Worm gearboxes with many combinations
Ever-Power offers an extremely wide selection of worm gearboxes. Due to the modular design the typical programme comprises many combinations when it comes to selection of equipment housings, mounting and interconnection options, flanges, shaft styles, kind of oil, surface treatments etc.
Sturdy and reliable
The design of the Ever-Power worm gearbox is simple and well proven. We only use top quality components such as properties in cast iron, metal and stainless, worms in the event hardened and polished metal and worm wheels in high-grade bronze of unique alloys ensuring the optimum wearability. The seals of the worm gearbox are given with a dirt lip which successfully resists dust and drinking water. In addition, the gearboxes are greased for life with synthetic oil.
Large self locking gearbox reduction 100:1 in a single step
As default the worm gearboxes allow for reductions of up to 100:1 in one step or 10.000:1 in a double lowering. An equivalent 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 more simple design.
A double reduction could be composed of 2 standard gearboxes or as a particular gearbox.
Compact design
Compact design is probably the key terms of the typical gearboxes of the Ever-Power-Series. Further optimisation can be achieved by using adapted gearboxes or particular gearboxes.
Low noise
Our worm gearboxes and actuators are extremely quiet. This is because of the very easy working of the worm equipment combined with the utilization of cast iron and great precision on component manufacturing and assembly. In connection with our accuracy gearboxes, we consider extra attention of any sound that can be interpreted as a murmur from the gear. Therefore the general noise degree of our gearbox is usually reduced to a complete minimum.
Angle gearboxes
On the worm gearbox the input shaft and output shaft are perpendicular to one another. This sometimes proves to become a decisive benefit making the incorporation of the gearbox substantially simpler and more compact.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 gear house and is ideal for direct suspension for wheels, movable arms and other parts rather than needing to build a separate suspension.
Self locking
For larger equipment ratios, Ever-Power worm gearboxes provides a self-locking result, which in many situations can be utilized as brake or as extra reliability. Also spindle gearboxes with a trapezoidal spindle will be self-locking, making them well suited for a wide selection of solutions.
In most gear drives, when traveling torque is suddenly reduced as a result of power off, torsional vibration, electricity outage, or any mechanical inability at the transmitting input part, then gears will be rotating either in the same route driven by the system inertia, or in the contrary path driven by the resistant output load because of gravity, springtime load, etc. The latter condition is known as backdriving. During inertial action or backdriving, the powered output shaft (load) turns into the traveling one and the generating input shaft (load) turns into the influenced one. There are many gear drive applications where outcome shaft driving is unwanted. As a way to prevent it, several types of brake or clutch gadgets are used.
However, there are also solutions in the apparatus transmitting that prevent inertial movement or backdriving using self-locking gears without the additional devices. The most common one is normally a worm equipment with a minimal lead angle. In self-locking worm gears, torque used from the load side (worm equipment) is blocked, i.e. cannot drive the worm. On the other hand, their application includes some restrictions: the crossed axis shafts’ arrangement, relatively high gear ratio, low swiftness, low gear mesh performance, increased heat era, etc.
Also, there will be parallel axis self-locking gears [1, 2]. These gears, unlike the worm gears, can employ any gear ratio from 1:1 and higher. They have the generating mode and self-locking function, when the inertial or backdriving torque is definitely put on the output gear. Primarily these gears had very low ( <50 percent) generating proficiency that limited their program. Then it had been proved [3] that large driving efficiency of this kind of gears is possible. Standards of the self-locking was analyzed in this article [4]. This paper explains the principle of the self-locking method for the parallel axis gears with symmetric and asymmetric teeth profile, and reveals their suitability for diverse applications.
Self-Locking Condition
Number 1 presents conventional gears (a) and self-locking gears (b), in the event of backdriving. Figure 2 presents regular gears (a) and self-locking gears (b), in the event of inertial driving. Virtually all conventional equipment drives possess the pitch point P situated in the active portion the contact line B1-B2 (Figure 1a and Figure 2a). This pitch point location provides low particular sliding velocities and friction, and, therefore, high driving efficiency. In case when such gears are powered by outcome load or inertia, they will be rotating freely, as the friction instant (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, applied to the gear
T’1 – driven torque, put on 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
To make gears self-locking, the pitch point P ought to be located off the dynamic portion the contact line B1-B2. There will be two options. Choice 1: when the idea P is placed between a centre of the pinion O1 and the point B2, where in fact the outer size of the apparatus intersects the contact series. This makes the self-locking possible, but the driving productivity will become low under 50 percent [3]. Option 2 (figs 1b and 2b): when the idea P is located between the point B1, where in fact the outer size of the pinion intersects the line contact and a center of the apparatus O2. This sort of gears could be self-locking with relatively substantial driving proficiency > 50 percent.
Another condition of self-locking is to have a enough friction angle g to deflect the force F’ beyond the guts of the pinion O1. It creates the resisting self-locking point in time (torque) T’1 = F’ x L’1, where L’1 can be a lever of the power F’1. This condition can 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 amount of teeth,
– involute profile angle at the tip of the gear tooth.
Design of Self-Locking Gears
Self-locking gears are customized. They cannot become fabricated with the specifications tooling with, for example, the 20o pressure and rack. This makes them extremely suited to Direct Gear Style® [5, 6] that provides required gear efficiency and from then on defines tooling parameters.
Direct Gear Style presents the symmetric equipment tooth created by two involutes of 1 base circle (Figure 3a). The asymmetric equipment tooth is created by two involutes of two unique base circles (Figure 3b). The tooth idea circle da allows avoiding the pointed tooth hint. The equally spaced teeth form the gear. The fillet profile between teeth is designed independently in order to avoid interference and offer minimum bending pressure. The working pressure angle aw and the speak to ratio ea are identified 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 large sliding friction in the tooth contact. If the sliding friction coefficient f = 0.1 – 0.3, it needs the transverse operating pressure position to aw = 75 – 85o. Therefore, the transverse get in touch with ratio ea < 1.0 (typically 0.4 - 0.6). Lack of 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 is often attained by using helical gears (Body 4). On the other hand, helical gears apply the axial (thrust) pressure on the apparatus bearings. The dual helical (or “herringbone”) gears (Determine 4) allow to pay this force.
High transverse pressure angles cause increased bearing radial load that may be up to four to five instances higher than for the traditional 20o pressure angle gears. Bearing selection and gearbox housing design should be done accordingly to hold this elevated load without extreme deflection.
App of the asymmetric the teeth for unidirectional drives allows for improved functionality. For the self-locking gears that are used to prevent backdriving, the same tooth flank can be used for both traveling and locking modes. In this instance asymmetric tooth profiles provide much higher transverse contact ratio at the offered pressure angle compared to 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 avoid inertial driving, diverse tooth flanks are used for traveling and locking modes. In this instance, asymmetric tooth account with low-pressure position provides high efficiency for driving setting and the contrary high-pressure angle tooth profile is used for reliable self-locking.
Testing Self-Locking Gears
Self-locking helical gear prototype units were made predicated on the developed mathematical designs. The gear info are presented in the Desk 1, and the check gears are offered in Figure 5.
The schematic presentation of the test setup is demonstrated in Figure 6. The 0.5Nm electric electric motor was used to drive the actuator. A acceleration and torque sensor was installed on the high-velocity shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was linked to the low speed shaft of the gearbox via coupling. The input and end result torque and speed data had been captured in the data acquisition tool and additional analyzed in a computer employing data analysis software program. The instantaneous productivity of the actuator was calculated and plotted for an array of speed/torque combination. Common driving effectiveness of the personal- locking gear obtained during evaluating was above 85 percent. The self-locking home of the helical equipment occur backdriving mode was as well tested. During this test the external torque was put on the output equipment shaft and the angular transducer confirmed no angular activity of suggestions shaft, which confirmed the self-locking condition.
Potential Applications
Initially, self-locking gears had been found in textile industry [2]. On the other hand, this sort of gears has many potential applications in lifting mechanisms, assembly tooling, and other gear drives where in fact the backdriving or inertial traveling is not permissible. Among such program [7] of the self-locking gears for a constantly variable valve lift program was suggested for an automobile engine.
Summary
In this paper, a theory of do the job of the self-locking gears has been described. Design specifics of the self-locking gears with symmetric and asymmetric profiles will be shown, and examining of the apparatus prototypes has proved fairly high driving effectiveness and efficient self-locking. The self-locking gears may find many applications in various industries. For instance, in a control devices where position balance is important (such as for example in automobile, aerospace, medical, robotic, agricultural etc.) the self-locking allows to attain required performance. Like the worm self-locking gears, the parallel axis self-locking gears are very 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.