self locking gearbox

Worm gearboxes with many combinations
Ever-Power offers an extremely wide range of worm gearboxes. Due to the modular design the typical programme comprises many combinations in terms of selection of equipment housings, mounting and connection options, flanges, shaft styles, kind of oil, surface remedies etc.
Sturdy and reliable
The look of the Ever-Power worm gearbox is simple and well proven. We just use top quality components such as houses in cast iron, metal and stainless, worms in the event hardened and polished steel and worm wheels in high-quality bronze of unique alloys ensuring the the best wearability. The seals of the worm gearbox are given with a dust lip which successfully resists dust and water. In addition, the gearboxes will be greased for life with synthetic oil.
Large reduction 100:1 in a single step
As default the worm gearboxes allow for reductions as high as 100:1 in one single step or 10.000:1 in a double decrease. An equivalent gearing with the same gear ratios and the same transferred ability is bigger when compared to a worm gearing. In the meantime, the worm gearbox is usually 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 typical 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 due to the very easy running of the worm equipment combined with the utilization of cast iron and great precision on element manufacturing and assembly. In connection with our precision gearboxes, we consider extra treatment of any sound that can be interpreted as a murmur from the gear. Therefore the general noise level 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 frequently proves to become a decisive gain making the incorporation of the gearbox noticeably simpler and more compact.The worm gearbox can be an angle gear. This is often an edge for incorporation into constructions.
Strong bearings in sturdy housing
The output shaft of the Ever-Power worm gearbox is very firmly embedded in the gear house and is perfect for direct suspension for wheels, movable arms and other areas rather than having to create a separate suspension.
Self locking
For larger equipment ratios, Ever-Ability worm gearboxes will provide a self-locking effect, which in many situations can be utilised as brake or as extra reliability. As well spindle gearboxes with a trapezoidal spindle are self-locking, making them ideal for a variety of solutions.
In most equipment drives, when driving torque is suddenly reduced because of this of power off, torsional vibration, vitality outage, or any mechanical inability at the tranny input aspect, then gears will be rotating either in the same way driven by the system inertia, or in the contrary path driven by the resistant output load due to gravity, springtime load, etc. The latter state is known as backdriving. During inertial motion or backdriving, the powered output shaft (load) turns into the traveling one and the traveling input shaft (load) turns into the driven one. There are many gear travel applications where result shaft driving is undesirable. So that you can prevent it, various kinds of brake or clutch gadgets are used.
However, additionally, there are solutions in the apparatus transmission that prevent inertial movement or backdriving using self-locking gears without any additional devices. The most typical one is a worm equipment with a minimal lead angle. In self-locking worm gears, torque applied from the strain side (worm gear) is blocked, i.e. cannot travel the worm. Nevertheless, their application includes some restrictions: the crossed axis shafts’ arrangement, relatively high equipment ratio, low swiftness, low gear mesh efficiency, increased heat era, etc.
Also, there are parallel axis self-locking gears [1, 2]. These gears, unlike the worm gears, can employ any equipment ratio from 1:1 and higher. They have the traveling mode and self-locking function, when the inertial or backdriving torque is put on the output gear. Initially these gears had very low ( <50 percent) traveling proficiency that limited their request. Then it had been proved [3] that huge driving efficiency of such gears is possible. Criteria of the self-locking was analyzed in this article [4]. This paper explains the theory of the self-locking method for the parallel axis gears with symmetric and asymmetric pearly whites profile, and reveals their suitability for numerous 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 gear drives possess the pitch level P situated in the active part the contact line B1-B2 (Figure 1a and Physique 2a). This pitch stage location provides low specific sliding velocities and friction, and, subsequently, high driving productivity. In case when such gears are motivated by outcome load or inertia, they are rotating freely, as the friction minute (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, applied to the gear
T’1 – driven torque, put on the pinion
F – driving force
F’ – driving 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 energetic portion the contact line B1-B2. There will be two options. Option 1: when the idea P is positioned between a centre of the pinion O1 and the point B2, where in fact the outer diameter of the apparatus intersects the contact line. This makes the self-locking possible, but the driving efficiency will become low under 50 percent [3]. Alternative 2 (figs 1b and 2b): when the idea P is placed between the point B1, where the outer size of the pinion intersects the series contact and a center of the gear O2. This sort of gears can be self-locking with relatively substantial driving performance > 50 percent.
Another condition of self-locking is to have a ample friction angle g to deflect the force F’ self locking gearbox beyond the guts of the pinion O1. It generates the resisting self-locking point in time (torque) T’1 = F’ x L’1, where L’1 is normally a lever of the power F’1. This condition could be provided as L’1min > 0 or
(1) Equation 1
(2) Equation 2
u = n2/n1 – gear ratio,
n1 and n2 – pinion and gear amount of teeth,
– involute profile position at the tip of the apparatus tooth.
Design of Self-Locking Gears
Self-locking gears are customized. They cannot always be fabricated with the requirements tooling with, for instance, the 20o pressure and rack. This makes them extremely ideal for Direct Gear Design® [5, 6] that delivers required gear performance and from then on defines tooling parameters.
Direct Gear Style presents the symmetric gear tooth created by two involutes of 1 base circle (Figure 3a). The asymmetric equipment tooth is shaped by two involutes of two unique base circles (Figure 3b). The tooth tip circle da allows avoiding the pointed tooth idea. The equally spaced teeth form the apparatus. The fillet profile between teeth was created independently in order to avoid interference and provide minimum bending pressure. The functioning 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
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 large 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 angle to aw = 75 – 85o. Subsequently, the transverse contact ratio ea < 1.0 (typically 0.4 - 0.6). Lack of the transverse get in touch with ratio should be compensated by the axial (or face) get in touch with ratio eb to guarantee the total speak to ratio eg = ea + eb ≥ 1.0. This can be attained by using helical gears (Physique 4). On the other hand, helical gears apply the axial (thrust) induce on the apparatus bearings. The double helical (or “herringbone”) gears (Determine 4) allow to compensate this force.
Large transverse pressure angles lead to increased bearing radial load that may be up to four to five circumstances higher than for the traditional 20o pressure angle gears. Bearing variety and gearbox housing design ought to be done accordingly to hold this increased load without extreme deflection.
Application of the asymmetric the teeth for unidirectional drives allows for improved functionality. 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 provide much higher transverse get in touch with ratio at the offered pressure angle than the symmetric tooth flanks. It makes it possible to reduce the helix position and axial bearing load. For the self-locking gears that used to avoid inertial driving, numerous tooth flanks are used for generating and locking modes. In this case, asymmetric tooth account with low-pressure angle provides high performance for driving setting and the opposite high-pressure angle tooth profile is utilized for reliable self-locking.
Testing Self-Locking Gears
Self-locking helical gear prototype pieces were made based on the developed mathematical products. The gear info are provided in the Table 1, and the test gears are offered in Figure 5.
The schematic presentation of the test setup is displayed in Figure 6. The 0.5Nm electric electric motor was used to operate a vehicle the actuator. An integrated speed and torque sensor was installed on the high-quickness shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was connected to the low swiftness shaft of the gearbox via coupling. The input and productivity torque and speed data were captured in the info acquisition tool and additional analyzed in a computer applying data analysis software program. The instantaneous efficiency of the actuator was calculated and plotted for an array of speed/torque combination. Standard driving efficiency of the self- locking gear obtained during assessment 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 applied to the output gear shaft and the angular transducer confirmed no angular motion of suggestions shaft, which verified the self-locking condition.
Potential Applications
Initially, self-locking gears had been used in textile industry [2]. On the other hand, this type of gears has many potential applications in lifting mechanisms, assembly tooling, and other equipment drives where the backdriving or inertial generating is not permissible. Among such application [7] of the self-locking gears for a continually variable valve lift system was suggested for an car engine.
In this paper, a principle of job of the self-locking gears has been described. Design specifics of the self-locking gears with symmetric and asymmetric profiles happen to be shown, and examining of the gear prototypes has proved fairly high driving efficiency and efficient self-locking. The self-locking gears could find many applications in various industries. For example, in a control devices where position stability is important (such as in automobile, aerospace, medical, robotic, agricultural etc.) the self-locking will allow to attain required performance. Like the worm self-locking gears, the parallel axis self-locking gears are very sensitive to operating circumstances. The locking reliability is affected by lubrication, vibration, misalignment, etc. Implementation of these gears should be finished with caution and needs comprehensive testing in every possible operating conditions.


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