A design method for constructing a hierarchical structure controller with control modules was proposed for synchronously
reconfiguring the control and machine of
reconfigurable machine tool(RMT). In this method,the entire controller and its individual control module at every level acted as a set consisting of a
finite state machine (FSM) with input & output event set pairs. Each pair of input & output event set was defined as a port of the control module, and the input event set on a given port formed the port-acceptable language. Thus, when the mechanical modules are assembled, the control modules can be connected using port language, which constructs the higher control module until the entire controller is connected. Thereby, the control and machine reconfiguration of RMTs occurs synchronously. Based on the introduction of FSM expression for discrete event systems, the definitions of control module with FSM, module combination, as well as the design and construction theory of modular controller was given. Using this theory, once the control modules are properly designed and connected, the resulting controller is guaranteed to be controllable.