Sensorless assistive torque design for a lower extremity exoskeleton

Abstract

For improving mobility of the elderly, it is desirable to use a lower limb exoskeleton to enhance strength and endurance for their daily life activities. This paper presents a novel design of assist torque generation and compliant motion of a knee joint for an exoskeleton robot. Based on a sensorless approach, a method is suggested to estimate the external torque and generate the assistance torque of the attached DC motor. The developed lower limb exoskeleton joint provides assistive torque in order to comply with motion of the user. In comparison with existing lower limb exoskeletons, the proposed exoskeleton robot can execute various training programs by adjusting the assisting torque with less sensors and reduced hardware complexity. Experimental results on a knee exoskeleton validate the proposed method. Desirable assistive torque can be generated to be compliant with a swing motion.

Development of Multi-axis Motor Control Systems for Lower Limb Robotic Exoskeleton

“…The α value was obtained as ~ 2 to 4, and the controller gain (K PN ) and speed controller time constants (T NN ) are given by Eqs. (9) and (10), respectively. The closed loop transfer function G CN (s) is given by Eq.…”

“…The exoskeletons designed by Aquirre and Peshkin [7] and Kong et al [8] employed a torque sensor and spring devices to compensate for the inertia of the mechanism. Yi et al [9] presented an active disturbance rejection control (ADRC)-based strategy, which was applied to track the human gait trajectory for a lower limb rehabilitation exoskeleton. Song et al [10] applied a novel design with an assistive torque generation and compliant motion of a knee for an LLRE.…”

“…The following studies on master controllers include the development of a robot control system [4], movement balance [6], gravity compensation [7][8][9], and gait control [10], resulting in heavy duty for the master controllers. These master controllers are involved in complex designs and large computations.…”

“…The major reason that computers were still used as master controllers is because similar functions could not be incorporated into a compact chip. Technically, a commercial motor controller could not provide sufficient responses for the robot's needs [7][8][9][10]. To achieve high performance, the design of motor controllers with servo drives for bandwidth improvement was presented [11,12], but the impact of the external load was not considered.…”

Knee-ankle-foot orthosis with powered knee for support in the elderly

“…Profound general reviews on powered lower extremity exoskeletons have been published by Dollar and Herr, 9 Herr, 10 and Casolo et al 11 Yan et al 12 have assessed strategies from a more technical point of view; here, the sensor configuration and actuation concepts represent the key features for reliable, comfortable, and long-time use of a powered KAFO. The dynamics of the leg can be retrieved by not only using angular sensors (encoders or potentiometers) 13–17 but also introducing strain gauges to the device. 18–20 For many devices, it is essential that ground reaction forces (GRF) are measured, and a smart combination of sensors is desirable.…”