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What is metrology?

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Measurement technology plays an important role in industry and technology. The decisive factor is the selected measurement method that is used. With the help of measurement technology, information is provided about the actual states of certain physical quantities. 

How does metrology work in detail? Metrology involves the determination of certain physical quantities using a wide variety of devices. During the measurement process, methods from mathematics, such as combinatorics, stochastics and error calculation, are also used. Measurement itself can be regarded as an experimental process that records the concrete value of a physical quantity as a multiple of a unit.

Metrology is a very broad term. At Q-Tech, we deal exclusively with length measurement technology and dimensional measurement technology. You want to know more about the individual data of our machines? Then take a look at our software and equipment.

Basics of measurement technology

First of all, you should know that all physical or chemical effects or laws that are present in the measurement are called the measurement principle.

 

The precise application of measuring devices, or technical solutions in general terms, is called a measurement procedure

Measurement methods , on the other hand, are general rules that govern the way in which a particular measurement value is determined. 

Basically, experts distinguish between direct measurement technology and indirect measurement technology.

Direct measurement

In direct measurement, you compare the measurand directly with a scale.

For example, you can use familiar tools such as a tape measure, ruler or caliper gauge. Although these tools have lost some of their importance in modern industry, they are still present in everyday life and are frequently used. 

The caliper gauge in particular still has a high value in industry today and is not missing in any workshop. With this cost-effective measuring device, you can perform direct length measurements on various components within a very short time.

Indirect measurement 

Indirect measurement is used when quantities cannot be measured directly

You proceed as follows: You take another quantity and determine the sought-after measurand from it - provided there is a direct and unambiguous relationship. 

For example, the distance between the earth and the moon could never be determined by direct comparison with a scale. However, it has already been possible for 30 years to determine the distance precisely by means of light or radio waves - and even to millimeter accuracy. 

Indirect measurements form the majority of measurement methods used in everyday life. 

Simultaneous measurement

You can understand the simultaneous measurement as an extension of the indirect measurement methods. During the procedure, a simultaneous measurement of different points results in the elimination of time errors. Furthermore, measurement deviations are minimized and the sources of systematic measurement errors are revealed.

Metrology

Measurement technology and the influence on quality

Measurement technology has always helped to uncover unknown relationships in the scientific field or to confirm regularities of a theoretical nature by means of an empirical experiment.

Advances in metrology have significantly contributed to raising the quality of products and production processes.

Due to the progressive development of quality, the demands on measurement technology are increasing.

Here are some examples: 

  • The increase in complexity of technical systems
  • The tolerances for certain properties are reduced
  • The speed of technical processes is increasing
  • The degree of automation of industrial processes is increasing
  • The production of components and assemblies is gradually specialized
  • The technical use of scientific knowledge is gaining more importance
  • The requirements for functional properties of products are increasing
  • The demand on production processes is increasing.

Measurement technology and the production process

 

The measurement of product quality in manufacturing usually takes place in these three phases: 

  1. Incoming inspection
  2. Intermediate control 
  3. Output control 

You can understand these points as a kind of scheme. This guarantees that the quality of the products is ensured at every stage of production and that possible errors are detected in good time at any point in the process.

Dimensional metrology

At Q-Tech, we specialize in dimensional metrology. This means that we measure everything that has to do with the size or dimensions of components

The corresponding physical quantity is the length

Even surface characteristics and roughnesses are basically nothing more than linear dimensions or depth distances. 

The appropriate subterm in metrology here is length metrology

The measured actual values allow a complete and three-dimensional assessment. In the best case, the component has been manufactured as it was originally designed. This enables smooth use later (e.g. assembly of the component)

Different technologies are used in our company:

  • Computed tomography 
  • Tactile measurement technology (portal measuring machines, contour graphs, roughness measuring devices, etc.) 
  • Optical 2D measurement technology (e.g. video measuring microscopes) 
  • Optical 3D measurement technology (e.g. 3D scanner) 

Computed tomography

In computed tomography, homogeneous components, such as plastic components or light metals, but also inhomogeneous components (fiber composites) are examined and recorded three-dimensionally

Computed tomography in metrology is not to be confused with the process of the same name from medicine. While medicine focuses on the examination of the human body, metrology deals exclusively with the examination of a component

Even before production, the actual metrological work and preparation of the measurement of the test specimens begins. The CAD data used serve as the basis. These are used to create a test plan or measurement program

The individual reference and measurement points of the component are precisely defined in the inspection plan. After the first near-series component has been manufactured, it is scanned in the ICT system. After scanning, the component is displayed in 3D volume data and read into the evaluation software.

Now the 3D point cloud is matched with the CAD design data.

Deviations are output in a log with the measuring software. For a better visualization, the display is also done in colors, which clarify the degree of deviation. These colored 3D representations are referred to as target/actual comparisons.

With the help of a CT scanner, you can see the complete inner and outer geometry of the workpiece. Even the smallest deviations and component defects can be localized with the CT scanner. 

Even soft materials, such as elastomers, can be precisely examined and tested metrologically using this method. 

More about CT here
Industrial computed tomography in manufacturing

Two-dimensional CT

In the two-dimensional method, a single layer of the object is examined and reconstructed. This is done with a radiographic inspection and detection with a line detector

Meanwhile, the X-ray source emits a fan beam. Subsequently, the numericallayer structure of the object is created by means of the recorded X-ray projections.

Advantages:

  • Detailed resolution
  • Low interference due to scattered radiation
  • Non-destructive testing of the component

In two-dimensional CT, the object to be measured is not rotated in industry. The systems are capable of measuring components in a single beam path. Two-dimensional CT is used in particular for inspecting damaged areas inside components and for recording two-dimensional dimensional data. 

Three-dimensional CT

Three-dimensional CT involves a rotation of the component to be measured. This enables the creation of complex 3D models. In the course of the measurement process, data models are created that consist of various points. These 3D models serve as an important foundation for performing an accurate quality inspection. 

Advantages: 

  • Testing of complex geometries
  • Complete collection of complex volume data
  • Non-destructive testing of the component

Disadvantages: 

  • Computers with high processing power and a lot of memory are needed
  • Three-dimensional measuring systems are more expensive than two-dimensional variants

Three-dimensional CT is frequently used as a method for reverse engineering. In addition, there are comprehensive damage analyses and geometry measurements for complex components.

Tactile measurement

Tactile measurement plays an important role in mechanical engineering. It is used in particular when optical methods reach their limits. 

Precise tolerance determinations in the micrometer range and large-area detection of workpiece surfaces are possible. 

The point coordinates are determined by means of probing with mechanical probe elements. These probes are made of hard metal, industrial ruby or silicon nitride. 

Even large and heavy workpieces can be measured in mechanical engineering using this method. 

Subsequently, the tester receives the desired information and results. Possible test elements and characteristics are for example:

  • Geometry
  • Flatness
  • Straightness
  • Roundness 

This data is of crucial importance for the metrologist. He can thus accurately check distances, angles, shape deviations, dimensions and position relationships and provide a meaningful quality determination

For the process, mainly gantry measuring machines are used, but also roughness gauges and conturographs are part of the tactile measuring technology. 

Areas of application for tactile measurement technology

 

The tactile measuring technique is mainly used in mechanical engineering, where the tolerances are very small .

Therefore, this process has proven itself especially in the following industrial sectors: 

  • Mold making 
  • Aerospace 
  • Automotive industry 
  • Foundries
  • Toolmaking 
  • Railroad industry 
  • Medical Technology 
  • Heavy Industry 
  • Plastics Technology 
  • Machine shops

There are a few things to consider in advance: Despite the low force that the probe exerts on the material surface, minimal deformation sometimes occurs in soft materials. 

Especially for thin or flexible components, alternative measurement methods should be used accordingly.

Metrology

Optical metrology

In contrast to tactile measurement, optical measurement systems measure objects with the aid of optical sensors. These can be laser scanners, projection systems or photogrammetry systems. 

The great advantage is that surface damage to the measured object is reliably avoided in the case of sensitive objects. Signs of wear also do not occur here. 

Transparent, but also shiny components place particularly high demands on the optical sensors. The reason is relatively simple: Measurement with light on reflective or even translucent material proves difficult or is not possible for the time being. 

Here, a scanning spray is often used before the measurement. This makes it easier for the sensors to detect the contours. 


More about optical metrology
Optical measurement technology - how it works in industry

Conclusion: Metrology is indispensable for maintaining quality.

It is clear that metrology contributes a crucial factor in testing and maintaining quality. 

As technical components become more and more sophisticated in the future, the measurement technology must also meet ever tougher requirements. 

Meanwhile, it is also possible to combine individual measurement techniques such as tactile measurements with optical methods to balance the advantages and disadvantages of each technique. 

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