Fast cars assembled faster with RFID

Industrial Embedded Systems — September 19, 2008

1In assessing how to improve efficiency and lower costs, automotive manufacturers should ask themselves the following question: Why scan when you can read during the normal flow of goods? This vehicle assembly application illustrates the benefits of swapping some barcode steps for RFID in a manufacturing environment.

A U.S. facility operated by one of Germany's most successful automotive manufacturing companies relies heavily on RFID to shorten production cycles and increase data collection quality during the process of assembling high-performance SUVs, roadsters, and coupes.

Not only does the RFID system save time and money by eliminating manual barcode scans, it also enhances logistics operations by connecting to the plant's Ethernet system, thus improving assembly parts planning and logistics for little additional cost.

Automating reads achieves better ROI

Automation cuts costs both directly, by reducing assembly times, increasing output per investment dollar, and minimizing waste, and indirectly, by increasing quality and manufacturing flexibility. Any optimization process with direct payback stands a much higher chance of making it through the decision-making process, which explains why the automotive company opted to install an RFID system.

Before the RFID system was implemented at the plant, the assembly line proceeded as follows. At the beginning of the process, engineers attached paperwork to the vehicles indicating which options and features needed to be installed. This paperwork also contained barcodes that were scanned at various line locations, activating vehicle-specific tests. A simple back-of-the-envelope calculation reveals how much time and money was expended scanning the barcodes, given the following factors:

  • Each car is scanned 50 times during the assembly process
  • A single scan - including locating the paperwork and barcode, picking the scanner gun, and placing it back in the cradle after the scan - takes 15 seconds
  • On average, 750 cars are built every day

The time spent to scan barcodes added up to more than 156 hours a day and resulted in thousands of dollars of unproductive time. By implementing RFID, the company alleviated these inefficiencies with a system that augments the existing barcode equipment and improves process time by automatically reading the required data as vehicles enter the assembly line.

Because cars sit on their wheels for a good portion of the assembly process, the company selected a long-range RFID system. With the goal of realizing greater ROI, the company installed a scan point for less than $10,000.

Less complexity results in higher availability

The RFID system implemented at this automotive manufacturing facility (Figure 1) is straightforward. Each line station consists of a single long-range RFID reader with integrated controller functionality. The reader offers several data ports, one of which is connected to the plant's Ethernet system. A second data port is used locally, sending the data previously read by the barcode scanner to the line PC or Programmable Logic Controller (PLC). In contrast to a more traditional RFID system fully controlled by a PLC, this system offloads the logic into the RFID reader.

Figure 1

Examining the steps of the assembly process demonstrates the benefits of using RFID:

  • At the beginning of the assembly process, paperwork containing assembly information and barcodes is printed and the data tag containing similar information is written and attached to the vehicle. In this case, the tag contains the car's VIN plus other information found in barcode form on the paperwork.
  • When the car enters an assembly step, the RFID reader retrieves data from the RFID tag. Because the reader is "intelligent", it can be configured to read a specific section of the tag. If an assembly step needs the VIN, the reader is configured to read the section of the tag containing the VIN. Once read, the information is pushed into the data port connected to the line PC or PLC like a barcode reader.
  • Internal logic then memorizes the tag. As a consequence, the VIN is sent only once to the PC/PLC, even if a worker blocks the tag. A simple time-based logic flushes this memory when needed.

Because the reader is always scanning for tags, assembly delay times are reduced by more than the time it takes the operator to manually scan a barcode. With read ranges up to 6 m, the reader can essentially read tag information on approach. This aids assembly stations that require additional mechanical setup steps. An example is a test roll booth where the wheelbase must be electrically adjusted to fit the vehicle being tested.

Because each reader is connected to the plant's Ethernet system (Figure 2), the position of each vehicle along the line is known. As soon as a vehicle is read, all the parts added to the vehicle between this point and the location of the previous read can be subtracted from the online stock. The old barcode system did not offer this type of data connection and, as a consequence, parts consumption adjustments were available only at the end of the assembly line. By offering greater connectivity, RFID significantly improved material logistics and enhanced parts replenishment precision, making parts storage areas along the line less crowded.

Figure 2

Hardware considerations

Several long-range RFID systems that use different basic technologies are currently competing on the market. Given the requirements in automotive applications, such as the ability to withstand physical abuse and function in an environment with a significant amount of metal, only a handful of systems are serious contenders.

Multipath problems and field nulls (areas in the read field where a tag simply will not read) must be considered. The application described in this article utilizes a microwave-based RFID system (Figure 3) that offers high performance in metallic environments and continuous read zones without dead spots.

Figure 3

Considering the significant savings achieved by removing the barcode scan times combined with logistical advantages, it is clear why this automotive manufacturer opted to implement an RFID system. While the automotive sector is one of the largest markets for RFID, other industries also can benefit from this technology.

Helge Hornis is manager of the Intelligent Systems Group for Pepperl+Fuchs in Twinsburg, Ohio. He has worked with users on RFID and sensor bus systems, managed integration projects for key customers, and helped develop a unique 3D position measuring system. He holds a seat on the board of AS-Interface USA, and has a PhD in Physics from the Georgia Institute of Technology.