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You are reading the documentation for an older Pickit release (3.2). Documentation for the latest release (3.4) can be found here.

Detection accuracy

The detection accuracy is impacted by both repeatability and trueness errors.

Detection trueness errors manifest as detected objects with completely wrong location, the so called false detections. For instructions on how to get rid of false detections refer to this article.

The reminder of this article addresses the second type of detection errors, namely the detection repeatability errors.

What is detection repeatability?

Due to measurement noise of the camera, detecting twice the same object does not lead to the exact same pick pose. Detection repeatability measures the variability of the object position across multiple detections. More precisely, we define the detection repeatability as the range of variation (in mm) of the detection pose of a fixed object. We typically check the average and maximum variation of the detected pick pose.

Detection repeatability gives a lower bound on the expected picking accuracy.

Note

The detection repeatability is application specific. It varies depending on the detected object, the camera and its distance, and detection settings (product file). Therefore, it is important to measure the repeatability in conditions as close as possible to your actual application.

Verifying the detection repeatability

To measure the detection repeatability of a given application, the simplest is to detect a fixed part multiple times and collect the detection poses. To ease the repeatability calculation, Pickit provides a spreadsheet that can easily be duplicated.

You can proceed as follows:

1. Use the detection repeatability calculation spreadsheet of the format of your choice

1. Google spreadsheet by clicking Use template.

2. Microsoft Excel spreadsheet by downloading the sheet.

2. Set up a repeatitive detection that always detects the same pick point of the same object (see tip below).

3. Detect the part and copy the object position (from the Objects table) in your detection repeatability calculation spreadsheet.

4. Repeat step 3 until the spreadsheet is filled.

5. The spreadsheet will show the average and maximum repeatability error.

Tip

A repeatitive detection should always detect the same pick point of the same object as first result in the Objects table. To get a repeatitive detection it is recommended to adapt the product file as follows:

1. Set an object higher than the others and use highest object ordering strategy.

2. Enable only one pick point.

3. For symmetrical objects, make sure that the pick point is exactly in the center of symmetry.

4. If a symmetry axis is explicitly specified, remove it.

5. Disable any tool flexibility.

Correcting the detection repeatability

To improve the repeatability of the detection, make sure to optimize your detection settings (product file). To do so, follow the general recommendations from the pages on avoiding false detections and increasing good detections.