self locking gearbox

Worm gearboxes with countless combinations
Ever-Power offers a very wide variety of worm gearboxes. As a result of modular design the standard programme comprises many combinations with regards to selection of gear housings, mounting and interconnection options, flanges, shaft models, type of oil, surface solutions etc.
Sturdy and reliable
The design of the Ever-Power worm gearbox is easy and well proven. We simply use high quality components such as properties in cast iron, aluminum and stainless, worms in case hardened and polished steel and worm tires in high-grade bronze of exceptional alloys ensuring the the best wearability. The seals of the worm gearbox are provided with a dirt lip which properly resists dust and water. Furthermore, 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 step or 10.000:1 in a double reduction. An comparative gearing with the same equipment ratios and the same transferred ability is bigger when compared to a worm gearing. At the same time, the worm gearbox is definitely in a more simple design.
A double reduction may be composed of 2 common gearboxes or as a particular gearbox.
Compact design
Compact design is one of the key words of the typical gearboxes of the Ever-Power-Series. Further optimisation can be achieved through the use of adapted gearboxes or unique gearboxes.
Low noise
Our worm gearboxes and actuators are extremely quiet. This is due to the very easy working of the worm gear combined with the utilization of cast iron and excessive precision on component manufacturing and assembly. In connection with our accuracy gearboxes, we take extra treatment of any sound which can be interpreted as a murmur from the apparatus. So the general noise level 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 typically proves to become a decisive edge producing the incorporation of the gearbox substantially simpler and smaller sized.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 very firmly embedded in the apparatus house and is perfect for immediate suspension for wheels, movable arms and other parts rather than needing to create a separate suspension.
Self locking
For larger equipment ratios, Ever-Vitality worm gearboxes will provide a self-locking impact, which in lots of situations works extremely well as brake or as extra reliability. Likewise spindle gearboxes with a trapezoidal spindle are self-locking, making them suitable for an array of solutions.
In most gear drives, when traveling torque is suddenly reduced therefore of power off, torsional vibration, vitality outage, or any mechanical failing at the tranny input part, then gears will be rotating either in the same way driven by the machine inertia, or in the opposite path driven by the resistant output load due to gravity, planting season load, etc. The latter condition is known as backdriving. During self locking gearbox inertial movement or backdriving, the powered output shaft (load) becomes the driving one and the generating input shaft (load) becomes the influenced one. There are lots of gear travel applications where result shaft driving is unwanted. So as to prevent it, various kinds of brake or clutch equipment are used.
However, additionally, there are solutions in the apparatus tranny that prevent inertial motion or backdriving using self-locking gears without any additional equipment. The most frequent one is usually a worm equipment with a low lead angle. In self-locking worm gears, torque utilized from the load side (worm equipment) is blocked, i.electronic. cannot travel the worm. Nevertheless, their application comes with some constraints: the crossed axis shafts’ arrangement, relatively high equipment 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 utilize any gear ratio from 1:1 and larger. They have the traveling mode and self-locking method, when the inertial or backdriving torque is applied to the output gear. Primarily these gears had very low ( <50 percent) generating efficiency that limited their app. Then it had been proved [3] that large driving efficiency of this kind of gears is possible. Criteria of the self-locking was analyzed in this posting [4]. This paper explains the basic principle of the self-locking method for the parallel axis gears with symmetric and asymmetric the teeth profile, and reveals their suitability for several applications.
Self-Locking Condition
Physique 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 the event of inertial driving. Virtually all conventional equipment drives possess the pitch level P situated in the active portion the contact series B1-B2 (Figure 1a and Determine 2a). This pitch level location provides low certain sliding velocities and friction, and, therefore, high driving efficiency. In case when this sort of gears are motivated by productivity load or inertia, they are rotating freely, as the friction point in time (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, applied to the pinion
F – driving force
F’ – traveling 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 should be located off the effective portion the contact line B1-B2. There are two options. Alternative 1: when the idea P is positioned between a center 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, but the driving performance will end up being low under 50 percent [3]. Alternative 2 (figs 1b and 2b): when the point P is positioned between your point B1, where in fact the outer size of the pinion intersects the line contact and a middle of the apparatus O2. This type of gears could be self-locking with relatively substantial driving effectiveness > 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 creates the resisting self-locking moment (torque) T’1 = F’ x L’1, where L’1 is normally a lever of the drive F’1. This condition could be offered 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 become fabricated with the expectations tooling with, for instance, the 20o pressure and rack. This makes them very well suited for Direct Gear Style® [5, 6] that provides required gear effectiveness and after that defines tooling parameters.
Direct Gear Design presents the symmetric gear tooth produced by two involutes of one base circle (Figure 3a). The asymmetric equipment tooth is shaped by two involutes of two different base circles (Figure 3b). The tooth idea circle da allows preventing the pointed tooth tip. The equally spaced the teeth form the gear. The fillet account between teeth was created independently to avoid interference and offer minimum bending stress. The functioning pressure angle aw and the contact ratio ea are defined 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 excessive sliding friction in the tooth get in touch with. If the sliding friction coefficient f = 0.1 – 0.3, it requires the transverse operating pressure position to aw = 75 – 85o. Due to this fact, the transverse contact ratio ea < 1.0 (typically 0.4 - 0.6). Insufficient 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 is often achieved by applying helical gears (Number 4). Even so, helical gears apply the axial (thrust) power on the gear bearings. The dual helical (or “herringbone”) gears (Physique 4) allow to compensate this force.
Substantial transverse pressure angles cause 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 should be done accordingly to hold this improved load without extreme deflection.
App of the asymmetric teeth for unidirectional drives permits improved efficiency. For the self-locking gears that are used to prevent backdriving, the same tooth flank can be used for both driving and locking modes. In this case asymmetric tooth profiles give much higher transverse get in touch with ratio at the given pressure angle than the symmetric tooth flanks. It creates it possible to lessen the helix angle and axial bearing load. For the self-locking gears which used to avoid inertial driving, distinct tooth flanks are being used for traveling and locking modes. In cases like this, asymmetric tooth profile with low-pressure position provides high efficiency for driving setting and the opposite high-pressure angle tooth account is utilized for reliable self-locking.
Testing Self-Locking Gears
Self-locking helical equipment prototype units were made predicated on the developed mathematical products. The gear info are provided in the Table 1, and the check gears are shown in Figure 5.
The schematic presentation of the test setup is proven in Figure 6. The 0.5Nm electric electric motor was used to drive the actuator. An integrated swiftness and torque sensor was attached on the high-rate shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was linked to the low quickness shaft of the gearbox via coupling. The input and productivity torque and speed details were captured in the data acquisition tool and further analyzed in a pc using data analysis software program. The instantaneous performance of the actuator was calculated and plotted for an array of speed/torque combination. Typical driving effectiveness of the personal- locking gear obtained during tests was above 85 percent. The self-locking house of the helical equipment set in backdriving mode was as well tested. In this test the exterior torque was applied to the output equipment shaft and the angular transducer revealed no angular motion of type shaft, which verified the self-locking condition.
Potential Applications
Initially, self-locking gears had been used in textile industry [2]. However, this type of gears has various potential applications in lifting mechanisms, assembly tooling, and other equipment drives where the backdriving or inertial generating is not permissible. One of such app [7] of the self-locking gears for a continuously variable valve lift program was advised for an vehicle engine.
Summary
In this paper, a theory of function of the self-locking gears has been described. Style specifics of the self-locking gears with symmetric and asymmetric profiles will be shown, and testing of the apparatus prototypes has proved comparatively high driving efficiency and reliable self-locking. The self-locking gears may find many applications in a variety of industries. For instance, in a control devices where position stability is very important (such as for example in auto, aerospace, medical, robotic, agricultural etc.) the self-locking allows to achieve required performance. Like the worm self-locking gears, the parallel axis self-locking gears are hypersensitive to operating conditions. The locking dependability is affected by lubrication, vibration, misalignment, etc. Implementation of the gears should be finished with caution and needs comprehensive testing in every possible operating conditions.