Worm gearboxes with countless combinations
Ever-Power offers a very wide range of worm gearboxes. As a result of modular design the standard programme comprises many combinations in terms of selection of equipment housings, mounting and connection options, flanges, shaft styles, type of oil, surface remedies etc.
Sturdy and reliable
The look of the Ever-Power worm gearbox is easy and well proven. We simply use top quality components such as houses in cast iron, aluminium and stainless, worms in case hardened and polished steel and worm tires in high-quality bronze of special alloys ensuring the ideal wearability. The seals of the worm gearbox are provided with a dirt lip which efficiently resists dust and normal water. Furthermore, the gearboxes will be greased forever 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 step or 10.000:1 in a double reduction. An equivalent gearing with the same gear ratios and the same transferred electricity is bigger when compared to a worm gearing. On the other hand, the worm gearbox is definitely in a far more simple design.
A double reduction could be composed of 2 normal gearboxes or as a particular gearbox.
Compact design
Compact design is one of the key terms of the typical gearboxes of the Ever-Power-Series. Further optimisation may be accomplished through the use of adapted gearboxes or unique gearboxes.
Low noise
Our worm gearboxes and actuators are extremely quiet. This is because of the very simple operating of the worm equipment combined with the consumption of cast iron and high precision on aspect manufacturing and assembly. In connection with our accuracy gearboxes, we consider extra attention of any sound which can be interpreted as a murmur from the gear. So the general noise level of our gearbox is reduced to an absolute minimum.
Angle gearboxes
On the worm gearbox the input shaft and output shaft are perpendicular to each other. This typically proves to become a decisive advantages producing the incorporation of the gearbox considerably simpler and more compact.The worm gearbox is an angle gear. This can often be an edge for incorporation into constructions.
Strong bearings in sound housing
The output shaft of the Ever-Power worm gearbox is quite firmly embedded in the gear house and is well suited for immediate suspension for wheels, movable arms and other areas rather than having to create a separate suspension.
Self locking
For larger gear ratios, Ever-Electrical power worm gearboxes provides a self-locking result, which in many situations works extremely well as brake or as extra security. Likewise spindle gearboxes with a trapezoidal spindle are self-locking, making them perfect for an array of solutions.
In most gear drives, when generating torque is suddenly reduced because of this of vitality off, torsional vibration, electricity outage, or any mechanical failure at the transmitting input area, then gears will be rotating either in the same direction driven by the machine inertia, or in the opposite way driven by the resistant output load because of gravity, planting season load, etc. The latter state is known as backdriving. During inertial movement or backdriving, the motivated output shaft (load) becomes the driving one and the generating input shaft (load) turns into the driven one. There are several gear drive applications where outcome shaft driving is unwanted. As a way to prevent it, several types of brake or clutch equipment are used.
However, there are also solutions in the apparatus transmitting that prevent inertial motion or backdriving using self-locking gears with no additional gadgets. The most frequent one is certainly a worm equipment with a minimal lead angle. In self-locking worm gears, torque applied from the strain side (worm gear) is blocked, i.e. cannot travel the worm. On the other hand, their application includes some constraints: the crossed axis shafts’ arrangement, relatively high equipment ratio, low quickness, low gear mesh efficiency, increased heat technology, etc.
Also, there happen to be parallel axis self-locking gears [1, 2]. These gears, unlike the worm gears, can make use of any equipment ratio from 1:1 and higher. They have the driving mode and self-locking setting, when the inertial or backdriving torque is normally applied to the output gear. Originally these gears had very low ( <50 percent) generating efficiency that limited their app. Then it had been proved [3] that excessive driving efficiency of this sort of gears is possible. Standards of the self-locking was analyzed in this post [4]. This paper explains the principle of the self-locking process for the parallel axis gears with symmetric and asymmetric tooth profile, and shows their suitability for distinct applications.
Self-Locking Condition
Shape 1 presents conventional gears (a) and self-locking gears (b), in the event of backdriving. Figure 2 presents standard gears (a) and self-locking gears (b), in case of inertial driving. Virtually all conventional equipment drives possess the pitch point P located in the active portion the contact line B1-B2 (Figure 1a and Number 2a). This pitch level location provides low particular sliding velocities and friction, and, as a result, high driving efficiency. In case when such gears are influenced by output load or inertia, they happen to be 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, put on the gear
T’1 – driven torque, put on the pinion
F – driving force
F’ – generating force, when the backdriving or inertial torque put on 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 effective portion the contact line B1-B2. There are two options. Option 1: when the idea P is placed between a center of the pinion O1 and the idea B2, where the outer diameter of the gear intersects the contact line. This makes the self-locking possible, however the driving performance will be low under 50 percent [3]. Choice 2 (figs 1b and 2b): when the idea P is placed between your point B1, where the outer size of the pinion intersects the brand contact and a center of the gear O2. This type of gears could be self-locking with relatively large driving effectiveness > 50 percent.
Another condition of self-locking is to truly have a sufficient friction angle g to deflect the force F’ beyond the guts of the pinion O1. It generates the resisting self-locking second (torque) T’1 = F’ x L’1, where L’1 is certainly a lever of the induce F’1. This condition can be shown 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 end of the gear tooth.
Design of Self-Locking Gears
Self-locking gears are customized. They cannot be fabricated with the specifications tooling with, for instance, the 20o pressure and rack. This makes them incredibly suited to Direct Gear Design® [5, 6] that provides required gear overall performance 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 equipment tooth is produced by two involutes of two numerous base circles (Figure 3b). The tooth tip circle da allows avoiding the pointed tooth suggestion. The equally spaced teeth form the apparatus. The fillet account between teeth was created independently in order to avoid interference and self locking gearbox provide minimum bending stress. The working pressure angle aw and the contact ratio ea are defined by the next 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 get in touch with. If the sliding friction coefficient f = 0.1 – 0.3, it requires the transverse operating pressure position to aw = 75 – 85o. Because of this, the transverse speak to 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 guarantee the total contact ratio eg = ea + eb ≥ 1.0. This is often achieved by applying helical gears (Determine 4). On the other hand, helical gears apply the axial (thrust) power on the apparatus bearings. The dual helical (or “herringbone”) gears (Body 4) allow to pay this force.
Excessive transverse pressure angles cause increased bearing radial load that could be up to four to five instances higher than for the traditional 20o pressure angle gears. Bearing variety and gearbox housing style should be done accordingly to hold this elevated load without unnecessary deflection.
Program of the asymmetric pearly whites for unidirectional drives permits improved performance. For the self-locking gears that are being used to prevent backdriving, the same tooth flank can be used for both traveling and locking modes. In this instance asymmetric tooth profiles give much higher transverse contact ratio at the provided 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 which used to avoid inertial driving, unique tooth flanks are being used for driving and locking modes. In this case, asymmetric tooth profile with low-pressure position provides high performance for driving function and the contrary high-pressure angle tooth profile can be used for reliable self-locking.
Testing Self-Locking Gears
Self-locking helical equipment prototype pieces were made based on the developed mathematical products. The gear data are presented in the Desk 1, and the check gears are presented in Figure 5.
The schematic presentation of the test setup is proven in Figure 6. The 0.5Nm electric motor was used to operate a vehicle the actuator. An integrated rate and torque sensor was attached on the high-rate shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was linked to the low acceleration shaft of the gearbox via coupling. The source and end result torque and speed information had been captured in the info acquisition tool and further analyzed in a pc using data analysis application. The instantaneous productivity of the actuator was calculated and plotted for a variety of speed/torque combination. Standard driving efficiency of the personal- locking equipment obtained during testing was above 85 percent. The self-locking property of the helical equipment occur backdriving mode was also tested. During this test the external torque was put on the output equipment shaft and the angular transducer revealed no angular movements of type shaft, which confirmed the self-locking condition.
Potential Applications
Initially, self-locking gears had been found in textile industry [2]. However, this kind 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 continually variable valve lift system was suggested for an car engine.
Summary
In this paper, a theory of do the job of the self-locking gears has been described. Style specifics of the self-locking gears with symmetric and asymmetric profiles will be shown, and evaluating of the gear prototypes has proved comparatively high driving productivity and trusted self-locking. The self-locking gears could find many applications in various industries. For example, in a control systems where position steadiness is essential (such as for example in automobile, aerospace, medical, robotic, agricultural etc.) the self-locking allows 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 damaged by lubrication, vibration, misalignment, etc. Implementation of these gears should be done with caution and requires comprehensive testing in all possible operating conditions.