Worm gearboxes with many combinations
Ever-Power offers a very wide variety of worm gearboxes. 
Because of the modular design the typical programme comprises many combinations in terms of selection of equipment housings, mounting and connection options, flanges, shaft models, type of oil, surface treatments etc.
Sturdy and reliable
The look of the Ever-Power worm gearbox is easy and well proven. We only use top quality components such as properties in cast iron, aluminum and stainless steel, worms in the event hardened and polished metal and worm wheels in high-grade bronze of specialized alloys ensuring the optimum wearability. The seals of the worm gearbox are provided with a dirt lip which efficiently resists dust and normal water. In addition, the gearboxes happen to 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 single step or 10.000:1 in a double lowering. An equivalent gearing with the same equipment ratios and the same transferred power is bigger than a worm gearing. Meanwhile, the worm gearbox is definitely in a far more simple design.
A double reduction may be composed of 2 standard 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 specialized gearboxes.
Low noise
Our worm gearboxes and actuators are extremely quiet. This is due to the very soft operating of the worm gear combined with the utilization of cast iron and huge precision on aspect manufacturing and assembly. Regarding the our accuracy gearboxes, we have extra care and attention of any sound that can be interpreted as a murmur from the apparatus. Therefore the general noise level of our gearbox is normally reduced to a complete minimum.
Angle gearboxes
On the worm gearbox the input shaft and self locking gearbox output shaft are perpendicular to one another. This frequently proves to become a decisive edge making the incorporation of the gearbox considerably simpler and smaller sized.The worm gearbox is an angle gear. This is often an edge for incorporation into constructions.
Strong bearings in solid 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 build a separate suspension.
Self locking
For larger equipment ratios, Ever-Electrical power worm gearboxes provides a self-locking effect, which in lots of situations can be used as brake or as extra security. Also spindle gearboxes with a trapezoidal spindle happen to be self-locking, making them suitable for a variety of solutions.
In most gear drives, when traveling torque is suddenly reduced consequently of electric power off, torsional vibration, electricity outage, or any mechanical failing at the transmitting input side, then gears will be rotating either in the same direction driven by the system inertia, or in the contrary course driven by the resistant output load due to gravity, planting season load, etc. The latter condition is called backdriving. During inertial motion or backdriving, the powered output shaft (load) turns into the generating one and the generating input shaft (load) becomes the driven one. There are numerous gear drive applications where result shaft driving is undesirable. So that you can prevent it, different types of brake or clutch equipment are used.
However, there are also solutions in the apparatus transmission that prevent inertial motion or backdriving using self-locking gears without any additional devices. The most typical one is a worm equipment with a low lead angle. In self-locking worm gears, torque used from the load side (worm equipment) is blocked, i.e. cannot drive the worm. Nevertheless, their application includes some limitations: the crossed axis shafts’ arrangement, relatively high gear ratio, low speed, low gear mesh productivity, increased heat generation, etc.
Also, there happen to be parallel axis self-locking gears [1, 2]. These gears, unlike the worm gears, can employ any gear ratio from 1:1 and bigger. They have the driving mode and self-locking method, when the inertial or backdriving torque is put on the output gear. At first these gears had very low ( <50 percent) driving performance that limited their program. Then it had been proved [3] that large driving efficiency of this sort of gears is possible. Standards of the self-locking was analyzed in this posting [4]. This paper explains the principle of the self-locking process for the parallel axis gears with symmetric and asymmetric tooth profile, and reveals their suitability for unique applications.
Self-Locking Condition
Figure 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. Almost all conventional gear drives possess the pitch point P situated in the active part the contact collection B1-B2 (Figure 1a and Number 2a). This pitch stage location provides low particular sliding velocities and friction, and, therefore, high driving effectiveness. In case when such gears are powered by productivity load or inertia, they are rotating freely, because the friction second (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, applied to the gear
T’1 – driven torque, put on 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
In order to make gears self-locking, the pitch point P should be located off the dynamic portion the contact line B1-B2. There will be two options. Choice 1: when the idea P is positioned between a middle of the pinion O1 and the idea B2, where the outer diameter of the apparatus intersects the contact line. This makes the self-locking possible, but the driving performance will be low under 50 percent [3]. Choice 2 (figs 1b and 2b): when the point P is positioned between your point B1, where the outer size of the pinion intersects the range contact and a centre of the apparatus O2. This type of gears could be self-locking with relatively high driving proficiency > 50 percent.
Another condition of self-locking is to truly have a sufficient friction angle g to deflect the force F’ beyond the center of the pinion O1. It generates the resisting self-locking moment (torque) T’1 = F’ x L’1, where L’1 is normally a lever of the force F’1. This condition could 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 number 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 incredibly well suited for Direct Gear Style® [5, 6] that provides required gear efficiency and from then on defines tooling parameters.
Direct Gear Design presents the symmetric gear tooth created by two involutes of 1 base circle (Figure 3a). The asymmetric equipment tooth is produced by two involutes of two unique base circles (Figure 3b). The tooth tip circle da allows preventing the pointed tooth suggestion. The equally spaced teeth form the apparatus. The fillet account between teeth is designed independently in order to avoid interference and offer minimum bending stress. The operating pressure angle aw and the speak to 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 contact. If the sliding friction coefficient f = 0.1 – 0.3, it requires the transverse operating pressure position to aw = 75 – 85o. Consequently, the transverse speak to ratio ea < 1.0 (typically 0.4 - 0.6). Lack of the transverse speak to ratio should be compensated by the axial (or face) speak to ratio eb to ensure the total speak to ratio eg = ea + eb ≥ 1.0. This can be attained by using helical gears (Body 4). However, helical gears apply the axial (thrust) pressure on the gear bearings. The dual helical (or “herringbone”) gears (Shape 4) allow to compensate this force.
Large transverse pressure angles result in increased bearing radial load that could be up to four to five circumstances higher than for the traditional 20o pressure angle gears. Bearing assortment and gearbox housing design ought to be done accordingly to hold this improved load without increased deflection.
Program of the asymmetric teeth for unidirectional drives permits improved effectiveness. For the self-locking gears that are being used to avoid backdriving, the same tooth flank can be used for both generating and locking modes. In cases like this asymmetric tooth profiles offer much higher transverse speak to ratio at the presented 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 that used to avoid inertial driving, distinct tooth flanks are used for driving and locking modes. In cases like this, asymmetric tooth profile with low-pressure angle provides high proficiency for driving mode 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 designs. The gear info are presented in the Desk 1, and the test gears are shown in Figure 5.
The schematic presentation of the test setup is shown in Figure 6. The 0.5Nm electric motor was used to drive the actuator. A built-in quickness and torque sensor was mounted on the high-speed shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was linked to the low velocity shaft of the gearbox via coupling. The suggestions and end result torque and speed details had been captured in the data acquisition tool and further analyzed in a computer applying data analysis computer software. The instantaneous efficiency of the actuator was calculated and plotted for a broad range of speed/torque combination. Common driving productivity of the self- locking gear obtained during examining was above 85 percent. The self-locking real estate of the helical equipment set in backdriving mode was also tested. During this test the external torque was applied to the output gear shaft and the angular transducer confirmed no angular movement of type shaft, which confirmed the self-locking condition.
Potential Applications
Initially, self-locking gears had been used in textile industry [2]. However, this type of gears has many potential applications in lifting mechanisms, assembly tooling, and other equipment drives where the backdriving or inertial generating is not permissible. One of such software [7] of the self-locking gears for a continuously variable valve lift program was recommended for an auto engine.
Summary
In this paper, a theory 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 testing of the apparatus prototypes has proved relatively high driving productivity and efficient self-locking. The self-locking gears may find many applications in a variety of industries. For example, in a control devices where position stability is vital (such as in auto, aerospace, medical, robotic, agricultural etc.) the self-locking will allow to accomplish required performance. Similar to the worm self-locking gears, the parallel axis self-locking gears are hypersensitive to operating conditions. The locking stability is damaged by lubrication, vibration, misalignment, etc. Implementation of the gears should be done with caution and requires comprehensive testing in all possible operating conditions.
