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Linear encoders rejuvenate lathes

A Newall Measurement Systems product story

Edited by the Engineeringtalk editorial team Aug 16, 2007

A-Tec Systems recently completed a contract to retrofit three tired Morando VLN12 VTLs at an aerospace manufacturer.

Retrofitting Newall absolute linear encoders to three ageing vertical turning lathes (VTLs) being used at a UK aerospace manufacturer has injected new life into the machines and helped eliminate expensive component scrap and rework rates through improved accuracy and repeatability.

Established for 20 years, Wigan-based systems integrator A-Tec Systems recently completed a contract to retrofit three tired Morando VLN12 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, ISO9001 registered A-Tec set about assessing the necessary work.

"The machines required a complete refurbishment as they were running Allen Bradley CNCs that were at least 25 years old", explains company partner Chris Hatfield.

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 would be 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 at the end user cost several thousands of pounds each.

Sending the quill into the chuck or component could destroy entire features and potentially scrap whole parts.

"The answer was to fit an absolute linear encoder to the bridge", explains Hatfield.

"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 didn't fit the bill".

A-Tec deemed the optimum solution was provided in the form of a Newall SHG-AF absolute linear encoder.

The design of these linear encoders allows installation in almost any position, unlike glass-scale linear encoders, which 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.

The SHG-AF 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 state.

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 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.

"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" continues Hatfield.

"What's 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".

Hatfield says that 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.

A-Tec Systems successfully manage 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.