IoT-enabled synchronization based on graduation intelligent manufacturing system

Abstract

In today’s fast-changing manufacturing industry, high product variety and varying demands have been overwhelming characteristics of manufacturing. From two motivating companies with such characteristics, severe problems including high-level work-in-process (WIP), unreasonable setups and substantial waiting/idle time are observed. This thesis discusses the wide range of production synchronization that is required for addressing these problems in different manufacturing scenarios. Firstly, two kinds of synchronization in a hybrid flow shop (HFS) with customer orders and setup times are investigated. One is job synchronization for the consistency of production progress of jobs in each customer order. The other one is setup synchronization to coordinate setup arrangements between adjacent stages. Corresponding synchronization mechanisms are proposed by using the radio frequency identification (RFID) enabled real-time production data. An advanced planning and scheduling (APS) system is developed for implementing synchronization mechanisms. Secondly, a simple, flexible and adaptive manufacturing paradigm – Graduation Intelligent Manufacturing System (GIMS) is proposed by analogy to the ticket queuing system of HKU graduation ceremony. Three kinds of tickets, namely the job tickets, setup tickets and operation tickets are designed for the JIT control of materials, flexible control of setups and adaptive control of uncertainties. An iBeacon-based overall IoT architecture consisting of smart tickets, smart gateways and their management services is developed for automatic production data collection, error prevention and disturbance detection. Upon the IoT architecture, intelligent location-sensitive APS and mobile execution services are developed to facilitate decisions and operations of different users. Thirdly, application of GIMS in HFS is presented. In HFS, production at each stage in each shift is treated as a basic unit of GIMS, where the three kinds of tickets are applied. Specific deployment of smart tickets and gateways for HFS are discussed. Synchronization mechanisms for job and setup synchronization for job sequencing and a cluster-based setup-restricted job queuing (CSJQ) approach for real-time scheduling are proposed. Their integration is applied to release jobs for accurate WIP control and determine setup tickets for flexible setup control. The intelligent implementation using the APS and mobile execution services is demonstrated. Fourthly, GIMS is extended to be applied in hybrid assembly cell lines (HACL). In HACL, movable trolleys are used for carrying materials, tools and performing assembly work. Fast and flexible reconfiguration of cell lines with very low cost can thus be realized. The dynamic and moving environment puts forward high requests on synchronization of part deliveries for workload control and synchronization of tool and machine resources for cell line reconfiguration. The three kinds of tickets, IoT architecture, intelligent APS and mobile execution services in GIMS are specifically modified and applied. A synchronization mechanism combining GA and heuristics is designed under GIMS to provide great adaptability to variances and disturbances.