Identify object on a conveyor belt

asked 2018-10-26 01:02:17 -0500

Hatmpatn gravatar image

updated 2018-10-26 16:39:51 -0500

Hello! I'm thinking of trying out openCV for my robot.

I want the program to be able to identify the metal parts on a conveyor belt that are single ones, and not the ones lying in clusters.

I will buy a raspberry pie with the raspberry pie camera module(is this a good idea for this project?).

I want the program to return the X-Y coordinate(or position of the pixel on the image) on a specific place on the metal part(so that the robot can lift it where it is supposed to be lifted). I would also want the program to have a adjustable degree of freedom of the orientation(rotation) of the single metal part to be localized.

Where do I even start?

A simple drawing of the robot

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An image of what the images could look like the program will process(have not bought the final camera yet and lighting).

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Here is the metal part I want to pick up from the conveyor belt.

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Comments

Binarize the image with color or greyscale thresholding and then do a cv::findContours(). Loop through contours filtering by contour size. For those contours within the accepted size bounds, compare moments, either Hu or Flusser, to the canonical item, maybe using Mahalnobis distance for a conscious false negative rate.

Der Luftmensch gravatar imageDer Luftmensch ( 2018-10-26 18:45:12 -0500 )edit

Thank you! I will start with your advice! Will I need to put a glare filter on the camera lens? Is raspberry pi camera module a good choice?

Hatmpatn gravatar imageHatmpatn ( 2018-10-29 07:05:23 -0500 )edit

Try to make your lighting more diffuse, there will be much less glare if there is ambient light and not a point light source. A single color highly saturated background would likely help as well, in which case you could try HSV thresholding.

Der Luftmensch gravatar imageDer Luftmensch ( 2018-11-13 12:02:17 -0500 )edit

I'm getting really close now!

I've changed the background to a bright orange.

My code is as follows:

-Take an image -Convert image from BGR to HSV -Threshold the image to filter out the orange -FindContours -Filter out the contours that doesnt match my wanted area. -Process the Moments and HuMoments of the contours that are left -Calculate the centroid from the Moments -Draw the contours and centroid in the original image

In the image I have 2 objects that are with their faces down and 2 object are face up. I only want the program to recognize the 2 object faced upwards. Im trying to print the Moments and HuMoments Array but dont know how to filter out values so that the face-down ones will be filtered out?

Hatmpatn gravatar imageHatmpatn ( 2018-11-27 09:04:12 -0500 )edit

area_min=3000 area_max=4000

for i in range(len(contours)):
    cnt=contours[i]
    area=cv2.contourArea(cnt)
    centres=[]
    if (area > area_min) and (area < area_max):
            moments=cv2.moments(contours[i])
            hu=cv2.HuMoments(moments)
            centres.append((int(moments['m10']/moments['m00']),int(moments['m01']/moments['m00'])))
            cv2.circle(image, centres[-1],3,(0,0,255),-1)
            cv2.drawContours(image, contours, i, (0,255,0), 2)

            #print(centres)
            print(moments)
Hatmpatn gravatar imageHatmpatn ( 2018-11-27 09:05:25 -0500 )edit

Resulting image: link text

The returned moments values are too long to attach. And also the HuMoments values.

Hatmpatn gravatar imageHatmpatn ( 2018-11-27 09:08:24 -0500 )edit

The sign of the final Hu moment can discriminate mirror images of contours (face-down vs. face-up in your case). Also, have a look at cv::Mahalanobis()for obtaining a probability (0-1) that a contour belongs to canonical class.

Der Luftmensch gravatar imageDer Luftmensch ( 2018-11-27 10:26:23 -0500 )edit

Thanks for the answers Der Luftmensch. I solved it by using the 7th argument of HuMoments which shows a - sign for the mirror images. Now I just want to move the centroids so that they are on typ of the big flat part where they will be picked up by the robot.

Hatmpatn gravatar imageHatmpatn ( 2018-11-27 13:45:58 -0500 )edit