SE452508B

SE452508B - Load bearing beam

Info

Publication number: SE452508B
Application number: SE8301527A
Authority: SE
Inventors: K Blomkvist; J O Nordvall
Original assignee: Asea Ab
Priority date: 1983-03-21
Filing date: 1983-03-21
Publication date: 1987-11-30
Also published as: SE8301527L; SE8301527D0

Abstract

The magnetic - elastic power transmitter comprises a load body, and at least on one measurement surface (2) is of magnetic material. On this surface are two parallelogram shaped areas (7,8) with parallel tracks. On the one area, the track is parallel to the main tension arising from the body being loaded, and on the other area, the track is at right-angles to the former. Both areas are accurately disposed and at a specific distance (9) relatively to one another. An E-shaped magnet core (20) is attached to the measurement surface with its central leg between and its outer leg outside the areas. A magnet flow is produced through the measurement surface with magnetising windings (21,23) on the outer legs. The central leg has a winding (22) for probing the differential flow through the central leg arising from the effect of load on the reluctance in the tracked areas.

Description

20 25 30 35 452 508 Balken i fig 1 är utförd med en urfräsning 2 på vardera sidan ungefär mitt på balkens längd, varigenom dels skjuvspänningen höjs i detta snitt, dels mät- ytor och tillhörande E-kärnor lätt kan skyddas. Urfräsningarnas bottenytor är vid omagnetísk balk belagda med ett magnetiskt ytskikt 21 vilket visas i fig 1A-A. 20 25 30 35 452 508 The beam in Fig. 1 is made with a milling cutter 2 on each side approximately in the middle of the length of the beam, whereby partly the shear stress is increased in this section, partly measuring surfaces and associated E-cores can be easily protected. The bottom surfaces of the millings are coated on a non-magnetic beam with a magnetic surface layer 21, which is shown in Figs. 1A-A.

En förstoring av en urfräsning med bottenytan som mätyta visas i fig 2. Två i huvudsak parallellogramformade områden 7 och 8 med relativt tätt frästa spår med bredden ungefär lika med djupet och ungefär lika med halva delningen har utformats med ett sådant område på vardera sidan av ett plant område 9 Omkring balkens neutralplan 0. I det ena området skall spåren vara i huvudsak paral- lella med den ena huvudspänningsriktningen, o+ i fig 1, i det andra området i huvudsak parallella med den andra huvudspänningsriktningen, o'. I närheten av balkens neutralplan är skjuvspänningen dominerande med huvudspänningarna i riktningarna i i N50 i förhållande till neutralplanet, och spåren har därför i huvudsak dessa riktningar. I fig 2 har emellertid spårens vinklar mot neutral- linjen betecknats med d respektive 8 och områdenas medelavstånd från neutral- - linjen har beteoknats med X respektive Y. I beroende av det magnetiska mate- rialets egenskaper och magnetiseringens styrka kan a ochß respektive X och Y väljas så i förhållande till varandra att optimal linearitet uppnås. Den teo- retiska grunden för reduktion av linearitetsfelet hos magnetoelastiska givare genom kombination av signaler i lämpliga proportioner från element med drag- spänning respektive tryckspänning är känd genom svenska patentet #05 766, även om förfaringssättet här är helt annorlunda.An enlargement of a milling with the bottom surface as the measuring surface is shown in Fig. 2. Two substantially parallelogram-shaped areas 7 and 8 with relatively densely milled grooves with the width approximately equal to the depth and approximately equal to half the pitch have been formed with such an area on each side of a flat area 9 Around the neutral plane 0 of the beam. In one area the grooves shall be substantially parallel to one main voltage direction, o + in Fig. 1, in the other area substantially parallel to the other main voltage direction, o '. In the vicinity of the neutral plane of the beam, the shear stress is dominant with the main stresses in the directions i in N50 in relation to the neutral plane, and the grooves therefore have mainly these directions. In Fig. 2, however, the angles of the grooves towards the neutral line have been denoted by d and 8, respectively, and the mean distances of the regions from the neutral line have been denoted by X and Y, respectively. Depending on the properties of the magnetic material and the strength of the magnetization, are chosen in relation to each other so that optimal linearity is achieved. The theoretical basis for reducing the linearity error of magnetoelastic sensors by combining signals in suitable proportions from elements with tensile stress and compressive stress, respectively, is known from Swedish patent # 05 766, although the procedure here is completely different.

Som tidigare nämnts har spåren ungefär samma bredd och djup, och de kvarstå- ende åsarna har ungefär nämnda bredd och följaktligen ungefär kvadratiskt tvärsnitt. En spänning vinkelrätt mot åsarna är därför praktiskt taget elimi- nerad på åsarnas toppytor, varför spänningen här liksom på åsarnas sidoytor nästan enbart utgöres av drag- eller tryckspänning i åsarnas riktning.As previously mentioned, the grooves have approximately the same width and depth, and the remaining ridges have approximately the said width and consequently approximately a square cross-section. A stress perpendicular to the ridges is therefore practically eliminated on the top surfaces of the ridges, which is why the tension here as well as on the side surfaces of the ridges consists almost exclusively of tensile or compressive stress in the direction of the ridges.

Om nu balken 1 påverkas av kraften F som i fig 1, kommer åsarnas ytor i om- råde 7 enligt fig 2 att väsentligen påverkas av dragspänningen o+, varvid deras permeabilitet ökar i dragriktningen vid material med positiv magneto- striktion. På motsvarande sätt kommer åsarnas ytor i område 8 enligt fig 1 att väsentligt påverkas av tryckspänningen o-, varvid deras permeabilitet minskar i tryckriktningen. Med den i fig 3 och fig U visade E-formade magnet- kärnan 20, med de från växelströmskällan 24 matade magnetiseringslindningarna 21 och 23, alstras ett magnetflöde, som passerar genom områdena 7 och 8 och 15 20 25 3 452 508 det mellanliggande området 9. Vid obelastad balk är reluktanserna lika i områdena 7 och 8, och något obalansflöde erhålles då ej genom mittbenet på den E-formade kärnan 20 och ej heller någon spänning i mätlindningen 22 på mittbenet. Vid belastad balk minskar reluktansen i området 7 och ökar 1 om- rådet 8, varvid ett mot kraften 1 huvudsak proportionellt obalansflöde er- hålles i mittbenet och en motsvarande signalspänning i den omgivande lind- ningen 22, medförande utslag på instrumentet 25. Som tidigare nämnts kan linearitetsfelen i stort sett elimineras genom lämpligt val av vinklarna a och B samt avstånden X och Y i fig 2.If the beam 1 is now affected by the force F as in Fig. 1, the surfaces of the ridges in area 7 according to Fig. 2 will be substantially affected by the tensile stress o +, their permeability increasing in the pulling direction in materials with positive magnetostriction. Correspondingly, the surfaces of the ridges in area 8 according to Fig. 1 will be substantially affected by the compressive stress o-, whereby their permeability decreases in the pressure direction. With the E-shaped magnetic core 20 shown in Figs. 3 and U, with the magnetizing windings 21 and 23 fed from the AC source 24, a magnetic flux is generated which passes through the regions 7 and 8 and the intermediate region 9. With unloaded beam, the reluctances are equal in the areas 7 and 8, and no imbalance flow is then obtained through the center leg of the E-shaped core 20 nor any voltage in the measuring winding 22 on the middle leg. When the beam is loaded, the reluctance in the area 7 decreases and increases in the area 8, whereby a substantially unbalanced flow towards the force 1 is obtained in the middle leg and a corresponding signal voltage in the surrounding winding 22, causing a rash on the instrument 25. As previously mentioned the linearity errors can be largely eliminated by appropriate selection of the angles a and B as well as the distances X and Y in Fig. 2.

I fig 5 visas en alternativ utformning av de magnetoelastiska elementen som kan vara förmånlig vid omagnetisk belastningskropp med magnetisk beläggning på mätytan. Med exempelvis etsning eller annan bearbetningsmetod har man dels framställt de önskade spårbilderna 7 och 8, dels tagit bort allt magne- tiskt material utom områdena med spår och de tre områdena 9, 10 och 11 mellan och utanför dessa för kontakt med den E-formade kärnan. Härigenom elimineras allt läckflöde på sidan av de mätande områdena, varigenom den erforderliga magnetiseringseffekten minskas.Fig. 5 shows an alternative design of the magnetoelastic elements which can be advantageous in the case of a non-magnetic load body with a magnetic coating on the measuring surface. With, for example, etching or another processing method, the desired groove images 7 and 8 have been produced, and all magnetic material except the areas with grooves and the three areas 9, 10 and 11 between and outside them for contact with the E-shaped core have been removed. . This eliminates all leakage flux on the side of the measuring areas, thereby reducing the required excitation effect.

Belastningskroppen kan givetvis utföras på många olika sätt. Utförandet som en i ena änden fast inspänd balk enligt fig 1 är endast anfört som exempel.The load body can of course be made in many different ways. The design as a beam fixed at one end according to Fig. 1 is given only as an example.

En annan mycket användbar form på belastningskroppen är en fritt upplagd balk med utpräglade upplagsytor i ändarna och en utpräglad kraftangreppsyta på mitten. Balken utformas med fyra skjuvpåkänningshöjande urfräsningar, två på var sin sida av balken placerade ungefär mitt emellan kraftangrepps- ytan och upplagsytorna. I samtliga urfräsningar utformas ovan beskrivna om- råden med spår och förses med E-formade kärnor med lindningar. Summan av de fyra mätsignalerna utgör då ett mått på den anbragta lasten.Another very useful shape of the load body is a freely supported beam with pronounced bearing surfaces at the ends and a pronounced force attack surface in the middle. The beam is designed with four shear stress-increasing cut-outs, two on each side of the beam placed approximately midway between the force-attack surface and the bearing surfaces. In all millings, the areas described above are designed with grooves and provided with E-shaped cores with windings. The sum of the four measurement signals then constitutes a measure of the applied load.

Claims

452 508 PATENT REQUIREMENTS

A magnetoelastic force transmitter consisting of a load body (1), which is made of magnetic material (21) at least on a measuring surface (2), characterized in that the load body on said measuring surface in two substantially parallelogram-shaped areas (7 , 8) is formed with parallel grooves, which in one area are substantially parallel to a main voltage occurring during loading of the load body and in the other area are substantially parallel to a corresponding second main voltage, the two areas being arranged substantially mirror-symmetrically in relation to and at some distance from each other, and that an E-shaped magnetic core (20) is attached to the measuring surface with the middle leg between and the outer legs outside said areas, and that alternating current-supplied windings (21, 23) are arranged on the outer legs for generating a magnetic flux. through said areas and the intermediate area and on the middle leg a winding (22) is arranged for sensing the difference flow through the middle leg, which by the effect of said main voltages on the reluctance in said grooved areas.

2. A magnetoelastic force transducer according to claim 1, characterized in that the load body (1) is designed as a beam fixed at one end with a neutral plane (0), loaded near the free end, and near the center of the beam on both sides if the beam is formed with shear stress-raising cut-outs (2) in the bottom surfaces of which the said groove is formed.

3. A magnetoelastic force transducer according to claim 1, characterized in that the load body is designed as a freely supported beam with a neutral plane (0) and with pronounced bearing surfaces at the ends and a pronounced force attack surface in the middle and formed with four shear stresses. raising cut-outs, two on each side of the beam, placed approximately midway between the force attack surface and the bearing surfaces, and with said grooves formed in the bottom of the cut-outs.

4. A magnetoelastic force transducer according to claims 1-3, characterized in that on each measuring surface the grooves in one area deviate (u) more from the main voltage in question than the grooves in the other area deviate (B) from the corresponding main voltage, and that an area with grooves (X) is further from the neutral plane than the other area (Y).