Absolute linear encoders breathe new life into VTLs
September 17th 2007 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.
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 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 Mr 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. 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 state.
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