Seam welding system, seam welding method, and method for producing a to-be-welded object with roller electrodes

A seam welding method comprising:

• moving a pair of roller electrodes along a welding line of a to-be-welded object using an electrode movement mechanism, the pair of roller electrodes being coupled to the electrode movement mechanism, configured to hold the to-be-welded object between circumferential surfaces of the pair of roller electrodes, configured to rotate while holding the to-be-welded object between the circumferential surfaces, and configured to perform seam welding on the to-be-welded object when a current flows between the pair of roller electrodes while the pair of roller electrodes are rotating and holding the to-be-welded object between the circumferential surfaces, the pair of roller electrodes being mounted on a frame that is directly pivotally coupled to the electrode movement mechanism about a rotational axis, the rotational axis extending in a direction orthogonal to axes about which the pair of roller electrodes rotate;
• determining a torque change in at least one of a plurality of drive sources;
• and
• controlling an amount by which the pair of roller electrodes rotate based on the determined torque change,
• wherein controlling the amount by which the pair of roller electrodes rotate includes keeping torques respectively acting on the pair of roller electrodes within a predetermined range by changing the amount by which the pair of roller electrodes rotate,
• wherein the plurality of drive sources are respectively configured to rotate the pair of roller electrodes and a joint of the electrode movement mechanism, and
• further comprising calculating the predetermined range based on a teaching time during which the pair of roller electrodes are rotated while current does not flow between the pair of roller electrodes in order to determine error in torques during welding using the pair of roller electrodes as compared with torques determined while current does not flow between the pair of roller electrodes.

A method for producing a to-be-welded object, the method comprising:

• moving a pair of roller electrodes along a welding line of a to-be-welded object using an electrode movement mechanism, the pair of roller electrodes being coupled to the electrode movement mechanism, configured to hold the to-be-welded object between circumferential surfaces of the pair of roller electrodes, configured to rotate while holding the to-be-welded object between the circumferential surfaces, and configured to perform seam welding on the to-be-welded object when a current flows between the pair of roller electrodes while the pair of roller electrodes are rotating and holding the to-be-welded object between the circumferential surfaces, the pair of roller electrodes being mounted on a frame that is directly pivotally coupled to the electrode movement mechanism about a rotational axis, the rotational axis extending in a direction orthogonal to axes about which the pair of roller electrodes rotate;
• determining a torque change in at least one of a plurality of drive sources;
• and
• controlling an amount by which the pair of roller electrodes rotate based on the determined torque change,
• wherein controlling the amount by which the pair of roller electrodes rotate includes keeping torques respectively acting on the pair of roller electrodes within a predetermined range by changing the amount by which the pair of roller electrodes rotate,
• wherein the plurality of drive sources are respectively configured to rotate the pair of roller electrodes and a joint of the electrode movement mechanism, and
• further comprising calculating the predetermined range based on a teaching time during which the pair of roller electrodes are rotated while current does not flow between the pair of roller electrodes in order to determine error in torques during welding using the pair of roller electrodes as compared with torques determined while current does not flow between the pair of roller electrodes.