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 typical programme comprises countless combinations with regards to selection of gear housings, mounting and interconnection options, flanges, shaft patterns, 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 top quality components such as residences in cast iron, light weight aluminum and stainless, worms in the event hardened and polished steel and worm wheels in high-grade bronze of specialized alloys ensuring the the best wearability. The seals of the worm gearbox are provided with a dirt lip which successfully resists dust and drinking water. In addition, the gearboxes happen to be greased forever with synthetic oil.
Large reduction 100:1 in one step
As default the worm gearboxes enable reductions as high as 100:1 in one single step or 10.000:1 in a double lowering. An comparative gearing with the same equipment ratios and the same transferred ability is bigger when compared to a worm gearing. In the meantime, the worm gearbox can be in a more simple design.
A double reduction may be composed of 2 normal gearboxes or as a special gearbox.
Compact design
Compact design is among the key terms of the standard gearboxes of the Ever-Power-Series. Further optimisation may be accomplished by using adapted gearboxes or particular gearboxes.
Low noise
Our worm gearboxes and actuators are really quiet. This is because of the very soft operating of the worm equipment combined with the consumption of cast iron and large precision on part manufacturing and assembly. In connection with our precision gearboxes, we take extra proper care of any sound that can be interpreted as a murmur from the apparatus. So the general noise level of our gearbox is definitely reduced to a complete 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 advantages making the incorporation of the gearbox substantially simpler and more compact.The worm gearbox is an angle gear. This can often be 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 apparatus house and is well suited for immediate 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 provides a self-locking result, which in lots of situations can be utilized as brake or as extra secureness. Likewise spindle gearboxes with a trapezoidal spindle are self-locking, making them suitable for an array of solutions.
In most gear drives, when generating torque is suddenly reduced therefore of 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 way driven by the machine inertia, or in the opposite path driven by the resistant output load because of gravity, early spring load, etc. The latter state is called backdriving. During inertial action or backdriving, the driven output shaft (load) turns into the generating one and the generating input shaft (load) becomes the driven one. There are various gear travel applications where end result shaft driving is undesirable. To be able to prevent it, various kinds of brake or clutch equipment are used.
However, there are also solutions in the gear transmission that prevent inertial movement or backdriving using self-locking gears without the additional equipment. The most common one is definitely a worm equipment with a low lead angle. In self-locking worm gears, torque used from the strain side (worm gear) is blocked, i.e. cannot drive the worm. However, their application comes with some limitations: the crossed axis shafts’ arrangement, relatively high equipment ratio, low quickness, low gear mesh efficiency, increased heat era, etc.
Also, there happen to be parallel axis self-locking gears [1, 2]. These gears, unlike the worm gears, can employ any gear ratio from 1:1 and higher. They have the driving 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) driving efficiency that limited their program. Then it was proved [3] that high driving efficiency of this kind of gears is possible. Requirements of the self-locking was analyzed in this article [4]. This paper explains the principle of the self-locking method for the parallel axis gears with symmetric and asymmetric pearly whites profile, and shows their suitability for distinct applications.
Self-Locking Condition
Shape 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. Pretty much all conventional gear drives possess the pitch point P located in the active portion the contact range B1-B2 (Figure 1a and Figure 2a). This pitch stage location provides low specific sliding velocities and friction, and, because of this, high driving productivity. In case when these kinds of gears are influenced by output load or inertia, they will be 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, applied to the gear
T’1 – driven torque, put on the pinion
F – driving force
F’ – generating force, when the backdriving or 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 ought to be located off the productive portion the contact line B1-B2. There will be two options. Option 1: when the point P is placed between a middle of the pinion O1 and the point B2, where the outer diameter of the apparatus intersects the contact line. This makes the self-locking possible, but the driving performance will become low under 50 percent [3]. Option 2 (figs 1b and 2b): when the point P is located between the point B1, where in fact the outer size of the pinion intersects the collection contact and a center of the apparatus O2. This kind of gears can be self-locking with relatively substantial driving productivity > 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 minute (torque) T’1 = F’ x L’1, where L’1 is certainly a lever of the force F’1. This condition could be provided as L’1min > 0 or
(1) Equation 1
or
(2) Equation 2
where:
u = n2/n1 – equipment ratio,
n1 and n2 – pinion and gear number of teeth,
– involute profile angle at the end of the gear tooth.
Design of Self-Locking Gears
Self-locking gears are custom. They cannot be fabricated with the self locking gearbox criteria tooling with, for example, the 20o pressure and rack. This makes them incredibly suited to Direct Gear Style® [5, 6] that delivers required gear effectiveness and after that defines tooling parameters.
Direct Gear Design presents the symmetric gear tooth produced by two involutes of 1 base circle (Figure 3a). The asymmetric gear tooth is created by two involutes of two different base circles (Figure 3b). The tooth idea circle da allows preventing the pointed tooth idea. The equally spaced the teeth form the gear. The fillet profile between teeth is designed independently in order to avoid interference and offer minimum bending anxiety. The working pressure angle aw and the get in touch with ratio ea are described 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 huge 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. Therefore, the transverse get in touch with ratio ea < 1.0 (typically 0.4 - 0.6). Lack of the transverse speak to ratio ought to be compensated by the axial (or face) contact ratio eb to ensure the total speak to ratio eg = ea + eb ≥ 1.0. This is often attained by employing helical gears (Number 4). Even so, helical gears apply the axial (thrust) induce on the apparatus bearings. The dual helical (or “herringbone”) gears (Physique 4) allow to compensate this force.
Excessive transverse pressure angles result in increased bearing radial load that could be up to four to five moments higher than for the conventional 20o pressure angle gears. Bearing variety and gearbox housing design should be done accordingly to carry this improved load without increased deflection.
Program of the asymmetric pearly whites for unidirectional drives permits improved overall performance. For the self-locking gears that are being used to prevent backdriving, the same tooth flank is used for both driving and locking modes. In this instance asymmetric tooth profiles offer much higher transverse speak to ratio at the given pressure angle than the symmetric tooth flanks. It makes it possible to lessen the helix angle and axial bearing load. For the self-locking gears that 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 proficiency for driving method and the contrary high-pressure angle tooth account can be used for reliable self-locking.
Testing Self-Locking Gears
Self-locking helical equipment prototype models were made based on the developed mathematical types. The gear info are provided in the Desk 1, and the check 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 drive the actuator. An integrated swiftness and torque sensor was attached on the high-velocity shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was linked to the low quickness shaft of the gearbox via coupling. The input and result torque and speed data had been captured in the info acquisition tool and further analyzed in a pc applying data analysis software program. The instantaneous proficiency of the actuator was calculated and plotted for a variety of speed/torque combination. Standard driving productivity of the personal- locking gear obtained during examining was above 85 percent. The self-locking real estate of the helical equipment set in backdriving mode was also tested. In this test the exterior torque was applied to the output gear shaft and the angular transducer showed no angular motion of type shaft, which confirmed the self-locking condition.
Potential Applications
Initially, self-locking gears were used in textile industry [2]. Nevertheless, this sort of gears has various potential applications in lifting mechanisms, assembly tooling, and other gear drives where the backdriving or inertial generating is not permissible. One of such program [7] of the self-locking gears for a continually variable valve lift system was suggested for an auto engine.
Summary
In this paper, a principle of work 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 evaluating of the gear prototypes has proved fairly high driving proficiency and reputable self-locking. The self-locking gears may find many applications in various industries. For example, in a control systems where position stableness is important (such as for example in automobile, 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 sensitive to operating conditions. The locking dependability is influenced by lubrication, vibration, misalignment, etc. Implementation of these gears should be done with caution and needs comprehensive testing in every possible operating conditions.