Overcoming the Challenges of Scanning Small Black Objects and Obtaining Highly Accurate Data

June 28, 2021

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A Process Walk-through with the OptimScan 5M

Constant study and further development of 3D scanning best practices in all types of industries are invaluable in order to obtain excellent digital data.

Systematically applying spray powder, effectively pasting reference points, small volume workpiece scanning skills, are important pillars of an efficient 3D scanning workflow. By means of correctly implementing these techniques, a large number of workpieces can be obtained with a high precision degree. This Metrology Monday we will take 3D scanning in the more difficult realm to deal with the high precision requirements of medical device measuring.

How to capture a 55mm black bone nail

Scanning Objecjt: 55mm black bone nail

Some types of objects are basically hard to capture: pieces with black or reflective surfaces or of very small size usually need some extra tools and technical skills to enable successful 3D scanning.

In this session, we will take the scanning of bone nails as an example to review these skills and see together how the OptimScan 5M industrial-grade 3D scanner can overcome these challenges.

Bone nail scanning is a project with high precision requirements. It can help us to simulate and study the effect of metallic implants on medical imaging and on the dosimetry of radiation therapy, as well as to reverse engineer bone nails. For all these types of applications strictly precise data is required.

As a metal implant in medical treatment, bone nails have two effects in radiation therapy.

1) The creation of metallic artefacts in medical images, reducing diagnostic accuracy.

2) The impact on the absorbed dose of drugs in the surrounding tissues.

Therefore, the use of 3D scanning to develop an accurate mathematical model of metallic implants is of great practical importance.

Step 1: Evaluation of the scanned parts

In order to obtain accurate data, it is necessary to first evaluate the objects to be scanned and determine their characteristics in order to prepare the pre-processing process. Through observation, the following characteristics of the bone nail can be observed.

Black surface material with reflective effect

The black and reflective surface material dictates that the bone nail needs to be powder coated prior to scanning.

Small size, only 55 mm in length
Small size, only 55 mm in length

The small size makes it impossible to use reference points for automated stitching, so the data needs to be manually stitched and merged by applying reference points to the underlay and using a transition stitch.

In the pre-processing part, spray powder and reference points need to be applied. In the data processing part, the data needs to be manually spliced and merged.

Step 2: Pre-processing

Powder coating.

Before spraying powder, shake the spray bottle to fully dissolve the developer powder; at the same time, avoid direct contact with the workpiece during the spraying process.

During the powder spraying process, it is necessary to keep a distance of about 15-20 cm from the sprayed workpiece and spray back and forth at a uniform speed.

Pasting reference points.

If the size of the workpiece is too small to apply reference points, in order to complete the scan stitching, you need to use the underlay to paste the points. When doing so, please keep in mind the following:

1) Paste the points on the turntable or fixture, choose the original reference points for your 3D scanner and paste them on the plane or curved surface, pay attention to apply randomly and not uniform. When pasting to avoid being too regular. Keep the reference points intact and clean.

2) Fix the workpiece on the turntable or fixture. No relative displacement should occur during the rotation and scanning process, otherwise, the data accuracy will be affected.

OptimScan 5M Plus
The pre-processed bone nail being scanned

Step 3: Manual splicing and merging of data

scan data
 Splicing and merging data

Depending on the complexity of the workpiece, two or more scans need to be performed to obtain several scans of the data.

Afterwards, the data can be manually stitched together with the corresponding points on the scanned data and merged into a whole after the data has been formed into a group.

Splicing and merging data
Splicing and merging data

You can obtain high accuracy data with OptimScan 5M if you evaluate the parts you want to scan correctly, conduct appropriate pre-processing according to the actual condition of the sample, and adjust the scanned data with certain proficiency.

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