Worm self locking gearbox gearboxes with countless combinations
Ever-Power offers a very wide variety of worm gearboxes. As a result of modular design the standard programme comprises countless combinations with regards to selection of gear housings, mounting and interconnection options, flanges, shaft styles, kind of oil, surface treatments 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 properties in cast iron, aluminium and stainless steel, worms in the event hardened and polished metal and worm wheels in high-quality bronze of special alloys ensuring the optimum wearability. The seals of the worm gearbox are given with a dirt lip which properly 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 enable reductions of up to 100:1 in one step or 10.000:1 in a double decrease. An comparative gearing with the same gear ratios 
and the same transferred vitality is bigger when compared to a worm gearing. In the meantime, the worm gearbox is normally 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 phrases of the typical gearboxes of the Ever-Power-Series. Further optimisation can be achieved by using adapted gearboxes or specialized gearboxes.
Low noise
Our worm gearboxes and actuators are really quiet. This is because of the very simple running of the worm gear combined with the application of cast iron and excessive precision on part manufacturing and assembly. Regarding the our accuracy gearboxes, we consider extra treatment of any sound that can be interpreted as a murmur from the apparatus. Therefore 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 one another. This typically proves to be a decisive gain making the incorporation of the gearbox considerably simpler and more compact.The worm gearbox can be an angle gear. This is normally an edge for incorporation into constructions.
Strong bearings in sound housing
The output shaft of the Ever-Power worm gearbox is very firmly embedded in the apparatus house and is suitable for immediate suspension for wheels, movable arms and other areas rather than having to build a separate suspension.
Self locking
For larger equipment ratios, Ever-Power worm gearboxes will provide a self-locking result, which in many situations can be utilised as brake or as extra protection. Likewise spindle gearboxes with a trapezoidal spindle happen to be self-locking, making them well suited for a wide selection of solutions.
In most gear drives, when generating torque is suddenly reduced therefore of electrical power off, torsional vibration, vitality outage, or any mechanical failure at the transmission input side, then gears will be rotating either in the same path driven by the machine inertia, or in the contrary direction driven by the resistant output load due to gravity, springtime load, etc. The latter state is known as backdriving. During inertial action or backdriving, the powered output shaft (load) turns into the driving one and the traveling input shaft (load) turns into the powered one. There are lots of gear travel applications where productivity shaft driving is unwanted. So that you can prevent it, various kinds of brake or clutch gadgets are used.
However, additionally, there are solutions in the gear transmitting that prevent inertial movement or backdriving using self-locking gears without the additional units. The most frequent one is certainly a worm gear with a minimal lead angle. In self-locking worm gears, torque used from the load side (worm equipment) is blocked, i.electronic. cannot drive the worm. Even so, their application includes some limitations: the crossed axis shafts’ arrangement, relatively high gear ratio, low quickness, low gear mesh proficiency, increased heat technology, etc.
Also, there will be parallel axis self-locking gears [1, 2]. These gears, unlike the worm gears, can employ any gear ratio from 1:1 and larger. They have the generating mode and self-locking function, when the inertial or backdriving torque is normally put on the output gear. Primarily these gears had very low ( <50 percent) generating proficiency that limited their app. Then it was proved [3] that high driving efficiency of these kinds of gears is possible. Standards of the self-locking was analyzed in this post [4]. This paper explains the theory of the self-locking procedure for the parallel axis gears with symmetric and asymmetric the teeth profile, and reveals their suitability for different 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 the event of inertial driving. Pretty much all conventional gear drives possess the pitch level P located in the active part the contact range B1-B2 (Figure 1a and Physique 2a). This pitch point location provides low specific sliding velocities and friction, and, consequently, high driving efficiency. In case when such gears are influenced by productivity load or inertia, they happen to be 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, applied to the pinion
F – driving force
F’ – driving force, when the backdriving or perhaps 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 should be located off the active portion the contact line B1-B2. There are two options. Choice 1: when the point P is placed between a middle of the pinion O1 and the idea B2, where in fact the outer diameter of the apparatus intersects the contact series. This makes the self-locking possible, but the driving productivity will end up being low under 50 percent [3]. Option 2 (figs 1b and 2b): when the idea P is placed between your point B1, where in fact the outer diameter of the pinion intersects the brand contact and a center of the gear O2. This kind of gears can be self-locking with relatively great driving effectiveness > 50 percent.
Another condition of self-locking is to truly have a enough friction angle g to deflect the force F’ beyond the center of the pinion O1. It generates the resisting self-locking moment (torque) T’1 = F’ x L’1, where L’1 is usually a lever of the drive F’1. This condition can be shown as L’1min > 0 or
(1) Equation 1
or
(2) Equation 2
where:
u = n2/n1 – gear ratio,
n1 and n2 – pinion and gear number of teeth,
– involute profile position at the end of the gear tooth.
Design of Self-Locking Gears
Self-locking gears are customized. They cannot always be fabricated with the benchmarks tooling with, for instance, the 20o pressure and rack. This makes them very ideal for Direct Gear Style® [5, 6] that provides required gear efficiency and after that defines tooling parameters.
Direct Gear Design presents the symmetric gear tooth produced by two involutes of one base circle (Figure 3a). The asymmetric gear tooth is created by two involutes of two distinct base circles (Figure 3b). The tooth idea circle da allows avoiding the pointed tooth hint. The equally spaced teeth form the gear. The fillet account between teeth is designed independently to avoid interference and offer minimum bending tension. The working pressure angle aw and the speak to 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 ruthless and high sliding friction in the tooth contact. If the sliding friction coefficient f = 0.1 – 0.3, it needs the transverse operating pressure position to aw = 75 – 85o. Due to this fact, 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 ensure the total contact ratio eg = ea + eb ≥ 1.0. This is often achieved by employing helical gears (Physique 4). Even so, helical gears apply the axial (thrust) power on the apparatus bearings. The twice helical (or “herringbone”) gears (Shape 4) allow to compensate this force.
Substantial transverse pressure angles bring about increased bearing radial load that may be up to four to five situations higher than for the traditional 20o pressure angle gears. Bearing assortment and gearbox housing design ought to be done accordingly to carry this improved load without unnecessary deflection.
Application of the asymmetric teeth for unidirectional drives allows for improved functionality. For the self-locking gears that are being used to avoid backdriving, the same tooth flank can be used for both traveling and locking modes. In this case asymmetric tooth profiles offer much higher transverse get in touch with ratio at the granted pressure angle than the symmetric tooth flanks. It makes it possible to lessen the helix position and axial bearing load. For the self-locking gears which used to prevent inertial driving, numerous tooth flanks are used for driving and locking modes. In this case, asymmetric tooth account with low-pressure angle provides high proficiency for driving function and the opposite high-pressure angle tooth account is employed for reliable self-locking.
Testing Self-Locking Gears
Self-locking helical equipment prototype models were made based on the developed mathematical designs. The gear info are presented in the Table 1, and the check gears are presented 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 built-in acceleration and torque sensor was installed on the high-rate shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was linked to the low swiftness shaft of the gearbox via coupling. The input and productivity torque and speed information were captured in the data acquisition tool and further analyzed in a pc employing data analysis software. The instantaneous efficiency of the actuator was calculated and plotted for an array of speed/torque combination. Ordinary driving performance of the personal- locking gear obtained during evaluating was above 85 percent. The self-locking property of the helical gear occur backdriving mode was likewise tested. In this test the exterior torque was put on the output equipment shaft and the angular transducer confirmed no angular movements of suggestions shaft, which verified the self-locking condition.
Potential Applications
Initially, self-locking gears were found in textile industry [2]. Nevertheless, this sort of gears has various potential applications in lifting mechanisms, assembly tooling, and other equipment drives where in fact the backdriving or inertial driving is not permissible. Among such software [7] of the self-locking gears for a continuously variable valve lift program was advised for an automotive engine.
Summary
In this paper, a basic principle of operate of the self-locking gears has been described. Design specifics of the self-locking gears with symmetric and asymmetric profiles are shown, and evaluating of the apparatus prototypes has proved comparatively high driving performance and efficient self-locking. The self-locking gears may find many applications in a variety of industries. For instance, in a control devices where position steadiness is vital (such as for example in auto, aerospace, medical, robotic, agricultural etc.) the self-locking allows to attain required performance. Like the worm self-locking gears, the parallel axis self-locking gears are sensitive to operating conditions. The locking dependability is damaged by lubrication, vibration, misalignment, etc. Implementation of these gears should be finished with caution and requires comprehensive testing in every possible operating conditions.
