EP0614521A1 - Capteur de force - Google Patents

Capteur de force

Info

Publication number
EP0614521A1
EP0614521A1 EP93921029A EP93921029A EP0614521A1 EP 0614521 A1 EP0614521 A1 EP 0614521A1 EP 93921029 A EP93921029 A EP 93921029A EP 93921029 A EP93921029 A EP 93921029A EP 0614521 A1 EP0614521 A1 EP 0614521A1
Authority
EP
European Patent Office
Prior art keywords
circuit elements
load
load cell
circuit
chains
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP93921029A
Other languages
German (de)
English (en)
Inventor
Peter James Little
Paul Harden
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Pifco Ltd
Original Assignee
Pifco Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Pifco Ltd filed Critical Pifco Ltd
Publication of EP0614521A1 publication Critical patent/EP0614521A1/fr
Withdrawn legal-status Critical Current

Links

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
    • G01L1/20—Measuring force or stress, in general by measuring variations in ohmic resistance of solid materials or of electrically-conductive fluids; by making use of electrokinetic cells, i.e. liquid-containing cells wherein an electrical potential is produced or varied upon the application of stress
    • G01L1/22—Measuring force or stress, in general by measuring variations in ohmic resistance of solid materials or of electrically-conductive fluids; by making use of electrokinetic cells, i.e. liquid-containing cells wherein an electrical potential is produced or varied upon the application of stress using resistance strain gauges
    • G01L1/2206—Special supports with preselected places to mount the resistance strain gauges; Mounting of supports
    • G01L1/2231—Special supports with preselected places to mount the resistance strain gauges; Mounting of supports the supports being disc- or ring-shaped, adapted for measuring a force along a single direction

Definitions

  • This invention relates to a load cell and in particular but not exclusively to a load cell for a suspension unit of an automotive vehicle.
  • load cells for obtaining load measurements in the form of electrical signals either for monitoring the load in structural members or to generate feedback signals as part of a control circuit.
  • the suspension units of automotive vehicles have been provided with such load signals as part of active suspension systems in which the instantaneous load experienced by each suspension unit of the vehicle is detected to allow optimum control of actuators determining suspension characteristics.
  • a load sensing member is connected between first and second load bearing structures and strain gauges are bonded to the member such that load transmitted between the structures via the member results in strain being observed in the member which can be sensed by means of the gauges to provide an output signal representative of the load.
  • a load cell comprising a plurality of strain gauges mounted on a load sensing member whereby in use the strain gauges facilitate measurement of strain produced in the member in response to an applied load, wherein the strain gauges comprise circuit elements of a thick film circuit of which a surface portion of the member constitutes a substrate.
  • An advantage of such a load cell is that a thick film circuit printing technique may be utilised to accurately and repeatedly position the circuit elements on the load sensing member.
  • the surface portion of the load sensing member is annular so as to extend radially between an outer annular portion of the member connected in use to a first load bearing structure and an inner annular portion of the member connected in use to a second load bearing structure, the circuit elements being oriented so as to be responsive to radial compression or tension due to bending of the surface portion whereby the load cell is adapted for measurement of loads comprising components of force directed along a load axis at right angles to the surface portion.
  • the circuit elements are substantially unifor ally distributed circumferentially around the annular surface portion.
  • the circuit elements are arranged such that a radially outermost annular array of circuit elements is provided adjacent to the outer annular portion and a radially innermost annular array of circuit elements is provided adjacent to the inner annular portion of the member.
  • the outer and inner arrays may thereby be subjected to strain of opposite sense i.e. compression/tension, such an arrangement lending itself to the use of a detector circuit in which extraneous effects such as temperature change can be cancelled by for example using a bridge circuit.
  • the radially outermost array comprises first and second chains of circuit elements, the circuit elements of each of the first and second chain being respectively connected in series and circumferentially distributed such that the radially outermost array is populated circumferentially with circuit elements alternately from the first and second chains, and wherein the radially innermost array comprises third and fourth chains of circuit elements, the circuit elements of each of the third and fourth chain being respectively connected in series and circumferentially distributed such that the radially innermost array is populated circumferentially with circuit elements alternately from the third and fourth chains.
  • the load cell comprises connection means operable to connect the circuit elements in a detector circuit in which the aggregrate resistance values of the first, second, third and fourth chains constitute first, second, third and fourth arms of a Wheatstone bridge circuit.
  • the circuit elements comprise thick film resistors. Such resistors can be printed in a single printing operation so as to have substantially uniform characteristics of resistivity and physical size. The size and position of each resistor is inherently accurately and repeatedly defined by the screen printing operations of standard thick film printing circuit techniques.
  • Figure 2 is a schematic circuit drawing of a bridge circuit for use with the load cell of Figure 1; and Figure 3 is a sectioned elevation of the load cell of Figure 1 fitted to a suspension unit of a vehicle.
  • a load cell 1 shown in Figure 1 comprises a load sensing member 2 which is annular in shape and formed from steel plate of 6.4 mm thickness with inner and outer radii of 38 and 82 mm respectively.
  • An outer annular portion 3 of the member 2 is provided with circumferentially spaced holes 4 by means of which the outer annular portion is bolted to a first load bearing structure 5 in use as shown in
  • the first load bearing structure 5 is a suspension mount for an automotive vehicle suspension unit.
  • the member 2 has an inner annular portion 6 which is provided with circumferentially spaced holes 7 by means of which the inner annular portion is bolted in use to a second load bearing structure 8 as shown in Figure 3.
  • the second load bearing structure 8 supports a damper of a vehicle suspension unit such that a rod 9 of the damper transmits predominantly vertical loads to the second load bearing structure 8 which is transmitted to the first load bearing structure 5 through the load sensing member 2.
  • the second load bearing structure 8 is a rigid steel disc located concentrically within the load sensing member 2 and the first load bearing structure 5 is a rigid annular steel plate located peripherally and concentrically with respect to the load sensing member 2.
  • a thick film printed circuit 10 is fabricated on the member 2 such that an annular surface portion 11 of the member 2 constitutes a substrate of the circuit, the annular surface portion extending coaxially with and radially intermediate the inner and outer annular portions 6 and 3 of the member 2.
  • the thick film printed circuit 10 is built up from successive layers applied to the substrate surface portion 11, the initial layer being an adhesion layer upon which a buffer layer 12 is printed.
  • a further layer comprising first conductive tracks 13 is printed on the buffer layer 12 and these tracks are partially overlaid by first and second dielectric layers 14 and 15 respectively.
  • a further layer comprising second conductor tracks 16 is printed over the first and second dielectric layers 14 and 15 and extends into contact with the first conductor tracks 13 to provide an interconnecting conductive network for circuit elements 17 which are printed as a further layer on the buffer layer 12 adjacent to the dielectric layers 14 and 15.
  • circuit elements 17 each comprise a square area of resistive material, each being printed at the same time in a single printing operation such that a uniform thickness of resistive material constitutes each circuit element, the net result being first and second annular arrays of circuit elements 18 and 19 respectively, each array constituted by sixty identical resistors which are uniformly circumferentially spaced.
  • the first array 18 of circuit elements is
  • ⁇ radially outermost and located adjacent to the outer annular portion 3 of the load sensing member 2 and the second array 19 of circuit elements is radially innermost so as to be positioned adjacent to the inner annular portion 6 of the load sensing member 2.
  • the first and second arrays 18 and 19 are located at positions such that vertical loading of the second load bearing structure 8 along a central load axis 20 will result in deformation of the surface portion 11 which constitutes the substrate ⁇ upon which the arrays 18 and 19 are fabricated.
  • an upwardly directed load along the load axis 20 will deform the load sensing member 2 such that the first array of circuit elements 18 is placed in compression and the second array 19 of circuit elements is placed in tension.
  • Each of the circuit elements 17 thereby acts as a strain gauge in that the resistance of each square element of resistive material as measured in a radial direction will depend upon the extent to which it is subjected to compression or tension, the effect of compression being to decrease resistance and the effect of tension being to increase resistance.
  • the first and second conductor tracks 13 and 16 provide interconnection between the circuit elements such that an electric current in a radial direction is maintained through each of the circuit elements.
  • the sixty circuit elements are connected in first and second chains 21 and 22, each of which chains consists of thirty circuit elements connected in series.
  • the circuit elements of the first and second chains 21 and 22 are each distributed around a complete circumference and are circumferentially distributed such that the array is populated with circuit elements alternately from the first and second chain.
  • Circuit elements of the first and second chains 21 and 22 are in other words interdigitated around the circumference of the thick film circuit 10.
  • the second array 19 of circuit elements similarly comprises third and fourth chains 23 and 24 respectively which are interconnected and interdigitated in like manner.
  • the first, second, third and fourth chains 21, 22, 23 and 24 respectively present aggregate resistance values Rl, R2, R3 and R4 respectively which are sensed by connection to output terminal pads 25, 26, 27 and 28 by means of a detector circuit 29 illustrated in Figure 2.
  • the detector circuit 29 is a conventional Wheatstone bridge circuit in which a source voltage is applied between the supply terminals 30 and 31 respectively and an output voltage is sensed between output terminals 32 and 33.
  • the output signal may thereby provide a signal which is representative of the applied load.
  • the sensitivity of the load cell 1 will depend upon the stiffness and hence the thickness of the load sensing member 2.
  • Rl, R2 , R3 , R4 are determined by the number of circuit elements in each chain and the resistivity of the paste used in printing the circuit elements. It is usual to use paste with the resistance of 10 kilohms per square as this provides a gauge factor of between 12 and 14. To reduce the bridge resistance to preferred levels it may be desirable to use pastes having a lower ohmic value such as 100 ohm paste thereby producing a gauge factor of approximately 2. This is equivalent to the gauge factor of metal foil gauges.
  • the load cell 1 is insensitive to components of load transverse to the load axis 20 because of the distributed nature of the circuit element 17 constituting each resistance Rl, R2, R3 , R4 of the detector circuit. If for example a transverse component of load is applied in a direction from left to right as viewed in Figure 3 such that the second load bearing structure 8 is urged to the right relative to the stationary first load bearing structure 5, the effect on the circuit elements constituting the first chain 21 will be that those elements on the right-hand side of the load axis 20 will experience a degree of compression in the radial direction and those to the left will experience a degree of tension. The nett effect on the aggregate resistance Rl of the first chain 21 will be zero however.
  • each of the second, third and fourth chains 22, 23 and 24 will experience similar compression and tension but with no nett effect on each of the resistance values R2 , R3 , R4. There will therefore be no consequent contribution to the output voltage of the detector circuit 29.
  • Insensitivity to such transverse forces depends on their being sufficient numbers of circuit elements in each chain for the resistance values of the circuit elements to be evenly circumferentially distributed and also will depend upon the extent to which the circuit elements represent identical performance characteristics. It is however well within the capabilities of conventional thick film circuit techniques to achieve a high degree of uniformity of such circuit elements and for the position of the respective elements to be accurately and repeatedly defined.
  • the load sensing member may be constructed from materials other than steel and in particular alternative metals such as aluminium may be used.

Landscapes

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

Abstract

Un capteur de force (1) comprend un élément de captage de force (2) sur lequel sont montées des jauges de contrainte présentant des éléments de circuits (18, 19) à couche épaisse, une partie de la surface de l'élément de captage constituant un substrat. Les éléments de circuit sont disposés en réseaux concentriques circulaires (18, 19) et sont orientés de façon qu'ils soient sensibles à la compression ou la tension radiale due au fléchissement de la surface de l'élément de captage. On peut utiliser le capteur de force dans un organe de suspension d'un véhicule automobile afin de mesurer une composante de force orientée à angle droit par rapport à la surface de l'élément de captage.
EP93921029A 1992-09-30 1993-09-30 Capteur de force Withdrawn EP0614521A1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
GB9220655 1992-09-30
GB9220655A GB2271185A (en) 1992-09-30 1992-09-30 Load cell
PCT/GB1993/002033 WO1994008216A1 (fr) 1992-09-30 1993-09-30 Capteur de force

Publications (1)

Publication Number Publication Date
EP0614521A1 true EP0614521A1 (fr) 1994-09-14

Family

ID=10722778

Family Applications (1)

Application Number Title Priority Date Filing Date
EP93921029A Withdrawn EP0614521A1 (fr) 1992-09-30 1993-09-30 Capteur de force

Country Status (3)

Country Link
EP (1) EP0614521A1 (fr)
GB (1) GB2271185A (fr)
WO (1) WO1994008216A1 (fr)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE10307978B4 (de) * 2003-02-24 2006-02-09 Siemens Ag Vorrichtung zur Bestimmung einer Kraft
JP2017113922A (ja) * 2015-12-22 2017-06-29 豊興工業株式会社 射出成形機

Family Cites Families (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4311980A (en) * 1978-10-12 1982-01-19 Fabrica Italiana Magneti Marelli, S.P.A. Device for pressure measurement using a resistor strain gauge
EP0053337B1 (fr) * 1980-11-29 1987-05-20 Tokyo Electric Co., Ltd. Cellule de mesure de charge et procédé pour sa manufacture
IT206925Z2 (it) * 1986-03-10 1987-10-19 Marelli Autronica Sensore a filo spesso in particolare sensore di pressione
US4836034A (en) * 1986-07-15 1989-06-06 Ricoh Company, Ltd. Force sensing apparatus
DE3714613A1 (de) * 1987-05-01 1988-11-17 Helmut Dr Ing Gassmann Waegezelle
US4974596A (en) * 1987-12-14 1990-12-04 Medex, Inc. Transducer with conductive polymer bridge
US5127277A (en) * 1989-07-26 1992-07-07 Lucas Industries Public Limited Co. Measuring loads on vehicle wheels
US5154247A (en) * 1989-10-31 1992-10-13 Teraoka Seiko Co., Limited Load cell
US5111702A (en) * 1990-06-22 1992-05-12 Hottinger Baldwin Measurements, Inc. Torsion ring transducer

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO9408216A1 *

Also Published As

Publication number Publication date
GB9220655D0 (en) 1992-11-11
WO1994008216A1 (fr) 1994-04-14
GB2271185A (en) 1994-04-06

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