Abstract: Iron roughneck is advanced drilling auxiliary operation equipment, and domestic iron roughnecks have many shortcomings in automation degree, clamping positioning accuracy and work smoothness. In order to solve the problem，a new type of iron roughneck structure and its hydraulic control system are designed in this paper. Firstly, through the machine-hydraulic co-simulation analysis, the axis deviation angle and radial force change of the drill pipes during the makeup and breakout process of the iron roughneck were studied. Then, the control system of the iron roughneck is optimized on this basis, and the synchronous motor and PID (proportional integral differential) control are used to further analyze the influence of increasing hydraulic cylinders input flow rate on the synchronous performance of the hydraulic cylinders, clamping positioning accuracy and radial force of the joint thread of the fixed plier and moving plier. The results show that PID control has better clamping effect than synchronous motor. When the input flow rate of a single hydraulic cylinder is 18 L/min, the x and y axial deviation angles of the drill pipe can be controlled within 0.10°and 0.06°when clamped with fixed plier, and the response speed is about 6.8 seconds. The distance between the center of gravity of the upper and lower drill pipes along the x and y axis directions can be respectively controlled within 1.93 and 2.85 mm, which ensures the clamping positioning accuracy, rapidity and stability of the fixed plier and the moving plier. The radial force curve of the joint thread also indicates that the unbalanced radial force between the drill pipe joints during the iron roughnecks punching (17.2 kN) is much greater than that of the spinning (641.0 N), which is more likely to cause the drill bit to wear.

Key words: iron roughneck, positioning accuracy, machine-hydraulic co-simulation analysis, unbalanced radial force；drilling