To ensure quality in tire manufacturing, 3D sensing is now being implemented at many in-process manufacturing steps for quality monitoring and rapid feedback of process variations. In-process measurement and control applications include measurement of width and thickness and groove locations of component strips, including guidance of components to proper locations into the tire building drum, splice integrity monitoring and profile monitoring of extrusions. For final inspection of finished tire geometry and uniformity, profile sensors provide complete 3D point cloud maps of sidewalls and treads for detection of small bulges and dents in sidewalls and measure radial runout in tire uniformity machines. For finished tires, 3D sensors also provide ability to read DOT and other embossed character codes for automated traceability applications.
Measurement of rubber components and products is challenging for most measurement technologies. Surfaces are soft and often gummy, easily deformed by contact transducers. Capacitive based sensors have low range and standoff, and are subject to errors from electrostatic charge buildup, and have difficulty accurately measuring high silica content materials. Measurement of rubber components can also be a significant challenge for laser and optical sensors due to black surfaces which scatter little light to the sensor imager and surfaces can vary significantly in texture and reflectivity. These challenges are overcome with today’s 3D sensors, which offer automated exposure control to ensure accurate measurements from rubber surfaces with varying surface qualities.
IN-PROCESS MEASUREMENT AND CONTROL APPLICATIONS
Tire manufacturing requires the layup of many components, with each component needing precise location on the drum or conveyor to ensure the finished tire meets precise specifications. Placement of components such as rubber strips and sidewalls on the drum is controlled by 3D profile sensors, which monitor both edges of the strip to determine the strip centerline with submillimeter accuracy to ensure correct positioning.
Gum rubber strips are 0.5mm thick x 12.7mm - 25.5mm wide
Many other placement applications throughout the assembly operation are monitored with 3D profile sensors, including positioning of multiple band bead filler strips, placement of gum strips on body plies, and measurement of splice overlaps.
Today’s smart all-in-one profile sensors provide an ideal solution to these in-process measurement and control applications. Built-in measurement tools for strip positions, including multiple groove location and depth measurement monitoring and automated alignment enable users to configure setup parameters, not requiring any measurement software development. Ability to store multiple geometry configurations in the sensor make changes between different recipes quick and simple, critical to minimize downtime for operations that make model changes multiple times per shift.
FINISHED TIRE FINAL INSPECTION
Finished tire geometry systems need to detect bulges and dents as small as ten microns, which represent internal defects. These imperfections can occur anywhere on the tire sidewall. To increase quality and improve product safety, these small areas of dimensional variation or defects must be detected with very high reliability. Cycle time is critical for final inspection, requiring full surface inspection in one revolution to meet throughput requirements.
Because of cycle time requirements, early sidewall inspection systems employed displacement sensors, mechanically repositioned to several paths on the sidewalls. This solution was limited because defects outside of the measurement paths were not detected.
With increased speed of measurement, today’s smart 3D profile sensors provide full surface point cloud geometry data to detect small defects anywhere on the sidewall surface, meeting stringent cycle time requirements. Two profile sensors are used in typical applications, one for each sidewall. A third sensor is often used to monitor radial runout of the tread.
Tire sidewalls contain extensive alphanumeric information in the form of raised or embossed characters. These include tire identification codes for sorting and DOT codes for tracking to the vehicle identification number at assembly. The common approach of reading alphanumeric characters with 2D imaging and optical character recognition software is not applicable for tire sidewalls because the raised or embossed characters are “black on black”, with effectively no contrast.
The solution to reading tire sidewall codes is to implement 3D sensing, imaging the characters as a height map. This height map can then be analyzed and converted to alphanumeric data by common optical character recognition programs. Smart sensors provide a GenTL driver to send data to compliant third party software to acquire and process 3D data.
Where tires are rotating, such as in uniformity inspection systems, a 3D profile sensor provides the data for automated character recognition. Where tires are stationary, a 3D snapshot sensor can generate the height map for character recognition.
An example of automatic reading of DOT codes is shown below. The upper image is a scan of the tire sidewall (flattened), and the lower image shows the 3D height map of the DOT code, with the alphanumeric code as read superimposed below the characters.
The flexibility of all-in-one smart sensors allows use of one common platform across multiple applications. This simplifies the inspection process and produces huge savings in training costs as employees only need to be trained on one system. Sensors with simple setup and multiple configuration capability meet the needs of tire manufacturers for in-process and final inspection as well as automated code reading.
Posted by Dr. Walt Pastorius