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
  • G01L1/2268—Arrangements for correcting or for compensating unwanted effects
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01G—WEIGHING
  • G01G19/00—Weighing apparatus or methods adapted for special purposes not provided for in the preceding groups
  • G01G19/08—Weighing apparatus or methods adapted for special purposes not provided for in the preceding groups for incorporation in vehicles
  • G01G19/12—Weighing apparatus or methods adapted for special purposes not provided for in the preceding groups for incorporation in vehicles having electrical weight-sensitive devices
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01G—WEIGHING
  • G01G3/00—Weighing apparatus characterised by the use of elastically-deformable members, e.g. spring balances
  • G01G3/12—Weighing apparatus characterised by the use of elastically-deformable members, e.g. spring balances wherein the weighing element is in the form of a solid body stressed by pressure or tension during weighing
  • G01G3/14—Weighing apparatus characterised by the use of elastically-deformable members, e.g. spring balances wherein the weighing element is in the form of a solid body stressed by pressure or tension during weighing measuring variations of electrical resistance
  • G01G3/1402—Special supports with preselected places to mount the resistance strain gauges; Mounting of supports
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01G—WEIGHING
  • G01G3/00—Weighing apparatus characterised by the use of elastically-deformable members, e.g. spring balances
  • G01G3/12—Weighing apparatus characterised by the use of elastically-deformable members, e.g. spring balances wherein the weighing element is in the form of a solid body stressed by pressure or tension during weighing
  • G01G3/14—Weighing apparatus characterised by the use of elastically-deformable members, e.g. spring balances wherein the weighing element is in the form of a solid body stressed by pressure or tension during weighing measuring variations of electrical resistance
  • G01G3/1414—Arrangements for correcting or for compensating for unwanted effects
• • 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
• • 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
  • G01L1/26—Auxiliary measures taken, or devices used, in connection with the measurement of force, e.g. for preventing influence of transverse components of force, for preventing overload
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
  • B65F—GATHERING OR REMOVAL OF DOMESTIC OR LIKE REFUSE
  • B65F3/00—Vehicles particularly adapted for collecting refuse
  • B65F3/02—Vehicles particularly adapted for collecting refuse with means for discharging refuse receptacles thereinto
  • B65F2003/022—Vehicles particularly adapted for collecting refuse with means for discharging refuse receptacles thereinto the discharging means comprising a device for determining the weight of the content of refuse receptacles

Definitions

• This invention relates to devices in which strain is measured to determine the value of a force, particularly an applied force, typically weight.
• the invention is especially suited to the measurement of loads on structures not specially designed for weight measurement.
• a carefully designed and machined device such as a load cell is employed, in conjunction with a load receptor such as a platform, bin, tank, hopper, silo, pan, etc.
• the load cell is a costly device of high grade material such as heat-treatable high tensile strength tool steel or aluminium, machined with precision to a geometry designed to minimise the sensitivity of the cell to extraneous strain and to minimise variations in the strain field orientation at the strain sensor location or locations.
• shearbea loadcell Another example is what is commonly known as a shearbea loadcell. Again, the structure of this type of loadcell is intended to provide sensitivity only to
• Strain in materials can arise from a variety of stress patterns due to a variety of forces such as shear forces, bending forces, torsional forces, tension forces, compression forces, etc.
• forces such as shear forces, bending forces, torsional forces, tension forces, compression forces, etc.
• a weight-receiving structure for example through a bin, pallet, bag or baled materials, and particularly where it is required to measure weight by strain measurement on a pre-existing structure which has not or cannot be designed for the minimisation of extraneous strain, such problems are less controllable. As result, little success has been achieved in obtaining reliable and accurate load measurement in such circumstances.
• weighing would desirably be implemented by fitting strain sensors to existing structures or structural components, or by incorporating components that would be simple and economic to produce, and convenient and non-critical to install.
• a further source of inaccuracy lies in the fact that electrical strain gauges exhibit a degree of transverse sensitivity, that is to say, they respond not only to strain in the direction of the primary axis of the gauge, but also to strains which are perpendicular to that axis. In environments of relatively uncontrolled secondary strain, such transverse sensitivity will lead to unpredictable error.
• the force which is to be measured (typically weight) will be referred to as the principal force and the strain which is measured as a measure of the principal force will be called the principal strain. Strain other than the principal strain will be called the secondary strain. Forces other than the principal force acting on the structure or otherwise giving rise to secondary strain will be referred to as secondary forces.
• the invention resides in apparatus in which a principal force which causes principal strain in a structure is measured by the response of a principal strain sensing means, characterised in that the apparatus further comprises means responsive to secondary strain caused by force other than said principal force, said secondary strain representing the influence of secondary force on the response of said principal strain sensing means.
• the invention resides in apparatus for the measurement of a load in ⁇ which shear strain is measured by principal strain sensing means having primary strain sensing axes orientated for response to shear strain arising from said load, characterised in that said apparatus includes secondary strain sensing means responsive to secondary strain being strain other than said shear strain, said secondary strain representing the influence on said principal strain sensing means of secondary force being force other than said load.
• the invention resides in apparatus for the measurement of a load in which compression strain is measured by principal strain sensing means having a primary strain sensing axis orientated for response to compression strain arising from said load, characterised in that said apparatus includes secondary sensing strain means responsive to secondary strain being strain other than said compression strain, said secondary strain representing the influence on said principal strain sensing means of secondary force being force other than said load.
• the invention resides in apparatus for the measurement of a load in which tension strain is measured by principal strain sensing means having a primary strain sensing axis orientated for response to tension strain arising from said load, characterised in that said apparatus includes secondary sensing strain means responsive to secondary strain being strain other than said tension strain, said secondary strain representing the influence on said principal strain sensing means of secondary force being force other than said load.
• the invention resides in load measurement apparatus including a load receiving body, first strain gauge means located on said body and orientated for response to shear in said body due to said load, second strain gauge means located adjacent said first strain gauge means and orientated for response to secondary strain being strain other than that due to said shear.
• the invention resides in load measurement apparatus including a load receiving body supported at spaced support regions, first and second strain gauge means located on said body and orientated for response to shear in said body due to said load, third and fourth strain gauge means respectively located adjacent said first and second strain gauge means and orientated for response to secondary strain being strain other than that due to said shear.
• the invention resides in apparatus for the measurement of a principal force on a structure, in which principal strain arising from said force is measured at a strain measurement location on the structure, characterised in that the apparatus further comprises means responsive to secondary strain at said location arising from secondary forces, said secondary strain representing the influence of said secondary forces on the measurement of said principal strain.
• the invention resides in apparatus for the measurement of a principal force on a structure, in which the primary sensing axis of principal strain gauge means is orientated for response to variation in said principal force, characterised in that the apparatus further comprises secondary strain gauge means the primary sensing axis of which is orientated for response to variation in secondary forces, the response of said secondary strain gauge means representing the influence of said secondary forces on the measurement of said principal strain.
• the origin of secondary strain is of no importance, as the correction of the principal force measurement proceeds without regard to the nature or mix of secondary strain. It is of course necessary to apply forces of known types to a device according to the invention during its calibration, when the influence of secondary strain on the principal strain sensor is observed, but once the apparatus has been calibrated it will operate transparently.
• Fig. 1 shows a load-supporting member embodying the present invention
• Fig. 2 is an end elevation of the member of Fig. 1
• Fig. 3 is a fragmentary sectional plan view taken on the line 3-3 of Fig. 1
• Fig. 4 is an elevation view of the gauging area from the direction 4 indicated in Fig. 3
• Fig. 5 is an elevation view of the gauging area from the direction 5 indicated in Fig. 3
• Fig. 6 is a circuit diagram illustrating the manner of interconnection of strain gauges in the embodiment with reference to Figs. 1 to 5
• Fig. 7 is a further circuit diagram illustrating the interconnection of strain gauges
• Fig. 8 is a side elevation of apparatus for calibrating the device illustrated in Figs. 1 to 5
• Fig. 9 is a further side elevation of the apparatus of Fig. 8
• Fig. 10 is a side elevation of a modified embodiment of the invention
• Fig. 11 is a side elevation of a further modified embodiment of the
• Fig. 12 is an isometric view of a further embodiment of the invention
• Fig. 13 is a side elevation view of a further embodiment of the invention
• Fig. 14 is a side elevation of a silo to which apparatus according to the invention has been applied
• Fig. 15 is a fragmentary detailed elevation of a support leg of the silo illustrated in Fig. 14
• Fig. 16 is a side elevation of a further embodiment of the invention
• Fig. 17 illustrates a further embodiment of the invention
• Fig. 18 shows in fragmentary side elevation a further embodiment of the invention
• Fig. 19 shows the device of Fig. 18 in end elevation.
• a load measuring device in which shear strain is measured as the principal strain.
• This device may be used as a substitute for a shear beam loadcell in applications where cost cannot justify the use of such a device, or where the problems of the influence of secondary force and stress described above cannot practically be overcome.
• the illustrated device 10 is in the form of an I-beam comprising a web 11 consisting of a flat steel plate referred to herein as a shearplate, and a pair of flanges 12. End plates 13 are provided for attaching the device to a support and to a load-bearing structure the load on which is to be measured.
• the I-beam may be fabricated for the purpose, or may simply be a commercially available beam of suitable dimensions for the purpose.
• the web 11 carries a pair of strain gauges 15a and 15b each of which comprises a pair of sensing grids orientated to respond to shear strain, with their primary axes at 45° to the axis of the beam. Normally one would locate such gauges at the neutral axis of the beam with respect to bending, shown at 14. In theory this ensures that cancellation of bending stresses will occur when gauges are connected in a Wheatstone bridge configuration.
• a first pair of secondary strain gauges 16a, 16b are located near the gauges 15a and 15b.
• the gauges 16a and 16b are Poisson ratio gauges, and comprise sensing grids orientated to respond to bending strain in that region in the plane of the shearplate 11 and compression or tension strain.
• the gauging region is, moreover, located away from the nominal neutral axis 14 to obtain a larger bending strain measurement than would be obtained at the neutral axis.
• a second pair of secondary strain gauges 17a, 17b may be mounted adjacent the gauges 15, with grids orientated to respond to bending of the shearplate 11 out of its plane in response to side loading of the device.
• the gauges 16 and 17 are preferably mounted on a common line with the principal gauges 15 parallel to the neutral axis 14, but in more complex structures the optimum position of the secondary gauges may be ascertained by experiment, in order to obtain a response from the gauges which mirrors as closely as possible the influence of the secondary strain on the principal gauge.
• Photoelastic examination of a model of the structure may be used to assist in the choice of location, particularly where secondary forces produce changes in the direction of the strain field in the region of the principal gauge.
• Fig. 6 shows the manner in which the strain gauges 15 and 16 may be interconnected to provide for correction of secondary stress, where only a single pair of secondary gauges 16 is used.
• the sensing grids of the gauge pairs 15a and 15b, and 16a and 16b are connected as Wheatstone bridges 18 and 19 between excitation voltage supply rails 20, 21.
• the bridge 19 is connected to the source of excitation voltage through dropping resistors 22 which serve to scale its output relative to that of the principal bridge 18, and the bridges are connected together with opposite polarity as shown.
• the device may be calibrated by the application of bending to the I-beam by any suitable means, to determine the necessary value of the resistors 22.
• the simple analogue technique for obtaining the requisite correction may also be used, although the presence of three interconnected bridges will require an iterative process to arrive at the correct value for the attenuating resistors.
• the outputs of the bridges may be processed digitally, as shown in Fig. 7, where the individual outputs of the three bridges 18, 19 and 23 are amplified and applied to a multiplexing analogue-to-digital converter 24 for passing to a computer. It is to be understood that it is not essential that the correcting strain measurement be a measurement of strain actually influencing the principal strain sensor, since the desired correction can be achieved as long as the correcting strain as measured is a function of that influence.
• a device of the kind illustrated in Figs. 1 to 5 and 7 can be calibrated for the effects of secondary strain by means of the apparatus shown in Figs. 8 and 9.
• the device 10 is mounted with the shearplate 11 vertical, by bolting down the end plate 13.
• the calibrating rig consists of a mounting plate 25. which is bolted to the upper end plate 13, this mounting plate carrying a vertical member 26 coplanar with the shearplate 11.
• a horizontal extension 27, also in the plane of the shearplate 11, is located near the upper end of the member 26, and is provided with two load positions 28 and 29 along its length. This configuration ensures that the vertical member 26, in line with the main axis of the device 10, applies to the device 10 only secondary force and secondary strain - in this case arising from compression force and the bending moment produced by the application of force at 28 or 29.
• the calibration is carried out by locating a weight (the value of which may not be known) at position 28 and recording the output of the principal and secondary strain gauges. The same weight is then applied at 29 and the gauge outputs again recorded.
• the recorded data will show the influence on the principal strain gauge of secondary strain in the plane of the shearplate 11, enabling the response of the principal gauge to be corrected for that influence.
• the test device is now rotated through 90° so that the arm 27 is now normal to the plane of the shearplate 11 as shown in Fig. 9, and weight (which need not be known) is again applied at the points 28 and 29, the outputs of the gauges again being recorded.
• the principal gauge 15 can be corrected for the influence of secondary force acting at right angles to the plane of the shearplate 11, which in normal use of the device 10 will be the horizontal plane.
• the device of Fig. 1 can be modified as shown in Fig. 10 by providing slots 30 in the upper an lower regions of the shearplate 11, or as shown in Fig. 11 where a thin section 31 is provided by simple machining of a vertical central portion of the shearplate, the gauges being located on this section.
• Figs. 1 to 5 Various approaches may be taken to the manner in which devices of the general kind illustrated in Figs. 1 to 5 are provided with means for attachment to supporting and load-bearing structures, given that the invention reduces the effect of secondary strains arising from the connection of the device with other structures and from the manner of application of the load.
• the end plates 13 can be slipped in to slots provided on the supporting and/or supported structure, eliminating the need for bolting.
• FIG. 12 shows an alternative arrangement in Fig. 12, where the endplates 13 are provided with a horizontal flange 32 serving as footing or load support - an arrangement unthinkable with prior art devices.
• Fig. 13 shows another alternative, in which the end plates 13 are fitted with vertical or horizontal bushes 33 to receive load transfer pins.
• strain gauges are applied to existing structures.
• the retro-fitting of weighing devices to existing structures for example by the installation of loadcells or by the fitting of "bolt on” or “weld on” strain sensing devices has in the past met with varying degrees of success.
• the relationship between measured strain and weight turned out to be quite unpredictable due for example to the effects of wind forces and bending distortion of the support structure under varying load conditions, differential temperature between the sensor and the support structure, and differing temperature coefficient as between the sensor and the structure.
• strain sensors for example strain gauges
• secondary strain due to temperature differentials can be largely eliminated, and the influence of secondary forces can be dealt with in accordance with the present invention by locating secondary strain sensors in a location where their output represents the influence of secondary strain on the principal strain sensors, and using the scaled outputs of the secondary sensors to counteract the influence of the secondary strain on the principal strain sensors.
• Figs. 14 and 15 show such an arrangement applied to a leg 35 of a silo support structure 34. Pairs of electrical resistance strain gauges 36a, 36b, 37a and 37b are applied to the opposite sides of the leg 35 with their grids aligned as shown in Fig. 15. The grids 36a and 36b are connected in a bridge for response to compression strain in the region, while grids 37a and 37b are connected in a second bridge for correcting response to bending strain in the region. Calibration of the gauges may be carried out by applying side loading and adjusting the correction applied from the grids 37a and 37b.
• the invention is applied to conveying apparatus, in this case a track 38 suspended on hangers 39.
• the force acting on the track between the hangers 39 is measured by means of shear gauges at gauging locations 40.
• the force to be measure will of course result in principal strain (shear strain) at the gauging locations.
• the section of track between the hangers will bend downwardly as the article passes between the hangers 39, resulting in secondary forces and secondary strain at the two gauging locations 40.
• FIG. 17 A generalised example of the application of the invention to devices in which, for instance, torque is of significance, either as the source of principal or a secondary strain, and indeed of the applicability of the invention to quite generalised structures, is provided by the idealised device shown in Fig. 17.
• four pairs of strain gauges are used, the second gauge of each pair being located on the opposite side of the structural member 41.
• Gauges 42 respond to torque
• gauges 44 respond to bending in the vertical plane as well as tension and compression
• gauges 43 respond to bending in the horizontal plane while their response to tension and compression will be cancelled when connected in Wheatstone bridge configuration
• gauges 45 to both shear and torque.
• Weight is assumed to be applied as shown at 46.
• the grids of each gauge pair are connected in bridges and the outputs of each bridge employed for compensation in the manner described above.
• the principal strain may be torque, where for example the torque is used as a measure of applied load.
• the principal strain may be bending, shear, tension or compression, with the calibration technique being chosen appropriately.
• FIGs. 18 and 19 an embodiment of the invention in which the gauging arrangement described in relation to the device illustrated in Figs. 1 to 5 is utilized on the forks of a vehicle for rubbish removal.
• the illustrated member 47 in this example of the invention is one of a pair of forks used for lifting and manoeuvring a rubbish skip, and for this purpose is mounted at its end 48 on a supporting structure not shown here.
• a gauging region 49 is located near the supported end of the member 47.
• a pair of flanges 50 are attached to the member 47 to increase the resistance of this section of the member 47 to side loading.
• Such forks are subjected at times to considerable side loading, often beyond the yield point of the unstiffened member, and the flanges 50 serve to reduce the risk that overload will result in permanent distortion of the gauged region of the fork.
• the gauges may be mounted in a recessed portion of the member to provide mechanical protection.
• the gauging region is provided with principal and secondary gauges in the manner described in connection with Figs. 1 to 5.

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• 1993
  • 1993-07-30 WO PCT/AU1993/000388 patent/WO1994003784A1/fr not_active Application Discontinuation
  • 1993-07-30 EP EP93917436A patent/EP0653053A4/fr not_active Withdrawn

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