3D Metrology vs. Machine Vision: Understanding the Differences

When researching a dimensional quality control solution, it is important to understand the difference between 3D scanners and machine vision systems. While both types of equipment are used in quality control, they are used to achieve different results.

3D Metrology

3D Metrology (or measurement) is the science of measurement in three dimensions (x, y, z). 3D measurement is often used in quality inspection – for example:

1. Manual measurement. Skilled human operators use calipers and gauges to take the required measurements of a manufactured part at specific points on its surface.
2. CMM (coordinate measuring machine). Like an automated caliper, a CMM uses touch-probe sensors to measure the required surface area of an object.
3. 3D scanners. Using light (such as lasers) rather than contact, the complete surface of an object is scanned in seconds at one time to obtain a dense “point cloud” of the object’s surface area.

Machine Vision

An example of machine-vision in action.

Machine Vision is a broad term describing a process that applies a variety of technologies – including  imaging – to a wide range of tasks. Some of those tasks may include measurement, but many do not.

For example, a machine vision system may be used to inspect manufactured products for defects such as surface blemishes or improperly applied caps or labels. They may be used to compare package sizes, sort packages, read barcodes, guide robots, and so on. These systems are typically custom-designed, or configured to perform a very specific set of inspection tasks.

Traditionally, machine vision systems are used to acquire and analyze two-dimensional (2D) images of manufactured products.

3D Scanners

By using methods such as triangulation and light pattern projection, machine vision can be used to create a 3D digital representation of a physical object. If the 3D representation is dimensionally accurate, it can be called a metrology-class 3D scanner, such as a ShapeGrabber 3D scanner. Metrology-class 3D scanning is particularly effective for quality inspection of parts that have complex shapes, compound curves and multiple features.

Example of 3D Scanning & Machine Vision Together

To fully understand the unique strengths of 3D measurement and machine vision, we’ll use the example of a product comprising two different plastic parts that are joined together.

A machine vision system could be placed beside or over top of the production line, capturing 2D images of the parts as moved along a conveyor belt. The system could be custom-designed to identify if any of the products had a faulty joint, and may be programmed to send instructions to other robots or human operators to remove the part or, in severe cases, to stop the line.

The ShapeGrabber Ai310 Automated 3D Scanner

A 3D scanner would be used offline to determine the cause of a recurring problem such as a faulty joint. The surface area of problem parts would be quickly scanned, brought into specialized software such as Polyworks Inspector or Geomagic Qualify, then compared to the part’s CAD model (or the scan of a known good part) to isolate the fit problem and investigate the cause (e.g. mold wear, warpage, twist, etc.).