手輪馬達電動輪椅之無力感測器動力輔助控制

Abstract

本文主旨在於建立手輪馬達電動輪椅的動力輔助系統，其主要處理的問題分為低速力矩控制的精度提升及動力輔助控制兩部分。在力矩控制上，要達到精確控制需有較準確的轉子位置，過去使用的數位霍爾感測器其解析度較低，難以滿足此需求。另外由於輪椅經常操作在低速區，由數位感測器測得的速度也會有較大落後，使得控制系統的頻寬降低。一般會使用高精度的編碼器來處理上述問題，但考量其成本較高，本文提出使用較便宜的線性霍爾感測器做為解決方案。在本文應用中，由於馬達內部磁鐵形狀使得感測器訊號有較嚴重的諧波成分，無法直接用於測量，故本文提出一套基於鎖相環的特殊觀測器，其中包含自適應濾波環節，可抑制訊號中主要的諧波成分，達到較穩定的估測。在動力輔助控制部分，本文利用干擾觀測器取代力感測器來估測人力輸入，其後透過阻抗控制的技術來使使用者在推動輪椅時能感受到合適的阻抗特性。輔助控制的目標可分為降低使用者須施加的推力及延長輪椅滑行距離，達成此兩目標需使動力輪對外界干擾力矩分別具有低阻抗及高阻抗兩種特性，故本文設計手推辨識算法來判定使用者是否在推動輪椅，依此來決定兩種阻抗模式的切換。本文方法經模擬驗證可行性，並以實際實驗來證明其效能。

The main objective of this research is to establish the power assist system for the proto-type powered wheelchair driven by rim motor. The main issue can be divided into two parts: improvement on accuracy of torque control in low speed region and design of power assist control sysytem. To achieve precise torque control, it is necessary to know accurate rotor position. However, the digital Hall-effect sensor used in the past research has a low resolution, which is difficult to meet the requirement. In addition, since the wheelchair is often operated in the low speed region, the speed estimated by the digital sensor will also contain large phase lag, which would reduce the bandwidth of the speed control loop. High-resolution encoders are generally used to deal with the above problems, but considering the higher cost, this paper proposes to use cheap linear Hall-effect sensors as a solution. In this application, because of the shape of the magnet using by the rim motor, the sensor signal contained large harmonic components and cannot be directly used for measurement, this paper proposes a specialized observer based on phase-locked loop, which includes adaptive filtering section. It can suppress the main harmonic components in the signal and achieve a more stable estimation. In regard to the power assisted control, this paper uses the disturbance observer instead of force sensors to estimate the human torque input, then through the technique of impedance control, the user could feel the appropriate impedance characteristics during the propulsion of the wheelchair. The objectives of the power assist control can be divided into two part: reduce the torque that the user must apply and extend the moving distance of the wheelchair. To achieve these goals, the powered wheel must have different impedance characteristic to the external torque disturbance. An identification algorithm is designed to determine whether the user is pushing the wheelchair, and accordingly determines the switching of the two impedance modes. The method of this paper is verified by simulation and its performance is proved by experiments.