ASTM WK43919

    New Test Method for Verification of Multi-Axis Force Measuring Platforms

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    Developed by Subcommittee: F04.15 | Committee F04 | Contact Staff Manager



    WK43919

    1. Scope

    1.1 This standard specifies procedures for performance verification of multi-axis force measuring platforms. 1.1.1 This standard provides a method to quantify the relationship between applied input force and force platform output signals across the manufacturers defined spatial working surface and specified force operating range. 1.1.2 This standard provides definition of the critical parameters necessary to quantify the behavior of multi-axis force measuring platforms and the methods to measure the parameters. 1.1.3 This standard presents methods for the quantification of spatially distributed errors and absolute measuring performance of the force platform at discrete spatial intervals and discrete force levels on the working surface of the platform. 1.1.4 This standard further defines certain important derived parameters, notably COP (center of pressure) and methods to quantify and report the measuring performance of such derived parameters at spatial intervals and force levels across the working range of the force platform. 1.1.5 This standard defines the requirements for a report suitable to characterize the force platforms performance and provide traceable documentation to be distributed by the manufacturer or calibration facility to the users of such platforms. 1.1.6 Dynamic characteristics and applications where the force platform is incorporated in other equipment, such as instrumented treadmills and stairs, are beyond the scope of this standard. 1.1.7 This standard is written for purposes of multi-axis force platform verification; however the methods and procedures are applicable to calibration of force platforms by manufacturers.

    Multi-axis force measuring platforms are used to measure the ground reaction forces produced at the interface between a subjects foot and the supporting ground surface. These platforms are used in various medical settings ranging from research to clinical applications. Of particular importance is the application of force platforms in the diagnosis and treatment of CP (cerebral palsy)(1,2). An estimated 8,000 to 10,000 (3) infants born each year will develop CP while todays affected population is over 764,000 patients(4). According to the National Institute of Health(5): Cerebral palsy cant be cured, but treatment will often improve a childs capabilities. Many children go on to enjoy near-normal adult lives if their disabilities are properly managed. Orthopedic surgery is often recommended when spasticity and stiffness are severe enough to make walking and moving about difficult or painful. Surgery to cut nerves. Selective dorsal rhizotomy (SDR) is a surgical procedure recommended for cases of severe spasticity when all of the more conservative treatments have failed to reduce spasticity or chronic pain. A surgeon locates and selectively severs over activated nerves at the base of the spinal column. SDR is most commonly used to relax muscles and decrease chronic pain in one or both of the lower or upper limbs. Quantitative gait analysis, using force platforms and motion capture systems provide a valuable tool in evaluating the patho-mechanics of CP children. This type of mechanical evaluation provides a quantitative basis for both orthopedic surgery and selective dorsal rhizotomy. In other words, surgical decisions are in part guided by information gained from the use of force platform measurements(6,7). More 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 helps in the guidance and planning of the surgery and provides an objective measure of the mechanical outcome of the surgical procedure. In addition to the clinical applications there are numerous medical and human performance research activities which rely on accurate measurement of ground reaction forces using force platform measurement instruments. As a standards organization ASTM has historically provided excellent standards for the calibration of force transducers and force measuring instrumentation. Force platforms however, are different from force transducers. Force platforms typically provide a large active working surface unlike force transducers which provide more or less point of interaction with the load applying environment. Moreover force platforms typically provide six D.O.F. (degree of freedom) measurements and are expected to be used in environments causing multi axial loading. 1. GCMAS Executive Board. Position Statement: Gait Analysis in Cerebral Palsy. www.GCMAS.org. 2009 Mar. 2. Lyon R, Liu X, Schwab J, Harris G. Kinematic and kinetic evaluation of the ankle joint before and after tendo achilles lengthening in patients with spastic diplegia. Journal of Pediatric Orthopaedics. 2005 Jul-Aug, 25(4):479-83. 3. United Cerebral Palsy Fact Sheet. 8-Feb-2012. http://www.ucp.org/uploads/media_items/cp-fact-sheet.original.pdf 4. Cerebral Palsy Magazine. http://www.cerebralpalsysource.com/Resources/magazine_cp/index.html 5. National Institutes of Health. Cerebral Palsy: Hope Through Research. http://www.ninds.nih.gov/disorders/cerebral_palsy/detail_cerebral_palsy.htm 6. Gage JR. Gait analysis. An essential tool in the treatment of cerebral palsy. Clinical Orthopaedic and Related Research, 1993 Mar, (288):126-34. 7. McCaw ST, DeVita P. Errors in alignment of center of pressure and foot coordinates affect predicted lower extremity torques. Journal of Biomechanics. (1995) Volume: 28, Issue: 8. Pages: 985-988.


    Keywords

    force measuring platforms

    The title and scope are in draft form and are under development within this ASTM Committee.

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    Work Item Status

    Date Initiated:
    11-04-2013

    Technical Contact:
    Cindy Samaan

    Item:
    007

    Ballot:
    F04 (14-05)

    Status:
    In Balloting