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Affordable Standard CMM Range Gains Additional Accuracy

Manufacturers wishing to inspect components machined to tight tolerances, but unwilling to invest in an expensive, ultra-high-accuracy coordinate measuring machine (CMM), now have the option of selecting an ALTERA C HA (high accuracy) from LK Metrology and available in five sizes.

The ceramic-bridge machines are constructed from the same component parts as the standard LK ALTERA C CMM range, but are optimised during build at the company’s Derbyshire production facility to deliver 16 percent higher accuracy during a measuring cycle, with 13 percent improved repeatability and 50 percent more scanning accuracy. Volumetric accuracy is from 1.3+L/350, repeatability from 0.0013 mm and scanning accuracy from 0.002 mm.

When implementing design improvements to the ALTERA C HA, particular attention was paid to upgrading the moving bridge. The spread of the air bearings supporting the main drive leg has been widened to increase the stiffness of the bridge assembly by 17 percent overall, which is particularly beneficial during high-speed movements. Advantages to the user are considerable, as measuring uncertainty when chasing tolerances down to microns is significantly better. For the same reason, the bearing mountings have been further stiffened and their alignment improved. Due to the increased dynamic forces in play when measuring on the fly, the new design is especially helpful when using a scanning probe.

Finite element analysis on the ALTERA C (left) and the ALTERA C HA (right) demonstrates that deflection throughout their structures is measured in microns. There is a 17 percent overall improvement in ALTERA C HA bridge stiffness compared with the standard ALTERA C due in part to a new design of main leg.

The pre-loaded, wrap-around air bearing configuration runs with a reduced air film thickness for low energy consumption and gives repeatable measurement results, even at fast axis speeds. Friction drives provide smooth motion together with exact positioning at continuously varying speeds, as well as zero backlash and overload protection.

Multi-sensor capability is provided, with the Renishaw PH10M motorised probe head able to deploy a touch-trigger probe, scanning probe or laser scanner. LK’s proprietary, DMIS-based, multi-sensor CAMIO software enables programming and measurement based on 3D CAD data as well as comprehensive reporting.

The five sizes of ALTERA C HA have a measuring envelope ranging from nominally 700 x 650 x 500 mm for the smallest CMM up to 1,500 x 850 x 650 mm for the largest. The machines are compact for the size of their respective measuring volumes and are also fast, accelerating at up to 1,390 mm/s/s for high inspection efficiency. They are equally at home in an inspection department or on the shop floor, especially as pneumatic anti-vibration mounts can be specified to isolate the CMM from nearby sources of low-frequency vibration, such as large machinery. Maintenance costs are low and all models carry an unrivalled 10-year accuracy guarantee covering dimensional stability.

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