The Situation
The safety mats at Tower Automotive''s Milwaukee Ranger frame plant were a high maintenance item in a welding environment and were cutting into productivity. Safety mats -- the industrial-scale cousins of the pressure-sensitive mats used to open grocery store doors -- were being used to safeguard automation when a worker was in the area, say to load parts or weld.
The safety mats not only required a lot of maintenance, they were also complicated to customize and wire. For example, mats must be specifically sized to fit the area they need to protect. And when production lines change, which they frequently do at Tower Automotive, new mats need to be ordered and installed, requiring a fair amount of carpentry and electrical work.
According to senior advanced electrical engineer Dave Sytkowski, this was unacceptable to Tower Automotive, a Tier 1 supplier of body structures, lower vehicle structures, suspension components and modules for nearly every major automotive manufacturer in the world. Tower Automotive strives to be a leader in the application of safety and technology and manufactures millions of full frames and front and rear subframes annually on highly automated assembly lines.
The Decision To Use PLS Scanners
Tower Automotive decided to employ alternate safety technology on the latest Ranger Line, built in 1997. (It continues to use safety mats to protect some smaller, less rugged areas.) The company considered a variety of options to meet its control reliability requirements. Among the possible solutions were light curtains, interlocked guarding, mechanical barriers, and proximity laser (PLS) scanners.
More than ten years ago, Tower began using PLS scanners from SICK based on maintenance, cost, and ease of installation. Flexibility -- the scanners are reprogrammable -- was also a top priority. SICK is a global leader in factory automation solutions and a leading manufacturer of sensors and safety systems for industrial applications.
The initial installation was handled by a systems integrator. SICK provided technical support and helped Tower Automotive staff get up to speed on the software, including how to program and maintain it.
Today, the plant uses roughly 40 PLS scanners from SICK to guard large areas with odd shapes. According to SICK, the PLS is often used to safeguard in and around robot cells and other automation in industrial manufacturing settings. One example of how Tower uses the PLS is to monitor walkways used by workers interacting with frame assemblies and fixtures. This interaction can put the worker in danger of being injured by overhead transfer of a frame as it moves from station to station along the assembly line with the PLS. If a worker is in this potentially hazardous area during an attempted transfer, the transfer is simply not allowed. When the workers leave the area and activate work complete buttons, the PLS re-enables transfer motion and allows the truck frame to unclamp and move to the next station.
The Results: Better Uptime, More Flexibility
Now those issues of safety-mat maintenance and associated lost productivity have lessened, says Sytkowski. In instances where a scanner needs to be serviced, it takes electricians 10 minutes to change the scanner and download the existing program from a laptop computer. "We have better recovery, compared to replacing and rewiring mats," he says.
The facility has seen an incremental improvement in uptime. Productivity is complex and many factors come into play, says Sytkowski. But there is a definite uptick stemming from reduced maintenance and downtime now that PLS scanners are used in place of many safety mats safeguarding large (6 ft x 20 ft) work areas. For example, one of the lines previously protected by safety mats came in at about 85% productivity. Newer lines employing PLS scanners surpass 90%.
Sytkowski says Tower Automotive''s facilities undergo constant change -- model changes, new improvements, adjustments to the configuration of where the operators stand, etc. The company greatly values the flexibility of the SICK PLS scanners and the ability to easily modify their programs, making the design or redesign process as smooth as possible. In these cases, Tower Automotive regularly uses state-of-the-art simulation software to map out an entire assembly process before the equipment is installed to ensure a robust process that meets safety, quality, and volume requirements.
PLS Scanners
The PLS scanner from SICK creates three independent sensing fields definable by Tower staff: two programmable protection zones and a "surveyed area." The rotational optical system uses a Class I infrared laser and allows the user to define two protection zones within a radius of 164 ft (50 meters) to fit the irregular contours of a hazardous area. Using the PLS Utility Software for Windows™ (included with the scanner) makes these user-friendly input modes available for configuring the protective zones.
As a stationary sensor, the PLS can safeguard hazardous areas, reducing the amount of mechanical barriers or safety mats, and minimizing inadvertent machine stops while protecting personnel. The PLS scanner can also be used horizontally or vertically, similar to a safety light curtain. Area scanning applications include contour measurement, product profiling, and long-range proximity sensing. It is also less sensitive to bright weld flashes and strobe lights, making it exceptionally suited to the environment at Tower Automotive and other automotive facilities.
Sytkowski says the PLS scanners perform quite well. "They even caught an oil leak while it was misting and before it had even formed a puddle," Sytkowski says. "The best thing about SICK''s PLS scanners is their flexibility, the ability to reprogram them when needs and requirements change. SICK PLS scanners are also used at a good number of other Tower Automotive facilities," he notes.