Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
  • G01L1/00—Measuring force or stress, in general
  • G01L1/12—Measuring force or stress, in general by measuring variations in the magnetic properties of materials resulting from the application of stress
  • G01L1/127—Measuring force or stress, in general by measuring variations in the magnetic properties of materials resulting from the application of stress by using inductive means
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
  • G01L1/00—Measuring force or stress, in general
  • G01L1/12—Measuring force or stress, in general by measuring variations in the magnetic properties of materials resulting from the application of stress
  • G01L1/125—Measuring force or stress, in general by measuring variations in the magnetic properties of materials resulting from the application of stress by using magnetostrictive means

Definitions

• 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.
• 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.
• 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.
• 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 «,
• the device 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.
• 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.
• Patent No. 2 129, 949 and European Patent 0, 010, 860.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• the measuring re ⁇ Grandes 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• the measuring body 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.
• 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.
• 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.
• 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.
• 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;
• 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.
• 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
• Figure 3 is a plan view of the thin web having magnetizing and sensing windings fitted thereto.
• FIG. 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
• FIG. 1 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.
• 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.
• 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.
• 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.
• 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.
• 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".
• 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.
• the web should have a thick ⁇ ness greater than 0.2 mm and suitably not greater than 10 mm.
• 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.
• 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.
• 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.
• 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.
• the height "h” of the web will suitably be equal to 25% of the height or vertical extension "h” of the measuring body.
• 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.
• a short-circuited winding is inserted through the two larger holes 17, 18, in order to compensate for temperature.
• this winding 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 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.
• 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.
• the web 11 will preferably correspond to at most 65% of the height or vertical extension of the measuring body.
• 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.

Landscapes

• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Force Measurement Appropriate To Specific Purposes (AREA)
• Measurement Of Force In General (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=20371644

Family Applications (1)

Country Status (4)

Families Citing this family (2)

Family Cites Families (5)

• 1988
  • 1988-03-10 SE SE8800860A patent/SE459212C/sv not_active IP Right Cessation
• 1989
  • 1989-03-09 WO PCT/SE1989/000117 patent/WO1989008826A1/en not_active Ceased
  • 1989-03-09 EP EP19890903840 patent/EP0403550A1/en not_active Withdrawn
  • 1989-03-09 AU AU32982/89A patent/AU3298289A/en not_active Abandoned

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events