Abstract: An inter-welding electrode moving amount detecting method includes the below steps: moving a driving section of electrode driving means having the driving section connected to at least one of a pair of electrodes provided to a welding gun; detecting an inter-welding electrode moving amount due to expansion/contraction of a nugget when a member to be welded is pressed, electrified and welded by the pair of electrodes; and obtaining the inter-welding electrode moving amounts by adding a moving amount of the driving section to an electrode moving direction due to the expansion/contraction of the nugget during welding and a deflection (alternatively, a strain amount) of the welding gun due to a pressing force.

Abstract: An inter-welding electrode moving amount detecting method includes the below steps: moving a driving section of electrode driving means having the driving section connected to at least one of a pair of electrodes provided to a welding gun; detecting an inter-welding electrode moving amount due to expansion/contraction of a nugget when a member to be welded is pressed, electrified and welded by the pair of electrodes; and obtaining the Inter-welding electrode moving amounts by adding a moving amount of the driving section to an electrode moving direction due to the expansion/ contraction of the nugget during welding and a deflection (alternatively, a strain amount) of the welding gun due to a pressing force.

Abstract: A welding gun has a coordinate system fixed thereto, and a sensor is fixed to the coordinate system. The sensor senses a mobile electrode moved in a position, and a position detector cooperates with the sensor to detect the position of the mobile electrode relative to the welding gun.

Abstract: Paired electrodes, of which a wear amount is detected, press workpieces to be welded, conducting a current therethrough, and have an inter-electrode displacement amount varying during the current conduction, which displacement amount is detected continuously from a reference position (a). Detected inter-electrode displacement amounts are corrected in dependence on the detected wear amount, and corrected inter-electrode displacement amounts (h) are based on to make a decision of a welding state of the workpieces.

Abstract: A welding spot is held between electrodes either biased with a controlled pressure, having a controlled voltage applied thereacross, and variations of an inter-electrode distance are detected for a welding quality control, in which the distance variations are time-integrated, a nugget size is estimated on a basis of the integration, and a decision is made of a conformity of welding quality based on an estimated nugget size.