Worm gearboxes with many combinations
Ever-Power offers an extremely broad range of worm gearboxes. Because of the modular design the typical programme comprises countless combinations when it comes to selection of gear housings, mounting and connection options, flanges, shaft models, kind of oil, surface remedies etc.
Sturdy and reliable
The design of the Ever-Power worm gearbox is simple and well proven. We just use top quality components such as houses in cast iron, aluminum and stainless, worms in case hardened and polished steel 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 effectively resists dust and drinking water. Furthermore, 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 reduction. An comparative gearing with the same gear ratios and the same transferred ability is bigger when compared to a worm gearing. At the same time, the worm gearbox is normally 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 one of the key words of the typical gearboxes of the Ever-Power-Series. Further optimisation can be achieved through the use of adapted gearboxes or exceptional gearboxes.
Low noise
Our worm gearboxes and actuators are extremely quiet. This is due to the very soft running of the worm gear combined with the usage of cast iron and substantial precision on aspect manufacturing and assembly. In connection with our accuracy gearboxes, we take extra care and attention of any sound that can be interpreted as a murmur from the apparatus. So the general noise level of our gearbox is usually reduced to an absolute minimum.
Angle gearboxes
On the worm gearbox the input shaft and output shaft are perpendicular to each other. This typically proves to become a decisive advantage making the incorporation of the gearbox substantially simpler and smaller sized.The worm gearbox can be an angle gear. This can often be an advantage for incorporation into constructions.
Strong bearings in sturdy housing
The output shaft of the Ever-Power worm gearbox is very firmly embedded in the gear house and is well suited for immediate suspension for wheels, movable arms and other areas rather than having to build a separate suspension.
Self locking
For larger gear ratios, Ever-Power worm gearboxes will provide a self-locking result, which in lots of situations can be used as brake or as extra protection. As well spindle gearboxes with a trapezoidal spindle happen to be self-locking, making them perfect for a wide range of solutions.
In most gear drives, when generating torque is suddenly reduced consequently of vitality off, torsional vibration, electricity outage, or any mechanical failing at the transmission input area, then gears will be rotating either in the same path driven by the system inertia, or in the opposite path driven by the resistant output load due to gravity, spring load, etc. The latter condition is called backdriving. During inertial action or backdriving, the powered output shaft (load) turns into the generating one and the traveling input 
shaft (load) turns into the powered one. There are plenty of gear drive applications where result shaft driving is undesirable. In order to prevent it, several types of brake or clutch products are used.
However, there are also solutions in the apparatus tranny that prevent inertial movement or backdriving using self-locking gears without the additional equipment. The most frequent one is usually 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 drive the worm. Even so, their application comes with some restrictions: the crossed axis shafts’ self locking gearbox arrangement, relatively high equipment ratio, low speed, low gear mesh proficiency, increased heat era, etc.
Also, there will be parallel axis self-locking gears [1, 2]. These gears, unlike the worm gears, can use any gear ratio from 1:1 and larger. They have the driving mode and self-locking mode, when the inertial or backdriving torque is usually put on the output gear. At first these gears had suprisingly low ( <50 percent) driving effectiveness that limited their program. Then it was proved [3] that great driving efficiency of this kind of gears is possible. Standards of the self-locking was analyzed in the following paragraphs [4]. This paper explains the theory of the self-locking process for the parallel axis gears with symmetric and asymmetric the teeth profile, and displays their suitability for diverse applications.
Self-Locking Condition
Number 1 presents conventional gears (a) and self-locking gears (b), in the event of backdriving. Figure 2 presents standard gears (a) and self-locking gears (b), in case of inertial driving. Practically all conventional equipment drives have the pitch level P located in the active portion the contact line B1-B2 (Figure 1a and Physique 2a). This pitch point location provides low specific sliding velocities and friction, and, subsequently, high driving performance. In case when this kind of gears are powered by outcome load or inertia, they will be rotating freely, because the friction second (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’ – driving 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 lively portion the contact line B1-B2. There are two options. Alternative 1: when the point P is placed between a centre of the pinion O1 and the point B2, where the outer size of the apparatus intersects the contact series. This makes the self-locking possible, however the driving productivity will always be low under 50 percent [3]. Choice 2 (figs 1b and 2b): when the point P is put between the point B1, where the outer diameter of the pinion intersects the series contact and a centre of the apparatus O2. This kind of gears can be self-locking with relatively substantial driving effectiveness > 50 percent.
Another condition of self-locking is to truly have a enough friction angle g to deflect the force F’ beyond the guts of the pinion O1. It generates the resisting self-locking second (torque) T’1 = F’ x L’1, where L’1 can be a lever of the induce F’1. This condition can be shown 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 angle at the end of the gear tooth.
Design of Self-Locking Gears
Self-locking gears are custom. They cannot end up being fabricated with the specifications tooling with, for instance, the 20o pressure and rack. This makes them extremely suited to Direct Gear Design® [5, 6] that delivers required gear functionality and from then on defines tooling parameters.
Direct Gear Style presents the symmetric equipment tooth created by two involutes of 1 base circle (Figure 3a). The asymmetric gear tooth is formed by two involutes of two different base circles (Figure 3b). The tooth tip circle da allows preventing the pointed tooth hint. The equally spaced tooth form the gear. The fillet profile between teeth was created independently in order to avoid interference and provide minimum bending stress. The functioning pressure angle aw and the contact ratio ea are defined 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. As a result, the transverse get in touch with ratio ea < 1.0 (typically 0.4 - 0.6). Insufficient the transverse speak to ratio should be compensated by the axial (or face) get in touch with ratio eb to ensure the total speak to ratio eg = ea + eb ≥ 1.0. This can be achieved by employing helical gears (Physique 4). On the other hand, helical gears apply the axial (thrust) power on the gear bearings. The twice helical (or “herringbone”) gears (Body 4) allow to compensate this force.
Huge transverse pressure angles cause increased bearing radial load that could be up to four to five times higher than for the traditional 20o pressure angle gears. Bearing selection and gearbox housing style ought to be done accordingly to hold this increased load without increased deflection.
Application of the asymmetric tooth for unidirectional drives allows for improved efficiency. For the self-locking gears that are being used to prevent backdriving, the same tooth flank is employed for both driving and locking modes. In cases like this asymmetric tooth profiles offer much higher transverse speak to ratio at the provided pressure angle than 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, different tooth flanks are used for traveling and locking modes. In this instance, asymmetric tooth account with low-pressure position provides high performance for driving setting and the opposite high-pressure angle tooth profile can be used for reliable self-locking.
Testing Self-Locking Gears
Self-locking helical equipment prototype models were made based on the developed mathematical models. The gear data are presented in the Table 1, and the check gears are provided in Figure 5.
The schematic presentation of the test setup is shown in Figure 6. The 0.5Nm electric engine was used to operate a vehicle the actuator. A built-in velocity and torque sensor was mounted on the high-speed shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was linked to the low rate shaft of the gearbox via coupling. The source and end result torque and speed details were captured in the info acquisition tool and further analyzed in a computer using data analysis software program. The instantaneous performance of the actuator was calculated and plotted for an array of speed/torque combination. Average driving proficiency of the personal- locking gear obtained during assessment was above 85 percent. The self-locking real estate of the helical gear occur backdriving mode was likewise tested. In this test the external torque was applied to the output gear shaft and the angular transducer showed no angular activity of insight shaft, which confirmed the self-locking condition.
Potential Applications
Initially, self-locking gears had been used in textile industry [2]. On the other hand, this sort 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. Among such app [7] of the self-locking gears for a consistently variable valve lift system was advised for an automobile engine.
Summary
In this paper, a basic principle of job of the self-locking gears has been described. Style specifics of the self-locking gears with symmetric and asymmetric profiles happen to be shown, and testing of the apparatus prototypes has proved fairly high driving effectiveness and trustworthy self-locking. The self-locking gears may find many applications in various industries. For example, in a control systems where position stability is important (such as in motor vehicle, 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 delicate to operating circumstances. The locking reliability is damaged by lubrication, vibration, misalignment, etc. Implementation of the gears should be finished with caution and requires comprehensive testing in every possible operating conditions.