Worm gearboxes with countless combinations
Ever-Power offers an extremely wide selection of worm gearboxes. Due to the modular design the typical programme comprises countless self locking gearbox combinations in terms of selection of gear housings, mounting and interconnection options, flanges, shaft designs, type of oil, surface remedies 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 residences in cast iron, lightweight aluminum and stainless, worms in the event hardened and polished steel and worm wheels in high-quality bronze of exceptional alloys ensuring the the best possible wearability. The seals of the worm gearbox are provided 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 enable reductions of up to 100:1 in one single step or 10.000:1 in a double reduction. An equivalent gearing with the same gear ratios and the same transferred power is bigger than a worm gearing. At the 
same time, the worm gearbox is certainly in a more simple design.
A double reduction may be composed of 2 common 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 through the use of adapted gearboxes or distinctive gearboxes.
Low noise
Our worm gearboxes and actuators are extremely quiet. This is due to the very soft operating of the worm gear combined with the utilization of cast iron and great precision on element manufacturing and assembly. In connection with our precision gearboxes, we take extra attention of any sound which can be interpreted as a murmur from the gear. Therefore the general noise degree of our gearbox can be reduced to an absolute minimum.
Angle gearboxes
On the worm gearbox the input shaft and output shaft are perpendicular to each other. This typically proves to be a decisive edge making the incorporation of the gearbox significantly simpler and smaller sized.The worm gearbox can be an angle gear. This is normally an edge 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 perfect for direct suspension for wheels, movable arms and other areas rather than needing to build a separate suspension.
Self locking
For larger equipment ratios, Ever-Electrical power 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 are self-locking, making them well suited for a variety of solutions.
In most equipment drives, when traveling torque is suddenly reduced because of this of electric power off, torsional vibration, electrical power outage, or any mechanical failing at the transmission input aspect, then gears will be rotating either in the same path driven by the machine inertia, or in the contrary course driven by the resistant output load because of gravity, planting season load, etc. The latter state is known as backdriving. During inertial action or backdriving, the influenced output shaft (load) turns into the generating one and the generating input shaft (load) turns into the influenced one. There are many gear travel applications where outcome shaft driving is undesirable. In order to prevent it, several types of brake or clutch devices are used.
However, there are also solutions in the apparatus transmission that prevent inertial movement or backdriving using self-locking gears with no additional gadgets. The most frequent one is certainly a worm equipment with a minimal lead angle. In self-locking worm gears, torque utilized from the strain side (worm gear) is blocked, i.electronic. cannot drive the worm. Nevertheless, their application comes with some restrictions: the crossed axis shafts’ arrangement, relatively high gear ratio, low swiftness, low gear mesh efficiency, increased heat generation, etc.
Also, there will be parallel axis self-locking gears [1, 2]. These gears, unlike the worm gears, can make use of any gear ratio from 1:1 and higher. They have the traveling mode and self-locking function, when the inertial or backdriving torque is applied to the output gear. At first these gears had very low ( <50 percent) generating proficiency that limited their request. Then it had been proved [3] that high driving efficiency of these kinds of gears is possible. Conditions of the self-locking was analyzed on this page [4]. This paper explains the principle of the self-locking procedure for the parallel axis gears with symmetric and asymmetric the teeth profile, and reveals their suitability for numerous applications.
Self-Locking Condition
Body 1 presents conventional gears (a) and self-locking gears (b), in the event 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 brand B1-B2 (Figure 1a and Figure 2a). This pitch stage location provides low certain sliding velocities and friction, and, as a result, high driving productivity. In case when these kinds of gears are driven by end result 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, put on the gear
T’1 – driven torque, applied to the pinion
F – driving force
F’ – generating 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 should be located off the effective portion the contact line B1-B2. There are two options. Choice 1: when the point P is placed between a middle of the pinion O1 and the idea B2, where the outer size of the gear intersects the contact range. This makes the self-locking possible, however the driving proficiency will become low under 50 percent [3]. Choice 2 (figs 1b and 2b): when the point P is put between your point B1, where in fact the outer diameter of the pinion intersects the line contact and a center of the gear O2. This type of gears can be self-locking with relatively great driving proficiency > 50 percent.
Another condition of self-locking is to have a satisfactory 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 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 angle at the tip of the gear tooth.
Design of Self-Locking Gears
Self-locking gears are customized. They cannot be fabricated with the requirements tooling with, for example, the 20o pressure and rack. This makes them extremely suitable for Direct Gear Design® [5, 6] that delivers required gear effectiveness and after that defines tooling parameters.
Direct Gear Style presents the symmetric equipment tooth created by two involutes of 1 base circle (Figure 3a). The asymmetric gear tooth is shaped by two involutes of two different base circles (Figure 3b). The tooth idea circle da allows avoiding the pointed tooth suggestion. The equally spaced teeth form the apparatus. The fillet profile between teeth was created independently to avoid interference and offer minimum bending anxiety. The working pressure angle aw and the speak to 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 excessive 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. Subsequently, 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 ensure the total get in touch with ratio eg = ea + eb ≥ 1.0. This can be achieved by using helical gears (Physique 4). However, helical gears apply the axial (thrust) pressure on the gear bearings. The twice helical (or “herringbone”) gears (Determine 4) allow to compensate this force.
Substantial transverse pressure angles lead to increased bearing radial load that could be up to four to five occasions higher than for the traditional 20o pressure angle gears. Bearing selection and gearbox housing style ought to be done accordingly to hold this increased load without increased deflection.
Program of the asymmetric teeth for unidirectional drives permits improved functionality. For the self-locking gears that are used to prevent backdriving, the same tooth flank is used for both driving and locking modes. In this instance asymmetric tooth profiles present much higher transverse contact ratio at the presented pressure angle compared to the symmetric tooth flanks. It creates it possible to reduce the helix angle and axial bearing load. For the self-locking gears which used to prevent inertial driving, distinct tooth flanks are used for traveling and locking modes. In this instance, asymmetric tooth account with low-pressure position provides high proficiency for driving method and the contrary high-pressure angle tooth profile is utilized for reliable self-locking.
Testing Self-Locking Gears
Self-locking helical gear prototype pieces were made predicated on the developed mathematical models. The gear info are presented in the Desk 1, and the test gears are shown 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. An integrated swiftness and torque sensor was installed on the high-acceleration shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was linked to the low swiftness shaft of the gearbox via coupling. The suggestions and result torque and speed details were captured in the info acquisition tool and further analyzed in a pc applying data analysis computer software. The instantaneous performance of the actuator was calculated and plotted for a variety of speed/torque combination. Normal driving efficiency of the personal- locking equipment obtained during assessment was above 85 percent. The self-locking real estate of the helical equipment occur backdriving mode was as well tested. During this test the exterior torque was put on the output gear shaft and the angular transducer showed no angular movements of input shaft, which confirmed the self-locking condition.
Potential Applications
Initially, self-locking gears had been used in textile industry [2]. On the other hand, this kind of gears has a large number of potential applications in lifting mechanisms, assembly tooling, and other equipment drives where in fact the backdriving or inertial traveling is not permissible. Among such request [7] of the self-locking gears for a consistently variable valve lift system was advised for an auto engine.
Summary
In this paper, a principle of function 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 gear prototypes has proved relatively high driving performance and trusted self-locking. The self-locking gears may find many applications in various industries. For example, in a control devices where position stability is essential (such as in automotive, aerospace, medical, robotic, agricultural etc.) the self-locking allows to attain required performance. Like the worm self-locking gears, the parallel axis self-locking gears are hypersensitive to operating conditions. The locking stability is afflicted by lubrication, vibration, misalignment, etc. Implementation of the gears should be done with caution and needs comprehensive testing in every possible operating conditions.
