問題與討論

在[37]有討論到用二度空間的位能場模型在某些情況下，機械手臂會 因為順著位能場的方向而產生不自然的結果，這個問題在我們使用的三度 空間位能場模型依舊存在。由於物體愈靠近邊界所受的推斥力愈大，因此 我們若把兩個手臂的基座設在靠近與終點反向邊界的位置，規劃過程中有 可能發生整個手臂的扭曲變形，甚至因為被推擠太過嚴重，造成最後兩節 無法接上而使得手臂斷裂。解決方式是針對各個手臂，在計算推斥力時，

對於終點相對方向的平面所算出來的推斥力，以較少的權值相加，如圖 5.16，對於右邊的主臂而言，由於終點平面在左邊，因此主臂在對最右邊 的平面作推斥力的計算時，就可以較小的權重來計算，本篇論文均採用原 來力的五分之一，因此主臂在往左邊移動時，會以類似首節牽引拉動後面 的小節前進，而不是受到力的不當影響，造成整個手臂往中間推擠。圖中 左邊的僕臂調整則是類似主臂的計算方式，受到更改權重的平面為最左邊 的平面。

圖 5.16 解決位能場先天問題的方式，對特定平面的授與不同權重值。

在大部分的環境中，由於僕臂需要閃避主臂而調整，因此僕臂到達終 點平面時間會較主臂的到達時間晚，但仍然有可能會有僕臂先到達的情況 發生(如例三)，而在這些僕臂先到達終點的例子當中，有一部分會因為僕 臂在到達後不再調整，主臂則因繼續前進而有可能與僕臂相撞的情形。解 決這種問題的方式有幾種：

1. 捨棄交錯式的規劃方法，讓主臂先規劃其路徑，到達終點之後，

再讓僕臂開始規劃。

2. 主臂先規劃前進路徑，僕臂則在主臂規劃的過程中先不前進，僅 作各節轉動調整來閃避主臂，其運動過程類似兩端固定的手臂，

在主臂規劃完成到達終點之後，僕臂開始作前進路徑規劃。

3. 利用原本的演算法先規劃完成，但僕臂到達之後，仍繼續作各節 的轉動調整，其運動過程類似兩端固定的手臂。

然而這樣的情況並不常見，因此可當作是特殊情況來處裡。

第六章 結論

本論文的目的在於對三維空間中的雙機械手臂作路徑規劃。我們所提 出的演算法，利用三度空間的廣義位能場模型，在工作空間中使障礙物對 手臂產生推斥力，不但保證手臂前進時所經過的路徑不會與障礙物或是彼 此碰撞，所規劃出來的路徑也能夠近乎平滑且連續。

相對於一般以組態空間為基礎的演算法，我們所提出的方法對於具有 高自由度的物體，並不需要花費大量的時間與資源建構組態空間，因此在 一般的環境之下，搜尋速度相當快速而且正確。

本論文利用「主僕式架構」以及「交錯式運行」來解決兩個機械手臂 的協調問題，由實驗證明，主僕式架構的確適合應用於雙機械手臂的環境 當中，透過推斥力讓僕臂在規劃路徑的過程中閃避主臂，可以讓兩個手臂 雙雙到達目的地，且透過交錯式的運行方法，在大部分的情況之下也都能 讓兩個手臂規劃完成各自的路徑。

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