Ortenburg, Germany-In terms of quiet
operation, extended lifetime, and high efficiency, crankshaft bearings play an
important role in engine design. Accurate measurement of bearing shell
thickness, consequently, helps ensure smooth running characteristics.
To grade and sort crankshaft bearing shells into as many as 10 separate classes, a leading engine manufacturer was looking for a method of measuring bearing shell thickness and profile down to 0.3 micrometers repetitive accuracy at 6 sigma reliability. In addition, the method had to be fast enough to accommodate auto industry production rates.
| Measurement system’s air cushion chute assembly is tailored to suit the bearing shell design.
A bearing measurement system based on Micro-Epsilon's capaNCDT capacitive displacement sensors met the challenge. Designed by Micro-Epsilon with input from the customer, the system relies on a cushion of air to transport the bearing shells and eliminate vibration and wear from the measurement system. Non-contacting operation, furthermore, prevents probe damage to the shell's surface. Here is the setup:
A capacitive sensor is positioned on either side of the bearing shell, the sensor axes being exactly aligned. By measuring the distance from each sensor to the shell, and knowing the distance between sensors, the PC--which receives the amplified signals--calculates shell thickness. The shape of each sensor face matches the half-round chute used to guide the shells on the cushion of air, while guard rings shield the measurement electrodes from the edge effects of electric fields.
To compensate for individual sensor linearity characteristics, as well as the effects of sensor mount thermal expansion, the measurement system automatically calibrates linearity. A reference bearing shell passes down the chute at intervals, stopping at the measurement point. The complete measurement system then linearizes by pneumatically altering reference shell position within the sensor measurement gap.
Micro-Epsilon's air cushion system plays a key role in this application. Johann Salzberger, the company's director of marketing and sales points out, "The air cushion eliminates many disadvantages associated with mechanical conveyor systems, which can be prone to vibration. If the bearing shell pitches or yaws due to vibration during measurement, the accuracy is seriously affected."
Additional details...Contact Richard Auxer, Micro-Epsilon, 3200 Glen Royal Rd., Ste. 110, Raleigh, NC 27612; Tel: (919) 787-9707.
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