Patent ID: 8754347

Claim:
A resistance spot welder comprising: a motor, having a shaft; a cylindrical casing; a hollow guide rod, inserted into the casing, and adapted to be moved in a linear direction along a center axis of the guide rod for moving a first electrode tip facing a second electrode tip provided at a gun arm; a ball nut, fixed in an inner circumference of the guide rod; a ball screw, fitted though the hall nut; a coupling, including a first fastening portion into which the shaft of the motor is inserted and a second fastening portion into which the ball screw is inserted and which is integral with and opposite to the first fastening portion, the first fastening portion defining a hollow cylinder concentric with the center axis and connecting to the second fastening portion via a step, the second fastening portion also defining a hollow cylinder concentric with the center axis; and a bearing, fitted between an outer circumference of the first fastening portion and an inner circumference of the casing, wherein, the guide rod is moved in the linear direction, between a first point where the guide rod is retracted toward a motor side and a second point where the guide rod is extended toward an electrode tip side, the first fastening portion and the second fastening portion are arranged in the linear direction, the first fastening portion being on the motor side, the second fastening portion being on the electrode tip side, and when the guide rod is positioned at the first point where the guide rod is retracted toward the motorside, the second fastening portion is disposed in the inner circumference of the hollow guide rod, wherein the inner circumference of the guide rod is no more than the outer circumference of the first fastening portion in diameter, and the inner circumference of the guide rod is no less than an outer circumference of the second fastening portion.