WheelWatch – Functional principle
WheelWatch is built around a high-resolution high speed digital camera consisting of a high resolution CMOS sensor, an integrated high performance flash and an image analysis processor. The digital camera features offers extremely short shutter speeds of just a few micro-seconds that are necessary for long duration tests. The high quality camera also ensures the system is robust and stable over time.
It provides data at a frequency of 490Hz, ideal for studying and optimizing static and dynamic chassis parameters. Measurements are controlled automatically and may be collected over long periods of time. The triggering function ensures that multiple sensors are fully synchronized.
The camera can be mounted at a distance of less than 500mm (20 in) from the fender. The camera processor uses TCP/IP protocol to communicate with the laptop computer which controls the system. The computer is placed in the test vehicle. The vehicle 12 Volt power system provides power during the test drive.
For the measurement of wheel movements, one camera for each wheel is mounted so that the wheel as well as part of the surrounding fender is visible. Special optical targets applied to the fender define the vehicle coordinate system. A lightweight carbon fiber wheel adapter is fixed to the wheel.
The position of the camera does not have to be stable as WheelWatch recalculates its position continuously using the reference targets on the vehicle fender. The wheel movement measurements are always provided in the vehicle coordinate system. Movements of the camera or camera mount do not influence measurement results, making the system inherently more stable than competing systems.
The driver manually triggers the beginning and end of a measurement session. No other interaction with WheelWatch is required. The high speed camera collects wheel measurements at a rate of up to 490 times per second.
The image processor analyzes the digital images in real time and passes the measurement values to the notebook computer. Wheel target positions and target trajectories are available shortly after the image acquisition. In addition, WheelWatch computes all six degrees of freedom of the wheel in the vehicle coordinate system.