Clutched elastic actuator to drive a lower limb exoskeleton hip joint for paraplegic patients

doi:10.16511/j.cnki.qhdxxb.2020.21.015

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Abstract

Lower limb exoskeletons can help paraplegic patients walk through rehabilitation. Powered exoskeletons do not require much muscle strength in the affected limbs, but the drive motors are rather large and heavy. Unpowered energy-storage exoskeletons do not require motors, but require more patient muscle strength which may cause fatigue during continuous use. This paper describes a clutched elastic actuator based on a ratchet mechanism that can be used as the hip joint driver for a lower limb of an exoskeleton. Patients rely on their upper limb and trunk muscles and crutches to slowly transfer the center of gravity during the support phase. The motor then stores energy during this motion in a torsional spring. During the swing phase, the torsional spring then quickly releases energy to help the patient step forward and complete a gait cycle. This paper presents a model for the driver during the support phase (spring energy storage) and the swing phase (spring energy release). The angular acceleration and deceleration are selected to minimize the peak power. Simulations show that the clutched elastic actuator significantly reduces the average power and the peak power compared with a motor and gearbox driving the patient's hip joint. Therefore, the system can have small low torque, low power motors to reduce the size and weight of the actuators and the entire exoskeleton.

Keywords exoskeletons compliant actuators clutched actuators ratchet mechanisms paraplegic

Corresponding Authors: Xinyu GUAN E-mail: guanxinyu@tsinghua.edu.cn

Issue Date: 26 November 2020

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	Yulin LIU
	Yinbo LI
	Renhao LU
	Xinyu GUAN
	Linhong JI

Cite this article:

Yulin LIU,Yinbo LI,Renhao LU, et al. Clutched elastic actuator to drive a lower limb exoskeleton hip joint for paraplegic patients[J]. Journal of Tsinghua University(Science and Technology), 2021, 61(1): 42-49.

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http://jst.tsinghuajournals.com/EN/10.16511/j.cnki.qhdxxb.2020.21.015 OR http://jst.tsinghuajournals.com/EN/Y2021/V61/I1/42

驱动器模型参数及人体模型参数








10.16511/j.cnki.qhdxxb.2020.21.015.T001表 1

参数符号	参数含义	参数数值
J_m	电机的转动惯量	44 g·cm²
J_g	齿轮减速箱相对于输出轴的转动惯量	9.4 g·cm²
J_s	小锥齿轮的转动惯量	3.1 g·cm²
J_b	大锥齿轮的转动惯量	204.5 g·cm²
N_g	齿轮减速箱的传动比	112.67
N_b	锥齿轮传动的传动比	3.615
η_g	齿轮减速箱的效率	0.74
η_b	锥齿轮传动的效率	0.95
k	扭簧的刚度	32.34 N·m/rad
g	重力加速度	9.8 m/s²
K_T	电机转矩常数	37.5 mN·m/A
K_E	电机转速常数	255 r/(min·V)
R	电机内阻	0.236 Ω
m_l	人腿质量	11.323 kg ^[15]
l_l	人腿质心距髋关节转轴的距离	0.383 m ^[15]
j_l	人腿相对于髋关节的转动惯量	2.834 kg·m² ^[16]

10.16511/j.cnki.qhdxxb.2020.21.015.T002

表 2

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