October 2009

Going to Great Lengths with HEIDENHAIN Scales

By Chris Weber, Product Manager,
Machine Tool

When it comes to big machines, and I mean really big machines, feedback requirements can be challenging. Traditional feedback methods included systems such as “rack & pinion”, low accuracy magnetic tapes, draw wire encoders, and glass butted to glass, but all of those systems involved compromises, typically with regards to accuracy and long term stability. For over 20 years, HEIDENHAIN has been making sealed linear encoders for lengths of up to 100 ft and beyond, and doing so without compromise.

HEIDENHAIN’s longest scale systems are the LBs which utilize a reflective stainless steel tape with a gold graduation (currently 40 µm) as the measuring standard providing a one-piece measuring system with 5 µm /meter accuracy. A series of aluminum extrusions are used to house this tape providing protection from contamination and an accurate mounting surface. Two end caps secure the tape and provide a pre-determined tension factor. The beauty of stainless steel is that it has a similar coefficient of expansion as the machine itself and in many cases the workpiece thus mitigating thermally induced errors.

The LB system is available in standard version and mirror image version (for gantry applications), and with its distance-coded reference marks, a very short traverse will re-establish reference position. Gone are the days of moving long axes to one end of the machine to reestablish home position.

The aircraft industry has been the chief recipient of the benefits of this system in recent years in applications from wing spar manufacturing, to drilling/riveting, carbon fiber placement and waterjet cutting. With aircraft getting larger (A 340 and 787), the LB 382 scales system has gained in popularity and market share. HEIDENHAIN Corporation recently sold and installed two of these LB systems in Michigan, each with a travel of over 240’ (look for a feature article on this application in a future issue of HeidenhaINFO).

In fact, in the last 20 years, HEIDENHAIN has sold over 130 miles of LB scale systems around the world, which is roughly equivalent to driving from Los Angeles to San Diego or Washington DC to Philadelphia.

So what does the future hold? Currently under development is the absolute version of this scale which will feature the purely serial EnDat 2.2 interface providing not only long measuring ranges but also no requirement to reference, as well as the ability to transmit not only position but also additional data between the measuring and control systems. Stay tuned.

 

Additional Resources

• More information about HEIDENHAIN linear scales
• More information about EnDat 2.2