# Intelligent Assembly Method of the Profiled Thermal Battery Pack Based on Improved DE Algorithm
## 4 Experimental Verification and Analysis
### Flatness Detection and Analysis  
Figure 17 depicts the sample points of the circular thermal battery. The position of the circular fastening screw on the plane of the bottom plate under test was taken as the origin, O, and the positions of the screws around it were marked as A, B, C, D, E, and F. The flatness of AOD, BOE, and COF in three straight directions was measured. Furthermore, the flatness of the whole thermal battery pack floor after assembly was obtained by analyzing the flatness error of the three straight lines. Figure 16: Flatness measurement of thermal battery pack assembly. (**a**) Measurement experiments on circular thermal batteries. (**b**) Measurement experiments on fan-shaped thermal batteries. Figure 15: Comparison of average iteration times. Figure 18 shows the straightness error curve before and after assembly of the upper and lower bottom panels of the thermal battery pack after measurement and calculation. Before assembly, the offset of the assembly frame bottom plate surface was less than 0.05 mm, which is considered a smooth surface of the thermal battery pack bottom plate before assembly. After assembly, the offset of the bottom plate was 0.5 mm, the height of the as-sembly frame was 145 mm, the offset accounted for 0.34% of the overall height, and the maximum offset was 0.67 mm. Figure 18 shows that the upper and lower bottom plates after assembly changed to the trend of \"concave in the middle and warped around\". The points tested on the measurement experiment platform of the fan-shaped battery pack set are shown in Figure 19, where the distance between each sample point of the  
Figure 17: Sample points of a circular thermal battery pack. Figure 18: Straightness error curve of the circular thermal battery pack. (**a**) Straightness error of upper bottom plate before assembly. (**b**) Straightness error of lower bottom plate before assembly. (**c**) Straightness error of upper bottom plate after assembly. (**d**) Straightness error of lower bottom plate after assembly. outer ring was 70 mm, and the distance between each point of the inner ring was 65 mm. When the measured straight line was perpendicular to the objective lens and the image could be found in the eyepiece, the first screw was 800 mm from the objective lens. After measurement and calculation, the straightness error curve before and after the assembly of the upper and lower base plates of this battery pack set is shown in Figure 20.  
Figure 19: Sample points of a fan-shaped thermal battery pack. Figure 20: Sample points of the fan-shaped thermal battery pack. As can be seen from Figure 20, the maximum offset of the surface of the base plate of the thermal battery pack before assembly was 0.025 mm, and again the surface of the base plate of the thermal battery pack before assembly could be considered as flat. After assembly, the offset of the base plate was 0.5 mm, accounting for 0.34% of the overall height, with a maximum offset of 0.57 mm. It is clear from the graph that the surface of the base plate was still \"concave in the middle and warped all around\" after the assembly of the battery pack. By analyzing the assembly results of the first two kinds of thermal battery packs, there was a situation of \"concave in the middle and warped around\" on the bottom sur-face of the assembly frame after assembly. This trend became more evident when the screw was close to the center. It was determined that the reason for this situation is that all screws were tightened in the same way and moment, so the screw closer to the middle area was squeezed more. Accordingly, an optimization method of the assembly process was proposed: the tightening torque of the middle part of the screw was multiplied by a coefficient of less than 1. Taking the round thermal battery pack as an example, the tightening torque of the screw at point O was reduced to 0.9 times of the original, and the tightening torque of other outer ring screws remained unchanged.