Worm gearboxes with many combinations
Ever-Power offers a very wide selection of worm gearboxes. Due to the modular design the typical programme comprises many combinations in terms of selection of gear housings, mounting and interconnection options, flanges, shaft designs, kind of oil, surface treatments etc.
Sturdy and reliable
The design of the Ever-Power worm gearbox is simple and well proven. We just use top quality self locking gearbox components such as properties in cast iron, aluminum and stainless steel, worms in case hardened and polished metal and worm tires in high-grade bronze of unique alloys ensuring the maximum wearability. The seals of the worm gearbox are provided with a dust lip which successfully resists dust and drinking water. Furthermore, the gearboxes happen to be greased forever with synthetic oil.
Large reduction 100:1 in a single step
As default the worm gearboxes enable reductions as high as 100:1 in one step or 10.000:1 in a double lowering. An equivalent gearing with the same equipment ratios and the same transferred ability is bigger than a worm gearing. On the other hand, the worm gearbox is normally in a far 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 words of the typical gearboxes of the Ever-Power-Series. Further optimisation can be achieved by using adapted gearboxes or specialized gearboxes.
Low noise
Our worm gearboxes and actuators are extremely quiet. This is due to the very even jogging of the worm equipment combined with the use of cast iron and large precision on element manufacturing and assembly. Regarding the our precision gearboxes, we consider extra treatment of any sound which can be interpreted as a murmur from the apparatus. So the general noise degree of our gearbox is normally reduced to a complete minimum.
Angle gearboxes
On the worm gearbox the input shaft and output shaft are perpendicular to each other. This often proves to become a decisive benefit making the incorporation of the gearbox significantly simpler and more compact.The worm gearbox can be an angle gear. This is often an advantage for incorporation into constructions.
Strong bearings in sturdy housing
The output shaft of the Ever-Power worm gearbox is very firmly embedded in the apparatus house and is ideal 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 result, which in many situations can be used as brake or as extra security. Also spindle gearboxes with a trapezoidal spindle are self-locking, making them ideal for a broad range of solutions.
In most gear drives, when traveling torque is suddenly reduced as a result of ability off, torsional vibration, power outage, or any mechanical failure at the transmission input side, then gears will be rotating either in the same way driven by the system inertia, or in the contrary way driven by the resistant output load due to gravity, spring load, etc. The latter state is known as backdriving. During inertial 
motion or backdriving, the powered output shaft (load) turns into the driving one and the driving input shaft (load) becomes the influenced one. There are numerous gear travel applications where productivity shaft driving is undesirable. So that you can prevent it, different types of brake or clutch units are used.
However, there are also solutions in the apparatus transmission that prevent inertial motion or backdriving using self-locking gears without any additional gadgets. The most typical one is normally a worm gear with a minimal lead angle. In self-locking worm gears, torque utilized from the strain side (worm gear) is blocked, i.e. cannot drive the worm. Even so, their application includes some constraints: the crossed axis shafts’ arrangement, relatively high gear ratio, low speed, low gear mesh productivity, increased heat technology, etc.
Also, there are parallel axis self-locking gears [1, 2]. These gears, unlike the worm gears, can make use of any gear ratio from 1:1 and bigger. They have the generating mode and self-locking setting, when the inertial or backdriving torque can be put on the output gear. In the beginning these gears had suprisingly low ( <50 percent) driving efficiency that limited their software. Then it had been proved [3] that high driving efficiency of such gears is possible. Requirements of the self-locking was analyzed in the following paragraphs [4]. This paper explains the theory of the self-locking procedure for the parallel axis gears with symmetric and asymmetric pearly whites profile, and shows their suitability for different applications.
Self-Locking Condition
Shape 1 presents conventional gears (a) and self-locking gears (b), in case of backdriving. Figure 2 presents standard gears (a) and self-locking gears (b), in the event of inertial driving. Virtually all conventional gear drives possess the pitch level P located in the active part the contact collection B1-B2 (Figure 1a and Figure 2a). This pitch stage location provides low specific sliding velocities and friction, and, as a result, high driving performance. In case when such gears are motivated by result load or inertia, they will be rotating freely, as the friction instant (or torque) isn’t sufficient to stop 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, put on the gear
T’1 – driven torque, put on the pinion
F – driving force
F’ – driving force, when the backdriving or perhaps inertial torque applied to the gear
aw – operating transverse pressure angle
g – arctan(f) – friction angle
f – average friction coefficient
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. Alternative 1: when the point P is positioned between a center of the pinion O1 and the point B2, where the outer size of the apparatus intersects the contact series. This makes the self-locking possible, but the driving efficiency will become low under 50 percent [3]. Option 2 (figs 1b and 2b): when the idea P is inserted between your point B1, where in fact the outer size of the pinion intersects the collection contact and a middle of the apparatus O2. This type of gears can be self-locking with relatively substantial driving productivity > 50 percent.
Another condition of self-locking is to truly have a ample friction angle g to deflect the force F’ beyond the guts 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 force F’1. This condition could be provided 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 position at the tip of the apparatus tooth.
Design of Self-Locking Gears
Self-locking gears are customized. They cannot always be fabricated with the specifications tooling with, for example, the 20o pressure and rack. This makes them incredibly suitable for Direct Gear Design® [5, 6] that delivers required gear overall performance and from then on defines tooling parameters.
Direct Gear Design presents the symmetric equipment tooth formed by two involutes of 1 base circle (Figure 3a). The asymmetric equipment tooth is produced by two involutes of two different base circles (Figure 3b). The tooth hint circle da allows avoiding the pointed tooth hint. The equally spaced teeth form the gear. The fillet profile between teeth is designed independently in order to avoid interference and offer minimum bending stress. The operating pressure angle aw and the get in touch with ratio ea are identified by the next 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 high pressure and large sliding friction in the tooth speak to. If the sliding friction coefficient f = 0.1 – 0.3, it requires the transverse operating pressure angle to aw = 75 – 85o. Therefore, the transverse get in touch with ratio ea < 1.0 (typically 0.4 - 0.6). Insufficient the transverse speak to ratio ought to be compensated by the axial (or face) speak to ratio eb to ensure the total speak to ratio eg = ea + eb ≥ 1.0. This could be attained by using helical gears (Shape 4). Even so, helical gears apply the axial (thrust) force on the apparatus bearings. The twice helical (or “herringbone”) gears (Shape 4) allow to compensate this force.
Great transverse pressure angles lead to increased bearing radial load that could be up to four to five times higher than for the traditional 20o pressure angle gears. Bearing selection and gearbox housing design ought to be done accordingly to hold this increased load without high deflection.
Request of the asymmetric the teeth for unidirectional drives permits improved overall performance. For the self-locking gears that are used to avoid backdriving, the same tooth flank is used for both traveling and locking modes. In this case asymmetric tooth profiles give much higher transverse speak to ratio at the provided pressure angle compared to the symmetric tooth flanks. It creates it possible to lessen the helix angle and axial bearing load. For the self-locking gears that used to avoid inertial driving, diverse tooth flanks are used for traveling and locking modes. In this instance, asymmetric tooth account with low-pressure angle provides high efficiency for driving setting and the opposite high-pressure angle tooth account is used for reliable self-locking.
Testing Self-Locking Gears
Self-locking helical equipment prototype units were made predicated on the developed mathematical versions. The gear data are shown in the Desk 1, and the check gears are offered in Figure 5.
The schematic presentation of the test setup is shown in Figure 6. The 0.5Nm electric motor was used to drive the actuator. An integrated speed and torque sensor was attached on the high-speed shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was linked to the low speed shaft of the gearbox via coupling. The source and output torque and speed info were captured in the data acquisition tool and additional analyzed in a computer employing data analysis application. The instantaneous effectiveness of the actuator was calculated and plotted for a variety of speed/torque combination. Normal driving effectiveness of the self- locking gear obtained during assessment was above 85 percent. The self-locking house of the helical gear set in backdriving mode was as well tested. During this test the exterior torque was put on the output gear shaft and the angular transducer confirmed no angular movement of source shaft, which confirmed the self-locking condition.
Potential Applications
Initially, self-locking gears had been used in textile industry [2]. However, this type of gears has a large number of potential applications in lifting mechanisms, assembly tooling, and other gear drives where in fact the backdriving or inertial driving is not permissible. Among such request [7] of the self-locking gears for a consistently variable valve lift system was suggested for an automobile engine.
Summary
In this paper, a basic principle of do the job of the self-locking gears has been described. Style specifics of the self-locking gears with symmetric and asymmetric profiles are shown, and testing of the apparatus prototypes has proved comparatively high driving effectiveness and reputable self-locking. The self-locking gears may find many applications in a variety of industries. For instance, in a control systems where position stableness is vital (such as for example in vehicle, aerospace, medical, robotic, agricultural etc.) the self-locking will allow to achieve required performance. Similar to the worm self-locking gears, the parallel axis self-locking gears are hypersensitive to operating conditions. The locking reliability is influenced by lubrication, vibration, misalignment, etc. Implementation of the gears should be finished with caution and requires comprehensive testing in every possible operating conditions.
