Self-centering mechanical arm

The invention discloses a self-centering mechanical arm, which comprises a first stage cylinder, a second stage cylinder, a finger seat and mechanical fingers, wherein each mechanical finger comprises a clamping part, a connecting part and a bearing part; the finger seat comprises a cylinder connecting part and finger connecting parts; a piston rod of the second stage cylinder is a conical surface piston rod, the second stage cylinder is connected with the first stage cylinder and is driven by the first stage cylinder to vertically reciprocate; the finger seat is connected with the lower end of the second stage cylinder through the cylinder connecting part; a roller is born inside the bearing part of each mechanical finger through a mandrel; each roller remains tangent with the conical surface of the conical surface piston rod. The self-centering mechanical arm provided by the invention eliminate the positioning error of a workpiece caused by dimensional tolerance through the synchronous centering movement of the cylinder, so as to enable a part to realize self-centering and positioning and make the centering and positioning to be more accurate and faster.