute tooth form produces tooth tip interference, it is not possible to effectively utilize this mechanism with one tooth difference. The solution to this problem is the one tooth difference planetary gear mechanism shown in Figure 2.7. This internal contact type planetary gear utilizes a circular arc tooth form internal gear and smooth trochoid type curve planet gears resulting in no tooth tip interference and large numbers of teeth in simultaneous mesh.
Next, Figure 2.8 shows an equal velocity internal gear mechanism.
In this mechanism, the center of the planetary gear (curved plate) rotates at high speed (ω1) around the input shaft while its body revolves at low speed (ω2). This structure which extracts the slow speed rotation by combining of circular arc tooth forms, as shown in Figure 2.8, is the equal velocity internal gear mechanism. Ultimately, the rotation of the planetary gear (curved plate) can be taken out to the output axis through inner pins. Since the inner pins are equally positioned around the concentric circle of the crank axis (input shaft) with center Os, they can be attached directly to the output shaft, making the input shaft (high speed axis) and the output shaft (high speed axis) concentric.
The Cyclo speed reducer cleverly combines these two mechanisms and uses rollers on the circular arc tooth profile as shown in Figure 2.9.
Figure 2.6 Principle of internal contact type planetary gear
1. Crank (K) / 2. Revolving input axis / 3. Rotating planetary gear (crank) / 4. Planetary gear (P) / 5. Fixed internal sun gear (S)
Figure 2.7 Mechanism of one tooth difference internal contact type planetary gear
1. Rotating angular speed of planetary gear / 2. Revolving angular speed of crank / 3. Crank Shaft / 4. Planetary gear (P) / 5. Fixed internal sun gear (S)
Figure 2.8 Equal velocity internal gear mechanism
1. e (Amount of eccentricity) / 2. 2e (Twice the eccentric amount) / 3. Planetary gear (curved plate) / 4. Inner pin
Figure 2.9 Cyclo speed reducer mechanism
1. e (Amount of eccentricity) / 2. 2e (Twice the eccentric amount / 3. Inner pin (with inner roller) / 4. Eccentric body / 5. Curved plate / 6. Outer pin (with outer roller)
Planetary gear has a pair of meshing gears where both gears rotate while one gear revolves around the axis of the other gear.
An external gear mounted on the fixed axis (center axis) is the sun gear (gear rotates around the fixed axis) and the meshed gear whose axis rotates around the sun gear is the planetary gear.
Consider the case of the planetary gear device shown in Figure 2.10 where planetary gear B (number of teeth= Zb) revolves (number of rotation = nc) around fixed sun gear A (number of teeth = Za) while rotating on its own center (number of rotation = nb).
Therefore, the number of rotations of a planetary gear device where rotating planetary gear B revolves around fixed sun gear A while rotating on its own axis is the sum of the number of rotations in 1. and 2. (Table 2.4)
As a result, A=0 if the sun gear is fixed and as arm C rotates, the number of rotations of planetary gear B is nb = (1+ Za/Zb) nc.
Let us give some conditions to this expression. In Figure 2.10, how many times does planetary gear B rotate when arm C (rotation support frame) rotates to the right once ? Suppose the number of teeth Za of sun gear A is 80, while the number of teeth Zb of planetary gear B is 40.
The number of rotation nb of planetary gear B is :
nb
= (1+Za/Zb)nc
= (1+80/40)X1 = 3
Therefore, it rotates to the right three times.
Figure 2.10 Planetary gear device
Figure 2.11 Arm C is fixed and A rotates clockwise
Figure 2.12 All is fixed and A rotates clockwise
Related links :
Know about gear types and relations between the two shafts
For more Flexible Coupling Typesinformation, please contact us. We will provide professional answers.