self locking gearbox

Worm gearboxes with countless combinations
Ever-Power offers an extremely wide range of worm gearboxes. Due to the modular design the standard programme comprises countless combinations with regards to selection of gear housings, mounting and interconnection options, flanges, shaft designs, type of oil, surface solutions etc.
Sturdy and reliable
The design of the Ever-Power worm gearbox is simple and well proven. We simply use high quality components such as homes in cast iron, lightweight aluminum and stainless, worms in case hardened and polished metal and worm wheels in high-grade bronze of exceptional alloys ensuring the the best possible wearability. The seals of the worm gearbox are given with a dirt lip which properly resists dust and drinking water. Furthermore, the gearboxes are 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 equipment ratios and the same transferred ability is bigger when compared to a worm gearing. On the other hand, the worm gearbox is in a more simple design.
A double reduction could be composed of 2 typical gearboxes or as a particular gearbox.
Compact design
Compact design is one of the key terms of the standard gearboxes of the Ever-Power-Series. Further optimisation may be accomplished through the use of adapted gearboxes or exceptional gearboxes.
Low noise
Our worm gearboxes and actuators are really quiet. This is due to the very easy running of the worm equipment combined with the use of cast iron and excessive precision on part manufacturing and assembly. Regarding the our precision gearboxes, we consider extra attention of any sound which can be interpreted as a murmur from the gear. So the general noise degree of our gearbox can be reduced to a complete minimum.
Angle gearboxes
On the worm gearbox the input shaft and output shaft are perpendicular to each other. This sometimes proves to be a decisive advantage making the incorporation of the gearbox significantly simpler and more compact.The worm gearbox can be an angle gear. This can often be an advantage 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 direct suspension for wheels, movable arms and other parts rather than needing to build a separate suspension.
Self locking
For larger gear ratios, Ever-Vitality worm gearboxes will provide a self-locking result, which in many situations works extremely well as brake or as extra reliability. Likewise spindle gearboxes with a trapezoidal spindle will be self-locking, making them perfect for an array of solutions.
In most equipment drives, when driving torque is suddenly reduced therefore of power off, torsional vibration, electrical power outage, or any mechanical failure at the tranny input aspect, then gears will be rotating either in the same course driven by the system inertia, or in the opposite path driven by the resistant output load because of gravity, springtime load, etc. The latter state is known as backdriving. During inertial action or backdriving, the driven output shaft (load) becomes the traveling one and the traveling input shaft (load) turns into the influenced one. There are lots of gear travel applications where productivity shaft driving is unwanted. So as to prevent it, various kinds of brake or clutch products are used.
However, additionally, there are solutions in the gear transmitting that prevent inertial action or backdriving using self-locking gears without the additional equipment. The most common one is certainly a worm gear with a low lead angle. In self-locking worm gears, torque applied from the strain side (worm gear) is blocked, i.electronic. cannot travel the worm. However, their application comes with some constraints: the crossed axis shafts’ arrangement, relatively high equipment ratio, low swiftness, low gear mesh performance, increased heat technology, etc.
Also, there will be self locking gearbox parallel axis self-locking gears [1, 2]. These gears, unlike the worm gears, can make use of any equipment ratio from 1:1 and larger. They have the generating mode and self-locking function, when the inertial or backdriving torque is certainly applied to the output gear. Originally these gears had suprisingly low ( <50 percent) generating efficiency that limited their application. Then it had been proved [3] that huge driving efficiency of this kind of gears is possible. Conditions of the self-locking was analyzed in the following paragraphs [4]. This paper explains the basic principle of the self-locking method for the parallel axis gears with symmetric and asymmetric teeth profile, and displays their suitability for distinct applications.
Self-Locking Condition
Number 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 case of inertial driving. Pretty much all conventional equipment drives have the pitch level P situated in the active portion the contact line B1-B2 (Figure 1a and Determine 2a). This pitch point location provides low specific sliding velocities and friction, and, consequently, high driving proficiency. In case when this sort of gears are influenced by end result load or inertia, they happen to be rotating freely, as the friction moment (or torque) is not 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 perhaps inertial torque applied to 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 should be located off the lively portion the contact line B1-B2. There are two options. Option 1: when the point P is positioned between a centre of the pinion O1 and the point B2, where the outer size of the gear intersects the contact series. This makes the self-locking possible, however the driving effectiveness will always be low under 50 percent [3]. Option 2 (figs 1b and 2b): when the idea P is placed between your point B1, where the outer diameter of the pinion intersects the line contact and a middle of the gear O2. This sort of gears can be self-locking with relatively great driving performance > 50 percent.
Another condition of self-locking is to truly have a satisfactory 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 can be a lever of the drive F’1. This condition can be presented as L’1min > 0 or
(1) Equation 1
or
(2) Equation 2
where:
u = n2/n1 – equipment ratio,
n1 and n2 – pinion and gear quantity of teeth,
– involute profile angle at the end of the apparatus tooth.
Design of Self-Locking Gears
Self-locking gears are customized. They cannot end up being fabricated with the specifications tooling with, for instance, the 20o pressure and rack. This makes them extremely ideal for Direct Gear Style® [5, 6] that provides required gear performance and after that defines tooling parameters.
Direct Gear Style presents the symmetric gear tooth formed by two involutes of one base circle (Figure 3a). The asymmetric gear tooth is shaped by two involutes of two distinct base circles (Figure 3b). The tooth hint circle da allows avoiding the pointed tooth tip. The equally spaced the teeth form the gear. The fillet profile between teeth was created independently to avoid interference and provide minimum bending anxiety. The working pressure angle aw and the contact 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 excessive 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. Due to this fact, the transverse get in touch with ratio ea < 1.0 (typically 0.4 - 0.6). Insufficient the transverse contact ratio ought to be compensated by the axial (or face) contact ratio eb to ensure the total get in touch with ratio eg = ea + eb ≥ 1.0. This could be achieved by employing helical gears (Number 4). Even so, helical gears apply the axial (thrust) induce on the apparatus bearings. The double helical (or “herringbone”) gears (Physique 4) allow to pay this force.
Great transverse pressure angles cause increased bearing radial load that could be up to four to five instances higher than for the conventional 20o pressure angle gears. Bearing collection and gearbox housing style ought to be done accordingly to carry this increased load without extreme deflection.
Application of the asymmetric the teeth for unidirectional drives permits improved efficiency. For the self-locking gears that are being used to avoid backdriving, the same tooth flank is utilized for both traveling and locking modes. In this instance asymmetric tooth profiles present much higher transverse get in touch with ratio at the offered pressure angle compared to the symmetric tooth flanks. It creates it possible to lessen the helix angle and axial bearing load. For the self-locking gears which used to prevent inertial driving, different tooth flanks are used for generating and locking modes. In this instance, asymmetric tooth account with low-pressure position provides high performance 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 gear prototype units were made predicated on the developed mathematical models. The gear data are provided in the Table 1, and the check gears are offered in Figure 5.
The schematic presentation of the test setup is proven in Figure 6. The 0.5Nm electric electric motor was used to operate a vehicle the actuator. A rate and torque sensor was attached on the high-swiftness shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was connected to the low quickness shaft of the gearbox via coupling. The input and result torque and speed information were captured in the info acquisition tool and additional analyzed in a computer using data analysis software program. The instantaneous productivity of the actuator was calculated and plotted for an array of speed/torque combination. Standard driving effectiveness of the personal- locking gear obtained during tests was above 85 percent. The self-locking home of the helical gear occur backdriving mode was as well tested. In this test the exterior torque was put on the output equipment shaft and the angular transducer revealed no angular movements of insight shaft, which verified the self-locking condition.
Potential Applications
Initially, self-locking gears were found in textile industry [2]. Even so, this sort of gears has various potential applications in lifting mechanisms, assembly tooling, and other gear drives where in fact the backdriving or inertial traveling is not permissible. One of such application [7] of the self-locking gears for a consistently variable valve lift system was advised for an car engine.
Summary
In this paper, a principle of function 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 examining of the gear prototypes has proved comparatively high driving effectiveness and trusted self-locking. The self-locking gears could find many applications in a variety of industries. For instance, in a control devices where position stableness is very important (such as for example in motor vehicle, aerospace, medical, robotic, agricultural etc.) the self-locking allows to achieve required performance. Similar to the worm self-locking gears, the parallel axis self-locking gears are very sensitive to operating circumstances. The locking dependability is afflicted by lubrication, vibration, misalignment, etc. Implementation of these gears should be finished with caution and needs comprehensive testing in all possible operating conditions.