What is a CMM - A Modern Perspective
Coordinate Measuring Machines (CMMs) have long been the gold standard. As a first-generation technology, traditional CMMs have led to modern CMMs by exposing strengths and limitations. By understanding where traditional CMMs meet industrial needs and where they fall short, modern CMMs bridge the gap between old and new. Overcoming modern challenges requires taking what works from traditions and advancing from there, building stronger resolutions, and creating new opportunities.
What is a Modern CMM?
A modern CMM is any device that collects X-Y-Z coordinate points for three-dimensional measurement. But the variety of modern CMMs didn’t appear overnight— it took years of research and science to break free from the limitations of traditional CMMs consisting of a granite table with a gantry and mechanical touch probe. Modern CMMs capitalize on the benefits that traditional CMMs provide but account for modern needs such as speed, versatility in measurement environments, and ease of use.
What are the traditional types of CMMs - advantages and disadvantages?
Known for high accuracy measurement results, CMMs have long been the standard for precision in metrology. Traditional CMMs typically use a granite table with a gantry and mechanical touch probe, requiring specialized programming skills to designate where the probe should touch various areas on the part to collect precise measurement points. But with CMM precision accuracy also comes the need for strict environmental specifications and parameters. For example, companies often build a Coordinate Measuring Machine room outfitted with special panels that create thermal and noise barriers, high walls to accommodate bridge size, and temperature and humidity controls that maintain a specific environment to ensure a proper measurement reading. Each type of traditional CMM comes with advantages and disadvantages, especially for modern metrology.
Types of Traditional CMMs
Generally, there are four types of traditional CMMs:
- Bridge CMMs: These are the most common type of traditional CMM. They have either a moving bridge or a fixed bridge with a three-axis structure.
- Advantage of Bridge CMMs: Many companies prefer this type of traditional CMM because they are lower in cost.
- Disadvantage of Bridge CMMs: The measurement stage is elevated, so each object or part must be reasonably small and light enough to be lifted and placed on the stage.
- Horizontal Arm CMMs: This traditional CMM comes in two types-- plate-mounted and two-runaway mounted. Its probes are attached to horizontal arms connected to vertical columns.
- Advantage of Horizontal Arm CMMs: Ideal for measuring thin parts or large, mounted objects out of normal reach.
- Disadvantage of Horizontal Arm CMMs: This type of traditional CMM is not as accurate, so it’s best to limit its application to tolerances 30 µm or larger.
- Cantilever CMMs: Typically found on shop floors, this type of traditional CMM often has automatic loading and unloading processes, ideal for small parts.
- Advantage of Cantilever CMMs: The design allows access to the part on three sides of the CMM. It is also typically more compact than other types of CMMs.
- Disadvantage of Cantilever CMMs: Part size capabilities are limited because the X-axis beam is not flexible.
- Gantry CMMs: This type of traditional CMM is usually installed onto the floor to handle the measurement of heavy, large objects without having to lift them onto a table like you would with other types of traditional CMMs.
- Advantage of Gantry CMMs: This traditional CMM can be customized to accommodate a larger measuring range if necessary.
- Disadvantage of Gantry CMMs: The weight of this traditional CMM creates stress on the facility's foundation, limiting its possible locations. To avoid damage to the CMM and the facility, the foundation where it's mounted must be strong.
Limitations of Traditional CMMs
The evident limitations of traditional CMMs include speed and accessibility since a specialized technician must program, operate, and analyze the resulting data. Ease of use also creates a problem, resulting in bottlenecks in production. Contributing to those bottlenecks is the time it takes to dissect CMM data as engineers struggle to decipher where the problematic areas by sifting through cryptic reports. However, for modern metrology, the true limitation comes from limiting what you can accomplish with a traditional CMM. In modern metrology, if you think of your measurement data as merely a means to communicate dimensional analysis, you’re missing the boat on many opportunities for growth.
What are the modern types of CMMs - advantages and disadvantages?
Many types of modern CMMs have developed out of necessity to resolve limitations left by traditional CMMs. While a modern CMM is any device that collects X-Y-Z 3D coordinate points, some modern CMMs provide additional advanced manufacturing capabilities. Picking up where traditional CMMs leave off, high accuracy is just the beginning for modern CMMs. With these options, the problem of touch probes constantly breaking is alleviated through non-contact optical measurement technologies.
- Laser Scanner Add-On to CMMs: Adding a laser scanner to a probe enhances traditional CMMs. The laser projects a line of laser light that moves along the object’s surface while cameras collect and triangulate measurement data.
- Advantage of Laser scanner add-on to CMMs: The resulting measurement data is visible, allowing for faster analysis. It can be a quick alternative if a company cannot upgrade existing technology to a standalone structured light system.
- Disadvantage of Laser scanner add-on to CMMs: Programming and measurement routines for free form surfaces can be challenging. The data often contains noise and is less accurate.
- Structured Light 3D Scanners: These modern CMMs, also known as OMMs (Optical Measuring Machines), employ the principle of triangulation by projecting a fringe pattern from an LED light source onto the object, while cameras look at the pattern and calculate the distance, resulting in millions of measurement data points.
- Advantage of Structured Light 3D Scanners: One of the many benefits of structured light 3D scanners is speed and accuracy. Scanning can be completed in minutes, depending on the size and scope of the project. A specialized technician isn’t needed to operate a structured light scanner because many are easy to use, which frees up staff availability to perform the scanning so that more work can get done in a day. The entire part’s surface is captured, creating a digital twin instead of pre-programmed selected points.
- Disadvantage of Structured Light 3D Scanners: The most significant disadvantage of structured light 3D scanners is measurement is limited to what the cameras can see, what’s in its line of sight. However, there are touch probe add-ons to capture hidden geometries, deep holes, and cavities.
3D scanners are designed to function in industrial environments and are often portable so that measurement can occur on the shop floor, in the production line, or any other place necessary. This advantage resolves the need for traditional CMM rooms with detailed environmental specifications.
Many skeptics of structured light 3D scanners wonder how accurate something can be if it doesn’t touch the part as a traditional CMM would. However, structured light scanners use similar principles as traditional CMMs, but expand upon them, allowing light to touch the object instead of probes. With structured light scanning comes the opportunity to digitize parts, providing data that helps manufacturers, product developers, and engineers to do more.
Metrology-grade 3D scanners can reach single-micron accuracy, meeting the requirements for parts with tight tolerances. With intelligent software integrated into these modern optical CMMs, manufacturers have a digital copy of a physical component within minutes. In the software, analysis is fast and often automatic, generating an accurate color map comprised of visual data. The data tells a story so engineers can quickly use their expertise to solve the problem instead of wasting time interpreting data that can be read in various ways. Data can be saved and shared with teams across the world, allowing for the versatility in collaboration necessary for success in manufacturing today.
Meet the Next Generation of CMMs
It’s true: traditional CMMs have long been the gold standard for accuracy in metrology. However, in modern manufacturing, it’s not enough to simply obtain high-accuracy results. Innovative industries like manufacturing, engineering, and product development thrive on next-generation technologies that accomplish more, from additive manufacturing and 3D printing to digital twin applications, reverse engineering, and beyond. Without the digital capabilities that 3D scanners provide, advancing manufacturing wouldn’t be possible.
Long gone are the days of sensitive metrology equipment, production bottlenecks, and endless rows of data to pour over during hours of analysis. You’re ready to meet the next generation of CMMs, so contact Capture 3D today and learn how we can help you go from limited to limitless.