Importance of Non-contact Profilometry for Coins

Currency is highly valued in modern society because it is traded for goods and services. Coin and paper bill currency circulates around the hands of many people. Constant transfer of physical currency creates surface deformation. Nanovea’s 3D Profilometer scans the topography of coins minted in different years to investigate surface differences.

Coin features are easily recognizable to the general public since they are common objects. A penny is ideal for introducing the strength of Nanovea’s Advanced Surface Analysis Software: Mountains 3D. Surface data collected with our 3D Profilometer allows for high level analyses on complex geometry with surface subtraction and 2D contour extraction. Surface subtraction with a controlled mask, stamp, or mold compares the quality of manufacturing processes while contour extraction identifies tolerances with dimensional analysis. Nanovea’s 3D Profilometer and Mountains 3D software investigates the submicron topography of seemingly simple objects, like pennies.

Measurement Objective

The full upper surface of five pennies were scanned using Nanovea’s High-Speed Line Sensor. The inner and outer radius of each penny was measured using Mountains Advanced Analysis Software. An extraction from each penny surface at an area of interest with direct surface subtraction quantified surface deformation.

 

Results and Discussion

3D Surface

The Nanovea HS2000 profilometer took only 24 seconds to scan 4 million points in a 20mm x 20mm area with a 10um x 10um step size to acquire the surface of a penny. Below is a height map and 3D visualization of the scan. The 3D view shows the High-Speed sensor’s ability to pick up small details unperceivable to the eye. Many small scratches are visible across the surface of the penny. Texture and roughness of the coin seen in the 3D view are investigated.

 

The contours of the penny were extracted and dimensional analysis obtained inner and outer diameters of the edge feature. The outer radius averaged 9.500 mm ± 0.024 while the inner radius averaged 8.960 mm ± 0.032. Additional dimensional analyses Mountains 3D can do on 2D and 3D data sources are distance measurements, step height, planarity, and angle calculations.

Figure 5 shows the area of interest for the surface subtraction analysis. The 2007 penny was used as the reference surface for the four older pennies. Surface subtraction from the 2007 penny surface shows differences between pennies with holes/peaks. Total surface volume difference is obtained from adding volumes of the holes/peaks. The RMS error refers to how closely penny surfaces agree with each other.


 

Conclusion

Nanovea’s High-Speed HS2000L scanned five pennies minted in different years. Mountains 3D software compared surfaces of each coin using contour extraction, dimensional analysis, and surface subtraction. The analysis clearly defines the inner and outer radius between the pennies while directly comparing surface feature differences. With Nanovea’s 3D profilometer’s ability to measure any surfaces with nanometer-level resolution, combined with Mountains 3D analysis capabilities, the possible Research and Quality Control applications are endless.