A self-aligning end-effector robot for individual joint training of the human arm

Abstract

<jats:p>Current evidence indicates that individual joint training with robotic devices can be as effective as multi-joint training for the arm. This makes a case for developing simpler and more compact robots for training individual joints of the arm. Such robots have the highest potential for clinical translation. To this end, the current work presents the kinematic design and optimization of a six degrees-of-freedom (<jats:italic>dof</jats:italic>) end-effector robot with three actuated <jats:italic>dof</jats:italic> and three non-actuated self-aligning <jats:italic>dof</jats:italic> for safe assisted training of the individual joints (shoulder or elbow) of the human arm, with relaxed constraints of the relative positioning of the human limb with respect to the robot. Further, we present a simple estimation procedure to automatically identify the kinematic parameters of the human limb essential for control of the human-robot closed kinematic chain.</jats:p>

Design and Characterization of a Self-Aligning End-Effector Robot for Single-Joint Arm Movement Rehabilitation

“…This paper presents the physical realization, optimization, and characterization of the endeffector robot -AREBOintroduced in our earlier work (Balasubramanian et al, 2021). The present work's novelty is the demonstration of using an end-effector robot for sensing and safe training of 3D single joint movements against gravity.…”

“…In the current study, we extend this previous work (Balasubramanian et al, 2021) by: (a) proposing a simplification to the previous kinematic structure, (b) designing, fabricating, and assembling a physical prototype of AREBO (Figure 1), and (c) developing and characterizing the robot controller for human-robot interaction during assisted training of the single-joint movements of the arm.…”

“…The robot link lengths (𝑟 1 , 𝑟 2 ) were optimized (like in Balasubramanian et al, 2021) for single joint movements of the arm by maximizing the robot's workspace and manipulability in a plane orthogonal to the longitudinal axis of the attached arm segment (𝐳 ℋ 3 in figure 4). A brute force search was implemented to find the optimal link lengths for the robot for different combinations of the arm parameters, namely the arm lengths, positions, and orientations of the human joint (ℋ 0 ) with respect to the robot (ℛ 0 ).…”

“…A trial was considered successful if the SJM reaches within ±5° of the target location. In this experiment, the de-weighting parameter for the first trial is chosen to be 0.3, i.e., 𝛼 [1] = 0.3.…”

“…Safe single-joint assisted training requires at least three actuated DOF to apply force in any direction to cause the desired rotary movement of the (arbitrarily oriented) human limb while avoiding undesirable forces that push or pull the limb segment from the joint. We recently proposed the design of a self-aligning 6 DOF end-effector robot, AREBO (Arm Rehabilitation Robot), which has three actuated and three unactuated DOF (Balasubramanian et al, 2021). The three actuated DOF allow the robot to apply safe forces at its endpoint that result in pure rotational movements about a joint.…”