self locking gearbox

Worm gearboxes with many combinations
Ever-Power offers a very wide variety 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 styles, kind of oil, surface solutions etc.
Sturdy and reliable
The design of the Ever-Power worm gearbox is simple and well proven. We only use high quality components such as homes in cast iron, lightweight aluminum and stainless steel, worms in case hardened and polished steel and worm wheels in high-grade bronze of unique alloys ensuring the the best possible wearability. The seals of the worm gearbox are given with a dust lip which successfully resists dust and normal water. Furthermore, the gearboxes are greased for life with synthetic oil.
Large reduction 100:1 in one step
As default the worm gearboxes allow for reductions as high as 100:1 in one step or 10.000:1 in a double lowering. An equivalent gearing with the same gear ratios and the same transferred power is bigger when compared to a worm gearing. Meanwhile, the worm gearbox is in a more simple design.
A double reduction may be composed of 2 standard gearboxes or as a special gearbox.
Compact design
Compact design is probably the key phrases of the standard 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 really quiet. This is due to the very simple running of the worm equipment combined with the application of cast iron and large precision on component manufacturing and assembly. In connection with our precision gearboxes, we consider extra treatment of any sound which can be interpreted as a murmur from the apparatus. Therefore the general noise degree of our gearbox is reduced to an self locking gearbox 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 benefit making the incorporation of the gearbox significantly simpler and smaller sized.The worm gearbox is 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 parts rather than having to build a separate suspension.
Self locking
For larger gear ratios, Ever-Electric power worm gearboxes provides a self-locking effect, which in many situations can be utilized as brake or as extra protection. Also spindle gearboxes with a trapezoidal spindle are self-locking, making them well suited for an array of solutions.
In most equipment drives, when generating torque is suddenly reduced consequently of electrical power off, torsional vibration, electricity outage, or any mechanical failing at the transmission input part, then gears will be rotating either in the same course driven by the system inertia, or in the opposite direction driven by the resistant output load due to gravity, early spring load, etc. The latter state 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) turns into the powered one. There are numerous gear drive applications where end result shaft driving is undesirable. So that you can prevent it, various kinds of brake or clutch units are used.
However, additionally, there are solutions in the apparatus transmission that prevent inertial movement or backdriving using self-locking gears with no additional units. The most frequent one is 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 drive the worm. Nevertheless, their application comes with some constraints: the crossed axis shafts’ arrangement, relatively high equipment ratio, low acceleration, low gear mesh performance, increased heat technology, etc.
Also, there will 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 mode, when the inertial or backdriving torque can be put on the output gear. Primarily these gears had very low ( <50 percent) generating performance that limited their application. Then it had been proved [3] that great driving efficiency of this kind of gears is possible. Standards of the self-locking was analyzed on this page [4]. This paper explains the theory of the self-locking method for the parallel axis gears with symmetric and asymmetric pearly whites profile, and displays their suitability for several applications.
Self-Locking Condition
Physique 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 case of inertial driving. Virtually all conventional equipment drives have the pitch stage P located in the active portion the contact brand B1-B2 (Figure 1a and Shape 2a). This pitch stage location provides low particular sliding velocities and friction, and, due to this fact, high driving proficiency. In case when such gears are motivated by output load or inertia, they are rotating freely, because the friction instant (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’ – 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
In order to make gears self-locking, the pitch point P should be located off the productive portion the contact line B1-B2. There are two options. Choice 1: when the point P is placed between a centre of the pinion O1 and the idea B2, where in fact the outer size of the apparatus intersects the contact series. This makes the self-locking possible, however the driving productivity will become low under 50 percent [3]. Choice 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 gear O2. This type of gears could be self-locking with relatively great driving effectiveness > 50 percent.
Another condition of self-locking is to truly have a ample friction angle g to deflect the force F’ beyond the center of the pinion O1. It creates the resisting self-locking minute (torque) T’1 = F’ x L’1, where L’1 is normally a lever of the drive F’1. This condition can 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 quantity of teeth,
– involute profile position at the end of the apparatus tooth.
Design of Self-Locking Gears
Self-locking gears are customized. They cannot end up being fabricated with the requirements tooling with, for instance, the 20o pressure and rack. This makes them incredibly well suited for Direct Gear Design® [5, 6] that provides required gear efficiency and from then on defines tooling parameters.
Direct Gear Design presents the symmetric gear 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 tip circle da allows avoiding the pointed tooth hint. The equally spaced pearly whites form the gear. The fillet profile between teeth is designed independently to avoid interference and provide minimum bending anxiety. The working pressure angle aw and the contact 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 high pressure and large sliding friction in the tooth speak to. If the sliding friction coefficient f = 0.1 – 0.3, it needs the transverse operating pressure angle to aw = 75 – 85o. Therefore, the transverse speak to ratio ea < 1.0 (typically 0.4 - 0.6). Insufficient the transverse contact ratio should be compensated by the axial (or face) contact ratio eb to guarantee the total get in touch with ratio eg = ea + eb ≥ 1.0. This could be attained by applying helical gears (Figure 4). However, helical gears apply the axial (thrust) power on the gear bearings. The double helical (or “herringbone”) gears (Physique 4) allow to compensate this force.
High transverse pressure angles lead to increased bearing radial load that may be up to four to five situations higher than for the conventional 20o pressure angle gears. Bearing assortment and gearbox housing style should be done accordingly to carry this increased load without unnecessary deflection.
Application of the asymmetric the teeth for unidirectional drives allows for improved overall performance. For the self-locking gears that are used to prevent backdriving, the same tooth flank is used for both traveling and locking modes. In this case asymmetric tooth profiles give much higher transverse get in touch with ratio at the offered pressure angle compared to the symmetric tooth flanks. It makes it possible to reduce the helix position and axial bearing load. For the self-locking gears which used to avoid inertial driving, diverse tooth flanks are used for traveling and locking modes. In cases like this, asymmetric tooth profile with low-pressure angle 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 units were made based on the developed mathematical models. The gear data are offered in the Desk 1, and the test gears are presented in Figure 5.
The schematic presentation of the test setup is demonstrated in Figure 6. The 0.5Nm electric motor was used to drive the actuator. An integrated acceleration and torque sensor was mounted on the high-swiftness shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was linked to the low rate shaft of the gearbox via coupling. The input and end result torque and speed info were captured in the data acquisition tool and additional analyzed in a computer applying data analysis software. The instantaneous efficiency of the actuator was calculated and plotted for an array of speed/torque combination. Ordinary driving efficiency of the personal- locking equipment obtained during assessment was above 85 percent. The self-locking property of the helical gear occur backdriving mode was likewise tested. During this test the external torque was put on the output gear shaft and the angular transducer confirmed no angular movements of source shaft, which verified the self-locking condition.
Potential Applications
Initially, self-locking gears had been used in textile industry [2]. Nevertheless, this kind 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 app [7] of the self-locking gears for a continuously variable valve lift program was advised for an automotive engine.
Summary
In this paper, a principle of work of the self-locking gears has been described. Style specifics of the self-locking gears with symmetric and asymmetric profiles will be shown, and assessment of the apparatus prototypes has proved comparatively high driving effectiveness and dependable self-locking. The self-locking gears may find many applications in a variety of industries. For example, in a control systems where position stableness is vital (such as for example in automobile, aerospace, medical, robotic, agricultural etc.) the self-locking allows to accomplish required performance. Similar to the worm self-locking gears, the parallel axis self-locking gears are hypersensitive to operating circumstances. The locking dependability is damaged by lubrication, vibration, misalignment, etc. Implementation of the gears should be finished with caution and needs comprehensive testing in every possible operating conditions.

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