Portable measuring arms from ROMER, also known as articulated arms or portable coordinate measuring machines (CMM), are used to generate very precise geometric information. These instruments capture the structural features of an object for use in quality control, for digital representation and/or for rapid reproduction.

The portable measuring arm is an easily transported, mobile instrument for the measurement of high-precision 3D coordinates within a spherical measurement volume centred around the sensor.

The user fastens the base of the measuring arm with the help of a tripod or a base plate in an absolutely stable position near the measured object. This highly stable base is one of the main prerequisites for high-precision measurement results.

One end of the measuring arm is fitted with a measuring probe. This may take the form of a mechanical probe for point measurement or a laser scanner capable of supplying tens of thousands of measured points per second. Other types of measuring probes can be used with a portable measuring arm. In principle, it is possible to connect any form of hand-guided measuring probe in any circumstances where the desired measured values have to be linked to high-precision positional data.

The measurement principle of the portable measuring arm is based on a combination of angular measurements (also known as axes or joints) and distance measurements. Each angle measurement is linked with the associated distance information using the principle of the polygon method. The combination of all the angle and distance information gives rise to a unique, high-precision 3D coordinate position of the measuring head.

The operator guides the portable measuring arm within the measurement volume and triggers the actual measurement as soon as the measuring tip is in the correct position.

Variants

The user has a choice of two different types of ROMER portable measuring arms: measuring arms with six axes and measuring arms with seven axes.

Six-axis measuring arms are mainly employed for tactile point measurement. Seven-axis measuring arms are usually used in conjunction with laser scanners. Laser scanners, but also other types of measuring probes, have to be able to rotate about their own axes to capture the data efficiently and quickly. To be able to do this, the portable measuring arm must have an additional (seventh) rotational axis.

Applications

The greatest advantage of a ROMER measuring arm is its portability. It can be used wherever the object to be measured is located. Typically the measured objects range from a few centimetres up to several metres in size, with dimensional tolerances in the 50 micron zone.
ROMER measuring arms are very common in the automobile industry, but are also used in shipbuilding and railway engineering.

Typical applications include the inspection of

• Production parts by scanning or single point measurements
• Press forms for wear
• Fixtures in process engineering

And three-dimensional capture of components for reverse engineering as CAD data or as the basis for rapid prototyping.

Trends

Through the use of new materials, ROMER measuring arms are becoming lighter without having to compromise on the requirements for accuracy. Furthermore, the latest arms are available with specific electronic interfaces, which allow the arms to integrate with the widest range of measurement sensors. The latest generation of ROMER measuring arms is fitted with angular encoders, which do not require to be referenced before measurement. This brings some enormous advantages for measuring in the tightest spaces and reduces start-up time.

Where measuring arms are always used in combination with a special measuring probe (e.g. laser scanner), stringent production quality assurance requirements call for all components to be specified and certified as a complete system. The latest ROMER products are also leading the way in this field.