Weld bead quality determining apparatus

• US 5,533,146 A
• Filed: 11/14/1994
• Issued: 07/02/1996
• Est. Priority Date: 09/11/1991
• Status: Expired due to Term

• Current Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: Iwai, Takao
• Primary Examiner(s): Couso, Jose L.
• Assistant Examiner(s): Do, Anh Hong
• Application Number:
  US08/341,040
• Time in Patent Office: 596 Days
• Field of Search: 382/1, 382/8, 382/100, 382/141, 382/150, 382/152, 219/130.01, 219/124.34, 219/121.63, 348/90, 348/719, 364/500
• US Class Current: 382/150
• CPC Class Codes: B23K 9/0956 using sensing means, e.g. optical

Abstract

An apparatus for determining quality of a weld bead of an welded assembly of different metal sheets, wherein a slit beam of light is obliquely thrown on the weld bead to make an illuminated band on an upper surface of the welded assembly. A CCD camera disposed above the welded bead photographs the illuminated band to make an image of the illuminated band. The image is treated in an image pretreatment device so that a surface of a transverse cross section of the weld bead can be expressed in the form of one-dimensional data. Characteristics of the cross section of the weld bead are extracted from the one-dimensional data and are compared with predetermined references in a personal computer so that it is determined whether the weld bead is acceptable. Since the speed of data treatment is high, an on-line and real-time determination of the quality of the weld bead is possible.

Claims

1. An apparatus for determining a quality of a weld bead, comprising:

a slit beam emitter for producing a slit beam of light and projecting the slit beam of light obliquely and downwardly on a weld bead joining metal sheets with a width direction of the slit beam of light perpendicular to a longitudinal direction of the weld bead so that the slit beam of light makes an illuminated band on an upper surface of a welded assembly of the metal sheets, a portion of the illuminated band crossing the weld bead being distorted from an extension of the remaining portion of the illuminated band corresponding to a configuration of an upper surface of the weld bead;

a CCD camera, disposed above the illuminated band and moved along the weld bead, for photographing the illuminated band and making a photograph plane, which includes an image of the illuminated band, for each position as the CCD camera is moved along the weld bead, the image of the illuminated band being brighter than a remaining portion of the photograph plane and having a brightest level at a width center of the image in a width direction of the image;

an image pretreatment device, connected to the CCD camera, for scanning each photograph plane along a scanning line which extends substantially perpendicularly to a longitudinal direction of the image and is moved in the longitudinal direction of the image, the image pretreatment device generating an analog signal corresponding to the image of the illuminated band, detecting, along the scanning line, opposite edges of the image of the illuminated band having a brightness level that is greater than a selected reference brightness level, the reference brightness level being selected from a predetermined number of different reference brightness levels by adopting a greatest one of the predetermined number of different reference brightness levels for which edges are detected as the selected reference brightness level, determining a width center of the image as a center of the width of the detected opposite edges of the image along the scanning line, and then converting at least a portion of a signal that corresponds to only the width center of the image into a digital signal for each position of the scanning line as it is moved in the longitudinal direction of the image at predetermined intervals;

a computer, connected to the image pretreatment device and including a memory and a RAM disk, for temporarily storing the digital signal produced by the image pretreatment device, wherein;

the digital signal is stored in the memory for each position of the scanning line as it is moved in the longitudinal direction of the image at predetermined intervals,

after scanning all of the positions of the scanning line, storing in the RAM disk one-dimensional data that corresponds to a center line of the image for each photograph plane,

the center line is based upon the width centers,

the computer reads all the data stored in the RAM disk after welding along a weld line between the metal sheets has been completed, determines characteristics of the image for each photograph plane, compares the characteristics of the image of each photograph plane with respective predetermined limits for an acceptable weld bead so as to determine whether the weld bead is acceptable;

an inspection controller, connected to the computer, for starting and stopping operation of the computer; and

a welding machine controller, connected to the inspection controller, for starting and stopping operation of a welding machine and a conveyor carrying said metal sheets, so that an unacceptable weld bead will not be conveyed to a subsequent manufacturing step.

2. An apparatus according to claim 1, wherein the slit beam emitter includes a semiconductor laser for emitting a laser beam, and a collimator lens and a cylindrical lens for collecting the laser beam emitted from the semiconductor laser into the slit beam.

3. An apparatus according to claim 1, wherein the image pretreatment device includes a display for displaying the photograph plane in which the image of the illuminated band extends in a vertical direction and the scanning line extends in a horizontal direction.

4. An apparatus according to claim 1, wherein the computer is a personal computer.

5. An apparatus according to claim 1, wherein the computer includes a RAM disk including a semiconductor memory.

6. An apparatus according to claim 1, wherein the predetermined number of reference brightness levels includes four different brightness levels.

7. An apparatus according to claim 1, wherein the computer further includes means for removing a noise from the center line of the image.

8. An apparatus according to claim 1, wherein the predetermined limits for an acceptable weld bead include limits for weld bead projection, weld bead shrinkage, weld bead width, weld bead undercutting, dislocation at the weld bead between the metal sheets, and discontinuity at the weld bead.

9. An apparatus according to claim 1, wherein the computer includes means for determining in real-time or without a time delay, whether the weld bead includes a defect exceeding a predetermined limit and means for issuing an instruction to stop welding if it detects a defect exceeding the limit in the weld bead.

10. An apparatus according to claim 1, wherein the weld bead is a laser-weld bead joining different metal sheets for one-piece stamping for an automobile panel.

11. An apparatus according to claim 1, wherein said digital signal corresponding to the width center of the image for each position of the scanning line is retained in said RAM disk until welding is completed, after which digital signals for each photograph plane are analyzed by said computer to determine the quality of the weld bead.

12. An apparatus according to claim 1, wherein said computer includes a memory for temporarily storing said digital signals fed from said image pretreatment device until scanning is completed for said photograph plane, after which said signals representing one photograph plane are stored in said RAM disk.