Topology optimization design of the height-adjustment mechanism of a shearer cable bending test machine

The bending-resistance test of shearer cables should be consistent with actual underground operating conditions, in which the cable dragging height, bending radius and contact state vary with different shearer models and cable specifications. Existing bending test machines generally perform dragging tests at a fixed height, which limits their ability to reproduce the real service state of shearer cables. To address this problem, a hydraulically assisted height-adjustment system based on rack-and-pinion transmission was designed in this study. Dynamic simulation, fatigue-life prediction and lightweight design of the height-adjustment mechanism were then carried out. A three-dimensional model of the height-adjustment mechanism was established according to the matching principle of shearer cable dragging height. An MCPT-1.9/3.3 cable with a specification of 3 × 185 + 1 × 95 + 4 × 10 was selected as the research object. A layered equivalent modeling method was adopted, and tensile tests of the strands and control-core conductors were conducted to determine the material parameters. The equivalent elastic modulus and Poisson's ratio of the assembled cable were obtained as 28,503 MPa and 0.394, respectively. A rigid-flexible coupled dynamic model of the height-adjustment mechanism was established in RecurDyn to analyze the dynamic stresses of the gear, rack, guide column, limit block and slider. Fatigue-life prediction was performed for the guide-column limiting-hole region under alternating loads. Topology optimization was further conducted using the variable-density method in OptiStruct. The results show that the maximum equivalent stresses of the gear and rack during the height-adjustment process are 73.27 MPa and 42.82 MPa, respectively. During the dragging process at a height of 1.8 m, the maximum equivalent stresses of the guide column, limit block and slider are 65.11 MPa, 45.89 MPa and 17.73 MPa, respectively, which are all lower than the allowable stress of the material. Based on the rainflow counting method and the Palmgren-Miner criterion, the fatigue life of the guide column is calculated. After topology optimization, the masses of the guide column, limit block, supporting plate, slider and guide-column sleeve are reduced by 37.7%, 55.6%, 36.4%, 51.9% and 5.6%, respectively. The total mass of the height-adjustment mechanism is reduced by 132.6 kg. The maximum equivalent stresses of the guide column, limit block and slider are reduced by 23.3%, 26.4% and 34.5%, respectively, and the optimized guide column still satisfies the fatigue-life design requirement. This study provides a theoretical basis for the optimized design of shearer cable bending test machines.