Worm gearboxes with countless combinations
Ever-Power offers a very broad range of worm gearboxes. Because of the modular design the typical programme comprises countless combinations in terms of selection of gear housings, mounting and interconnection options, flanges, shaft styles, type 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, aluminium and stainless steel, worms in the event hardened and polished metal and worm tires in high-grade bronze of particular alloys ensuring the optimum wearability. The seals of the worm gearbox are provided with a dirt lip which properly resists dust and drinking water. In addition, the gearboxes are greased for life with synthetic oil.
Large reduction 100:1 in one step
As default the worm gearboxes allow for 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 vitality is bigger than a worm gearing. Meanwhile, the worm gearbox is 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 among the key words of the typical gearboxes of the Ever-Power-Series. Further optimisation can be achieved by using adapted gearboxes or special gearboxes.
Low noise
Our worm gearboxes and actuators are extremely quiet. This is due to the very smooth running of the worm equipment combined with the consumption of cast iron and substantial precision on part manufacturing and assembly. Regarding the our precision gearboxes, we have extra proper care of any sound which can be interpreted as a murmur from the gear. So the general noise level of our gearbox is reduced to a complete minimum.
Angle gearboxes
On the worm gearbox the input shaft and output shaft are perpendicular to each other. This frequently proves to become a decisive edge producing the incorporation of the gearbox significantly simpler and smaller sized.The worm gearbox can be an angle gear. This is often an advantage for incorporation into constructions.
Strong bearings in sound 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 areas rather than needing to build a separate suspension.
Self locking
For larger equipment ratios, Ever-Vitality worm gearboxes will provide a self-locking result, which in many situations can be utilized as brake or as extra protection. Likewise spindle gearboxes with a trapezoidal spindle will be self-locking, making them ideal for a wide range of solutions.
In most gear drives, when generating torque is suddenly reduced consequently of power off, torsional vibration, electrical power outage, or any mechanical failing at the tranny input part, then gears will be rotating either in the same course driven by the system inertia, or in the contrary course driven by the resistant output load because of gravity, springtime load, etc. The latter state is called backdriving. During inertial motion or backdriving, the motivated output shaft (load) turns into the traveling one and the traveling input shaft (load) becomes the influenced one. There are several gear travel applications where output shaft driving is undesirable. In order to prevent it, various kinds of brake or clutch devices are used.
However, there are also solutions in the apparatus tranny that prevent inertial movement or backdriving using self-locking gears without any additional equipment. The most typical one is a worm gear with a minimal lead angle. In self-locking worm gears, torque applied from the strain side (worm gear) is blocked, i.e. 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 proficiency, increased heat generation, etc.
Also, there will be 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 function, when the inertial or backdriving torque is certainly put on the output gear. Primarily these gears had suprisingly low ( <50 percent) traveling effectiveness that limited their program. Then it was proved [3] that substantial driving efficiency of this kind of gears is possible. Conditions of the self-locking was analyzed on this page [4]. This paper explains the basic principle of the self-locking procedure for the parallel axis gears with symmetric and asymmetric teeth profile, and displays their suitability for diverse applications.
Self-Locking Condition
Body 1 presents conventional gears (a) and self-locking gears (b), in the event 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 point P situated in the active part the contact range B1-B2 (Figure 1a and Determine 2a). This pitch level location provides low specific sliding velocities and friction, and, consequently, high driving productivity. In case when this kind of gears are motivated by end result load or inertia, they will be 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, put on the gear
T’1 – driven torque, put on the pinion
F – driving force
F’ – traveling force, when the backdriving or perhaps inertial torque applied to 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 energetic portion the contact line B1-B2. There will be two options. Alternative 1: when the point P is placed between a center of the pinion O1 and the idea B2, where in fact the outer diameter of the gear intersects the contact brand. This makes the self-locking possible, but the driving effectiveness will become low under 50 percent [3]. Option 2 (figs 1b and 2b): when the idea P is placed between the point B1, where the outer diameter of the pinion intersects the range contact and a centre of the apparatus O2. This kind of gears could be self-locking with relatively excessive driving proficiency > 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 minute (torque) T’1 = F’ x L’1, where L’1 can be a lever of the pressure 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 self locking gearbox position at the tip of the gear tooth.
Design of Self-Locking Gears
Self-locking gears are customized. They cannot be fabricated with the criteria tooling with, for instance, the 20o pressure and rack. This makes them very ideal for Direct Gear Style® [5, 6] that provides required gear efficiency and after that defines tooling parameters.
Direct Gear Design presents the symmetric equipment tooth created by two involutes of 1 base circle (Figure 3a). The asymmetric gear tooth is produced by two involutes of two diverse base circles (Figure 3b). The tooth hint circle da allows avoiding the pointed tooth tip. The equally spaced tooth form the gear. The fillet profile between teeth was created independently in order to avoid interference and provide minimum bending tension. The working pressure angle aw and the get in touch with ratio ea are identified 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 substantial 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. Subsequently, the transverse get in touch with ratio ea < 1.0 (typically 0.4 - 0.6). Lack of the transverse contact ratio should be compensated by the axial (or face) contact ratio eb to guarantee the total speak to ratio eg = ea + eb ≥ 1.0. This could be achieved by applying helical gears (Body 4). Even so, helical gears apply the axial (thrust) pressure on the gear bearings. The double helical (or “herringbone”) gears (Body 4) allow to compensate this force.
Huge transverse pressure angles bring about increased bearing radial load that may be up to four to five occasions higher than for the traditional 20o pressure angle gears. Bearing assortment and gearbox housing design should be done accordingly to hold this improved load without excessive deflection.
Application of the asymmetric pearly whites for unidirectional drives permits improved efficiency. For the self-locking gears that are being used to avoid 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 provided pressure angle than the symmetric tooth flanks. It makes it possible to lessen the helix angle and axial bearing load. For the self-locking gears that used to avoid inertial driving, distinct tooth flanks are being used for generating and locking modes. In this instance, asymmetric tooth account with low-pressure angle provides high effectiveness for driving function and the contrary high-pressure angle tooth account is utilized for reliable self-locking.
Testing Self-Locking Gears
Self-locking helical equipment prototype models were made predicated on the developed mathematical designs. The gear info are provided in the Table 1, and the check gears are offered in Figure 5.
The schematic presentation of the test setup is demonstrated in Figure 6. The 0.5Nm electric engine was used to drive the actuator. A velocity and torque sensor was mounted on the high-velocity shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was linked to the low velocity shaft of the gearbox via coupling. The input and result torque and speed info were captured in the data acquisition tool and additional analyzed in a computer employing data analysis computer software. The instantaneous performance of the actuator was calculated and plotted for a variety of speed/torque combination. Ordinary driving performance of the self- locking equipment obtained during examining was above 85 percent. The self-locking house of the helical gear set in backdriving mode was as well tested. During this test the exterior torque was applied to the output gear shaft and the angular transducer showed no angular motion of input shaft, which confirmed the self-locking condition.
Potential Applications
Initially, self-locking gears had been used in textile industry [2]. Nevertheless, this type of gears has a large number of potential applications in lifting mechanisms, assembly tooling, and other equipment drives where the backdriving or inertial traveling is not permissible. Among such application [7] of the self-locking gears for a consistently variable valve lift system was suggested for an vehicle engine.
Summary
In this paper, a basic principle of do the job of the self-locking gears has been described. Design specifics of the self-locking gears with symmetric and asymmetric profiles will be shown, and screening of the apparatus prototypes has proved relatively high driving performance and efficient self-locking. The self-locking gears may find many applications in various industries. For instance, in a control devices where position stableness is vital (such as for example in car, aerospace, medical, robotic, agricultural etc.) the self-locking will allow to accomplish required performance. Like the worm self-locking gears, the parallel axis self-locking gears are sensitive to operating conditions. The locking reliability is afflicted by lubrication, vibration, misalignment, etc. Implementation of the gears should be finished with caution and needs comprehensive testing in all possible operating conditions.