self locking gearbox

Worm gearboxes with many combinations
Ever-Power offers an extremely wide range of worm gearboxes. As a result of modular design the typical programme comprises many combinations when it comes to selection of equipment housings, mounting and interconnection options, flanges, shaft models, kind of oil, surface treatments etc.
Sturdy and reliable
The design of the Ever-Power worm self locking gearbox gearbox is easy and well proven. We only use high quality components such as houses in cast iron, light weight aluminum and stainless, worms in case hardened and polished metal and worm tires in high-quality bronze of special alloys ensuring the maximum wearability. The seals of the worm gearbox are provided with a dust lip which efficiently resists dust and drinking water. In addition, the gearboxes will be greased forever with synthetic oil.
Large reduction 100:1 in a single step
As default the worm gearboxes allow for reductions of up to 100:1 in one step or 10.000:1 in a double lowering. An comparative gearing with the same gear ratios and the same transferred electric power is bigger than a worm gearing. At the same time, the worm gearbox can be in a far more simple design.
A double reduction could 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 through the use of adapted gearboxes or specialized gearboxes.
Low noise
Our worm gearboxes and actuators are extremely quiet. This is because of the very simple jogging of the worm gear combined with the application of cast iron and huge precision on element manufacturing and assembly. Regarding the our accuracy gearboxes, we take extra treatment of any sound which can be interpreted as a murmur from the gear. So the general noise level of our gearbox is usually reduced to an absolute minimum.
Angle gearboxes
On the worm gearbox the input shaft and output shaft are perpendicular to each other. This often proves to become a decisive benefits making the incorporation of the gearbox significantly simpler and smaller sized.The worm gearbox is an angle gear. This can often be an advantage for incorporation into constructions.
Strong bearings in stable housing
The output shaft of the Ever-Power worm gearbox is quite firmly embedded in the gear house and is ideal for direct suspension for wheels, movable arms and other areas rather than having to build a separate suspension.
Self locking
For larger equipment ratios, Ever-Power worm gearboxes provides a self-locking result, which in lots of situations can be utilised as brake or as extra reliability. Also spindle gearboxes with a trapezoidal spindle will be self-locking, making them well suited for a variety of solutions.
In most gear drives, when generating torque is suddenly reduced consequently of ability off, torsional vibration, power outage, or any mechanical failing at the transmitting input area, then gears will be rotating either in the same course driven by the system inertia, or in the opposite path driven by the resistant output load due to gravity, springtime load, etc. The latter condition is known as backdriving. During inertial motion or backdriving, the influenced output shaft (load) becomes the generating one and the driving input shaft (load) becomes the powered one. There are numerous gear travel applications where output shaft driving is unwanted. So as to prevent it, different types of brake or clutch products are used.
However, additionally, there are solutions in the gear transmission that prevent inertial movement or backdriving using self-locking gears without the additional devices. The most typical one is usually 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. However, their application comes with some constraints: the crossed axis shafts’ arrangement, relatively high gear ratio, low rate, low gear mesh effectiveness, increased heat era, etc.
Also, there will be parallel axis self-locking gears [1, 2]. These gears, unlike the worm gears, can utilize any gear ratio from 1:1 and bigger. They have the generating mode and self-locking function, when the inertial or backdriving torque is normally applied to the output gear. In the beginning these gears had suprisingly low ( <50 percent) generating proficiency that limited their software. Then it was proved [3] that great driving efficiency of this sort of gears is possible. Requirements of the self-locking was analyzed in this posting [4]. This paper explains the basic principle of the self-locking process for the parallel axis gears with symmetric and asymmetric pearly whites profile, and displays their suitability for unique applications.
Self-Locking Condition
Shape 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. Virtually all conventional gear drives have the pitch point P located in the active part the contact series B1-B2 (Figure 1a and Shape 2a). This pitch stage location provides low specific sliding velocities and friction, and, because of this, high driving effectiveness. In case when this sort of gears are motivated by outcome load or inertia, they happen to be rotating freely, as the friction minute (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 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 productive portion the contact line B1-B2. There are two options. Alternative 1: when the point P is positioned between a center of the pinion O1 and the idea B2, where in fact the outer size of the apparatus intersects the contact series. This makes the self-locking possible, but the driving productivity will always be 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 center of the apparatus 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 center of the pinion O1. It creates the resisting self-locking point in time (torque) T’1 = F’ x L’1, where L’1 is certainly 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 – equipment ratio,
n1 and n2 – pinion and gear amount of teeth,
– involute profile position at the tip of the apparatus tooth.
Design of Self-Locking Gears
Self-locking gears are customized. They cannot always be fabricated with the expectations tooling with, for instance, the 20o pressure and rack. This makes them extremely suitable for Direct Gear Style® [5, 6] that provides required gear overall 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 equipment tooth is formed by two involutes of two unique base circles (Figure 3b). The tooth hint circle da allows preventing the pointed tooth idea. The equally spaced teeth form the gear. The fillet account between teeth is designed independently to avoid interference and provide minimum bending tension. The functioning pressure angle aw and the contact 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 high 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. Consequently, the transverse get in touch with ratio ea < 1.0 (typically 0.4 - 0.6). Lack of the transverse get in touch with ratio ought to be compensated by the axial (or face) speak to ratio eb to guarantee the total get in touch with ratio eg = ea + eb ≥ 1.0. This is often attained by applying helical gears (Determine 4). Nevertheless, helical gears apply the axial (thrust) force on the gear bearings. The dual helical (or “herringbone”) gears (Shape 4) allow to pay this force.
High transverse pressure angles result in increased bearing radial load that could be up to four to five times higher than for the conventional 20o pressure angle gears. Bearing collection and gearbox housing style ought to be done accordingly to hold this elevated load without unnecessary deflection.
Request of the asymmetric teeth for unidirectional drives allows for improved effectiveness. For the self-locking gears that are used to avoid backdriving, the same tooth flank can be used for both driving and locking modes. In this case asymmetric tooth profiles present much higher transverse get in touch with ratio at the given pressure angle than the symmetric tooth flanks. It makes it possible to reduce the helix angle and axial bearing load. For the self-locking gears that used to avoid inertial driving, several tooth flanks are used for traveling and locking modes. In cases like this, asymmetric tooth profile with low-pressure position provides high efficiency for driving method and the contrary high-pressure angle tooth profile is used for reliable self-locking.
Testing Self-Locking Gears
Self-locking helical gear prototype pieces were made based on the developed mathematical versions. The gear info are presented in the Desk 1, and the check gears are shown in Figure 5.
The schematic presentation of the test setup is displayed in Figure 6. The 0.5Nm electric electric motor was used to drive the actuator. A acceleration and torque sensor was attached on the high-speed shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was linked to the low rate shaft of the gearbox via coupling. The type and output torque and speed details had been captured in the info acquisition tool and additional analyzed in a computer applying data analysis software program. The instantaneous effectiveness of the actuator was calculated and plotted for a variety of speed/torque combination. Typical driving efficiency of the self- locking equipment obtained during testing was above 85 percent. The self-locking real estate of the helical gear set in backdriving mode was likewise tested. During this test the exterior torque was applied to the output equipment shaft and the angular transducer revealed no angular movement of insight shaft, which verified the self-locking condition.
Potential Applications
Initially, self-locking gears were used in textile industry [2]. On the other hand, this sort of gears has many potential applications in lifting mechanisms, assembly tooling, and other gear drives where the backdriving or inertial generating is not permissible. One of such request [7] of the self-locking gears for a consistently variable valve lift system was suggested for an automobile engine.
Summary
In this paper, a principle of work of the self-locking gears has been described. Style specifics of the self-locking gears with symmetric and asymmetric profiles are shown, and tests of the gear prototypes has proved fairly high driving performance and reliable self-locking. The self-locking gears may find many applications in a variety of industries. For instance, in a control devices where position steadiness is very important (such as for example in motor vehicle, aerospace, medical, robotic, agricultural etc.) the self-locking allows to attain required performance. Similar to the worm self-locking gears, the parallel axis self-locking gears are sensitive to operating circumstances. The locking stability is influenced by lubrication, vibration, misalignment, etc. Implementation of the gears should be finished with caution and requires comprehensive testing in every possible operating conditions.

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