self locking gearbox

Worm gearboxes with countless combinations
Ever-Power offers a very wide variety of worm gearboxes. Due to the modular design the typical programme comprises countless combinations in terms of selection of gear housings, mounting and connection options, flanges, shaft designs, kind 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 homes in cast iron, aluminum and stainless, worms in case hardened and polished metal and worm wheels in high-grade bronze of specialized alloys ensuring the ideal wearability. The seals of the worm gearbox are provided with a dust lip which successfully resists dust and drinking water. In addition, 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 lowering. An comparative gearing with the same gear ratios and the same transferred power is bigger than a worm gearing. On the other hand, the worm gearbox is normally in a more simple design.
A double reduction may be composed of 2 standard gearboxes or as a particular gearbox.
Compact design
Compact design is probably the key terms of the typical gearboxes of the Ever-Power-Series. Further optimisation can be achieved by using adapted gearboxes or distinctive gearboxes.
Low noise
Our worm gearboxes and actuators are extremely quiet. This is because of the very soft working of the worm equipment combined with the utilization of cast iron and large precision on element manufacturing and assembly. Regarding the our precision gearboxes, we take extra attention of any sound which can be interpreted as a murmur from the apparatus. So the general noise degree of our gearbox is usually reduced to an absolute minimum.
Angle gearboxes
On the worm gearbox the input shaft and output shaft are perpendicular to one another. This generally proves to be a decisive gain making the incorporation of the gearbox significantly simpler and smaller sized.The worm gearbox can be an angle gear. This is normally an edge for incorporation into constructions.
Strong bearings in sturdy housing
The output shaft of the Ever-Power worm gearbox is very firmly embedded in the apparatus house and is ideal for direct suspension for wheels, movable arms and other areas rather than having to create a separate suspension.
Self locking
For larger gear ratios, Ever-Electric power worm gearboxes provides a self-locking impact, which in lots of situations can be utilized as brake or as extra reliability. As well spindle gearboxes with a trapezoidal spindle are self-locking, making them well suited for a wide range of solutions.
In most equipment drives, when generating torque is suddenly reduced as a result of electric power off, torsional vibration, ability outage, or any mechanical failure at the transmitting input side, then gears will be rotating either in the same way driven by the system inertia, or in the opposite direction driven by the resistant output load because of gravity, spring load, etc. The latter condition is known as backdriving. During inertial motion or backdriving, the motivated output shaft (load) turns into the generating one and the generating input shaft (load) turns into the powered one. There are various gear travel applications where result shaft driving is unwanted. So as to prevent it, several types of brake or clutch units are used.
However, additionally, there are solutions in the apparatus self locking gearbox transmission that prevent inertial movement or backdriving using self-locking gears with no additional devices. The most frequent one is certainly a worm gear with a minimal lead angle. In self-locking worm gears, torque utilized from the load side (worm gear) is blocked, i.electronic. cannot travel the worm. Nevertheless, their application comes with some constraints: the crossed axis shafts’ arrangement, relatively high gear ratio, low rate, low gear mesh proficiency, increased heat generation, etc.
Also, there happen to be parallel axis self-locking gears [1, 2]. These gears, unlike the worm gears, can use any equipment ratio from 1:1 and higher. They have the generating mode and self-locking method, when the inertial or backdriving torque is certainly applied to the output gear. Originally these gears had very low ( <50 percent) generating efficiency that limited their software. Then it was proved [3] that substantial driving efficiency of this sort of gears is possible. Criteria of the self-locking was analyzed in this article [4]. This paper explains the principle of the self-locking procedure for the parallel axis gears with symmetric and asymmetric pearly whites profile, and reveals their suitability for diverse applications.
Self-Locking Condition
Physique 1 presents conventional gears (a) and self-locking gears (b), in the event of backdriving. Figure 2 presents conventional gears (a) and self-locking gears (b), in case of inertial driving. Pretty much all conventional gear drives have the pitch level P situated in the active part the contact line B1-B2 (Figure 1a and Shape 2a). This pitch level location provides low specific sliding velocities and friction, and, consequently, high driving proficiency. In case when this sort of gears are driven by productivity load or inertia, they happen to be rotating freely, as the friction instant (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’ – 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 should be located off the lively portion the contact line B1-B2. There are two options. Option 1: when the idea P is positioned between a center of the pinion O1 and the point B2, where in fact the outer diameter of the apparatus intersects the contact collection. This makes the self-locking possible, however the driving efficiency will become low under 50 percent [3]. Option 2 (figs 1b and 2b): when the idea P is inserted between the point B1, where the outer size of the pinion intersects the collection contact and a middle of the apparatus O2. This kind of gears could be self-locking with relatively high driving efficiency > 50 percent.
Another condition of self-locking is to truly have a enough friction angle g to deflect the force F’ beyond the guts of the pinion O1. It creates the resisting self-locking point in time (torque) T’1 = F’ x L’1, where L’1 is definitely a lever of the drive F’1. This condition can be offered as L’1min > 0 or
(1) Equation 1
or
(2) Equation 2
where:
u = n2/n1 – equipment ratio,
n1 and n2 – pinion and gear amount of teeth,
– involute profile position at the tip of the gear tooth.
Design of Self-Locking Gears
Self-locking gears are custom. They cannot be fabricated with the specifications tooling with, for example, the 20o pressure and rack. This makes them incredibly suitable for Direct Gear Style® [5, 6] that provides required gear effectiveness and after that defines tooling parameters.
Direct Gear Design presents the symmetric gear tooth formed by two involutes of 1 base circle (Figure 3a). The asymmetric gear tooth is produced by two involutes of two distinct base circles (Figure 3b). The tooth suggestion circle da allows avoiding the pointed tooth idea. The equally spaced tooth form the gear. The fillet profile between teeth was created independently to avoid interference and provide minimum bending stress. The functioning pressure angle aw and the get in touch with 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 huge sliding friction in the tooth contact. If the sliding friction coefficient f = 0.1 – 0.3, it requires the transverse operating pressure angle to aw = 75 – 85o. Therefore, the transverse get in touch with ratio ea < 1.0 (typically 0.4 - 0.6). Lack of the transverse contact ratio ought to be compensated by the axial (or face) get in touch with ratio eb to ensure the total get in touch with ratio eg = ea + eb ≥ 1.0. This could be attained by employing helical gears (Figure 4). However, helical gears apply the axial (thrust) push on the apparatus bearings. The twice helical (or “herringbone”) gears (Figure 4) allow to compensate this force.
High transverse pressure angles bring about increased bearing radial load that may be up to four to five instances higher than for the traditional 20o pressure angle gears. Bearing selection and gearbox housing design ought to be done accordingly to hold this improved load without increased deflection.
Program of the asymmetric the teeth for unidirectional drives allows for improved overall performance. For the self-locking gears that are used to avoid backdriving, the same tooth flank is used for both driving and locking modes. In this instance asymmetric tooth profiles give much higher transverse get in touch with ratio at the offered pressure angle compared to the symmetric tooth flanks. It makes it possible to reduce the helix position and axial bearing load. For the self-locking gears that used to prevent inertial driving, numerous tooth flanks are used for traveling and locking modes. In cases like this, asymmetric tooth account with low-pressure angle provides high productivity for driving setting and the opposite high-pressure angle tooth account is used for reliable self-locking.
Testing Self-Locking Gears
Self-locking helical gear prototype models were made based on the developed mathematical types. The gear data are offered in the Desk 1, and the test gears are shown in Figure 5.
The schematic presentation of the test setup is demonstrated in Figure 6. The 0.5Nm electric electric motor was used to operate a vehicle the actuator. An integrated acceleration and torque sensor was mounted on the high-quickness shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was linked to the low speed shaft of the gearbox via coupling. The suggestions and outcome torque and speed information had been captured in the data acquisition tool and additional analyzed in a computer using data analysis software. The instantaneous productivity of the actuator was calculated and plotted for an array of speed/torque combination. Average driving effectiveness of the self- locking equipment obtained during evaluating was above 85 percent. The self-locking real estate of the helical equipment occur backdriving mode was likewise tested. In this test the exterior torque was applied to the output equipment shaft and the angular transducer revealed no angular activity of source shaft, which verified the self-locking condition.
Potential Applications
Initially, self-locking gears had been used in textile industry [2]. On the other hand, this kind of gears has many potential applications in lifting mechanisms, assembly tooling, and other equipment drives where in fact the backdriving or inertial driving is not permissible. Among such request [7] of the self-locking gears for a continuously variable valve lift system was advised for an motor vehicle engine.
Summary
In this paper, a theory of job of the self-locking gears has been described. Style specifics of the self-locking gears with symmetric and asymmetric profiles are shown, and tests of the apparatus prototypes has proved relatively high driving proficiency and trustworthy self-locking. The self-locking gears could find many applications in various industries. For instance, in a control devices where position steadiness is very important (such as for example in auto, 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 sensitive to operating conditions. The locking stability is affected by lubrication, vibration, misalignment, etc. Implementation of these gears should be done with caution and requires comprehensive testing in every possible operating conditions.