The 4th industrial revolution (Industry 4.0) is emerging. The core concepts of Industry 4.0 are the IoT (Internet of Things) and Cyber Physical System (CPS). The aim of this paper is to propose a multilayer structure for an open CPS architecture. We illustrate cases of FANUC and Mitsubishi Electric, which are competing in factory automation. Comparing these companies, we analyze CPS in factories of both companies. The concept of open CPS architecture draws upon the idea of a technology stack with “unit of analysis” not an individual smart connected product but the IoT for a production or construction site.