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Calibration method for camera

Evtimov

#27944

Calibration method for camera | 7 April, 2004

Hello! We created a machine with full vision recognition system and we want to improve our calibration methods for centering the camera. What is not clear is how can we center the camera against the center of the nozel? I know you all use different kind of mashines, so please tell me some of the ways you know for calibrating the camera center. Any idea would be appreciaeted! Thank you in advance! I wait for a lot of answers.

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#27949

Calibration method for camera | 7 April, 2004

Your machine will have to have a reference position. From this reference position, you determine all other machine positions. If the camera is attached to the head, you could place a glass slug and measure camera-nozzle offset, by placing the slug with the head nozzle and measure the X and Y distance with the camera. You can also lower the nozzle in silly putty and leave an inprint of the nozzle. Move the camera over this inprint and measure the offset with the encoder of the X and Y axis.

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Ken

#27960

Calibration method for camera | 7 April, 2004

My favorite kind of calibration is where the machine learns what it did incorrectly. Then fixes itself!

However, there are many types of machines that rely on human feedback as to the results of what it did.

nozzle calibrations involve many factors. are you using CCD or line-scan camera's? Are the image chips analog or digital? This will determine how complex your system will become....

1. vision height vs. mounting height. If the vision height is different than the mounting height, your camera must be perpendicular to the nozzle (z-axis). If not, then an x-y deviation will result during mounting. However, a correction table could be used to eliminate the camera alignment OR even simpler is to have the vision height EQUAL to the mount height. By putting both operations in the same z-axis position, you eliminate the x-y shift as a function of z-height.

2. upwared looking camera position is adjusted or "bore-sighted" as a function of mounting a precision glass slug. The error of the mounted slug is used to determine the offset postion. This part is mounted at 4 major rotation angles to determine tool run-out (eliptical tool path). Eliptical tool path x-y deviations can be eliminated by always visioning the part AT the final mounting angle. This may be time consuming or not possible if this is a multi-head system using a line-scan architechure.

There are many techniques for sighting a camera. Some are more accurate than others. What is your target accuracy / repeatability?

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Evtimov

#27966

Calibration method for camera | 8 April, 2004

The camera is in the head. Sorry forgot to tell you.Stefan now I do the calibration with inprint in a putty. Ken I am looking for accuracy when I calibrate the camera. Tell me more about that slug. What is it like? Where to place it? How to use it?

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Ken

#27978

Calibration method for camera | 8 April, 2004

Well, the precision glass is for upward looking camera's. It essentially is a "perfect part". Vapor deposition lithography on glass (for Cte stability)....basically the part pattern (or part fids) is compared to its target location (same pattern on glass plate). Then you make a judgement on its (machine) performance, generate correction (offsets) and retest until acceptable limits are achieved.

In your case you need to find the center of a moving camera. There are techniques that compare a fiducail position in 3 quadrants to x-y positional movements on the encoders and then determine the camera's center (and angle) in the x-y axis plane.

There are kits available for machine calibration.

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