基於虛擬化技術之即時EtherCAT控制平台

Abstract

工具機是目前製造業的核心技術之一，透過自動化的流程，進而達到高效率生產的目的。然而，機台控制器的實現常遇到許多瓶頸，如：一、控制器與機內馬達間的溝通需要大量的頻寬與高度的即時性；二、控制器需要操作友善的使用者介面；三、工程師常需要遠途飛行、親臨現場調整少許的參數以防止機台故障。為了解決前述問題，目前的控制器採用EtherCAT作為場線的通訊協定，但仍無法同時解決上述的即時性問題、操作介面問題，以及長途飛行所耗費的成本問題。 在本論文中，我們提出一個以EtherCAT為通訊基礎的PC-based控制器。透過本論文所提出的控制器架構，EtherCAT的控制流程可以即時地完成。搭配現代虛擬化的技術，使得多元的人機介面（Human Machine Interface）可以在即時性的保證下實現以因應不同的需求而擴充。另外，我們設計了一個遠端監控的工具以透過網路傳送相關的控制參數給機台，使得我們可以遠端控制機台上的馬達。我們透過對EtherCAT從站裝置傳送命令以驗證控制器的即時性、可擴充性以及遠端的可控性。在即時性實驗當中，在有壓力測試的情形下，整體系統最大反應時間的抖動量（Maximum response time jitter）只影響了大約14.28\%。在可擴充性實驗當中，控制器可同時支持最多十台虛擬機器（Virtual Machine）。在多台高負載虛擬機器同時執行的情況下，整體系統反應時間的抖動量壓在22 $\mu$s以下。 我們證明了本論文所提出的遠端機制比一般的遠端控制程式來得有效率。在遠端控制實驗當中，我們遠端工具的封包傳輸量比一般遠端控制程式還少了19.16\%。在系統有大量圖形處理需求時，我們遠端工具的傳輸數據量只影響大約0.032\%。

Machine tool technologies are the key technologies for manufacturing industries. The realization of the machine tool controllers often encounters many bottlenecks and challenges. The communication between a machine tool controller and a servo driver requires high bandwidth and precise time determinism. To face the challenge, EtherCAT is adopted as the fieldbus communication protocol in the existing controllers. However, performance of the computing system can hardly meet the real-time requirement of a machine tool. Second, the controller needs a friendly user interface for operations. The friendly user interface is normally a tradeoff in choosing the underlying operating system for the controller. Third, maintenance cost is high since a field engineer needs to be on-site in person for adjusting controlling parameters in the cases of failure. A remote control mechanism is required to reduce the travel cost in the above cases. In this paper, we present a PC-based machine tool controller supporting the real-time EtherCAT communication protocol. With the proposed design, EtherCAT operations can be performed within a deterministic time period. Diverse HMIs are realized by adopting the modern virtualization technologies with a guaranteed real-time performance. In such a way, the HMI can be scalable to support different purposes. A remote monitor is also designed for a field engineer so he can send proper control parameters to the controller over the Internet. We verify the real-time capability, scalability and remote controllability of the proposed design by conducting several experiments and tests. In the real-time capability test, the maximum differentiate ratio of jitters in our design is 14.28\% than expected, when the system is under a stress test. In the scalability test, the controller can sustain at most 10 VMs at the same time. The absolute jitter is bounded below 22 $\mu$s with duplicate heavy-loaded VMs. We also prove that our remote control design is more efficient than using a Remote Desktop Protocol Service (RDP service). In the experiments, we show that the transmission cost of our design is 19.16\% less than the RDP service. The maximum differentiate ratio of the total packet size in our design is about 0.032\% than expected, when the system is handling heavy graphical events.