E AMEICA SOCIEY O MECAICA EGIEES 0G240 4 E. 4 St., Yr, .Y. 00 h St hll nt b rpnbl fr ttnt r pnn dvnd n ppr r .n n t tn f th St r f t vn r Stn, r prntd n It pbltn may ln prntd nl It th ppr I pblhd n n ASME nl. pr r vlbl I fr ASME fr fftn nth ltr th tn. r4d n USA. Copyright © 1990 by ASME vlpnt f Cpt, ht Wht Mnt rn Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1990/79085/V005T14A012/2400068/v005t14a012-90-gt-240.pdf by guest on 29 September 2021 CAWO MEEKS nd ICO SECE ACO — Advnd Cntrl hnl, In. rthrd, Clfrn 24 ASAC (3) advances in miniaturized, integrated circuit, solid state electronics. A novel magnetic bearing design was created that uses permanent magnets to generate the primary magnetic field and attraction These developments have lifted the most significant barriers to electromagnets for stabilization and control. This approach uses a application of magnetic suspension to a multitude of modem machines. geometrically efficient arrangement with a combination of axially flowing permanent magnet field and a circumferentially flowing electromagnetic Magnetic bearings offer the advantages of very long life and high field. This design was compared analytically with other types of magnetic reliability by (1) the elimination of wear out and fatigue failure modes and, bearing designs. The design comparison showed the new design to be 50% (2) elimination of a lubrication supply and circulation system, and (3) by lighter weight and 50% lower in power consumption than all providing a way to avoid the single point failure limitation of conventional electromagnetic designs of equivalent performance. A demonstration bearing designs. Additionally, the very low rotational axis torques of model of this new approach built and tested for performance at low magnetic bearings make possible lower bearing power loss, higher shaft speeds. This test model successfully demonstrated the feasibility of accuracy pointing systems, high resolution instruments, and improved this new approach. rotor dynamics for pumps. Future pumps and turbine engines may be operated at higher efficiencies because the large clearances typically used in magnetic bearings, and elimination of operating temperature limitations of liquid lubricants, may allow the bearings to survive high and low nltr temperatures associated with high efficiency thermodynamic cycles and cryogenic fluid pumping. A = pl f r ( 2) = flx dnt (G The one serious disadvantage of magnetic bearings is they are b = tr vrbl = 2 significantly larger and heavier than their rolling element bearing = fr (tn counterparts. The purpose of this work was to address methods for = rn p ( reducing the size and weight of magnetic bearings. The improvements = v lnth f nt ndtn vrtn suggested are compared with the known state-of-the-art in prior magnetic = prblt f fr p bearing design. .0 ACKGOU 2.0 A COMAISO SUY O ESIG AOACES Magnetic levitation has been a topic of serious engineering interest for over 150 years. A literature survey by the author revealed that during the A brief comparison study was made to review the state-of-the-art in lt 2 r vr 0 dffrnt nt pnn t hv bn magnetic bearings and to determine the optimum design approach for high developed and tested. However, the realization of the potential advantages stiffness, high load applications such as pumps, turbines, and pointing and of magnetic bearings escaped scientists and designers until three tracking gimbals. Both active and passive (semi-passive) design schemes important, relatively recent, developments: were studied and the relative merits of various design approaches were compared. (1) advances in high energy product permanent magnet materials (over 30 X 10 6 Gauss-Oersted The approach used was to establish a set of requirements typical of small energy product); pumps and to design four types of magnetic bearings to meet the requirements and to compare the resulting designs for size, weight and (2) the development of high-saturation flux ferromagnetic power consumption. Magnetic bearing design is, of course, a highly materials, and; heuristic process and there are always trade-offs between size, weight and rntd t th G rbn nd Arnn Cnr nd Exptn—n 4, 0—rl, l power consumption. However, by using the same materials, same coil A = wave length of magnetic induction variation power density, and same magnetic materials design limits (saturation flux, coercive strength, and magnetic induction), a reasonably objective The concept of Figure 2-1c uses the principle of a magnetic circuit comparison of relative merits of various design approaches can be made. always seeking a geometry that minimizes the reluctance of the ferromagnetic circuit to develop forces that align or i.e., maintain 2. rnpl f Oprtn ndn th th d f th rtnlr rtn lnt pl faces. In the configuration shown, radial stability is attained, but at the The state-of-the-art review illustrated that many different types of expense of axial instability that must be overcome with active control. magnetic bearing designs have been constructed and tested. Although there Several designs using the "reluctance centering" princi ple are reported in are a multitude of different magnetic bearing design approaches, they are the literature for spacecraft attitude control wheels (6,7,8,9,10,11) all simply combinations of three principles of operation. Figure 2-1 illustrates the three magnetic principles used in all practical magnetic The force per unit area, or "magnetic pressure", of reluctance Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1990/79085/V005T14A012/2400068/v005t14a012-90-gt-240.pdf by guest on 29 September 2021 bearings constructed to date. centering magnetic bearings in the passive plane is: (from reference 11) Q B2 COMMES COCE A = [2] OSIUY SAOS ^ SOS YA 0 ACIEY COOE EOUIES 2 SEOS O EGEE O EEOM SAY O EQUIES EECICA OWE O where: Q is a geometric constant that varies from a theoretical MA MAGEIC ES maximum of 0.33 to less than 0.1 O AGE COS EQUIE O OUCE MAGEIC ES A 0 cons) n• AY•UE The magnetic gaps of designs 2a and 2c can, of course, be energized by .d l .n,ln 0 passive permanent magnets or electromagnet coils. The use of permanent a) Attrtn letrnt magnets to energize the air gaps, and electromagnets for control, yields some unique characteristics that are not apparent just from examination of [4YEM YAUYE MOS 0 AIAY SAEAIAY `. USAE (EQUIES OYOY I SEO the characteristics of elements 2-la, and c. The use of permanent magnet 0 AIA COUEAU IS AIAY energization of the bearing air gaps makes possible: SAEAIAY USAE 0 IC O OUCE UE O OMOGEEI ES MAGE * less power consumption for the same load capacity or same MAEIAS tffn, O OUCSIY OEMS WI MAGES b pln prnnt nt * a meta-stable system that can be operated at almost zero control COO . power when external disturbance loads are zero. 0 AIAY SAE * a linear force vs control current system which can lead to 0 AIAY USAE considerable simplification in the servo control system design. 0 EQUIES OY I SEO COO A new, fourth, concept, shown below in Figure 3-1, was developed by adding permanent magnets to energize the radial working air gap of the all electromagnetic, actively controlled bearing. This design has several ltn ntrn advantages over the all electromagnetic bearing approach as will be illustrated below. r 2. Mnt rn n rnpl. 2.2 lt f n Cnpt Cprn Std Attraction electroma nets, as shown in Figure 2-la, have been used in a variety of designs ( ,2,) with from one to five active servo controls Four candidate design were created from the concepts of Figure 2-1 (i.e., X, Y, Z, and cross coupling control for &x, ty and &z). for comparison with a new, permanent magnet bias concept. The designs were developed analytically using the common design criteria of Table The force per unit air gap area, or "magnetic pressure" (F/A), of 2. electromagnetic attraction bearings is: (from reference 4) I PARAMETER VALUE B2 A — [2] Radial load .................................................................356 N (80 pounds ) 2 Moment load ..........................................................18.0 N-M (160 in-lb) Shaft air gap diameter ......................................................3.0 (1.187 inch) The use of permanent magnets in repulsion, as illustrated in Figure Radial stiffness .....................................4.38 x 104 N/cm (2.5 x 104 lb/in) 2-lb, was originally conceived of by Backers(5) and yields a bearing that is Ferromagnetic material magnetic saturation limit ..............10,000 Gauss radially stable using passive magnets, however, it is axially unstable and Coil temperature rise .......................................................................70 0 C requires at least one degree of active control. Permanent magnet energy product ...................30 x 106 Gauss-Oersteds The force per unit air gap area, or "magnetic pressure", of bl 2. n rtr nd trl prprt d fr permanent magnet repulsion bearings is: (from reference 5) prn td B2 Figure 2-1 is a compilation of the results of this design comparison. A b - b [22] 4 where: b = 2ag/A ESIG COCE I ^ W Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1990/79085/V005T14A012/2400068/v005t14a012-90-gt-240.pdf by guest on 29 September 2021 EMAE MAGE AIA EUSIO EUCACE CEEIG A EECOMAGEIC IAS ACIE COO ACIE AIA SAIIAIO AIA AIA COMIAIO AIA AAMEE AIA ACUAO(S EAIG A AIA EAIG EAIG (OA ) OUSIE IAMEE ( 6. 2 h .8 8.8 (.46 In. 6. (. n. ) AI GA IAMEE ( .0(.8 In. .0 .0 .0 (.8 Irt .0 (.8 Irt ) EG 22 (4.8 In. 0. 22 8.8 . In. 22 (4.8 In.) MAIMUM OCE OUU 6 80 b.