In metrology, precision and accuracy are paramount for ensuring quality in manufacturing processes. Leveraging advanced technologies such as 3D scanners and Coordinate Measuring Machines (CMMs) in industries like Automotive and Aeronautics achieve precise measurements essential for quality control.

It is significant to evaluate the performance of an industrial 3D scanner when quality and precision are crucial. In this context, ISO 10360-08 provides a rigorous framework for testing and validating the quality of 3D scanners using the terms P Form test and P Size test. However, an incomplete or erroneous understanding of this standard can lead to suboptimal choices of 3D scanning technologies, negatively affecting the quality control of produced parts. To shed better light on the subject, we will delve into two aspects that are often a source of confusion: the P Form and P Size tests, as well as the interpretation of test results expressed in terms of 1 sigma (±1σ) or 2 sigma (±2σ.)

Assessing 3D scanner accuracy. Kreon Skyline Eyes 3D scanner

What is the difference between P Size and P Form tests?

The confusion between these two types of tests can lead to an inadequate assessment of the performance of a 3D scanner.

P Form: This test determines the distribution of points on a scanned surface.

It can be used to assess measurement noise. Carried out on a calibrated sphere, it draws an envelope round the sphere (like a shell) covering 95% of scanned points (2 σ). For the test result, the thickness of the shell is divided by two as it is expressed at ±2 σ. The closer the value to zero, the less noisy the point cloud.

Explanation of Pform test

P Size: This test determines the scanning error when measuring a dimension.

Carried out on a reference sphere, it gives the difference between the diameter measured by the scanner (deduced by the least squares method from 95% of scanned points) and the actual diameter of the scanned sphere. The closer the result is to 0, the more accurate the scanner is when measuring the size of geometric shapes.

Explanation of Psize test

4 possible cases of accuracy and precision

4 illustrations of possible cases of accuracy and precision

Learn more about ISO 10360-08 standard.

In the field of metrology, ISO 10360-08 tests are used to analyse and evaluate a 3D measurement system, both its accuracy (through P Size test) and its precision (through the consistency of P Form and P Size tests). A precisely calibrated sphere (or plane) is essential for rigorous testing.

These parameters help ensure that measurements meet the required quality standards and provide reliable data for various industrial applications, including quality control, inspection, and reverse engineering.

What is 2 sigma? Is it the same as ±2 sigma?

Standard deviation is a statistical metric that quantifies the amount of variability or dispersion of a set of values. Specifically, it measures how much individual points deviate on average from the mean (average) measurement value.

Within the metrology industry, σ (sigma) is utilized to assess the consistency and reliability of measurements obtained from the high-tech 3D scanners. It helps to understand the precision of these scanning tools.

Manipulation of the precision of a 3D scanner with reference based on the P Form test

Sometimes, manufacturers are tempted to manipulate tests to promote their products. A notable example concerns the specification of the form deviation (P Form). A notable example of this is seen in the specification of form deviation (P Form) for scanner measurements. Consider two scanners, one with a form error of 15 µm and another with 18 µm.

At initial inspection, the first scanner might appear superior. However, its form error is calculated using 1 sigma (σ), capturing only 68% of the most accurate points, in contrast to the second scanner which uses 2 sigma (σ), encompassing 95% of data points (refer to the figure below). Consequently, the second scanner will probably outperform the first. Although a keen observer might recognize this tactic, specialized tests designed by manufacturers can often make it exceedingly challenging to fairly compare products.

More productivity thanks to 3D scanning with CMM

Coordinate measuring machines (CMMs) are advanced tools that automatically measure objects accurately in three-dimensional space using sensors and software. These machines can be programmed to measure specific points or scan entire surfaces, creating digital models of objects. However, CMMs used with probes are limited for acquiring details and complex geometries and are not very fast. Therefore, a professional 3D scanner integrated with a CMM is an excellent solution for digitizing small details and a fast-acquiring metrology tool accelerating measurement processes on CMM.

Explanation of Sigma

Scanning system accuracy, what can be expected?

comparison table

With the help of the table, we can see, that the measurements taken from a 3D scanner while integrated with the CMM are more precise (14 µm) as compared with a scanner mounted on a measuring arm.

Calibration of the 3D scanners

Over a while, the accuracy and measuring result of advanced 3D scanners can be affected by long use. Recalibration means checking and adjusting your scanner so you can be sure it continues to meet the specifications guaranteed by Kreon.

Discover in 7 points why recalibration of a 3D scanner is so important.

Kreon 3D Scanners

Metrology grade 3D scanners are a valuable addition to CMMs to meet production and return on investment requirements, gain control time and maximize the potential of CMM machines. 

Use in Industrial Applications 

The Kreon Zephyr III 3D scanners offer enhanced versatility and cost-effectiveness by seamlessly transitioning between applications on both a Coordinate Measuring Machine (CMM) and a Kreon measuring arm. These scanners boast exceptional scanning capabilities, providing a significant advantage for diverse purposes such as inspection, First Article Inspection (FAI), reverse engineering, rapid prototyping, and other ambitious goals. 

 

The accuracy with the Kreon Zephyr III scanner range

Their outstanding measurement accuracy, reaching up to 5 µm (±2σ) with the Zephyr III 50, is crucial in delivering expected outcomes. Engineered for scanning the tiniest details, the Zephyr III 50 also boasts a fine resolution of 15 µm. 

 

Meeting growing productivity needs with the Zephyr III range

Available with 300 mm, 150 mm or 50 mm laser lines, the Zephyr III 3D scanners are high-end products which can easily scan the most complex parts in record time. As a versatile product, it is fully automated on CMM covering all needs for 3D measurements from auto-calibrating the position of the scanner to using a probe directly under the scanner.

Zephyr III 300 3D scanner

Kreon ISO certification

Kreon certifies its products to ensure complete confidence in your 3D measurements. The Kreon scanners are calibrated and certified by ISO 10360-08 standards. True to their specifications, Kreon scanners seamlessly integrate into a rigorous quality approach. Kreon offers warranty and maintenance plans to ensure the long-term reliability of the product’s specifications.

ISO logo in red

In summary, understanding ISO standards correctly and grasping parameters like P Size and P Form are essential to achieving manufacturing precision. Quality products are a direct result of a strong commitment to adhering to norms.

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