In order to ensure the stable and safe operation of coal mining machinery, the qualitative indexes in the life evaluation index system of coal mining machinery gear transmission system are only allowed to change in a certain range. When the change range exceeds the corresponding threshold, the operation state of coal mining machinery gear transmission system will change, and its working life will be seriously affected. As shown in the figure, the operation state of the coal mine mechanical wheel drive system changes with qualitative variables.

It can be seen from the figure that when the change range of the original value of the qualitative index exceeds the deterioration value, the operation of the coal mine mechanical gear transmission system will deviate from the normal operation state. When the change range of the original value exceeds the warning value, the operation state of the coal mine mechanical gear transmission system will be abnormal, which may cause the mechanical failure of the coal mine. When the change range of the original value exceeds the dangerous value, it is necessary to That is, stop the machine to check the gear transmission system of the coal mine machinery to ensure the safe operation of the coal mine machinery.

Whether the threshold value of the original value of the qualitative index is reasonable or not will seriously affect the quantitative evaluation results of the life of the coal mine mechanical gear transmission system. If the threshold value is too low, though the change of the index state is very small, it will also have a great impact on the evaluation results. If the threshold value is too high, the evaluation result will not change greatly although the indicator state changes greatly.

When standardizing the qualitative indexes in the life evaluation of coal mine mechanical gear transmission system, in order to deal with the indexes conveniently, the target layer is recorded as layer a and the criterion layer is layer B. There are four factors (B1, B2, B3, B4) to deal with the indexes, which are gear damage, gear lubrication, load characteristics and other factors. The subcriterion layer is layer C, with 16 factors (C1, C2, C3, C4… C16) is the ratio of the crack width of the tooth surface to the width of the tooth, the ratio of the maximum area of pitting to the area of the tooth, the ratio of the maximum size of pitting to the value of the die, the ratio of the maximum depth of pitting to the value of the die, the ratio of the gluing area to the area of the tooth, the ratio of the depth of the gluing groove to the value of the die, the ratio of the sum of the consumption on both sides of the worn tooth root to the value of the normal die, the viscosity of the lubricating oil, the moisture, the mechanical impurities, the ratio of The ratio of wheel cycle times to its average cycle times, the ratio of gear cycle times to design cycle times, machining error, assembly error, impact load and use maintenance.