Worm gearboxes with countless combinations
Ever-Power offers an extremely wide selection of worm gearboxes. Because of the modular design the standard programme comprises many combinations with regards to selection of gear housings, mounting and interconnection options, flanges, shaft patterns, type of oil, surface procedures etc.
Sturdy and reliable
The design of the Ever-Power worm self locking gearbox gearbox is easy and well proven. We just use top quality components such as houses in cast iron, aluminum and stainless, worms in case hardened and polished metal and worm wheels in high-quality bronze of specialized alloys ensuring the ideal wearability. The seals of the worm gearbox are provided with a dust lip which properly resists dust and normal water. Furthermore, the gearboxes happen to be greased forever with synthetic oil.
Large reduction 100:1 in a single step
As default the worm gearboxes allow for reductions as high as 100:1 in one single step or 10.000:1 in a double decrease. An equivalent gearing with the same equipment ratios and the same transferred ability is bigger when compared to a worm gearing. In the meantime, the worm gearbox is in a far more simple design.
A double reduction may be composed of 2 typical gearboxes or as a particular gearbox.
Compact design
Compact design is among the key words of the typical gearboxes of the Ever-Power-Series. Further optimisation may be accomplished through the use of adapted gearboxes or special gearboxes.
Low noise
Our worm gearboxes and actuators are really quiet. This is because of the very soft operating of the worm equipment combined with the application of cast iron and substantial precision on aspect manufacturing and assembly. In connection with our accuracy gearboxes, we consider extra attention of any sound that can be interpreted as a murmur from the apparatus. Therefore the general noise degree of our gearbox is reduced to a complete minimum.
Angle gearboxes
On the worm gearbox the input shaft and output shaft are perpendicular to each other. This quite often proves to be a decisive edge making the incorporation of the gearbox significantly simpler and smaller sized.The worm gearbox can be 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 quite firmly embedded in the apparatus house and is ideal for direct 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 effect, which in many situations can be used as brake or as extra security. As well spindle gearboxes with a trapezoidal spindle happen to be self-locking, making them suitable for a wide variety of solutions.
In most equipment drives, when traveling torque is suddenly reduced therefore of power off, torsional vibration, power outage, or any mechanical inability at the tranny input aspect, then gears will be rotating either in the same way driven by the system inertia, or in the contrary route driven by the resistant output load due to gravity, planting season load, etc. The latter state is known as backdriving. During inertial movement or backdriving, the influenced output shaft (load) becomes the generating one and the traveling input shaft (load) becomes the motivated one. There are various gear drive applications where outcome shaft driving is undesirable. As a way to prevent it, several types of brake or clutch products are used.
However, additionally, there are solutions in the gear transmitting that prevent inertial motion or backdriving using self-locking gears without any additional equipment. The most common one can be a worm gear with a low lead angle. In self-locking worm gears, torque used from the strain side (worm gear) is blocked, i.electronic. cannot drive the worm. On the other hand, their application comes with some constraints: the crossed axis shafts’ arrangement, relatively high gear ratio, low acceleration, low gear mesh efficiency, increased heat era, etc.
Also, there will be 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 traveling mode and self-locking setting, when the inertial or backdriving torque is definitely applied to the output gear. Originally these gears had very low ( <50 percent) driving productivity that limited their request. Then it had been proved [3] that large driving efficiency of this kind of gears is possible. Requirements of the self-locking was analyzed in this post [4]. This paper explains the basic principle of the self-locking process for the parallel axis gears with symmetric and asymmetric pearly whites profile, and displays their suitability for diverse applications.
Self-Locking Condition
Determine 1 presents conventional gears (a) and self-locking gears (b), in the event of backdriving. Figure 2 presents conventional gears (a) and self-locking gears (b), in case of inertial driving. Pretty much all conventional equipment drives have the pitch stage P situated in the active part the contact range B1-B2 (Figure 1a and Number 2a). This pitch level location provides low particular sliding velocities and friction, and, subsequently, high driving effectiveness. In case when this sort of gears are driven by outcome load or inertia, they are 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, put on the gear
T’1 – driven torque, applied to the pinion
F – driving force
F’ – traveling force, when the backdriving or perhaps 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 will be two options. Alternative 1: when the idea P is placed between a center of the pinion O1 and the idea B2, where in fact the outer diameter of the apparatus intersects the contact brand. This makes the self-locking possible, but the driving proficiency will end up being low under 50 percent [3]. Choice 2 (figs 1b and 2b): when the point P is positioned between the point B1, where the outer diameter of the pinion intersects the range contact and a centre of the gear O2. This type of gears could be self-locking with relatively substantial driving performance > 50 percent.
Another condition of self-locking is to have a satisfactory friction angle g to deflect the force F’ beyond the center of the pinion O1. It generates the resisting self-locking point in time (torque) T’1 = F’ x L’1, where L’1 can be a lever of the pressure F’1. This condition could be shown 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 position at the tip of the gear tooth.
Design of Self-Locking Gears
Self-locking gears are custom. They cannot be fabricated with the expectations tooling with, for instance, the 20o pressure and rack. This makes them very suited to Direct Gear Design® [5, 6] that delivers required gear performance and after that defines tooling parameters.
Direct Gear Style presents the symmetric equipment tooth created by two involutes of one base circle (Figure 3a). The asymmetric equipment tooth is shaped by two involutes of two different base circles (Figure 3b). The tooth hint circle da allows preventing the pointed tooth tip. The equally spaced pearly whites form the gear. The fillet account between teeth was created independently in order to avoid interference and provide minimum bending stress. The working pressure angle aw and the contact ratio ea are identified 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 contact. If the sliding friction coefficient f = 0.1 – 0.3, it requires the transverse operating pressure angle to aw = 75 – 85o. Subsequently, the transverse speak to ratio ea < 1.0 (typically 0.4 - 0.6). Insufficient the transverse speak to ratio ought to be compensated by the axial (or face) get in touch with ratio eb to guarantee the total get in touch with ratio eg = ea + eb ≥ 1.0. This can be attained by applying helical gears (Number 4). On the other hand, helical gears apply the axial (thrust) drive on the apparatus bearings. The double helical (or “herringbone”) gears (Number 4) allow to compensate this force.
Huge transverse pressure angles cause increased bearing radial load that may be up to four to five times higher than for the traditional 20o pressure angle gears. Bearing variety and gearbox housing style should be done accordingly to carry this elevated load without increased deflection.
Software of the asymmetric pearly whites for unidirectional drives allows for improved efficiency. 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 provide much higher transverse speak to ratio at the presented pressure angle compared to the symmetric tooth flanks. It makes it possible to lessen the helix angle and axial bearing load. For the self-locking gears which used to prevent inertial driving, distinct tooth flanks are used for traveling and locking modes. In this instance, asymmetric tooth account with low-pressure angle provides high effectiveness for driving function and the contrary high-pressure angle tooth account is used for reliable self-locking.
Testing Self-Locking Gears
Self-locking helical gear prototype pieces were made based on the developed mathematical types. The gear data are offered in the Desk 1, and the test gears are presented in Figure 5.
The schematic presentation of the test setup is shown in Figure 6. The 0.5Nm electric motor was used to operate a vehicle the actuator. A built-in quickness and torque sensor was installed on the high-swiftness shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was linked to the low quickness shaft of the gearbox via coupling. The input and output torque and speed facts were captured in the info acquisition tool and additional analyzed in a computer employing data analysis program. The instantaneous effectiveness of the actuator was calculated and plotted for a broad range of speed/torque combination. Standard driving effectiveness of the self- locking equipment obtained during testing was above 85 percent. The self-locking real estate of the helical equipment set in backdriving mode was likewise tested. In this test the external torque was put on the output gear shaft and the angular transducer confirmed no angular activity of insight shaft, which verified the self-locking condition.
Potential Applications
Initially, self-locking gears were found in textile industry [2]. Nevertheless, this type of gears has various potential applications in lifting mechanisms, assembly tooling, and other gear drives where in fact the backdriving or inertial traveling is not permissible. One of such program [7] of the self-locking gears for a consistently variable valve lift system was recommended for an automobile engine.
Summary
In this paper, a theory of work of the self-locking gears has been described. Style specifics of the self-locking gears with symmetric and asymmetric profiles will be shown, and assessment of the gear prototypes has proved fairly high driving productivity and reputable self-locking. The self-locking gears could find many applications in various industries. For example, in a control systems where position balance is essential (such as for example in automotive, aerospace, medical, robotic, agricultural etc.) the self-locking will allow to attain required performance. Like the worm self-locking gears, the parallel axis self-locking gears are hypersensitive to operating conditions. The locking dependability is influenced by lubrication, vibration, misalignment, etc. Implementation of these gears should be finished with caution and requires comprehensive testing in every possible operating conditions.
