High-Speed Sensors for Tire Footprint Testing
When it comes to high-speed tire testing, there are only a few methods available to capture an entire tire contact patch while rotating at speed:
1. The glass plate camera system. This involves building infrastructure on a test track where a glass plate is embedded into the track surface. Below the track a high-speed camera is pointed up at the glass plate to capture the tire image as the vehicle rolls over the plate. The systems are custom built and require in-house developed methods to correlate greyscale in the image to pressure. CONS: This is not a NIST traceable measurement and there is no way to correlate this inferred pressure with real pressure.
2. The single strip method. Typically, this is a 1-2 cm wide strip that the tire passes over multiple times, usually on a rotating drum. After hundreds of rotations, a composite image is constructed. CONS: This method requires multiple rotations in order to construct a composite image and does not capture the entire footprint in a single pass.
3. An array of 3-axis load cells which can measure x, y, and z axis forces. CONS: This technology is limited in spatial resolution and is limited in drive-over speed.
Until now, there have been no viable options that provide accurate high-resolution tire footprint pressure measurements for dynamic testing
A high frame rate is important because it will allow the user to capture the dynamics of the rolling tire. If the frame rate is too low, it will not be able to capture the tire as it rolls continuously
Spatial resolution is also important. A high spatial resolution allows the end user to image the fine details in a tire such as sipes, grooves, tie bars, and notches. Using a sensor with too low a resolution will blur these features with surrounding features and prevent the user from visualizing the dynamic interaction that these features have with rolling speed.
Why does it matter?
A tire passing over the sensor at high speed requires the sensor to be scanned at a speed high enough to capture the entire contact patch as the tire traverses the sensor, and at multiple instances. If the sensor is scanned too slowly, the image can be artificially distorted since the tire will move before the scan is completed; something akin to a camera with a slow shutter speed trying to photograph a moving object. Second, the sensing dielectric must be able to react quickly enough in order to accurately measure dynamically changing contact pressures applied by a tire moving at high speed.
How XSENSOR high speed sensors are different.
The XSENSOR High Speed Tire system allows the user to capture the tire contact and pressure data at various speeds. The system can be assembled and configured to record data within 10 minutes. The Tire Tool automatically measures the center line length, tire width, net to gross contact (land to sea) ratio, rectangular ratio, average pressures, peak pressures etc., and presents the data in an easy to read format.
The system can capture many clear and full frames at various speeds. The user can select a single image, an average of several images, or a composite image of the tire traversing the sensor. The data is available within seconds of recording and little to no post processing is required. This enables engineers to review that data immediately while on the track, make adjustments, and get immediate feedback on the changes. This is important if the access to the track is limited and if you want to complete all your testing in one go.
The in-depth tire contact and pressure data allows you to build simulation models of the tire behaviour at various speeds, or even validate your existing simulation models.
Unlike other systems, the XSENSOR High Speed Tire system comes with an ISO 17025 accredited calibration which assures the user that measurements made with different systems at different locations are consistent as opposed to a proprietary “calibration” process for a glass plate that has no international standards for traceability or any way to confidently compare against a known reference standard.
The XSENSOR High Speed Tire system can capture several complete frames of data at speeds over 100km/h. XSENSOR’s High Speed Tire pressure imaging system provides the end user a solution to accurately measure the dynamic interaction between the tire and surface while still being portable.
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