Method and apparatus for determining the voltage at the electrodes of a spot welding gun

• US 9,889,520 B2
• Filed: 05/12/2010
• Issued: 02/13/2018
• Est. Priority Date: 05/14/2009
• Status: Active Grant

• Current Assignee: Fronius International GmbH (G&K Privatstiftung)
• Original Assignee: Fronius International GmbH (G&K Privatstiftung)
• Inventors: Ennsbrunner, Helmut, Gschmeidler, Thomas
• Primary Examiner(s): STAPLETON, ERIC S
• Application Number:
  US13/319,763
• Publication Number:
  US 20120048834A1
• Time in Patent Office: 2,834 Days
• Field of Search: 219 911, 219109, 219110, 2191171, 219118, 21912114, 21912146, 21912164, 21912183, 21912185, 700 32- 34, 700108-111, 700166, 702 65, 702 66, 702 81- 84, 73850
• 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 11/258 the measured parameter being a voltage

Abstract

A method and an apparatus for determining the temporal curve of the voltage (u_e(t)) at the electrodes (3) of a spot welding gun (1) during a spot welding process as an indicator of the welding quality, wherein the electrodes (3) are fastened to gun arms (2) that can be moved relative to each other are provided. The apparatus includes a device (9) for measuring a measuring voltage (u_m(t)) between the electrodes (3), that measuring device (9) being connected to measuring leads (6) extending along the gun arms (2), and further includes a compensating coil (7) for measuring a compensating voltage (u_k(t)) for compensating measuring errors within measuring leads. In order to determine the temporal curve of the voltage (u_e(t)) at the electrodes (3) of the spot welding gun (1) during a spot welding process as precisely as possible, the device (9) for measuring the measuring voltage (u_m(t)) and the device (10) for measuring the compensating voltage (u_k(t)) are designed as separate units for separate detection and are connected to a device (11) for processing the detected values.

Claims

1. A method for determining a temporal curve of a voltage (u_e(t)) at the electrodes of a spot welding gun during a spot welding process as an indicator of welding quality, the method comprising the steps of:

a) fastening the electrodes to gun arms that can be moved relative to each other;

b) measuring a measuring voltage (u_m(t)) via measuring leads;

c) measuring a compensating voltage (u_k(t)) using a compensating coil;

wherein the measuring voltage (u_m(t)) and the compensating voltage (u_k(t)) are detected separately and at least one of the measuring voltage and the compensating voltage are detected at a frequency of between 2 kHz and 10 kHz;

d) determining a relation (v(t)) between the measuring voltage (u_m(t)) and the compensating voltage (u_k(t)) at times when erratic voltage changes occur;

e) multiplying said compensating voltage (u_k(t)) by the determined relation (v(t)) to obtain a relative voltage value; and

f) determining the electrode voltage (u_e(t)) by subtracting the relative voltage value obtained by multiplying the compensating voltage (u_k(t)) by the determined relation (v(t)) from the measuring voltage (u_m(t));

digitizing at least one voltage reading on at least one gun body;

wherein the relation (v(t)) is continuously determined during the spot welding process; and

wherein a part of an area defined by the measuring leads is covered by the compensating coil.

2. The method according to claim 1, wherein a voltage drop (u_L(t)) at a resistance of feed lines is subtracted from the measuring voltage (u_m(t)) adjusted by an induced voltage (u_i(t)) for determining the electrode voltage (u_e(t)).

3. The method according to claim 2, wherein an ohmic resistance of feed lines for determining a voltage drop (u_L(t)) during a spot welding process is previously determined without components to be welded.

4. The method according to claim 1, wherein the measuring voltage (u_m(t)) and the compensating voltage (u_k(t)) are digitalized separately on said gun body and are supplied to a processing device on said gun body.

5. The method according to claim 1, wherein the measuring voltage (u_m(t)) and the compensating voltage (u_k(t)) and/or magnitudes derived therefrom are stored.