Apparatus for monitoring spot welding process and method of the same

• US 6,335,504 B1
• Filed: 12/15/2000
• Issued: 01/01/2002
• Est. Priority Date: 12/15/2000
• Status: Expired due to Fees

• Current Assignee: Essor International Incorporated
• Original Assignee: Essor International Incorporated
• Inventors: Wan, Li-Xue, Ling, Shih-Fu
• Primary Examiner(s): Shaw, Clifford C.
• Application Number:
  US09/736,263
• Time in Patent Office: 382 Days
• Field of Search: 219/109, 219/110
• US Class Current: 219/109
• CPC Class Codes: B23K 11/257 the measured parameter being an electrical current

Abstract

The present invention discloses an apparatus and a method for monitoring the quality of a spot welding process. The measured electric current and voltage signals between electrodes of a spot welding system are converted into digital data first. Then the two digital data are processed to obtain their complex forms via Hillbert transform respectively to construct their imaginary part. Finally, the electrical impedance Z_in is obtained from dividing the complex form of digital voltage by the complex form of digital current. The electrical impedance Z_in can be applied to compare with historical data to diagnose the quality of spot-welding points.

Claims

1. An apparatus for monitoring a welding process of a spot-welding means, said spot-welding means including a pair of electrodes;

said apparatus comprising;

a current measuring means for measuring electric current signal between said electrodes;

a voltage measuring means for measuring electric voltage signal between said electrodes;

at least one analog to digital converter for converting said measured current and voltage signals into digital current i(t) and digital voltage v(t);

a processing unit for calculating an electrical impedance(Z_in) between said electrodes of said spot-welding means according to the equation;

$Z_{\mathrm{in}}=\frac{V<br><br>\left(t\right)}{I<br><br>\left(t\right)},$

wherein,

2. The apparatus as claimed in claim 1 further comprising a data analyzer and a memory means, said data analyzer using for comparing said electrical impedance (Z_in) with historical data stored in said memory means, said historical data related to different quality results of a spot-welding process.

3. The apparatus as claimed in claim 2, wherein said historical data being an electrical impedance corresponding to a joint formed with expulsion.

4. The apparatus as claimed in claim 2 further comprising an indicator for showing a comparing conclusion when said electrical impedance (Z_in) coincides with said historical data.

5. The apparatus as claimed in claim 1, wherein said output unit comprising a displaying device for displaying said electric impedance (Z_in).

6. A method for monitoring a welding process of a spot-welding means, said spot-welding means including a pair of electrodes;

said method comprising steps of;

(a) measuring electrical current signal and voltage signal between said electrodes of said spot-welding means, and converting the same to digital current i(t) and digital voltage v(t) respectively;

(b) calculating an electrical impedance (Z_in) between said electrodes of said spot-welding means with the equation;

$Z_{\mathrm{in}}=\frac{V<br><br>\left(t\right)}{I<br><br>\left(t\right)},$

wherein,

7. The method as claimed in claim 6 further comprising step (d) after said step (c), comparing said electrical impedance (Z_in) with historical data, said historical data related to different quality results of a spot-welding process.

8. The method as claimed in claim 7, wherein said historical data being an electrical impedance corresponding to a joint form with expulsion.

9. The method as claimed in claim 7 further comprising step (e) after said step (d), showing a comparing conclusion when said electrical impedance (Z_in) coincides with said historical data.