Object profile measuring method and apparatus

• US 5,739,912 A
• Filed: 12/20/1996
• Issued: 04/14/1998
• Est. Priority Date: 04/26/1991
• Status: Expired due to Fees

• Current Assignee: Nippon Telegraph and Telephone Corporation
• Original Assignee: Nippon Telegraph and Telephone Corporation
• Inventors: Ishii, Akira
• Primary Examiner(s): Pham, Hoa Q.
• Application Number:
  US08/770,800
• Time in Patent Office: 480 Days
• Field of Search: 356/376, 356/375, 356/1, 356/2, 356/4, 356/5, 356/445, 250/214 AL, 250/214 B, 250/214 C, 219/124.1, 219/124.34, 219/130.01, 219/130.51, 358/36, 358/37, 358/166, 358/167
• US Class Current: 356/602
• CPC Class Codes: G01B 11/24 for measuring contours or curvatures

Abstract

A method and apparatus for object profiling is disclosed wherein a laser beam generated by a laser diode 102 is directed to the object surface 101, the apparatus scans the surface 101 and receives the illuminated point image by a charge storage type one-dimensional array of light receiving elements 107; the array 107 is scanned every predetermined period so as to sense a position of the illuminated point image; the object surface coordinates are then obtained by the principle of triangulation, and thereby profile of the object surface 101 can be measured. The laser beam generated by laser diode 102 is intermittent such that the beam is turned on/off at intervals of a predetermined time, preferably ranging from 10 ns to 100 ns. The received signal during unilluminated (turned-off) period delays one period via the FIFO 119-3, while that during the illuminated (turned-on) period is supplied to the subtraction unit 119-6 without delay. The subtraction unit 119-6 subtracts the signal of the unilluminated period from that of the illuminated period. The external interference light due to arc light of a welding torch, etc., ordinarily having a fluctuation frequency of much lower than 100 kHz, irradiates the array 107 at an almost equal intensity in both of the illuminated and unilluminated periods, so that the interference components can be eliminated by subtraction.

Claims

1. A method for measuring an external profile of an object in robotic arc-welding, said method being based on triangulation operations and capable of performing a measurement under existence of arc light with fluctuating intensity at relatively low frequency, said method for measuring an external profile comprising the steps of:

intermittently emitting a laser beam onto a surface of said object at a sufficiently shorter time interval than a fluctuation period of intensity of the arc-light;

repeatedly sensing reflected light from said surface during a predetermined sensing period in synchronism with emission of the laser beam, by means of a plurality of charge storage type light receiving elements arrayed in line;

generating output signals responsive to said reflected laser beam and to the arc light;

generating delayed signals, for said output signals, delayed by one line period of the charge storage type light receiving array;

obtaining difference values between said output signals and said delayed signals so that said difference values are indicative of the difference between output signals while said laser beam is on and while said laser beam is off to enable elimination of influence of said arc light; and

determining positions of points on said surface based on said difference values.

2. A method for measuring an external profile of an object according to claim 1, wherein said predetermined sensing period is equal to or shorter than 100 microseconds.

3. An apparatus for measuring an external profile of an object in robotic arc welding, said apparatus being based on triangulation operations and capable of performing a measurement under existence of arc light, the intensity of which fluctuates over time at relatively low frequency, said apparatus for measuring an external profile comprising:

a plurality of charge storage type light receiving elements arrayed in line for repeatedly sensing reflected light from a surface of said object during a sensing period of a predetermined interval and generating output signals;

laser means for intermittently emitting a laser beam onto the surface in synchronism with said sensing period in such a way that the surface is illuminated;

delay means for generating delayed output signals of said light receiving elements delayed by said predetermined time interval;

calculating means for obtaining difference values between said output signals of said light receiving elements and said delayed signals, which correspond to difference values between output signals of said light receiving elements while said laser beam is on and output signals of said light receiving elements while said laser beam is off, thereby eliminating influence of said arc light, and for determining positions of points on said surface based on the difference values.

4. An apparatus for measuring an external profile of an object according to claim 3 wherein said sensing period is equal to or shorter than 100 microseconds.

5. An apparatus for measuring an external profile of an object in arc-welding according to claim 3, wherein said charge storage type light receiving element, comprise a CCD line sensor with 1×

N arrayed light receiving elements, wherein N is a natural number.

6. A method for measuring an external profile in robotic arc-welding,

said method being based on triangulation operations and capable of performing a measurement under existence of arc light with fluctuating intensity, said method for measuring an external profile comprising the steps of:

intermittently emitting a laser beam onto a surface of said object at predetermined time intervals and scanning the laser beam on the surface of said object;

repeatedly sensing reflected light from said surface during a predetermined sensing period in synchronism with emission of the laser beam, by means of a plurality of charge storage type light receiving elements arrayed in line;

generating first sensing output signals for a turned-on period of said laser beam, as either first as-sensed output signals or first delayed output signals delayed by said predetermined sensing period;

generating second output signals for a turned-off period of said laser beam, as either second delayed output signals or second as-sensed output signals, respectively, depending on whether the first sensing output signals are first as-sensed output signals or first delayed output signals, respectively, second delayed output signals being delayed by said predetermined sensing period;

obtaining a difference value between each of said first and second as-sensed output signals and the respective concurrent one of said second and first delayed output signals so that said difference values are indicative of a difference between output signals while said laser beam is on and while said laser beam is off to enable elimination of influence of said arc light; and

determining positions points on said surface based on said difference values;

wherein said predetermined sensing period is determined to be shorter than a fluctuation period of said intensity of said arc light, and

wherein the method further includes the step of repetitively adding current difference values to enable suppression of fluctuation of the difference values.

7. An apparatus for measuring an external profile of an object in arc welding, said apparatus being based on triangulation operations and capable of performing a measurement under existence of arc light, the intensity of which fluctuates over time, said apparatus for measuring an external profile comprising:

a plurality of charge storage type light receiving elements arrayed in line for repeatedly sensing reflected light from a surface of said object with a predetermined sensing period;

laser means for intermittently emitting a laser beam onto said surface in synchronism with the sensing of the reflected light in such a way that said surface is illuminated;

scanning means for scanning said laser beam on the surface of the object;

output means for generating first output signals for a turned-on period, said first output signals being either as-sensed output signals or delayed output signals delayed by said turned-on period;

output means for generating second output signals as either delayed output signals delayed by said predetermined period or as-sensed output signals, respectively, depending on whether the first output signals are as-sensed or delayed, said second output signals being for said turned-off period of the laser beam;

calculating means for obtaining difference values between each pair of respective concurrent ones of said first and second output signals of said light receiving elements, which correspond to difference values between output signals of said light receiving elements while said laser beam is on and output signals of said light receiving elements while said laser beam is off, thereby eliminating influence of said arc light, and for determining positions of points on said surface based on said difference values;

wherein said predetermined sensing period is determined to be shorter than a fluctuation period of said intensity of said arc light, and

wherein said calculating means further includes a means for repetitively adding a current difference value to the aforesaid obtained difference values and averaging the difference values to enable suppression of fluctuation of the difference values.