self locking gearbox

Worm gearboxes with many combinations
Ever-Power offers an extremely wide variety of worm gearboxes. As a result of modular design the typical programme comprises countless combinations in terms of selection of equipment housings, mounting and interconnection options, flanges, shaft models, type of oil, surface treatments etc.
Sturdy and reliable
The look of the Ever-Power worm gearbox is simple and well proven. We only use top quality components such as houses in cast iron, light weight aluminum and stainless steel, worms in case hardened and polished metal and worm tires in high-quality bronze of particular alloys ensuring the maximum wearability. The seals of the worm gearbox are given with a dust lip which successfully resists dust and water. In addition, the gearboxes are greased for life with synthetic oil.
Large reduction 100:1 in one step
As default the worm gearboxes enable reductions of up to 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 vitality is bigger than a worm gearing. In the meantime, the worm gearbox is in a more simple design.
A double reduction may be composed of 2 standard gearboxes or as a particular gearbox.
Compact design
Compact design is probably the key phrases of the typical gearboxes of the Ever-Power-Series. Further optimisation may be accomplished through the use of adapted gearboxes or exceptional gearboxes.
Low noise
Our worm gearboxes and actuators are really quiet. This is due to the very clean operating of the worm equipment combined with the application of cast iron and huge precision on part manufacturing and assembly. In connection with our accuracy gearboxes, we consider extra care of any sound which can be interpreted as a murmur from the apparatus. So the general noise degree of our gearbox is certainly 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 advantages making the incorporation of the gearbox noticeably simpler and more compact.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 immediate self locking gearbox suspension for wheels, movable arms and other areas rather than needing to build a separate suspension.
Self locking
For larger gear ratios, Ever-Electric power worm gearboxes provides a self-locking impact, which in many situations can be used as brake or as extra protection. As well spindle gearboxes with a trapezoidal spindle are self-locking, making them perfect for a wide range of solutions.
In most gear drives, when generating torque is suddenly reduced because of this of electrical power off, torsional vibration, electrical power outage, or any mechanical inability at the transmission input part, then gears will be rotating either in the same way driven by the system inertia, or in the contrary direction driven by the resistant output load due to gravity, spring load, etc. The latter condition is called backdriving. During inertial action or backdriving, the influenced output shaft (load) turns into the generating one and the generating input shaft (load) becomes the driven one. There are numerous gear drive applications where end result shaft driving is unwanted. As a way to prevent it, various kinds of brake or clutch devices are used.
However, there are also solutions in the gear transmission that prevent inertial motion or backdriving using self-locking gears with no additional products. The most frequent one is usually a worm equipment with a minimal lead angle. In self-locking worm gears, torque applied from the load side (worm equipment) is blocked, i.e. cannot travel the worm. However, their application includes some constraints: the crossed axis shafts’ arrangement, relatively high gear ratio, low quickness, low gear mesh efficiency, increased heat generation, etc.
Also, there will be parallel axis self-locking gears [1, 2]. These gears, unlike the worm gears, can utilize any equipment ratio from 1:1 and higher. They have the traveling mode and self-locking function, when the inertial or backdriving torque is definitely put on the output gear. Initially these gears had very low ( <50 percent) traveling performance that limited their app. Then it was proved [3] that high driving efficiency of these kinds of gears is possible. Conditions of the self-locking was analyzed in this post [4]. This paper explains the theory of the self-locking method for the parallel axis gears with symmetric and asymmetric pearly whites profile, and reveals their suitability for diverse applications.
Self-Locking Condition
Determine 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. Practically all conventional gear drives have the pitch stage P located in the active portion the contact range B1-B2 (Figure 1a and Determine 2a). This pitch point location provides low specific sliding velocities and friction, and, therefore, high driving efficiency. In case when these kinds of gears are motivated by result load or inertia, they are rotating freely, as 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, put on the gear
T’1 – driven torque, applied to 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 ought to be located off the dynamic portion the contact line B1-B2. There will be two options. Alternative 1: when the point P is positioned between a center of the pinion O1 and the idea B2, where the outer diameter of the gear intersects the contact range. This makes the self-locking possible, but the driving proficiency will end up being low under 50 percent [3]. Alternative 2 (figs 1b and 2b): when the idea P is located 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 excessive driving proficiency > 50 percent.
Another condition of self-locking is to truly have a satisfactory friction angle g to deflect the force F’ beyond the center of the pinion O1. It creates the resisting self-locking moment (torque) T’1 = F’ x L’1, where L’1 can be a lever of the power F’1. This condition could 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 number of teeth,
– involute profile angle at the tip of the apparatus tooth.
Design of Self-Locking Gears
Self-locking gears are custom. They cannot be fabricated with the specifications tooling with, for instance, the 20o pressure and rack. This makes them extremely ideal for Direct Gear Style® [5, 6] that provides required gear performance and from then on defines tooling parameters.
Direct Gear Style presents the symmetric gear tooth produced by two involutes of 1 base circle (Figure 3a). The asymmetric gear tooth is shaped by two involutes of two numerous base circles (Figure 3b). The tooth idea circle da allows preventing the pointed tooth suggestion. The equally spaced teeth form the apparatus. The fillet profile between teeth is designed independently in order to avoid interference and provide minimum bending anxiety. The operating 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 ruthless and substantial sliding friction in the tooth speak to. If the sliding friction coefficient f = 0.1 – 0.3, it needs the transverse operating pressure angle to aw = 75 – 85o. Therefore, the transverse contact ratio ea < 1.0 (typically 0.4 - 0.6). Lack of the transverse contact ratio should be compensated by the axial (or face) get in touch with ratio eb to ensure the total contact ratio eg = ea + eb ≥ 1.0. This can be achieved by applying helical gears (Physique 4). Even so, helical gears apply the axial (thrust) pressure on the apparatus bearings. The double helical (or “herringbone”) gears (Physique 4) allow to compensate this force.
High transverse pressure angles bring about increased bearing radial load that may be up to four to five circumstances higher than for the traditional 20o pressure angle gears. Bearing collection and gearbox housing style ought to be done accordingly to carry this increased load without abnormal deflection.
Program of the asymmetric pearly whites for unidirectional drives permits improved effectiveness. For the self-locking gears that are being used to prevent backdriving, the same tooth flank can be used for both traveling 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 reduce the helix angle and axial bearing load. For the self-locking gears which used to avoid inertial driving, unique tooth flanks are used for generating and locking modes. In this instance, asymmetric tooth profile with low-pressure position provides high performance for driving method and the contrary high-pressure angle tooth account is used for reliable self-locking.
Testing Self-Locking Gears
Self-locking helical equipment prototype pieces were made predicated on the developed mathematical models. The gear data are offered in the Desk 1, and the test gears are presented 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. An integrated rate and torque sensor was mounted on the high-rate shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was linked to the low swiftness shaft of the gearbox via coupling. The insight and result torque and speed facts were captured in the data acquisition tool and additional analyzed in a computer employing data analysis software. The instantaneous efficiency of the actuator was calculated and plotted for a wide range of speed/torque combination. Typical driving productivity of the personal- locking equipment obtained during assessment was above 85 percent. The self-locking real estate of the helical equipment set in backdriving mode was also tested. During this test the external torque was put on the output equipment shaft and the angular transducer revealed no angular motion of input shaft, which confirmed the self-locking condition.
Potential Applications
Initially, self-locking gears were used in textile industry [2]. However, this kind of gears has many potential applications in lifting mechanisms, assembly tooling, and other equipment drives where the backdriving or inertial generating is not permissible. Among such software [7] of the self-locking gears for a constantly variable valve lift program was suggested for an vehicle engine.
Summary
In this paper, a principle of operate of the self-locking gears has been described. Style specifics of the self-locking gears with symmetric and asymmetric profiles will be shown, and evaluating of the gear prototypes has proved relatively high driving performance and reliable self-locking. The self-locking gears could find many applications in various industries. For example, in a control devices where position balance is vital (such as in auto, 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 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.

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