Planetary gearbox: cost-effective and power saving solution

February 12, 2015 12:59 pm

 In today’s competitive world planetary gearing is becoming more popular, cost and power saving gearings and used in a wide range of applications as alternative to other type of gearboxes.
IntroductionEpicyclic gearing or planetary gearing is a gear system consisting of one or more outer gears, or planet gears, revolving about a central, or sun gear. Typically the planet gears are mounted on a movable arm or carrier which itself may rotate relative to the sun gear. Epicyclic gearing systems also incorporate the use of an outer ring gear or annulus, which meshes with the planet gears. Planetary gears (or epicyclic gears) are typically classified as simple and compound planetary gears.
Simple planetary gears have one sun, one ring, one carrier, and one planet set. Compound planetary gears involve one or more of the following three types of structures: meshed-planet (there are at least two more planets in mesh with each other in each planet train), stepped-planet (there exists a shaft connection between two planets in each planet train), and multi-stage structures (the system contains two or more planet sets). Compared to simple planetary gears, compound planetary gears have the advantages of larger reduction ratio, higher torque-to-weight ratio, and more flexible configurations.
The axes of all gears are usually parallel, but for special cases like pencil sharpeners they can be placed at an angle, introducing elements of bevel gear. Further, the sun, planet carrier and annulus axes are usually coaxial.
RatioOne of the planetary gearsets from its transmission has a ring gear with 72 teeth and a sun gear with 30 teeth. Lots of different gear ratios can be obtained out of this gear set, assures the company.
Why planetary?The efficiency loss in a planetary gear train is 3 per cent per stage. This type of efficiency ensures that a high proportion of the energy being input is transmitted through the gearbox, rather than being wasted on mechanical losses inside the gearbox.
The load in a planetary gear train is shared among multiple planets; therefore torque capability is greatly increased. Formula goes as the more planets in the system, the greater load ability and the higher the torque density.
In addition, the planetary gear train also provides stability due to an even distribution of mass and increased rotational stiffness. Torque applied radially onto the gears of a planetary gear train is transferred radially by the gear, without lateral pressure on the gear teeth. They provide multiple kinematic combinations, purely torsional reactions, and coaxial shafting. Planetary gear trains are compact in size, cost effective and higher ratio can be achieved.
Planetary gear trains provide high power density in comparison to standard parallel axis gear trains. Any type of mounting can be possible, and used in wide range of applications.
LimitationsDisadvantages include high bearing loads, constant lubrication requirements, inaccessibility, design complexity and low thermal rating.
ApplicationsGear trains are used in representing the phases of moon on a watch or clock dial. It is also used for driving a conventional two-disk lunar phase display off the day-of-the-week shaft of the calendar. It also finds applications in sugar industries, chemical industries, cement industries, wind mill, marine industries, material handling, construction machineries, crane applications, mining industries, conveyor, paper mills, robotic drive, automatic transmission vehicles, low backlash drive, electric and hydraulic winches, decanter applications, track drives and  many more
 Authored by –
Shinde MMManager Design – Gear Box Division, Involute Technologies Pvt. Ltd. Alandi – Markal, Dhanore, Tal. Khed, Dist. Pune 412 105Email: mmshinde@involutegear.com, www.involutegear.com