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Unlocking Your CMM Error Map
Unlocking Your CMM Error Map

Unlocking Your CMM Error Map

Added to MTDCNC by Measurement Solutions on 04 August 2016

A new “Error Map in a Box” from Measurement Solutions unlocks the error map on any CMM

Often regarded as the standard for measurement in most manufacturing companies, co-ordinate measuring machines (CMM’s) provide the highest level of measuring accuracy across a wide range of components. In order to achieve that accuracy, machines must be maintained and calibrated on a regular basis, with internationally recognised standards now in place to ensure that your machine is measuring as expected.

If you were to travel back a short period in time, you will find that the major components of most CMM’s were built from granite, enabling each of the guideways to be manufactured mechanically straight and square to extremely high tolerances. While this guaranteed high accuracy for the end-user, it also made CMM’s expensive and quite slow when measuring, even at full speed. Such machines still exist and can be found in daily use, due to their longevity and reliability. In contrast, modern day CMM’s are designed with measuring speed and price in mind. As the market demands lower cost machines, manufacturers have to compromise on build quality by utilising lower grade and lightweight materials, such as aluminium. Despite this, users still expect CMM’s to be as accurate, if not more accurate than ever before, even though the materials used and the basic mechanical accuracy of modern CMM’s does not come close to that of the old granite machines. In response, CMM manufacturers developed a solution based on software compensation – the CMM Error Correction Map, a complex file of adjustment data that compensates for all of the errors attributed to a CMM’s mechanical geometry.

The accuracy of a typical 3-axis bridge CMM is susceptible to 21 potential error sources, involving parameters such as scale, straightness, pitch, roll and yaw of the 3 primary axes, plus the squareness errors between the axes. Due to the mechanical build quality of the machine and the materials used, these values vary depending where the probe is located in the measuring volume. The CMM manufacturers are able to create a matrix of compensation values, which can be applied to the probe location as it moves around in real-time. In this way, the machine scale readings are automatically compensated by the machine’s measuring software, often by several microns, to adjust the values to a corrected and accurate 3D location.

However, as the compensation has to be done through software, many manufacturers saw an opportunity to use the error map to secure future service revenues. As there is no ISO standard or general “open format” for error map files, it is often the case that the error map file on a CMM is unique to the machine manufacturer or the software version, and is then password protected, software encrypted, or requires a specific application software to open the file to gain access to the contents if they ever need to be changed following an annual certification. While it is possible for any CMM to be verified to national standards by any CMM service organisation, many CMM users are effectively forced to use the original CMM supplier in order to have their machine adjusted should there be any repairs or adjustments necessary – until now.

Accredited by UKAS to carry out the verification of CMM’s to ISO10360 standards, Measurement Solutions of Derby have been inundated by customer requests to find a way around the “locked error map” on their CMM’s. Working in partnership with other expert CMM service companies having the same issues, the company is now offering the MapBox3D “CMM error map in a box”, which enables CMM users to be unlocked from the error-map-trap that is faced by many today. The device acts like a “black box” that can be connected to most CMM’s, providing the company with full access to create, read and modify the built-in CMM error map, completely removing the need to depend solely on the original supplier of your CMM. The Managing Director of Measurement Solutions, Iain Caville, sees this as a major development in the CMM service industry; he comments “So many of our existing and potential customers have expressed concern and frustration due to being trapped by a locked error map, that we felt we had to do something. With the customer’s error map locked down, CMM suppliers have been able to protect potentially years of service business, in many cases quite unfairly and without justification, and often at an inflated price. Even though the error map is owned by the customer, as it is unique to that customer’s machine, they have no choice as to which company is able to correct the machine when required. Our customers expressed a desire to have the choice to use a third party service partner like Measurement Solutions, in exactly the same way they do for their existing production machine tools. The new MapBox3D tool has been produced to provide that possibility”.

Installation of the MapBox3D is relatively straightforward, as it can work with any make of CMM, any make of CMM controller, any measuring software, and any combination thereof. An engineer from Measurement Solutions will perform a series of simple measurement tests before installing the box, and once the system is installed and configured, the same tests will be performed again to confirm that the machine is ready to use. In some cases, installation may result in the machine having a better accuracy than before, due to the additional capabilities of the MapBox3D’s advanced error mapping capabilities. Measurement Solutions also point out that in many cases they can provide a UKAS verification of any CMM without having to resort to using the MapBox3D, as it is only needed when a locked error map needs to be modified due to changes in the geometry of the machine. Measurement Solutions see this unique tool as the perfect solution in cases where adjusting a locked error map is the only option available to the customer. Alternatively, even if it is not actually required to certify their CMM, some customers will opt to install the MapBox3D anyway just to be able to free themselves from only having one calibration option (the OEM), thereby unlocking the CMM and giving them the freedom of choice to use any CMM service provider in the future.

The MapBox3D is only available in the UK from Measurement Solutions, however the company is currently looking at the possibility of providing the system to other 3rd party service providers in the UK. Measurement Solutions offers a complete range of CMM services including UKAS certification of CMM’s and portable measuring arms, general maintenance and breakdown services, machine relocation, plus software and hardware retrofits to all makes of CMM. 

 

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