self locking gearbox

Worm gearboxes with countless combinations
Ever-Power offers a very wide variety of worm gearboxes. Because of the modular design the standard programme comprises countless combinations when it comes to selection of equipment housings, mounting and connection options, flanges, shaft patterns, type of oil, surface treatment options 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 properties in cast iron, light weight aluminum and stainless steel, 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 provided with a dust lip which effectively resists dust and normal water. In addition, the gearboxes happen to be greased for life with synthetic oil.
Large reduction 100:1 in one step
As default the worm gearboxes allow for reductions of up to 100:1 in one single step or 10.000:1 in a double reduction. An comparative gearing with the same gear ratios and the same transferred electric power is bigger than a worm gearing. In the meantime, the worm gearbox can be in a more simple design.
A double reduction may be composed of 2 typical gearboxes or as a special gearbox.
Compact design
Compact design is probably the key words of the standard gearboxes of the Ever-Power-Series. Further optimisation may be accomplished through the use of adapted gearboxes or specialized gearboxes.
Low noise
Our worm gearboxes and actuators are extremely quiet. This is due to the very easy jogging of the worm gear combined with the utilization of cast iron and huge precision on component manufacturing and assembly. In connection with our accuracy gearboxes, we consider extra health care of any sound which can be interpreted as a murmur from the apparatus. Therefore the general noise level of our gearbox is definitely reduced to an absolute minimum.
Angle gearboxes
On the worm gearbox the input shaft and output shaft are perpendicular to each other. This frequently proves to be a decisive benefits producing the incorporation of the gearbox significantly simpler and smaller sized.The worm gearbox is an angle gear. This is normally 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 suitable for immediate suspension for wheels, movable arms and other areas rather than needing to build a separate suspension.
Self locking
For larger gear ratios, Ever-Ability worm gearboxes provides a self-locking effect, which in lots of situations can be used as brake or as extra security. As well spindle gearboxes with a trapezoidal spindle will be self-locking, making them well suited for an array of solutions.
In most equipment drives, when generating torque is suddenly reduced because of this of ability off, torsional vibration, electricity outage, or any mechanical inability at the transmitting input part, then gears will be rotating either in the same course driven by the system inertia, or in the opposite direction driven by the resistant output load due to gravity, early spring load, etc. The latter state is known as backdriving. During inertial motion or backdriving, the driven output shaft (load) turns into the traveling one and the driving input shaft (load) becomes the influenced one. There are many gear drive applications where end result shaft driving is undesirable. So that you can prevent it, different types of brake or clutch devices are used.
However, additionally, there are solutions in the gear tranny that prevent inertial movement or backdriving using self-locking gears without the additional products. The most typical one can be a worm equipment with a minimal 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 includes some constraints: the crossed axis shafts’ arrangement, relatively high gear ratio, low quickness, low gear mesh proficiency, increased heat generation, etc.
Also, there are 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 traveling mode and self-locking mode, when the inertial or backdriving torque is usually applied to the output gear. Initially these gears had very low ( <50 percent) driving performance that limited their request. Then it was proved [3] that great driving efficiency of such gears is possible. Standards of the self-locking was analyzed in this post [4]. This paper explains the basic principle of the self-locking procedure for the parallel axis gears with symmetric and asymmetric teeth profile, and shows their suitability for distinct applications.
Self-Locking Condition
Determine 1 presents conventional gears (a) and self-locking gears (b), in the event of backdriving. Figure 2 presents typical 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 portion the contact range B1-B2 (Figure 1a and Figure 2a). This pitch point location provides low particular sliding velocities and friction, and, subsequently, high driving performance. In case when such gears are driven by output load or inertia, they are rotating freely, because the friction point in time (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
In order to make gears self-locking, the pitch point P ought to be located off the lively portion the contact line B1-B2. There happen to be two options. Choice 1: when the idea P is placed between a centre of the pinion O1 and the point B2, where the outer size of the gear intersects the contact range. This makes the self-locking possible, but the driving efficiency will always be low under 50 percent [3]. Alternative 2 (figs 1b and 2b): when the point P is put between your point B1, where the outer size of the pinion intersects the collection contact and a centre of the gear O2. This kind of gears can be self-locking with relatively high driving proficiency > 50 percent.
Another condition of self-locking is to have a adequate friction angle g to deflect the force F’ beyond the guts of the pinion O1. It creates the resisting self-locking second (torque) T’1 = F’ x L’1, where L’1 is certainly a lever of the power F’1. This condition could be presented as L’1min > 0 or
(1) self locking gearbox Equation 1
or
(2) Equation 2
where:
u = n2/n1 – gear ratio,
n1 and n2 – pinion and gear quantity of teeth,
– involute profile position at the end of the gear tooth.
Design of Self-Locking Gears
Self-locking gears are customized. They cannot become fabricated with the expectations tooling with, for example, the 20o pressure and rack. This makes them extremely well suited for Direct Gear Design® [5, 6] that delivers required gear efficiency and after that defines tooling parameters.
Direct Gear Design presents the symmetric gear tooth created by two involutes of one base circle (Figure 3a). The asymmetric gear tooth is formed by two involutes of two unique base circles (Figure 3b). The tooth suggestion circle da allows preventing the pointed tooth suggestion. The equally spaced tooth form the gear. The fillet profile between teeth was created independently to avoid interference and offer minimum bending anxiety. The working pressure angle aw and the contact ratio ea are identified 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 requires the transverse operating pressure angle to aw = 75 – 85o. Consequently, the transverse speak to ratio ea < 1.0 (typically 0.4 - 0.6). Lack of the transverse speak to 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 can be achieved by employing helical gears (Physique 4). Nevertheless, helical gears apply the axial (thrust) pressure on the apparatus bearings. The dual helical (or “herringbone”) gears (Figure 4) allow to compensate this force.
Huge transverse pressure angles result in increased bearing radial load that may be up to four to five occasions higher than for the conventional 20o pressure angle gears. Bearing variety and gearbox housing style ought to be done accordingly to hold this improved load without extreme deflection.
Request of the asymmetric teeth for unidirectional drives allows for improved effectiveness. For the self-locking gears that are used to prevent backdriving, the same tooth flank is employed for both traveling and locking modes. In cases like this asymmetric tooth profiles give much higher transverse speak to ratio at the presented 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 being used for generating and locking modes. In this instance, asymmetric tooth profile with low-pressure angle provides high effectiveness for driving method and the contrary high-pressure angle tooth account is employed for reliable self-locking.
Testing Self-Locking Gears
Self-locking helical equipment prototype models were made predicated on the developed mathematical models. The gear data are provided in the Desk 1, and the test gears are provided in Figure 5.
The schematic presentation of the test setup is shown in Figure 6. The 0.5Nm electric motor was used to operate a vehicle the actuator. A swiftness and torque sensor was installed on the high-acceleration shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was linked to the low acceleration shaft of the gearbox via coupling. The type and outcome torque and speed facts had been captured in the data acquisition tool and additional analyzed in a computer using data analysis software. The instantaneous effectiveness of the actuator was calculated and plotted for a wide selection of speed/torque combination. Standard driving effectiveness of the self- locking gear obtained during assessment was above 85 percent. The self-locking home of the helical gear set in backdriving mode was as well tested. During this test the external torque was applied to the output gear shaft and the angular transducer confirmed no angular movement of input shaft, which verified the self-locking condition.
Potential Applications
Initially, self-locking gears were found in textile industry [2]. On the other hand, this sort of gears has a large number of potential applications in lifting mechanisms, assembly tooling, and other equipment drives where in fact the backdriving or inertial generating is not permissible. Among such application [7] of the self-locking gears for a consistently variable valve lift system was recommended for an vehicle engine.
Summary
In this paper, a principle of do the job of the self-locking gears has been described. Style specifics of the self-locking gears with symmetric and asymmetric profiles are shown, and evaluating of the apparatus prototypes has proved relatively high driving efficiency and reputable self-locking. The self-locking gears may find many applications in a variety of industries. For instance, in a control systems where position stability is essential (such as in automobile, aerospace, medical, robotic, agricultural etc.) the self-locking will allow to accomplish required performance. Like the worm self-locking gears, the parallel axis self-locking gears are delicate to operating circumstances. The locking reliability is damaged by lubrication, vibration, misalignment, etc. Implementation of these gears should be finished with caution and requires comprehensive testing in all possible operating conditions.