Sensor technology key for tire inspection system
As tire specifications become more stringent, the need for faster and more accurate quality inspection for tire uniformity and appearance is critical.
Commercial Time Sharing Inc. (CTI, Akron, OH) is a system integration and software engineering firm specializing in multiple level manufacturing automation. For the tire industry, CTI's specialty is to strip an outdated tire uniformity machine and completely rebuild and upgrade the control system. The equipment is used to measure sidewall undulation, lateral runout, bulges, and depressions in passenger and truck tire production.
CTI's second generation tire testing and optimization control (TTOC) and tire sidewall inspection system (TSIS) are continually improved to inspect higher proficiency tires and new sidewall styles.
To compliment the TTOC-II system, CTI needed a sensor that could identify tire deformities quickly and accurately within seconds. Real time measurements had to be made accurately on rapidly moving objects, regardless of surface texture, color, speed, temperature or different ambient light conditions. It also had to be able to handle the improved test cycle times of the TTOC-II system of 17 seconds or lower. This meant that the sensor had to inspect the tire in one revolution or one second or less. Bottom line: The sensor had to be about 10 times faster and more accurate than the overall system cycle time and system accuracy.
CTI selected the Selcom Optocator 2201 sensor from LMI Technologies Inc. (Detroit, MI).
"We selected this sensor because of its performance when measuring through black lettering, lube oil or other obstacles," says Ron Symens, president of CTI. "The small spot size of 200 microns also allows CTI to filter out high frequency signals and still detect and measure low frequency bulges and dents."
Throughout the industry, quality control in less-than-perfect conditions such as tires with oil or black/white lettering has been difficult. The problem lies in the data filtering that needs to be achieved to identity "friendly" and "unfriendly" data points on the tire's surface.
For the CTI application, the two opposing LMI laser sensors are mounted on a solid transport system that indexes on the tire during inspection. Dimensons of the sensors are 145 mm (5.7 in.) long by 80 mm (3.15 in) high by 50 mm (1.87 in.) wide. Weight is 0.9 kg (2 lb.).
Optocator 2201, a relative distance measurement sensor, identifies tire deformities and provides an X/Y plot of bulge, dents, depressions, and location of lettering on the sidewall.
The laser triangulation based sensor uses a semi-conductor laser diode together with the optics to project a 0.02 mm (0.078 in.) laser spot on the target surface.
Sample rate is 16 kHz, standoff distance 95 mm (3.75 in.) and measuring range up to 32 mm (1.26 in.). Four thousand readings are made of each profile, with the tire spinning at 60 revolutions per second. Up to five profiles can be made during a standard tire uniformity test.
The TTOC-II/TSIS system monitors the signals from the sensors which provide an X/Y plot of bulges, dents, depressions, and location of lettering on the sidewall. The type of depression is identified along with how wide it is at the base, the dimension of its slopes and other such project geometrics.
As long as the target surface stays within the measurement range, a portion of the diffusely scattered light from the laser spot will be focused by the imaging object into a position-sensitive detector. An internal feedback loop automatically compensates for differences in detected light intensity due to the object's color and texture. Signal outputs include both analog and digital (RS-422 or RS-232). The sensor is protected in an IP50/NEMA 12 air purge system for dust and heat protection.
For more information about:
LMI Technologies, www.lmint.com
Commercial Time Sharing, www.comtime.com