Worm gearboxes with countless combinations
Ever-Power offers an self locking gearbox extremely wide range of worm gearboxes. Due to the modular design the standard programme comprises countless combinations when it comes to selection of equipment housings, mounting and connection options, flanges, shaft styles, kind of oil, surface therapies etc.
Sturdy and reliable
The look of the Ever-Power worm gearbox is simple and well proven. We just use top quality components such as residences in cast iron, lightweight aluminum and stainless steel, worms in case hardened and polished metal and worm tires in high-grade bronze of particular alloys ensuring the the best possible wearability. The seals of the worm gearbox are given with a dirt lip which efficiently resists dust and water. In addition, the gearboxes are 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 step or 10.000:1 in a double reduction. An equivalent gearing with the same gear ratios and the same transferred electrical power is bigger than a worm gearing. Meanwhile, the worm gearbox can be in a more simple design.
A double reduction could be composed of 2 normal gearboxes or as a special gearbox.
Compact design
Compact design is one of the key terms of the standard gearboxes of the Ever-Power-Series. Further optimisation can be achieved by using adapted gearboxes or exceptional gearboxes.
Low noise
Our worm gearboxes and actuators are extremely quiet. This is due to the very smooth running of the worm equipment combined with the use of cast iron and high precision on part manufacturing and assembly. Regarding the our accuracy gearboxes, we have extra proper care of any sound which can be interpreted as a murmur from the gear. So the general noise level of our gearbox can be reduced to an absolute minimum.
Angle gearboxes
On the worm gearbox the input shaft and output shaft are perpendicular to one another. This typically proves to become a decisive gain 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 solid housing
The output shaft of the Ever-Power worm gearbox is very firmly embedded in the gear house and is well suited 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-Power worm gearboxes provides a self-locking impact, which in lots of situations works extremely well as brake or as extra secureness. Likewise spindle gearboxes with a trapezoidal spindle are self-locking, making them perfect for a variety of solutions.
In most gear drives, when driving torque is suddenly reduced consequently of electricity off, torsional vibration, electricity outage, or any mechanical failing at the transmitting input part, then gears will be rotating either in the same direction driven by the machine inertia, or in the contrary way driven by the resistant output load because of gravity, early spring load, etc. The latter state is called backdriving. During inertial action or backdriving, the motivated output shaft (load) turns into the traveling one and the driving input shaft (load) turns into the driven one. There are numerous gear travel applications where result shaft driving is unwanted. To be able to prevent it, various kinds of brake or clutch units are used.
However, additionally, there are solutions in the apparatus tranny that prevent inertial action or backdriving using self-locking gears without the additional products. The most typical one is a worm gear with a low lead angle. In self-locking worm gears, torque used from the load side (worm equipment) is blocked, i.e. cannot drive the worm. Nevertheless, their application includes some restrictions: the crossed axis shafts’ arrangement, relatively high gear ratio, low velocity, low gear mesh productivity, increased heat generation, etc.
Also, there will be parallel axis self-locking gears [1, 2]. These gears, unlike the worm gears, can use any gear ratio from 1:1 and bigger. They have the generating mode and self-locking method, when the inertial or backdriving torque is normally put on the output gear. Primarily these gears had suprisingly low ( <50 percent) generating effectiveness that limited their program. Then it was proved [3] that great driving efficiency of this sort of gears is possible. Standards of the self-locking was analyzed on this page [4]. This paper explains the principle of the self-locking procedure for the parallel axis gears with symmetric and asymmetric tooth profile, and shows their suitability for unique applications.
Self-Locking Condition
Shape 1 presents conventional gears (a) and self-locking gears (b), in case of backdriving. Figure 2 presents regular gears (a) and self-locking gears (b), in the event of inertial driving. Practically all conventional gear drives possess the pitch level P situated in the active portion the contact brand B1-B2 (Figure 1a and Physique 2a). This pitch stage location provides low certain sliding velocities and friction, and, therefore, high driving proficiency. In case when these kinds of gears are motivated by output load or inertia, they happen to be rotating freely, as the friction point in time (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, put on the gear
T’1 – driven torque, put on the pinion
F – driving force
F’ – traveling 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 active portion the contact line B1-B2. There will be 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 range. This makes the self-locking possible, however the driving performance will be low under 50 percent [3]. Option 2 (figs 1b and 2b): when the point P is placed between the point B1, where in fact the outer size of the pinion intersects the brand contact and a middle of the apparatus O2. This sort of gears can be self-locking with relatively large driving effectiveness > 50 percent.
Another condition of self-locking is to have a enough 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 a lever of the force F’1. This condition could be presented as L’1min > 0 or
(1) Equation 1
or
(2) Equation 2
where:
u = n2/n1 – gear ratio,
n1 and n2 – pinion and gear quantity of teeth,
– involute profile angle at the tip of the gear tooth.
Design of Self-Locking Gears
Self-locking gears are customized. They cannot always be fabricated with the requirements tooling with, for example, the 20o pressure and rack. This makes them incredibly suitable for Direct Gear Style® [5, 6] that provides required gear functionality 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 formed by two involutes of two several base circles (Figure 3b). The tooth suggestion circle da allows avoiding the pointed tooth idea. The equally spaced the teeth form the apparatus. The fillet profile between teeth is designed independently in order to avoid interference and offer minimum bending anxiety. The operating pressure angle aw and the contact ratio ea are described 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 high pressure and substantial 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. Because of this, the transverse contact ratio ea < 1.0 (typically 0.4 - 0.6). Lack of the transverse contact ratio should 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 using helical gears (Physique 4). However, helical gears apply the axial (thrust) pressure on the gear bearings. The dual helical (or “herringbone”) gears (Determine 4) allow to pay this force.
Great transverse pressure angles lead to increased bearing radial load that could be up to four to five moments higher than for the conventional 20o pressure angle gears. Bearing selection and gearbox housing design ought to be done accordingly to hold this increased load without excessive deflection.
Application of the asymmetric the teeth for unidirectional drives permits improved performance. For the self-locking gears that are being used to avoid backdriving, the same tooth flank can be used for both generating and locking modes. In this instance asymmetric tooth profiles give much higher transverse get in touch with ratio at the provided pressure angle than the symmetric tooth flanks. It creates it possible to reduce the helix position and axial bearing load. For the self-locking gears which used to avoid inertial driving, numerous tooth flanks are being used for driving and locking modes. In this instance, asymmetric tooth profile with low-pressure position provides high proficiency for driving mode and the opposite high-pressure angle tooth profile can be used 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 presented in the Desk 1, and the check gears are shown in Figure 5.
The schematic presentation of the test setup is proven in Figure 6. The 0.5Nm electric engine was used to drive the actuator. An integrated rate and torque sensor was attached on the high-rate shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was connected to the low rate shaft of the gearbox via coupling. The suggestions and outcome torque and speed details had been captured in the data acquisition tool and further analyzed in a pc employing data analysis application. The instantaneous proficiency of the actuator was calculated and plotted for a variety of speed/torque combination. Normal driving productivity of the personal- locking equipment obtained during assessment was above 85 percent. The self-locking house of the helical gear occur backdriving mode was also tested. During this test the exterior torque was applied to the output equipment shaft and the angular transducer demonstrated no angular motion of source shaft, which verified the self-locking condition.
Potential Applications
Initially, self-locking gears had been used in textile industry [2]. Even so, this sort of gears has many potential applications in lifting mechanisms, assembly tooling, and other equipment drives where the backdriving or inertial driving is not permissible. One of such software [7] of the self-locking gears for a constantly variable valve lift program was suggested for an automotive engine.
Summary
In this paper, a theory of job of the self-locking gears has been described. Design specifics of the self-locking gears with symmetric and asymmetric profiles are shown, and screening of the apparatus prototypes has proved relatively high driving performance and dependable self-locking. The self-locking gears may find many applications in a variety of industries. For instance, in a control devices where position steadiness is important (such as for example in vehicle, 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 delicate to operating circumstances. The locking stability is damaged by lubrication, vibration, misalignment, etc. Implementation of the gears should be done with caution and needs comprehensive testing in all possible operating conditions.