Intro to shadowgraphs, 3D scanners, CMMs & multi sensor systems
This article will examine the differences between traditional and sensor-based metrology, and analyse the different technologies available from coordinate measuring machines, scanners and shadowgraphs through to optical measuring machines, and explain how sensor-based metrology can improve production efficiency in a variety of industries.
For more information, and discover more about metrology in general – you can read our – What is metrology? blog post.
Traditional metrology
Traditional metrology has been used in manufacturing for decades and allows for measuring and testing devices with high accuracy and precision. It relies on a variety of techniques, such as gauging the size and shape of objects to measure them. While this method may work well for certain applications, it does not allow for the accuracy and precision that modern sensors can provide.
Traditional metrology is limited in its ability to quantify the dimensional characteristics of an object as it moves through the production line. This can lead to delays and inaccuracy in the measurement process and ultimately reduce the efficiency and productivity of the production line. To solve this problem, many manufacturers have turned to sensor-based metrology.
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.
Coordinate measuring machine (CMM)
Coordinate measurement machines have long been a staple of the production floor. Known for accurate measures by using a probe to sense discrete points on the surface of an object, a CMM (Coordinate measuring machine) moves a probe, such as a laser scanner probe or physical touch probe along the XYZ axes to make measurements, particularly in complex parts with hard-to-reach places.
The benefits of CMM systems are plentiful, as there are distinct productivity and accuracy benefits compared to using traditional metrology methods. Rarely causing problems on the shop-floor, and a rigid, sturdy, reliable operator, a good CMM can last for a long time.
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 – 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 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.
Non-contact measurements can typically made using lasers or optical measuring machines. See below…
3D Laser Scanners
3D Laser 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.
Optical Measuring Machines (OMM)
Optical measuring machines (OMM) 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. 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.
Multi-sensor measuring machines
The holy grail of all measuring machine options, multi-sensor technology allows for full versatility in metrology. Available to use with touch probes, lasers, rotaries and high-resolution optics, measurements have never been so accurate, easy and fast.
OGP is the leading manufacturer of multi-sensor technology, offering easy-to-use software within world-class machinery at the cutting-edge of metrology. Combining all technologies listed above – multi-sensor really is the all in one solution for every inspection requirement.
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 OGP UK today to talk about metrology, and the time and money it can save you.