# Simulation on Cooperative Changeover of Production Team Using Hybrid Modeling Method
## 3 Hybrid Simulation Model of Production System  
### Frame of Hybrid Simulation Model  
The frame of hybrid simulation model is shown in Figure 1. It consists of simulation inputs, simulation outputs, model of discrete production process, integration interface of hybrid model and multi-agent model. In the multi-agent system, the interaction between agents follows the contract network protocol which distributes the tasks in the system by introducing the tendering-bidding-winning mechanism of the market ([PERSON] et al., 2016). The task assignment in the production system consists of two phases. In the first phase, the manager agent, as a tenderer, generates a production task based on the production state  
Figure 1: Frame of hybrid simulation model. data and issues the task to operator agents. In the second phase, the winner of the first phase needs to determine whether to launches cooperation. If so, the winner of the first phase will become a tenderer in the second phase, and then send the assisted task to the rest of operator agents. In the background of production systems, the bidder is referred to as the applicant of the task in two phases, and the winner of the second phase is referred to as the assistant. * The simulation inputs include a production scenario and a cooperative changeover strategy. Firstly, according to the proportion of new product orders in total orders, the production scenarios are divided into four kinds: only producing of mature products, small-scale introduction of new products, middle-scale introduction of new products and large-scale introduction of new products. Secondly, cooperative changeover strategies are also divided into four kinds: non-cooperative strategy, cooperative strategy for mature products, cooperative strategy for new products and totally cooperative strategy. The non-cooperative strategy refers to the strategy that the operator directly conducts the changeover operation independently rather than launches cooperation. For the other three strategies, the operator will send an assisted changeover task to the other operators for a particular type of products. If there is only one applicant, the applicant will be confirmed as the assistant of the operator to conduct the changeover operation cooperatively; if there is more than one applicant, the applicant with the highest skill level will be confirmed as the assistant; if there is no applicant, the operator will conduct the changeover operation independently. * The simulation outputs include two evaluation indicators. Firstly, manufacturers hope to have the new products on the market as soon as possible. Therefore, improving production efficiency is an essential object for them. In this paper, production cycle is used to measure production efficiency, which represents the effective production cycle with the non-working hours excluded. Secondly, due to the high cost of skill training, the skills to conduct the changeover operation independently are usually mastered by a small number of operators, which results in a large difference in workload among operators. Workload Balance Level (WBL) is used to measure the workload difference among operators and calculated using: \[\text{WBL}=\frac{\sum_{k=1}^{K}\text{tl}_{k}/K}{\sqrt{\sum_{k=1}^{K}\left( \text{tl}_{k}-\sum_{k=1}^{K}\text{tl}_{k}/K\right)^{2}/(K-1)}},\] (1) where \(tl_{k}\) represents the total workload of operator k, and K represents the number of operators. * The model of discrete production process is established by discrete-event modeling method and collected information, such as the layout of the facilities and the process route of each product type in the production system. * The integration interface of hybrid model is used to implement the interaction between the model of discrete production process and multi-agent model, such as transferring production state data to the multi-agent model and driving operator agents to participate in the production process.