self locking gearbox

Worm gearboxes with many combinations
Ever-Power offers an extremely wide variety of worm gearboxes. Because of the modular design the standard programme comprises countless combinations with regards to selection of equipment housings, mounting and connection options, flanges, shaft designs, kind of oil, surface procedures etc.
Sturdy and reliable
The look of the Ever-Power worm gearbox is simple and well proven. We simply use top quality components such as houses in cast iron, aluminium and stainless, worms in the event hardened and polished steel and worm tires in high-grade bronze of specialized alloys ensuring the ideal wearability. The seals of the worm gearbox are given with a dust lip which efficiently resists dust and water. Furthermore, the gearboxes are greased for life 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 single step or 10.000:1 in a double reduction. An comparative gearing with the same equipment ratios and the same transferred electrical power is bigger than a worm gearing. In the meantime, the worm gearbox is usually in a far more simple design.
A double reduction may be composed of 2 normal gearboxes or as a special gearbox.
Compact design
Compact design is one of the key words of the typical gearboxes of the Ever-Power-Series. Further optimisation may be accomplished by using adapted gearboxes or unique gearboxes.
Low noise
Our worm gearboxes and actuators are really quiet. This is due to the very soft working of the worm equipment combined with the consumption of cast iron and high precision on component manufacturing and assembly. Regarding the our accuracy gearboxes, we have extra treatment of any sound which can be interpreted as a murmur from the gear. Therefore the general noise level of our gearbox is definitely reduced to a complete minimum.
Angle gearboxes
On the worm gearbox the input shaft and output shaft are perpendicular to one another. This quite often proves to be a decisive benefit making the incorporation of the gearbox substantially simpler and more compact.The worm gearbox is an angle gear. This can often be an self locking gearbox advantage for incorporation into constructions.
Strong bearings in sound housing
The output shaft of the Ever-Power worm gearbox is very firmly embedded in the apparatus house and is ideal for direct suspension for wheels, movable arms and other parts rather than having to create a separate suspension.
Self locking
For larger gear ratios, Ever-Ability worm gearboxes will provide a self-locking impact, which in many situations works extremely well as brake or as extra protection. Also spindle gearboxes with a trapezoidal spindle will be self-locking, making them well suited for an array of solutions.
In most gear drives, when driving torque is suddenly reduced therefore of electric power off, torsional vibration, ability outage, or any mechanical failure at the transmission input area, then gears will be rotating either in the same path driven by the system inertia, or in the opposite way driven by the resistant output load due to gravity, springtime load, etc. The latter condition is called backdriving. During inertial movement or backdriving, the influenced output shaft (load) becomes the generating one and the generating input shaft (load) turns into the driven one. There are many gear drive applications where productivity shaft driving is unwanted. In order to prevent it, different types of brake or clutch devices are used.
However, additionally, there are solutions in the gear tranny that prevent inertial action or backdriving using self-locking gears without any additional devices. The most frequent one is definitely a worm equipment with a minimal lead angle. In self-locking worm gears, torque used from the strain side (worm gear) is blocked, i.e. cannot drive the worm. Even so, their application comes with some limitations: the crossed axis shafts’ arrangement, relatively high equipment ratio, low acceleration, low gear mesh productivity, increased heat era, etc.
Also, there happen to be parallel axis self-locking gears [1, 2]. These gears, unlike the worm gears, can use any gear ratio from 1:1 and bigger. They have the traveling 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) driving performance that limited their app. Then it was proved [3] that high driving efficiency of these kinds of gears is possible. Criteria of the self-locking was analyzed in this article [4]. This paper explains the theory of the self-locking process for the parallel axis gears with symmetric and asymmetric the teeth profile, and shows their suitability for distinct applications.
Self-Locking Condition
Body 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 the event of inertial driving. Almost all conventional equipment drives have the pitch level P located in the active part the contact brand B1-B2 (Figure 1a and Figure 2a). This pitch stage location provides low certain sliding velocities and friction, and, as a result, high driving proficiency. In case when such gears are motivated by end result load or inertia, they are rotating freely, because the friction minute (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, applied to the gear
T’1 – driven torque, applied to the pinion
F – driving force
F’ – generating 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 ought to be located off the lively portion the contact line B1-B2. There will be two options. Alternative 1: when the point P is positioned between a middle of the pinion O1 and the idea B2, where in fact the outer size of the apparatus intersects the contact collection. This makes the self-locking possible, however the driving performance will be low under 50 percent [3]. Alternative 2 (figs 1b and 2b): when the idea P is positioned between your point B1, where in fact the outer diameter of the pinion intersects the line contact and a centre of the apparatus O2. This kind of gears can be self-locking with relatively huge driving efficiency > 50 percent.
Another condition of self-locking is to have a ample friction angle g to deflect the force F’ beyond the center of the pinion O1. It generates the resisting self-locking instant (torque) T’1 = F’ x L’1, where L’1 is certainly a lever of the pressure 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 position at the tip of the apparatus tooth.
Design of Self-Locking Gears
Self-locking gears are custom. They cannot become fabricated with the requirements tooling with, for example, the 20o pressure and rack. This makes them incredibly suitable for Direct Gear Design® [5, 6] that provides required gear efficiency and from then on defines tooling parameters.
Direct Gear Style presents the symmetric gear tooth created by two involutes of one base circle (Figure 3a). The asymmetric gear tooth is created by two involutes of two several base circles (Figure 3b). The tooth suggestion circle da allows avoiding the pointed tooth hint. The equally spaced pearly whites form the apparatus. The fillet profile between teeth was created independently in order to avoid interference and provide minimum bending tension. The functioning pressure angle aw and the speak to ratio ea are defined 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 high pressure and huge sliding friction in the tooth contact. If the sliding friction coefficient f = 0.1 – 0.3, it needs the transverse operating pressure angle to aw = 75 – 85o. Because of this, the transverse contact 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 guarantee the total get in touch with ratio eg = ea + eb ≥ 1.0. This can be achieved by employing helical gears (Shape 4). Nevertheless, helical gears apply the axial (thrust) push on the apparatus bearings. The double helical (or “herringbone”) gears (Number 4) allow to compensate this force.
Great 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 should be done accordingly to carry this increased load without increased deflection.
App of the asymmetric the teeth for unidirectional drives permits improved performance. For the self-locking gears that are used to avoid backdriving, the same tooth flank can be used for both generating and locking modes. In this case asymmetric tooth profiles present much higher transverse get in touch with ratio at the presented pressure angle than the symmetric tooth flanks. It makes it possible to lessen the helix position and axial bearing load. For the self-locking gears which used to prevent inertial driving, diverse tooth flanks are used for driving and locking modes. In this instance, asymmetric tooth profile with low-pressure position provides high efficiency for driving function and the opposite high-pressure angle tooth account is used for reliable self-locking.
Testing Self-Locking Gears
Self-locking helical gear prototype units were made based on the developed mathematical types. The gear data are provided 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. A swiftness and torque sensor was installed on the high-rate shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was connected to the low quickness shaft of the gearbox via coupling. The insight and outcome torque and speed information were captured in the info acquisition tool and further analyzed in a computer using data analysis application. The instantaneous effectiveness of the actuator was calculated and plotted for a variety of speed/torque combination. Typical driving performance of the self- locking equipment obtained during tests was above 85 percent. The self-locking real estate of the helical equipment occur backdriving mode was also tested. During this test the external torque was put on the output equipment shaft and the angular transducer showed no angular movement of input shaft, which verified the self-locking condition.
Potential Applications
Initially, self-locking gears were used in textile industry [2]. Even so, this type of gears has many potential applications in lifting mechanisms, assembly tooling, and other equipment drives where the backdriving or inertial traveling is not permissible. Among such program [7] of the self-locking gears for a continually variable valve lift system was suggested for an automobile engine.
Summary
In this paper, a basic 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 assessment of the apparatus prototypes has proved fairly high driving proficiency and dependable self-locking. The self-locking gears may find many applications in a variety of industries. For example, in a control devices where position steadiness is essential (such as for example in car, 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 delicate to operating conditions. The locking stability is affected by lubrication, vibration, misalignment, etc. Implementation of these gears should be finished with caution and requires comprehensive testing in every possible operating conditions.