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Dedicated, automatic tire sidewall inspection.

Bytewise Measurement Systems, a manufacturer of precise, non-contact product and process measurement systems, has introduced a dedicated sidewall bulge/dent inspection system. By utilizing precision laser triangulation measurement technology in the tire final inspection process, Bytewise is providing the opportunity for improved product quality, reduced scrap and downgrade savings, and improved operating efficiencies to tire manufacturing customers worldwide.

The dedicated sidewall inspection system is a standalone, automatic, finished tire sidewall inspection system that provides precise, accurate measurement of tire defects such as bulges and depressions in the tire sidewall. All defects are identified, even narrow bulges on single-ply tires. False positive readings have been reduced significantly relative to traditional measurement technologies, providing significant labor savings. The fixturing is simple and reliable, thereby reducing maintenance requirements by up to 90%. Powerful software tools are providing value beyond simple pass/fail determination, and cycle times are substantially reduced.

Why measure tire sidewalls?

There are primarily two reasons for inspecting the sidewall of a radial tire:

* To identify tires which may have visually objectionable characteristics such as a depression; and

* To identify tires which may have structural defects such as bulges.

A depression in the inflated tire sidewall is the result of a local "strong point" in the sidewall generally caused by an excessive fabric body ply splice. A more critical structural defect is a local "weak point" in the tire sidewall that often results in a bulge in the inflated tire sidewall. These bulges are generally the result of a lack of sufficient fabric body ply cords caused by a narrow or an open body ply splice.

Principle of operation

The dedicated sidewall inspection system is a stand-alone machine that utilizes laser measurement technology incorporated into an automatic tire inflation/rotation machine. Tires are first identified by a bar code or similar system, and the tire is automatically centered, chucked and rotated. Two laser triangulation sensors are then automatically positioned horizontally and vertically using the company's three-axis positioning system. Multiple circumferential tracks can be measured using 4,096 data points. Each measurement point itself is the average of all digital laser samples that occur in the 1/4,096 portion of the rotation. This technology is referred to as bandwidth optimization and is an important method for achieving high performance results.

This dedicated system configuration is beneficial for companies requiring automatic tire sidewall inspection outside (usually downstream) of the uniformity process. With a typical total cycle time of less than 20 seconds, the dedicated system can often accommodate tires routed from multiple TUO (tire uniformity optimizer) machines. In addition, manufacturers often measure tire sidewall defects using a higher inflation pressure than that of the uniformity cycle. Measuring the tire sidewall outside of the uniformity process allows greater flexibility in test inflation pressure without affecting uniformity processing cycle time.

Benefits of laser measurement technology

Historically, tire manufacturers have used contacting probes, capacitive sensors or laser triangulation sensors for sidewall measurements. Contacting probes require slow rotation speeds which reduce cycle time and "clean" tracks on the tire sidewall. Capacitive sensors require careful calibration, multi-axis positioning and clean tracks on the tire sidewall. Laser triangulation sensors can overcome each of these obstacles and provide additional benefits.

The dedicated sidewall inspection system utilizes 16 kHz Selcom laser triangulation sensors. The high rate of sampling frequency allows tire rotation speeds of up to 120 rpm. In addition, the laser sensors have a large stand-off (approximately the distance from the sensor to the measurement surface) and measurement range which greatly reduces the risk of damaged sensors caused from mis-chucked tires. Also, laser sensors are not required to be perpendicular to the measurement surface, thus eliminating the need for multi-axis positioning.

Letter elimination software

Perhaps the most significant benefit of laser measurement technology is the high-resolution digital signal that can be utilized to effectively filter sidewall letters, designs, pin vents and flash. The company has developed a powerful and unique software filtering process which consistently eliminates these sidewall features to produce a true measurement of the tire sidewall surface for defect analysis. This "letter elimination" software eliminates the need to measure the tire sidewall on a "clear" circumferential track and enables much greater flexibility in where the tire sidewall can be measured to identify critical defects.

In figure 3, the gray line represents the raw laser data. The black line represents the results of the letter elimination software filtering process. As shown, letters and raised features on the tire sidewall are effectively filtered prior to the defect analysis. The result is that defects "hidden" among raised sidewall features can be accurately detected.



The dedicated sidewall inspection system provides tire manufacturers with an effective alternative to automatic tire sidewall defect measurement outside of the uniformity cycle that can significantly improve operating efficiencies in the inspection of finished tires. The stand-alone configuration can process tires from multiple TUO machines and allow for greater flexibility in test inflation pressure. In addition, the dedicated sidewall inspection system provides improved measurement capability and results with fewer false positives and lower labor costs. High speed measurement and processing result in faster cycle times. Fewer axes of motion and off-the-shelf component utilization result in less downtime and lower maintenance costs. And finally, state-of-the-art software and "letter elimination" signal processing provides better tire evaluations and new tools for investigating tires.

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Article Details
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Author:O'Neil, Erik
Publication:Rubber World
Date:May 1, 2000
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