Worm gearboxes with many combinations
Ever-Power offers a very wide variety of worm gearboxes. As a result of modular design the typical programme comprises countless combinations when it comes to selection of gear self locking gearbox housings, mounting and interconnection options, flanges, shaft styles, kind of oil, surface therapies etc.
Sturdy and reliable
The look of the Ever-Power worm gearbox is simple and well proven. We simply use high quality components such as houses in cast iron, metal and stainless steel, worms in case hardened and polished steel and worm wheels in high-quality bronze of specialized alloys ensuring the the best wearability. The seals of the worm gearbox are given with a dirt lip which efficiently resists dust and normal water. In addition, the gearboxes happen to be greased for life with synthetic oil.
Large reduction 100:1 in one step
As default the worm gearboxes allow for reductions of up to 100:1 in one step or 10.000:1 in a double reduction. An equivalent gearing with the same equipment ratios and the same transferred electric power is bigger when compared to a worm gearing. In the meantime, the worm gearbox can be in a far more simple design.
A double reduction may be composed of 2 regular gearboxes or as a particular gearbox.
Compact design
Compact design is among the key phrases of the standard 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 equipment combined with the utilization of cast iron and substantial precision on element manufacturing and assembly. In connection with our precision gearboxes, we take extra care of any sound that can be interpreted as a murmur from the apparatus. So the general noise degree of our gearbox is usually reduced to an absolute minimum.
Angle gearboxes
On the worm gearbox the input shaft and output shaft are perpendicular to each other. This frequently proves to become a decisive benefit producing the incorporation of the gearbox significantly simpler and more compact.The worm gearbox is an angle gear. This can often be an advantage for incorporation into constructions.
Strong bearings in sturdy housing
The output shaft of the Ever-Power worm gearbox is quite firmly embedded in the apparatus house and is perfect for direct suspension for wheels, movable arms and other parts rather than needing to build a separate suspension.
Self locking
For larger equipment ratios, Ever-Power worm gearboxes will provide a self-locking effect, which in many situations can be used as brake or as extra security. As well spindle gearboxes with a trapezoidal spindle will be self-locking, making them perfect for a wide variety of solutions.
In most equipment drives, when traveling torque is suddenly reduced as a result of electric power off, torsional vibration, vitality outage, or any mechanical failure at the transmitting input side, then gears will be rotating either in the same path driven by the machine inertia, or in the contrary route driven 
by the resistant output load due to gravity, springtime load, etc. The latter condition is called backdriving. During inertial motion or backdriving, the powered output shaft (load) turns into the driving one and the driving input shaft (load) turns into the motivated one. There are plenty of gear travel applications where outcome shaft driving is unwanted. So as to prevent it, various kinds of brake or clutch gadgets are used.
However, there are also solutions in the gear transmission that prevent inertial movement or backdriving using self-locking gears without the additional equipment. The most typical one is a worm gear with a low lead angle. In self-locking worm gears, torque utilized from the strain side (worm equipment) is blocked, i.electronic. cannot travel the worm. On the other hand, their application includes some limitations: the crossed axis shafts’ arrangement, relatively high gear ratio, low swiftness, low gear mesh performance, increased heat generation, etc.
Also, there happen to be parallel axis self-locking gears [1, 2]. These gears, unlike the worm gears, can utilize any gear ratio from 1:1 and bigger. They have the traveling mode and self-locking function, when the inertial or backdriving torque is definitely put on the output gear. Originally these gears had suprisingly low ( <50 percent) generating productivity that limited their request. Then it had been proved [3] that substantial driving efficiency of this sort of gears is possible. Criteria of the self-locking was analyzed in this article [4]. This paper explains the principle of the self-locking process for the parallel axis gears with symmetric and asymmetric the teeth profile, and reveals their suitability for diverse applications.
Self-Locking Condition
Figure 1 presents conventional gears (a) and self-locking gears (b), in case of backdriving. Figure 2 presents regular gears (a) and self-locking gears (b), in the event of inertial driving. Practically all conventional gear drives possess the pitch point P located in the active portion the contact collection B1-B2 (Figure 1a and Shape 2a). This pitch point location provides low specific sliding velocities and friction, and, due to this fact, high driving efficiency. In case when these kinds of gears are motivated by outcome load or inertia, they will be rotating freely, as the friction minute (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, put on the pinion
F – driving force
F’ – traveling force, when the backdriving or perhaps inertial torque put on 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 dynamic portion the contact line B1-B2. There are two options. Alternative 1: when the idea P is placed between a center of the pinion O1 and the idea B2, where the outer size of the apparatus intersects the contact line. 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 put between your point B1, where the outer size of the pinion intersects the line contact and a centre of the gear O2. This sort of gears can be self-locking with relatively high driving effectiveness > 50 percent.
Another condition of self-locking is to have a adequate friction angle g to deflect the force F’ beyond the guts of the pinion O1. It generates the resisting self-locking moment (torque) T’1 = F’ x L’1, where L’1 is usually a lever of the pressure F’1. This condition could be provided as L’1min > 0 or
(1) Equation 1
or
(2) Equation 2
where:
u = n2/n1 – equipment ratio,
n1 and n2 – pinion and gear quantity of teeth,
– involute profile angle at the tip of the gear tooth.
Design of Self-Locking Gears
Self-locking gears are customized. They cannot end up being fabricated with the criteria tooling with, for example, the 20o pressure and rack. This makes them very suitable for Direct Gear Design® [5, 6] that provides required gear effectiveness and from then on defines tooling parameters.
Direct Gear Design presents the symmetric gear tooth produced by two involutes of 1 base circle (Figure 3a). The asymmetric gear tooth is formed by two involutes of two different base circles (Figure 3b). The tooth hint circle da allows avoiding the pointed tooth hint. The equally spaced the teeth form the apparatus. The fillet profile between teeth was created independently to avoid interference and provide minimum bending pressure. The operating pressure angle aw and the get in touch with ratio ea are defined 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 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 position to aw = 75 – 85o. Because of this, the transverse speak to ratio ea < 1.0 (typically 0.4 - 0.6). Lack of the transverse speak to ratio should be compensated by the axial (or face) get in touch with ratio eb to guarantee the total contact ratio eg = ea + eb ≥ 1.0. This could be achieved by using helical gears (Shape 4). Nevertheless, helical gears apply the axial (thrust) power on the apparatus bearings. The dual helical (or “herringbone”) gears (Body 4) allow to compensate this force.
Large transverse pressure angles bring about increased bearing radial load that may be up to four to five situations higher than for the conventional 20o pressure angle gears. Bearing collection and gearbox housing design ought to be done accordingly to hold this improved load without high deflection.
Application of the asymmetric pearly whites for unidirectional drives allows for improved overall performance. For the self-locking gears that are used to prevent backdriving, the same tooth flank is utilized for both driving and locking modes. In this case asymmetric tooth profiles provide much higher transverse speak to ratio at the provided pressure angle compared to the symmetric tooth flanks. It makes it possible to reduce the helix angle and axial bearing load. For the self-locking gears that used to avoid inertial driving, diverse tooth flanks are being used for traveling and locking modes. In this instance, asymmetric tooth profile with low-pressure position provides high performance for driving setting and the contrary high-pressure angle tooth account is utilized for reliable self-locking.
Testing Self-Locking Gears
Self-locking helical gear prototype sets were made predicated on the developed mathematical designs. The gear info are presented in the Table 1, and the test 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 operate a vehicle the actuator. A rate and torque sensor was mounted on the high-acceleration 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 information had been captured in the data acquisition tool and further analyzed in a pc employing data analysis program. The instantaneous efficiency of the actuator was calculated and plotted for a wide variety of speed/torque combination. Typical driving productivity of the self- locking gear obtained during evaluating was above 85 percent. The self-locking property of the helical gear occur backdriving mode was likewise tested. In this test the exterior torque was put on the output equipment shaft and the angular transducer demonstrated no angular motion of suggestions shaft, which confirmed the self-locking condition.
Potential Applications
Initially, self-locking gears were used in textile industry [2]. On the other hand, this sort of gears has various potential applications in lifting mechanisms, assembly tooling, and other equipment drives where the backdriving or inertial traveling is not permissible. One of such request [7] of the self-locking gears for a continually variable valve lift program was advised for an vehicle engine.
Summary
In this paper, a theory of do the job of the self-locking gears has been described. Design specifics of the self-locking gears with symmetric and asymmetric profiles will be shown, and examining of the apparatus prototypes has proved relatively high driving productivity and dependable self-locking. The self-locking gears may find many applications in a variety of industries. For example, in a control devices where position balance is vital (such as for example in vehicle, aerospace, medical, robotic, agricultural etc.) the self-locking allows to accomplish required performance. Like the worm self-locking gears, the parallel axis self-locking gears are hypersensitive to operating conditions. The locking stability is affected by lubrication, vibration, misalignment, etc. Implementation of these gears should be done with caution and requires comprehensive testing in every possible operating conditions.