Solutions for web length, position and speed feedback

For many roll feed applications, determining the length of the web material is an important part of the machine process. This can be as simple as a requirement to measure the overall length of a web or, for instance, to precisely align multiple printed layers or synchronise a stamping operation on a section of the web material.

Wachendorff’s LMS series length measurement systems combine its ruggedised industrial shaft encoders with an integrated measuring wheel that is friction driven by direct contact with any roll cylinder in a cantilevered arm arrangement, providing positional feedback with a linear resolution from 1 millimetre to 8 microns. Rather than source positional information from a servomotor- or motor/gearhead-mounted encoder, which would have some degree of lost motion or hysteresis related to the encoder’s proximity to the actual reference point, Wachendorff’s LMS length measurement systems are directly located at or very close to the working point on the web to provide optimal accuracy.

With full support in the UK from Variohm EuroSensor, Wachendorff’s exclusive distribution partner, a wide range of custom matched length measurement systems are available that will allow the customer’s control system to source length, position, and speed information from incremental or absolute encoders through a wide choice of optional interfaces.

For all Wachendorff length measurement systems, the encoder and measurement wheel assembly is mounted on the spring-loaded arm which includes an integral adapter plate that facilitates direct mounting on the customer’s machine – or the system can be supplied with an application customised angle bracket. The contact pressure between the measuring wheel and the web material is completely adjustable thanks to a spring-loaded cantilevered arm design that includes a patented tooth grid mechanism, allowing simple and repeatable preload force adjustment in steps of 5 N.

The assembly also compensates for uneven fluctuation in the measured web material whilst ensuring complete unbroken contact. Practically any type of web material can be accommodated with several measuring wheel surfaces available. As the length measurement system can be easily swung from its fixed position to a resting position by adjusting just one captive screw, setup and adjustment is made easy with minimal delay in material changeover and maintenance time.

The LMSCA series is an ultra-compact length measuring system that includes Wachendorff’s WDGP series, 36 mm diameter incremental encoders in a variety of mounting configurations for use with measuring wheel diameters typically from 145 to 200 mm. With a resolution up to 16,384 ppr, the LMSCA can achieve web length measurement down to 12.5 microns per pulse.

The encoder delivers A, B, and N channels with inverted signals from a 4.75 to 32V DC supply, in TTL or HTL as well as a choice of CAN, J1939, SSI or RS485 outputs. An M12 connector makes installation straightforward. For larger systems, Wachendorff’s LMSMA series typically include WDGI series 58 mm diameter incremental encoders for resolution to 25,000 ppr and 8 microns per pulse linear measurement – with measurement wheels from 200 to 500 mm diameter.

For both product types, the encoder’s IP67 protection rating (IP65 at the shaft input) and high radial and axial force specification guarantees durability in any machine setting.

Whilst these are typical encoder configurations, any type of Wachendorff encoder technology may be fitted to the length measurement systems including absolute encoders.