Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
  • G01L5/00—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes
  • G01L5/0009—Force sensors associated with a bearing
  • G01L5/0019—Force sensors associated with a bearing by using strain gages, piezoelectric, piezo-resistive or other ohmic-resistance based sensors
• • 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
  • G01L1/2268—Arrangements for correcting or for compensating unwanted effects
  • G01L1/2281—Arrangements for correcting or for compensating unwanted effects for temperature variations
• • 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
  • G01L1/2287—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 constructional details of the strain gauges
  • G01L1/2293—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 constructional details of the strain gauges of the semi-conductor type
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
  • G01L3/00—Measuring torque, work, mechanical power, or mechanical efficiency, in general
  • G01L3/02—Rotary-transmission dynamometers
  • G01L3/04—Rotary-transmission dynamometers wherein the torque-transmitting element comprises a torsionally-flexible shaft
  • G01L3/10—Rotary-transmission dynamometers wherein the torque-transmitting element comprises a torsionally-flexible shaft involving electric or magnetic means for indicating
  • G01L3/108—Rotary-transmission dynamometers wherein the torque-transmitting element comprises a torsionally-flexible shaft involving electric or magnetic means for indicating involving resistance strain gauges

Definitions

• the invention relates to a strain gauge, a sensor for measuring the longitudinal and transverse deformations of an area of a structural element comprising such a gauge, and a rolling bearing incorporating at least one such sensor.
• the use of thick-layer type strain gauges is known.
• the gauges used comprise a pattern of a piezoresistive material and a pair of terminals arranged on either side of said pattern along a main direction of measurement according to which the electric current flows.
• the gauge is then disposed on the deformation zone so that the deformations of said zone induce those of the pattern and thus a variation of the resistance of said pattern, said variations being able to be measured to determine the deformation values of the zone.
• the pattern is sensitive to the deformations that it undergoes in its principal axis of measurement, but also to those which take place perpendicularly to this axis. Indeed, the variation of the resistance R x along the main axis according to the deformations undergone can be written:
• the object of the invention is to overcome this drawback by proposing in particular a strain gauge for separately measuring the resistance variations of the pattern along two directions, so that the deformations undergone along these two directions can be calculated independently.
• the invention proposes a strain gauge comprising a substrate on which are formed a pattern of electrically resistive material and two pairs of terminals in electrical contact with said pattern, said pattern forming a continuous resistive medium. in directions respectively longitudinal and transverse and said terminals being formed on either side of the pattern in the direction respectively longitudinal for one pair and transverse for the other pair, so as to be able to measure the electrical resistance of the pattern along said longitudinal directions and transverse.
• the invention proposes a sensor for measuring the deformations of an area of a structural element, said sensor comprising:
• a chopping circuit which is connected to the terminals of the gauge for alternately measuring the electrical voltage in the longitudinal and transverse directions;
• a voltage signal processing device which is arranged to calculate the deformations respectively along the longitudinal and transverse directions.
• the invention proposes a rolling bearing comprising a fixed member, a rotating member and at least one row of rolling bodies arranged in a raceway which is formed between said members so as to allow their relative rotation, said bearing integrating at least one such sensor, the substrate being transferred to the fixed member so as to measure the longitudinal and transverse deformations respectively; of the fixed member which are induced during the rotation of the bearing.
• FIG. 1 shows a hash circuit which is connected to the terminals of a strain gauge according to the invention
• FIGS. 2 and 5 are diagrammatic views of five geometers of a material pattern for a strain gauge according to the invention.
• FIG. 3 are top view representations of three embodiments of a material pattern for a strain gauge according to the invention.
• FIGS. 4 are perspective views of an embodiment of a bearing incorporating sensors according to the invention, showing two different states of charge.
• a sensor for measuring the deformations of an area of a structural element.
• the sensor incorporates a strain gauge comprising a substrate 1, for example ceramic, on which is formed at least one pattern 2 of electrically resistive material, in particular a piezoresistive or magnetostrictive material, so as to translate a mechanical stress into electrical resistance.
• the pattern 2 forms a continuous resistive medium in directions respectively longitudinal x and transverse y, for example the pattern 2 is formed of a continuous layer of material.
• the material may comprise a glass paste incorporating conductive particles, and the pattern 2 may be deposited on the substrate 1 in thick layer by screen printing.
• the gauge further comprises two pairs of terminals 3 made of electrically conductive material, in particular metal such as silver, which are formed on the substrate 1 to be in electrical contact with the pattern 2.
• the terminals 3 may be made by thick-film screen printing of a material paste, and this prior to the formation of said pattern.
• the terminals can be of any shape, including rectangular, triangular, circular ....
• the senor measures the deformations of an area of a fixed member of a rolling bearing also comprising a rotating member and at least one row of rolling bodies arranged in a raceway which is formed between said members of so as to allow their relative rotation.
• the bearing is a motor vehicle wheel bearing and the substrate 1 is fixed on a flat surface 4 formed on the periphery of the outer ring 5.
• the sensor makes it possible to measure the deformations of the outer ring 5 which are in particular due to the passage of the rolling bodies during rotation, said deformations then being periodic and approximable by a sinusoid.
• the bearing comprises two rows of balls which are arranged coaxially in a raceway respectively provided between the fixed outer ring 5 and the inner rotating ring 6.
• the fixed ring 5 is provided with means for fixing the chassis that are formed a flange 7 comprising four radial projections 7 in which an axial hole 8 is formed to allow fixing by screwing.
• the senor comprises a plurality of gauges which are arranged on the same substrate 1. More specifically, two groups of three aligned patterns 2 are formed on the substrate 1 which is rigidly fixed to the fixed ring 5, for example by bonding or welding, to transmit the deformations from the flat 4 to the patterns 2.
• the substrate 1 is positioned on the flat 4 to have each group of gages substantially facing a raceway and in the general direction of rotation.
• the bearing shown comprises four sensors which are equidistributed around the outer ring 5, the signals from the sensors can be used by a computer to determine the forces applied during rotation on the fixed ring 5 and / or on an integral element of the rotating ring 6, as described in the document FR-2 839 553.
• Figures 4 schematically a bump-shaped deformation on the surface of the outer ring 5 according to two bearing load states, the first ( Figure 4a) substantially radial and the second ( Figure 4b) moved in the axial direction y.
• the distortion has a component of ⁇ following the general axis of rotation x and a dyy component along the y axis.
• the amplitude of the bump and its position relative to the patterns 2 changes according to the state of load, this development being representative of the contact angle between the ball and the raceway.
• the bearing force of the balls on the raceway is determined by its amplitude but also by its direction of application, that is to say by the contact angle.
• the invention provides for measuring the deformation of the patterns 2 along the two directions, respectively longitudinal (S xx ) and transverse ( ⁇ yy ) which is substantially parallel to the axis of rotation of the bearing, so as to allow measurement of the longitudinal and transverse deformations respectively of the fixed ring; 5 which are induced during the rotation of the bearing.
• the gauge comprises two pairs of terminals 3 which are formed on either side of the pattern 1 in the direction respectively longitudinal x for one pair and transverse y for the other pair, so as to be able to measure the variations of electrical resistance of the pattern according to said longitudinal and transverse directions.
• the contact between each terminal 3 and the pattern 1 extends substantially perpendicular to the direction in which the pair of said terminal is formed, so that the current lines are arranged substantially in the direction of the pair.
• Figures 2 represent possible geometries for the pattern 2 and the arrangement of the corresponding terminals 3, the distance between the terminals 3 of the pairs being identical.
• the geometries represented are:
• grooves 9 in the pattern 2 it is possible to make grooves 9 in the pattern 2, said grooves being arranged to improve the maintenance of the current lines in said pattern respectively along the longitudinal and transverse directions.
• This technique called trimming or resistance adjustment, allows to retouch the screenprinted geometry to give it the desired geometry.
• the grooves 9 can be made using a laser, sand or any other technique, so as to completely cut the electrical conduction through the layer of material forming the pattern 2.
• a groove 9 can be made between each terminal 3 so as to avoid forming easy paths for the current via said terminals, said grooves being L-shaped (FIG. 3a), in the median plane between the terminals 3 (FIG. 3b) or curved ( Figure 3c).
• the thickness of the groove 9 may be of the order of 0.1 mm.
• the embodiment according to FIG. 3b makes it possible to have the wider terminals 3 for a central area of the reduced pattern 2 while maintaining the current lines parallel to the respectively transverse and longitudinal directions.
• the sensor hashing circuit is described, said circuit being connected to the terminals 3 of a gauge according to FIG. 2a for alternately measuring the electrical voltage in the longitudinal (V x ) and transverse directions ( V y ).
• the circuit comprises a current generator 10 and two switches 11, 12 which are controlled to pass the current i alternately between the terminals 3 of a pair.
• the measurement frequency of the voltages V x , V y is chosen to be able to assume that the deformations S xx and ⁇ yy have not varied between two times of measurement.
• the processing device may comprise an amplifier, a filter, an analog / digital converter and a deformation calculation processor.
• the sensor may comprise a processing device common to at least two gauges, said processing device then comprising means for multiplexing the signals from each of the gauges.
• hybrid circuit type technologies allow to integrate on the substrate 1, in addition to the strain gauge or gauges, the hashing circuit and / or the treatment device on the substrate.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Chemical & Material Sciences (AREA)
• Analytical Chemistry (AREA)
• Measurement Of Length, Angles, Or The Like Using Electric Or Magnetic Means (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

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Family Applications (1)

Country Status (3)

Families Citing this family (2)

Family Cites Families (2)

• 2007
  • 2007-11-16 FR FR0708080A patent/FR2923907B1/fr not_active Expired - Fee Related
• 2008
  • 2008-11-05 EP EP08871827A patent/EP2210076A2/de not_active Withdrawn
  • 2008-11-05 WO PCT/FR2008/001556 patent/WO2009095553A2/fr active Application Filing

Non-Patent Citations (1)

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