# Switch-Off Policies in Job Shop Controlled by Workload Control Concept
## 1 Introduction  
Environmental sustainability and energy costs are crucial topics in manufacturing systems. The importance of identifying new solutions to improve the energy efficiency of manufacturing systems is essential to reduce the emission of greenhouse gases and the energy bill. Energy savings is the main way to meet the climate change targets set by countries around the world [1]. About 24% and 5% of global greenhouse gas emissions are related, respectively, to industrial energy consumption and industrial processes [2]. Then, the success of the reduction in energy consumption and increment in renewable energy sources depends strongly on industrial energy efficiency [3]. Moreover, the installed power of renewable energy sources grew from 2011 to 2020 continuously [4], with the main contribution by solar and wind energy, about 91%. This expansion is also due to the reduction in installation costs of renewable sources [5]. Among the methodologies proposed for the reduction of energy consumption, the switch-off approach [6] is a promising strategy. This approach does not change the manufacturing processes, and no new technology or expensive equipment is necessary. The switch-off policy works like the start and stop of the cars to reduce the energy consumed in the idle state. The fields of industrial applications can be different, such as CNC machining operation, welding, plastic deformation, and many other manufacturing processes.  
The switch-off policies are mainly proposed for flow lines [7, 8], but few works have studied these policies in job-shop manufacturing systems [9]. The job-shop systems are characterized by a variable routing of the parts for which it is more complex to introduce switch-off policies than in flow line systems. The introduction of a switch-off policy in job-shop systems needs to use information about the system as the production planning model. A production planning control used for job shops that work in make-to-order is the WorkLoad Control (WLC) approach [10, 11].  
The switch-off policies proposed in the literature evaluate the upstream, downstream, or both buffers for production lines. The research proposes the introduction of switch-off policies in job-shop systems using the information of the WorkLoad Control method.  
The introduction of the WLC method allows the evaluation of the direct workload in the queues of the machines with the indirect workload (WLC) to improve the switch-off/on decisions. It aims to pursue a trade-off between energy reduction and manufacturing system performance. Simulation models are used to test the proposed switch-off policies considering the manufacturing performance, energy reduction, and the number of on/off activities. The number of switches on/off activities is not studied in the literature but can be relevant for the influence on the reliability of the machines.  
This paper is organized as follows. Section 2 discusses the literature review about the switch-off policies in manufacturing systems. Section 3 describes the manufacturing system context under the workload control policy. Section 4 explains the switch-off policies based on workload computation. The simulation experiments and the numerical results are discussed in Section 5. Section 6 provides the conclusions and future research path.