Ring and bore measuring systems (ring check) are automatic metrology stations dedicated to the complete dimensional inspection of inner diameter, ovality, cylindricity, surface roughness and geometric quality of rings, bores, holes and hollow cylindrical components. They use rotating inductive probes, laser sensors, pneumatic gauges or cameras depending on the accuracy required and on the size of the component. They are indispensable in the quality control of series production in the automotive, bearing, hydraulics and valve sectors.
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Operating principle
Ring check stations differ according to their probing principle. In rotating-probe versions, a precision motorized system rotates one or more inductive probes (LVDT) inside the bore, recording diameter variations along the circumference and reconstructing the 2D geometry of the section. In multiple-probing versions, several static probes at different heights and angles measure multiple points of the bore simultaneously, calculating ovality, conicity and taper. Laser versions use internal triangulation sensors that rotate or are distributed so as to cover the entire circumference.
Measured parameters
Ring check systems provide: mean diameter, maximum and minimum diameter (with angular location), ovality (out-of-roundness), cylindricity (over several sections at different heights), conicity (taper) along the bore axis, parallelism and perpendicularity with respect to a datum. Typical accuracies are in the order of 0.5 to 2 µm on the diameter and 0.1 to 0.5 µm on ovality, with cycle times of a few seconds per part. Angular resolution is 0.1° to 1° depending on the model.
Industrial applications
Ring check stations are used for the dimensional inspection of bearing rings (inner and outer) before assembly, of cylinder liners of combustion engines (inspection of the internal geometry, critical for performance), of piston and valve seats, of bores in hydraulic components, of sealing rings and of flanges and drilled hubs. Measuring speed and the level of automation make 100% inspection possible in high-throughput series production.
Software and data
The dedicated software manages automatic calibration with master rings, definition of geometric and dimensional tolerances, generation of polar profile charts, calculation of form parameters in accordance with ISO 12181 (out-of-roundness), reporting compliant with the quality requirements of the sector, and SPC statistics with process capability calculation. Integration with MES systems allows individual parts to be traced. The ability to export in Q-DAS format makes advanced analysis with dedicated statistical software easier.
Standards and selection criteria
The metrological characteristics of ring check systems follow ISO 12181 (out-of-roundness), ISO 12180 (cylindricity) and ISO 14253 for the declaration of conformity. Periodic calibration uses high-precision master rings calibrated to ISO 17025. The choice of system depends on the bore dimensions (range), the acceptance tolerances, the required cycle time, the flexibility needed for several product codes, integration with the line and automation requirements (manual or robotic loading and unloading).
The recent evolution toward robotized ring check systems with integrated vision cameras also allows surface inspection of the bore (detection of scoring, porosity and surface defects) at the same time as the dimensional measurement, providing complete quality control in a single pass. This integration is particularly appreciated in the inspection of high-end engine liners and of critical hydraulic components.
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