# Implementation of Explosion Safety Regulations in Design of a Mobile Robot for Coal Mines
## 4 Implementation of IEC 60079 for TeleRescuer
### Flameproof Enclosure  
The requirements resulting from the standards place big demands on the design of the covers of the individual components of the robot. The most important is the encapsulation of the robot body, which houses eight robot motors, a battery subsystem, and the main control system. The design requirements are based on standard EN 60079-1--Explosive atmospheres--Part 1: Equipment protection by flameproof enclosure \"d\" [30], which specifies requirements for wall thickness, strength and resistance to the potential explosion of methane within the robot, contact surfaces of detachable parts, etc.  
In designing the shape of the robot encapsulation, strength analyses of individual parts were performed continuously to achieve the optimal shape, strength, and weight ratio with respect to the potential pressure that could cause methane explosion inside the robot body. These analyzes were performed in the PTC Creo Simulate 3.0 CAD system, more details about the methodology can be found in [31]. The following example will demonstrate inspection and optimization of the top cover under which the robot control system is located inside the body (Figures 4 and 7).  
In order to verify and optimize the top cover, it was necessary to create a computational model. The model contains a simplified assembly of the frame and the cover, with a contact between them. The frame is fixed and the cover is connected by screws, which are simulated as idealized Fastener  
Figure 6: Separation of TeleRescuer subsystems.  
elements (Figure 8). Based on the specification, the material \"Stainless Steel 1.4462\" was used for calculations (tensile strength Rm = 950 MPa, proof stress Re = 500 MPa).  
A pressure of 3 MPa was applied on the inner surfaces of the cover. This value simulates the explosion of methane inside the robot body and it is based on experiments from [32; 33], increased by a safety factor. Results of the analysis are shown in the following figures.  
Figure 9 shows the stress distribution on the cover. The red areas represent stress peaks reaching up to 1900 MPa, which means that the cover could be seriously damaged by the explosion and the flameproof enclosure protection could be broken. It was thus necessary to modify the design on the cover to lower the stress peaks.  
The final modified design of the cover is shown in Figure 10. The stress peaks are between 580 and 650 MPa, which does not exceed Rm and the cover would not be destroyed.  
Figure 8: Computational model of the top cover assembly.  
Figure 7: Main robot body with the top cover.  
Figure 9: Stress distribution during an explosion simulation (initial design).  
Another very important test is for any possible gaps between individual parts of the enclosure caused by the inner explosion. The maximum gap size is controlled by EN 60079-1 ([29]: table \"Minimum width of joint and maximum gap for enclosures of Groups I, IIA and IIB\"), which in the case of a planar gap with the length bigger than 25 mm (the actual gap length is 30 mm, see Figure 11) and inner volume larger than 2000 cm\({}^{3}\) (the actual volume is approx. 40,000 cm\({}^{3}\)) allows for a maximum width of the gap 0.5 mm for Group I.  
The simulation results show that the contact surface between the top cover and the bottom frame deforms during the explosion and a gap appears. The width of this gap is different on the inner and outer edge of the cover and changes with the position along the edge (Figures 11 and 12), but it never exceeds the allowed limit (the maximum is 0.474 mm, which is less than 0.5 mm).  
Figure 11: Top cover deformation.  
Figure 10: Stress distribution during an explosion simulation (final design).