Part tilt & rotation throwing off pick coords

    Hello All,

    I am using a fanuc robot (LR mate with R-30iB mate) and a Cognex 2d VisionPro system to pick randomly presented parts. The parts are all sitting on a flat plane, however they can be in any rotation. Some of these parts have features that make them not sit flat on the pick plane, therefore making them not perpendicular to the camera. This combined with the random rotation is causing the coords that the vision system sends to the robot to change up to ~5mm when the part is rotated.

    I had an idea to transform the image to just the area around the located part after an initial location (using PMRedline tool), then run that image thru some kind of calibration to get rid of the perspective distortion from the part tilt and get an accurate part location within that image.

    This is all to say, is there a simpler way to solve the problem of parts being tilted in relation to the camera?

    Thanks for any help you all can offer!

  • Lemster68 October 10, 2023 at 6:20 PM

    Approved the thread.

    Well, depending on if your camera is mounted on the robot one good way is to take the coordinates you get. Reposition the camera over the part and repeat the procedure. Once you have done that a couple of times the error will be negligable.

    Another way is to pick a longer focal length and move camera further away, as that will make the distortion from perspective smaller the further away you are. keep in mind that when translating a feature detection to a point in space it will be projected on to your calibration plane.

    Another tip is to not teach the whole contour, pick something that will not be affected as much. And something that is as close to your calibration plane as possible. and if it is not in your calibration plane, recalibrate at an appropriate height or recalculate the given coordinates to the actual coordinates in which the feature you are locating is at. I tend to do this often, especially with short focal lengths/wide fields of view or when product height is varying.

    avoid locating things simultaneously that are skewed or at diffrent heights as that will impact the precision you can and will ultimately achieve.

    Later on once you´ve done all that, you can still compensate by strategy. eg. grip the part several times to center it. drag and push against it to know where it is at. use a distance sensor to find or locate a specific feature to fine tune where exactly to pick the part, (eg a cylindrical part with a hole in it.).

    That for starters. Been awhile since i' ve done anything cognex related but i'm sure there is somekind of perspective transform available. but I do not see an easy way of implementing it and having an easy way to refer back to calibrated real world coordinates in the transformed image so it wouldn't be my first approach.

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