Many assembly operations begin with the scanning of a 1D or 2D bar code. The code might tell an assembler what parts to install and how to install them. It might automatically configure a screwdriver for the correct torque, angle and fastening sequence for that specific assembly. Or, it might automatically set the force and displacement settings on a servo press.
Bar code scanning is also critical for traceability and inventory management. The codes provide data about what parts and subassemblies were installed, who installed them, when they were installed, and how many have been used.
For such a fast and simple operation, engineers have several options for scanning codes. For example, they can choose between laser-based and vision-based systems.
“The market is shifting away from laser-based readers and toward vision-based readers,” observes Logan Welch, machine vision technical sales specialist at Balluff Inc., whose company offers both types of code-scanning technologies. “Laser-based readers are primarily for reading 1D codes—the classic bar code—and those codes don’t hold much information. Manufacturers are increasingly using 2D codes today, and you need a vision-based system to read them.”
Laser-based readers are inexpensive and can scan codes at high speeds, adds Felix Klebe, marketing manager for sensors and advanced sensing at Omron Automation Americas. Laser-based readers do not require additional lighting and are not affected by external illumination. Compared with vision-based readers, laser-based readers have better depth of field and a wider field of view. As a result, they are more tolerant of slight shifts in the position of the items being scanned.
“Vision-based readers can compensate with auto focus, but they’re not as fast as laser-based scanners,” he says. “On the other hand, with vision-based systems, the same hardware can perform both code reading and vision inspection.”
Vision-based readers are more flexible than laser-based readers. In addition to 1D bar codes, they read plain text and 2D codes, such as Data Matrix, QR or Maxi codes. They can read poor quality codes better than laser scanners, and they can read codes from multiple directions.
Fixed vs. Handheld
Engineers can also choose between fixed and handheld systems. Handheld systems have the advantage of mobility, which is great for warehouse or dock applications. With the current concern over COVID-19, many handheld readers can be operated in hands-free mode, and some have hygienic designs, so they can be cleaned and disinfected.
“Handheld readers give you some flexibility,” Welch points out. “With a handheld reader, you can bring the reader to the code. You can manipulate the reader, rather than the code. For instance, think of when you’re at the grocery store, and you need to scan a code on a flexible package, like a bag of chips. You can manipulate the package to straighten out the code and make it easier to read. Well, what if that bag of chips was a pallet of automotive transmissions? You can’t reposition of the pallet, but you can position the reader anywhere you want.”
If the application calls for reading parts or boxes moving on a conveyor, then a small fixed reader is a good choice. A fixed reader saves the time needed to pick up the reader, scan the code, and set it back down again.
In addition, fixed readers have a much smaller form factor than handheld readers, says Klebe. For example, the MicroHAWK V430-F code reader from Omron measures just 44.5 by 44.5 25.4 millimeters. Rated IP65 or IP67, the reader features X-Mode advanced decoding algorithms; advanced data output formatting; liquid-lens autofocus for reading codes at different distances; and optional LED lighting for extra illumination in red, white, blue or infrared. Sensor resolution ranges from 0.3 to 5 megapixels. A variety of interfaces are available, including Ethernet and Profinet.
Code-reading technology has advanced in recent years to accommodate changing needs in the automotive, aerospace and medical device industries.
As with any electronic technology, the hardware has become smaller, faster and more powerful. Sensor resolution has increased, too. And, with the growing interest in Industry 4.0 technologies, today’s code readers offer a variety of network connectivity options.
However, the real progress has been made in the software, says Klebe. Advanced decoding algorithms give today’s readers the ability to read damaged codes, small codes, low-contrast codes, and codes on curved or glossy surfaces. Software improvements also enable readers to scan a variety of products on the same line.
The new BVS HS-P handheld bar code readers from Balluff read all common 2D, 1D and stacked bar codes quickly and reliably. The HDW variant can read high-resolution codes (to 2.5 mil for 1D) as well as large areas (up to DIN A4) from a distance of up to 70 centimeters. The DPW variant is optimized for reading codes marked directly on parts. The reader offers industry standard IP 65 protection and can withstand repeated drops on concrete from a distance of up to 2 meters. Wireless models with Bluetooth give users maximum mobility up to 100 meters from the base station.
Tips and Tricks
For optimal results in a code-reading application, start with a high-quality code, advises Welch. “I high-contrast code is best—black on white or dark on light is ideal,” he says.
As with any machine vision application, lighting is critical. Off-angle lighting will minimize glare and allow the sensor to read the entire code.
Many manufacturers are using vision sensors not to read codes, but to inspect them for quality. “Manufacturers need to ensure that a code can be read throughout the supply chain,” says Klebe. “You might be using a high-quality code reader, but the guy in a warehouse in the next state might not be.”
When specifying code-reading technology, engineers are well-advised to consider not just their current needs, but their future needs, as well. “You don’t want to be boxed in by your technology,” says Klebe. “Will the size of the part or product change over time? Someday, you might need to read a smaller code. How will your information needs change? What data will you be tracking in the future?"