An FPGA implementation of hard-wired sequence control system based on PLC software

Although a Programmable Logic Controller (PLC) has been widely adopted for the sequence control of industrial machinery, its performance does not always satisfy the recent requirements in large and highly responsive systems. With the state-of-the-art FPGA technology, it is possible to implement a control program with hard-wired logic for higher response and reduced implementation cost/space. This approach is also worthwhile for transmigration of legacy PLC software into forthcoming FPGA-based control hardware. This study presents a systematic method to implement a hard-wired sequence control from PLC software. PLC instructions are converted into VHDL codes, and then implemented as logic circuit with various peripheral functions. Productive PLC programs were examined with Mitsubishi Electric FX2N PLC and Altera Stratix II FPGA, and were shown to fit into a common FPGA chip. A straightforward Sequential design was estimated to be 184 times faster than PLC, while a performance-oriented Flat design was estimated to be 44 times faster than Sequential design (i.e., 8050 times faster than PLC). A practical perfect layer winder system was actually built and successfully operated with our FPGA control board, whose logic design was implemented with our tools.