Sensors and data acquisition system provide real-time visibility of grinding system operation.

High-performance materials such as ceramics, optics, and alloy steels are manufactured using abrasive grinding technology. Until now, the grinding wheel and process conditions have been difficult to measure in production.

A new, instrumented spindle provides real-time force information that allows adaptive control of the grinding process. This approach provides information to the machine controller that is used to maintain quality in the presence of changing conditions. Previously, the time required to make a part was kept constant while quality varied. Now, the machine controller makes adjustments to maintain quality in the shortest possible time. The quality remains constant, but the process time varies.

The instrumented spindle has embedded, non-contact sensors that measure the time-varying gap between the rotor and stator. This gap is converted to a force using the known stiffness of the air bearing spindle. The instrumented spindle may be configured as a smaller, higher- speed spindle with milli-Newton force resolution at speeds up to 20 kRPM. Larger configurations also are available with much higher load capacity.

The bandwidth of the instrument is currently 100 Hz, with future improvements planned to increase the dynamic range. Data acquisition hardware and a custom software interface from National Instruments of Austin, TX, provide realtime feedback to the operator or to the machine controller with the appropriate digital or analog inputs.

Several grinding phenomena are of particular interest to the precision grinding community, including workpiece contact detection, workpiece defect detection, grinding wheel loading and dressing condition, and coolant issues. The instrumented spindle provides the information required for the manufacturing engineer to pursue a deterministic approach to process control. Individual process variables may be studied systematically to obtain a clear understanding of the key operating parameters.