Worm gearboxes with many combinations
Ever-Power offers a very wide selection of worm gearboxes. As a result of modular design the standard programme comprises many combinations with regards to selection of gear housings, mounting and connection options, flanges, shaft styles, type of oil, surface treatments 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 houses in cast iron, light weight aluminum and stainless steel, worms in case hardened and polished steel and worm tires in high-grade 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 drinking water. In addition, 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 single step or 10.000:1 in a double lowering. An comparative gearing with the same gear ratios and the same transferred electricity is bigger than a worm gearing. In the meantime, the worm gearbox is in a more simple design.
A double reduction could be composed of 2 common gearboxes or as a special 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 specialized gearboxes.
Low noise
Our worm gearboxes and actuators are really quiet. This is because of the very smooth operating of the worm gear combined with the utilization of cast iron and huge precision on component manufacturing and assembly. Regarding the our precision gearboxes, we have extra care of any sound which can be interpreted as a murmur from the apparatus. So the general noise level of our gearbox is reduced to a complete minimum.
Angle gearboxes
On the worm gearbox the input shaft and output shaft are perpendicular to one another. This quite often proves to become a decisive advantages making the incorporation of the gearbox substantially simpler and more compact.The worm gearbox is an angle gear. This is normally an advantage for incorporation into constructions.
Strong bearings in sound housing
The output shaft of the Ever-Power worm gearbox is quite firmly embedded in the apparatus house and is well suited for direct suspension for wheels, movable arms and other areas rather than having to create a separate suspension.
Self locking
For larger equipment ratios, Ever-Electricity worm gearboxes provides a self-locking result, which in lots of situations can be utilised as brake or as extra security. As well spindle gearboxes with a trapezoidal spindle happen to be self-locking, making them perfect for a wide range of solutions.
In most equipment drives, when driving torque is suddenly reduced consequently of ability off, torsional vibration, electrical power outage, or any mechanical failing at the tranny input part, then gears will be rotating either in the same route driven by the machine inertia, or in the contrary way driven by the resistant output load because of gravity, planting season load, etc. The latter condition is called backdriving. During inertial motion or backdriving, the powered output shaft (load) becomes the traveling one and the traveling input shaft (load) turns into the driven one. There are numerous gear drive applications where outcome shaft driving is unwanted. In order to prevent it, various kinds of brake or clutch equipment are used.
However, there are also solutions in the apparatus tranny that prevent inertial motion or backdriving using self-locking gears without the additional units. The most frequent one is normally a worm gear with a minimal lead angle. In self-locking worm gears, torque used from the strain side (worm gear) is blocked, i.electronic. cannot travel the worm. Even so, their application includes some limitations: the crossed axis shafts’ arrangement, relatively high equipment ratio, low rate, low gear mesh productivity, increased heat era, etc.
Also, there are parallel axis self-locking gears [1, 2]. These gears, unlike the worm gears, can employ any equipment ratio from 1:1 and higher. They have the generating mode and self-locking method, when the inertial or backdriving torque is usually applied to the output gear. Primarily these gears had very low ( <50 percent) generating performance that limited their application. Then it was proved [3] that substantial driving efficiency of such gears is possible. Conditions of the self-locking was analyzed in this posting [4]. This paper explains the basic principle of the self-locking method for the parallel axis gears with symmetric and asymmetric tooth profile, and reveals their suitability for different applications.
Self-Locking Condition
Body 1 presents conventional gears (a) and self-locking gears (b), in case of backdriving. Figure 2 presents conventional gears (a) and self-locking gears (b), in the event of inertial driving. Practically all conventional equipment drives have the pitch point P situated in the active part the contact line B1-B2 (Figure 1a and Number 2a). This pitch point location provides low particular sliding velocities and friction, and, due to this fact, high driving proficiency. In case when this kind of gears are powered by output load or inertia, they will be rotating freely, as the friction minute (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’ – driving 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
To make gears self-locking, the pitch point P should be located off the effective portion the contact line B1-B2. There happen to be two options. Alternative 1: when the point P is placed between a middle of the pinion O1 and the point B2, where in fact the outer size of the apparatus intersects the contact range. This makes the self-locking possible, but the driving efficiency will end up being low under 50 percent [3]. Option 2 (figs 1b and 2b): when the point P is put between the point B1, where the outer diameter of the pinion intersects the brand contact and a centre of the gear O2. This kind of gears could be self-locking with relatively large driving productivity > 50 percent.
Another condition of self-locking is to have a satisfactory friction angle g to deflect the force F’ beyond the self locking gearbox center of the pinion O1. It generates the resisting self-locking moment (torque) T’1 = F’ x L’1, where L’1 is usually a lever of the pressure F’1. This condition could be presented as L’1min > 0 or
(1) Equation 1
or
(2) Equation 2
where:
u = n2/n1 – equipment ratio,
n1 and n2 – pinion and gear quantity of teeth,
– involute profile position at the end of the apparatus 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 extremely well suited for Direct Gear Design® [5, 6] that provides required gear functionality and from then on defines tooling parameters.
Direct Gear Design presents the symmetric equipment tooth produced by two involutes of one base circle (Figure 3a). The asymmetric equipment tooth is created by two involutes of two distinct base circles (Figure 3b). The tooth suggestion circle da allows avoiding the pointed tooth suggestion. The equally spaced teeth form the gear. The fillet profile between teeth was created independently to avoid interference and provide minimum bending anxiety. 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 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 get in touch with ratio ea < 1.0 (typically 0.4 - 0.6). Lack of the transverse get in touch with 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 can be attained by employing helical gears (Figure 4). On the other hand, helical gears apply the axial (thrust) force on the apparatus bearings. The double helical (or “herringbone”) gears (Physique 4) allow to pay this force.
Substantial transverse pressure angles lead to increased bearing radial load that could be up to four to five moments higher than for the traditional 20o pressure angle gears. Bearing collection and gearbox housing style ought to be done accordingly to carry this elevated load without excessive deflection.
Program of the asymmetric tooth for unidirectional drives permits improved effectiveness. For the self-locking gears that are used to avoid backdriving, the same tooth flank is used for both generating and locking modes. In this case asymmetric tooth profiles give much higher transverse speak to ratio at the given pressure angle than the symmetric tooth flanks. It makes it possible to lessen the helix position and axial bearing load. For the self-locking gears which used to avoid inertial driving, unique tooth flanks are used for driving and locking modes. In this instance, asymmetric tooth profile with low-pressure position provides high effectiveness for driving function and the contrary high-pressure angle tooth account can be used for reliable self-locking.
Testing Self-Locking Gears
Self-locking helical gear prototype models were made based on the developed mathematical styles. The gear info are shown in the Desk 1, and the check gears are shown in Figure 5.
The schematic presentation of the test setup is displayed in Figure 6. The 0.5Nm electric motor was used to operate a vehicle the actuator. A built-in rate and torque sensor was mounted on the high-swiftness shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was connected to the low rate shaft of the gearbox via coupling. The type and result torque and speed data were captured in the data acquisition tool and additional 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. Typical driving productivity of the self- locking gear obtained during screening was above 85 percent. The self-locking house 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 showed no angular motion of type shaft, which confirmed the self-locking condition.
Potential Applications
Initially, self-locking gears had been used in textile industry [2]. However, this sort of gears has various potential applications in lifting mechanisms, assembly tooling, and other equipment drives where in fact the backdriving or inertial driving is not permissible. Among such app [7] of the self-locking gears for a consistently variable valve lift system was recommended for an vehicle engine.
Summary
In this paper, a basic principle of do the job of the self-locking gears has been described. Design specifics of the self-locking gears with symmetric and asymmetric profiles happen to be shown, and tests of the apparatus prototypes has proved fairly high driving efficiency and efficient self-locking. The self-locking gears could find many applications in various industries. For instance, in a control devices where position stability is essential (such as for example in automotive, aerospace, medical, robotic, agricultural etc.) the self-locking allows to accomplish required performance. Similar to the worm self-locking gears, the parallel axis self-locking gears are delicate to operating conditions. The locking reliability 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.