Real-time work-in-progress management for smart object-enabled ubiquitous shop-floor environment

Recent developments in wireless technologies have created opportunities for developing next-generation manufacturing systems with real-time traceability, visibility and interoperability in shop-floor planning, execution and control. This article proposes a work-in-progress management framework based on smart objects such as radio frequency identification/Auto-ID devices and web service technologies in a ubiquitous manufacturing (UM) environment. Under this framework, two types of services (data source service and gateway data service) and WIPA (work-in-progress agent) are designed and developed to manage and control the real-time materials and information flows to improve the optimal planning and control of the entire shop floor. During production execution, real-time visibility explorers are provided for operators and supervisors to reflect the real-time situation of current manufacturing environment. It follows a simple but effective principle: what you see is what you do and what you do is what you see. Production disturbances could thus be detected and fed back to decision makers for implementing closed-loop shop-floor control. In addition, some important standards such as ISA 95 and business-to-manufacturing markup language (B2MML) are adopted to establish the information model and schemas of WIP called wipML (work-in-progress markup language). Based on B2MML and wipML, the real-time manufacturing information can be effectively encapsulated, shared and exchanged between gateways, WIPA and heterogeneous enterprise information systems. The presented framework is studied and demonstrated using a near real-life simplified shop floor that consists of typical manufacturing objects.