Worm gearboxes with countless combinations
Ever-Power offers an extremely wide range of worm gearboxes. As a result of modular design the typical programme self locking gearbox comprises countless combinations with regards to selection of gear housings, mounting and interconnection options, flanges, shaft models, kind of oil, surface solutions etc.
Sturdy and reliable
The look of the Ever-Power worm gearbox is simple and well proven. We simply use high quality components such as properties in cast iron, aluminium and stainless steel, worms in the event hardened and polished steel and worm tires in high-grade bronze of unique alloys ensuring the the best wearability. The seals of the worm gearbox are given with a dust lip which successfully resists dust and water. In addition, the gearboxes happen to 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 single step or 10.000:1 in a double decrease. An comparative gearing with the same equipment ratios and the same transferred power is bigger than a worm gearing. At the same time, the worm gearbox is usually in a more simple design.
A double reduction could be composed of 2 typical gearboxes or as a special gearbox.
Compact design
Compact design is among the key phrases of the typical gearboxes of the Ever-Power-Series. Further optimisation can be achieved by using adapted gearboxes or unique gearboxes.
Low noise
Our worm gearboxes and actuators are extremely quiet. This is because of the very even jogging of the worm gear combined with the usage of cast iron and large precision on part manufacturing and assembly. In connection with our precision gearboxes, we consider extra proper care of any sound that can be interpreted as a murmur from the gear. Therefore the general noise degree of our gearbox is definitely reduced to a complete minimum.
Angle gearboxes
On the worm gearbox the input shaft and output shaft are perpendicular to one another. This frequently proves to become a decisive benefit producing the incorporation of the gearbox considerably simpler and smaller sized.The worm gearbox is an angle gear. This is often an advantage for incorporation into constructions.
Strong bearings in sound housing
The output shaft of the Ever-Power worm gearbox is very firmly embedded in the apparatus house and is perfect for immediate suspension for wheels, movable arms and other areas rather than needing 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 security. As well spindle gearboxes with a trapezoidal spindle happen to be self-locking, making them perfect for an array of solutions.
In most equipment drives, when driving torque is suddenly reduced therefore of electric power off, torsional vibration, electric power outage, or any mechanical failing at the transmission input part, then gears will be rotating either in the same direction driven by the system inertia, or in the opposite course driven by the resistant output load due to gravity, spring load, etc. The latter state is known as backdriving. During inertial movement or backdriving, the driven output shaft (load) turns into the driving one and the generating input shaft (load) turns into the powered one. There are numerous gear travel applications where end result shaft driving is undesirable. So as to prevent it, several types of brake or clutch gadgets are used.
However, there are also solutions in the gear transmission that prevent inertial action or backdriving using self-locking gears without the additional devices. The most typical one is a worm equipment with a low lead angle. In self-locking worm gears, torque used from the strain side (worm gear) is blocked, i.e. cannot drive 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 proficiency, increased heat technology, etc.
Also, there are 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 mode, when the inertial or backdriving torque can be applied to the output gear. Primarily these gears had very low ( <50 percent) generating proficiency that limited their application. Then it was proved [3] that high driving efficiency of these kinds of gears is possible. Conditions of the self-locking was analyzed on this page [4]. This paper explains the theory of the self-locking method for the parallel axis gears with symmetric and asymmetric tooth profile, and shows their suitability for distinct applications.
Self-Locking Condition
Figure 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 the event of inertial driving. Pretty much all conventional equipment drives possess the pitch point P situated in the active portion the contact brand B1-B2 (Figure 1a and Shape 2a). This pitch stage location provides low certain sliding velocities and friction, and, subsequently, high driving performance. In case when this sort of gears are driven by outcome load or inertia, they happen to be rotating freely, because 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, 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
In order to make gears self-locking, the pitch point P ought to be located off the productive portion the contact line B1-B2. There happen to be two options. Choice 1: when the idea P is positioned between a center of the pinion O1 and the idea B2, where the outer diameter of the gear intersects the contact range. This makes the self-locking possible, however the driving proficiency will be low under 50 percent [3]. Option 2 (figs 1b and 2b): when the point P is located between your point B1, where the outer diameter of the pinion intersects the series contact and a center of the apparatus O2. This kind of gears can be self-locking with relatively great driving proficiency > 50 percent.
Another condition of self-locking is to truly have a ample friction angle g to deflect the force F’ beyond the center of the pinion O1. It generates the resisting self-locking minute (torque) T’1 = F’ x L’1, where L’1 is certainly a lever of the push F’1. This condition could 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 angle at the end of the gear tooth.
Design of Self-Locking Gears
Self-locking gears are customized. They cannot become fabricated with the requirements tooling with, for instance, the 20o pressure and rack. This makes them incredibly ideal for Direct Gear Style® [5, 6] that delivers required gear performance and after that defines tooling parameters.
Direct Gear Style presents the symmetric gear tooth produced by two involutes of 1 base circle (Figure 3a). The asymmetric gear tooth is created by two involutes of two distinct base circles (Figure 3b). The tooth hint circle da allows preventing the pointed tooth hint. The equally spaced the teeth form the apparatus. The fillet profile between teeth was created independently to avoid interference and offer minimum bending stress. The operating pressure angle aw and the get in touch with 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 high pressure and large sliding friction in the tooth get in touch with. If the sliding friction coefficient f = 0.1 – 0.3, it needs the transverse operating pressure angle to aw = 75 – 85o. Therefore, the transverse contact ratio ea < 1.0 (typically 0.4 - 0.6). Lack of the transverse speak to ratio ought to be compensated by the axial (or face) get in touch with ratio eb to guarantee the total contact ratio eg = ea + eb ≥ 1.0. This is often attained by employing helical gears (Number 4). However, helical gears apply the axial (thrust) pressure on the gear bearings. The double helical (or “herringbone”) gears (Physique 4) allow to pay this force.
Huge transverse pressure angles result in increased bearing radial load that may be up to four to five circumstances higher than for the traditional 20o pressure angle gears. Bearing selection and gearbox housing design should be done accordingly to hold this improved load without high deflection.
Request of the asymmetric tooth for unidirectional drives allows for improved performance. For the self-locking gears that are being used to prevent backdriving, the same tooth flank is used for both traveling and locking modes. In this instance asymmetric tooth profiles provide much higher transverse get in touch with ratio at the granted pressure angle compared to the symmetric tooth flanks. It makes it possible to lessen the helix position and axial bearing load. For the self-locking gears that used to avoid inertial driving, diverse tooth flanks are being used for driving and locking modes. In this instance, asymmetric tooth profile with low-pressure angle provides high effectiveness for driving function and the opposite high-pressure angle tooth account is utilized for reliable self-locking.
Testing Self-Locking Gears
Self-locking helical equipment prototype models were made predicated on the developed mathematical products. The gear data are offered in the Desk 1, and the check gears are provided in Figure 5.
The schematic presentation of the test setup is demonstrated in Figure 6. The 0.5Nm electric motor was used to operate a vehicle the actuator. A built-in rate and torque sensor was installed on the high-quickness shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was connected to the low swiftness shaft of the gearbox via coupling. The suggestions and result torque and speed info were captured in the data acquisition tool and further analyzed in a computer applying data analysis computer software. The instantaneous effectiveness of the actuator was calculated and plotted for a wide range of speed/torque combination. Normal driving effectiveness of the self- locking gear obtained during examining was above 85 percent. The self-locking house of the helical equipment occur backdriving mode was likewise tested. During this test the exterior torque was applied to the output gear shaft and the angular transducer revealed no angular movements of suggestions shaft, which confirmed the self-locking condition.
Potential Applications
Initially, self-locking gears were used in textile industry [2]. On the other hand, this sort of gears has many potential applications in lifting mechanisms, assembly tooling, and other equipment drives where the backdriving or inertial traveling is not permissible. One of such program [7] of the self-locking gears for a continually variable valve lift system was recommended for an auto 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 happen to be shown, and evaluating of the apparatus prototypes has proved comparatively high driving efficiency and trustworthy self-locking. The self-locking gears may find many applications in a variety of industries. For instance, in a control systems where position stableness is very important (such as for example in automotive, aerospace, medical, robotic, agricultural etc.) the self-locking allows to attain required performance. Similar to the worm self-locking gears, the parallel axis self-locking gears are delicate to operating conditions. The locking stability is afflicted by lubrication, vibration, misalignment, etc. Implementation of the gears should be finished with caution and needs comprehensive testing in all possible operating conditions.