New coordinate measurement machines from LK

Louise Davis

A range of CMMs has been introduced by LK Metrology. The new Alterac machines are available in three sizes - 7.7.5, 10.7.5, and 10.7.7 - their respective X,Y,Z axis movements being 700 x 650 x 500 mm, 1,000 x 650 x 500 mm and 1,000 x 650 x 650 mm. Typical applications are likely to be found in the aerospace, automotive, medical and other industries with demanding inspection requirements.

Alterac is at home in an inspection department or on the shop floor as pneumatic mounts isolate the CMM from nearby sources of low frequency vibration such as large machinery. The control may be either stand-alone, or integrated into the machine base with a keyboard on an arm at the side, giving the customer a choice that best suits the installation site. The latter option also facilitates relocation of the equipment once installed. The inclusion of Renishaw encoders with 0.05 μm resolution optical scales for high volumetric accuracy not only leads to outstanding metrology but also provides immunity to the ingress of contaminants.
Measurements taken with a touch-trigger probe at a series of points, ideal for acquiring information on dimensional accuracy, is increasingly being augmented by continuous-contact probing (analogue scanning) and laser scanning to allow high speed collection of data on complex freeform surfaces. Alterac measuring machines are able to deploy all three types of sensor. Such flexible data acquisition boosts measurement throughput to avoid bottlenecks in the metrology department, provides an awareness of component conformance, and meets manufacturers' requirement for a CMM that underpins concurrent engineering practices to speed time to market for new products.
The CMM structure has been optimised using computer aided solid modelling and finite element analysis, particularly within the bridge section, and is finely tuned to maximise stiffness, reduce vibration and provide smoothness of axis motion, all of which are fundamental to delivering high accuracy measurements. Such is LK's confidence in its design methods that it offers a 10 year guarantee covering dimensional stability.
All guideways use LK-designed, low maintenance, pre-loaded air bearings of wrap-around design offering 3.5 times higher stiffness than standard air bearings. They run with a reduced air film thickness for low energy consumption and give repeatable measurement results, even at fast axis speeds. Friction drives provide smooth motion and exact positioning at continuously varying speeds, as well as zero backlash, overload protection and low maintenance costs.
Careful selection of materials in the machine construction includes, as with all LK CMMs, the use of ceramic for the moving bridge and spindle. It is more than three times stiffer than aluminium yet only one-third heavier by volume, resulting in higher machine acceleration and speed. Ceramic does not stress-relieve like aluminium, leading to better long-term dimensional stability. The thermal expansion coefficient of ceramic, which is similar to that of granite but four times lower than aluminium's, makes the structure highly resilient to thermal movement. Moreover, ceramic is three times harder than aluminium, so is more resistant to abrasive wear and indentation.






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