1、Designation: F3109 16Standard Test Method forVerification of Multi-Axis Force Measuring Platforms1This standard is issued under the fixed designation F3109; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision.
2、 A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This standard specifies procedures for performanceverification of multi-axis force platforms commonly used formeasuring ground react
3、ion forces during gait, balance andother activities.1.1.1 This standard provides a method to quantify therelationship between applied input force and force platformoutput signals across the manufacturers defined spatial work-ing surface and specified force operating range.1.1.2 This standard provide
4、s definitions of the critical pa-rameters necessary to quantify the behavior of multi-axis forcemeasuring platforms and the methods to measure the param-eters.1.1.3 This standard presents methods for the quantificationof spatially distributed errors and absolute measuring perfor-mance of the force p
5、latform at discrete spatial intervals anddiscrete force levels on the working surface of the platform.1.1.4 This standard further defines certain important derivedparameters, notably COP (center of pressure) and methods toquantify and report the measuring performance of such derivedparameters at spa
6、tial intervals and force levels across theworking range of the force platform.1.1.5 This standard defines the requirements for a reportsuitable to characterize the force platforms performance andprovide traceable documentation to be distributed by themanufacturer or calibration facility to the users
7、 of suchplatforms.1.1.6 Dynamic characteristics and applications where theforce platform is incorporated in other equipment, such asinstrumented treadmills and stairs, are beyond the scope of thisstandard.1.1.7 This standard is written for purposes of multi-axisforce platform verification; however t
8、he methods and proce-dures are applicable to calibration of force platforms bymanufacturers.1.2 The values stated in SI units are to be regarded as thestandard. Other metric and inch-pound values are regarded asequivalent when required.1.3 This standard does not purport to address all of thesafety c
9、oncerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E4 Practices for Force Verification
10、of Testing MachinesE74 Practice of Calibration of Force-Measuring Instrumentsfor Verifying the Force Indication of Testing Machines3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 center of pressure (COP), nthe spatial point in asystem at which a single equivalent force balance
11、s the sum ofboth the distributed forces and the distributed moments actingon the system.3.1.2 COP error, ndifference between the COP x-y posi-tion reported by the force platform (or calculated from theforce platform outputs) and the actual x-y location of theapplied Fz verification force.3.1.3 cross
12、talk or crosstalk error, nsensitivity of an un-loaded output channel corresponding to an unloaded axis whena force or a moment is applied to a different axis.3.1.4 force platform origin, nthe position on the forceplatform, specified by the manufacturer, where x, y, and z = 0.The origin serves as a r
13、eference position for the COP x andCOP y locations, locations for uniaxial forces applied duringverification, and for calculating output moments due to inputforces. The origin may be at a different x-y-z position from theforce platforms geometric center. The force platform origin issometimes called
14、the electro-mechanical origin.3.1.5 Fx and Fy, nforces orthogonal to Fz, assigned perFig. 1 which follows the right-hand coordinate system (“right-hand rule”) convention for directionality.1This test method is under the jurisdiction of ASTM Committee F04 on Medicaland Surgical Materials and Devices
15、and is the direct responsibility of SubcommitteeF04.15 on Material Test Methods.Current edition approved Aug. 1, 2016. Published September 2016. DOI:10.1520/F3109-16.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual B
16、ook of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.1.6 Fz, nforce that is orthogonal to the working surfaceof the platform. Fz and
17、 z distances are positive going down-ward when the force platform is mounted on the floor.3.1.7 moment, na vector equal to the cross product of aposition vector and a force vector. Given a position vector d =x, y, z relative to a given origin where a force F = Fx, Fy,Fz is applied then the component
18、s of the moment vector M =Mx, My, Mz relative to the origin are:Mx=yFzzFyMy=zFxxFzMz=xFyyFx3.1.8 Mx, My and Mz, nmoments around the x, y and zaxes, respectively, following the right-hand coordinate systemconvention for directionality.3.1.9 multi-axis force plate, nsynonym for multi-axisforce platfor
19、m.3.1.10 multi-axis force platform, na transducer with a flatmeasuring surface capable of measuring three orthogonalforces, three orthogonal moments, and directly or indirectlymeasuring the center of pressure x-y position.3.1.11 serialized calibration values, ncalibration valuesthat apply to a speci
20、fic force platform with a specific serialnumber. The calibration values may be used in the forceplatform, in an amplifier, or in a computer that makes up acalibrated force-measuring platform system.3.1.12 traceable force standard, na force transducer ordead weight that is traceable to national stand
21、ards and is moreaccurate than the instrumentation that is being verified. In thismethod, if dead weights are used then corrections for gravityshall be applied perASTM E4 and their center of mass shall bespatially balanced around the axis of loading such that forcesapplied to the force platform are a
22、pplied at a known location.3.1.13 uniaxial force, nforce that is only in the directionof the intended axis without imparting forces in the twoorthogonal axes. For example, applying Fz uniaxially shall notcause Fx or Fy forces greater than 10% of the Fz to Fx or Fzto Fy crosstalk specified by the for
23、ce platforms manufacturer.3.1.14 working surface, nthe flat area of the platformwhere ground reaction forces are measured while patients orsubjects perform activities such as walking, standing, running,and other activities. In most applications the working surface isoriented horizontally and is the
24、top surface of the forceplatform.3.1.15 x-y-z position, nthe position where the force veri-fication vector is applied with respect to the force platformsorigin.4. Summary of Test Method4.1 This standard method has three sections:4.1.1 Uniaxial forces are applied to the force platform usingtraceable
25、force standards. The forces are applied for at least 5force values over a range of positions spanning the manufac-turers specified working surface dimensions. The force plat-forms outputs are recorded at each force and position. Becausethe force platform provides a working surface of finite dimen-si
26、on on which forces will be applied, it is necessary tocharacterize all errors at sufficiently small intervals over thatworking surface to ensure adequate quality of measurement atall locations of force application. In this standard, a grid patternto ensure proper spatial characterization of errors i
27、s presented(see Fig. 2).4.1.2 The recorded force platform outputs are analyzed at allforces and positions to compare the force platforms Fx, Fy, Fz,Mx, My, Mz, COP x and COP y measuring errors and crosstalkFIG. 1 Force Platform Orthogonal Coordinate ConventionsF3109 162performance with the manufactu
28、rers specifications. Thesecomparisons determine whether the force platform is success-fully verified.4.1.3 A report which includes graphical presentation of theresults shall be prepared.5. Significance and Use5.1 Multi-axis force measuring platforms are used to mea-sure the ground reaction forces pr
29、oduced at the interfacebetween a subjects foot or shoe and the supporting groundsurface. These platforms are used in various settings rangingfrom research laboratories to healthcare facilities. The use offorce platforms has become particularly important in gaitanalysis where clinical evaluations hav
30、e become a billableclinical service.5.2 Of particular importance is the application of forceplatforms in the treatment of cerebral palsy (CP) (1, 2).3Anestimated 8,000 to 10,000 infants born each year will developCP (3) while todays affected population is over 764,000patients (4). Quantitative gait
31、analysis, using force platformsand motion capture systems, provide a valuable tool in evalu-ating the pathomechanics of children with CP. This type ofmechanical evaluation provides a quantitative basis for treatingneuromuscular conditions. In other words, surgical decisionsare in part guided by info
32、rmation gained from the use of forceplatform measurements (5, 6).5.3 Another application is treatment of spina bifida.Accord-ing to the Gait and Clinical Movement Analysis Society(GCMAS) (7), an instrumented gait analysis is the Standard ofExpert Care for children with gait abnormalities secondary t
33、ospina bifida. The main objective of diagnostic gait analysis is todefine the pathological consequences of neural tube defects asthey relate to gait. The use of instrumented gait analysis allowsphysicians to determine which surgical or non-surgical inter-ventions would provide the best outcome.5.4 M
34、ore recently force platforms have been used for pre-and post-surgical evaluation of TKA (total knee arthroplasty)and THA (total hip arthroplasty) patients. Such data providesan objective measure of the mechanical outcome of the surgicalprocedure.5.5 In addition to the clinical applications there are
35、 numer-ous medical and human performance research activities whichrely on accurate measurement of ground reaction forces usingmulti-axis force platform measurement instruments.5.6 As a standards organization ASTM has historicallyprovided excellent standards for the calibration of force trans-ducers
36、and force-measuring instrumentation. Force platforms,however, are different from force transducers. Force platformstypically provide a large active working surface unlike forcetransducers which provide more or less point of interactionwith the load-applying environment. Moreover, force plat-forms ty
37、pically provide six-axis measurements and are ex-pected to be used in environments causing multi-axial loading.6. Apparatus6.1 The apparatus shall have the following attributes:3The boldface numbers in parentheses refer to the list of references at the end ofthis standard.FIG. 2 Illustration of Spat
38、ial Grid Pattern Used to Apply Forces for Force Platform VerificationF3109 1636.1.1 The apparatus shall apply all Fx, Fy and Fz forcesusing a traceable force standard. SeeASTM Standard E74-13a,Sections 5 and 6.6.1.2 The apparatus shall apply all forces using a single, flatcontact pad to concentrate
39、force distribution as might beencountered during heel strike. The shape and dimensions ofthe contact pad shall be specified in the report.6.1.3 The apparatus shall apply all forces uniaxially in anaxis that is coincident with the axis of the force platform beingverified. For example, Fz shall be app
40、lied perpendicular to theforce platforms working surface without causing Fx or Fyforces greater than 10% of the Fz to Fx or Fz to Fy crosstalkspecified by the force platforms manufacturer.6.1.4 The apparatus shall measure and report the position ofthe applied forces with an accuracy of 60.1mm.6.1.5
41、The apparatus shall be located in an environment withsufficient stability that verification results are unaffected byenvironmental variations.6.1.6 The apparatus shall be at a steady-state operatingcondition before verification begins so that the equipment itselfdoes not introduce any errors.6.1.7 C
42、are shall be taken to minimize transient vibrationswhen verification is being performed.6.2 Users of this standard shall ensure that the forceplatforms serialized calibration information provided by themanufacturer is in effect. For example, if the force platformrequires the end user to apply calibr
43、ation files from a computeror to use the force platform with an amplifier as a matched pair,the user of this standard shall ensure that the force platform (orforce platform and amplifier combination) is using the correctforce platforms serialized calibration values before beginningverification.7. Ve
44、rification Procedure7.1 Before proceeding with the verification, a warm-upperiod with all electronics powered may be necessary toachieve stable temperatures and outputs. Reviewing the forceplatform manufacturers recommendations regarding awarm-up period is recommended.7.2 Before any forces are appli
45、ed to the force platform,ensure that the traceable force standard is not touching theforce platform then zero the outputs of all six force platformoutputs and, if used, the traceable force transducer. This stepmay be repeated at each position.7.3 Note that all x-y-z positions in the verification pro
46、cedureare relative to the force platforms origin as defined in section3.1.7.4 Apply Fz to the working surface of the force platform.7.4.1 Apply Fz at points making up an evenly spaced gridspanning the force platforms working surface. There should be100 or more positions. Spacing in x and y should be
47、 no greaterthan 25.4mm (25.4mm increments for x and 25.4mm incre-ments for y). Use of fewer positions or larger spacing incre-ments shall be noted and justified in the report. The spacingbetween measurements shall be sufficiently close so that theuncertainty of the force platforms outputs due to int
48、erpolationbetween positions is less than the force platforms specifiedaccuracy. The x and y positions where Fz is applied shall bemeasured with an accuracy of 60.1mm.7.4.2 At each x-y position, apply 5 or more different Fzforces. Begin with a minimum force that is no less than 5% andno greater than
49、10% of the force platforms Fz full-scale.Monotonically increase the applied force and end at the forceplatform manufacturers specified Fz full-scale capacity. Foreach applied Fz and x-y position, record the force applied bythe force standard (either the output of the standard forcetransducer cell or the force applied by the standard weights);the x and y positions of Fz; and the force platforms outputs Fx,Fy, Fz, Mx, My, Mz, and, if provided by the force platform,COP x, and COP y. The COP is frequently not a direct outputof the for
