Metrology Technologies: Strengths and Differences

OGP metrology machines are advanced platforms that often combine multiple sensors to analyse an object. Despite the general evolution of measuring machines, they still differ in their strengths and methods.

There are several different technologies that can group these machines together, as we’ll explore below:

CMMs

Coordinate-measuring machines obtain an accurate geometry of a part by taking a series of specific points from its surface. This can be done using a probe such as a physical touch probe or a laser scanning probe. The probes themselves move along the X, Y, and Z axes, though machines like OGP’s FlexPoint utilise articulating probe heads to achieve more complex positioning.

OGP’s measurement machines can work with proprietary ZONE3 software to automatically generate sensor paths. This means that optimised use of a CMM – such as the Vantage – needs no complex operator input. CMMs are commonly composed of materials such as granite for vibration dampening.

CMM metrology technologies offer adaptable and versatile measurement solutions for complex parts. Tricky features such as blind holes and easily deformable materials can still be measured accurately by using the right sensors for the job. The most effective use of a CMM within a manufacturing environment is placed as an inline metrology solution, measuring parts as they created to check against tolerances and specifications.

CMMs can range in size from portable to huge stationary constructions, often built with bridge designs that allow a wide range of movement.

Non-contact measurement

Non-contact measurement systems typically employ high-quality optics to measure parts. Paired with sophisticated lighting, large fields-of-view, and technologies such as distortion-free telecentric lenses, these machines become exceptionally equipped for taking part data. Non-contact measurement is ideal for analysing parts that are fragile and easily deformed, or for selections of parts that have differing geometries.

White light sensors are commonly employed for such tricky-to-measure parts. These sensors typically harness specially designed lenses to differentially refract white light depending on wavelengths. Distance measurements can be made by sensors that capture this light, allowing depth and thickness readings to be taken from translucent materials, as well as surface measurements.

Non-contact measurement machines lead to a rapid processing rate that makes them desirable for their repeatability and throughput. For businesses manufacturing small, fragile, or observationally challenging parts, non-contact measurement may yield better results than even a multi-sensor CMM, dependent upon the machine.

Shadowgraphs

Also known as profile projectors or optical comparators. Shadowgraphs in a metrology context were first brought about for screw thread inspection with the first patent for such a machine granted in 1929. Light is projected onto the part to be measured and the resulting silhouette is magnified. The silhouette can then be measured in various ways, such as with superimposed graduations on the screen acting like rulers, moving the part stage and reading the distances the stage moved relative to a zeroed point, or with advanced analysis software.

Shadowgraphs still win themselves popularity due to the simplicity of their operation. However, this is also their biggest setback, particularly in the context of modern manufacturing. As parts grow smaller and more complex, and with tighter tolerances necessary, such manual technology as a visual comparator no longer presents a fully reliable option.

A skilled operator can still get a lot from a shadowgraph, but when compared to faster, more accurate metrology technologies with the capacity to analyse multiple parts and with CAD programming support, the former becomes almost entirely obsolete.

Scanners

Scanners are able to obtain detailed surface characterisations of parts. They can do this quickly and accurately without software alignment or registration. Scanners such as the OGP ShapeGrabber obtain their readings with great ease of use and are ideal for moulded plastics, castings, and machined parts. This fidelity is applicable across a range of materials, colours, and finishes.

With the right configuration, a ShapeGrabber machine can gather over 1.5 million data points per second. After an initial scan, the same scanning parameters may be used for subsequent parts, delivering consistent results irrespective of operator skill or experience. For the right workflow, applied metrology in the form of a scanner is a fast and easy process that delivers a wealth of important data and quality assurance.

Choosing the Right Option for You

The needs and applications of applied metrology differ from business to business. Likewise, the best metrology technologies for the job need special consideration on a case-by-case basis.

Luckily, OGP UK has a dedicated team of experts who can guide you to the best metrology machine for you. Whether it’s a multisensory CMM or a laser scanner, OGP UK’s award-winning staff can answer any of your questions.

Contact us today to talk about metrology, and the time and money it can save you.