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When measuring large objects such as tractors, it is a challenge to use traditional coordinate measuring machines (CMMs). Not only a large and expensive CMM is required, any position change of the measurement object during the inspection measurement will result in losing the alignment. These challenges are met by the Metris K-Series optical CMM1, a portable optical CMM that auto-aligns permanently the measurement object by tracking reference points attached to the object.
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As such, this uto-alignment functionality obsoletes the requirement for manual and time consuming re-alignments. The K-series system comprises a camera system with 3 camera units, a hand-held SpaceProbe for touch probe measurements and a portable controller with measurement and analysis software.
The key decisive factor to select the K-series portable system was the combination of extended measurement volume, flexibility, and both static as well as dynamic capabilities of the system," explains Product Engineering Manager Gerald Werner from the department Development Chassis of John Deere tractor manufacturing in Mannheim. "Another important benefit is the possibility to measure the prototypes directly in the workshop without having to transport them to the metrology hall. This saves a lot of time and enables us to fulfill the time-to-market requirements much faster then previously. In the past, measuring complete tractors was almost impossible for us. Only single parts or subcomponents of the complete vehicle were measured. The so-called "auto-alignment" is an additional advantage towards an articulated arm CMM and another reason for us to select a K-Series system".
By using three reference markers on the object, it is possible to measure all small movements dynamically and in an absolute way. The main advantages we get from the auto-alignment is that, when the tractor position changes, the initial alignment measured with the SpaceProbe is automatically updated. The auto-alignment also enables to reposition the camera system in order to measure hidden areas or to even further extend the measurement volume.
The 17m3 measurement volume easily covers the cabin and a tractor side in a single position. The ergonomic hand-held SpaceProbe allows the user to freely measure around the whole vehicle. The SpaceProbe can be equipped with long, automatically recognized touch probes for e.g. interior measurements. By relocating the camera system, the user can reach any point on the tractor while using the initial coordinate system. The portability of the K- series enables frequent position changes.
An additional advantage is that beside the application in coordinate measurement technology, the K-system is also specialized in dynamic measurements for e.g. suspension analysis or structure movement analysis.
Applications
John Deere uses the K-System for R&D purposes in Product Engineering. With the SpaceProbe, the user can easily compare complex parts with virtual part data (CAD). The K-System provides fast and accurate dimensional information enabling a comparison towards the nominal data in the inspection software.
When it comes to the testing applications, the camera system can detect the smallest movements of the structure by measuring the small infra-red K-LED’s The dynamics software „DMM" outputs functional correlations, enabling to identify dimensional deviations as well as variations in the structure of the components.
Highly precise
Our demand for 0.1 mm of accuracy over the measurement rage is easily fulfilled by the K-system." says Michael Biedermann from the Product Engineering workshop. The K-system is pre-calibrated and can be fine-tuned by the user at any time. Even the smallest influences (e.g. by temperature) can be compensated.
Anton Nirenberg, likewise from the Product Engineering workshop, attaches particular importance on high functionality and reliability: "Our workshop is often flooded with sun, but the K600 environment light filtering function operates excellently." This filtering function optimizes the applicability and robustness for measuring in all kind of industrial environments.
Investing in metrology’s future
An important benefit is that beside the traditional SpaceProbe, a 3D surface scanner- the Metris K-Scan- is available for the K- Series system. This K-Scan is a joint development using Metris and Krypton technology and enables to rapidly digitize surfaces with a handheld device.
1 The K-series system is produced by Metris that has acquired Krypton in April 2005.
Download: John Deere uses Optical CMM for inspection of agricultural machines (PDF file)
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