# Switch-Off Policies in Job Shop Controlled by Workload Control Concept
## 7 Conclusions and Future Developmental Paths  
The research proposed in this paper extends the switch-off method to reduce energy consumption in job-shop systems. A production control method used in the job shop system is workload control; in the literature, the effects of the switch-off policies in these systems were not studied.  
Then, the research proposed in this paper introduces the switch-off method in manufacturing systems controlled by a workload control approach to reduce energy consumption. In response, our first research question asked: what is the impact of switch-off policies in a job-shop system controlled by the workload mechanism?  
The simulation results have demonstrated how the switch-off policies can reduce the energy consumption of the manufacturing system by reducing the energy consumed in the idle state of the machines. The upstream policy, proposed in the literature, allows for drastically reducing energy consumption, but the number of turns on/off of the machines is very high, and the performance measures of the manufacturing system are the worst.  
Then, the policies proposed that include the workload computation of the control mechanism allow us to obtain a better trade-off between energy consumption and manufacturing system performance. Moreover, the number of turns on/off of the machines is lower with the proposed switch-off policies.  
The analysis of the different values of idle power and warm-up characteristics answers our second research question: what is the impact on the main performance measures of the combinations of the turn-off/on mechanism also based on the power consumed in the states of the machines?  
The idle and warm-up power characteristics impact the manufacturing performance and energy consumption, as shown by the ANOVA analysis. The simulations show how the proposed policy based on workload computation is more robust against these parameters. Moreover, policy 5, based on workload control data, is not affected by the warm-up power and time.  
At the managerial level, the simulation supports the decision maker in choosing the better switch-off policy for energy consumption reduction and the manufacturing performance target. The simulation helps the decision maker because it allows for estimating both the productivity and energy performance of the manufacturing systems. The potential industrial applications can involve production systems where CNC machines are used. Recent CNC machines are capable of switching into energy-saving modes or even shutting down completely. For example, [29] argued how in an aircraft small-parts supplier, there is an idle period of 16% of the machines, and this can reduce the energy consumption by about 13% with a switch-off policy. Therefore, the proposed method can support industrial cases with several CNC machines (such as cutting operations) or auxiliary tools such as air compressed for welding tasks. This is because both the CNC machines and air-compressed auxiliary tools can easily be turned off and on.  
This research, following the works proposed in the literature, concerns a manufacturing system with dedicated machines; a future development path can investigate the impact of machine flexibility. A limitation of the proposed method is that the flexibility of the machines is not considered, and the method works with a determined routing of the jobs. Another limit is the processing time, which should have lower variability to aid the proposed model. A future research path can investigate the impact of workload control and a switch-off policy on the peak power constraint due to the energy provider.  
**Funding:** This research received no external funding.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Not applicable.  
**Conflicts of Interest:** The authors declare no conflict of interest.