Browsing by Author "Zhou, Hui"

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    Creation of a control system for plasma delivery to increase automation and stability.
    (2016-09) Zhou, Hui; Endrino, José L.; Jourdain, Renaud
    Surface figuring of extremely large telescopes (ELT) addresses a highly challenging manufacture issue for the field of ultra precision. [1] High form accuracy and rapid fabrication are needed for ELT primary mirror surface figuring. In Cranfield University, Plasma Figuring (PF) [2] is used as a main method to correct ELT mirror surface figure error. The non-contact based material removal process brings PF to a high level of accuracy (under 1nm RMS level). Some other great features of PF are the capability to work at atmospheric pressure, the low-cost of consumables. Other figuring methods make use of vacuum chamber (ion beam Figuring) which are expensive. On the other hand magnetorheological finishing requires expensive consumables. Although PF is dominant for the surface correction of metre scale surfaces, challenges still exist to improve the automation and stabilization of the plasma source. In the context of ever-increasing dimensions of optical components, there is a need for improving the robustness and securing the performance of the unique Plasma Delivery System (PDS) available in Cranfield. The current PDS is based on an inductive output L-type radio frequency (RF) circuit, Inductively Coupled Plasma (ICP) torch and computer numerically controlled (CNC) motion system. The combination of optical component surface dimensions and the material removal rate of the plasma jet lead to significant processing duration. Based on the existing PDS for our unique Plasma Figuring machine named Helios1200, we designed an enhanced PDS version. The novel design was given the capability to detect phases and automatically tune the impedance of the plasma. The novel control capability is aiming at secure the process determinism, assisting the machine operator by tuning key electrical components of the RF network and monitoring crucial processing parameters. Furthermore, specific assistances were provided during the three identified processing phases (ignition phase, regular operation and critical circumstance) of the plasma processing. Our design addressed particular functions on each phases to ensure an optimum performance during the Plasma Figuring process.
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    ItemOpen Access
    Design of a motorised plasma delivery system for ultra-precision large optical fabrication
    (IOP, 2020-09-02) Zhou, Hui; Bennett, Adam; Castelli, Marco; Jourdain, Renaud; Guo, Jiang; Yu, Nan
    A unique plasma figuring (PF) process was created and demonstrated at Cranfield University for manufacturing extremely large telescopes. The atmospheric pressure processing is faster and more cost-effective than other finishing processes; thus, providing an important alternative for large optical surfaces. The industrial scale manufacturing of thousands of ultra-precision metre-scale optics requires a robust PF machine: this requirement is achieved by making the plasma delivery system (PDS) performance repeatable. In this study, a dedicated PDS for large optical manufacturing was proposed to meet the industrial requirement. The PDS is based on an L-type radiofrequency (RF) network, a power supply, and an inductively coupled plasma torch. However, the complexities of these technologies require an in depth understanding of the integrated components that from the PDS. A smart control system for the modified PDS was created. This novel control system aims to make the characterization process deterministic: by automating the tuning of critical electrical components in the RF network, which is achieved by the use of in-line metrology. This paper describes the main design aspects. The PDS was tested with a good correlation between capacitance and RF frequencies. The robust PDS design enables a stable discharge of plasma with a low deviation of RF signals during the total 15 hours' tes