Newall absolute linear encoders used in VTL upgrades

Established for 20 years, systems integrator A-Tec Systems Ltd recently completed a contract to retrofit three Morando VLN12 vertical turning lathes (VTLs) at an aerospace manufacturer. The machines were being moved to a new facility, which the customer deemed to be an opportune moment to implement a programme of refurbishment. Specialising in the rebuild and retrofit of CNC machine tools, A-Tec set about assessing the necessary work.

Company partner Chris Hatfield states: "The machines required a complete refurbishment, as they were running Allen Bradley CNCs that were at least 25 years old. From a control perspective, this meant a new CNC, a new panel and new servo-drives."

The bridge axis on an Italian-built Morando VTL carries the X and Z axes. A fundamental flaw in the configuration of the pre-retrofit machines was that any movement of the bridge by the operator would require the DRO reading to be input manually as an offset into the CNC. This is prone to operator error, particularly over three shifts when communication problems were common. The result of any errors could be costly; the special alloys used in the aerospace sector are expensive – some component billets cost several thousand pounds each. Moreover, accidentally sending the quill into the chuck or component could destroy entire features and potentially scrap whole parts.

Twin requirements

Mr Hatfield says: "The answer was to fit an absolute linear encoder to the bridge. There were two main requirements here: firstly the encoder had to offer good resistance to potential contamination in the form of swarf, oil and coolant; and secondly it had to be easy to mount. In both cases a conventional glass-scale type encoder did not fit the bill."

A-Tec specified a Newall SHG-AF absolute linear encoder. The design of these linear encoders allows installation in almost any position, unlike glass-scale linear encoders that usually need to be installed with the lip seal facing downwards to prevent contamination. Self-aligning fixing brackets permit virtually effortless scale mounting, needing only a single hole for each set of brackets.

A-Tec's preferred CNC for the VTLs was Fanuc. With this in mind, the selection of the SHG-AF was even more certain, as it has a protocol that is proprietary to Fanuc and available on the majority of Fanuc control systems. The Fanuc CNC makes a request for positional data and the encoder responds correctly with data within a strictly controlled time.

Developed to meet a wide range of feedback applications, the SHG-AF absolute linear encoder provides a true absolute position immediately upon power-up. The encoder does not use batteries or static memory to retain the positional data. True position can be re-acquired once power is applied, regardless of duration or power-off movements.

Interface to CNC

Interface software developed by A-Tec means that any offset movement of the bridge by the operator (even in-cycle movement) is now relayed to the CNC automatically.

Mr Hatfield says: "On each machine we mounted the Newall encoder in an unprotected position on the side of the column, safe in the knowledge that any contamination would not affect its performance. What is more, thanks to Newall's two-point suspension system, there was no need to provide a machined surface for mounting, or create a spar using spacers."

According to Mr Hatfield, since the encoders have been fitted there have been no incidents of bridge-related failures, which previously were the biggest single contributor to component damage.

About A-Tec Systems

A-Tec Systems successfully manages a diverse range of projects, varying in complexity from servo and CNC control retrofits to bespoke turnkey machines designed from the ground up. In each case the control system, servo drives and interface software are designed specifically to meet customer needs.