self locking gearbox

Worm gearboxes with countless combinations
Ever-Power offers an extremely wide variety of worm gearboxes. As a result of modular design the standard programme comprises many combinations when it comes to selection of equipment housings, mounting and interconnection options, flanges, shaft models, kind of oil, surface procedures etc.
Sturdy and reliable
The design of the Ever-Power worm gearbox is easy and well proven. We only use high quality components such as homes in cast iron, light weight aluminum and stainless, worms in the event hardened and polished steel and worm wheels in high-grade bronze of distinctive alloys ensuring the the best wearability. The seals of the worm gearbox are provided with a dust lip which properly resists dust and water. Furthermore, the gearboxes will be 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 ability is bigger than a worm gearing. In the meantime, the worm gearbox can be in a far more simple design.
A double reduction may be composed of 2 standard gearboxes or as a particular gearbox.
Compact design
Compact design is among the key phrases of the typical gearboxes of the Ever-Power-Series. Further optimisation can be achieved through the use of adapted gearboxes or specialized gearboxes.
Low noise
Our worm gearboxes and actuators are extremely quiet. This is because of the very even running of the worm gear combined with the consumption of cast iron and high precision on aspect manufacturing and assembly. Regarding the our precision gearboxes, we consider extra attention of any sound that can be interpreted as a murmur from the apparatus. So the general noise degree of our gearbox is normally reduced to an absolute minimum.
Angle gearboxes
On the worm gearbox the input shaft and output shaft are perpendicular to one another. This often proves to become a decisive benefit making the incorporation of the gearbox significantly simpler and more compact.The worm gearbox can be an angle gear. This is normally an advantage for incorporation into constructions.
Strong bearings in sound housing
The output shaft of the Ever-Power worm gearbox is quite firmly embedded in the gear house and is well suited for direct suspension for wheels, movable arms and other areas rather than needing to create a separate suspension.
Self locking
For larger gear ratios, Ever-Electric power worm gearboxes will provide a self-locking impact, which in lots of situations can be utilised as brake or as extra secureness. Also spindle gearboxes with a trapezoidal spindle will be self-locking, making them perfect for a wide variety of solutions.
In most gear drives, when generating torque is suddenly reduced therefore of power off, torsional vibration, ability outage, or any mechanical inability at the transmitting input part, then gears will be rotating either in the same path driven by the system inertia, or in the opposite course driven by the resistant output load because of gravity, planting season load, etc. The latter state is known as backdriving. During inertial motion or backdriving, the motivated output shaft (load) becomes the driving one and the self locking gearbox traveling input shaft (load) becomes the driven one. There are several gear travel applications where productivity shaft driving is undesirable. So as to prevent it, several types of brake or clutch products are used.
However, additionally, there are solutions in the gear transmitting that prevent inertial motion or backdriving using self-locking gears with no additional devices. The most typical one is usually a worm equipment with a low lead angle. In self-locking worm gears, torque utilized from the load side (worm equipment) is blocked, i.electronic. cannot travel the worm. Even so, their application comes with some restrictions: the crossed axis shafts’ arrangement, relatively high equipment ratio, low acceleration, low gear mesh proficiency, increased heat generation, etc.
Also, there are parallel axis self-locking gears [1, 2]. These gears, unlike the worm gears, can employ any equipment ratio from 1:1 and larger. They have the traveling mode and self-locking method, when the inertial or backdriving torque is put on the output gear. In the beginning these gears had very low ( <50 percent) traveling effectiveness that limited their program. Then it was proved [3] that large driving efficiency of this kind of gears is possible. Standards of the self-locking was analyzed in this post [4]. This paper explains the principle of the self-locking procedure for the parallel axis gears with symmetric and asymmetric tooth profile, and displays their suitability for diverse applications.
Self-Locking Condition
Shape 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. Pretty much all conventional gear drives possess the pitch stage P located in the active part the contact series B1-B2 (Figure 1a and Physique 2a). This pitch stage location provides low specific sliding velocities and friction, and, consequently, high driving productivity. In case when this sort of gears are driven by outcome load or inertia, they are rotating freely, as the friction moment (or torque) is not 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, 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 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 dynamic portion the contact line B1-B2. There are 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 collection. This makes the self-locking possible, however the driving efficiency will end up being low under 50 percent [3]. Alternative 2 (figs 1b and 2b): when the point P is positioned between the point B1, where in fact the outer size of the pinion intersects the series contact and a centre of the apparatus O2. This kind of gears can be self-locking with relatively substantial driving efficiency > 50 percent.
Another condition of self-locking is to truly have a adequate friction angle g to deflect the force F’ beyond the guts of the pinion O1. It generates the resisting self-locking minute (torque) T’1 = F’ x L’1, where L’1 can be a lever of the force F’1. This condition could 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 amount of teeth,
- involute profile position at the tip of the apparatus tooth.
Design of Self-Locking Gears
Self-locking gears are customized. They cannot always be fabricated with the standards tooling with, for instance, the 20o pressure and rack. This makes them incredibly suited to Direct Gear Design® [5, 6] that delivers required gear overall performance and after that defines tooling parameters.
Direct Gear Style presents the symmetric gear tooth shaped 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 idea circle da allows preventing the pointed tooth hint. The equally spaced pearly whites form the gear. The fillet account between teeth is designed independently to avoid interference and provide minimum bending anxiety. The working pressure angle aw and the speak to 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 high pressure and great 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. Subsequently, the transverse contact ratio ea < 1.0 (typically 0.4 - 0.6). Insufficient the transverse get in touch with ratio should be compensated by the axial (or face) speak to ratio eb to guarantee the total contact ratio eg = ea + eb ≥ 1.0. This can be achieved by employing helical gears (Shape 4). Even so, helical gears apply the axial (thrust) push on the apparatus bearings. The dual helical (or “herringbone”) gears (Body 4) allow to compensate this force.
High transverse pressure angles cause increased bearing radial load that could be up to four to five situations higher than for the traditional 20o pressure angle gears. Bearing selection and gearbox housing style ought to be done accordingly to hold this elevated load without high deflection.
Software of the asymmetric tooth for unidirectional drives permits improved performance. For the self-locking gears that are being used to avoid backdriving, the same tooth flank is used for both traveling and locking modes. In this instance asymmetric tooth profiles provide much higher transverse speak to ratio at the given pressure angle compared to the symmetric tooth flanks. It creates it possible to reduce the helix position and axial bearing load. For the self-locking gears that used to avoid inertial driving, diverse tooth flanks are used for generating and locking modes. In this case, asymmetric tooth account with low-pressure angle provides high effectiveness for driving function and the contrary high-pressure angle tooth profile can be used for reliable self-locking.
Testing Self-Locking Gears
Self-locking helical gear prototype models were made predicated on the developed mathematical styles. The gear data are offered in the Table 1, and the check gears are shown in Figure 5.
The schematic presentation of the test setup is displayed in Figure 6. The 0.5Nm electric engine was used to drive the actuator. A rate and torque sensor was mounted on the high-rate shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was linked to the low quickness shaft of the gearbox via coupling. The input and outcome torque and speed facts had been captured in the data acquisition tool and further analyzed in a computer using data analysis computer software. The instantaneous proficiency of the actuator was calculated and plotted for a variety of speed/torque combination. Normal driving efficiency of the self- locking equipment obtained during screening was above 85 percent. The self-locking house of the helical equipment set in 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 activity of insight shaft, which verified the self-locking condition.
Potential Applications
Initially, self-locking gears were found in textile industry [2]. However, this kind of gears has many potential applications in lifting mechanisms, assembly tooling, and other gear drives where the backdriving or inertial traveling is not permissible. One of such app [7] of the self-locking gears for a constantly variable valve lift program was advised for an vehicle 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 relatively high driving effectiveness and reputable self-locking. The self-locking gears could find many applications in various industries. For instance, in a control devices where position stability is important (such as in automobile, aerospace, medical, robotic, agricultural etc.) the self-locking will allow to accomplish required performance. Similar to the worm self-locking gears, the parallel axis self-locking gears are sensitive to operating conditions. The locking dependability is damaged by lubrication, vibration, misalignment, etc. Implementation of these gears should be done with caution and needs comprehensive testing in all possible operating conditions.