Design and implementation of a statechart based reconfigurable elevator controller

This paper presents a simple and clear method to design and implement a reconfigurable elevator controller using an FPGA, which can be implemented for an elevator with any (N) number of floors, with specified inputs and outputs. A model based design approach was followed. We started from a state chart model developed for a prototype elevator with three floors. Extension of the model for a variable number of floors was considered. Controller for the prototype system was implemented in ladder logic on a PLC and the limitations of that approach with regard to re-configurability were identified: viz., in the extension of elevator controller for `N' no of floors. Next VHDL code was developed for a reconfigurable elevator controller where, by changing a variable corresponding to the required number of floors, the suitable code can be generated. The controller thus generated can be implemented in an FPGA. The method was successfully tested on a Xilinx Spartan 3AN FPGA.

I. Introduction

In control and automation industry, Programmable Logic Controllers (PLCs) are commonly used to implement controls for complex reactive systems, primarily because of their easy programming environments based on IEC-61131–3. However, they are meant for sequential event processing and not for hard real-time reactive environments which require parallel processing capabilities. In contrast, Field Programmable Gate Arrays (FPGAs), which are inherently parallel, can be used to develop controls for more complex systems with large number of inputs and outputs. In addition to reconfigurability, it consumes less power and it can provide comparatively low response times and flexibility in expansion of designs.