In any sporting activity, the equipment used has to be fine-tuned appropriately as it can contribute significantly to performance. In snowboarding and skiing, the sharpness of a board or ski can considerably affect performance, making it of paramount importance at the highest level of competition.
In order to produce a new level of sharpening precision and also to measure the resistance of ski edge for a wide range of conditions and surfaces, a prototype device has been designed by the Worcester Polytechnic Institute Sports Engineering Lab that allows precise and accurate 3D imaging and measurement of ski edge.
Methodology
This novel device, unlike presently available methods, helps to determine sharpness by applying a specific load to a material such as a snow simulation material or ice at a fixed angle to the edge. This causes movement parallel and perpendicular to the edge, which is measured as shown in figure 1. The geometry is measured and curvature is determined as functions of scale and position over the edge.
By performing linear regression analyses of performance versus curvature as a function of scale correlations are determined. Using a laser scanning confocal microscope, Evident LEXT OLS4000, ski edges are measured. Heron’s method is used to calculate curvatures.
Basic Principle of Performance Measurements
Figure 1 shows the basic principle of performance measurements.
Figure 1. Basic principle of device performance measurements
The WPI Sports Engineering Lab has developed the ski edge measuring device for providing athletes, skiing facilities, equipment manufacturers and coaches with a new level of accuracy and helps users to determine resistance to skidding perpendicular to an edge as well as sliding along an edge.
By using the LEXT OLS4000, this device can be used to create 3D topographic ski edge measurements, particularly direct measurement and the characterization of edge curvature.
The Importance of Proper Edge Roughness
A ski or snowboard’s performance largely depends on its sharpness. If the edge is dull, it may cause issues in recreational and racing skiing. If there are icy hard-surface conditions, control issues are magnified by dull edges. In the world of racing, edges need to be sharper so as to cut at high speeds with skis positioned at a sharp angle. Also highly sharp edges can result in injury and must be treated with adequate care both while being handled and while in use.
Skiing Relative to Machining
Skidding or cutting through snow with skis at a very high angle, as shown in Figure 2, is very similar to a tool (the ski) cutting through a work piece (the snow). The cutting force on the tool is equal to the turning force on the skis. The edge angle of the ski (more than 90° when skidding) is comparable to the rake angle of the tool. The limiting factor that determines how much of a rake angle the skis can withstand while skidding or cutting through the snow, is the sharpness of the skis, in a similar way to the sharpness of a tool.
Figure 2. Skidding, made possible by highly sharpened ski edges.
Ski Edge Curvature
The team at WPI Sports Engineering Lab, led by Dr Christopher Brown, set out to create a novel way of looking at ski edge curvature by developing their new ski edge imaging and measuring device, which provides an extremely precise means of viewing and analyzing ski edge roughness.
By combining a physical assembly, as shown in Figure 3, which is designed to offer optimal ski edge viewing with a laser scanning confocal microscope, as shown in Figure 4, Dr Brown’s team pioneered a novel way to determine ski edge sharpness by precisely characterizing ski edge curvature.
Figure 3. Assembly prototype at WPI manufacturing labs. Edge sharpness configuration tests resistance perpendicular to ski edge. Load frame can be rotated to test resistance parallel to ski edge.
Figure 4. Evident LEXT OLS4000 laser scanning confocal microscope.
Roughness Imaging and Analysis
The new ski edge measurement system enables users to create and study 3D topographic images of ski edge curvature. In order to showcase the effectiveness of the system, the WPI Sports Engineering Lab created and analyzed the following images of ski edges (Figures 6 to 10) created with a variety of sharpening techniques. Figure 5 shows the terminology with a standard ski edge.
Figure 5. This diagram represents the basic layout of and terminology associated with a standard ski edge.
Figure 6. Profile of ski edge with no modifications.
Figure 7. Same ski edge after sharpening with a file.
Figure 8. Same ski edge after sharpening with a ceramic stone.
Figure 9. This shows a ski edge that has been sharpened with only a file using the standard method.
Figure 10. The ski edge from Figure 9 after an additional standard-method sharpening with a ceramic stone.
Inferences
The following inferences were drawn by Dr Brown and his team based on these 3D topographic images:
- The direction of the burr at the tip of the ski edge is determined by the method of sharpening.
- This bur can be advantageous in offering traction on turns, however it can also cause friction of straight paths, reducing the skier’s speed.
- When compared to an unsharpened ski, a ski sharpened with just a file is smoother.
- When compared to a ski sharpened with a file, a ski sharpened with a stone is smoother.
- Progressively sharpening beginning from a standard file and moving to a specialized sharpening stone will greatly decrease the surface roughness of the ski edge and provide a smoother ride to the skier.
Conclusion
The implementation of direct geometric 3D confocal microscopy has enabled a superior level of curvature imaging and edge measurement using this new device. The microscope enables the calculation of curvature versus position and scale, a new calculation method used exclusively by this patent-pending system.
As curvature varies with scale and position, curvature characterization has been problematic. By their work with this new ski edge measurement system, WPI Sports Engineering Lab is pioneering multi-scale position-specific curvature characterization. This new system has been prototyped and designed to measure ski edge resistance to both skidding perpendicular to an edge and sliding along an edge. A provisional patent has been filed.
This information has been sourced, reviewed and adapted from materials provided by Evident Corporation - Industrial Microscopy.
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