Inline Metrology with Smart 3D Sensors Achieves 100% Quality

According to smart 3D sensor manufacturer LMI Technologies the challenge for manufacturing is how to bring metrology-grade accuracy and precision to high-speed inline processes in order to achieve 100% quality control.

Today quality control processes fall into two distinct environments:

  1. Metrology laboratories where first article parts are digitized offline typically using contact-based solutions
  2. Parts are inspected in fast-moving inline processes using non-contact optical methods.

Both of the above solutions have their own approaches to ensuring quality.

The laboratory environment is clean, controlled and slow-paced. Time is not so critical and the emphasis instead placed on measurement precision and accuracy.

Tactile Based: The metrology world relies on tactile-based solutions. CMM machines using touch probes are
programmed to digitize target parts. Tool changers are often used to exchange one probe styli for another specialized for the type of geometry that is being probed. The touch probe determines the overall resolution and point density that can be achieved to build a 3D model. CMMs, while highly accurate, are slow to setup, program and measure. Regular calibration is required to ensure 3D points are accurately translated from a coordinate measuring machine to real-world coordinates. Calibration is a necessary process to ensure the CMM can reliably deliver 3D data.

The factory environment is anything but clean, quiet and slow. There are multiple inspection cells or stations, transport systems such as conveyor belts, fast-moving parts and robots—all working together dynamically.

3D Optical Sensors: Speed is the major differentiation between metrology and inline inspection environments. In the factory, conveyors and robot motion are all optimized to maximize production output. Scan acquisition times are often measured in microseconds with measurement cycle times in milliseconds. Inline inspection requires non-contact scanning of the target. The most common solutions for digitization are laser triangulation and structured light 3D sensors. Lasers are typically used for inspecting moving parts while structured light is used for applications with a ‘static’ target object.

In order for measuring sensors to fit within an automated inspection system, they must be compact and designed for industrial use (i.e., fully sealed and passively cooled to protect against the harsh factory environment). There is no possibility to linearize measuring devices once they are installed in factory machinery which means inspection sensors must be factory pre-calibrated to produce measurements in standard units on power up maintaining high accuracy over many years of operation. Pre-calibration ensures that each sensor meets a traceable metrology verification process to deliver consistent, uniform results.

100% quality control is not the ability to scan the entire surface of a single part; it is the ability to scan every single part on the production line. The best method for achieving this goal is inline inspection—which requires a combination of metrology-grade precision and non-contact, high-speed inspection capabilities.

Inline metrology involves scanning, measurement and control—all done inline while a part is in motion. The part is scanned with non-contact optical methods to produce a highly detailed 3D model offering sufficient resolution to measure critical features.
For moving parts, a laser line profiler generates 3D profiles in the direction of travel to generate a surface of the scan target. This surface information represents the geometry or shape of the part. Shape information is unique to 3D and critical to achieving quality control.
Using built-in measurement tools, users can setup many measurements depending on what critical features are required for inspection—whether it is hole diameter, step height, angle, or relationship between features.
Based on pass/fail criteria, the final step is to communicate measurement outcomes to factory machinery—either to activate rejection or sorting hardware or send part measurement data over the factory network. Built-in factory protocols support direct communication over the factory network with PLCs and robots.

Achieving 100% Quality Control with 3D Smart Sensors

3D smart sensors combine metrology-grade accuracy, precision and repeatability with advanced inspection-level capabilities and design and are easy to use. Features such as web-browser driven point and click environment for rapid configuration, built-in measurement tools and rich I/O for communicating results make it easy for factory technicians to get the results they need. Real-time measurement capabilities minimize lag between data acquisition and visualization, which means factories can consistently meet their throughput targets. Laser profilers and structured light snapshot sensors leverage proven 3D technologies to meet the challenges of inline quality control.

Bringing GD&T Inline

While GD&T has traditionally been reserved for offline applications, LMI has identified a strong market need for the use of GD&T in the inline production environment. Leveraging GD&T for inline inspection is a potentially game-changing solution to simplify the setup for quality control of parts by providing manufacturers with an international design language that meets ISO standards. GD&T is a natural quality standard for inline QC applications where specific geometric elements on parts or features must be verified to meet production specifications.

The challenge of supporting GD&T in an inline environment is in acquiring a metrology-accurate 3D model of the part, in addition to meeting the fast cycle times required for inline production. Traditional offline solutions such as CMMs are unable to meet these requirements, which prevents GD&T from migrating to an inline setting.

Future 3D Smart Sensors with Built-In GD&T

LMI believes that building a user experience based on GD&T callouts using a 3D smart sensor would simplify quality control setup. 3D smart sensors are designed for metrology grade digitization and “smart” algorithm processing to deliver GD&T results. As a result, the future would see process control engineers set up a 3D smart sensor to carry out quality control on new parts by translating the GD&T tolerance data from drawings into digital callouts applied to scanned 3D surfaces. Dashboards could monitor and report on tolerance variation during production in a language that directly relates to the design drawings and support process engineers to tune and maintain 100% quality control.

LMI believe GD&T analysis could be brought inline and used to examine the conformity of manufactured parts. LMI sees this as the future—a non-contact, automated inspection system that can easily apply GD&T for inline applications to help manufacturers monitor for part tolerances.

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