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LMI: Measuring Circular Edges with Smart 3D Technology

Circular parts and features are one of the most common geometric shapes found in manufacturing today. The ability to accurately and efficiently measure their diameter and roundness deviation have a direct impact on part performance and lifetime. Roundness contributes to function and performance in a variety of ways, not least of which is maintaining a lubricating film between mating components (e.g., between automotive cylinders and pistons).

This is why quality control engineers need to have a robust automated inspection method with standard measurement algorithms that meet the requirements for diameter and roundness inspection.

 Surface Circular Edge Tool

With Surface Circular Edge in Gocator®, the user can easily achieve high-precision measurements on different types of circular features with a single powerful measurement tool––regardless of part orientation, and without the complex component setups and unreliable results that come with using traditional methods (e.g., rotational drum or vee-block).

By scanning the circular object with a laser profiler or snapshot sensor, the built-in Surface Circular Edge tool can then measure the inner and outer edges of a circle. For example, it can measure the inside or outside diameter of tubes or pipes, disk-like features, or the X/Y position of their center points.

How It Works

The Circular Edge tool in Gocator® fits a circle to a circular edge in the scan data, using either height map or intensity data. The edge can be the outer edge of a disc-like feature or the inner edge of a hole. The tool allows engineers to measure the position and radius of circular features and determine roundness error.

In the following sample images, the tool is used to measure the outer edge of a circular feature.

2D view     

3D view

The Surface Circular Edge tool uses one of four standard methods to calculate roundness. The choice of method affects the other measurements.

  • Least Square Circle (LSC)
  • Minimum Zone Circle (MZC)
  • Maximum Inscribed Circle (MIC)
  • Minimum Circumscribed Circle (MCC)

The tool can also generate circle and center point geometric features that Feature tools can take as input for measurement.

This video will explain more.

Calipers, Extracted Paths, and Edge Points

To fit a circle to the scan data, the Surface Circular Edge tool starts by overlaying evenly spaced calipers along a circular path defined by the region of interest.

Rectangular calipers (dark blue) placed along circular path (dark blue), constrained by the region of interest (yellow).

The circular path can optionally be partial, and start at a defined orientation around the Z axis. The circular path can be as short as 1/4 of a circle, letting it work with rounded corners. Calipers extend vertically to fill the entire region of interest.

Internally, the tool extracts profiles from the data within each caliper, running from the end of the caliper closest to the center of the tool’s region of interest to the end farthest from the center. The tool then searches for steps in each profile that meet the criteria set by the tool’s settings, such as minimum height, direction (whether it is rising or falling), and so on. The tool places an edge point on each selected step. It then uses the edge points in all the calipers to fit a circle. Finally, the various characteristics of the fitted circle are returned as measurements.

Measurements, Features, and Settings

Here are three examples of the different types of measurements the Surface Circular Edge tool can generate:

 

  • XY position of the center of the fitted circle, respectively.

 

  • Radius of the fitted circle.

  • Roundness or circularity of the edge points with respect to the reference circle of the selected roundness error method set in Fit Type.

 

Summary

By scanning the circular object with a laser profiler or snapshot sensor, the built-in Surface Circular Edge tool can measure the inner and outer edges of a circle such as the inside or outside diameter of tubes or pipes, disk-like features, or the X/Y position of their center points.

The Surface Circular Edge tool can also calculate the roundness error of circular features using one of four standard methods depending on the individual inspection requirements, which gives the engineer greater flexibility in the types of parts and features they can measure.

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