This article will cover how the accuracy tests of the Calibry Mini were conducted.
The Calibry Mini by Thor3D is stated to feature an accuracy of up to 0.07 mm (0.0027 inch). What exactly does this mean? This means that under the normal conditions, the deviation in measurements of any single point can be 70 microns in any direction. This doesn’t mean that the deviation will always be 70 microns. It can be smaller, it can be bigger. The number is approximate and can vary depending on several factors that will be mentioned in the article.
How was it calculated? What tests were conducted?
The first thing to do was to order a certified reference material (two spheres made from aluminum oxide that are placed on the bar and located 70 mm away from each other). These spheres were measured using a certified metrological equipment with the 6 microns of guaranteed accuracy.
What’s next?
The certified reference material was scanned with the Calibry Mini at the room temperature of 20 °C. The scanner was calibrated right before the procedure. It was located at a 90 ° angle to the object during the process. The windows were curtained to avoid bright illumination..
The geometry tracking mode in Calibry Nest (versions 3.3.41 and 3.4.141) were used to get the model in standard STL file formats. The scans were done with the resolutions of 0.15, 0.2 and 0.3 mm. Each data set was exported to Geomagic Design X software (v 2020.0.4) afterwards. The program detected two spheres and found out their centers. Then it calculated the distance between the centers.
The results:
Calibry Nest Version | Scan number | Resolution: 0.15 mm | Deviation at 0.15 mm | Resolution 0.2 mm | Deviation at 0.2 mm | Resolution 0.3 mm | Deviation at 0.3 mm |
3.3.41 | 1 | 70.0080 | 0.0280 | 70.0036 | 0.0236 | 69.9892 | 0.0092 |
2 | 69.9431 | 0.0369 | 69.9531 | 0.0269 | 69.9411 | 0.0389 | |
3 | 70.0181 | 0.0381 | 70.0167 | 0.0367 | 70.0212 | 0.0416 | |
3.4.141 | 1 | 69.9949 | 0.0149 | 69.9992 | 0.0192 | 69.9983 | 0.0183 |
2 | 69.9676 | 0.0124 | 69.9442 | 0.0358 | 69.9750 | 0.0050 | |
3 | 69.9899 | 0.0099 | 69.9714 | 0.0086 | 69.9691 | 0.0109 |
The average deviation of those 18 scans was 0.02305 mm (23 microns). The source data can be downloaded here (150MB).
The test conditions were changed later to find out how one or several factors would affect the accuracy. For example, an uncalibrated device was used to scan the reference material. The deviation was 192 microns (or 0.1926 mm). Getting the room temperature colder or scanning under direct bright sunlight were also conducted. The factors affected the results negatively.
Below are the recommendations for getting accurate scans.
Calibrate the scanner before the scanning process using the board that is included in the device's packaging.
Regulate the room temperature to 20 °C and close the curtains to avoid bright light and overexposure.
Scan the objects at a 90 ° angle.
Keep the distance between yourself and an object. The built-in screen will show real-time data and indicate when you’re in the ‘green zone’.
Get enough data. For example, during the tests there were around 800-1000 frames per scanning session.
In the geometry scanning mode, use the pieces of crumpled paper and place them around an object to provide additional geometry that will help during post-processing.
Why is the stated accuracy 0.07 mm?
Yes, the scanner can consistently provide a better accuracy than stated in the documentation. But a user cannot always meet all of the recommendations. Dozens of tests were conducted before the announcement of the Calibry Mini in 2020. Some were done under the perfect conditions, while the others were deliberately conducted under the worse ones. The list number is the average one, since the manufacturer knows that the consumers can not always use the scanner in a perfectly lit room or calibrate the device before every scanning session or keep the room temperature at a certain degree.
Conclusion
Certified metrological equipment warrants certain accuracy for each use if you follow the manufacturer recommendations perfectly. Such scanners are usually very expensive and are not easy to use. The Calibry Mini by Thor3D isn’t a certified metrological equipment but it can provide consistently accurate results for less money if you follow advice and recommendations listed above.
