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Worm gearboxes with countless combinations
Ever-Power offers an extremely wide range of worm gearboxes. Because of the modular design the standard programme comprises countless combinations with regards to selection of equipment housings, mounting and connection options, flanges, shaft styles, type of oil, surface treatment options etc.
Sturdy and reliable
The look of the Ever-Power worm gearbox is easy and well proven. We just use high quality components such as houses in cast iron, light weight aluminum and stainless, worms in the event hardened and polished steel and worm wheels in high-grade bronze of unique alloys ensuring the ideal wearability. The seals of the worm gearbox are provided with a dirt lip which properly resists dust and water. Furthermore, the gearboxes happen to be greased forever with synthetic oil.
Large reduction 100:1 in one step
As default the worm gearboxes allow for reductions of up to 100:1 in one single step or 10.000:1 in a double decrease. An comparative gearing with the same equipment ratios and the same transferred electric power is bigger than a worm gearing. Meanwhile, the worm gearbox can be in a more simple design.
A double reduction may be composed of 2 common gearboxes or as a special gearbox.
Compact design
Compact design is one of the key words of the typical gearboxes of the Ever-Power-Series. Further optimisation may be accomplished by using adapted gearboxes or particular gearboxes.
Low noise
Our worm gearboxes and actuators are really quiet. This is due to the very soft operating of the worm equipment combined with the utilization of cast iron and self locking gearbox excessive precision on component manufacturing and assembly. In connection with our precision gearboxes, we consider extra treatment of any sound which can be interpreted as a murmur from the gear. Therefore the general noise degree of our gearbox can be reduced to a complete minimum.
Angle gearboxes
On the worm gearbox the input shaft and output shaft are perpendicular to each other. This generally proves to become a decisive benefits producing the incorporation of the gearbox considerably simpler and more compact.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 quite firmly embedded in the apparatus house and is suitable for direct suspension for wheels, movable arms and other parts rather than having to build a separate suspension.
Self locking
For larger gear ratios, Ever-Power worm gearboxes will provide a self-locking impact, which in lots of situations can be used as brake or as extra security. Likewise spindle gearboxes with a trapezoidal spindle are self-locking, making them perfect for a wide range of solutions.
In most equipment drives, when driving torque is suddenly reduced therefore of ability off, torsional vibration, electric power outage, or any mechanical failure at the tranny input part, then gears will be rotating either in the same path driven by the machine inertia, or in the contrary 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 driven output shaft (load) turns into the generating one and the traveling input shaft (load) becomes the powered one. There are various gear drive applications where result shaft driving is undesirable. So as to prevent it, various kinds of brake or clutch units are used.
However, additionally, there are solutions in the apparatus transmitting that prevent inertial action or backdriving using self-locking gears without any additional gadgets. The most typical one is normally 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 travel the worm. Even so, their application comes with some limitations: the crossed axis shafts’ arrangement, relatively high gear ratio, low swiftness, low gear mesh productivity, increased heat era, etc.
Also, there will 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 higher. They have the traveling mode and self-locking method, when the inertial or backdriving torque can be applied to the output gear. In the beginning these gears had suprisingly low ( <50 percent) traveling performance that limited their request. Then it had been proved [3] that high driving efficiency of this sort of gears is possible. Conditions of the self-locking was analyzed in the following paragraphs [4]. This paper explains the basic principle of the self-locking method for the parallel axis gears with symmetric and asymmetric the teeth profile, and reveals their suitability for different applications.
Self-Locking Condition
Shape 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. Pretty much all conventional gear drives have the pitch stage P located in the active part the contact collection B1-B2 (Figure 1a and Physique 2a). This pitch level location provides low certain sliding velocities and friction, and, therefore, high driving performance. In case when this sort of gears are influenced by result load or inertia, they happen to be rotating freely, because the friction instant (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, put on the pinion
F – driving force
F’ – driving 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 should be located off the active portion the contact line B1-B2. There will be two options. Alternative 1: when the point P is placed between a middle of the pinion O1 and the point B2, where in fact the outer size of the apparatus intersects the contact brand. This makes the self-locking possible, but the driving productivity will end up being low under 50 percent [3]. Alternative 2 (figs 1b and 2b): when the point P is put between your point B1, where in fact the outer size of the pinion intersects the brand contact and a centre of the gear O2. This kind of gears can be self-locking with relatively high driving productivity > 50 percent.
Another condition of self-locking is to truly have a adequate friction angle g to deflect the force F’ beyond the guts of the pinion O1. It generates the resisting self-locking moment (torque) T’1 = F’ x L’1, where L’1 is definitely a lever of the drive 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 number of teeth,
– involute profile angle at the tip of the apparatus tooth.
Design of Self-Locking Gears
Self-locking gears are customized. They cannot always be fabricated with the criteria tooling with, for instance, the 20o pressure and rack. This makes them very suited to Direct Gear Style® [5, 6] that delivers required gear overall performance and after that defines tooling parameters.
Direct Gear Style presents the symmetric gear tooth created by two involutes of one base circle (Figure 3a). The asymmetric gear tooth is created by two involutes of two unique base circles (Figure 3b). The tooth tip circle da allows avoiding the pointed tooth suggestion. The equally spaced tooth form the apparatus. The fillet account between teeth is designed independently to avoid interference and provide minimum bending tension. The working pressure angle aw and the speak to ratio ea are described 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 large 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. Due to this fact, the transverse contact ratio ea < 1.0 (typically 0.4 - 0.6). Insufficient the transverse speak to ratio ought to be compensated by the axial (or face) contact ratio eb to guarantee the total contact ratio eg = ea + eb ≥ 1.0. This can be attained by employing helical gears (Shape 4). Nevertheless, helical gears apply the axial (thrust) force on the gear bearings. The dual helical (or “herringbone”) gears (Figure 4) allow to compensate this force.
Substantial transverse pressure angles lead to increased bearing radial load that could be up to four to five occasions higher than for the traditional 20o pressure angle gears. Bearing collection and gearbox housing design should be done accordingly to carry this increased load without increased deflection.
Software of the asymmetric the teeth for unidirectional drives allows for improved efficiency. For the self-locking gears that are used to prevent backdriving, the same tooth flank is used for both traveling and locking modes. In this case asymmetric tooth profiles give much higher transverse contact ratio at the offered pressure angle compared to the symmetric tooth flanks. It creates it possible to lessen the helix angle and axial bearing load. For the self-locking gears that used to avoid inertial driving, several tooth flanks are being used for driving and locking modes. In this case, asymmetric tooth account with low-pressure position provides high effectiveness for driving setting and the contrary high-pressure angle tooth account is employed for reliable self-locking.
Testing Self-Locking Gears
Self-locking helical gear prototype units were made based on the developed mathematical versions. The gear data are presented in the Table 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. An integrated rate and torque sensor was mounted on the high-acceleration shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was connected to the low swiftness shaft of the gearbox via coupling. The type and end result torque and speed info had been captured in the data acquisition tool and further analyzed in a pc employing data analysis software program. The instantaneous effectiveness of the actuator was calculated and plotted for a variety of speed/torque combination. Average driving productivity of the personal- locking gear obtained during assessment 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 applied to the output gear shaft and the angular transducer revealed no angular movements of source shaft, which verified the self-locking condition.
Potential Applications
Initially, self-locking gears had been found in textile industry [2]. Even so, this type of gears has a large number of potential applications in lifting mechanisms, assembly tooling, and other gear drives where in fact the backdriving or inertial generating is not permissible. One of such program [7] of the self-locking gears for a continuously variable valve lift program was suggested for an vehicle engine.
Summary
In this paper, a basic principle of work of the self-locking gears has been described. Design specifics of the self-locking gears with symmetric and asymmetric profiles are shown, and examining of the apparatus prototypes has proved fairly high driving performance and reputable self-locking. The self-locking gears may find many applications in various industries. For example, in a control devices where position stableness is very important (such as for example in vehicle, 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 stability is afflicted by lubrication, vibration, misalignment, etc. Implementation of the gears should be finished with caution and needs comprehensive testing in every possible operating conditions.