Design Advantages of Four-bar Linkage Planar Robotic Arm for Upper-extremity Rehabilitation
Khemwutta Pornpipatsakul, Wasutha Chuengwutigool, Ronnapee Chaichaowarat
Abstract
Nowadays, rehabilitation with robots has become famous. Upper extremity rehabilitation is one of the most common requirements for stroke patients. The 2-DOF planar arm is the simplest mechanism used for rehabilitation robots. The series robot has the second motor located at the end of the first link, which causes high inertia around the first motor’s axis due to its mass. The counter moment of the second motor while accelerating the second link also affects the first link. To handle this problem, the four-bar linkage planar robot was introduced. The second motor was repositioned to the base with the axis coincident with the first motor. This paper emphasizes the advantages of the proposed four-bar parallel arm configuration over the conventional series design in terms of sensitivity and actuation torque. The calculation shows that the sensitivity of the endpoint position is improved from 25.7 mm to 25.3 mm per 0.05 radian of motor rotation. The actuation torque required from each motor for stabilizing the end-effector subjected to the interaction force was simulated. About 25.6% of actuation peak torque can be reduced for the first motor, which allows a lower gear reduction ratio with higher backdrivability to be chosen. The hardware prototype was built to validate the mapping between actuation torque and endpoint force. The correctness of the endpoint force is confirmed with the R-squared values over 0.95 in both cartesian axes. The result of this study provides a guideline for designing a planar robotic arm for rehabilitation.