Control of spot weld quality by infrared thermal sensing

• US 4,214,164 A
• Filed: 07/19/1978
• Issued: 07/22/1980
• Est. Priority Date: 07/19/1978
• Status: Expired due to Term

• Current Assignee: Vanzetti Infrared & Computer System Incorporated
• Original Assignee: Vanzetti Infrared & Computer System Incorporated
• Inventors: Traub, Alan C., Vanzetti, Riccardo
• Primary Examiner(s): Willis, Davis L.
• Application Number:
  US05/926,055
• Time in Patent Office: 734 Days
• Field of Search: 250/338, 250/339, 250/340, 250/342, 250/358 R, 73/342, 73/355 R, 73/355 EM
• US Class Current: 250/338.1
• CPC Class Codes: B23K 11/25 Monitoring devices
• CPC Class Codes: G01N 25/72 Investigating presence of flaws

Abstract

Control of spot weld quality is effected by observing the progress of heat generation within the weld and initiating automatic corrective action if the heating rate is initially too high or too low. A flexible optical fiber bundle has one end located in the welding tip and the other end optically coupled to an infrared detector. Due to the excellent thermal conductivity of the copper material of the welding tip, thermal energy is conducted very rapidly for a short distance into the tip during the weld formation so that the infrared detector produces an output signal proportional to the weld temperature. This signal is sampled and compared with a previously-recorded signal corresponding to the heating rate that produced a good spot weld in the material being welded.

Claims

1. A method of automatically operating a spot welder comprising the steps of:

during each weld measuring the temperature produced within one of a pair of welding tips to produce a thermal signal proportional to the temperature of the weld instant by instant;

sampling said thermal signal and digitally storing a value corresponding to the sampled thermal signal produced for a good weld; and

thereafter, comparing said thermal signal with a signal proportional to the stored digital value to generate a control signal for controlling the welding power of said spot welder during each weld.

2. The method according to claim 1 wherein said step of measuring is performed by optically conducting infrared radiation from a hole in said one of a pair of welding tips to an infrared detector.

3. A control system for a spot welder having a pair of welding tips which are brought into contact with material to be welded, said control system comprising:

a flexible optical fiber bundle, one end of which is positioned in a hole in one of said pair of welding tips, said hole projecting toward a contact face of the one welding tip;

an infrared detector located remotely from said one welding tip, the other end of said flexible optical fiber bundle being positioned to direct radiation emanating from the bottom of said hole in said one welding tip onto said infrared detector, said infrared detector producing a thermal signal proportional to the temperature of a weld being made instant by instant;

means for selectively sampling said thermal signal and digitally storing a value corresponding to the sampled thermal signal; and

means for selectively comparing said thermal signal with a signal proportional to the stored digital value to generate a control signal for controlling the welding power of said spot welder.

4. The control system according to claim 3 further comprising mode selection means for exclusively selecting for operation one or the other of said means for selectively sampling and digitally storing, and said means for selectively comparing.