Linear encoder saves cost by reducing waste

When Special Metals Wiggin Ltd wanted to improve process repeatability and reduce waste from its cut-off operations for high-nickel, high-performance alloys, the company turned to an established sawing machine supplier Burkett Cutmaster and its strategic partner and special-purpose machine builder Ripon Technical Services. The result was an automated sawing and bar/profile handling system that exceeded the company's existing manual cut-off capability in terms of reliability and accuracy, thanks largely to a MAG-TS incremental linear encoder supplied by Newall Measurement Systems.

With over 60 years experience between them, Birkett Cutmaster and Ripon Technical Services have developed a healthy niche in the design, manufacture and commissioning of cut-off, special-purpose machinery and materials handling equipment to suit a broad range of industrial and analytical environments and applications. The project for Special Metals Wiggin involved a combination of pooled expertise, as Ripon's managing director Andrew Stott explains: "Together we have done a number of cut-off saws with end-stop capability. We are gaining a strong reputation for this kind of project, which in this instance involved producing a system that would replace manual methods currently being deployed by the end user."

With many special alloys for the aerospace and power generation industries, such as Inconel, Incoloy, Nimonic and Monel, costing up to £25 to £30 per kilogram, any waste can be expensive. Prior to installing the new cut-off machine, Special Metals Wiggin was using manual methods that carried a tolerance of several millimetres. The potential savings that would be generated by implementing an accurate, repeatable cut-off process were plain to see.

Higher accuracy required

Mr Stott says: "We could have used a traditional 'hard stop' to control the cut-off length, but due to the variety of sections involved (bar, profile, etc), the customer was keen on achieving greater accuracy with respect to end-stop positioning."

Having had Newall linear encoders retrofitted to two borers in the Leeds machine shop of the 18-employee company, Ripon Technical Services made Newall the first port of call again. A cost-effective Newall MAG-TS incremental linear encoder was selected, which comprises a flexible tape scale mounted on a fixed machine surface. A reader head, which is fastened to the moving part to be measured, is arranged such that it travels in alignment with the scale. A stainless steel cover strip is supplied to protect the encoded tape.

The tape scale is made up of a flexible magnetic rubber strip, sandwiched between a backing strip and a cover strip made from thin stainless steel. The encoded tape contains magnetic poles that are placed at 2mm intervals along its length. As the incremental sensor in the reader head passes over the tape, the magnetic field is converted to an electrical signal, which is sampled by a micro controller. The field between the markers varies sinusoidally, from which the micro controller can determine the position of the sensor in relation to each marker. The analogue information is converted into an industry-standard RS422 (TTL) differential quadrature signal.

Versatile and flexible

For applications where the mounting surface is uneven, the tape scale can be attached to an optional twin-track backing bar, supported by stand-offs, while the flexible nature of the tape scale makes the encoder suitable for rotary as well as linear applications.

In terms of accuracy, the MAG-TS encoder (+/-0.025mm) far exceeds any applications required by Special Metals Wiggin. Installed in February 2007, the capability of the system is well inside the cutting tolerances of 6mm, potentially saving the company several millimetres of material with every cut.

Furthermore, the repeatability of the special machine with its MAG-TS encoder ensures there is no longer any danger of cutting the stock short, which, of course, can result in the whole length being wasted.

The MAG-TS linear encoder is part of the Newall family of linear encoders that includes a range of inductive linear encoders sealed to IP67. The devices are available in incremental versions.

Ripon updated the proven Birkett Cutmaster saw design to meet current legislative requirements and also integrated three conveyors, measuring, guarding, electrical control and transfer systems to provide a bespoke full turnkey system.