SPOT WELDING SYSTEM INCLUDING SPOT WELDING GUN

• US 20140291300A1
• Filed: 03/17/2014
• Published: 10/02/2014
• Est. Priority Date: 03/28/2013
• Status: Active Grant

• Current Assignee: Fanuc Corporation
• Original Assignee: Fanuc Corporation
• Inventors: Amagata, Yasuhiro
• Granted Patent: US 9,440,306 B2
• Time in Patent Office: Days
• US Class Current: 219/90
• CPC Class Codes: B23K 11/115 by means of two electrodes placed opposite one another on both sides of the welded parts
• CPC Class Codes: B23K 11/253 the measured parameter being a displacement or a position
• CPC Class Codes: B23K 11/3009 Pressure electrodes
• CPC Class Codes: B23K 11/311 the actuating device comprising an electric motor
• CPC Class Codes: B23K 11/315 with one electrode moving on a linear path

Abstract

A spot welding system (1) includes a welding pressure command generating unit (31) which generates a reference welding pressure command for a spot welding gun by applying pressure to workpieces to be welded between two electrode tips and at least one detective welding pressure command, an elastic displacement quantity deviation calculating unit (32) calculating, as an elastic displacement quantity deviation, a rotational position deviation between the rotational position of a servomotor when the reference welding pressure command is used and the rotational position of the servomotor when at least one detective welding pressure command is used, and an estimating unit (34) which estimates that there is an abnormality in the spot welding gun when the deviation between the elastic displacement quantity deviation based on the reference welding pressure command and at least one detective welding pressure command and the reference displacement quantity deviation is greater than a predetermined value.

Claims

1. A spot welding system including a spot welding gun welding workpieces to be welded under pressure between a movable electrode tip driven by a servomotor and a stationary electrode tip facing the movable electrode tip, the spot welding system comprising:

an encoder measuring a rotational position of the servomotor;

a welding pressure command value generating unit generating a reference welding pressure command value for the spot welding gun and at least one detective welding pressure command value for applying pressure to the workpieces to be welded between the movable electrode tip and the stationary electrode tip;

an elastic displacement quantity deviation calculating unit calculating, as an elastic displacement quantity deviation in the spot welding gun, a rotational position deviation between a rotational position of the servomotor when the servomotor is driven in accordance with the reference welding pressure command value and a rotational position of the servomotor when the servomotor is driven in accordance with the at least one detective welding pressure command value;

a storage unit storing the elastic displacement quantity deviation as a reference displacement quantity deviation determined by the elastic displacement quantity deviation calculating unit in a condition where the spot welding gun has been adjusted to be able to properly exert welding pressure; and

an estimating unit estimating that there is an abnormality in the spot welding gun when a deviation between an elastic displacement quantity deviation determined by the elastic displacement quantity deviation calculating unit based on the reference welding pressure command value and the at least one detective welding command value in a condition where a welding pressure of the spot welding gun needs to be readjusted and the reference displacement quantity deviation stored in the storage unit, is greater than a predetermined value.

2. The spot welding system according to claim 1, further comprising a warning unit indicating occurrence of an abnormality in the spot welding gun to the outside when the estimating unit estimates that there is an abnormality in the spot welding gun.

3. The spot welding system according to claim 1, further comprising a display unit displaying the deviation between the elastic displacement quantity deviation and the reference displacement quantity deviation.

4. The spot welding system according to claim 1, further comprising a storage unit storing the deviation between the elastic displacement quantity deviation and the reference displacement quantity deviation together with a timestamp in chronological order.

5. The spot welding system according to claim 4, further comprising a display unit displaying the deviation between the elastic displacement quantity deviation and the reference displacement quantity deviation together with a timestamp in chronological order.

6. The spot welding system according to claim 1, further comprising a welding pressure deviation calculating unit multiplying the deviation between the elastic displacement quantity deviation and the reference displacement quantity deviation by a spring constant of the spot welding gun to obtain a welding pressure deviation.

7. The spot welding system according to claim 6, further comprising a welding pressure correcting unit correcting a torque command value to be provided to the servomotor during a pressure application operation or a rotational position command value to be provided to the servomotor during a pressure application operation based on the welding pressure deviation calculated by the welding pressure calculating unit, when the welding pressure deviation calculated by the welding pressure calculating unit is smaller than a first predetermined deviation value.

8. The spot welding system according to claim 7, wherein when the welding pressure deviation calculated by the welding pressure deviation calculating unit is greater than or equal to the first predetermined deviation value, a correction by the welding pressure deviation correcting unit is not made.

9. The spot welding system according to claim 8, further comprising a warning unit indicating occurrence of an abnormality in the spot welding gun to the outside when the welding pressure deviation calculated by the welding pressure deviation calculating unit is greater than or equal to a second predetermined deviation value.

10. The spot welding system according to claim 6, further comprising a display unit displaying the welding pressure deviation.

11. The spot welding system according to claim 6, further comprising a storage unit storing the welding pressure deviation together with a timestamp in chronological order.

12. The spot welding system according to claim 11, comprising a display unit displaying the welding pressure deviation together with a timestamp in chronological order.