TY - JOUR
T1 - Variable Impedance Control for pHRI
T2 - Impact on Stability, Agility, and Human Effort in Controlling a Wearable Ankle Robot
AU - Arnold, James
AU - Lee, Hyunglae
N1 - Funding Information:
Manuscript received October 14, 2020; accepted February 11, 2021. Date of publication February 24, 2021; date of current version March 15, 2021. This letter was recommended for publication by Associate Editor Jeremy DeLaine Brown and J.-H. Ryu Editor upon evaluation of the reviewers’ comments. This work was supported by National Science Foundation Awards #1846885 and #1925110. (Corresponding author: Hyunglae Lee.) The authors are with the School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, AZ 85287 USA (e-mail: jmarnol6 @asu.edu; hyunglae.lee@asu.edu).
Publisher Copyright:
© 2016 IEEE.
PY - 2021/4
Y1 - 2021/4
N2 - This letter introduces a variable impedance controller which dynamically modulates both its damping and stiffness to improve the trade-off between stability and agility in coupled human-robot systems and reduce the human user's effort. The controller applies a range of robotic damping from negative to positive values to either inject or dissipate energy based on the user's intent of motion. The controller also estimates the user's intent of direction and applies a variable stiffness torque to stabilize the user towards an estimated ideal trajectory. To evaluate the controller's ability to improve the stability/agility trade-off and reduce human effort, a study was designed for human subjects to perform a 2D target reaching task while coupled with a wearable ankle robot. A constant impedance condition was selected as a control with which to compare the variable impedance condition. The position, speed, and muscle activation responses were used to quantify the user's stability, agility, and effort, respectively. Stability was quantified spatially and temporally, with both overshoot and stabilization time showing no statistically significant difference between the two experimental conditions. Agility was quantified using mean and maximum speed, with both increasing from the constant impedance to variable impedance condition by 29.8% and 59.9%, respectively. Effort was quantified by the overall and maximum muscle activation data, both of which showed a ∼10% reduction in effort. Overall, the study demonstrated the effectiveness of the variable impedance controller.
AB - This letter introduces a variable impedance controller which dynamically modulates both its damping and stiffness to improve the trade-off between stability and agility in coupled human-robot systems and reduce the human user's effort. The controller applies a range of robotic damping from negative to positive values to either inject or dissipate energy based on the user's intent of motion. The controller also estimates the user's intent of direction and applies a variable stiffness torque to stabilize the user towards an estimated ideal trajectory. To evaluate the controller's ability to improve the stability/agility trade-off and reduce human effort, a study was designed for human subjects to perform a 2D target reaching task while coupled with a wearable ankle robot. A constant impedance condition was selected as a control with which to compare the variable impedance condition. The position, speed, and muscle activation responses were used to quantify the user's stability, agility, and effort, respectively. Stability was quantified spatially and temporally, with both overshoot and stabilization time showing no statistically significant difference between the two experimental conditions. Agility was quantified using mean and maximum speed, with both increasing from the constant impedance to variable impedance condition by 29.8% and 59.9%, respectively. Effort was quantified by the overall and maximum muscle activation data, both of which showed a ∼10% reduction in effort. Overall, the study demonstrated the effectiveness of the variable impedance controller.
KW - Physical human-robot interaction
KW - impedance control
KW - intent recognition
KW - wearable robots
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U2 - 10.1109/LRA.2021.3062015
DO - 10.1109/LRA.2021.3062015
M3 - Article
AN - SCOPUS:85101772257
SN - 2377-3766
VL - 6
SP - 2429
EP - 2436
JO - IEEE Robotics and Automation Letters
JF - IEEE Robotics and Automation Letters
IS - 2
M1 - 9362246
ER -