self locking gearbox

Worm gearboxes with countless combinations
Ever-Power offers an extremely wide selection of worm gearboxes. Due to the modular design the standard programme comprises countless combinations in terms of selection of gear housings, mounting and interconnection options, flanges, shaft patterns, type of oil, surface treatments etc.
Sturdy and reliable
The design of the Ever-Power worm gearbox is simple and well proven. We only use top quality components such as houses in cast iron, aluminium and stainless steel, worms in the event hardened and polished metal and worm tires in high-grade bronze of specialized alloys ensuring the the best possible wearability. The seals of the worm gearbox are given with a dirt lip which effectively resists dust and drinking water. Furthermore, the gearboxes will be greased forever 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 decrease. An comparative gearing with the same equipment ratios and the same transferred power is bigger when compared to a worm gearing. In the mean time, the worm gearbox can be in a far more simple design.
A double reduction could be composed of 2 normal gearboxes or as a special gearbox.
Compact design
Compact design is one of the key terms of the standard gearboxes of the Ever-Power-Series. Further optimisation can be achieved by using adapted gearboxes or exceptional gearboxes.
Low noise
Our worm gearboxes and actuators are really quiet. This is because of the very soft running of the worm gear combined with the use of cast iron and huge precision on part manufacturing and assembly. Regarding the our accuracy gearboxes, we self locking gearbox consider extra attention of any sound which 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 one another. This sometimes proves to be a decisive advantages making 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 sound housing
The output shaft of the Ever-Power worm gearbox is quite firmly embedded in the apparatus house and is well suited 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 result, which in lots of situations can be utilised as brake or as extra security. Likewise spindle gearboxes with a trapezoidal spindle will be self-locking, making them ideal for a variety of solutions.
In most equipment drives, when generating torque is suddenly reduced as a result of electric power off, torsional vibration, electrical power outage, or any mechanical inability at the transmitting input aspect, then gears will be rotating either in the same course driven by the machine inertia, or in the opposite course driven by the resistant output load because of gravity, spring load, etc. The latter state is called backdriving. During inertial action or backdriving, the motivated output shaft (load) turns into the traveling one and the driving input shaft (load) turns into the driven one. There are numerous gear travel applications where outcome shaft driving is undesirable. So that you can prevent it, various kinds of brake or clutch units are used.
However, there are also solutions in the apparatus transmitting that prevent inertial movement or backdriving using self-locking gears with no additional devices. The most common one is definitely a worm equipment with a low lead angle. In self-locking worm gears, torque utilized from the load side (worm equipment) is blocked, i.e. cannot travel the worm. On the other hand, their application includes some constraints: the crossed axis shafts’ arrangement, relatively high equipment ratio, low rate, 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 use any equipment ratio from 1:1 and bigger. They have the generating mode and self-locking setting, when the inertial or backdriving torque is usually applied to the output gear. Originally these gears had suprisingly low ( <50 percent) driving performance that limited their application. Then it was proved [3] that excessive driving efficiency of these kinds of gears is possible. Conditions 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 teeth profile, and shows their suitability for unique applications.
Self-Locking Condition
Shape 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. Pretty much all conventional equipment drives have the pitch point P situated in the active portion the contact brand B1-B2 (Figure 1a and Number 2a). This pitch point location provides low specific sliding velocities and friction, and, due to this fact, high driving effectiveness. In case when such gears are influenced by result load or inertia, they will be rotating freely, because the friction moment (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’ – generating force, when the backdriving or 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 will be two options. Option 1: when the point P is positioned between a center of the pinion O1 and the point B2, where in fact the outer diameter of the apparatus intersects the contact series. This makes the self-locking possible, however the driving proficiency will always be low under 50 percent [3]. Option 2 (figs 1b and 2b): when the idea P is located between your point B1, where in fact the outer size of the pinion intersects the range contact and a centre of the gear O2. This kind of gears could be self-locking with relatively great driving performance > 50 percent.
Another condition of self-locking is to have a adequate friction angle g to deflect the force F’ beyond the center of the pinion O1. It creates the resisting self-locking second (torque) T’1 = F’ x L’1, where L’1 is 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 angle at the tip of the gear tooth.
Design of Self-Locking Gears
Self-locking gears are custom. They cannot end up being fabricated with the benchmarks tooling with, for instance, the 20o pressure and rack. This makes them extremely suitable for Direct Gear Design® [5, 6] that delivers required gear performance and after that defines tooling parameters.
Direct Gear Style presents the symmetric equipment tooth formed by two involutes of one base circle (Figure 3a). The asymmetric gear tooth is produced by two involutes of two distinct base circles (Figure 3b). The tooth hint circle da allows preventing the pointed tooth suggestion. The equally spaced teeth form the gear. The fillet profile between teeth is designed independently in order to avoid interference and provide minimum bending tension. The operating pressure angle aw and the get in touch with 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 high pressure and huge sliding friction in the tooth speak to. If the sliding friction coefficient f = 0.1 – 0.3, it needs the transverse operating pressure position to aw = 75 – 85o. Consequently, the transverse get in touch with 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 guarantee the total speak to ratio eg = ea + eb ≥ 1.0. This could be achieved by employing helical gears (Body 4). However, helical gears apply the axial (thrust) induce on the gear bearings. The dual helical (or “herringbone”) gears (Shape 4) allow to pay this force.
Great transverse pressure angles result in increased bearing radial load that could be up to four to five instances higher than for the conventional 20o pressure angle gears. Bearing assortment and gearbox housing design ought to be done accordingly to carry this elevated load without increased deflection.
Application of the asymmetric tooth for unidirectional drives allows for improved effectiveness. For the self-locking gears that are being used to avoid backdriving, the same tooth flank is employed for both traveling and locking modes. In this instance asymmetric tooth profiles present much higher transverse speak to 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 prevent inertial driving, unique tooth flanks are used for traveling and locking modes. In this case, asymmetric tooth profile with low-pressure position provides high performance for driving function and the contrary high-pressure angle tooth account can be used for reliable self-locking.
Testing Self-Locking Gears
Self-locking helical gear prototype models were made predicated on the developed mathematical models. The gear info are presented in the Desk 1, and the check gears are provided in Figure 5.
The schematic presentation of the test setup is displayed in Figure 6. The 0.5Nm electric motor was used to operate a vehicle the actuator. A speed and torque sensor was mounted on the high-swiftness shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was linked to the low velocity shaft of the gearbox via coupling. The insight and output torque and speed data had been captured in the info acquisition tool and additional analyzed in a pc applying data analysis computer software. The instantaneous productivity of the actuator was calculated and plotted for a variety of speed/torque combination. Normal driving performance of the personal- locking equipment obtained during examining was above 85 percent. The self-locking home of the helical gear occur backdriving mode was also tested. During this test the exterior torque was put on the output gear shaft and the angular transducer confirmed no angular movements of source shaft, which confirmed the self-locking condition.
Potential Applications
Initially, self-locking gears had been found in textile industry [2]. On the other hand, this kind of gears has many potential applications in lifting mechanisms, assembly tooling, and other gear drives where the backdriving or inertial generating is not permissible. One of such request [7] of the self-locking gears for a constantly variable valve lift program was suggested for an car engine.
Summary
In this paper, a basic principle of operate of the self-locking gears has been described. Style specifics of the self-locking gears with symmetric and asymmetric profiles happen to be shown, and tests of the gear prototypes has proved relatively high driving effectiveness and dependable self-locking. The self-locking gears could find many applications in a variety of industries. For instance, in a control systems where position balance is essential (such as for example in vehicle, aerospace, medical, robotic, agricultural etc.) the self-locking will allow to accomplish required performance. Similar to the worm self-locking gears, the parallel axis self-locking gears are sensitive to operating circumstances. The locking stability is afflicted by lubrication, vibration, misalignment, etc. Implementation of these gears should be done with caution and requires comprehensive testing in all possible operating conditions.