Demystifying CMM: Understanding the Basics of Coordinate Measuring Machines

Demystifying CMM: Understanding the Basics of Coordinate Measuring Machines

Dec 08, 2023

The precise size and geometry of parts are vital when manufacturing prototypes or actual products. Any errors in dimensions can have a significant impact on the entire production process.

To address this issue, high-tolerance measuring machines known as Coordinate Measuring Machines (CMM) were developed. In this article, we will provide an introduction to CMMs and answer the commonly asked question: “What is a CMM?”

Basics of Coordinate Measuring Machines

What is a CMM?

The coordinate measuring machine (CMM) is a crucial tool in the manufacturing process for ensuring precise geometry and physical dimensions. Traditionally, measurements were taken using hand tools or optical comparators, but these methods had limitations and potential for errors. The CMM, on the other hand, provides an accurate and efficient solution.

A CMM machine utilizes coordinate technology to measure the dimensions of machine or tool parts. It can measure height, width, and depth in the X, Y, and Z axes. Depending on the complexity of the CMM machine, it can also record measurement data. This advanced measuring machine is particularly suitable for measuring large and complex components.

The CMM is controlled either by a computer or an operator. It offers 6 degrees of freedom (DOF), allowing it to read measurements from various angles and directions. Due to its versatility and precision, it has become an indispensable tool in modern manufacturing processes.

The importance of coordinate measuring machines

The significance of coordinate measuring machines is paramount in today’s metrology industry. Traditional methods of handheld inspection have limitations and heavily rely on the inspector’s skillset.

This leaves room for poorly manufactured components to go undetected, ultimately reaching the end customer. However, with the advancement in production designs and the complexity of components, certain properties can only be precisely measured using a CMM.

The impact is profound as CMMs save businesses both time and money while enhancing their manufacturing processes. This improvement allows them to gain a competitive edge, leading to increased profitability.

The importance of coordinate measuring machines

Types of coordinate measuring machines

There are four types of coordinate measuring machines (CMMs), each with its own structure and advantages.

Bridge-type coordinate measuring machine

The first type is the bridge-type CMM, which is the most common. Bridge-type CMMs can be further classified into mobile workbench and mobile bridge types. These machines have a stable anchoring design that ensures accurate measurements. They come in both stationary and portable options, with the latter being hardened to withstand the harsh conditions of a machine shop. However, bridge CMMs are typically limited to measuring small to medium-sized parts that can be easily lifted and placed on a table.

bridge type cmm

Gantry type three coordinate measuring machine

Gantry-type CMMs feature two upright columns with a crossbeam connecting them. This configuration provides excellent stability during measurements, making it suitable for larger and heavier parts. Gantry CMMs are commonly found in industries such as automotive and aerospace.

Gantry type three coordinate measuring machine

Cantilever type three coordinate measuring machine

The second type of CMM is the cantilever type. Cantilever CMMs have a single arm with a probe attached at one end. This design allows for flexible measurement in tight spaces or areas that are difficult to access. Cantilever CMMs are often used for measuring intricate and complex parts.

Cantilever type three coordinate measuring machine

Horizontal arm three-coordinate measuring instrument

The fourth type of CMM is the horizontal arm style, where the probe is attached to a horizontal arm that moves along tracks mounted on an overhead beam or surface plate. This design allows for large-scale measurement of heavy objects without compromising accuracy.

Horizontal arm three-coordinate measuring instrument

How does a coordinate measuring machine work?

A coordinate measuring machine (CMM) functions by utilizing a probe to make physical contact with different points on the object, gathering valuable data on its dimensions and shape.

This data is meticulously analyzed and utilized to generate highly precise measurements and comprehensive reports.

The CMM operates through a sophisticated system of XYZ axes, enabling it to maneuver the probe with pinpoint accuracy along various planes. Moreover, state-of-the-art CMMs incorporate optical or laser sensors for non-contact measurements.

While advanced CMMs boast an array of additional capabilities, dimensional measurement remains the fundamental application of this powerful technology.

Benefits and limitations of coordinate measuring machines

Coordinate measuring machines (CMM) are essential instruments in the realm of production. They offer numerous advantages that greatly surpass their limitations.

We will delve into a comprehensive exploration of the multitude of benefits associated with employing a CMM, while also addressing some important considerations regarding its limitations.

Benefits of utilizing a coordinate measuring machine

Enhanced efficiency and cost savings

Coordinate measuring machines have become an essential component in the manufacturing process due to their accuracy. Particularly when producing intricate tools, coordinate measuring machines is a good choice for dimensional measurement, ultimately resulting in significant reductions in production costs and time expenditure.

Reliable quality assurance

Unlike conventional methods of measuring mechanical part dimensions, three-dimensional coordinate measuring machines provide a steadfast tool for ensuring quality. They can digitally measure and analyze parts, while offering a wide range of services such as dimensional analysis, CAD comparison, tool certification, and reverse engineering to uphold rigorous quality standards.

Decreased reliance on operators

As CMM machines are computer-controlled, human involvement is reduced. This reduction serves to mitigate potential risks associated with operational errors.

Constraints of utilizing Coordinate Measuring Machines (CMMs)

A critical requirement is surface contact

In order to accurately measure a part, the probe utilized in the coordinate measuring machine must make contact with its surface. However, attention must be paid when dealing with delicate or fragile surfaces, as prolonged contact may result in damage to the part.

Defects can occur on soft materials

When employing probes on parts crafted from soft materials like rubber and elastomers, caution should be exercised since it can cause deformation of the part, leading to inaccuracies during digital analysis.

Probe selection is paramount

Different types of probes are employed in CMM machines. The choice of probe depends on various factors such as part size, design specifications, and probe capabilities. Failure to select an appropriate probe may compromise measurement precision.

Common Questions about CMM

Can the ambient temperature significantly affect the measurement results of a 3D coordinate measuring instrument?

The 3D coordinate measuring machine is a sophisticated measurement system that combines light, machinery, electricity, computer, and control technology. As a result, numerous factors can impact the uncertainty of its measurement results.

However, for smaller and mid-sized coordinate measuring machines, the most significant factor that influences measurement uncertainty is the deviation of ambient temperature from the standard measurement temperature (20°C).

To ensure accurate results from the three-dimensional coordinate system, it is crucial to strictly control the ambient temperature within the range specified in the machine’s manual.

What are the common error types of coordinate measuring machines?

The common error types of coordinate measuring machines can be categorized into static error and dynamic error. Static errors are characterized by a consistent, stable level of error, while dynamic errors increase over time.

To effectively compensate for errors, it is important to have a clear understanding of these two error types and select the appropriate method accordingly.

What are the common error compensation methods for coordinate measuring machines?

The most commonly used error compensation methods for coordinate measuring machines are temperature compensation, software correction compensation, and other types of compensation.

The software correction compensation method is particularly prevalent in practical applications as it effectively compensates for dynamic errors in three-dimensional coordinate measuring machines.

How to keep the temperature in the measuring room balanced and stable?

There are several solutions to maintaining a balanced and stable temperature in the measuring room.

1. The measuring machine software can employ linear correction and temperature correction to adjust for the temperature effect based on the environmental conditions during on-site calibration.

2. It is important to keep heat sources like electrical equipment and computers at a reasonable distance from the measuring machine.

3. When choosing an air conditioner, it is recommended to opt for an inverter model with strong temperature control capabilities. Additionally, careful planning of the air conditioner’s installation location is crucial, ensuring that it does not blow directly onto the measuring machine. To maintain a balanced indoor air temperature, it is advisable to adjust the air conditioning wind direction upward to stimulate ample air circulation throughout the space.

4. Thermal insulation measures should be implemented in computer rooms, with doors and windows closed tightly to minimize temperature loss and avoid exposure to sunlight. Lastly, strict management of the measurement room should be enforced to prevent unnecessary personnel from lingering in the area.

Does the detection system of the 3D coordinate measuring machine affect the measurement results?

The measurement results of a three-dimensional coordinate measuring machine can be affected by its detection system. In this process, the probe makes contact with the workpiece being measured and sends a signal.

The control system and computer then collect the coordinates of the probe and perform necessary calculations to obtain the desired measurement results. Currently, most coordinate machine probes are designed as switch-type, which can lead to different contact points when detecting at different positions.

This design principle introduces detection errors that directly impact the uncertainty of the measurement results. Therefore, it is crucial to minimize these errors for accurate measurements.

While CMM offers various benefits, our 3D scanners, including the KSCAN-Magic 3D scanner, SIMSCAN 3D scanner, color 3D scanner, TrackScan 3D System, etc., surpass these advantages.

They are more portable, provide unprecedented accuracy, simplicity, speed, and efficiency, all while maintaining metrology-grade precision.

Discover our Handheld 3D Scanners for Optimal Measurements

To ensure optimal measurements and streamline quality control, we encourage you to discover our Handheld 3D Scanners. With our advanced scanners, you can achieve precise and efficient measurements, enhancing your overall manufacturing processes.

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Demystifying CMM: Understanding the Basics of Coordinate Measuring Machines


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