Quality Applications

LMI L1 Line Scanner Benefits n Sixty profiles-per-second measurement n Resolution of 1/16 in. (1.5875 mm) and a depth of view of 16 in. to 22 in. (406 mm to 559 mm) n Temperature range of 32ºF to 105ºF (0ºC to 40ºC) www.lmint.com

Laser Sensor System Reduces Downtime and Improves Error Detection
LMI L1 Line Scanner

PDM Technology Inc., a custom machinery and automation systems integrator, recently faced the challenge of engineering and manufacturing a versatile test and inspection system to be used in an aerosol can production line by a large consumer products facility in southeast Wisconsin. The inspection system was required to continually adapt to a variety of different product lines, manufacturing variations and harsh environmental stimuli while reducing manual programming and downtime. To meet these requirements, PDM turned to Laser Measurement International (LMI), a noncontact laser measurement manufacturer based in Detroit, for a laser measurement solution.

 The consumer products company that needed PDM's services already had in place an inspection system that utilized a grayscale vision system to detect defects such as missing caps and cans, inverted caps and cans, folded box flaps, cans on top of cases, and raised cans. Once a defect was detected, the system tripped a diverter that conveyed the defective product to a quality control area. At best, the system detected about 99 percent of the defects; however, problems arose when the packaging line included products of differing colors and sizes.

 The vision system was also extremely sensitive to environmental changes, such as ambient light levels. Once these slight variations were introduced, the system would malfunction, leading to several hours of downtime. Problems incurred when the packaging line was changed to handle cans of a different size, color or number per case included testing errors from misreadings, extensive manual programming and excessive downtime in setting up each product line.

 PDM had successfully used LMI sensors in several previous applications. So, managers looked to the same company for a rugged sensor that would meet this project's application requirements while operating under poor lighting and environmental conditions and having the capability to easily differentiate product variations from actual defects.

 After explaining and analyzing the manufacturer's application and PDM machine-building requirements, LMI recommended the L1 Line Scanner, a noncontact 3-D device capable of producing 60 profiles per second (pps). The key to the L1 sensor's use in this application is its insensitivity to the environmental and manufacturing changes that hindered the old system. This increased accuracy and decreased downtime by eliminating the need to manually program the packaging system each time a different can or box combination was on the line. The 3-D system is much easier to program and more reliable than other 2-D systems, according to PDM.

 "Once we had tested the L1, we knew it was the best way to alleviate most of the manufacturer's headaches," says David Baker, president of PDM. "Our software package interfaces great with the LMI sensors, a big challenge with some other sensor companies' products."

 For setup, the operator selects a preprogrammed product class. The custom defect software from PDM automatically calibrates the inspection system by passing three correct cartons under the sensor. The system then calculates all required parameters and begins actual defect testing on the fourth carton.

 The L1 sensor is positioned directly above open cartons being conveyed to a case sealer. If the L1 measurement results are skewed compared to the master parameters, the carton is forced onto a diverter, a process that reduces downtime and damage to the case sealer. The system helps prevent cases with missing products from reaching the customer and reduces customer complaints, additional paperwork and the need for reshipments.

 The Class III 3-D L1 scanner is designed for high-density profiles in a variety of configurations. Each scan head has a 120-degree field of vision for optimum measurement, and each L1 can be used as a stand-alone unit or in combination with two or more sensors. By combining two or more modular scanner heads, a full 3-D image can be measured.

 The L1's fast 60 pps speed ensures accurate testing data. The scanner has a resolution of 1/16 in. (1.5875 mm) and a depth of view of 16 in. to 22 in. (406 mm-559 mm). The sensor is built to NEMA-4 (IP 65) standards and enclosed in an aluminum housing and can operate at temperatures from 32° to 105°F (0º to 40ºC). Like the other LMI sensors, the L1 scanners use a measurement principle referred to as "optical laser triangulation." With this principle, a fixed beam of light is projected from the sensor to the surface to be measured. When the light hits the surface, it scatters in all directions. The sensor collects part of this scattered light and maps the contour of the scanned article while also generating a profile. The CCD technology allows the profile to be filtered or otherwise processed for accuracy. As the relative distance between the sensor and measured surface changes, the position of the image on the detector changes proportionally, making it possible to measure the location of the measured surface accurately and repeatedly.