Zhu Junxi, Jiao Chunhai, Dominguez Israel, Yu Shuangyue, Su Hao
Laboratory of Biomechatronics and Intelligent Robotics, Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, NC 27695 USA.
IEEE ASME Trans Mechatron. 2022 Aug;27(4):1837-1845. doi: 10.1109/tmech.2022.3176255. Epub 2022 Jun 3.
High-performance prostheses are crucial to enable versatile activities like walking, squatting, and running for lower extremity amputees. State-of-the-art prostheses are either not powerful enough to support demanding activities or have low compliance (low backdrivability) due to the use of high speed ratio transmission. Besides speed ratio, gearbox design is also crucial to the compliance of wearable robots, but its role is typically ignored in the design process. This paper proposed an analytical backdrive torque model that accurately estimate the backdrive torque from both motor and transmission to inform the robot design. Following this model, this paper also proposed methods for gear transmission design to improve compliance by reducing inertia of the knee prosthesis. We developed a knee prosthesis using a high torque actuator (built-in 9:1 planetary gear) with a customized 4:1 low-inertia planetary gearbox. Benchtop experiments show the backdrive torque model is accurate and proposed prosthesis can produce 200 Nm high peak torque (shield temperature <60°C), high compliance (2.6 Nm backdrive torque), and high control accuracy (2.7/8.1/1.7 Nm RMS tracking errors for 1.25 m/s walking, 2 m/s running, and 0.25 Hz squatting, that are 5.4%/4.1%/1.4% of desired peak torques). Three able-bodied subject experiments showed our prosthesis could support agile and high-demanding activities.
高性能假肢对于下肢截肢者进行诸如行走、下蹲和跑步等多种活动至关重要。最先进的假肢要么动力不足，无法支持高要求的活动，要么由于使用高速比传动而具有低顺应性（低回驱性）。除了速比之外，齿轮箱设计对于可穿戴机器人的顺应性也至关重要，但其作用在设计过程中通常被忽视。本文提出了一种解析回驱扭矩模型，该模型能够准确估计来自电机和传动装置的回驱扭矩，为机器人设计提供参考。基于该模型，本文还提出了齿轮传动设计方法，通过降低膝关节假肢的惯性来提高顺应性。我们开发了一种膝关节假肢，它使用了一个高扭矩致动器（内置9:1行星齿轮）和一个定制的4:1低惯性行星齿轮箱。台式实验表明，回驱扭矩模型是准确的，所提出的假肢能够产生200 Nm的高峰值扭矩（屏蔽温度<60°C）、高顺应性（2.6 Nm回驱扭矩）和高控制精度（对于1.25 m/s的行走、2 m/s的跑步和0.25 Hz的下蹲，均方根跟踪误差分别为2.7/8.1/1.7 Nm，分别为所需峰值扭矩的5.4%/4.1%/1.4%）。三名健全受试者的实验表明，我们的假肢能够支持敏捷且高要求的活动。
