輪腳複合機器人之穩定輪腳轉換策略

Abstract

本文主要探討新型輪腳複合式平台於輪腳轉換時之軌跡規劃以及穩定度分析，新型輪腳複合式平台搭載之輪腳機構為五連桿內接七連桿的雙自由度機構，能夠在輪模式以輪機構移動並且於腳模式使用一般四足機器人常見之步態移動，但複雜的構型也使其在運動學計算上較為困難，為了使機器人能夠於兩種模式中順暢且平穩的切換，本研究首先離線規劃單足之輪腳轉換軌跡，以平穩且有效率切換為目的，藉由順向運動學大量生成軌跡後由成本函數篩選出最符合要求之軌跡。 在機器人的模式切換上，輪模式與腳模式之作動範圍並不相同，進行模式切換需對齊各輪足機構之相位，本研究提出一種輪腳轉換規劃演算法，分配各腳在輪腳轉換過程中的行為以及軌跡，在持續前進的同時完成各輪足機構之相位對齊，以完成快速且平穩的轉換，過程中機器人並不會產生轉向以及打滑的多餘動態，並且演算法內之參數可依照機器人所處情境更改，以增加其應用彈性。本研究同時使用力角穩定性分析判斷機器人於輪腳轉換過程之穩定性，並且以此進行踏點以及機身動態的修改，使機器人順暢完成轉換，並且平穩進入中樞模式產生器以銜接腳模式步態。最後，以模擬軟體以及實驗驗證所提出之輪腳轉換規劃可行性以及應用範圍。

This study discusses trajectory planning and stability analysis during wheel-leg transformation of a novel wheel-leg transformable robot. The platform is equipped with a five-bar linkages-based mechanism that is internally connected to a seven-bar linkage, providing 2 degrees of freedom. It can move in wheel mode using the wheeled mechanism and adopt common quadruped robot gaits in legged mode. However, its complex configuration poses challenges in kinematic calculations. To enable smooth and stable switching between the two modes, this study first offline plans the trajectory for single-leg wheel-to-leg transformation. The objective is to achieve smooth and efficient switching, and a large number of trajectories are generated through forward kinematics. These trajectories are then filtered based on a cost function to select the most suitable ones that meet the requirements. In the context of mode switching in robots, the operating ranges of the wheeled mode and legged mode are not the same. Aligning the phases of each wheel-leg mechanism is necessary for mode switching. This study proposes a wheel-leg transformation planning algorithm that assigns behaviors and trajectories to each leg during the transformation process. The algorithm ensures the alignment of the wheel-leg mechanisms' phases while the robot continues to move forward, enabling fast and smooth transformations. The algorithm avoids unnecessary dynamics such as steering and slipping. Moreover, the parameters within the algorithm can be adjusted according to the robot's specific situation, increasing its application flexibility. This study also employs a stability analysis using force-angle stability measurement to assess the robot's stability during the wheel-to-leg transformation. Based on the analysis results, adjustments are made to the footholds and body dynamics, ensuring the robot completes the transformation smoothly and seamlessly enters the central pattern generator to connect with legged mode gaits. Finally, the proposed wheel-leg transformation planning is validated through simulations and experiments, demonstrating its feasibility and applicability.