## 5 Results and Discussion
### Two Cleaning Measures  
On the basis of the proposed contact transmission model, the effectiveness of the two cleaning measures was analyzed with respect to the reduction in oil concentration on various surfaces in the workshop. The two cleaning measures were cleaning the workbench and cleaning the gloves of workers. As the workpieces produced by the production area are the source of oil contamination, the spread of oil contamination in the assembly area depends on that attached to the workpieces produced in the production area. Therefore, these two cleaning measures are more effective for surfaces in the production area. Figure 9 shows the relationship between the oil contamination reduction rate on all surfaces and different cleaning rates under different cleaning frequencies after adopting the two cleaning measures. The results show that regardless of the cleaning measure, under the same cleaning frequency, the cleaning effect of all surfaces is positively correlated with the cleaning rate. Cleaning the workbench is more effective than cleaning the gloves of workers in terms of reducing the oil concentration on all surfaces. This finding can be attributed to the wide gap in the area ratio between the workbench and the gloves of workers. In this study, the area of the workbench is 0.5 m\({}^{2}\), whereas the area of the glove is only 0.02 m\({}^{2}\). Assuming the oil contamination concentration on the workbench is equivalent to that of the gloves, the difference is apparent. Furthermore, although cleaning the gloves can greatly reduce their amount of oil contamination, when these gloves come in contact with the workbench, the amount of oil contamination transferred from the workbench to the gloves accounts for a relatively small proportion of the total oil contamination on the workbench. When the frequency of cleaning gloves reaches once every 10 min and the cleaning efficiency reaches 90%, the reduction rate of all surfaces is approximately 20%, which is much lower than the reduction rate that can be achieved when cleaning the workbench (approximately 65%). Figure 10 shows the oil contamination reduction rate of the workbench in the production area, which is significantly greater than that in the assembly area. At the fastest cleaning frequency (every 10 min) and the highest cleaning efficiency (90%), the oil contamination reduction rate can reach approximately 85%. However, the oil contamination reduction rate in the assembly area is generally low, and when the cleaning frequency is constant, the reduction rate fluctuates with the cleaning efficiency. This finding may be explained by the automatic transport vehicles being randomly sent to the assembly unit when transporting the workpieces. Sometimes, the workpieces with low oil contamination are evenly distributed to the assembly station; at other times, the workpieces with low oil contamination are only distributed to certain assembly tables, and the other assembly  
Figure 9: Relationship between oil contamination reduction rate on all surfaces and different cleaning rates under different cleaning frequencies: (**a**) cleaning the worker’s gloves and (**b**) cleaning the workbench in the production area. tables are assigned to workpieces with high oil contamination. At these times, the average oil contamination reduction rate of the assembly tables is lower than that under even distribution. In general, cleaning the workbenches in the production area can meet the goal of reducing the oil contamination concentration in various areas of the workshop. The above analysis suggests a functional relationship between the reduction rate of oil contamination concentration on different surfaces and the cleaning frequency and cleaning efficiency, especially in the production area. Subsequently, the change in oil contamination concentration of the workbench in the production area is fitted. A power function relationship also exists between the oil contamination concentration of the workbench in the production area and the cleaning efficiency.