Worm gearboxes with many combinations
Ever-Power offers an extremely broad range of worm gearboxes. Due to the modular design the standard programme comprises many combinations when it comes to selection of gear housings, mounting and connection options, flanges, shaft models, kind of oil, surface solutions etc.
Sturdy and reliable
The look of the Ever-Power worm gearbox is simple and well proven. We just use high quality components such as properties in cast iron, light weight aluminum and stainless, worms in case hardened and polished metal and worm tires in high-quality bronze of specialized alloys ensuring the the best wearability. The seals of the worm gearbox are given with a dust lip which efficiently resists dust and normal water. Furthermore, the gearboxes are greased forever with synthetic oil.
Large reduction 100:1 in one step
As default the worm gearboxes enable reductions of up to 100:1 in one step or 10.000:1 in a double reduction. An comparative gearing with the same equipment ratios and the same transferred electricity is bigger when compared to a worm gearing. In the meantime, the worm gearbox is in a far more simple design.
A double reduction could be composed of 2 standard gearboxes or as a special gearbox.
Compact design
Compact design is one of the key terms of the typical gearboxes of the Ever-Power-Series. Further optimisation can be achieved by using adapted gearboxes or unique gearboxes.
Low noise
Our worm gearboxes and actuators are really quiet. This is because of the very smooth running of the worm equipment combined with the application of cast iron and large precision on element manufacturing and assembly. In connection with our accuracy gearboxes, we have extra health care of any sound which 
can be interpreted as a murmur from the apparatus. Therefore the general noise degree of our gearbox is certainly reduced to an absolute minimum.
Angle gearboxes
On the worm gearbox the input shaft and output shaft are perpendicular to one another. This typically proves to become a decisive advantages producing 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 stable housing
The output shaft of the Ever-Power worm gearbox is quite firmly embedded in the gear house and is suitable for immediate suspension for wheels, movable arms and other areas rather than having to create a separate suspension.
Self locking
For larger equipment ratios, Ever-Electricity worm gearboxes provides a self-locking effect, which in many situations works extremely well as brake or as extra security. Likewise spindle gearboxes with a trapezoidal spindle are self-locking, making them perfect for an array of solutions.
In most gear drives, when generating torque is suddenly reduced therefore of ability off, torsional vibration, power outage, or any mechanical inability at the tranny input side, then gears will be rotating either in the same path driven by the system inertia, or in the opposite way driven by the resistant output load because of gravity, planting season load, etc. The latter condition is known as backdriving. During inertial movement or backdriving, the influenced output shaft (load) turns into the driving one and the traveling input shaft (load) becomes the driven one. There are various gear travel applications where end result shaft driving is undesirable. In order to prevent it, different types of brake or clutch devices are used.
However, there are also solutions in the apparatus transmitting that prevent inertial action or backdriving using self-locking gears with no additional units. The most frequent one is a worm gear with a low lead angle. In self-locking worm gears, torque utilized from the load side (worm gear) is blocked, i.electronic. cannot drive the worm. However, their application includes some restrictions: the crossed axis shafts’ arrangement, relatively high gear ratio, low speed, low gear mesh effectiveness, increased heat era, etc.
Also, there are parallel axis self-locking gears [1, 2]. These gears, unlike the worm gears, can utilize any equipment ratio from 1:1 and larger. They have the driving mode and self-locking function, when the inertial or backdriving torque is certainly applied to the output gear. Primarily these gears had very low ( <50 percent) generating proficiency that limited their software. Then it was proved [3] that high driving efficiency of this sort of gears is possible. Requirements of the self-locking was analyzed in this post [4]. This paper explains the basic principle of the self-locking process for the parallel axis gears with symmetric and asymmetric the teeth profile, and reveals their suitability for several applications.
Self-Locking Condition
Body 1 presents conventional gears (a) and self-locking gears (b), in the event of backdriving. self locking gearbox Figure 2 presents conventional gears (a) and self-locking gears (b), in the event of inertial driving. Pretty much all conventional equipment drives have the pitch level P situated in the active part the contact line B1-B2 (Figure 1a and Number 2a). This pitch level location provides low certain sliding velocities and friction, and, therefore, high driving effectiveness. In case when this kind of gears are powered by result load or inertia, they will be rotating freely, because the friction moment (or torque) is not 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 happen to be two options. Choice 1: when the point P is placed between a centre of the pinion O1 and the point B2, where the outer size of the apparatus intersects the contact collection. This makes the self-locking possible, but the driving effectiveness will always be low under 50 percent [3]. Choice 2 (figs 1b and 2b): when the idea P is inserted between the point B1, where the outer diameter of the pinion intersects the line contact and a center of the apparatus O2. This type of gears can be self-locking with relatively large driving productivity > 50 percent.
Another condition of self-locking is to truly have a sufficient friction angle g to deflect the force F’ beyond the center of the pinion O1. It generates the resisting self-locking minute (torque) T’1 = F’ x L’1, where L’1 is certainly a lever of the induce F’1. This condition can be shown as L’1min > 0 or
(1) Equation 1
or
(2) Equation 2
where:
u = n2/n1 – equipment ratio,
n1 and n2 – pinion and gear amount of teeth,
– involute profile position at the tip of the gear tooth.
Design of Self-Locking Gears
Self-locking gears are customized. They cannot always be fabricated with the specifications tooling with, for instance, the 20o pressure and rack. This makes them incredibly suitable for Direct Gear Style® [5, 6] that delivers required gear functionality and from then on defines tooling parameters.
Direct Gear Style presents the symmetric equipment tooth formed by two involutes of one base circle (Figure 3a). The asymmetric equipment tooth is formed by two involutes of two distinct base circles (Figure 3b). The tooth suggestion circle da allows preventing the pointed tooth idea. The equally spaced pearly whites form the apparatus. The fillet profile between teeth is designed independently to avoid interference and offer minimum bending anxiety. The working pressure angle aw and the contact ratio ea are described 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 ruthless and huge sliding friction in the tooth get in touch with. If the sliding friction coefficient f = 0.1 – 0.3, it needs the transverse operating pressure angle to aw = 75 – 85o. Consequently, the transverse speak to ratio ea < 1.0 (typically 0.4 - 0.6). Insufficient the transverse contact ratio ought to be compensated by the axial (or face) contact ratio eb to ensure the total contact ratio eg = ea + eb ≥ 1.0. This is often achieved by applying helical gears (Shape 4). On the other hand, helical gears apply the axial (thrust) induce on the apparatus bearings. The double helical (or “herringbone”) gears (Shape 4) allow to pay this force.
High transverse pressure angles result in increased bearing radial load that could be up to four to five moments higher than for the traditional 20o pressure angle gears. Bearing selection and gearbox housing design should be done accordingly to carry this improved load without excessive deflection.
Application of the asymmetric pearly whites for unidirectional drives permits improved overall performance. For the self-locking gears that are used to prevent backdriving, the same tooth flank is employed for both generating and locking modes. In cases like this asymmetric tooth profiles give much higher transverse speak to ratio at the offered pressure angle compared to the symmetric tooth flanks. It creates it possible to reduce the helix position and axial bearing load. For the self-locking gears which used to avoid inertial driving, unique tooth flanks are being used for traveling and locking modes. In this case, asymmetric tooth account with low-pressure angle provides high effectiveness for driving method and the contrary high-pressure angle tooth profile is employed for reliable self-locking.
Testing Self-Locking Gears
Self-locking helical equipment prototype pieces were made based on the developed mathematical styles. The gear info are shown in the Desk 1, and the test gears are offered in Figure 5.
The schematic presentation of the test setup is proven in Figure 6. The 0.5Nm electric motor was used to drive the actuator. An integrated rate and torque sensor was attached on the high-speed shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was linked to the low swiftness shaft of the gearbox via coupling. The type and output torque and speed facts were captured in the data acquisition tool and further analyzed in a computer applying data analysis application. The instantaneous proficiency of the actuator was calculated and plotted for a variety of speed/torque combination. Typical driving effectiveness of the personal- locking equipment obtained during assessment was above 85 percent. The self-locking property of the helical gear set in backdriving mode was also tested. In this test the exterior torque was put on the output gear shaft and the angular transducer showed no angular movement of input shaft, which confirmed the self-locking condition.
Potential Applications
Initially, self-locking gears had been found in textile industry [2]. Even so, this kind of gears has various potential applications in lifting mechanisms, assembly tooling, and other equipment drives where the backdriving or inertial driving is not permissible. One of such request [7] of the self-locking gears for a constantly variable valve lift system was recommended for an auto engine.
Summary
In this paper, a principle of do the job of the self-locking gears has been described. Design specifics of the self-locking gears with symmetric and asymmetric profiles are shown, and testing of the gear prototypes has proved fairly high driving efficiency and reliable self-locking. The self-locking gears could find many applications in a variety of industries. For example, in a control devices where position steadiness is very important (such as for example in automotive, aerospace, medical, robotic, agricultural etc.) the self-locking allows to attain required performance. Similar to the worm self-locking gears, the parallel axis self-locking gears are sensitive to operating conditions. The locking stability is influenced by lubrication, vibration, misalignment, etc. Implementation of these gears should be finished with caution and requires comprehensive testing in every possible operating conditions.
