Worm gearboxes with many combinations
Ever-Power offers a very wide self locking gearbox variety of worm gearboxes. As a result of modular design the standard programme comprises countless combinations in terms of selection of gear housings, mounting and interconnection options, flanges, shaft models, kind of oil, surface solutions etc.
Sturdy and reliable
The design of the Ever-Power worm gearbox is simple and well proven. We just use top quality components such as houses in cast iron, aluminium and stainless, worms in the event hardened and polished metal and worm wheels in high-quality bronze of unique alloys ensuring the optimum wearability. The seals of the worm gearbox are given with a dust lip which successfully resists dust and normal water. In addition, the gearboxes will be greased forever with synthetic oil.
Large reduction 100:1 in one step
As default the worm gearboxes allow for 
reductions as high as 100:1 in one single step or 10.000:1 in a double reduction. An comparative gearing with the same gear ratios and the same transferred power is bigger when compared to a worm gearing. At the same time, the worm gearbox can be in a more simple design.
A double reduction may be composed of 2 typical gearboxes or as a special gearbox.
Compact design
Compact design is among the key terms of the typical gearboxes of the Ever-Power-Series. Further optimisation may be accomplished by using adapted gearboxes or distinctive gearboxes.
Low noise
Our worm gearboxes and actuators are extremely quiet. This is because of the very even running of the worm gear combined with the use of cast iron and high precision on aspect manufacturing and assembly. In connection with our accuracy gearboxes, we consider extra care of any sound that can be interpreted as a murmur from the apparatus. So the general noise level of our gearbox is definitely reduced to an absolute minimum.
Angle gearboxes
On the worm gearbox the input shaft and output shaft are perpendicular to one another. This sometimes proves to become a decisive gain producing the incorporation of the gearbox substantially simpler and smaller sized.The worm gearbox can be an angle gear. This is often an edge for incorporation into constructions.
Strong bearings in sound housing
The output shaft of the Ever-Power worm gearbox is quite firmly embedded in the apparatus house and is suitable for immediate suspension for wheels, movable arms and other parts rather than needing to build a separate suspension.
Self locking
For larger gear ratios, Ever-Ability worm gearboxes provides a self-locking effect, which in lots of situations can be utilised as brake or as extra security. Also spindle gearboxes with a trapezoidal spindle happen to be self-locking, making them suitable for a wide variety of solutions.
In most gear drives, when generating torque is suddenly reduced as a result of electric power off, torsional vibration, vitality outage, or any mechanical failure at the transmitting input part, then gears will be rotating either in the same course driven by the system inertia, or in the contrary route driven by the resistant output load because of gravity, spring load, etc. The latter state is known as backdriving. During inertial action or backdriving, the driven output shaft (load) becomes the driving one and the traveling input shaft (load) turns into the driven one. There are numerous gear drive applications where end result shaft driving is unwanted. As a way to prevent it, various kinds of brake or clutch products are used.
However, there are also solutions in the gear tranny that prevent inertial movement or backdriving using self-locking gears with no additional devices. The most frequent one is normally a worm equipment with a low lead angle. In self-locking worm gears, torque utilized from the strain side (worm gear) is blocked, i.e. cannot travel the worm. Even so, their application comes with some constraints: the crossed axis shafts’ arrangement, relatively high gear ratio, low quickness, low gear mesh effectiveness, increased heat technology, etc.
Also, there will be parallel axis self-locking gears [1, 2]. These gears, unlike the worm gears, can use any gear ratio from 1:1 and bigger. They have the driving mode and self-locking mode, when the inertial or backdriving torque is normally applied to the output gear. At first these gears had very low ( <50 percent) driving productivity that limited their app. Then it was proved [3] that substantial driving efficiency of these kinds of gears is possible. Requirements of the self-locking was analyzed on this page [4]. This paper explains the principle of the self-locking method for the parallel axis gears with symmetric and asymmetric teeth profile, and shows their suitability for different applications.
Self-Locking Condition
Body 1 presents conventional gears (a) and self-locking gears (b), in the event of backdriving. Figure 2 presents conventional gears (a) and self-locking gears (b), in case of inertial driving. Pretty much all conventional gear drives possess the pitch stage P situated in the active part the contact line B1-B2 (Figure 1a and Figure 2a). This pitch stage location provides low particular sliding velocities and friction, and, subsequently, high driving efficiency. In case when this sort of gears are powered by outcome load or inertia, they are rotating freely, because the friction point in time (or torque) isn’t sufficient to avoid rotation. In Figure 1 and Figure 2:
1- Driving pinion
2 – Driven gear
db1, db2 – base diameters
dp1, dp2 – pitch diameters
da1, da2 – outer diameters
T1 – driving pinion torque
T2 – driven gear torque
T’2 – driving torque, applied to the gear
T’1 – driven torque, applied to the pinion
F – driving force
F’ – driving force, when the backdriving or inertial torque applied to the gear
aw – operating transverse pressure angle
g – arctan(f) – friction angle
f – average friction coefficient
In order to make gears self-locking, the pitch point P ought to be located off the active portion the contact line B1-B2. There will be two options. Option 1: when the idea P is placed between a center of the pinion O1 and the point B2, where the outer size of the gear intersects the contact series. This makes the self-locking possible, but the driving performance will be low under 50 percent [3]. Choice 2 (figs 1b and 2b): when the point P is positioned between the point B1, where in fact the outer diameter of the pinion intersects the collection contact and a center of the apparatus O2. This kind of gears could be self-locking with relatively high driving effectiveness > 50 percent.
Another condition of self-locking is to truly have a adequate friction angle g to deflect the force F’ beyond the center of the pinion O1. It creates the resisting self-locking second (torque) T’1 = F’ x L’1, where L’1 is definitely a lever of the pressure F’1. This condition can be shown as L’1min > 0 or
(1) Equation 1
or
(2) Equation 2
where:
u = n2/n1 – gear ratio,
n1 and n2 – pinion and gear amount of teeth,
– involute profile angle at the end of the apparatus tooth.
Design of Self-Locking Gears
Self-locking gears are customized. They cannot be fabricated with the standards tooling with, for example, the 20o pressure and rack. This makes them incredibly well suited for Direct Gear Design® [5, 6] that provides required gear performance and from then on defines tooling parameters.
Direct Gear Design presents the symmetric gear tooth produced by two involutes of one base circle (Figure 3a). The asymmetric gear tooth is produced by two involutes of two distinct base circles (Figure 3b). The tooth idea circle da allows preventing the pointed tooth idea. The equally spaced the teeth form the gear. The fillet profile between teeth is designed independently in order to avoid interference and provide minimum bending stress. The working pressure angle aw and the get in touch with ratio ea are described by the following formulae:
– for gears with symmetric teeth
(3) Equation 3
(4) Equation 4
– for gears with asymmetric teeth
(5) Equation 5
(6) Equation 6
(7) Equation 7
where:
inv(x) = tan x – x – involute function of the profile angle x (in radians).
Conditions (1) and (2) show that self-locking requires ruthless and large sliding friction in the tooth contact. If the sliding friction coefficient f = 0.1 – 0.3, it needs the transverse operating pressure angle to aw = 75 – 85o. Therefore, the transverse speak to ratio ea < 1.0 (typically 0.4 - 0.6). Lack of the transverse get in touch with ratio ought to be compensated by the axial (or face) contact ratio eb to guarantee the total get in touch with ratio eg = ea + eb ≥ 1.0. This is often achieved by employing helical gears (Figure 4). However, helical gears apply the axial (thrust) power on the gear bearings. The dual helical (or “herringbone”) gears (Determine 4) allow to compensate this force.
Huge transverse pressure angles lead to increased bearing radial load that may be up to four to five moments higher than for the traditional 20o pressure angle gears. Bearing collection and gearbox housing design ought to be done accordingly to hold this elevated load without high deflection.
Application of the asymmetric tooth for unidirectional drives permits improved performance. For the self-locking gears that are being used to prevent backdriving, the same tooth flank can be used for both traveling and locking modes. In this case asymmetric tooth profiles provide much higher transverse speak to ratio at the given pressure angle than the symmetric tooth flanks. It makes it possible to reduce the helix position and axial bearing load. For the self-locking gears which used to avoid inertial driving, numerous tooth flanks are being used for traveling and locking modes. In this instance, asymmetric tooth account with low-pressure angle provides high performance for driving function and the contrary high-pressure angle tooth account is employed for reliable self-locking.
Testing Self-Locking Gears
Self-locking helical equipment prototype units were made predicated on the developed mathematical designs. The gear data are provided in the Desk 1, and the test gears are provided in Figure 5.
The schematic presentation of the test setup is displayed in Figure 6. The 0.5Nm electric motor was used to drive the actuator. A built-in quickness and torque sensor was installed on the high-rate shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was linked to the low speed shaft of the gearbox via coupling. The suggestions and productivity torque and speed info had been captured in the data acquisition tool and additional analyzed in a computer employing data analysis program. The instantaneous proficiency of the actuator was calculated and plotted for a variety of speed/torque combination. Standard driving effectiveness of the personal- locking gear obtained during screening was above 85 percent. The self-locking property of the helical gear occur backdriving mode was also tested. During this test the external torque was applied to the output equipment shaft and the angular transducer confirmed no angular motion of insight shaft, which confirmed the self-locking condition.
Potential Applications
Initially, self-locking gears were used in textile industry [2]. On the other hand, this kind of gears has many potential applications in lifting mechanisms, assembly tooling, and other equipment drives where in fact the backdriving or inertial generating is not permissible. One of such app [7] of the self-locking gears for a consistently variable valve lift system was recommended for an motor vehicle engine.
Summary
In this paper, a basic principle of work of the self-locking gears has been described. Style specifics of the self-locking gears with symmetric and asymmetric profiles are shown, and evaluating of the gear prototypes has proved comparatively high driving performance and trustworthy self-locking. The self-locking gears may find many applications in a variety of industries. For example, in a control systems where position steadiness is very important (such as in automotive, aerospace, medical, robotic, agricultural etc.) the self-locking will allow to attain required performance. Like the worm self-locking gears, the parallel axis self-locking gears are delicate to operating conditions. The locking stability is influenced by lubrication, vibration, misalignment, etc. Implementation of the gears should be done with caution and needs comprehensive testing in all possible operating conditions.
