以Ethernet為基礎的即時運動控制技術之研究

Abstract

Ethernet目前已成為一般最常用的區域網路技術，Ethernet由於價格便宜、速度快及可靠度高使其成為商用網路應用的主要選擇，Ethernet目前也逐漸應用於工業自動化及運動控制系統。本論文主要探討應用Ethernet於即時運動控制系統的可行性，以及實現一個以Ethernet為基礎的多軸運動控制系統。由於Ethernet在媒介的存取控制(MAC)是採用CSMA/CD協定，會造成傳輸時間的不確定性，本文將區域網路分成控制網路與對外網路，在控制網路內利用軟體模擬記號(token)的方式，保證不會產生資料傳遞碰撞的情況，確保在固定時間內完成一個即時多工系統所需要的資料傳遞。實現一個PC-Based的運動控制系統，除了即時網路之外，還需要一個即時作業系統，本文分析了幾種主要的即時作業系統，並介紹如何在這些即時作業系統下實現即時Ethernet網路。在實現方面，本文採用RTX即時多工系統，配合支援Ethernet網路的馬達驅動器，建構一個以即時多工作業系統與網路為基礎的多軸運動控制系統。由於時間與經費的限制，本階段是以RS232作為傳輸介面，進行系統的驗證，未來將以RTX的RT-TCP/IP模組進行系統的整合驗證。本論文配合RTX即時串列埠驅動程式，完成了以RS-232為基礎的三軸同動運動控制系統。此外，本文也完成了以PC-RTX與RS-232為基礎的即時伺服系統的整合與實驗，伺服迴路的取樣時間可達到1 msec，伺服控制程序可在PC端完成。在PC端所發展的軟體包含運動控制、即時網路驅動程式和人機監控程式，運動控制系利用DDA的方式規劃運動軌跡，配合LabVIEW完成人機監控程式。

Ethernet has become the most popular LAN technologies for commercial networks due to its low price, high transmission rate, and robustness. Ethernet has also extended its applications to real-time control networks for manufacturing automation systems and advanced motion control systems. This thesis makes a research on the feasibility in application of Ethernet in multi-axis motion control systems. Because Ethernet adopts the CSMA/CD protocol in medium access control (MAC) layer, this will result non-deterministic transmission time. In order to solve this problem, we separate the networks into two subnets: Control Networks (CN) and Corporate Information Networks (CIN). We develop a software-based token ring passing mechanism to avoid collisions in the Control Networks, which can guarantee that data can be exchanged during a specified and deterministic time interval. To implement a real-time motion control in a PC-Based system, we also need a real-time operating system (RTOS). This paper has studied and compared several major RTOS in applications to motion control. We also describe how to implement real-time Ethernet networks in these RTOS. For experimental verification, we adopt RTX in the implementation of the network-based real-time motion control system. In the current development stage, we realize the real-time communication via the basic RS-232 serial interface. This thesis has presented the implementation of a PC RTX-based 3-axis digital motion control system using the standard RS-232. This provides a low cost solution for PC-based industrial controller in realizing advanced motion control systems. We also construct a PC-based real-time servo system based on the RTX, the sampling rate can be up to 1 msec, the control algorithm can be realized using PC-based C language, and the torque control command can be sent to the a digital servo drive via the RS-232. On the PC side, we also develop system monitoring software, motion control software using the DDA algorithm, and interface drivers for LabVIEW. Experimental results are given to illustrate the performance of the constructed system.