self locking gearbox

Worm gearboxes with many combinations
Ever-Power offers a very wide selection of worm gearboxes. As a result of modular design the standard programme comprises countless combinations when it comes to selection of equipment housings, mounting and connection options, flanges, shaft designs, kind of oil, surface treatments etc.
Sturdy and reliable
The look of the Ever-Power worm gearbox is easy and well proven. We just use top quality components such as properties in cast iron, aluminum and stainless, worms in the event hardened and polished metal and worm tires in high-quality bronze of particular alloys ensuring the the best possible wearability. The seals of the worm gearbox are provided with a dust lip which properly resists dust and normal water. Furthermore, the gearboxes are greased for life with synthetic oil.
Large reduction 100:1 in one 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 lowering. An equivalent gearing with the same equipment ratios and the same transferred vitality is bigger when compared to a worm gearing. At the same time, the worm gearbox is usually in a more simple design.
A double reduction may be composed of 2 normal gearboxes or as a particular gearbox.
Compact design
Compact design is probably the key terms of the standard gearboxes of the Ever-Power-Series. Further optimisation can be achieved through the use of adapted gearboxes or unique gearboxes.
Low noise
Our worm gearboxes and actuators are extremely quiet. This is because of the very simple running of the worm gear combined with the use of cast iron and huge precision on element manufacturing and assembly. Regarding the our accuracy gearboxes, we consider extra care and attention of any sound that can be interpreted as a murmur from the gear. So the general noise degree of our gearbox is 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 gain making the incorporation of the gearbox noticeably simpler and smaller sized.The worm gearbox can be an angle gear. This can often be an advantage for incorporation into constructions.
Strong bearings in sturdy housing
The output shaft of the Ever-Power worm gearbox is quite firmly embedded in the apparatus house and is suitable for direct suspension for wheels, movable arms and other parts rather than needing to create a separate suspension.
Self locking
For larger gear ratios, Ever-Ability worm gearboxes provides a self-locking effect, which in lots of situations can be utilized as brake or as extra secureness. Likewise spindle gearboxes with a trapezoidal spindle will be self-locking, making them well suited for an array of solutions.
In most gear drives, when traveling torque is suddenly reduced as a result of electrical power off, torsional vibration, electrical power outage, or any mechanical failing at the tranny input aspect, then gears will be rotating either in the same way driven by the system inertia, or in the opposite direction driven by the resistant output load because of gravity, springtime load, etc. The latter state is called backdriving. During inertial movement or backdriving, the motivated output shaft (load) turns into the generating one and the traveling input shaft (load) turns into the driven one. There are numerous gear travel applications where productivity shaft driving is undesirable. As a way to prevent it, different types of brake or clutch equipment are used.
However, there are also solutions in the gear transmitting that prevent inertial movement or backdriving using self-locking gears without the additional gadgets. The most frequent one can be a worm gear with a minimal lead angle. In self-locking worm gears, torque utilized from the load side (worm equipment) is blocked, i.e. cannot travel the worm. Even so, their application includes some constraints: the crossed axis shafts’ arrangement, relatively high gear ratio, low acceleration, low gear mesh performance, increased heat generation, etc.
Also, there are parallel axis self-locking gears [1, 2]. These gears, unlike the worm gears, can make use of any equipment ratio from 1:1 and higher. They have the traveling mode and self-locking mode, when the inertial or backdriving torque is certainly put on the output gear. Primarily these gears had suprisingly low ( <50 percent) generating performance that limited their app. Then it had been proved [3] that high driving efficiency of these kinds of gears is possible. Conditions of the self-locking was analyzed in this posting [4]. This paper explains the basic principle of the self-locking method for the parallel axis gears with symmetric and asymmetric the teeth profile, and shows their suitability for several applications.
Self-Locking Condition
Determine 1 presents conventional gears (a) and self-locking gears (b), in case of backdriving. Figure 2 presents typical gears (a) and self-locking gears (b), in the event of inertial driving. Almost all conventional equipment drives possess the pitch level P located in the active part the contact series B1-B2 (Figure 1a and Number 2a). This pitch stage location provides low specific sliding velocities and friction, and, consequently, high driving performance. In case when this sort of gears are powered by productivity load or inertia, they will be rotating freely, as the friction moment (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’ – 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
In order to make gears self-locking, the pitch point P should be located off the energetic portion the contact line B1-B2. There will be two options. Alternative 1: when the idea P is placed between a center of the pinion O1 and the point B2, where in fact the outer size of the gear intersects the contact range. This makes the self-locking possible, but the driving efficiency will end up being low under 50 percent [3]. Alternative 2 (figs 1b and 2b): when the point P is placed between the point B1, where the outer size of the pinion intersects the line contact and a centre of the apparatus O2. This sort of gears can be self-locking with relatively huge driving productivity > 50 percent.
Another condition of self-locking is to truly have a ample friction angle g to self locking gearbox 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 normally a lever of the power F’1. This condition can be presented 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 end of the gear tooth.
Design of Self-Locking Gears
Self-locking gears are custom. They cannot be fabricated with the standards tooling with, for instance, the 20o pressure and rack. This makes them extremely suitable for Direct Gear Style® [5, 6] that delivers required gear performance and from then on defines tooling parameters.
Direct Gear Design presents the symmetric equipment tooth produced by two involutes of one base circle (Figure 3a). The asymmetric gear tooth is formed by two involutes of two numerous base circles (Figure 3b). The tooth suggestion circle da allows avoiding the pointed tooth idea. The equally spaced teeth form the apparatus. The fillet account between teeth was created independently in order to avoid interference and offer minimum bending stress. The working 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 requires the transverse operating pressure angle to aw = 75 – 85o. Due to this fact, the transverse speak to ratio ea < 1.0 (typically 0.4 - 0.6). Insufficient the transverse contact ratio should be compensated by the axial (or face) get in touch with ratio eb to guarantee the total get in touch with ratio eg = ea + eb ≥ 1.0. This can be attained by using helical gears (Shape 4). Even so, helical gears apply the axial (thrust) induce on the gear bearings. The double helical (or “herringbone”) gears (Physique 4) allow to compensate this force.
Great transverse pressure angles cause increased bearing radial load that may be up to four to five moments higher than for the conventional 20o pressure angle gears. Bearing selection and gearbox housing style should be done accordingly to hold this improved load without unnecessary deflection.
Application of the asymmetric tooth for unidirectional drives allows for improved effectiveness. For the self-locking gears that are used to avoid backdriving, the same tooth flank is employed for both traveling and locking modes. In cases like this asymmetric tooth profiles offer much higher transverse contact ratio at the given pressure angle compared to the symmetric tooth flanks. It makes it possible to reduce the helix angle and axial bearing load. For the self-locking gears which used to avoid inertial driving, numerous tooth flanks are used for generating and locking modes. In cases like this, asymmetric tooth account with low-pressure position provides high efficiency for driving setting and the contrary high-pressure angle tooth account is employed for reliable self-locking.
Testing Self-Locking Gears
Self-locking helical gear prototype sets were made predicated on the developed mathematical products. The gear data are provided in the Desk 1, and the test gears are provided in Figure 5.
The schematic presentation of the test setup is demonstrated in Figure 6. The 0.5Nm electric engine was used to operate a vehicle the actuator. A swiftness and torque sensor was mounted on the high-velocity shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was connected to the low speed shaft of the gearbox via coupling. The insight and result torque and speed details had been captured in the info acquisition tool and additional analyzed in a computer using data analysis software. The instantaneous proficiency of the actuator was calculated and plotted for a wide variety of speed/torque combination. Normal driving proficiency of the self- locking equipment obtained during evaluating was above 85 percent. The self-locking real estate of the helical gear occur backdriving mode was also tested. During this test the exterior torque was put on the output gear shaft and the angular transducer revealed no angular movement of type shaft, which confirmed the self-locking condition.
Potential Applications
Initially, self-locking gears were found in textile industry [2]. Nevertheless, this sort of gears has a large number of potential applications in lifting mechanisms, assembly tooling, and other equipment drives where in fact the backdriving or inertial driving is not permissible. Among such request [7] of the self-locking gears for a continuously variable valve lift program was suggested for an vehicle engine.
Summary
In this paper, a basic principle of do the job of the self-locking gears has been described. Style specifics of the self-locking gears with symmetric and asymmetric profiles are shown, and assessment of the apparatus prototypes has proved relatively high driving efficiency and reputable self-locking. The self-locking gears could find many applications in various industries. For example, in a control systems where position steadiness is vital (such as for example in car, aerospace, medical, robotic, agricultural etc.) the self-locking allows to accomplish required performance. Like the worm self-locking gears, the parallel axis self-locking gears are very sensitive to operating conditions. The locking dependability is afflicted by lubrication, vibration, misalignment, etc. Implementation of the gears should be finished with caution and needs comprehensive testing in every possible operating conditions.