self locking gearbox

Worm gearboxes with countless combinations
Ever-Power offers a very broad range of worm gearboxes. Due to the 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 therapies etc.
Sturdy and reliable
The look of the Ever-Power worm gearbox is easy and well proven. We only use top quality components such as houses in cast iron, metal and stainless steel, worms in case hardened and polished steel and worm wheels in high-quality bronze of specialized alloys ensuring the optimum wearability. The seals of the worm gearbox are provided with a dust lip which properly resists dust and drinking water. In addition, the gearboxes are greased forever 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 single step or 10.000:1 in a double lowering. An self locking gearbox comparative gearing with the same equipment ratios and the same transferred ability is bigger when compared to a worm gearing. In the meantime, the worm gearbox is certainly in a far more simple design.
A double reduction may be composed of 2 normal gearboxes or as a particular gearbox.
Compact design
Compact design is one of the key phrases of the typical 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 extremely quiet. This is due to the very even jogging of the worm gear combined with the use of cast iron and great precision on component manufacturing and assembly. In connection with our accuracy gearboxes, we have extra health care of any sound which can be interpreted as a murmur from the gear. So the general noise degree 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 typically proves to become a decisive advantage producing the incorporation of the gearbox noticeably simpler and smaller sized.The worm gearbox is an angle gear. This is often an edge for incorporation into constructions.
Strong bearings in solid housing
The output shaft of the Ever-Power worm gearbox is very firmly embedded in the apparatus house and is perfect for immediate suspension for wheels, movable arms and other areas rather than having to build a separate suspension.
Self locking
For larger gear ratios, Ever-Electricity worm gearboxes will provide a self-locking result, which in many situations works extremely well as brake or as extra security. Also spindle gearboxes with a trapezoidal spindle happen to be self-locking, making them suitable for a wide selection of solutions.
In most gear drives, when driving torque is suddenly reduced as a result of power off, torsional vibration, electrical power outage, or any mechanical inability at the transmitting input area, 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 motion or backdriving, the motivated output shaft (load) becomes the driving one and the driving input shaft (load) becomes the powered one. There are many gear drive applications where end result shaft driving is undesirable. To be able to prevent it, several types of brake or clutch equipment are used.
However, there are also solutions in the apparatus transmitting that prevent inertial motion or backdriving using self-locking gears without the additional devices. The most frequent one is normally a worm gear with a low lead angle. In self-locking worm gears, torque applied from the load side (worm gear) is blocked, i.e. cannot travel the worm. However, their application includes some constraints: the crossed axis shafts’ arrangement, relatively high equipment ratio, low quickness, low gear mesh efficiency, increased heat generation, etc.
Also, there happen to be parallel axis self-locking gears [1, 2]. These gears, unlike the worm gears, can employ any equipment ratio from 1:1 and higher. They have the driving mode and self-locking function, when the inertial or backdriving torque is normally applied to the output gear. Primarily these gears had very low ( <50 percent) generating productivity that limited their software. Then it was proved [3] that substantial driving efficiency of this kind of gears is possible. Conditions of the self-locking was analyzed in this post [4]. This paper explains the principle of the self-locking process for the parallel axis gears with symmetric and asymmetric pearly whites profile, and shows their suitability for different applications.
Self-Locking Condition
Physique 1 presents conventional gears (a) and self-locking gears (b), in case of backdriving. Figure 2 presents regular gears (a) and self-locking gears (b), in case of inertial driving. Almost all conventional gear drives possess the pitch level P located in the active portion the contact series B1-B2 (Figure 1a and Physique 2a). This pitch stage location provides low certain sliding velocities and friction, and, due to this fact, high driving effectiveness. In case when these kinds of gears are powered by output load or inertia, they will be rotating freely, as the friction point in time (or torque) isn’t 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, applied to the gear
T’1 – driven torque, applied to the pinion
F – driving force
F’ – driving 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
To make gears self-locking, the pitch point P should be located off the productive portion the contact line B1-B2. There happen to be two options. Option 1: when the idea P is placed between a centre of the pinion O1 and the idea B2, where the outer diameter of the apparatus intersects the contact line. This makes the self-locking possible, however the driving proficiency will become low under 50 percent [3]. Choice 2 (figs 1b and 2b): when the idea P is inserted between your point B1, where in fact the outer diameter of the pinion intersects the collection contact and a center of the apparatus O2. This sort of gears could be self-locking with relatively great driving proficiency > 50 percent.
Another condition of self-locking is to have a enough friction angle g to deflect the force F’ beyond the guts of the pinion O1. It creates the resisting self-locking second (torque) T’1 = F’ x L’1, where L’1 is definitely 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 number of teeth,
– involute profile angle at the tip of the gear tooth.
Design of Self-Locking Gears
Self-locking gears are customized. They cannot end up being fabricated with the standards tooling with, for instance, the 20o pressure and rack. This makes them incredibly suitable for Direct Gear Style® [5, 6] that delivers required gear effectiveness and after that defines tooling parameters.
Direct Gear Design presents the symmetric equipment tooth formed by two 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 suggestion circle da allows preventing the pointed tooth tip. The equally spaced the teeth form the apparatus. The fillet account between teeth is designed independently in order to avoid interference and provide minimum bending pressure. The operating pressure angle aw and the contact ratio ea are defined 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 huge sliding friction in the tooth contact. If the sliding friction coefficient f = 0.1 – 0.3, it requires the transverse operating pressure angle 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 ought to be compensated by the axial (or face) contact ratio eb to guarantee the total get in touch with ratio eg = ea + eb ≥ 1.0. This is often attained by employing helical gears (Body 4). Even so, helical gears apply the axial (thrust) induce on the apparatus bearings. The twice helical (or “herringbone”) gears (Body 4) allow to compensate this force.
Great transverse pressure angles bring about increased bearing radial load that could be up to four to five circumstances higher than for the traditional 20o pressure angle gears. Bearing variety and gearbox housing design ought to be done accordingly to hold this increased load without high deflection.
App of the asymmetric teeth for unidirectional drives permits improved functionality. For the self-locking gears that are used to prevent backdriving, the same tooth flank is employed for both generating and locking modes. In cases like this asymmetric tooth profiles give much higher transverse contact ratio at the provided pressure angle compared to the symmetric tooth flanks. It makes it possible to lessen the helix angle and axial bearing load. For the self-locking gears which used to avoid inertial driving, different tooth flanks are being used for generating and locking modes. In cases like this, asymmetric tooth profile with low-pressure angle provides high performance for driving mode and the opposite high-pressure angle tooth account is utilized for reliable self-locking.
Testing Self-Locking Gears
Self-locking helical equipment prototype pieces were made based on the developed mathematical designs. The gear data are shown in the Table 1, and the check gears are offered in Figure 5.
The schematic presentation of the test setup is proven in Figure 6. The 0.5Nm electric motor was used to drive the actuator. A built-in quickness and torque sensor was installed on the high-velocity shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was connected to the low velocity shaft of the gearbox via coupling. The input and result torque and speed facts had been captured in the info acquisition tool and additional analyzed in a computer employing data analysis software. The instantaneous efficiency of the actuator was calculated and plotted for an array of speed/torque combination. Average driving performance of the self- locking equipment obtained during tests was above 85 percent. The self-locking house of the helical gear set in backdriving mode was also tested. During this test the external torque was put on the output gear shaft and the angular transducer showed no angular activity of type shaft, which confirmed the self-locking condition.
Potential Applications
Initially, self-locking gears had been found in textile industry [2]. However, this sort of gears has many potential applications in lifting mechanisms, assembly tooling, and other equipment drives where in fact the backdriving or inertial traveling is not permissible. One of such software [7] of the self-locking gears for a continuously variable valve lift system was recommended for an car 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 happen to be shown, and evaluating of the gear prototypes has proved relatively high driving productivity and reputable self-locking. The self-locking gears could find many applications in various industries. For example, in a control devices where position steadiness is essential (such as for example in automotive, 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 delicate to operating conditions. The locking dependability is afflicted by lubrication, vibration, misalignment, etc. Implementation of these gears should be done with caution and requires comprehensive testing in every possible operating conditions.