Worm self locking gearbox gearboxes with many combinations
Ever-Power offers a very broad range 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 remedies etc.
Sturdy and reliable
The look of the Ever-Power worm gearbox is simple and well proven. We just use high quality components such as residences in cast iron, metal and stainless steel, worms in the event hardened and polished metal and worm tires in high-grade bronze of specialized alloys ensuring the the best wearability. The seals of the worm gearbox are provided with a dust lip which efficiently resists dust and drinking water. Furthermore, the gearboxes happen to be 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 decrease. An equivalent gearing with the same equipment ratios and the same transferred power is bigger than 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 standard 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 through the use of adapted gearboxes or particular gearboxes.
Low noise
Our worm gearboxes and actuators are really quiet. This is because of the very smooth running of the worm gear combined with the application of cast iron and substantial precision on component manufacturing and assembly. Regarding the our precision gearboxes, we take extra care and attention of any sound that can be interpreted as a murmur from the gear. So the general noise level of our gearbox is definitely reduced to an absolute minimum.
Angle gearboxes
On the worm gearbox the input shaft and output shaft are perpendicular to each other. This sometimes proves to become a decisive benefit producing the incorporation of the gearbox noticeably simpler and more compact.The worm gearbox can be an angle gear. This is often an edge for incorporation into constructions.
Strong bearings in stable housing
The output shaft of the Ever-Power worm gearbox is very firmly embedded in the gear 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-Electricity worm gearboxes provides a self-locking result, which in lots of situations can be utilised as brake or as extra security. Likewise spindle gearboxes with a trapezoidal spindle happen to be self-locking, making them suitable for a variety of solutions.
In most equipment drives, when traveling torque is suddenly reduced therefore of electrical power off, torsional vibration, electricity outage, or any mechanical inability at the transmitting input aspect, then gears will be rotating either in the same path driven by the system inertia, or in the opposite path driven by the resistant output load due to gravity, spring load, etc. The latter condition is known as backdriving. During inertial action or backdriving, the driven output shaft (load) becomes the driving one and the traveling input shaft (load) becomes the powered one. There are plenty of gear drive applications where productivity shaft driving is unwanted. To be able to prevent it, different types of brake or clutch equipment are used.
However, there are also solutions in the gear tranny that prevent inertial action or backdriving using self-locking gears without any additional gadgets. The most common one is normally a worm gear with a minimal lead angle. In self-locking worm gears, torque utilized from the load side (worm gear) is blocked, i.e. cannot drive the worm. However, their application includes some limitations: the crossed axis shafts’ arrangement, relatively high gear ratio, low velocity, low gear mesh productivity, increased heat era, etc.
Also, there are parallel axis self-locking gears [1, 2]. These gears, unlike the worm gears, can use any equipment ratio from 1:1 and bigger. They have the generating mode and self-locking method, when the inertial or backdriving torque is usually put on the output gear. Originally these gears had suprisingly low ( <50 percent) generating effectiveness that limited their software. Then it had been proved [3] that huge driving efficiency of these kinds of gears is possible. Standards of the self-locking was analyzed in this posting [4]. This paper explains the principle of the self-locking method for the parallel axis gears with symmetric and asymmetric the teeth profile, and reveals 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 conventional gears (a) and self-locking gears (b), in case of inertial driving. Pretty much all conventional gear drives have the pitch stage P situated in the active part the contact series B1-B2 (Figure 1a and Number 2a). This pitch point location provides low particular sliding velocities and friction, and, consequently, high driving proficiency. In case when these kinds of gears are motivated by output load or inertia, they will be rotating freely, as the friction point in time (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, applied to the pinion
F – driving force
F’ – driving 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
In order to make gears self-locking, the pitch point P ought to be located off the active portion the contact line B1-B2. There happen to be two options. Option 1: when the idea P is placed between a middle of the pinion O1 and the idea B2, where in fact the outer size of the apparatus intersects the contact line. This makes the self-locking possible, however the driving efficiency will be low under 50 percent [3]. Option 2 (figs 1b and 2b): when the point P is put between your point B1, where the outer diameter of the pinion intersects the collection contact and a centre of the apparatus O2. This type of gears can 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 center of the pinion O1. It generates the resisting self-locking minute (torque) T’1 = F’ x L’1, where L’1 is certainly a lever of the drive 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 amount of teeth,
– involute profile angle at the end 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 very suited to Direct Gear Design® [5, 6] that provides required gear effectiveness and from then on defines tooling parameters.
Direct Gear Design presents the symmetric equipment tooth shaped by two involutes of 1 base circle (Figure 3a). The asymmetric gear tooth is produced by two involutes of two numerous base circles (Figure 3b). The tooth idea circle da allows preventing the pointed tooth tip. The equally spaced tooth form the apparatus. The fillet profile between teeth is designed independently to avoid interference and offer minimum bending pressure. The operating pressure angle aw and the speak to 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 high pressure and huge sliding friction in the tooth get in touch with. If the sliding friction coefficient f = 0.1 – 0.3, it requires the transverse operating pressure angle to aw = 75 – 85o. Because of this, the transverse get in touch with ratio ea < 1.0 (typically 0.4 - 0.6). Insufficient the transverse speak to ratio ought to 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 (Number 4). However, helical gears apply the axial (thrust) pressure on the apparatus bearings. The twice helical (or “herringbone”) gears (Number 4) allow to compensate this force.
High transverse pressure angles result in increased bearing radial load that could be up to four to five occasions higher than for the traditional 20o pressure angle gears. Bearing variety and gearbox housing style should be done accordingly to carry this elevated load without excessive deflection.
Application of the asymmetric teeth for unidirectional drives permits improved efficiency. For the self-locking gears that are used to avoid backdriving, the same tooth flank is utilized for both driving and locking modes. In cases like this asymmetric tooth profiles offer much higher transverse contact 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 which used to avoid inertial driving, diverse tooth flanks are being used for generating and locking modes. In this case, asymmetric tooth account with low-pressure angle provides high proficiency for driving method and the opposite high-pressure angle tooth profile is used for reliable self-locking.
Testing Self-Locking Gears
Self-locking helical gear prototype units were made based on the developed mathematical products. The gear data are shown in the Desk 1, and the check gears are provided in Figure 5.
The schematic presentation of the test setup is displayed in Figure 6. The 0.5Nm electric motor was used to operate a vehicle the actuator. A built-in quickness and torque sensor was mounted on the high-quickness shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was linked to the low swiftness shaft of the gearbox via coupling. The input and end result torque and speed facts had been captured in the info acquisition tool and further analyzed in a computer applying data analysis software program. The instantaneous performance of the actuator was calculated and plotted for a variety of speed/torque combination. Average driving effectiveness of the personal- locking gear obtained during testing was above 85 percent. The self-locking house of the helical gear set in backdriving mode was also tested. In this test the external torque was put on the output equipment shaft and the angular transducer demonstrated no angular motion of type shaft, which confirmed the self-locking condition.
Potential Applications
Initially, self-locking gears were found in textile industry [2]. Even so, this type of gears has a large number of potential applications in lifting mechanisms, assembly tooling, and other gear drives where in fact the backdriving or inertial traveling is not permissible. Among such request [7] of the self-locking gears for a constantly variable valve lift system was recommended for an automotive engine.
Summary
In this paper, a principle of operate of the self-locking gears has been described. Design specifics of the self-locking gears with symmetric and asymmetric profiles will be shown, and screening of the apparatus prototypes has proved fairly high driving efficiency and trustworthy self-locking. The self-locking gears could find many applications in a variety of industries. For instance, in a control devices where position balance is vital (such as for example in car, aerospace, medical, robotic, agricultural etc.) the self-locking allows to accomplish required performance. Similar to the worm self-locking gears, the parallel axis self-locking gears are hypersensitive to operating circumstances. The locking dependability is damaged by lubrication, vibration, misalignment, etc. Implementation of the gears should be done with caution and needs comprehensive testing in every possible operating conditions.