## 2 Problem Description  
An illustration of the EAHFSP considered in this study is provided in Figure 1.  
The EAHFSP is briefly described as follows. There are \(n\) products \(P_{1},P_{2},\cdots,P_{k},\cdots,P_{n}\), each product is produced by assembling a set of components \(PP=\{PP_{1},PP_{2},\cdots,PP_{r},\cdots,P_{n}\}\), \(N_{k}\) indicates a set of the required components of product \(P_{k}\) and \(w=\sum_{k=1}^{n}\lvert N_{k}\rvert\) denotes the total number of components. For each product \(P_{k}\), the production process mainly contains the manufacturing stage and the assembly stage. At the manufacturing stage, each component \(PP_{r}\) is processed in a hybrid flow shop with \(m\) stages, and each processing stage consists of \(\lvert S_{i}\rvert\geq 2\) unrelated parallel machines with a set of speeds \(V=\{v_{1},v_{2},\cdots v_{l},\cdots,v_{d}\}\). In the processing mode, \(p_{rijl}\) indicates \begin{table}
\begin{tabular}{c c c} \hline \hline
**Difference** & **The Previous Literature** & **This Work** \\ \hline Problem model & The existing studies on AHFSP only consider efficiency-oriented objectives ([10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23]); energy-related criteria are considered in other assembly scheduling problems ([24; 25; 26; 27]) and HFSP ([28; 29; 30; 31]). & A problem model of EAHFSP is built to optimize both efficiency-dependent and energy-related objectives. It is the first time that energy-saving criterion is investigated in AHFSP, which is more general and complex than other energy-efficient assembly scheduling problems and EHFSP. \\ \hline Optimization algorithm & Most of existing ABCs for shop scheduling problems are often modified by integrating other optimization algorithms; two phases: the employed bee phase and the onlooker bee phase are implemented in the same way ([37; 38; 39; 40; 41; 42; 43]). & A novel ABC based on population diversity is proposed to control the selection pressure and improve the diversity of food sources. \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Difference between this work and the previous literature. Figure 1: An illustration of the EAHFSP. the processing time of component \(PP_{r}\) on an unrelated parallel machine \(M_{ij}\) with speed \(v_{l}\), where \(M_{ij}\) is the \(jth\) machine at processing stage \(i\). Once the manufacturing of \(|N_{k}|\) components required by product \(P_{k}\) is finished, these components are transferred to the final assembly operation. There is only one assembly machine \(M_{a}\) at the assembly stage, and the speed of \(M_{a}\) remains constant during the assembly operation. \(A_{k}\) indicates the assembly time for product \(P_{k}\), and C\({}_{k}\) is the completion time for \(P_{k}\). The following assumptions are considered in the EAHFSP:  
All components and machines are available and independent at any time. The handling and transportation time of the components are ignored. No preemption or interruption is allowed in the processing and assembly process. Each component should be manufactured or assembled on one machine at most. Each machine processes no more than one component at a time. The manufacturing of each component and the assembly of each product must be conducted in sequence. In this study, the energy consumption of products during manufacturing and assembly processes is considered. Machines at the manufacturing and assembly stage exist in two modes: the working mode and the stand-by mode. Therefore, the total energy consumption (TEC) can be divided into four modules: energy consumption of manufacturing machines in the working mode (\(EC_{1}\)), energy consumption of manufacturing machines in the stand-by mode (\(EC_{2}\)), energy consumption of assembly machines in the working mode (\(EC_{3}\)), and energy consumption of assembly machines in the stand-by mode (\(EC_{4}\)).