手輪馬達驅動式電動輪椅之控制系統的研發

Abstract

本研究開發一用於手輪馬達驅動電動輪椅之控制系統，目標係使此輪椅上配備之手輪馬達在速度調控或追蹤的動態響應達到上升時間短、超調量小，並具有最小顫動之特性。此控制系統採用主僕式，上、下控制器之架構，本研究中研發的項目包含人機介面、搖桿訊號處理、輪椅運動控制、手輪馬達速度控制、以及通訊協定等。透過上控制器之差速演算法，計算出左右輪之期待轉速；下控制器以此為參考轉速，進行手輪馬達之閉迴路速度控制。本研究基於比例積分微分速度控制，於下控制器加入參考輸入前饋、事件觸發取樣、與切換模式策略等，重點在探討手輪馬達應用不同速度閉迴路控制架構，在馬達空載及輪椅路測等情況下之性能。事件觸發取樣的概念係以霍爾感測器訊號之變化作為控制器運算之觸發條件，取代以固定時間間隔取樣的方式。運用切換控制模式的策略，可針對馬達啟動、追蹤速度、與剎車等三個模式設計不同的控制方法。實驗結果顯示，以本研究所提出的控制器能有效降低最大超越量及速度波動，同時維持可接受的上升時間，尤其在低速的調控或追蹤。運動控制方面，利用最小顫動路徑的最佳化概念，求得一條具有舒適性之物理意義的速度曲線，未來可建置於上控制器之速度產生器中。參照中華民國國家標準之輪椅指導綱要第六節中之測試指標，應用本研究提出之控制系統，手輪馬達驅動式電動輪椅可以達到與市售產品相當之速度與加速度性能表現，並符合標準中規範之測試指標項目。

This study is to design a control system for the electric wheelchair powered by rim motors (rim motor wheelchair). The goal of this study is to achieve the dynamic responses with short rise time, small overshoot and minimum-jerk in both regulation and tracking control of rim motors. The control system is based on master-slave architecture which consists of upper and lower controllers. Human-machine interface, joystick signal processing, wheelchair motion control, motor speed control, and the communication protocol are developed in this study. The desired speed of each motor is computed according to a steering algorithm in the upper controller, and the closed-loop speed control of motor is performed in lower controllers. We investigate speed performance of rim motors in open-loop control scheme and develop a closed-loop speed controller for the rim motors. The controllers are based on PID (proportional integral derivative) control. Besides, the improvements of control performance can be achieved by employing some techniques such as input feed forward, event-based sampling, and switching control strategy. The concept of event-based control used in the system is sensor-triggered rather than time-triggered, where the sensor triggering signal is from Hall sensors. And the purpose of switching control strategy is to apply an effective control method according to the operating conditions such as soft-start mode, tracking mode, and braking mode. The study focuses on the comparisons of performance between the developed one and the existed, under different testing conditions. The experimental results show that by using the speed controller developed in this study, magnitude of both overshoot and speed fluctuations are suppressed effectively and still maintained acceptable rise time. Furthermore, we construct a minimum-jerk velocity profile to provide a smooth reference velocity for wheelchair. This profile can be implemented in future systems. Finally, we follow the test items stated in CNS14964-6 to evaluate the performance of velocity and acceleration. Experimental result shows that based on the developed control system the rim motor wheelchair is competitive to another commercial electric wheelchair in the aspect of velocity and acceleration. Meanwhile, the items listed in the standard are fulfilled.