PDM Technology, Inc., a custom machinery and automation systems integrator, was recently challenged to engineer and manufacture a versatile test and inspection system to be used in a large consumer products facility's aerosol can production line.

PDM's client, a consumer products company in southeast Wisconsin, had an inspection system in place 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 case, or raised cans. Once a defect was detected, the system tripped a diverter that conveyed the defective box to a quality control area.

At best, the system detected approximately 99% of defects. However, a problem arose when packaging line products differed in cap colors and sizes as a result of manufacturing variations, rather than actual defects. The fast vision system was also extremely sensitive to environmental changes and product variables including ambient light levels and cap color. Once these slight variations were introduced, the system would malfunction, leading to several hours of downtime to make programming adjustments.

Increased testing errors from misreadings, extensive manual programming, and excessive downtime in setting up each product line occurred when the packaging line had to be changed in size, color, and number of cans per case.

Thus the new inspection system needed to adapt continually to a variety of product lines, manufacturing variations, and harsh environmental stimuli, while reducing the need for manual programming and downtime. To meet these requirements, PDM turned to Laser Measurement International (LMI), a non-contact laser measurement manufacturer in Detroit, MI, for a laser measurement solution. PDM had used LMI sensors successfully in numerous other applications and looked to them to find a rugged sensor that would meet this project's application requirements, and that could operate under poor light and environmental conditions while having the capability to easily differentiate between product variations and actual defects.

After explaining and analyzing the manufacturer's application and PDM machine building requirements, LMI specified the L1 Line Scanner, a 3D non-contact device capable of producing 60 profiles per second.

The key to the L1 sensor's use in this application is its insensitivity to the environmental and manufacturer changes that hindered the old system. This increased accuracy and decreased downtime by eliminating the need for manual programming each time a different can/box combination was online. The 3D system is much easier to program and more reliable than other 2D systems, according to PDM.

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

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 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 versus the master parameters, the carton is forced onto a diverter, reducing downtime and damage to the case sealer. The system overall helps prevent cases with missing products from reaching the customer, thus reducing customer complaints, additional paperwork, and reshipments.

How the L1 Scanner Works

The Class III 3-dimensional 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. Each L1 scanner head can be used as a standalone unit or in combination with two or more sensors. By combining two or more modular scanner heads, a full 3D image can be measured.

The fast 60 profiles per second ensures accurate testing data. The scanner has a resolution of 1/16 in. (1.5875 mm) and a depth of view of 16-22 in.(406-559 mm). The sensor is built to NEMA-4 (IP 65) standards and enclosed in an aluminum housing, and can operate at temperatures from 32°-105°F (0°-40°C).

Like the other LMI sensors, the L1 scanners use the optical laser triangulation measurement principle. 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 out the contour of the scanned article, while also generating a profile. 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.

"Many companies and OEMs come to us with measurement challenges and we normally find a non-contact sensor for their needs that will reduce waste, enhance quality, and increase yield," according to David Allen, general sales manager for North America. "If not, we often can modify one of our more than 50 industrial sensors to meet their most stringent application requirements."