self locking gearbox

Worm gearboxes with countless combinations
Ever-Power offers an extremely wide selection of worm gearboxes. Due to the modular design the typical programme comprises many combinations with regards to selection of equipment housings, mounting and interconnection options, flanges, shaft styles, type of oil, surface procedures etc.
Sturdy and reliable
The design of the Ever-Power worm gearbox is easy and well proven. We just use high quality components such as homes in cast iron, light weight aluminum and stainless steel, worms in case hardened and polished steel and worm tires in high-quality bronze of particular alloys ensuring the maximum wearability. The seals of the worm gearbox are provided with a dirt lip which efficiently resists dust and normal water. In addition, 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 reduction. An equivalent gearing with the same gear ratios and the same transferred electricity is bigger than a worm gearing. On the other hand, the worm gearbox is definitely in a far more simple design.
A double reduction may be composed of 2 regular gearboxes or as a particular gearbox.
Compact design
Compact design is probably the key terms of the standard gearboxes of the Ever-Power-Series. Further optimisation can be achieved by using adapted gearboxes or special gearboxes.
Low noise
Our worm gearboxes and actuators are extremely quiet. This is because of the very smooth running of the worm gear combined with the utilization of cast iron and huge precision on element manufacturing and assembly. In connection with our precision gearboxes, we have extra proper care of any sound that can be interpreted as a murmur from the apparatus. Therefore the general noise level of our gearbox is reduced to an absolute minimum.
Angle gearboxes
On the worm gearbox the input shaft and output shaft are perpendicular to each other. This often proves to be a decisive benefits making the incorporation of the gearbox considerably 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 very firmly embedded in the apparatus house and is perfect for immediate suspension for wheels, movable arms and other parts rather than having to build a separate suspension.
Self locking
For larger gear ratios, Ever-Power worm gearboxes will provide a self-locking effect, which in lots of situations can be utilized as brake or as extra secureness. As well spindle gearboxes with a trapezoidal spindle happen to be self-locking, making them suitable for a wide range of solutions.
In most gear drives, when traveling torque is suddenly reduced because of this of vitality off, torsional vibration, electrical power outage, or any mechanical inability at the tranny input area, then gears will be rotating either in the same way driven by the machine inertia, or in the contrary direction driven by the resistant output load because of gravity, early spring load, etc. The self locking gearbox latter condition is known as backdriving. During inertial movement or backdriving, the powered output shaft (load) becomes the driving one and the driving input shaft (load) turns into the powered one. There are many gear drive applications where end result shaft driving is undesirable. To be able to prevent it, several types of brake or clutch products are used.
However, additionally, there are solutions in the apparatus tranny that prevent inertial motion or backdriving using self-locking gears without the additional gadgets. The most typical one can be a worm equipment with a low lead angle. In self-locking worm gears, torque used from the load side (worm equipment) is blocked, i.e. cannot travel the worm. However, their application comes with some limitations: the crossed axis shafts’ arrangement, relatively high gear ratio, low speed, low gear mesh effectiveness, increased heat technology, etc.
Also, there will be parallel axis self-locking gears [1, 2]. These gears, unlike the worm gears, can use any gear ratio from 1:1 and bigger. They have the traveling mode and self-locking mode, when the inertial or backdriving torque is definitely put on the output gear. Initially these gears had very low ( <50 percent) driving effectiveness that limited their program. Then it had been proved [3] that high driving efficiency of such gears is possible. Requirements of the self-locking was analyzed in this post [4]. This paper explains the basic principle of the self-locking process for the parallel axis gears with symmetric and asymmetric the teeth profile, and reveals their suitability for diverse applications.
Self-Locking Condition
Figure 1 presents conventional gears (a) and self-locking gears (b), in the event of backdriving. Figure 2 presents regular gears (a) and self-locking gears (b), in the event of inertial driving. Pretty much all conventional equipment drives possess the pitch stage P located in the active part the contact line B1-B2 (Figure 1a and Physique 2a). This pitch stage location provides low particular sliding velocities and friction, and, subsequently, high driving productivity. In case when these kinds of gears are driven by result load or inertia, they are rotating freely, as the friction second (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, 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
To make gears self-locking, the pitch point P ought to be located off the energetic portion the contact line B1-B2. There happen to be two options. Option 1: when the point P is positioned 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 productivity will be low under 50 percent [3]. Alternative 2 (figs 1b and 2b): when the point P is inserted between the point B1, where the outer diameter of the pinion intersects the collection contact and a middle of the apparatus O2. This type of gears can be self-locking with relatively large driving productivity > 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 generates the resisting self-locking instant (torque) T’1 = F’ x L’1, where L’1 is usually a lever of the push F’1. This condition can be provided as L’1min > 0 or
(1) Equation 1
(2) Equation 2
u = n2/n1 – gear ratio,
n1 and n2 – pinion and gear number of teeth,
– involute profile angle at the tip of the apparatus tooth.
Design of Self-Locking Gears
Self-locking gears are customized. They cannot always be fabricated with the specifications tooling with, for instance, the 20o pressure and rack. This makes them extremely well suited for Direct Gear Design® [5, 6] that provides 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 equipment tooth is created by two involutes of two numerous base circles (Figure 3b). The tooth hint circle da allows avoiding the pointed tooth tip. The equally spaced pearly whites form the gear. The fillet account between teeth was created independently to avoid interference and provide minimum bending anxiety. The operating pressure angle aw and the get in touch with 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
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 substantial sliding friction in the tooth speak to. If the sliding friction coefficient f = 0.1 – 0.3, it requires the transverse operating pressure position to aw = 75 – 85o. Consequently, the transverse speak to ratio ea < 1.0 (typically 0.4 - 0.6). Lack of the transverse contact ratio should be compensated by the axial (or face) get in touch with ratio eb to guarantee the total get in touch with ratio eg = ea + eb ≥ 1.0. This could be achieved by applying helical gears (Physique 4). On the other hand, helical gears apply the axial (thrust) force on the apparatus bearings. The dual helical (or “herringbone”) gears (Number 4) allow to compensate this force.
Large transverse pressure angles bring about increased bearing radial load that may be up to four to five moments higher than for the conventional 20o pressure angle gears. Bearing selection and gearbox housing design should be done accordingly to hold this elevated load without excessive deflection.
Application of the asymmetric tooth for unidirectional drives permits improved effectiveness. For the self-locking gears that are used to prevent backdriving, the same tooth flank is used for both generating and locking modes. In this instance 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 angle and axial bearing load. For the self-locking gears that used to prevent inertial driving, several tooth flanks are used for driving and locking modes. In cases like this, asymmetric tooth account with low-pressure angle provides high productivity for driving method and the opposite high-pressure angle tooth account is utilized for reliable self-locking.
Testing Self-Locking Gears
Self-locking helical equipment prototype sets were made based on the developed mathematical versions. The gear data are presented in the Table 1, and the test gears are provided in Figure 5.
The schematic presentation of the test setup is demonstrated in Figure 6. The 0.5Nm electric engine was used to operate a vehicle the actuator. A built-in quickness and torque sensor was mounted on the high-velocity shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was linked to the low swiftness shaft of the gearbox via coupling. The source and result torque and speed facts had been captured in the info acquisition tool and further analyzed in a pc employing data analysis software. The instantaneous proficiency of the actuator was calculated and plotted for a wide selection of speed/torque combination. Common driving performance of the self- locking gear obtained during screening was above 85 percent. The self-locking property of the helical gear occur backdriving mode was also tested. During this test the external torque was applied to the output gear shaft and the angular transducer demonstrated no angular activity of insight shaft, which verified the self-locking condition.
Potential Applications
Initially, self-locking gears had been found in textile industry [2]. Nevertheless, this sort of gears has a large number of potential applications in lifting mechanisms, assembly tooling, and other gear drives where in fact the backdriving or inertial generating is not permissible. One of such program [7] of the self-locking gears for a continuously variable valve lift program was recommended for an motor vehicle 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 will be shown, and testing of the gear prototypes has proved comparatively high driving performance and trustworthy self-locking. The self-locking gears may find many applications in a variety of industries. For instance, in a control systems where position balance is important (such as in automotive, aerospace, medical, robotic, agricultural etc.) the self-locking will allow to achieve required performance. Like the worm self-locking gears, the parallel axis self-locking gears are hypersensitive to operating conditions. The locking reliability is influenced by lubrication, vibration, misalignment, etc. Implementation of these gears should be finished with caution and requires comprehensive testing in every possible operating conditions.


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