In the warehouse of a major direct sales jewelry company, pickers place jewelry boxes on two conveyors that transport them to packing stations. A 1D bar code on each box is read by ID readers located above the conveyor and based on this identification each box is diverted to the correct packing station. The laser scanners in place were designed to read A and B quality bar codes, which the jewelry company had planned to begin putting on its boxes.
However, the company was unable to get the A and B quality bar codes from its manufacturer and the system was trying to read C and D quality bar codes. Thus, the scanners were only able to read 96.5 percent of the bar codes, requiring two full-time people to handle the read failures.
Cornerstone Automation, the systems integrator involved in the project, collected all of the boxes that could not be read in a day and asked Cognex, a leading developer of vision based ID readers, if it could offer a solution. Cognex's Cognex DM 302L vision-based reader read every one of the read failures. The new ID readers have increased read rates to above 99.9 percent and saved 75 hours per week in read failure handling.
Bar code reading challenge
The jewelry boxes are about 3 inches wide x 3 inches deep x 1.5 inches tall. A half inch wide x 1 inch long 1D bar code is placed by the manufacturer on the front end of the lid of the box so it faces forward. The quality of these bar codes leaves much to be desired.
Boxes containing higher volume products are stored in the magazine of 7 foot tall automatic order selection dispensers located on either side of the conveyor. When a wave of orders is run, the dispensers automatically eject the boxes needed to fill the wave onto the conveyor. The lower volume items are stored in conventional shelves. This portion of the order is transmitted to pickers who collect these items manually and place them on the conveyor. The boxes vary somewhat in height so they are placed lid-down on the conveyor to minimize the variation in the height of the bar code above the conveyor. No attempt is made to orient the bar codes in a specific direction. When the bar code reaches the packing area, diverters push each box off the conveyor into the station of the packer responsible for the order for which the box is intended.
This automated system is highly efficient but it depends heavily on the ability of the bar code reader to read the bar code on nearly every box traveling down each line at a rate of about 60 per minute or 1 per second. After the codes are read, a labeling machine prints a larger 3 inch x 3 inch label and applies it to the bottom of the jewelry box. This larger label is easily read by the laser scanners used to control the diverter machines that direct the boxes to the correct packing station. In the past, a scanning tunnel was positioned upstream from the packing stations that used four laser scanners each pointing at one of the four sides of the boxes to read the smaller labels. These readers offer some advantages such as simplicity, low cost and ease of use.
But lasers have difficulty reading codes in a degraded condition, at varying angles and in different positions. Because they see only a single scan line at a time, laser scanners have a limited ability to read codes that are in any way different from an ideal image. The laser scanners used in the past were able to read the vast majority of bar codes but the approximately 3.5 percent of codes that they were not capable of reading constituted more than 2,000 boxes in a typical day. These codes needed to be manually read and a label needed to printed and applied by hand to each box. Even when the ID readers were working perfectly, two people needed to be ready to handle any read failures because the items that could not be read would not reach the packing stations which in turn would stop the packers from filling orders until the read failures were corrected.
Move to vision-based technology
The jewelry company asked Cornerstone Automation to improve the read rates on the poor quality bar codes on the line. Since the line was originally installed, substantial improvements in vision-based ID reading technology have provided new cost effective options in addressing this challenge. The basic idea behind image-based technology is that the reader captures an image and uses a series of algorithms to process the image to make it easier to read. A typical algorithm searches the entire image for the code and identifies the position and orientation of the code for easy reading. Other algorithms handle degradations in code quality due to differences in material types and surfaces. Image-based ID readers can also read two-dimensional codes like Data Matrix that hold a much larger volume of data, providing redundancy that can enable the code to be read even when it is damaged.
"We brought Cognex in and asked if they could help with the read failures," says Michael Doke, partner with Cornerstone Automation. "Cognex asked us to collect all of the bar codes that the laser scanners could not read in a day. Cognex brought one of their vision-based scanners in and set it up and it read every single one of those bar codes."
Cognex recommended the DataMan 302L fixed-mount bar code reader for this application. The DataMan 302L has a resolution of 1,280 x 1,024 pixels and liquid lens variable autofocus technology that is suitable for applications that require a large depth of field. The liquid lens uses two iso-density liquids—oil is an insulator while water is a conductor. Varying the voltage across the liquid-liquid interface leads to a change of curvature, which in turn changes the focal length of the installed optical lens. The liquid lens keeps the code in focus even when the distance from the camera to the code is changing, which happens because the bar codes can be located anywhere on the wheels.
With image-based technology, there are four steps to reading a bar code: take an image of the bar code; find the bar code in the image; generate a signal; and decode the signal. Up to now, image-based bar code readers have been limited by the poor fidelity and low speed of the image analysis methods used to find bar codes and extract 1-D signals for decoding. Hotbars technology used in Cognex DataMan 300 series ID readers redefines the signal generation phase of the process. The software decoding algorithm must provide a good "signal" to the decoder to ensure it can be read. Hotbars focuses on signal generation to make decoding better and faster. It improves the signal quality and drastically increases the speed of signal acquisition.
Hotbars is approximately 20 times faster than traditional methodologies used to generate signals. Due to the increase in speed the software has more time available for decoding, which in turn enables DataMan to read bar codes that are incredibly damaged at fast speeds without requiring special hardware technology. When Hotbars is combined with advances in image formation including high-intensity LEDs, liquid lenses and megapixel sensors, the result is an advanced bar code reader that delivers the promise of solid-state, digital technology while not yielding performance to opto-mechanical laser scanners.
Implementing the solution
Four Cognex 302L ID readers were set up in four different directions at a distance of 12 to 16 inches from the box at a 20 degree angle to the conveyor belt. The four ID readers were configured using group triggering so that all four readers acquire an image simultaneously and then combine their individual read results to form a composite result. The four readers are continuously on and configured for self triggering so that they trigger whenever they detect a code. Whenever any reader detects a code, the master reader generates and transmits a read result to an industrial PC, simplifying the task of collecting and processing read results from multiple readers.
The new readers provide better than 99.9 percent read rate. This dramatic improvement in read rates has made it possible for the two people previously assigned to manually read the labels to be moved to more productive tasks. The end result is that the jewelry direct seller has eliminated a major headache and significantly reduced its distribution costs.
About Cornerstone Automation
Cornerstone Automation is a full service automation system integrator that designs, fabricates, programs, installs, and supports automated control and monitoring systems for manufacturing, material handling and OEM applications. Founded in 1995, Cornerstone Automation serves customers throughout the mid-Atlantic and Northeast regions.