self locking gearbox

Worm gearboxes with many combinations
Ever-Power offers a very wide variety of worm gearboxes. As a result of modular design the standard programme comprises many combinations when it comes to selection of equipment housings, mounting and connection 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 top quality components such as homes in cast iron, light weight aluminum and stainless, worms in the event hardened and polished metal and worm wheels in high-grade bronze of exceptional alloys ensuring the the best wearability. The seals of the worm gearbox are given with a dust lip which effectively 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 enable reductions as high as 100:1 in one single step or 10.000:1 in a double reduction. An equivalent gearing with the same gear ratios and the same transferred electric power is bigger than a worm gearing. Meanwhile, the worm gearbox is usually 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 one of the key words of the standard gearboxes of the Ever-Power-Series. Further optimisation may be accomplished by using adapted gearboxes or distinctive gearboxes.
Low noise
Our worm gearboxes and actuators are really quiet. This is due to the very easy working of the worm gear combined with the application of cast iron and substantial precision on part manufacturing and assembly. In connection with our precision gearboxes, we take extra care of any sound which can be interpreted as a murmur from the apparatus. So the general noise degree of our gearbox is normally 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 edge making the incorporation of the gearbox considerably simpler and smaller sized.The worm gearbox is an angle gear. This can often be 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 ideal for direct suspension for wheels, movable arms and other parts rather than needing to create a separate suspension.
Self locking
For larger gear ratios, Ever-Electric power worm gearboxes will provide a self-locking result, which in many situations works extremely well as brake or as extra secureness. Also spindle gearboxes with a trapezoidal spindle are self-locking, making them ideal for a variety of solutions.
In most equipment drives, when traveling torque is suddenly reduced because of this of electricity off, torsional vibration, electric power outage, or any mechanical failure at the tranny input area, then gears will be rotating either in the same way driven by the system inertia, or in the contrary way driven by the resistant output load because of gravity, springtime load, etc. The latter state is called backdriving. During inertial motion or backdriving, the influenced output shaft (load) turns into the traveling one and the generating input shaft (load) turns into the motivated one. There are plenty of gear travel applications where outcome shaft driving is unwanted. So as to prevent it, different types of brake or clutch equipment are used.
However, there are also solutions in the gear tranny that prevent inertial motion or backdriving using self-locking gears with no additional products. The most typical one is normally a worm equipment with a minimal lead angle. In self-locking worm gears, torque used from the strain side (worm equipment) is blocked, i.e. cannot travel the worm. However, their application comes with some limitations: the crossed axis shafts’ arrangement, relatively high gear ratio, low rate, low gear mesh productivity, increased heat generation, etc.
Also, there are parallel axis self-locking gears [1, 2]. These gears, unlike the worm gears, can use any equipment ratio from 1:1 and larger. They have the driving mode and self-locking setting, when the inertial or backdriving torque is certainly applied to the output gear. In the beginning these gears had very low ( <50 percent) driving productivity that limited their request. Then it had been proved [3] that huge 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 process for the parallel axis gears with symmetric and asymmetric the teeth profile, and displays their suitability for unique applications.
Self-Locking Condition
Body 1 presents conventional gears (a) and self-locking gears (b), in the event of backdriving. Figure 2 presents typical gears (a) and self-locking gears (b), in case of inertial driving. Pretty much all conventional gear drives have the pitch level P situated in the active portion the contact series B1-B2 (Figure 1a and Body 2a). This pitch point location provides low specific sliding velocities and friction, and, subsequently, high driving proficiency. In case when these kinds of gears are powered by productivity load or inertia, they will be rotating freely, because the friction point in time (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’ – 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 active 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 point B2, where in fact the outer diameter of the gear intersects the contact collection. This makes the self-locking possible, but the driving proficiency will always be low under 50 percent [3]. Option 2 (figs 1b and 2b): when the point P is inserted between the point B1, where the outer size of the pinion intersects the range contact and a center of the gear O2. This type of gears can be self-locking with relatively large driving productivity > 50 percent.
Another condition of self-locking is to truly have a sufficient friction angle g to deflect the force F’ beyond the guts of the pinion O1. It generates the resisting self-locking point in time (torque) T’1 = F’ x L’1, where L’1 is a lever of the pressure F’1. This condition can be presented as L’1min > 0 or
(1) Equation 1
or
(2) Equation 2
where:
u = n2/n1 – equipment ratio,
n1 and n2 – pinion and gear amount of teeth,
– involute profile position at the tip of the gear tooth.
Design of Self-Locking Gears
Self-locking gears are custom. They cannot end up being fabricated with the standards tooling with, for example, the 20o pressure and rack. This makes them extremely ideal for Direct Gear Design® [5, 6] that provides required gear functionality and from then on defines tooling parameters.
Direct Gear Design presents the symmetric gear tooth shaped by two self locking gearbox involutes of one base circle (Figure 3a). The asymmetric equipment tooth is formed by two involutes of two unique base circles (Figure 3b). The tooth tip circle da allows preventing the pointed tooth tip. The equally spaced tooth form the gear. The fillet profile between teeth is designed 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 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 excessive 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 angle 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 contact 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 is often achieved by using helical gears (Determine 4). Nevertheless, helical gears apply the axial (thrust) force on the gear bearings. The double helical (or “herringbone”) gears (Number 4) allow to compensate this force.
High transverse pressure angles lead to increased bearing radial load that could be up to four to five occasions higher than for the conventional 20o pressure angle gears. Bearing variety and gearbox housing design ought to be done accordingly to carry this improved load without extreme deflection.
Program 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 utilized for both driving and locking modes. In this case asymmetric tooth profiles give much higher transverse speak to ratio at the given 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, distinct tooth flanks are used for driving and locking modes. In this instance, asymmetric tooth profile with low-pressure position provides high productivity for driving method and the contrary high-pressure angle tooth account is used for reliable self-locking.
Testing Self-Locking Gears
Self-locking helical gear prototype units were made predicated on the developed mathematical styles. The gear data are offered in the Table 1, and the check gears are presented in Figure 5.
The schematic presentation of the test setup is proven in Figure 6. The 0.5Nm electric electric motor was used to drive the actuator. An integrated speed and torque sensor was attached on the high-acceleration shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was linked to the low acceleration shaft of the gearbox via coupling. The type and result torque and speed info were captured in the info acquisition tool and further analyzed in a computer applying data analysis application. The instantaneous productivity of the actuator was calculated and plotted for a variety of speed/torque combination. Standard driving performance of the self- locking equipment obtained during examining was above 85 percent. The self-locking house of the helical equipment occur backdriving mode was likewise tested. In this test the exterior torque was put on the output equipment shaft and the angular transducer demonstrated no angular movement of type shaft, which confirmed the self-locking condition.
Potential Applications
Initially, self-locking gears were found in textile industry [2]. Nevertheless, this kind of gears has many potential applications in lifting mechanisms, assembly tooling, and other gear drives where in fact the backdriving or inertial generating is not permissible. Among such program [7] of the self-locking gears for a consistently variable valve lift program was suggested for an vehicle engine.
Summary
In this paper, a principle of function of the self-locking gears has been described. Design specifics of the self-locking gears with symmetric and asymmetric profiles will be shown, and tests of the apparatus prototypes has proved relatively high driving efficiency and trustworthy self-locking. The self-locking gears could find many applications in various industries. For example, in a control systems where position stableness is very important (such as in auto, aerospace, medical, robotic, agricultural etc.) the self-locking will allow to attain required performance. Like the worm self-locking gears, the parallel axis self-locking gears are hypersensitive to operating circumstances. The locking stability is afflicted by lubrication, vibration, misalignment, etc. Implementation of the gears should be finished with caution and requires comprehensive testing in every possible operating conditions.