self locking gearbox

Worm gearboxes with many combinations
Ever-Power offers an extremely wide range of worm gearboxes. Due to the modular design the typical programme comprises many combinations with regards to selection of gear housings, mounting and interconnection options, flanges, shaft designs, type of oil, surface procedures etc.
Sturdy and reliable
The design of the Ever-Power worm gearbox is easy and well proven. We just use top quality components such as houses in cast iron, lightweight aluminum and stainless, worms in the event hardened and polished steel and worm tires in high-grade bronze of specialized alloys ensuring the optimum wearability. The seals of the worm gearbox are provided with a dust lip which efficiently resists dust and normal water. In addition, the gearboxes are greased for life with synthetic oil.
Large reduction 100:1 in one step
As default the worm gearboxes enable reductions as high as 100:1 in one single step or 10.000:1 in a double decrease. An comparative gearing with the same gear ratios and the same transferred electric power is bigger when compared to a worm gearing. In the mean time, the worm gearbox is in a far more simple design.
A double reduction could be composed of 2 typical gearboxes or as a special gearbox.
Compact design
Compact design is probably the key phrases of the standard gearboxes of the Ever-Power-Series. Further optimisation can be achieved through the use of adapted gearboxes or distinctive gearboxes.
Low noise
Our worm gearboxes and actuators are extremely quiet. This is self locking gearbox because of the very smooth jogging of the worm gear combined with the application of cast iron and substantial precision on element manufacturing and assembly. In connection with our accuracy gearboxes, we take extra care of any sound which can be interpreted as a murmur from the gear. So the general noise level of our gearbox is reduced to a complete minimum.
Angle gearboxes
On the worm gearbox the input shaft and output shaft are perpendicular to one another. This frequently proves to be a decisive advantages making the incorporation of the gearbox significantly simpler and more compact.The worm gearbox can be an angle gear. This is often an advantage for incorporation into constructions.
Strong bearings in solid housing
The output shaft of the Ever-Power worm gearbox is quite firmly embedded in the apparatus 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-Electricity worm gearboxes provides a self-locking effect, which in many situations works extremely well as brake or as extra secureness. As well spindle gearboxes with a trapezoidal spindle are self-locking, making them suitable for an array of solutions.
In most equipment drives, when driving torque is suddenly reduced consequently of ability off, torsional vibration, vitality outage, or any mechanical inability at the tranny input part, then gears will be rotating either in the same path driven by the system inertia, or in the opposite direction driven by the resistant output load because of gravity, spring load, etc. The latter state is known as backdriving. During inertial action or backdriving, the driven output shaft (load) becomes the driving one and the driving input shaft (load) turns into the driven one. There are plenty of gear drive applications where result shaft driving is undesirable. So as to prevent it, various kinds of brake or clutch products are used.
However, there are also solutions in the apparatus tranny that prevent inertial movement or backdriving using self-locking gears without any additional units. The most typical one is certainly a worm gear with a low lead angle. In self-locking worm gears, torque utilized from the load side (worm gear) is blocked, i.e. cannot travel the worm. Nevertheless, their application comes with some limitations: the crossed axis shafts’ arrangement, relatively high equipment ratio, low rate, low gear mesh proficiency, increased heat era, 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 setting, when the inertial or backdriving torque is normally put on the output gear. Initially these gears had very low ( <50 percent) driving productivity that limited their application. Then it was proved [3] that great driving efficiency of such gears is possible. Criteria of the self-locking was analyzed in this posting [4]. This paper explains the theory of the self-locking procedure for the parallel axis gears with symmetric and asymmetric the teeth profile, and displays their suitability for several applications.
Self-Locking Condition
Physique 1 presents conventional gears (a) and self-locking gears (b), in case of backdriving. Figure 2 presents standard gears (a) and self-locking gears (b), in the event of inertial driving. Practically all conventional gear drives possess the pitch stage P situated in the active portion the contact brand B1-B2 (Figure 1a and Determine 2a). This pitch point location provides low certain sliding velocities and friction, and, because of this, high driving performance. In case when this sort of gears are powered by end result load or inertia, they happen to be rotating freely, as the friction instant (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, 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
In order to make gears self-locking, the pitch point P ought to be located off the energetic 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 diameter of the apparatus intersects the contact line. This makes the self-locking possible, however the driving proficiency will be low under 50 percent [3]. Choice 2 (figs 1b and 2b): when the idea P is placed between your point B1, where the outer size of the pinion intersects the range contact and a center of the gear O2. This sort of gears can be self-locking with relatively large driving effectiveness > 50 percent.
Another condition of self-locking is to have a satisfactory friction angle g to deflect the force F’ beyond the guts of the pinion O1. It generates the resisting self-locking point in time (torque) T’1 = F’ x L’1, where L’1 is normally a lever of the push F’1. This condition could be shown as L’1min > 0 or
(1) Equation 1
or
(2) Equation 2
where:
u = n2/n1 – gear ratio,
n1 and n2 – pinion and gear quantity of teeth,
– involute profile position at the end of the apparatus tooth.
Design of Self-Locking Gears
Self-locking gears are customized. They cannot always be fabricated with the requirements tooling with, for instance, the 20o pressure and rack. This makes them extremely suitable for Direct Gear Style® [5, 6] that delivers required gear overall performance and from then on defines tooling parameters.
Direct Gear Style presents the symmetric gear tooth formed by two involutes of 1 base circle (Figure 3a). The asymmetric equipment tooth is created by two involutes of two distinct base circles (Figure 3b). The tooth hint circle da allows avoiding the pointed tooth suggestion. The equally spaced pearly whites form the gear. The fillet account between teeth is designed independently in order to avoid interference and provide minimum bending anxiety. 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 requires the transverse operating pressure angle to aw = 75 – 85o. Because of this, the transverse speak to ratio ea < 1.0 (typically 0.4 - 0.6). Lack of the transverse contact ratio should be compensated by the axial (or face) get in touch with ratio eb to ensure the total speak to ratio eg = ea + eb ≥ 1.0. This is often achieved by employing helical gears (Figure 4). Nevertheless, helical gears apply the axial (thrust) power on the gear bearings. The double helical (or “herringbone”) gears (Body 4) allow to pay this force.
Huge transverse pressure angles result in increased bearing radial load that may be up to four to five circumstances higher than for the conventional 20o pressure angle gears. Bearing assortment and gearbox housing style ought to be done accordingly to hold this elevated load without excessive deflection.
Request of the asymmetric tooth for unidirectional drives permits improved efficiency. For the self-locking gears that are used to prevent backdriving, the same tooth flank is employed for both driving and locking modes. In this case asymmetric tooth profiles present much higher transverse contact ratio at the provided 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 that used to prevent inertial driving, unique tooth flanks are used for traveling and locking modes. In this case, asymmetric tooth account with low-pressure angle provides high effectiveness for driving mode and the contrary high-pressure angle tooth account is used for reliable self-locking.
Testing Self-Locking Gears
Self-locking helical gear prototype models were made based on the developed mathematical designs. The gear info are shown in the Desk 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 operate a vehicle the actuator. An integrated swiftness and torque sensor was installed on the high-swiftness shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was connected to the low rate shaft of the gearbox via coupling. The source and productivity torque and speed data were captured in the data acquisition tool and further analyzed in a computer applying data analysis software. The instantaneous proficiency of the actuator was calculated and plotted for an array of speed/torque combination. Normal driving efficiency of the personal- locking gear obtained during screening was above 85 percent. The self-locking house of the helical gear occur backdriving mode was also tested. In this test the external torque was applied to the output gear shaft and the angular transducer revealed no angular motion of insight shaft, which confirmed the self-locking condition.
Potential Applications
Initially, self-locking gears had been used in textile industry [2]. Nevertheless, this type of gears has various potential applications in lifting mechanisms, assembly tooling, and other gear drives where in fact the backdriving or inertial driving is not permissible. One of such request [7] of the self-locking gears for a constantly variable valve lift system was suggested for an vehicle engine.
Summary
In this paper, a theory 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 tests of the apparatus prototypes has proved fairly high driving proficiency and efficient self-locking. The self-locking gears could find many applications in various industries. For example, in a control systems where position steadiness is important (such as in auto, aerospace, medical, robotic, agricultural etc.) the self-locking will allow to attain required performance. Similar to the worm self-locking gears, the parallel axis self-locking gears are delicate to operating circumstances. The locking reliability is affected by lubrication, vibration, misalignment, etc. Implementation of the gears should be done with caution and needs comprehensive testing in every possible operating conditions.