Scanning probe speeds co-ordinate measurements

A novel analogue scanning probe offers the promise of both higher throughput and better accuracy for users of co-ordinate measuring machines.

Manufacturers wishing to inspect their components on a co-ordinate measuring machine (CMM) more quickly and to a higher degree of accuracy than is possible using a touch-trigger probe may specify the new option of an analogue scanning probe offered by CMM manufacturer, LK Group.

The company will provide this latest type of constant-contact probe for its own CMMs or any other supplier's measuring machine using LK's latest range of motion controllers.

The system contains new scanning algorithms for both known and unknown profiles, as well as automatic recovery tools for robustness of operation.

To maximise performance, calibration tools are included for full error correction of the analogue probe.

This extensive additional functionality is available using LK's standard software products.

As with so many developments in metrology, the move towards analogue probing has been led by the automotive industry which is constantly looking to reduce costs associated with manufacturing.

For example, engine, gearbox and powertrain inspection applications are emerging in car plants worldwide.

The aerospace industry has also been quick to capitalise on the technology.

Other applications requiring high measuring speed and accuracy exist in turbine blade manufacture, mould and tool making, the medical sector and many other industries that require reverse engineering, where advantage can be taken of the more comprehensive data that is generated on the shape of a component as well as the position of machined features.

Availability of this additional information is the reason for the willingness of certain manufacturers to pay a little extra for analogue probing.

Commented Alex Chisholm, Technical Director of LK, "It allows users to get closer to their products and feed more comprehensive data back to their CAD departments so that designs may be continually improved".

"The other major benefit is in quality control of the process being used to manufacture a part, rather than of the part itself.

The wealth of information that comes from an analogue probing routine provides extra data for more comprehensive statistical analysis".

"The resulting SPC enables better control over manufacture, allowing, for example, earlier detection of tool wear.

In theory you should never produce scrap, as all features on a component should be maintained within tolerance all of the time".

LK's development work was carried out in collaboration with a US automobile manufacturer using a car cylinder head as the component under test.

The industry average time for inspecting this part using a touch-trigger probe on a CMM is 12min.

By the time LK's analogue system was perfected, the same cycle was completed in under 7.5min, using scan velocities exceeding 14m/min over the four valve seats, guides, six cam bores, the front and rear planes and gasket face.

With time savings of this order - nearly 40% for the above cylinder head application - it is easy to see the cost benefits that may be derived in mass production environments using SPC techniques, or in plants operating 100% inspection.

Apart from a reduction in quality control staff, in many cases companies are able to operate with fewer CMMs, saving capital expenditure as well.

Concluded Chisholm, "Low force analogue probes offer all the versatility of touch-trigger probes, including toolchanging, plus some extra benefits such as the ability to use longer styli.

It is also faster and provides more comprehensive data, albeit at a slightly higher cost".

"Currently less than 1% of CMMs are fitted with this technology, but I predict that as its advantages become more widely recognised, a quarter of machines will be thus equipped within the foreseeable future".

(This was Engineeringtalk's Top Story on 22 November 2002).

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