self locking gearbox

Worm gearboxes with many combinations
Ever-Power offers a very wide range of worm gearboxes. Due to the modular design the typical programme comprises many combinations when it comes to selection of gear housings, mounting and interconnection options, flanges, shaft designs, type of oil, surface therapies etc.
Sturdy and reliable
The design of the Ever-Power worm gearbox is easy and well proven. We only use high quality components such as houses in cast iron, aluminum and stainless, worms in the event hardened and polished metal and worm wheels in high-quality bronze of distinctive alloys ensuring the maximum wearability. The seals of the worm gearbox are provided with a dust lip which properly resists dust and drinking water. Furthermore, the gearboxes will be greased for life with synthetic oil.
Large reduction 100:1 in a single step
As default the worm gearboxes enable reductions of up to 100:1 in one step or 10.000:1 in a double reduction. An equivalent gearing with the same gear ratios and the same transferred vitality is bigger than a worm gearing. In the meantime, 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 among the key words of the typical gearboxes of the Ever-Power-Series. Further optimisation may be accomplished by using adapted gearboxes or specialized gearboxes.
Low noise
Our worm gearboxes and actuators are extremely quiet. This is because of the very clean running of the worm gear combined with the use of cast iron and substantial precision on element manufacturing and assembly. In connection with our accuracy gearboxes, we have extra treatment of any sound that can be interpreted as a murmur from the gear. 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 output shaft are perpendicular to one another. This frequently proves to be a decisive benefits producing the incorporation of the gearbox significantly simpler and more compact.The worm gearbox is an angle gear. This is often an advantage for incorporation into constructions.
Strong bearings in solid housing
The output shaft of the Ever-Power worm gearbox is quite firmly embedded in the gear house and is ideal for immediate suspension for wheels, movable arms and other parts rather than having to build a separate suspension.
Self locking
For larger gear ratios, Ever-Electrical power worm gearboxes will provide a self-locking impact, 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 perfect for an array of solutions.
In most gear drives, when traveling torque is suddenly reduced because of this of electrical power off, torsional vibration, electrical power outage, or any mechanical inability at the transmitting input part, then gears will be rotating either in the same course driven by the machine inertia, or in the opposite route driven by the resistant output load due to gravity, planting season load, etc. The latter condition is known as backdriving. During inertial motion or backdriving, the driven output shaft (load) becomes the traveling one and the traveling input shaft (load) turns into the powered one. There are plenty of gear travel applications where outcome shaft driving is unwanted. To be able to prevent it, different types of brake or clutch equipment are used.
However, additionally, there are solutions in the apparatus tranny that prevent inertial action or backdriving using self-locking gears with no additional units. The most typical one can be a worm equipment with a low lead angle. In self-locking worm gears, torque utilized from the strain side (worm gear) is blocked, i.e. cannot drive the worm. On the other hand, their application comes with some limitations: the crossed axis shafts’ arrangement, relatively high gear ratio, low swiftness, low gear mesh effectiveness, increased heat generation, 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 higher. They have the generating mode and self-locking setting, when the inertial or backdriving torque is normally put on the output gear. In the beginning these gears had very low ( <50 percent) generating performance that limited their software. Then it had been proved [3] that huge driving efficiency of these kinds of gears is possible. Conditions of the self-locking was analyzed in this post [4]. This paper explains the principle of the self-locking procedure for the parallel axis gears with symmetric and asymmetric pearly whites profile, and shows their suitability for distinct 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 case of inertial driving. Almost all conventional equipment drives have the pitch stage P situated in the active part the contact line B1-B2 (Figure 1a and Number 2a). This pitch level location provides low specific sliding velocities and friction, and, as a result, high driving effectiveness. In case when this kind of gears are motivated by output load or inertia, they are rotating freely, because the friction second (or torque) is not 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’ – generating 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 ought to be located off the productive portion the contact line B1-B2. There happen to be two options. Alternative 1: when the idea P is positioned between a middle of the pinion O1 and the idea B2, where the outer diameter of the gear intersects the contact series. This makes the self-locking possible, however the driving proficiency will end up being low under 50 percent [3]. Option 2 (figs 1b and 2b): when the point P is positioned between your point B1, where in fact the outer size of the pinion intersects the line contact and a middle of the apparatus O2. This sort of gears can be self-locking with relatively excessive driving proficiency > 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 creates the resisting self-locking instant (torque) T’1 = F’ x L’1, where L’1 is certainly a lever of the push 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 end of the apparatus tooth.
Design of Self-Locking Gears
Self-locking gears are custom. They cannot always be fabricated with the specifications tooling with, for instance, the 20o pressure and rack. This makes them very suitable 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 created by two involutes of 1 base circle (Figure 3a). The asymmetric equipment tooth is formed by two involutes of two diverse base circles (Figure 3b). The tooth hint circle da allows avoiding the pointed tooth suggestion. The equally spaced the teeth form the gear. The fillet account between teeth is designed independently to avoid interference and provide minimum self locking gearbox bending stress. The working 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 ruthless and great sliding friction in the tooth speak to. If the sliding friction coefficient f = 0.1 – 0.3, it requires the transverse operating pressure angle to aw = 75 – 85o. Due to this fact, the transverse get in touch with ratio ea < 1.0 (typically 0.4 - 0.6). Insufficient the transverse get in touch with ratio should be compensated by the axial (or face) speak to ratio eb to ensure the total get in touch with ratio eg = ea + eb ≥ 1.0. This could be achieved by using helical gears (Determine 4). Even so, helical gears apply the axial (thrust) force on the apparatus bearings. The dual helical (or “herringbone”) gears (Figure 4) allow to compensate this force.
Excessive transverse pressure angles result in increased bearing radial load that could be up to four to five times higher than for the traditional 20o pressure angle gears. Bearing collection and gearbox housing design ought to be done accordingly to hold this elevated load without abnormal deflection.
Application of the asymmetric tooth for unidirectional drives allows for improved overall performance. For the self-locking gears that are used to prevent backdriving, the same tooth flank can be used for both generating and locking modes. In this case asymmetric tooth profiles offer much higher transverse get in touch with ratio at the offered 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 prevent inertial driving, several tooth flanks are being used for traveling and locking modes. In this case, asymmetric tooth profile with low-pressure angle provides high efficiency for driving mode and the contrary high-pressure angle tooth profile is used for reliable self-locking.
Testing Self-Locking Gears
Self-locking helical equipment prototype sets were made based on the developed mathematical versions. The gear data are presented in the Table 1, and the test gears are presented in Figure 5.
The schematic presentation of the test setup is proven in Figure 6. The 0.5Nm electric engine was used to drive the actuator. An integrated rate and torque sensor was mounted on the high-speed shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was connected to the low acceleration shaft of the gearbox via coupling. The insight and output torque and speed facts had been captured in the data acquisition tool and additional analyzed in a pc applying data analysis program. The instantaneous performance of the actuator was calculated and plotted for a broad range of speed/torque combination. Typical driving performance of the self- locking gear obtained during testing was above 85 percent. The self-locking house of the helical gear 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 motion of type shaft, which verified the self-locking condition.
Potential Applications
Initially, self-locking gears had been used in textile industry [2]. Even so, this kind of gears has various 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 request [7] of the self-locking gears for a continually variable valve lift system was recommended for an automobile engine.
Summary
In this paper, a theory of function 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 gear prototypes has proved relatively high driving effectiveness and trustworthy self-locking. The self-locking gears may find many applications in various industries. For instance, in a control systems where position steadiness is vital (such as for example in automobile, aerospace, medical, robotic, agricultural etc.) the self-locking allows to accomplish required performance. Similar to the worm self-locking gears, the parallel axis self-locking gears are very sensitive to operating circumstances. The locking dependability is afflicted by lubrication, vibration, misalignment, etc. Implementation of these gears should be done with caution and needs comprehensive testing in every possible operating conditions.