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ELECTROMAGNETIC MACHINES WITH UNCONVENTIONAL MOTION.NEW CONSTRUCTIVE AND FUNCTIONAL SOLLUTIONS.

CODOIU GH. REMUS, “PETRU MAIOR” UNIVERSITY OF TG. MURES

Key words: electric motors with unconventional motion, driving electromagnets, electric step motors,electromagnetic oscillating motors, constructive and functional optimization.

Abstract: Constructive and functional improvements of the electromagnetic oscillating motors aim tothe increase of electromagnetic specific force and it refers to proper electromagnetic oscillating motors(EMOM) and to electromagnetic vibrators (EMV). These improvements are extended also to theelectric step motors (EMS) - linear, rotating - and to the driving electromagnets (DEM).

1. Introduction

The oscillatory behavior of mobile armature (MA) characterizes the most difficult service ofelectromagnetic actuators: electromagnets, step motors, proper oscillating motors.

The use of electromagnets and electric step motors into a reversible rating leads to therealization of electromagnetic motors with oscillating mobile armature. That is why anyconstructive and functional perfecting of electromagnetic oscillating motors (EMOM) will bebeneficial also to the less heavy ratings typical for usual operation of driving electromagnets(DEM) and electric step motors (ESM). Thus the conception and optimization ofelectromagnetic oscillating motors (EMOM), followed by some topological adjustments andby certain electric control peculiarities, will represent also essential improvements ofreciprocating driving electromagnets (RDEM) and of electric step motors (ESM).

The main purpose of the research, concerning the EMOM, RDEM and ESM’s perfecting, willbe oriented to the improvement of the sole technological-economic factor inferiorcomparatively with the competitive solutions (electro-mechanic and hydro-pneumatic ones)namely the specific electromagnetic force (relating to active materials consumption).

Based on the author’s research respecting EMOM’s improvement [1][2] the paper extends theobtained results to other electromagnetic actuators and motors with unconventionalkinematics (RDEM, ESM), nay to continuous, rotary – conventional - ones.

2. EMOM’s constructive and functional improvements

The increase of the specific electromagnetic force refers to proper EMOM - with transversalmagnetic flux (EMOMTF) - and also to electromagnetic vibrators (EMV) - with longitudinalmagnetic flux (EMOMLF). The first category (EMONTF) will be simply named EMOM andthe second EMV.

The most advantageous EMOM / VEM variants [1,2] result to be:

a) EMOM / EMV equipped with DC excitation (windings or permanent magnets);

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b) EMOM / EMV having “bridge” shaped magnetic diagrams – Fig.1 (the magneto-motiveforce sources are placed into branches of the bridge and the variable reluctances are placedinto the diagonals of the bridge);

c) EMOM / EMV having deeply - saturated zones of the iron (“two-sided” mobile armaturesof EMV - Fig.2, or “passing” mobile armatures among the salient poles of “multi-stack”EMOM’s stator - Fig.3, 4).

The presence of the DC excitation ameliorates very much the power factor of the workingwindings (AC supplied).

The “bridge” shape of the magnetic circuit ensures the integral use, on the whole duration offunctional cycle, of the coils copper and of the magnetic circuit’s iron (except the iron of theone ”two-sided” MA - EMV case).

The profound saturation (EMOM), or adequate saturation (EMV) of the MA’s iron ensuresthe increase of the electromagnetic specific force and also determinates the linearization of themathematical model.

Fig. 1. Bridge shaped equivalentmagnetic diagrams (for the two senses of

working alternating current).

Fig. 2. General view (without chassis) ofthe patented electromagnetic vibrator

(FMAX=10kN, 2XM=1mm).

The above-mentioned advantages, of EMV with double “U” type magnetic circuit [3], Fig.2,are reduced because of the presence of powerful magnetic leakage fluxes. These are forced bythe saturating ampere-turns of the DC excitation and AC working coils and they are limitedby the copper’s transversal thickness of the coils which are placed on the stator magneticcolumns.

A constructive solution which eliminates this disadvantage (see Fig.5 a, b, c) has a planeshaped magnetic circuit (like that of equivalent magnetic diagram, Fig.1). The two MA, whichalternatively short-circuit the diagonally placed poles, will result to be longer and thereforethis constructive solution will be used (only) in cases with important inertial mechanic loads.Another EMV constructive solution - having only one excitation coil and one (armature)working coil crossed on a common disc-shaped lamellated magnetic core - is in course ofpatent obtaining.

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Fig. 3. Proposed EMOM-TF; working principle; a) cross section; b) longitudinal section;c) feed and control scheme; d), e) wave form of the currents.

In accordance with the technical solution sketched in Fig.3 the author has achieved a series oforiginal EMOM prototypes destined to linear reciprocating drive of:- car fuel pumps;- piston compressors;- vertical shaper tools for small pieces;and also as oscillo-percussive actuators (electromagnetic hammers) – Fig. 4.

Fig. 4. EMOM-TF based oscillo-percussive actuators (electromagnetic hammers) realizedby the author.

Diminution to a major size of the stator iron and cooper consumption for EMOMS presentedin Fig.3, 4 - tributary of double stator “Marinescu” constructive variant, from which it wasinspired - was carried out by a constructive-topological modification shown in Fig. 6 b), c) – 7b), and 7 a) respectively. Figures 6 b), c) – 7 b) show a constructive alternative having distinct(with regard to the winding cores) longitudinal magnetic yokes which are narrowed in axialdirection. Figure 7 a) presents another constructive alternative with a “H”-shaped coil corewhich also allows the axial distribution of magnetic flux. The improved economical technicalsolution alternative (with regard to active materials consumption) is also in course of patentgetting. With respect to the MA’s iron consumption we must mentioned the integral use of

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that. This fact confers the highest dynamics comparatively with any other constructivesolution.

Fig. 5. Electromagnetic vibrator with longitudinal flux (EMV): a) b) cross and longitudinalsections; c) realized prototype

Concerning the functional principle of above mentioned type of EMV/EMOM (or of RDEMin dynamic ratings) one must underline the formal identity for all cases. Very briefly, withregard to Fig. 3, we will present the essential elements. Electrical supplying of DC excitation,and of AC working windings, with i1 and i2 currents (see their senses shown in Fig. 3a) has asconsequence the preponderant magnetization of the air-gaps corresponding to the verticalsalient poles. Thus the mobile armature will be attracted into maximum magnetic co-energyposition. The opposite semi-period of the i2 alternating current will lead to a rise inpreponderant magnetization of horizontal salient poles air-gaps and thus the MA will beattracted into their position.

Fig. 6. Details of the EMOM-TFmagnetic circuits

Fig. 7. Two EMOM (TF) realized with thehelp of the magnetic circuit components

shown in Fig. 6

Mechanical oscillations frequency of synchronous EMOM/EMV is imposed by electricalfrequency of alternating current, and maximum stroke 2Xm=2τ of EMOM (see Fig. 3b) is, byconstruction, considerably equal to the common step of iron lamination for MA and salientpoles. For EMV the maximum stroke is the momentary air-gaps sum between the twocorresponding stator polar faces.

3. Extension of EMOM/EMV improvement to electric step motors (ESM)

Essential advantage of EMOM with internal MA (see Figs 3,…,6), namely the permanent andintegral use of the MA’s iron, justifies their utilization to oscillating drive of low inertialmechanical loads .

Electromagnetic oscillating motors can be operated as proper oscillo-motors (one step forwardand one step backward) but also as stepper motors (n step forward and n step backward). The

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fundamental idea of this kind of ESM is so that two (or more, in general case m) coaxial-linear/rotary – axially shifted EMOM stators to be mounted so as to collaborate upon a single”multi-stack ” MA (having iron lamination packets uniformly displaced on the same shaftwith 2τ pole pitch ) ; see Fig. 3b for linear constructive alternative with m=2 individualoscillo-motors. The shift – in the motional direction – between two neighboring stators isequal to the τ/m distance.

The cooperation between the two (or in general m) oscillo-motors (EMOM) is realized by anadequate control of the (m individual machines) w2

’ … w2m working windings currents .

Between the two i2’ ,i2

” alternative currents of w2’, w2

” working windings (m=2 case) theremust be a temporal phase displacement of π/2 el.rad.

Fig. 8. Linear step motor with mobile “stator” and fixed MA (support, guidance): a)constructive and mounting details; b) general view.

The resulted step length is τ/2, or τ/4 for positioning by only one stator or simultaneously bythe both stators. The linear stepping speed will be v=2τf .

The more decrease of the ESM step is possible using the well known method of “microstepping”, which is realized by the “micro step” control of the sinusoidal currents flowingthrough complementary working windings.

In the case of high stroke linear ESM it is imposed the “inverted” constructive solution,having a mobile “stator” and a fastened MA (by its consolidation with the help of a motionguidance). See Fig. 8a – presenting the situation prior to fixing mobile stators in a commonchassis, and Fig. 8b - general view of ESM’s mounted state.

The constructive and functional concept of the linear ESM (see Figs. 6, 7 and 9) can beextrapolated to create rotating ESM characterized by a good utilization of the rotor iron. Theprototype represented in Fig. 10 has entire magnetic circuit manufactured of solid iron. Thetechnological reprojection of the magnetic circuit – made up of electrical steel sheets, and alsothe improvement of axial “centering-guiding” system, open new ways of realizing rotatingESM with high dynamic qualities.

Finally it is possible the use of high force electromagnetic vibrators (EMV) , with smallmechanical oscillations (fraction of mm), for obtaining linear electric step motors (ESM),“jogging ” along fixed guides. That is possible by an adequately-controlled intermittentstiffening of the stator and MA with regard to a support. The stiffening is made with help ofthe fastening electromagnets.

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Fig. 9. High force linear ESM prototypewith mobile MA (tool-holder bar):

FMAX=1400 N, vMAX=1 m/s (at f=50 Hz).

Fig. 10. High dynamic qualities rotatingESM prototype: step 3,75˚, max. torque1,2 Nm, max. speed 500 RPM (50 Hz).

The work winding alternating current pulses must be adequately synchronized with thesequential control of the fixing electromagnets.

Thus it occurs the mechanical rectifying of the alternating electromagnetic force whichactuates between the two mobile parts (stator, MA).

This operation mode, as mechanical rectifier, permits two usage possibilities of “jogging”linear ESM:a) stepping displacement of entire EMV along a fixed support ;b) stepping displacement of the tool holder bar with respect to the stator (which is stiffened

to foundation) .

The periodical fastening is realized alternatively either in connection with a static support –case a) - or relating to the tool-holder bar - case b).

Bibliography:

[1] CODOIU, GH.R.: Cercetări cu privire la acţionările cu oscilomotoare cu mişcarerectilinie. Teză de doctorat, Universitatea”Transilvania” din Braşov, 2000.

[2] CODOIU, GH.R.: Maşini şi sisteme electromagnetice de acţionare oscilantă. Sinteză,teorie optimizări. Editura Universităţii “Petru Maior”, Tg. Mureş, 2000.

[3] CODOIU, GH.R.: Vibrator electromagnetic. Brevet România nr. 108133 B1/1994.