The Introduction of Planetary Gearbox

Planetary gears are very popular due to their advantages such as high power density, companctness, and multiple and large compact gear ratios and load sharing among planets. Gearing arrangement is comrised of four different elements that produce a wide range of speed ratios in compact layout. These elecments are, Sun gear, an extenally toothed ring gear co-axial with the gear train Annulus, an internally toothed ring gear coaxial with ghe gear train Planets, externally toothed gears with mesh with the sun and anulus, and Planet Carrier, a support structure for planets, co-axial with the train. Planetary gear reducer motor system as shown in Figure 1 is typically used to perform speed reduction due to serveral advantages over conventional parallel shaft gear systems.

Planetary gears are also used to advantages over conventional parallel shaft gear systems. Planetary gears are also used to obtain high power density, large reduction in small volume, pure torsional reactions and multiple shafting. Another advantage of the planetary gearbox arrangement is load distribution. If the number of planets in the system are more the ability of load shearing is greater and the higher the torque density. The planetary gear box arrangment also creats greater and the higher the torque density. The planetary gearbox arrangment also creates greater stability due to the even distribution of mass and increased rotational stiffiness.

In recent years, enhancement of interior quietness in passenger cars. Automobiles is an important factor for influencing occupant comfort. Planetary gear sets are essential components of automatic transmissions because of their compact size and wide gear ratio range. They produce high speed reductions in compact spaces, greater load sharing, higher torque to weight ratio, diminished bearing loads and reduced noise and vibration. A Despite their advantage, the noise induced by the vibration of planetary gear systems remains a key concern. Planetary gears have receive considerably less research attention than single mesh gear paris. This paper focus on the study o two PGTs with different phasing (angular positions) while keeping every individual set unchanged.

This figure shows that the basic layout planetary gear train in which there is one Sun gear. Three Planet gear and one ring gear. They can produce the high speed reduction in compact space and having greater load shearing capacity & high torque to weight ratio.

Planetary basics — ratios, helix angles, axial loads, crowning

A planetary gearhead takes a high-speed, low-torque input, say from an electric motor, then increases torque and reduces speed at the output by the gearhead ratio. This lets motors run at higher, more-efficient rpms in equipment that operates at low speeds. It also reduces inertia reflected back to the motor, increasing stability. And using a planetary gearhead often lets machine builders reduce the size and cost of motion-control hardware.

Planetary units with helical gears, rather than spur gears, have a larger contact ratio. The contact ratio is the number of teeth in mesh at any given moment. While typical spur gearing has a 1.5 contact ratio, helical gearing more than doubles it to 3.3. Benefits of higher contact ratios include:

• 30 to 50% more torque capacity than equivalent spur-type planetary gearing.
• Better load sharing, which increases life.
• Smoother and quieter operation.
• Backlash reduced by as much as 2 arc-min.

The gearhead’s helix angle also has a significant impact on performance because the greater the angle, the more teeth in the mesh at any one time. So increasing the helix angle from the typical 12° up to 15° raises torque capacity by 17 to 20%; and by as much as 40% over straight-cut spur gears. Gears with a 15° helix angle also emit less noise.

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Introduction of Induction Servo Motors

Induction Servo Motors are the most commonly used motors in many applications. These are also called as Asynchronous Motors, because an Induction Leadshine servo motor always runs at a speed lower than synchronyous speed. Synchronous speed means the speed of the rotating magnetic field in the stator.

Principle of Induction Servo Motor:

When a three phase supply is given to the stator, a rotating field produces induced e.m.f. in rotor windings which cause induced currents tend to propose the action, producing them and therefore they circulate in such a manner that a torque is produced in the rotor tending it to cause it to flow the rotating field and thus reduce the relative motion which is producing the induced currents.

Induction Servo motor speed

Induction Servo motor works as follows: Electricity is supplied to the stator, which produces a magnetic field. This magnetic field moves around the rotor at synchronous speed. Rotor currents produce secondary magnetic field, which is trying to fight the stator magnetic field, which causes the rotor to rotate. However, in practice, the servo motor driver never runs at synchronous speed but the “base rate” is lower. The difference between the two speeds is the “slip / slide” that increases with increasing load. Slip only occurs in an Induction Servo motor. To avoid slip ring can be fitted a sliding / slip ring, and the motor is called “motor slip ring / slip ring motor”.

The following equation can be used to calculate the percentage of slip / slide (Parekh, 2003):

% Slip = (Ns – Nb) / Ns x 100

Where:
Ns = synchronous speed in RPM
Nb = base speed in RPM

The relationship between load, speed and torque
graph torque vs. speed three-phase AC Induction Servo motor with the current set. When the motor (Parekh, 2003):
• Start turns lights are flame high initial currents and low torque (“pull-up torque”).
• Achieve 80% of full speed, the torque is at the highest level (“pull-out torque”) and the current begins to drop.
• At full speed, or synchronous speed, torque and stator currents down to zero.

Construction

The stator of an Induction Servo motor consists of poles carrying supply current to induce a magnetic field that penetrates the rotor. To optimize the distribution of the magnetic field, the windings are distributed in slots around the stator, with the magnetic field having the same number of north and south poles. Induction Servo motors are most commonly run on single-phase or three-phase power, but two-phase motors exist; in theory, Induction Servo motors can have any number of phases. Many single-phase motors having two windings can be viewed as two-phase motors, since a capacitor is used to generate a second power phase 90° from the single-phase supply and feeds it to the second motor winding. Single-phase motors require some mechanism to produce a rotating field on startup. Cage Induction Servo motor rotor’s conductor bars are typically skewed to reduce noise.

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