CMM: Coordinate Measuring Machine

CMM

In manufacturing end-user and production parts, it is critical that the object’s physical dimensions and geometric properties suit those 3D models on which its design was based on. Even if a calculation is just marginally off, it can jeopardize the entire manufacturing cycle and set you back to square one. This is why coordinate measuring machines are important.

The CMM is a type of Computer Numeric Control Machine, CNC, that utilizes motorized maneuverable tools and platforms to carry out specific instructions. This system is controlled by a computer system that uses machine control instructions such as G-code and M-code to execute specific functions.

The introduction of CMMs increased the efficiency, accuracy, and flexibility of quality assurance of industrial components. These advantages all stem from their programmability and compatibility with CAD programs.

This article will go over the basic and general idea of Coordinate Measuring Machine and give valuable insights on limitations, possibilities, and the value of CMM to the industry.

The History of Coordinate Measuring Machines

Its history starts with introducing the very first 2-Axes universal measuring machine, the YZ machine as it was called, was developed by Sheffield Corporation in the mid-1940s. The YZ machine was used to measure an active Hydrogen bombshell at the laboratory in Oak Ridge, Tennessee, as a proof of its accuracy.

Now, the success achieved in the accuracy of the 2-axes measurement machine sparked an even bigger craze within the science and engineering community and spurred them to developing the new 3-axes universal measuring machine. In the early 1960s, two companies had successfully finished the race, and there were Italian Digital Electronic Automation, DEA S.P.a and Ferranti of Scotland.

In the end, the first coordinate measuring machines were manual and had operators who manually guided them in performing measurements.

Today, CMM’s are driven automatically by computer applications, with other improvements well on the way. One of them, being the improved compatibility of CAD programs like SolidFace with CMM, more on this later.  

coordinate  probe measuring
emasuring The Probe of a Coordinate Measuring Machine Taking Measurements

What’s CMM

CMM is short for Coordinate Measuring Machine. It is an advanced measurement machine that accurately measures the geometry of complex and large components along three-dimensional Cartesian coordinate system (X, Y, and Z axes) using touch-triggers, scanning/vision probing tools, etc. the machine aims to ensure precise points on the surface of an object being measured.

The CMM also takes readings in 6-degrees of freedom. A degree of freedom is the number of final value each measurement has. In the case of CMM, it’s up to six.

The operations of a Coordinate Measuring Machine, can be manually controlled by an operator or automatically (CNC) through the use of computer programs and software.

Measurement is done by the probe that’s attached to a third moving axis. The probe can be mechanical, laser, optical, or white light.

More so, CMM is now the cornerstone of most industrial process that requires highly precise objects and machine parts. Industries where the physical integrity of their manufactured products is paramount, because CMM allows manufacturers to meet original design requirements or stringent Quality Control requirements.

Why Do I Need a CMM

Traditional handheld inspection methods have their weaknesses, as they rely heavily on the expertise of the inspecting parts personnel. Parts fabricated incorrectly can go undetected and be dispatched to customers.

However, as the production process becomes more sophisticated, components are rendered more complicated, meaning that certain features can only be calculated accurately with a coordinate measuring machine.

With the need to fast-track and streamline inspection processes in businesses, CMM inspection offers more completions of milestones in a fraction of the time, while ensuring the results are more accurate, and in compliance to the ever-increasing customer demands.

The bottom line, CMM will always save time and money for your business, and would also allow your company to deliver more profitable work.

Coordinate measuring machine
Coordinate Measuring Machine

Types of Coordinate Measuring Machines

There are four basic types of coordinate measuring machines, and they are:

Cantilever CMM

The Cantilever CMM is one of the earliest types of CMM made and developed by Ferranti in Scotland in the 1970s. The Cantilever CMM machine isn’t so popular anymore and is only produced in small numbers.

They mostly used as shop floor hard bearing machines, because of their automatic loading and unloading characteristics. The Cantilever CMM machine are generally used for measuring relatively small parts and object and their structure provides open access to the operator on three sides.

Bridge CMM

The bridge CMM is currently the most popular type of CMM available due to its basic structure and simplicity of build. The Bridge CMM is typically a 3D CMM machine, that allows probe movement along its three Cartesian coordinates axes. Each axis has a sensor that monitors the position of the probe on that particular axis, with the aid of a micrometer precision.

So when the probe makes contacts with an object, its three-position sensors immediately detect the particular location of one point on the object’s surface. This process is repeated, causing the probe to move each time, to create a “point cloud”, which defines the surface area of interest.  

Also, the Bridge machine has a low building cost and has a great ability to maintain accuracy repeatedly over a long time. Most Bridge CMMs are built with precision granite plates and two legs that support the X-axis carriage.

Before moving on, 95% of all Bridge machines run on the air bearing, which allows for frictionless movement and minimizes mechanical interactions, that are responsible for heat and wear. This is why the Bridge CMMs are described as the work-horses of the CMMs.

Gantry CMM

On the other hand, Gantry CMM machines are very large (giants) CMM machines that are useful for predominantly very large or heavy objects, that require the kind of high precision provided by the Bridge machine. The Gantry is mostly mounted directly to the floor and therefore are dead loads to the structure.

Horizontal Arm CMM

The Horizontal Arm CMM was first produced in Germany by Steifelmayer. And were initially used as scribing tool that operated manually. Companies like Bendix and Sheffield continued the production of the Horizontal Arm machine and gradually transform their components from scribers to probes.

horizontal arm coordinate measuring machine
Horizontal Arm CMM

There are two main types of Horizontal Arm CMMs and they’re Plate Mounted and Two Runway Mounted.

In the Plate Mounted Horizontal Arm CMM, the column is mounted on a large surface plate that’s made of steel. A part of the machine runs on a top-mounted plate. The Plate mounted Horizontal Arm is generally inexpensive and less accurate and more stable than other CMM systems.  

Conversely, Two Runway Mounted Horizontal Arm CMM runs on a dedicated beam and not a mounting plate. With this feature, the Two Runway Mounted design provides the utmost flexibility.

Major Components of a Coordinate Measuring Machine

The main components of CMM itself are listed below:

  • Machine Control System  
  • Prob System
  • Controllers & Software
  • Air Bearing
  • Scales & Encoders
  • Servo motors
  • Joystick

The Machine

The coordinate measuring machine was made to replace the need for human investigation. This is why CMM machine components are built to imitate the flexibility of a human arm, which makes it more possible for them to reach the complex parts that could naturally not be probed by other standards axis machines.

That said, CMM machines could come in various sizes, from the super-size of the Gantry machine to the more portable size of the Horizontal arm.

Also, The CMM machines use air bearing, to transport sample products easily, ensuring frictionless travel. With the movement of sample products along the XY plane, the third axis, Z axis is provided for, by the use of vertical quill or spindle, that moves across the center of the carriage.

The main structure of the CMM is these three axes of motion. The materials used in the making of its moving frame has changed over the years. From the Granite and steel of its early days to the aluminum alloy of today.

Probing System

The Probing system is made of a joystick part and operates in similar ways as with a modern remote-controlled car. The electronic touch trigger probe is a type of probing system that has greatly improved the accuracy and precision of production.

Now, the probe system is a contact device and uses stylus components in carrying out its interactive production, supported with the aid of the machine.

The probe system collects the data on the Cartesian coordinates (X, Y, and Z-axis) from the object being worked on and simultaneously sends them to the computer for reference. Which in turn allows the probe to respond accordingly.

Also, they’re several types of probing systems, with the latest of the bunch being the scanning probe. The scanning probe drag along the surface of the part of the model being produced to take points at specified intervals. It’s more accurate and faster as well.

Controllers & Software

The third part of the CMM machine is the operation/handling method. This is done by the computer, through the CMM software or an operator. They’re both responsible for the use and operation of the CMM in its measuring duties.

The controller is any person or computer that performs complicated activities like data analysis and regular updates of the CMM system, which makes it possible for its automation.

Working Principles of Coordinate Measuring Machine

CMM uses it Prob to record 3-dimensional coordinates (X, Y, Z coordinates) of the object being measured. These generated points are analyzed by the regression algorithm, which forms the basis for referencing the object with design standards.

coordinate measuring machine

How CMM Works

Each machine component or working object is designed using suitable CAD software, to ensure maximum performance and manufacturing accuracy. The CAD software helps ensure a lot of factors for the material being produced like the best material suitable for the purpose, etc.

It’s after this process and several other vettings, testing, and approval stages before this working objects are sent for manufacturing. it’s in this manufacturing phase that the CMM is used to ensure quality control.

The CMM uses a wide range of contact and non-contact probes to carry out numerous kinds of measurements on the working objects. This system works similarly as your finger when it traces the coordinates on a map. The data collected by the CMM’s Prob is comprehensively analyzed using computer software.

Examples of What CMM Can Measure

CMM provides automated metrological computations for all kinds of complex dimensions. In recent times improvements have been made on the features that CMM machines can measure. For simplicity, we’ll only mention a few of them. Here’s a list of the basic things the CMM can measure:

  • Straightness
  • Flatness
  • Roundness
  • Cylindricity
  • Conicity
  • Angularity

Generations of CMM

The generations of CMM is a breakdown of the development of the CMM from the days of its invention to our days of its massive adoption and innovation.

Manual CMM

The manual CMM is common with old-school CMMs, as they fully utilize human engaged operators. They’re less expensive and often faster to set up than their digital counterparts. Though excessive human error hinders the manual CMM in highly precise manufacturing activities.

DCC (Digital Computer Control) CMM

DCC CMM is the direct opposite of manual CMM, as they replace human operators with computer ‘brains’. The computers are programmed and calibrated for each activity through the aids of software and other programs of the computer systems. However, they still rely on the minimal human operation to complete their activities.

Portable Laser Scanner

Portable Laser Scanner CMM uses futuristic laser and capacitive video technologies to provide quick instantaneous measurements for working products in three dimensions.

Advantages of CMM

CMM Hardware Can Last For A Long Time

If the machine is handled properly, it won’t wear out throughout its useful life. It can need a motor change or a few parts, but its basic machine is expected to last for many years. This means that you will not have to upgrade your CMM anymore.

Works Better with Software

Today, the graphical aided applications like SolidFace can access and store a wealth of information that is significantly increasing. Metrology experts also say the software remains more affordable, accurate, user-friendly, and standardized.

The Machine Could Simply Be Upgraded By Upgrading Your Software

Some coordinate measuring machines, CMM can have five-time software updates, and will still deliver the same efficiency. Most CMM owners will ask for a software upgrade more times than they would ask for a hardware upgrade.

New Models are More Resistant to Environmental Factors

Most would like to have a CMM on the shop floor to boost efficiency, and today’s measuring machines allow you to do just that. They are now more resistant to influences from most shop floors, such as vibrations and changes in temperature, rendering these major problems of the past, none and void.

Others Advantages Include

  • High Precision and Accuracy
  • Requires less labor, while Improving Productivity
  • Single Setup and Reduced Setup Time

Disadvantages of Coordinate Measuring Machine

There Is No Standardization

Today, computers are run by hundreds of different types of CMMs, thousands of suppliers, and numerous software programs. This means that software synchronization between coordinate measuring machines, CMM can be difficult to coordinate and collaborate together.

CMM Systems Can Be Complicated To Operate For Novices

Not all CMM users are familiar with the concepts of coordinate measuring machines. Such machines are often run by engineering and production professionals, and they need to work fast, so they need to produce more parts to make money. They don’t have as much time as high-end engineers, so they need simpler systems.

More Disadvantages Include

  • Significant building cost for the foundation of the Gantry machines.
  • Complete lack of any kind of handiness. Unlike Bridge machines that can move relatively easily either by riggers or forklift trucks and can be calibrated quickly for service, with fewer troubles. Gantry machines can’t be readily moved and need major disassembling and reassembling to be relocated.
  • Some CMM like Gantry takes up a tremendous amount of space in the factory.

CMM CAD/CAM Compatibility

Engineers have been pushing the idea of what’s possible with CMM for over a decade, and this has resulted in breakthroughs in Digital Product Definition (DPD). Engineers have always recognized the need for collaboration between CMM and CAD platforms, hence the reason for the creation of programming language like DMIS (Dimensional Measuring Interface Standards), which is used for translating CAD data to CMM software data.

But, with the development of the Direct CAD Interface (DCI), the dreams of engineers have finally been achieved as users of CAD applications like SolidFace can now directly communicate with the CMM Software.

Benefits of Using CMM Machines In Your Production

Some of the advantages of using a CMM machine to measure your component may seem obvious by now, but there is a whole range of reasons why this method should be incorporated into your workflow of production. Here are the main advantages which a CMM machine can offer:

Save Time And Money

Once a functional prototype or part has been produced, the success of this outcome depends entirely on the accuracy and precision of the part. Measurement technologies such as CMM machines are extremely important as rapid manufacturing techniques are becoming capable of producing more complex objects.

Other measuring techniques require that parts be taken into a laboratory or removed from the production floor. CMM machines provide a quicker and more accurate route to measuring the component, effectively reducing costs and time in development.

Quality Assurance Is Guaranteed

While different tools can digitally measure and analyze your component, very few give the reliability that a CMM machine does. A CMM machine inspection offers unbeatable services such as dimensional analysis, CAD comparison, tool certification, and reverse engineering to check confidently any aspect of your design.

Versatile With Several Samples And Techniques

While complex parts and assemblies can seem difficult to calculate, CMM machines are compatible with a variety of measurements and instruments that can be customized to accurately capture the design dimensions.

Limitations of CMM Machine Inspection

While a CMM machine can undoubtedly play a crucial role in the production process, there are a few drawbacks to be taken into account before and while using the CMM.  Here are some factors which must be assessed before using a CMM machine:

The Probe Must Touch The Surface Of The Object

Except for the modern probe types, regular probe instrument used on a CMM system is needed to make physical contact with a surface for measurement. Although this may not be a concern for prototypes and tough components, this process may potentially damage delicate surfaces.

Soft Parts May Lead To Defects

If you choose to manufacture a piece for soft materials, such as rubbers or elastomers, the probe can cause the surface to cave in when it hits the component, causing digital inspection defects.

The Correct Sample Has To Be Chosen

Various types of samples can be used with a CMM machine depending on the measured component. When it comes to measuring different design features and measurements, each stylus offers different capabilities.

Choosing the Right CMM

Finally, when there’s a need to single out one CMM for yourself or your production needs, not a factor can or should determine the best application for you. Some factors to be considered include:

  • The CMM type
  • The Probe type
  • CMM Software
  • CMM cost
  • Seek Professional Advice

Cost of CMM Machines

Today, the CMMs price range ranges from about $30 K to over $1 M, depending on the requirements of the manufacturer. Similarly, the cost of various types of probes/sensors ranges from a few thousand dollars to tens of thousands.

Conclusion: Should You Consider CMM Machine Inspection in Your Production

Ensuring that the produced components are similar to the digitally designed model is becoming more important as our production phase into high-accuracy projects like Space Rockets and other Digital products.

The continued concerns for the utmost integrity of production products and components will increase the emphasis on CMM device and their popularity in every aspect of manufacturing, to meet the growing appetite for perfection.