Worm gearboxes with countless combinations
Ever-Power offers an extremely wide range of worm gearboxes. Due to the modular design the typical programme comprises countless combinations with regards to selection of equipment housings, mounting and interconnection options, flanges, shaft models, type of oil, surface remedies etc.
Sturdy and reliable
The design of the Ever-Power worm gearbox is simple and well proven. We only use high quality components such as residences in cast iron, lightweight aluminum and stainless, worms in the event hardened and polished metal and worm wheels in high-grade bronze of specialized alloys ensuring the the best wearability. The seals of the worm gearbox are given with a dirt lip which efficiently resists dust and drinking water. Furthermore, the gearboxes are greased for life with synthetic oil.
Large reduction 100:1 in a single 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 equipment ratios and the same transferred electrical power is bigger when compared to a worm gearing. At the same time, the worm gearbox is definitely in a far more simple design.
A double reduction may be composed of 2 normal gearboxes or as a particular gearbox.
Compact design
Compact design is probably the key phrases of the standard gearboxes of the Ever-Power-Series. Further optimisation may be accomplished by using adapted gearboxes or special gearboxes.
Low noise
Our worm gearboxes and actuators are really quiet. This is due to the very clean jogging of the worm gear combined with the use of cast iron and high precision on part manufacturing and assembly. In connection with our precision gearboxes, we take extra health care of any sound that can be interpreted as a murmur from the gear. So the general noise level of our gearbox is certainly reduced to a complete minimum.
Angle gearboxes
On the worm gearbox the input shaft and output shaft are perpendicular to one another. This sometimes proves to be a decisive edge producing the incorporation of the gearbox significantly simpler and more compact.The worm gearbox can be an angle gear. This is normally an edge for incorporation into constructions.
Strong bearings in stable housing
The output shaft of the Ever-Power worm gearbox is quite firmly embedded in the apparatus house and is perfect for immediate suspension for wheels, movable arms and other parts rather than having to create a separate suspension.
Self locking
For larger equipment ratios, Ever-Electrical power worm gearboxes provides a self-locking result, which in many situations can be used as brake or as extra secureness. Also spindle gearboxes with a trapezoidal spindle will be self-locking, making them well suited for a variety of solutions.
In most gear drives, when traveling torque is suddenly reduced therefore of electric power off, torsional vibration, vitality outage, or any mechanical failing at the transmitting input part, then gears will be rotating either in the same course driven by the machine inertia, or in the contrary path driven by the resistant output load because of gravity, springtime load, etc. The latter condition is known as backdriving. During inertial motion or backdriving, the powered output shaft (load) becomes the generating one and the driving 
input shaft (load) becomes the powered one. There are several gear travel applications where productivity shaft driving is self locking gearbox undesirable. So as to prevent it, different types of brake or clutch devices are used.
However, additionally, there are solutions in the apparatus tranny that prevent inertial motion or backdriving using self-locking gears without the additional devices. The most frequent one is a worm equipment with a minimal lead angle. In self-locking worm gears, torque applied from the load side (worm equipment) is blocked, i.electronic. cannot drive the worm. Even so, their application comes with some constraints: the crossed axis shafts’ arrangement, relatively high gear ratio, low quickness, low gear mesh performance, increased heat era, etc.
Also, there are parallel axis self-locking gears [1, 2]. These gears, unlike the worm gears, can employ any gear ratio from 1:1 and higher. They have the generating mode and self-locking mode, when the inertial or backdriving torque is definitely applied to the output gear. Initially these gears had suprisingly low ( <50 percent) generating effectiveness that limited their program. Then it had been proved [3] that large driving efficiency of these kinds of gears is possible. Requirements of the self-locking was analyzed on this page [4]. This paper explains the principle of the self-locking process for the parallel axis gears with symmetric and asymmetric teeth profile, and shows their suitability for numerous applications.
Self-Locking Condition
Determine 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 case of inertial driving. Pretty much all conventional equipment drives possess the pitch level P located in the active portion the contact range B1-B2 (Figure 1a and Number 2a). This pitch level location provides low specific sliding velocities and friction, and, due to this fact, high driving performance. In case when these kinds of gears are powered by end result load or inertia, they happen to be rotating freely, as the friction minute (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, applied to the gear
T’1 – driven torque, applied to the pinion
F – driving force
F’ – traveling 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
In order to make gears self-locking, the pitch point P ought to be located off the energetic portion the contact line B1-B2. There happen to be two options. Option 1: when the point P is placed between a center of the pinion O1 and the idea B2, where the outer size of the apparatus intersects the contact range. This makes the self-locking possible, but the driving productivity will become low under 50 percent [3]. Option 2 (figs 1b and 2b): when the idea P is located between the point B1, where the outer diameter of the pinion intersects the brand contact and a middle of the apparatus O2. This type of gears can be self-locking with relatively huge driving effectiveness > 50 percent.
Another condition of self-locking is to have a sufficient friction angle g to deflect the force F’ beyond the guts of the pinion O1. It creates the resisting self-locking instant (torque) T’1 = F’ x L’1, where L’1 is usually a lever of the power F’1. This condition could be provided as L’1min > 0 or
(1) Equation 1
or
(2) Equation 2
where:
u = n2/n1 – gear ratio,
n1 and n2 – pinion and gear amount of teeth,
– involute profile position at the end of the gear tooth.
Design of Self-Locking Gears
Self-locking gears are custom. They cannot become fabricated with the benchmarks tooling with, for instance, the 20o pressure and rack. This makes them very ideal for Direct Gear Design® [5, 6] that delivers required gear performance and after that defines tooling parameters.
Direct Gear Style presents the symmetric gear tooth formed by two involutes of 1 base circle (Figure 3a). The asymmetric gear tooth is shaped by two involutes of two several base circles (Figure 3b). The tooth idea circle da allows preventing the pointed tooth suggestion. The equally spaced tooth form the gear. The fillet profile between teeth is designed independently to avoid interference and offer minimum bending anxiety. The functioning pressure angle aw and the get in touch with 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 high pressure and huge 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 position to aw = 75 – 85o. Because of this, the transverse get in touch with ratio ea < 1.0 (typically 0.4 - 0.6). Insufficient the transverse contact ratio should be compensated by the axial (or face) speak to ratio eb to guarantee the total contact ratio eg = ea + eb ≥ 1.0. This could be achieved by using helical gears (Number 4). Nevertheless, helical gears apply the axial (thrust) power on the gear bearings. The dual helical (or “herringbone”) gears (Body 4) allow to compensate this force.
Excessive transverse pressure angles bring about increased bearing radial load that may be up to four to five circumstances higher than for the conventional 20o pressure angle gears. Bearing variety and gearbox housing design should be done accordingly to carry this increased load without abnormal deflection.
App of the asymmetric teeth for unidirectional drives permits improved performance. For the self-locking gears that are being used to prevent backdriving, the same tooth flank is used for both driving and locking modes. In cases like this asymmetric tooth profiles provide much higher transverse contact ratio at the provided pressure angle than the symmetric tooth flanks. It creates it possible to lessen the helix position and axial bearing load. For the self-locking gears which used to prevent inertial driving, distinct tooth flanks are being used for generating and locking modes. In this case, asymmetric tooth account with low-pressure position provides high proficiency for driving method and the contrary high-pressure angle tooth account is utilized for reliable self-locking.
Testing Self-Locking Gears
Self-locking helical equipment prototype units were made based on the developed mathematical products. The gear info are presented in the Desk 1, and the check gears are presented in Figure 5.
The schematic presentation of the test setup is shown in Figure 6. The 0.5Nm electric electric motor was used to drive the actuator. A acceleration and torque sensor was mounted on the high-velocity shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was connected to the low quickness shaft of the gearbox via coupling. The insight and productivity torque and speed details had been captured in the data acquisition tool and additional analyzed in a pc employing data analysis software program. The instantaneous proficiency of the actuator was calculated and plotted for a wide variety of speed/torque combination. Average driving effectiveness of the self- locking gear obtained during tests was above 85 percent. The self-locking real estate of the helical gear set in backdriving mode was also tested. During this test the exterior torque was put on the output gear shaft and the angular transducer demonstrated no angular movement of input shaft, which verified the self-locking condition.
Potential Applications
Initially, self-locking gears had been used in textile industry [2]. However, this sort of gears has many potential applications in lifting mechanisms, assembly tooling, and other equipment drives where the backdriving or inertial generating is not permissible. Among such application [7] of the self-locking gears for a constantly variable valve lift program was advised for an auto engine.
Summary
In this paper, a basic principle 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 evaluating of the apparatus prototypes has proved fairly high driving efficiency and efficient self-locking. The self-locking gears may find many applications in various industries. For instance, in a control systems where position balance is very important (such as in car, aerospace, medical, robotic, agricultural etc.) the self-locking allows to accomplish required performance. Like the worm self-locking gears, the parallel axis self-locking gears are very sensitive to operating conditions. The locking dependability is influenced by lubrication, vibration, misalignment, etc. Implementation of the gears should be done with caution and requires comprehensive testing in all possible operating conditions.