Linxuan Zhang

Balancing and sequencing of stochastic mixed-model assembly U-lines to minimise the expectation of work overload time

A mixed-model assembly U-line is a flexible production system capable of manufacturing a variety of similar models, and it has become popular as an important component of the just-in-time production system. However, it poses new challenges for the optimal design of assembly lines because both the task assignment and the production sequence affect the workload variance among workstations. As a consequence, this paper addresses the line balancing problem and the model sequencing problem jointly and proposes a 0–1 stochastic programming model. In this model, task times are assumed to be stochastic variables independently distributed with normal distributions and the objective is to minimise the expectation of work overload time for a given combination of cycle time and number of workstations. To solve the problem, a simulated annealing-based algorithm is developed, which can also be used to minimise the absolute deviation of workloads in a deterministic environment. The experimental results for a set of benchmark problems show that the proposed algorithm outperforms the existing algorithms in terms of solution quality and running time.

Federated integration of networked manufacturing service platforms

Networked manufacturing is an advanced manufacturing pattern that was born of information technologies and suits the networked economic environment. Networked manufacturing service platforms have been widely established to support this new pattern. Since the island problems are retarding further development of networked manufacturing, integration of existing networked manufacturing platforms is in demand. A federated integration mode is proposed to integrate the existing networked manufacturing platforms and provide a large-scale distributed resource sharing and cooperative environment. The nature of federated integration is discussed, and the architecture of federated integration system was put forward along with a set of rules and three types of integration services. Two key issues in federated integration are discussed in detail. One is the federation management, including the hierarchy of federations, the basic states of federations and the state-keeping mechanism using factory/instance pattern. The other issue is the authentication, authorization and access control in across-platform applications. Finally, an implementation is presented.

A Prototype Architecture for Assembly-Oriented Cyber-Physical Systems

ACPS is a new generation intelligent system based on the embedded systems, sensing technology and networked connectivity. As a typical application of CPS, it has many special features different from the traditional systems. According to these features, a four-layer architecture is proposed which consists of Physical Layer, Network Layer, Co-processing Layer and Application Layer. Furthermore, some research directions and challenges of ACPSs are suggested, and the ultimate goal is to develop foundations and techniques for building safe and effective ACPSs.

A Simulation System Based on OGRE and PhysX for Flexible Aircraft Assembly

Assembly simulation is an important step in the process of digital aircraft manufacturing planning which helps engineers find the defects in the preassembly plan and fix them before practical assembly. In this paper, a simulation system for flexible aircraft assembly is proposed. It uses OGRE and PhysX as the development platform instead of customizing commercial CAD/CAM platforms or implementing the system through OpenGL directly. The reason for choosing open source tools to implement the system is described in detail first. Then the architecture of the system is presented and introduced. Meanwhile, an example is given to illustrate the simulation process which consists of motion simulation and collision analysis. Finally the evaluate system that consists of assembly feasibility analysis, tolerance analysis and ergonomic analysis is described.

A hybrid PSO/SA algorithm for bi-criteria stochastic line balancing with flexible task times and zoning constraints

This paper addresses a stochastic assembly line balancing problem with flexible task times and zoning constraints. In this problem, task times are regarded as interval variables with given lower and upper bounds. Machines can compress processing times of tasks to improve the line efficiency, but it may increase the equipment cost, which is defined via a negative linear function of task times. Thus, it is necessary to make a compromise between the line efficiency and the equipment cost. To solve this problem, a bi-objective chance-constrained mixed 0–1 programming model is developed to simultaneously minimize the cycle time and the equipment cost. Then, a hybrid Particle swarm optimization algorithm is proposed to search a set of Pareto-optimal solutions, which employs the simulated annealing as a local search strategy. The Taguchi method is used to investigate the influence of parameters, and accordingly a suitable parameter setting is suggested. Finally, the comparative results show that the proposed algorithm outperforms the existing algorithms by obtaining better solutions within the same running time.

Synergic Motion Trajectory Planning for Airplane Docking Based on 6PURU Parallel Mechanism

Motion planning issues encountered in assembling airplanes by employing the 6PURU parallel mechanism are analyzed in this paper. A sine curve of the change rate of acceleration, which is called as jerk in the following text, is proposed for uniaxial flexible acceleration and deceleration planning based on the optimal time and velocity and acceleration constraints. Compared with other curves, the proposed curve can realize a continuous n-order derivative and the smooth change of the speed and acceleration. The method is computationally simple and suitable for programming. In addition, a multiaxial coordinated movement scheme is proposed. The motion trajectory is no longer simply split into many single-direction trajectories nor are all single-direction planning trajectories combined directly. The multiaxial coordinated movement scheme aims to achieve synergic movement in multiple directions to ensure smoothness of the movement in the event of a kinematic error when maintaining a stable value. If the movement fails to achieve this goal, driving force mutations will deteriorate the effect of synergic movement. A physical model of the parallel mechanism is developed in sim Mechanics, and a holistic system model is completed in SIMULINK. The feasibility of the new planning algorithm is simulated and tested, and then, the multiaxial synergic movement planning method is proposed and verified.

A Federated Integration of Networked Manufacturing Platforms

Networked manufacturing platforms have been widely used for their advantages, and integration of networked manufacturing platforms can provide a large-scale distributed cooperative environment. For commercial consideration, sometimes the integration is expected to be totally decentralized. The architecture for integration of networked manufacturing platforms and the hierarchy of federations are presented. The basic states of the federations are discussed. The factory/instance pattern is used to keep the state information, which is a key element of the federation management and other functions. Both the basic factory/instance pattern and the WS-resource factory/instance pattern are proposed in detail. Finally, the implementation is illustrated with the structure of a federated node

A dynamic delivery strategy for material handling in mixed-model assembly lines using decentralized supermarkets

Material handling has become one of the major challenges in modern production management. Consequently, this paper intends to investigate the part delivery of mixed-model assembly lines with decentralized supermarkets and tow trains. Besides, uncertain exception disturbances, including tow train failures and adjustments of the production sequence, are also considered. To solve this problem, a heuristic-based dynamic delivery strategy is proposed, which dynamically schedules the route, departure time, quantities and types of loaded parts for each tour. To evaluate the performance of this strategy, it is used to solve an instance in comparison with the periodic delivery strategy, experimental results are reported and their performances are compared under different metrics. Moreover, a multi-scenario analysis is employed to determinate the long-term decisions, including the number of tow trains and the route layout. Finally, the critical storage is suggested to be set for each station to avoid part starvation resulting from disturbances, and its effect on the delivery performance is investigated.

Simulation-Based Control for CPS Application to Aircraft Flexible Assembly

Based on the ideology of cyber physical systems and combining the requirements of aircraft flexible assembly, this paper puts forward ACPS (Assembly-oriented Cyber Physical Systems) and demonstrates its architecture via contrasting between ACPS and traditional assembly system. By taking aircraft components docking as an example, this paper also introduces ACPS’s software and hardware requirements, system composition, functional module division of assembly simulation control system, as well as key issues to resolve. ACPS then will be actualized to improve the level of aircraft assembly as well as provide theoretical and experimental support for next generation smart assembly systems.

Symbiotic Simulation of Assembly Quality Control in Large Gas Turbine Manufacturing

Assembly quality control is a vital problem in large gas turbine manufacturing. Assembly quality may not meet the requirements though each manufactured part’s precision is within its range. The paper discusses the assembly quality analysis and control in large gas turbine manufacturing. An intelligent assembly quality control solution using symbiotic simulation is proposed, which combines ON-line Simulation Module (ONSM) with OFF-line Simulation Module (OFFSM). Its mechanisms and partial techniques are discussed. In the end, a measurement simulation of a corporation’s gas turbine using Virtual Assembly Supported System (VASS) is realized, which verifies the mechanisms of the solution.