Engineers at Siemens Energy & Automation in Batavia, Ill., designed three types of interlock switches, each of which had a dozen possible variations. But then they had to devise a method to track parts and assemble them. Volume was going to be relatively low, so a palletized assembly system would be too costly. Instead, they chose to break down the process into several steps and assign them to simple, independent assembly stations. This still left them with the problem of tracking parts to make sure the right interlock switches were being manufactured. Siemens engineers decided to use plastic part bins to move parts and assemblies between stations. To track them, they use I-button memory chips from Dallas Semiconductors as ID tags.
The buttons are permanently affixed to the bins. They communicate with a workstation computer through two spring-loaded pins connected to the computer's serial port. The computer assigns the button an identifier, as well as a switch catalog number and quantity. After the switches are built, the ID button tells a laser marker what to write on the switches and also helps it count and keep track of batches. When the bin is empty, the ID tag is erased and ready for reuse. Though the buttons are not as convenient to use as traditional radio-frequency identification tags (they need physical contact to download or upload data), they provide a cost-effective method of part tracking in low-volume manufacturing. And unlike bar coding, they do not require manual intervention to be recoded and reused.