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Rigid SBD actuator guides extraction system on diamond lathe

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With the need to equip its Ultra-Precision diamond lathe with an effective swarf extraction system, the Ultra-Precision Structured Surfaces (UPS2) Department at Cranfield University sought the help of Glyndwr Innovations. The result was the development of a bespoke, stand alone system whose extraction head is guided by a HepcoMotion Sealed Belt Driven linear actuator (SBD), specified for its accuracy, rigidity and suitability for use in hostile environments.

Rigid SBD actuator guides extraction system on diamond latheGlyndwr Innovations was originally one of the Welsh Government Technium Optic centres set up to develop and promote high technology. It retains a close association with Glyndwr University but is now an independent company that undertakes a wide range of opto-mechanical project work. This is sourced from both commercial companies and other research-based centres of excellence such as Cranfield University.

The lathe in the UPS2 Department at Cranfield is used to cut highly accurate patterns into very high-value copper drums or discs, which become the master patterns for the manufacture of optical films for advanced display screens and other optical films. Swarf from the process had been compromising the quality of the turned surfaces, so the introduction of an extraction system became imperative.

Working in partnership with the UPS2 Department, Glyndwr Innovations proposed a standalone system whose construction was initially based on off-the-shelf components for both the extraction process and the linear motion required. Ultimately, however, to achieve the performance required, the majority of system elements were custom designed and locally manufactured. One exception was the SBD linear actuator, a standard modular product from HepcoMotion.

The SBD linear actuator was needed to enable the system’s extraction hose and nozzle to track the toolpost on the UPS2 diamond lathe as it traversed the work piece. Initially the extraction elements were specified – an extendable rigid pipe, a flexible nozzle connection and an adjustable nozzle with noise reducer. Assembled, they created an approximate mass for actuation of around 30kg and with this value established, the next step was to source the most suitable linear motion system.

High loads and demanding duty cycles

Several linear motion suppliers were rejected on the grounds of lead time and cost. Ultimately HepcoMotion was chosen. The company’s Sealed Belt Drive was judged to meet all the design and performance needs of this application and it brought the added benefit of being sourced within the UK; HepcoMotion manufactures all its products for the Global market in Devon. The HepcoMotion Sealed Belt Drive (SBD) was designed for applications characterised by high loads and demanding duty cycles. It also introduced a brand new method of sealing that proved an important quality for the design requirements given to Glyndwr Innovations.

Andrew Sayle, a Senior Mechanical Engineer with the company explains: “As well as potentially damaging coolants, cutting fluids and cleaning agents, the swarf coming off the machine can often be extremely fine, down to micron level. Whilst the extraction system is very efficient there had to be an additional safeguard for keeping the swarf away from moving parts.”

For several reasons the inherent rigidity of the SBD was a significant benefit to the design team. Firstly it allowed them to achieve two-axis motion without the need for an additional structural member, reducing the overall mass to be actuated.

The stiffness of SBD also contributes to the performance of the UPS2 diamond lathe. The machine is capable of turning surfaces with less than 2 nanometers Ra value, but this quality is impaired by any vibration. This is the reason why the extraction system is isolated from the lathe, and it was a key driver in the specification of the supremely rigid HepcoMotion SBD.

Limited space

Space constraint was another design consideration. As the lathe operates in a special enclosure that is environmentally controlled to minimise changes in humidity and temperature, space for additional equipment is limited. Andrew Sayle continues: “This severely restricted our ability to design a suitable framework onto which everything could be mounted. The stiffness, weight and size of the SBD drive allowed us to work within these limitations and reduce the size of the framework to fit in the enclosure.”

The positioning accuracy required for this application was +/-1mm, well within the capability of the SBD. The reason for this specification was not to do with tracking process, however, as the 50mm diameter nozzle follows a 1mm tool tip, providing a considerable positioning margin. It was to ensure the nozzle did not come into contact with the extraction system and risk potential damage.

The extraction system designed by Glyndwr Innovations has now been assembled and fully tested. It just remains for a gap in the production schedule to be identified by Cranfield University for it to be integrated into the lathe enclosure.

To find out more about the HepcoMotion Sealed Belt Driven linear actuator (SBD), go to www.hepcomotion.com.

 
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