Worm gearboxes with many combinations
Ever-Power offers an self locking gearbox extremely wide selection of worm gearboxes. Due to the modular design the standard programme comprises many combinations when it comes to selection of gear housings, mounting and connection options, flanges, shaft models, kind of oil, surface treatments etc.
Sturdy and reliable
The look of the Ever-Power worm gearbox is easy and well proven. We simply use high quality components such as houses in cast iron, light weight aluminum and stainless steel, worms in case hardened and polished steel and worm wheels in high-quality bronze of specialized alloys ensuring the maximum wearability. The seals of the worm gearbox are provided with a dust lip which successfully resists dust and water. Furthermore, the gearboxes are greased forever with synthetic oil.
Large reduction 100:1 in one step
As default the worm gearboxes allow for reductions as high as 100:1 in one step or 10.000:1 in a double decrease. An equivalent gearing with the same gear ratios and the same transferred power is bigger than a worm gearing. Meanwhile, the worm gearbox is normally in a far more simple design.
A double reduction could be composed of 2 common 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 can be achieved by using adapted gearboxes or particular gearboxes.
Low noise
Our worm gearboxes and actuators are extremely quiet. This is because of the very easy running of the worm gear combined with the use of cast iron and large precision on component manufacturing and assembly. In connection with our accuracy gearboxes, we take extra treatment of any sound which can be interpreted as a murmur from the apparatus. So the general noise degree of our gearbox is normally reduced to an absolute minimum.
Angle gearboxes
On the worm gearbox the input shaft and output shaft are perpendicular to one another. This often proves to become a decisive gain making the incorporation of the gearbox considerably simpler and more compact.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 very 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 equipment ratios, Ever-Ability worm gearboxes provides a self-locking effect, which in lots of situations works extremely well as brake or as extra reliability. Also spindle gearboxes with a trapezoidal spindle will be self-locking, making them suitable for an array of solutions.
In most equipment drives, when driving torque is suddenly reduced consequently of electric power off, torsional vibration, electric power outage, or any mechanical failing at the transmission input side, then gears will be rotating either in the same path driven by the machine inertia, or in the opposite direction driven by the resistant output load due to gravity, springtime load, etc. The latter condition is known as backdriving. During inertial action or backdriving, the driven output shaft (load) turns into the traveling one and the driving input shaft (load) becomes the motivated one. There are numerous gear drive applications where outcome shaft driving is unwanted. To be able to prevent it, various kinds of brake or clutch products are used.
However, additionally, there are solutions in the apparatus transmitting that prevent inertial action or backdriving using self-locking gears with no additional devices. The most typical one is usually a worm gear with a minimal lead angle. In self-locking worm gears, torque applied from the load side (worm gear) is blocked, i.electronic. cannot travel the worm. However, their application includes some constraints: the crossed axis shafts’ arrangement, relatively high equipment ratio, low swiftness, low gear mesh proficiency, increased heat generation, etc.
Also, there will be parallel axis self-locking gears [1, 2]. These gears, unlike the worm gears, can utilize any equipment ratio from 1:1 and bigger. They have the traveling mode and self-locking setting, when the inertial or backdriving torque is normally put on the output gear. In the beginning these gears had suprisingly low ( <50 percent) driving efficiency that limited their request. Then it had been proved [3] that great driving efficiency of this sort of gears is possible. Conditions of the self-locking was analyzed in this posting [4]. This paper explains the principle of the self-locking procedure for the parallel axis gears with symmetric and asymmetric the teeth profile, and shows their suitability for distinct applications.
Self-Locking Condition
Physique 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 the event of inertial driving. Pretty much all conventional gear drives have the pitch point P situated in the active part the contact series B1-B2 (Figure 1a and Figure 2a). This pitch stage location provides low certain sliding velocities and friction, and, due to this fact, high driving proficiency. In case when these kinds of gears are influenced by result load or inertia, they are rotating freely, as the friction point in time (or torque) is not sufficient to avoid 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’ – driving 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
To make gears self-locking, the pitch point P ought to be located off the productive portion the contact line B1-B2. There are two options. Alternative 1: when the point P is positioned between a center of the pinion O1 and the point B2, where the outer diameter of the apparatus intersects the contact brand. This makes the self-locking possible, but the driving efficiency will become low under 50 percent [3]. Alternative 2 (figs 1b and 2b): when the idea P is placed between the point B1, where in fact the outer size of the pinion intersects the collection contact and a middle of the gear O2. This sort of gears could be self-locking with relatively great driving productivity > 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 generates the resisting self-locking moment (torque) T’1 = F’ x L’1, where L’1 is certainly a lever of the drive 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 amount of teeth,
– involute profile angle at the end of the gear tooth.
Design of Self-Locking Gears
Self-locking gears are custom. They cannot always be fabricated with the expectations tooling with, for example, the 20o pressure and rack. This makes them incredibly suited to Direct Gear Design® [5, 6] that provides required gear effectiveness and from then on defines tooling parameters.
Direct Gear Style presents the symmetric equipment tooth formed by two involutes of one base circle (Figure 3a). The asymmetric equipment tooth is formed by two involutes of two distinct base circles (Figure 3b). The tooth tip circle da allows preventing the pointed tooth hint. The equally spaced teeth form the apparatus. The fillet account between teeth was created independently to avoid interference and provide minimum bending tension. The operating 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 ruthless and huge 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. Therefore, the transverse contact 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 guarantee the total get in touch with ratio eg = ea + eb ≥ 1.0. This could be attained by using helical gears (Figure 4). However, helical gears apply the axial (thrust) force on the gear bearings. The twice helical (or “herringbone”) gears (Shape 4) allow to pay this force.
Substantial transverse pressure angles result in increased bearing radial load that may be up to four to five times higher than for the conventional 20o pressure angle gears. Bearing selection and gearbox housing design should be done accordingly to hold this improved load without extreme deflection.
Software of the asymmetric teeth for unidirectional drives allows for improved overall performance. For the self-locking gears that are used to prevent backdriving, the same tooth flank can be used for both driving and locking modes. In this case asymmetric tooth profiles present much higher transverse speak to ratio at the provided pressure angle compared to the symmetric tooth flanks. It creates it possible to reduce the helix position and axial bearing load. For the self-locking gears that used to avoid inertial driving, numerous tooth flanks are used for driving and locking modes. In this case, asymmetric tooth profile with low-pressure angle provides high effectiveness for driving method and the opposite high-pressure angle tooth account is employed for reliable self-locking.
Testing Self-Locking Gears
Self-locking helical equipment prototype pieces were made predicated on the developed mathematical versions. The gear info are shown in the Desk 1, and the test gears are provided in Figure 5.
The schematic presentation of the test setup is proven in Figure 6. The 0.5Nm electric electric motor was used to drive the actuator. A quickness and torque sensor was attached on the high-acceleration shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was connected to the low rate shaft of the gearbox via coupling. The suggestions and end result torque and speed details were captured in the data acquisition tool and further analyzed in a pc using data analysis software. The instantaneous effectiveness of the actuator was calculated and plotted for an array of speed/torque combination. Common driving effectiveness of the personal- locking gear obtained during evaluating 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 put on the output equipment shaft and the angular transducer showed no angular movements of insight shaft, which verified the self-locking condition.
Potential Applications
Initially, self-locking gears had been found in textile industry [2]. Even so, this kind of gears has many potential applications in lifting mechanisms, assembly tooling, and other gear drives where the backdriving or inertial driving is not permissible. Among such software [7] of the self-locking gears for a constantly variable valve lift system was advised for an vehicle engine.
Summary
In this paper, a principle of job 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 apparatus prototypes has proved relatively high driving performance and reliable self-locking. The self-locking gears could find many applications in a variety of industries. For example, in a control systems where position steadiness is important (such as for example in motor vehicle, 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 very sensitive to operating circumstances. The locking stability is afflicted by lubrication, vibration, misalignment, etc. Implementation of the gears should be done with caution and requires comprehensive testing in every possible operating conditions.