A Novel Sensor Foil to Measure Ski Deflections: Development and Validation of a Curvature Model

Abstract

The ski deflection with the associated temporal and segmental curvature variation can be considered as a performance-relevant factor in alpine skiing. Although some work on recording ski deflection is available, the segmental curvature among the ski and temporal aspects have not yet been made an object of observation. Therefore, the goal of this study was to develop a novel ski demonstrator and to conceptualize and validate an empirical curvature model. Twenty-four PyzoFlex® technology-based sensor foils were attached to the upper surface of an alpine ski. A self-developed instrument simultaneously measuring sixteen sensors was used as a data acquisition device. After calibration with a standardized bending test, using an empirical curvature model, the sensors were applied to analyze the segmental curvature characteristic (m−1) of the ski in a quasi-static bending situation at five different load levels between 100 N and 230 N. The derived curvature data were compared with values obtained from a high-precision laser measurement system. For the reliability assessment, successive pairs of trials were evaluated at different load levels by calculating the change in mean (CIM), the coefficient of variation (CV) and the intraclass correlation coefficient (ICC 3.1) with a 95% confidence interval. A high reliability of CIM −1.41–0.50%, max CV 1.45%, and ICC 3.1 > 0.961 was found for the different load levels. Additionally, the criterion validity based on the Pearson correlation coefficient was R2 = 0.993 and the limits of agreement, expressed by the accuracy (systematic bias) and the precision (SD), was between +9.45 × 10−3 m−1 and −6.78 × 10−3 m−1 for all load levels. The new measuring system offers both good accuracy (1.33 × 10−3 m−1) and high precision (4.14 × 10−3 m−1). However, the results are based on quasi-static ski deformations, which means that a transfer into the field is only allowed to a limited extent since the scope of the curvature model has not yet been definitely determined. The high laboratory-related reliability and validity of our novel ski prototype featuring PyzoFlex® technology make it a potential candidate for on-snow application such as smart skiing equipment.

Validation of a Sensor-Based Dynamic Ski Deflection Measurement in the Lab and Proof-of-Concept Field Investigation

“…While carving, the turn radius can be changed by the manipulation of the ski deflection based on alterations in the applied skiing technique (e.g., applied forces, edge angle, body position). However, it is an oversimplification to assume a homogeneous deflection behavior (=constant radius) along the ski; rather, temporal and segmental differences in the curvature ( ) occur depending on the skiing technique and the quality of a turn [ 3 , 7 ]. Accordingly, it is not possible to deduce the deflection behavior based on the turn radius; instead, the characteristic along the ski is decisive.…”

“…The strain gauge-based approaches have not been tested for reliability or validity from a scientific point of view, and consequently the studies are limited for proof-of-concept investigations. In contrast, a novel PyzoFlex ® prototype has already been tested for reliability and validity in a quasi-static setting with a high-precision laser measurement system [ 7 ]. A curvature model was developed and the calibrated data provided both good accuracy (1.33 × 10 −3 m −1 ) and high precision (4.14 × 10 −3 m −1 ) [ 7 ].…”

Curvature Detection with an Optoelectronic Measurement System Using a Self-Made Calibration Profile

“…As a practical application, various ski-specific deformations of Alpine skis (e.g., simulation of ski bending during a carved turn) in three-dimensional space can be systematically analyzed in the laboratory. In addition to Alpine skis [ 23 , 24 ], other measurement objects such as snowboards [ 29 ], cross-country skis and poles [ 30 ] or jumping skis [ 31 ] can also be utilized. Furthermore, an OMS can be used to calibrate bending sensors in both static and dynamic settings, eliminating the need for a complex and difficult-to-adjust laser measurement system in the tree-dimensional space.…”

“…Specifically, no one has yet analyzed the curvature (w″) of objects using a 3D motion capture system and, consequently, no accuracy data is available. The w″ seems to be an important parameter of Alpine skis [ 24 ], and can be measured by a high-precision laser measurement system in the laboratory. Both the bending stiffness curve [ 23 , 25 , 26 , 27 , 28 , 29 ] and the segmental ski deflection [ 24 ] can be described based on w″.…”

“…The w″ seems to be an important parameter of Alpine skis [ 24 ], and can be measured by a high-precision laser measurement system in the laboratory. Both the bending stiffness curve [ 23 , 25 , 26 , 27 , 28 , 29 ] and the segmental ski deflection [ 24 ] can be described based on w″. For the three-dimensional detection of w″, a laser measuring system has limited suitability, because a very complex setup with several laser units and measuring slides is required.…”