Problem: In engine assembly lines that use mechanical flags and bar codes for model discrimination and process instructions, the production line sometimes has to be stopped because of mechanical failures or other factors, such as not being able to read the bar codes because of oil or coolant. Although mixed production lines can be handled, increasing diversification of client needs has led to further increases in the number of different models, and switching between different types of operation must be performed with more efficiency and stability than ever before. Mount Data Carriers (ID Tags) to the pallets or jigs. Write model information and process information to the Data Carriers, read the information at each process station, and, based on this information, switch the operation type (if necessary) and perform processing. After completing a process, enable the processing completion flag for that process."