Worm gearboxes with countless combinations
Ever-Power offers an self locking gearbox extremely broad range of worm gearboxes. Because of the modular design the typical programme comprises countless combinations when it comes to selection of equipment housings, mounting and interconnection options, flanges, shaft styles, kind of oil, surface treatment options 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 properties in cast iron, aluminium and stainless steel, worms in the event hardened and polished steel and worm tires in high-grade bronze of specialized alloys ensuring the the best wearability. The seals of the worm gearbox are provided with a dirt lip which successfully resists dust and drinking water. Furthermore, the gearboxes will be greased for life with synthetic oil.
Large reduction 100:1 in a single step
As default the worm gearboxes enable reductions as high as 100:1 in one step or 10.000:1 in a double reduction. An equivalent gearing with the same equipment ratios and the same transferred power is bigger than a worm gearing. In the meantime, the worm gearbox is in a far more simple design.
A double reduction may be composed of 2 common gearboxes or as a particular gearbox.
Compact design
Compact design is among the key terms of the standard 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 due to the very smooth running of the worm gear combined with the utilization of cast iron and excessive 
precision on component manufacturing and assembly. In connection with our precision gearboxes, we have extra proper care of any sound which can be interpreted as a murmur from the gear. Therefore the general noise degree of our gearbox is definitely reduced to an absolute minimum.
Angle gearboxes
On the worm gearbox the input shaft and output shaft are perpendicular to each other. This sometimes proves to become a decisive advantages producing the incorporation of the gearbox noticeably simpler and smaller sized.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 very firmly embedded in the apparatus house and is suitable 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-Power worm gearboxes provides a self-locking result, which in many situations can be utilised as brake or as extra secureness. Also spindle gearboxes with a trapezoidal spindle are self-locking, making them suitable for an array of solutions.
In most equipment drives, when traveling torque is suddenly reduced therefore of electrical power off, torsional vibration, electricity outage, or any mechanical inability at the tranny input area, then gears will be rotating either in the same way driven by the machine inertia, or in the opposite route driven by the resistant output load because of gravity, early spring load, etc. The latter condition is known as backdriving. During inertial movement or backdriving, the influenced output shaft (load) becomes the traveling one and the traveling input shaft (load) turns into the motivated one. There are lots of gear drive applications where end result shaft driving is unwanted. As a way to prevent it, several types of brake or clutch products are used.
However, additionally, there are solutions in the apparatus transmission that prevent inertial movement or backdriving using self-locking gears with no additional products. The most frequent one is a worm gear with a low lead angle. In self-locking worm gears, torque applied from the strain side (worm equipment) is blocked, i.electronic. cannot travel the worm. Even so, their application includes some limitations: the crossed axis shafts’ arrangement, relatively high gear ratio, low velocity, low gear mesh efficiency, increased heat era, etc.
Also, there happen to be parallel axis self-locking gears [1, 2]. These gears, unlike the worm gears, can make use of any gear ratio from 1:1 and bigger. They have the driving mode and self-locking setting, when the inertial or backdriving torque is normally applied to the output gear. At first these gears had suprisingly low ( <50 percent) generating efficiency that limited their request. then it had been proved [3] large driving of these kinds gears is possible. conditions the self-locking was analyzed in this article [4]. paper explains basic principle process for parallel axis with symmetric and asymmetric pearly whites profile, reveals suitability distinct 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 case of inertial driving. Virtually all conventional equipment drives have the pitch level P situated in the active portion the contact series B1-B2 (Figure 1a and Body 2a). This pitch point location provides low certain sliding velocities and friction, and, because of this, high driving productivity. In case when such gears are influenced by end result load or inertia, they will be rotating freely, because the friction minute (or torque) isn’t 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, applied to 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
To make gears self-locking, the pitch point P ought to be located off the active portion the contact line B1-B2. There are two options. Alternative 1: when the point P is placed between a middle of the pinion O1 and the point B2, where the outer diameter of the apparatus intersects the contact line. This makes the self-locking possible, however the driving productivity will become low under 50 percent [3]. Choice 2 (figs 1b and 2b): when the idea P is positioned between the point B1, where in fact the outer size of the pinion intersects the collection contact and a middle of the apparatus O2. This type of gears could be self-locking with relatively great driving proficiency > 50 percent.
Another condition of self-locking is to have a ample friction angle g to deflect the force F’ beyond the center of the pinion O1. It generates the resisting self-locking instant (torque) T’1 = F’ x L’1, where L’1 is certainly a lever of the pressure F’1. This condition can be offered 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 always be fabricated with the benchmarks tooling with, for example, the 20o pressure and rack. This makes them extremely suited to Direct Gear Style® [5, 6] that delivers required gear efficiency and after that defines tooling parameters.
Direct Gear Style presents the symmetric equipment tooth shaped by two involutes of 1 base circle (Figure 3a). The asymmetric gear tooth is formed by two involutes of two numerous base circles (Figure 3b). The tooth idea circle da allows avoiding the pointed tooth idea. The equally spaced tooth form the apparatus. The fillet profile between teeth is designed independently in order to avoid interference and offer minimum bending tension. The working pressure angle aw and the speak to 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 huge 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. Therefore, the transverse get in touch with ratio ea < 1.0 (typically 0.4 - 0.6). Insufficient the transverse get in touch with ratio should be compensated by the axial (or face) speak to ratio eb to ensure the total get in touch with ratio eg = ea + eb ≥ 1.0. This is often achieved by using helical gears (Body 4). However, helical gears apply the axial (thrust) pressure on the apparatus bearings. The double helical (or “herringbone”) gears (Shape 4) allow to compensate this force.
Excessive transverse pressure angles cause increased bearing radial load that may be up to four to five moments higher than for the conventional 20o pressure angle gears. Bearing collection and gearbox housing style should be done accordingly to carry this increased load without excessive deflection.
Application of the asymmetric tooth for unidirectional drives permits improved functionality. For the self-locking gears that are used to prevent backdriving, the same tooth flank is utilized for both generating and locking modes. In this instance asymmetric tooth profiles present much higher transverse contact ratio at the granted pressure angle compared to 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 generating and locking modes. In this instance, asymmetric tooth profile with low-pressure position provides high efficiency for driving function and the opposite high-pressure angle tooth account is employed for reliable self-locking.
Testing Self-Locking Gears
Self-locking helical equipment prototype models 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 displayed in Figure 6. The 0.5Nm electric electric motor was used to drive the actuator. An integrated quickness and torque sensor was attached on the high-acceleration shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was connected to the low quickness shaft of the gearbox via coupling. The insight and end result torque and speed facts were captured in the info acquisition tool and additional analyzed in a pc using data analysis program. The instantaneous proficiency of the actuator was calculated and plotted for a variety of speed/torque combination. Average driving efficiency of the self- locking equipment obtained during tests was above 85 percent. The self-locking house of the helical gear occur backdriving mode was as well tested. In this test the external torque was applied to the output equipment shaft and the angular transducer confirmed no angular movements of insight shaft, which verified the self-locking condition.
Potential Applications
Initially, self-locking gears had been used in textile industry [2]. On the other hand, this kind of gears has a large number of 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 consistently variable valve lift program was advised for an vehicle engine.
Summary
In this paper, a basic principle of operate 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 gear prototypes has proved fairly high driving productivity and trusted self-locking. The self-locking gears may find many applications in a variety of industries. For example, in a control systems where position steadiness is very important (such as 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 very sensitive to operating conditions. The locking dependability is afflicted by lubrication, vibration, misalignment, etc. Implementation of these gears should be finished with caution and requires comprehensive testing in every possible operating conditions.
