AGMA-06FTM04-2006.pdf
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1、06FTM04 Precision Planetary Servo Gearheads by: G.G. Antony, Neugart USA LP and A. Pantelides, mG miniGears North America TECHNICAL PAPER American Gear Manufacturers Association Copyright American Gear Manufacturers Association Provided by IHS under license with AGMA Licensee=Boeing Co/5910770001 No
2、t for Resale, 07/25/2008 02:03:59 MDTNo reproduction or networking permitted without license from IHS -,-,- Precision Planetary Servo Gearheads Gerhard G. Antony, Neugart USA LP and Arthur Pantelides, mG miniGears North America The statements and opinions contained herein are those of the author and
3、 should not be construed as an official action or opinion of the American Gear Manufacturers Association. Abstract Modern automated machineries are increasingly using flexible high dynamic servomotors because of their ability to speed up and flexibly automate complex motions these machineries need t
4、o perform. Planetary gearheads are used frequently inconjunction withservomotors tomatch theinertias, lowerthe motorspeed, boost the torque, and at the same time provide a sturdy mechanical interface for pulleys, cams, drums and other mechanical components. This paper addressing following topics: -m
5、ain reasons why the planetary (epicyclical gear systems) are the preferred choice for ”servo applications” (applications using servo motors); -what influencing the positioning accuracy repeatability of a planetary servo gear; -helical gears in planetary systems; -the rating practices establishing a
6、transparent ”comparability” of different torque listings; -introduction of a simple reliable method to the required gearbox torque rating for a servo-application based on the selected motor toque data. Copyright 2006 American Gear Manufacturers Association 500 Montgomery Street, Suite 350 Alexandria
7、, Virginia, 22314 October, 2006 ISBN: 1-55589-886-6 Copyright American Gear Manufacturers Association Provided by IHS under license with AGMA Licensee=Boeing Co/5910770001 Not for Resale, 07/25/2008 02:03:59 MDTNo reproduction or networking permitted without license from IHS -,-,- 1 Precision Planet
8、ary Servo Gearheads Gerhard G. Antony, PhD, Neugart USA LP with contributions from Arthur Pantelides, mG miniGears North America Because of their versatility as well as their ability to speed-up and automate a wide-range of highly- complex motion sequence programs required in many of todays industri
9、es, computer-controlled, programmable, highly dynamic-capable servo mo- tors areincreasinglybeingusedinmodernmachin- ery required in complex automation applications. Precision planetary gearheads are frequently used in conjunction with such servo motors in order to: balance inertial loading conditio
10、ns seen during fre- quent speed cycling sequences, decrease motor speeds, and boost torque, while at the same time, provide a robust mechanical interface for pulleys, cams, drums, and other mechanical transmission components. This paper shall present a foundation and funda- mental approach for under
11、standing why theplane- tary system is the preferred design choice for servo gearheads; clear up some misconceptions about planetaryservo gearheads;compare ratingpractic- esbyestablishingatransparentcomparabilityofdif- ferenttorquelistings;andintroduceasimpleandre- liable method of determining the re
12、quired gearbox torque rating for a selected servo motor/gearbox application. Main topics covered in the paper shall be: -The planetary (epicyclic) gear system as the “system of choice” for servo gearheads; -The best “balanced” planetary ratio from a torque density point of view; -The gearhead design
13、 influence on positioning- accuracy and repeatability; -Typical dynamic servo applications and servo gearhead torque ratings; -How to establish comparative torque ratings; -Sizing/selection of servo gearheads for match- ing AC servo motorsin automationapplications. 1. The Planetary (Epicyclical) Gea
14、r System as the “System of Choice” for Servo Gearheads Frequentmisconceptionsregardingplanetary gears systems involve backlash:planetary sys- temsareusedforservogearheadsbecause oftheir inherent low backlash; low backlash is the main characteristic requirement for a servo gearboxes; backlash is a me
15、asure of the precision of theplane- tary gearbox. The fact is, fixed-axis, standard, “spur” gear ar- rangement systems can be designed and built just as easily for low backlash requirements. Further- more, low backlash is not an absolute requirement forservo-based automationapplications. Amoder- ate
16、ly-lowbacklashisadvisable(inapplicationswith very high start/stop, forward/reverse cycles)to avoid internal shock loads in the gear mesh. That said, with todays high-resolution motor-feedback devices and associated motion controllersit iseasy to compensate for backlash anytime there is a change in t
17、he rotation or torque-load direction. If,forthe moment,we discountbacklash, thenwhat are the reasons for selecting a more expensive, seeminglymorecomplexplanetarysystemsforser- vo gearheads?What advantages do planetary gears offer? High Torque Density - - Compact Design An important requirement for
18、automation applica- tions is high torque capability in a compact and light package. This high torque density requirement (a high torque/volume or torque/weight ratio) is impor- tant for automation applications with changing high dynamic loads in order to avoid additional system inertia. Depending up
19、on the number of planets, planetary systems distribute the transferred torque through multiple gear mesh points. This means a planetary gear with say three planets can transfer threetimes the torque of a similar sized fixed-axis “standard” spur gear system. Reference Figure 1. Copyright American Gea
20、r Manufacturers Association Provided by IHS under license with AGMA Licensee=Boeing Co/5910770001 Not for Resale, 07/25/2008 02:03:59 MDTNo reproduction or networking permitted without license from IHS -,-,- 2 Fixed axis “standard” gearPlanetary “Epicyclical” gear system Figure 1. Rotational Stiffne
21、ss/Elasticity High rotational stiffness, or minimal elastic windup, is important for applications with elevated position- ing accuracy and repeatability requirements; espe- cially under fluctuating loading conditions. The load distribution unto multiple gear mesh points means theloadissupportedbyNco
22、ntacts(whereN=num- ber of planet gears) increasing the torsional stiff- ness of the gearbox by factor N. This means itcon- siderably lowers the lost motion compared to a similarsizestandardgearbox;andthisiswhatisde- sired. Low Inertia Added inertia results in an additional torque/energy requirement
23、for bothacceleration anddeceleration. The smaller gears in planetary systemresult inlow- er inertia. Compared to a same torque rating stan- dard gearbox, it is a fair approximation to say that the planetary gearbox inertia is smaller by the square of the number of planets. Again, this advan- tageisr
24、ootedinthedistributionor“branching”ofthe load into multiple gear mesh locations. High Speeds Servomotors run at high rpm, hence a servo gear- box must also operate in a reliable manner at high input speeds. For servomotors 3,000 rpm is practi- cally the standard and in fact speeds are constantly inc
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