DEVICE FOR MEASURING AND/OR REGISTERING MECHANICAL FORCES, AND A METHOD OF MANUFACTURING A MEASURING BODY FOR USE IN THE DEVICE

Abstract: The invention relates to a device for measuring and/or registering mechanical forces (F) with the aid of a measuring body (1) which can be influenced by the force to be measured. The measuring body is configured with a web (11) in which transverse forces and/or shear stresses occurrent in the web and dependent on the value of the force, can be evaluated with the aid of a magnetizing winding (3) and a sensing winding (4). The web (11) has a limited extension in relation to the measuring body (1) and has a limited thickness (t) such that evaluation of occurrent forces and/or stresses in accordance with magnetoelastic principles will take place substantially in or in the immediate vicinity of a neutral plane (23) located on the measuring body. The invention also relates to a method for the manufacture of such a measuring body.

Description: TITLE OF THE INVENTION: Device for measuring and/or registering mechani¬ cal forces . and a method of manufacturing a measuring body for use in the device. TECHNICAL FIELD The present invention relates primarily to a device which is intended for measuring and/or registering mechanical forces and which comprises a measuring body capable of being influenced by the force to be measured, said measuring body being configured with a thin web which is oriented in the direction of said force and in which transverse forces or shear forces occurring in the web can be evaluated with the aid of a magnetizing coil and a sensing coil. Devices of this kind are called shear force transducers and are based on magnetoelastic effects and principles. Consequently, such devices are also referred to as magnetoelastic force transducers or load cells. The present invention thus relates primarily to a device which utilizes magnetoelastic principles and with which these principles are applied to shear force or trans¬ verse force transducers with which shear forces genera- ted by a force applied to a beam or a measuring body for measuring purposes and occurrent in a thin web provided in the central part of the measuring body can be evalu¬ ated. It is known that the shear forces (N/mm 2 ) which occur in each measuring body are in a precise, determined rela¬ tionship with the transverse forces (N) occurring in said body, which fact should be borne in mind in the following description when only one of these magnitudes is mentioned. The invention also relates to a method of producing an effective measuring body for use in said device«, BACKGROUND PRIOR ART Various different kinds of devices intended for measur¬ ing and/or registering mechanical forces and using different principles herefor are known to the art. In order for a device of this kind to achieve any marked technical-economical significance, it is most essential that the device is highly sensitive to the force to be registered in relation to its sensitivity to disturbance forces of different kinds, such as displacement at the load contact point, laterally acting forces, torque, etc. Of those devices previously known, mention is made here refer solely to that category of device in which a beam, a measuring body, is firmly mounted at one end on a support and in which the free end of the body is loaded with the force to be measured and registered. This will not exclude, however, the alternative in which a beam freely mounted at its ends is loaded centrally with the force to be measured and which in other res- pects is configured for evaluating occurrent shear forces or transverse forces in those regions located between respective ends of the beam and beneath the force application point. The measuring body is provided between the force appli¬ cation point and its anchorage point, preferably cen¬ trally of these two points, with measuring recesses which are positioned diametrically opposite one another on both sides of the measuring body, such as to define between said recesses a central web portion from which transverse forces or, alternatively, shear stresses occurring in the web and being commensurate with the value of the force applied are evaluated. It is known to the art to evaluate these shear stresses with the aid of principles other than those on which the invention is based, by affixing strain gauge foil to the web. Examples of this principle are illustrated and described in the U.S. Patent No. 4, 237, 727, U.K. Patent No. 2, 129, 949 and European Patent 0, 010, 860. It is also known that a force transducer which operates in accordance with the magnetoelastic principle and which utilizes the so-called shear beam technique of the aforementioned kind can be dimensioned with shear stress elevating recesses which extend inwardly from the sides of the body, so as to obtain a sufficiently high level of shear stresses in relation to disturbing mechanical stresses deriving from displacement of the load applica¬ tion point, from laterally acting forces and torque. Thus, it has been considered suitable to dimension the cross-section through the measuring recess in a manner such that the occurrent transverse force (or shear stresses), i.e. the force to be measured, is supported by the residual material located between the measuring recesses, so as to obtain large shear stresses in this region, whereas flexural forces, torque and lateral forces, on the other hand, are taken up by the material located externally of said recesses, and therewith ensure that only small disturbance stresses will occur in the bottom surfaces, or web, of the measuring reces¬ ses. It has also been established that when these transverse forces are evaluated with the aid of a strain gauge, i.e. filament foil firmly adherred to the web, it is preferable to dimension the measuring body and to adapt the shape and thickness of the web such that maximum shear stresses in the order of 200 N/mm 2 will occur in the web at maximum load. In order to enable such high shear stresses to be achieved, it has been necessary to give the web located between the recesses a thickness in the order of 6 mm in the case of, for instance, a 5 tonne load cell, in order to provide a load cell whose physical dimensions are suitable for practical use. As before mentioned, it is known to measure the trans¬ verse forces occurring on transverse loaded beam-like measuring bodies, with the aid of magnetoelastic ef¬ fects. An exemplifying embodiment of this method is described in Swedish Published Specification 452 508, in which the bottom surfaces or the web of the shear-force elevating recesses are utilized with the aid of sep¬ arate, external devices, E-cores, for registering the stresses generated by the transverse force. That which has previously been mentioned with regard to permitting substantially the whole of the load to be carried by the web located between the measuring re¬ cesses, such as to suppress the effect of disturbance stresses originating from undesirable forces, also applies in the case of this particular application. This device, however, suffers serious drawbacks connec¬ ted with the non-linear magnetoelastic principles ap¬ plied. These limitations originate partly from the re- quirement of shear stresses as low as 50 N/mm 2 in order to obtain the desired low linearity deviation, and partly because this method of measuring stress with the aid of an air gap between the measuring surface and the E-core makes it extremely difficult to achieve the same degree of sensitivity in registration on both sides of the measuring body. In comparison with the aforementioned 5 tonne load cell, the material thickness between the measuring recesses needs to be increased by a factor of four, from 6 to 24 mm, if conventional physical values and dimensioning rules for the load cell are to be achieved. Furthermore, the difficulties encountered in obtaining the same degree of registration sensitivity in the two mutually opposite measuring recesses on the measuring body render it impossible to fully compensate for mecha¬ nical disturbance stresses engendered by lateral forces, torque, etc., which cannot be fully compensated for, particularly when applying the linearity compensation method proposed in Published Specification 452 508 (compare at length the description of this compensating method in Swedish patent specification 311 573). The situation is further impaired due to the necessity of increasing the thickness of the material located between the measuring recesses by a factor of four (4) , in accordance with the aforegoing, since a large thick- ness will impair the relationship between those shear stresses to be measured and the occurrent disturbance stresses, because undesirable force components will influence the loading surfaces of the measuring body, not only by lowering the shear stresses but also by increasing the level of disturbance stresses. A further example of a known method of measuring occur¬ rent shear forces on transverse-loaded beam-like measur¬ ing bodies with the aid of magnetoelastic techniques is described and illustrated in the Swedish Patent Specifi¬ cation 326 844, according to which the measuring body is configured from plates which form a core in the form of a beam which is anchored at one end and subjected to transverse loads at its other end, and in which winding accommodating holes are located around the neutral plane of the beam for evaluating shear stresses generated by the force applied. One serious limitation with a device of this kind, however, is that it is not sufficiently strong mechani¬ cally to withstand the lateral forces and torsion forces to which it is subjected, without the lamination frac¬ turing, primarily due to the configuration of the lami¬ nation. Consequently, in order to enable the device to be used in practice, it must be incorporated in an outer casing which is intended to relieve the laminate of occurring, undesirable force components. In addition to this is the inadequate suppression of the effect of disturbance stresses originating from torsional forces and lateral forces, which is explained by the fact that the windings for registering the shear stresses do not only pass around the measuring body at locations close to the neutral plane of the lateral forces acting on the body, but also around material located on the sides of the measuring body. As a result, it is necessary to compensate a large positive registration contribution acting from one side of the measuring body and caused, e.g., by the lateral force, with an equally as large negative contribution from the other side of the measur- ing body. This cannot be effected in practice, because, inter alia, different material characteristics of the lamination plates cause the responsiveness in registra¬ tion of the stresses on one side to deviate from the responsiveness in registration on the other side, which in turn results in incomplete compensation. By way of further example of load cells and measuring bodies which utilize the magnetoelastic principle and in which the magnetizing coil and sensing coil are carried in four holes, reference is made to the description and drawings of Swedish Patent Specification 391 032, ac¬ cording to which the measuring body is positioned be¬ tween two parallel-controlled, force transmission parts. It is generally known that measuring bodies, so-called shear beam transducers, of the afore-described kind, afford important advantages, insomuch that they have a - simple mechanical construction, can be readily installed and are capable of measuring and/or registering accur- ately mechanical forces free from the influence of irrelevant force components, and it is also known that the solution to the problem of evaluating relevant shear forces on the basis of strain gauge techniques are rela¬ tively more expensive, due to the requirements placed by a thin foil strain gauge on its assembly, installation and protection against external influences. It is also known that a magnetoelastic transducer has the advantage of being of simple mechanical structure, inter alia with respect to fitting of the windings, requires little external protection, is robust, can withstand environmental conditions and can be over¬ loaded. Finally, reference is made to the device illustrated and described in the prior German published specification 22 63 646, relating to the evaluation of an occurrent force with the aid of magnetoelastic principles. According to this German specification, a separate measuring core can be inserted in a through-passing conical hole and the magnetoelastic properties of the core utilized to evaluate occurrent force loads. The measuring core is pressed into the conical hole and abuts the walls thereof under tension engendered by four shoulders on the measuring core or on the wall of the hole. This pre-loads the measuring core before any load is placed on the measuring body. The value of this pre- load may vary and it is consequently necessary to cal¬ ibrate each individual device in respect of the pre¬ load. When a load is applied, this abutment of the measuring core may be poor and/or icroslips may occur at the shoulder abutment surfaces, which can jeopardise the accuracy of the measuring result. In those instances when the measuring core is manufactured in the form of an adhesively bonded sheet-metal pack and is pressed into a conical hole, the costs of manufacture are very high. In addition, a high degree of accuracy is required with respect to the measuring core, uniform conical and hole dimensions and configuration, all of which imply a serious risk of rejection and manufacturing faults. Furthermore, a conical measuring core is difficult to position exactly, with respect to the depth of a conical hole and can be subjected to lateral forces and torsion forces therein. SUMMARY OF ThE INVENTION TECHNICAL PROBLEMS The object of the present invention is primarily to provide a force transducer which is highly insensitive to lateral forces and torsion forces but which will nevertheless afford the advantages obtained with shear force techniques, as described in the aforegoing, com- bined with the structural simplicity, robustness and environmental durability of the magnetoelastic techni¬ que. When considering the present state of the art as descri- bed above, it will be seen that a technical problem resides in the ability to provide a technical solution which is not encumbered with the previously discussed limitations of known devices and with devices which measure magnetoelastically the shear stresses or trans- verse forces induced in a beam-like transversally loaded measuring body by the force applied to the beam. To this end, the measuring body should preferably comprise a suitable, solid material and recesses should preferably be formed, for instance, between the anchorage point of the body and its free end in a manner to form at the center of gravity of the cross-section a web-like con¬ figuration which is thin in relation to the width of the measuring body, said shear forces being registered at said gravitational centre point, while forming suitable holes in the web for accommodating a magnetizing coil and a sensing coil in a manner such that registration of the stresses induced by said load will take place sub¬ stantially on, or immediately in the vicinity of the neutral plane of lateral forces acting oh the measuring body. This will provide the requisite measuring accuracy and, at the same time, the greatest possible in- sensitivity to lateral forces and torsion forces. However, the provision, for instance, of two holes in the web of the measuring body will result in the occur¬ rence of significantly higher mechanical stresses and strains in the material located between the holes where the stresses are registered, due to known stress concen¬ trations which are to be expected around each hole when a load is applied to the measuring body. When this is taken into account and attention is also paid to the fact that the non-linear magnetoelastic transducers employed require stresses as low as 50-100 N/mm 2 in order to achieve the low linearity deviation desired, it will be realised that the load on the web must be reduced considerably, preferably from 5 to 10 times. Compared with the previously mentioned example of a 5 tonne load cell having a web thickness of 6 mm, this would mean that the magnetoelastic load cell would have a volume greater than 5-10 times that of the cells based on the strain gauge technique, which cannot be accepted in practice. Furthermore, the web cannot be made appreciably thicker than 6 mm, which excludes the possi- bilities of using a load cell in the higher load re- gions, for instance regions from 1-50 tonnes. Consequently, load cells which work in accordance with magnetoelastic principles and based on the shear beam technique, where the web is dimensioned to support sub¬ stantially the whole of the load, can only be used for very small loads. When studying the state of the prior art as described above, it will be seen that a qualified technical pro¬ blem is one of realizing that a load transducer which works in accordance with magnetoelastic principles can be given a simpler configuration, resulting in a more accurate result, when the web is made of the same ma- terial as the actual measuring body itself, therewith creating conditions for mutually the same metallurgical states in both the web and the measuring body. It will also be seen that another technical problem is one of realizing that in order to satisfy the aforesaid desideratum, it is necessary to connect the web metal- lurgically to the measuring body (integrated or with a metallic or atomic connection or bond) . The fact that it is possible, in this way, to eliminate drawbacks associated with microslips, which occur in all friction joints, is a highly qualified, technical reali¬ zation. It will also be seen that a further technical problem resides in the provision of a device for measuring and/or registering mechanical forces, based on the magnetoelastic principle, in which the force acting on the measuring body is predominently supported by the actual measuring beam itself, instead of being carried by the thin web formed in said body, therewith enabling the measuring body used to be made very rigid and there¬ with afford small shear stresses in the web, which small shear stresses can be evaluated readily and accu- rately with the application of magnetoelastic princi¬ ples, without the troublesome influence of bending forces and similar disturbance forces. It will also be seen that a technical problem resides in the ability of providing a measuring body whose outer dimensions primarily determine the measuring area in question, i.e. a larger measuring area, larger measuring body dimensions, without needing to change the size, thickness and shape of the web or of the windings used. It will also be understood that a further technical problem is one of being able to choose a web thickness which is of such small value as to render negligible disturbance stresses originating from lateral forces and torsion forces, but of su _officient thickness to enable changes in transversal force or shear stress to be evaluated in accordance with magnetoelastic principles. A further technical problem is one of being able to provide a simple measuring body which utilizes magneto¬ elastic principles and which is suitable for use with large forces, for instances with forces ranging from one to fifty tonnes. A further technical problem resides in the provision of a measuring body which is torsionally rigid against lateral forces, bending forces and torsional forces, and therewith insensitive to disturbances originating from such forces. It will also be understood that a technical problem also resides in the ability of dimensioning the measuring recess on both sides of the measuring body in a manner suitable for application of the magnetoelastic techni¬ que, such as to obtain the best possible relationship between the sensitivity of registration of the force- induced shear stresses in the web and the sensitivity to undesirable tension forces originating from irrelevant force components acting on the measuring body. Another technical problem is one of realizing that two large and two smaller holes shall be incorporated in the web, of which the larger holes are intended to accommo¬ date the magnetizing winding, and that the centres shall be positioned in a neutral plane on the measuring body, or in the immediate vicinity of said neutral plane, whereas the two smaller holes shall be placed at a distance from and on both sides of said neutral plane. This hole arrangement will eliminate still further the effect of undesirable mechanical stresses on the regis¬ tration of the force. It will also be seen that a qualified technical problem encountered with a measuring body of the aforesaid kind and operating in accordance with magnetoelastic princi¬ ples is one of realizing that in order to obtain an accurate, robust and simple measuring device, the web extension shall have a given smallest ratio to the vertical extension of the measuring body. A further technical problem is one of realizing that temperature compensation can be effected by inserting through the two larger holes intended for the magneti- zing coil a short-circuited winding having a pre-deter- mined number of turns. Finally, it will be seen that a technical problem re¬ sides in the provision of a simple method for the manu- facture of a measuring body which successfully solves one or more of the aforesaid technical problems and realizations. SOLUTION For the purpose of solving one more of the aforesaid technical problems and for attempting to eliminate, or at least to reduce the drawbacks associated with prior art techniques, there is proposed a device according to claims 1-14 and a method for the manufacture of a mea¬ suring body associated with said device in accordance with claims 15-21. Thus, with the aim of solving one or more of the afore- mentioned technical problems, the present invention provides primarily a device for measuring and/or regis¬ tering mechanical forces, which comprises a measuring body capable of being influenced by the force to be measured, said measuring body being provided on respec- tive opposite sides thereof with two measuring recesses which form therebetween a web in which transverse forces or shear stresses occurring in said web and contingent on the size of the force applied can be evaluated with the aid of magnetoelastic principles. According to the present invention, the measuring re¬ cesses are formed in a manner to leave therebetween a thin web centrally in the measuring body, said web being provided with a magnetizing winding and a sensor winding which are surrounded by holes extending through the web, and in which the web is given a thickness so limited that the registration of the stresses created by the transverse force occur substantially in a neutral plane of the lateral forces acting on the measuring body. It is also proposed that the thin web shall have an extension which is so restricted in relation to the measuring body that the force applied will be taken up in a cross-section through the web to more than 50% of the material of the measuring body located externally of the web. In accordance with advantageous embodiments of the inventive concept, it is proposed that the web shall have a thickness greater than 0.2 mm but smaller than 10 mm, preferably a thickness of from 1 to 4 mm. It is also proposed that the web has incorporated there¬ in two large and two smaller holes, of which the two large holes are intended to accommodate and to surround the magnetizing winding and the two smaller holes are intended to accommodate and to surround the central win¬ ding. The centres of the two large holes are positioned on or in the immediate vicinity of a neutral line or neutral plane on which the force acting on the measuring body is to be measured. The centres of respective smaller holes are located on a line which is positioned preferably at right angles to said neutral line and located on each side of said neutral line, at a distance therefrom. It is also proposed that the web will occupy at most 65% of the vertical extension or height of the measuring body, and that in all events the web shall be dimen¬ sioned so that the shear stresses occurring therein, prior to introducing the measuring holes, will be less than 50 N/mm 2 at maximum load on the measuring body. It is also proposed that a short-circuited winding is introduced through the holes for the magnetizing wind- ing, so as to compensate for temperatures, and in that this winding is given a number of turns suitable for such temperature compensation. With a starting point from a device of the kind illus- trated and described in German published specification 22 63 646, it is proposed in accordance with the present invention that the web is formed in the measuring body with the aid of two diametrically opposed measuring recesses or holes. Respective measuring recesses or holes shall be given the least possible extension in relation to the measur¬ ing body but shall have a size sufficient to surround the magnetizing winding and sensing winding. The web shall be thin, normally from 2 to 3 mm, and will form a metallurgical connection with the remainder of the measuring body. In accordance with a further aspect of the invention, the inventive device for measuring and/or registering mechanical forces includes a measuring body which is intended to be acted upon by said forces and which has a part of reduced cross-section presenting a measuring core made of ferromagnetic material and having formed therein through-passing holes for receiving a mag¬ netising winding and a sensing winding effective for evaluating transversal forces and/or shear stresses in accordance with magnetoelastic principles, said tran¬ sverse forces and said shear stresses being contingent on the magnitude of said forces. The measuring body of this aspect of the inventive device has formed therein two mutually opposing measuring recesses with an inter¬ mediate web which forms said measuring core, said web being formed integrally with and consisting of the same material as the measuring body, wherein a sensing win¬ ding is fitted into the holes in said web subsequent to forming the web and the holes in situ in the measuring body. According to another aspect of the invention there is proposed an alternative method of manufacturing a meas¬ uring body which will afford a solution to one or more of the aforesaid technical problems. The measuring body is adapted for measuring and/or registering mechanical forces and is provided with a web portion. The measuring body is intended to be loaded by said force in a manner such that transverse forces and/or shear stresses will occur in the web, these forces being capable of evaluation with the aid of a . magnetizing winding and a sensing winding. In accordance with the inventive method, there is formed in the measuring body two diametrically opposed measur¬ ing recesses or holes such as to provide a web which is oriented in a neutral plane on the measuring body and which is connected to the remainder of the measuring body through a metallurgical connection, said holes preferably being milled in the body. The recesses or holes will have the smallest possible cross-sectional area, and said area will exceed insig¬ nificantly the space required to accommodate the mag¬ netizing winding and sensing winding. The recesses or holes are also formed in a manner to provide a thin web, i.e. a web whose thickness is from 0.2 to 10 mm, preferably from 1 to 4 mm. In accordance with— he method, the web has formed there¬ in four through-passing holes, the sensing winding being wound through two mutually opposing holes, and the magnetizing winding being wound through the two remain- ing, mutually opposing holes. The cross-sectional area of the measuring recesses or holes is chosen such that more than 50%, preferably at least more than 75% of the expected, applied force in a cross-section through the web is supported by the mat¬ erial of the measuring body located externally of the web. It is also proposed that the web is provided with two large holes and two smaller holes, of which the large holes are intended to accommodate the winding turns of the magnetizing winding and the smaller holes are in¬ tended to accommodate the winding turns of the sensing winding, when said turns are inserted through the holes. Two large holes for the magnetizing winding shall be located closely adjacent one another, with the centres of said holes lying on or in the proximity of a trans¬ verse-force neutral line on the measuring body. According to one aspect of the invention there is prop¬ osed a method of manufacturing a device for measuring and/or registering mechanical forces, the device com¬ prising a measuring body. The measuring body presents a part of reduced cross-section in which there is included a measuring core made of ferromagnetic material and inc¬ orporating through holes for the accommodation of a magnetizing winding and a sensing winding respectively for evaluation of transverse forces and/or shear stre- sses in accordance with magnetoelastic principles, these transverse forces and/or shear stresses being contingent on the value of the aforesaid force. In accordance with this aspect of the inventive method it is proposed a) that in manufacture the measuring body is provided with two diametrically opposed measuring recesses or holes in a manner to leave an intermediate web in the neutral plane of occurrent lateral forces on the measur- ing body, said web forming the measuring core; b) that two mutually opposing first holes and two mutu¬ ally opposing second holes are formed in the web; c) that said sensing winding is wound through said two first holes; and d) that said magnetizing winding is wound through said two second holes. In addition herewith, it is proposed that the measuring recesses or holes are machined in the body, preferably milled therein, particularly with the aid of a shank end miller, and that the holes for accommodating the wind- ings are also machined in the web (11), preferably drilled therein, or formed by sparking techniques. ADVANTAGES Those advantages primarily associated with an inventive device for measuring and/or registering mechanical forces reside in the provision of conditions which enable the magnetoelastic technique to be combined with the strain gauge technique, therewith enabling more accurate registration of the mechanical forces acting on a measuring body and therewith also enabling the crea¬ tion of conditions which will enable solely the dim¬ ensions of the measuring body to be chosen in respect of a desired measuring range in combination with the ab¬ ility of providing a web of limited thickness and ext¬ ension and which bonds metallurgically with the re¬ mainder of the measuring body, and therewith of provid¬ ing conditions for obtaining a load cell which is insen- sitive to undesirable force components. The primary characteristic features of a device con- structed in accordance with the present invention are set forth in the characterising clause of the following claim 1, and the primary characteristic features of a method for the manufacture of a measuring body for use in said device are set forthin the characterising clause of the following claim 14. BRIEF DESCRIPTION OF THE DRAWINGS An exemplifying embodiment of the invention at present preferred and having characteristic features significant of the present invention will now be described in more detail with reference to the accompanying drawings, in which Figure 1 is a side view of a device for measuring and/or registering mechani¬ cal forces and comprising a rigidly mounted measuring body; Figure 2 is a sectional view of the measuring body which incorporates a thin web, and illustrates the shear stress dis¬ tribution in the case of a loaded beam; and Figure 3 is a plan view of the thin web having magnetizing and sensing windings fitted thereto. DESCRIPTION OF AN EMBODIMENT AT PRESENT PREFERRED Figure 1 illustrates a device for measuring and/or registering mechanical forces "F", comprising a measur¬ ing body 1 of circular cross-section which is made of homogenous steel material and rigidly mounted in can¬ tilever fashion, the force "F" to be measured being applied to the free end of the measuring body 1. The measuring body incorportes between its rigidly anchored end lb and its free end la a thin web 11, seen more clearly from Figure 2, in which transversal forces or shear stresses occurring in the web and contingent on the value of the force "F" can be evaluated with the aid of a magnetizing coil 3 and a sensing coil 4. The rigid anchorage lb of the measuring body is effected with the aid of an L-shaped support 5, one part 5a of which is provided with a circular hole which is adapted to the outer, circular cross-section of the measuring body 1, and the other part 5b of which is intended to support against and be secured to a supporting surface Also shown in Figure 1 is an evaluating unit or measur¬ ing unit 7 for measuring and/or registering the value of the mechanical force "F" and equipped with the necessary electric cables 8 for connection to the magnetizing winding 3 and the requisite electric cables 9 for con¬ nection to the sensing winding 4. The cables 8 may be supplied with an a.c. voltage having a frequency of 100 Hz. Since the construction of the unit 7 is previously known in principle and does not constitute any part of the present invention, the particular construction of the measuring unit will not be described in detail here. The current and voltage required to operate the measuring unit 7 is supplied through an electric contact 10. The web 11 is shown in more detail in Figure 2, and is given a limited extension relative to the measuring body 1 such that the applied force "F" is taken up,in a cross-section through the web, predominently by mea¬ suring body material located externally of the web, preferably by above 50% of said material. This material is reference 12 and 13 in Figure 2. Figure 2 also illustrates an imagined distribution of the shear stresses (N/mm 2 ) in the measuring body 1 which has a thin web in accordance with the invention and which is loaded in the manner illustrated in Figure 1, but with the exclusion of holes 17, 18, 19 and 20. In this case, the shear stresses occurring in the cross- section of the measuring body 1 shall be distributed so that the maximum shear stresses occurring in the parts 12 and 13 (at reference 11a) are smaller than the shear stresses occurring in the web (at reference lib) by a factor of 5. In the case of the illustrated embodiment, the measuring body 1 has a circular cross-section, although it will be understood that measuring bodies of other cross sections fall within the scope of the inventive concept. It will also be understood that although the web 11 of the illustrated embodiment is formed by two diametri¬ cally opposed, circular measuring recesses or holes 14, 15, these recesses or holes may also have a cross sec¬ tional shape other than circular. In the case of the Figure 2 embodiment, the hole 15 has a height or depth "h" whereas the total height or verti¬ cal extension of the measuring body 1 is referenced "H". Primarily, the web 11 shall have a smallest possible extension, although the web must be of such dimension as to be capable of accommodating four holes 17, 18 and 19, 20 respectively, of which the pair of holes 17, 18 are intended to accommodate the magnetizing winding 3, whereas the pair of holes 19, 20 are intended to acco - modate the sensing winding 4. The web 11 has a thickness "t" which shall be as small as possible. In practice, the web should have a thick¬ ness greater than 0.2 mm and suitably not greater than 10 mm. Preferably, the web thickness "t" will be from 1 to 4 mm, the lower limit being a condition of machining circumstances when the measuring body is homogenous. As will be seen from Figure 3, the two holes 17 and 18 are larger than the two holes 19 and 20, the two larger holes being intended to accommodate and surround the magnetizing winding 3, whereas the two smaller holes 19 and 20 are adapted to accommodate and surround the sens¬ ing winding 4. It is also proposed that the centres of each of the two larger holes 17 and 18 are located on or in the vicinity of a neutral line or neutral plane 21 on which the force "F" is intended to be applied on the measuring body 1. The centres of respective smaller holes 19, 20 are located on a line 22 which extends preferably at right angles to the neutral line 21 and which is positioned at a distance from the line 21 corresponding approximately to half the distance of the extension of said web 11 from said neutral plane 21. As before mentioned, the web 11 is circular in shape and is formed by two diametrically opposed circular recesses or bores formed in the measuring body, and it is pro¬ posed in this respect that the web 11 of height "h" shall take up at most 65% of the height or vertical extension "H" of the measuring body. In the case of a load cell intended for weights of 5 tonnes, the height "h" of the web will suitably be equal to 25% of the height or vertical extension "h" of the measuring body. In view of the fact that magnetoelastic principles are applied in evaluating shear stresses occurring in the web 11 and responsive to the value of the force "F", and since the magnetoelastic effect is not a linear function of the variation of the shear stress in relation to said force, the value of the shear stress can only be evalu¬ ated with the aid of magnetoelastic principles when the shear stresses are low in value. It is proposed that the web is dimensioned such that the shear stress occurring therein prior to the introduction of the measuring holes will be less than 50 N/mm 2 at the centre of the web. Finally, it is proposed in accordance with the invention that a short-circuited winding is inserted through the two larger holes 17, 18, in order to compensate for temperature. Although this winding is not shown in Figure 3, it may have between 1 and 15 turns, depending upon the temperature to be compensated. A winding com¬ prised of coarse gauge wire will require fewer turns than a winding comprising a more slender wire. The choice of wire gauge and the number of wire turns will depend upon the temperature to be compensated. The greater the calculated counter-current flowing through the magnetizing holes the greater the temperature com¬ pensation. Furthermore, the measuring body 1 may consist of a solid, steel material machined in a manner to form the thin web 11. The web shall be kept sufficiently thin, since field penetration is poor when the web 11 is too thick, which will result in measuring problems of a technical nature. Since the magnetoelastic principles applied are based on non-linear phenomenon, the properties of the material used are highly significant. The invention provides a possibility of forming larger holes 17, 18 for a large magnetizing winding (thick, several turns) , which is required in the case of homoge¬ nous material in the measuring body 1 which is not- readily magnetised. It has been found that such a device will reduce the sensitivity to disturbing forces. Although the afore-described measuring body 1 has been illustrated as a material part in which two measuring recesses 14, 15 have been formed, it will be understood that the body may equally as well comprise three parts, one part containing the recess 14, a further part con¬ taining the recess 11 and still a further part contain¬ ing the recess 15, said parts being firmly connected to one another. The aforesaid parts may also be made of mutually different materials. The invention is based on maintaining a thin web 11 which is positioned centrally of the measuring body. Consequently, registration of the stresses induced by forces "F" will take place essentially in or in the immediate vicinity of a neutral plane 23 for lateral forces acting on the measuring body. Undesirable disturbance stresses increase linearily with the distance from the neutral plane 23 and the distur¬ bance stresses originating from lateral forces and portion forces are negligible and zero in said plane 23. In this way, practically solely stresses induced by the force F will be registered. With respect to dimensioning of the measuring body, it is proposed that at least 50%, for instance about 75% of the applied force "F" will be carried by the material of the measuring body located externally of the web 11. In the case of a load cell constructed for 1.0 tonne, this value will be about 70%, and in the case of a load cell constructed for 5.0 tonne, said value will be about 95%. The web 11 will preferably correspond to at most 65% of the height or vertical extension of the measuring body. In the case of a load cell constructed for 1.0 tonne, this value will be 50%, whereas in the case of a load cell constructed for 5.0 tonne, said value will be 30%. As an alternative, it is proposed that the recesses 14 and 15 are formed by a larger, outer recess and an inner narrower recess in between which the web 11 is formed. It will be understood that the invention is not restric¬ ted to the afore-described and illustrated embodiment, and that modifications can be made within the scope of the inventive concept as defined in the following claims.

Claims: CLAIMS 1. A device for measuring and/or registering mechanical forces (F) with the aid of a measuring body (l) which can be influenced by the force applied in the measuring process, said measuring body being configured with a web (11) in which occurrent transverse forces and/or shear stresses, whose values are contingent on the value of the said force can be evaluated with the aid of a mag- netizing coil (3) and a sensing coil (4), characterised in that the web (11) has a limited extension in relation to the measuring body (1) and presents a limited thick¬ ness (t) such that evaluation of occurrent forces and/or stresses effected on magnetoelastic principles will take place substantially in or in the immediate vicinity of a neutral plane (23) on the measuring body (1) for lateral forces acting on said body. 2. A device according to claim 1, characterised in that the applied force (F) is carried, in a cross-section through the web (11), to more than 50% by the measuring body material (12, 13) located externally of the web. 3. A device according to claim 1 or claim 2, charac- terised in that the web (11) has a thickness which exceeds 0.2 mm and which is smaller than 10 mm, prefer¬ ably a thickness of from 1 to 4 mm. 4. A device according to claim 1, characterised in that the web (11) has provided therein two large holes (17, 18) and two smaller holes (19, 20), the two large holes accommodating a magnetizing winding (3) and the two smaller holes accommodating a sensing winding (4) . 5. A device according to claim 4, characterised in that the centres of the two holes (17, 18) accommodating the magnetising winding (3) are positioned on or adjacent to the neutral line (21) of the measuring body for the force (F) acting sustantially laterally on the measuring body. 6. A device according to claim 5, characterised in that the centres of the two holes (19, 20) for accommodating the sensing winding are positioned on a line (22) which is positioned preferably at right angles to said neutral line (21). 7. A device according to claim 1, 2 or 3, characterised in that at least 75% of the applied force (F) is sup¬ ported by the material (12, 13) of the measuring body located externally of the web (11). 8. A device according to claim 1, characterised in that the web (11) equals at most 65% of the height or verti- cal extension of the measuring body (1) . 9. A device according to any one of the preceding claims, characterised in that the web (11) is so dimen- sioned, prior to forming said winding holes, that the shear stresses occurring therein when a load is applied to the measuring body will be smaller than 50 N/mm 2 . 10. A device according to any of claims 4-9, charac- terised in that extending through the magnetizing holes is a short-circuited coil for temperature compensation. 11. A device accordig to claim 10, characterised in that the winding comprises from between 1 and 15 winding turns. 12. A device according to claim 1 in which the web (11) is oriented substantially in a neutral plane (23) on the measuring body for lateral forces acting on said measur¬ ing body (1), characterised in that the web is formed in the measuring body by two diametrically opposed measur¬ ing recesses or holes (14, 15); in that respective measuring recesses or holes have a limited extension in relation to the measuring body (1) but of sufficient area to embrace the magnetising winding and the sensing winding; and in that the web has a small thickness and forms a metallurgical (atomic) connection with the remainder of the measuring body. 13. A device according to claim 1 or 12, characterised in that two through-passing holes (17, 18) in the web are intended to surround the magnetising winding (3) and are oriented along a line which forms a right angle to the direction in which the force acts; and in that two through-passing holes (19, 20) in the web, intended to surround the sensing winding, are oriented along a line which is parallel to the direction in which said force (F) acts. 14. A device for measuring and/or registering mechanical forces (F) in accordance with any one of the preceding claims and manufactured in accordance with the method of claims 15-21 below, comprising a measuring body (1) which is intended to be acted upon by said forces and which has a part of reduced cross-section exhibiting a measuring core (11) of ferromagnetic material having through-passing holes (17, 18 and 19, 20 respectively), for accommodation of a magnetising winding (3) and a sensing winding (4) for the evaluation of transverse forces and/or stresses in accordance with magnetoelastic principles, the value of said forces being contingent on the value of said force (f), characterised in that the measuring body (1) has two mutually opposed measuring recesses (14, 15) which define therebetween a web (11) forming said measuring core; and in that said magnetis- ing winding (3) and said sensing winding (4) are wound in said holes (17, 18; and 19, 20 respectively) in said web subsequent to having formed said web and said holes in situ in the measuring body (1) . 15. A method of manufacturing a measuring body adapted for measuring and/or registering mechanical forces (F), said body having a web (11) which is intended to be loaded by said force such that transverse forces and/or shear forces will occur in the web (11), said forces being evaluated with the aid of a magnetising winding (4), characterised by: a) forming in said measuring body two diametrically opposed measuring recesses or holes (14, 15) together with a web (11) which is located on a neutral plane (23) on the measuring body and which is connected metal- lurgically with the remainder of the measuring body; b) selecting a cross-sectional hole area or recess area which insignificantly exceeds the space required to accommodate the magnetising winding and the sensing winding; c) selecting a thin web thickness, e.g. a web thickness of 0.2-10mm, preferably l-4mm; d) forming four through-passing holes (17, 18, 19, 20) in the web; e) inserting the sensing winding (4) through two mutu¬ ally opposed holes (19, 20), and f) inserting the magnetising winding (3) through the two remaining mutually opposing holes (17, 18). 16. A method according to claim 15 or 16, characterised in that the cross-sectional area of the measuring recess or hole is chosen such that an expected, applied force will be supported, in a cross-section in the web (11), to more than 50%, preferably at least 75% by the mate¬ rial (12, 13) of the measuring body located outside the web (11) . 17. A method according tb claim 15 or 16, characterised by forming in the web (11) two large holes (17, 18) and two smaller holes (19, 20), the large holes being in¬ tended accommodate the magnetising winding (3) and the two small holes being intended to accommodate the sens¬ ing winding (4) . 18. A method according to claim 17, characterised in that the centres of respective two large holes are positioned on or in the vicinity of a neutral line (21) located on the measuring body and forming a right angle to the direction in which the force applied acts. 19. A method according to claim 17, characterised in that the measuring recesses or holes are formed by milling, particularly with the aid of a shank end and miller. 20. A method of manufacturing a device for measuring and/or registering mechanical forces (F) , said device including a measuring body (1) which has a part of reduced cross-section which exhibits a measuring core (11) of ferromagnetic material having through-passing holes (17, 18, 19, 20) for accommodating the magnetising winding (3) and a sensing winding (4) respectively, said windings being intended for evaluating occurrent trans- verse forces and/or shear stresses in accordance with magnetoelastic principles, said transverse forces and/or shear stresses being contingent on the value of the applied force (F), characterised in that; a) when manufacturing the measuring body there are provided two diametrically opposed measuring recesses or holes (14, 15) such as to leave an intermediate web (11) in the neutral plane (23) of the measuring body for occurrent lateral forces, said web forming said measur¬ ing core. b) there are provided in said web (11) two mutually opposing first holes (19, 20) and two mutually opposing second holes (17, 18); c) the sensing winding (4) is inserted through said two first holes (19), 20); and d) the magnetising winding (3) is inserted through said second holes (17, 18). 21. A method according to claim 20, characterised in that the measuring recesses (14, 15) for holes are machined in said body, preferably milled, particularly with the aid of a shank end miller; and in that the holes (17, 18 and 19, 20) for accommodating respective windings (3, 4) are also machined in the web (11), preferably drilled therein or formed by sparking techni- ques.

Inventors: VALDEMARSSON STEFAN, VALDEMARSSON, STEFAN
Applicants: VALDEMARSSON STEFAN, VALDEMARSSON, STEFAN
Application year: 1989
Main classification: G01L1
IPC codes: G01L1