A Novel Inverse Kinematics Method for Upper-Limb Exoskeleton under Joint Coordination Constraints

Abstract

In this study, we address the inverse kinematics problem for an upper-limb exoskeleton by presenting a novel method that guarantees the satisfaction of joint-space constraints, and solves closed-chain mechanisms in a serial robot configuration. Starting from the conventional differential kinematics method based on the inversion of the Jacobian matrix, we describe and test two improved algorithms based on the Projected-Gradient method, that take into account jointspace equality constraints. We use the Harmony exoskeleton as a platform to demonstrate the method. Specifically, we address the joint constraints that the robot maintains in order to match anatomical shoulder movement and the closed-chain mechanisms used for the robot's joint control. Results show good performances of the proposed algorithms, which are confirmed by the ability of the robot to follow the desired taskspace trajectory while ensuring the fulfilment of joint-space constraints, with a maximum error of about 0.05 degrees.

Kinematic of the Position and Orientation Synchronization of the Posture of a n DoF Upper-Limb Exoskeleton with a Virtual Object in an Immersive Virtual Reality Environment

“…The inverse kinematics problem consists of finding the configuration of the articular coordinates of the exoskeleton so that its end-effector is positioned and oriented according to a certain spatial location and pose [65][66][67][68].…”

Review on Patient-Cooperative Control Strategies for Upper-Limb Rehabilitation Exoskeletons

“…In the latter case, a proper inverse-kinematics algorithm includes inter-joint coordination constraints within the optimization problem. The algorithm exploits the kinematic redundancy of the robot (e.g., through the swivel angle) to reconfigure the exoskeleton according to the scapulohumeral rhythm and computes the desired joint trajectories ( Dalla Gasperina et al, 2020 ).…”

“…The robotic exoskeleton consists of seven degrees-of-freedom (DOFs) for each arm: five DOFs are used to assist the shoulder and the scapulohumeral rhythm, one DOFs assists the elbow flexion/extension, and one operates the wrist pronation/supination. The authors developed a baseline controller that implements active modalities with joint-coordination constraints ( Kim and Deshpande, 2015 ; Dalla Gasperina et al, 2020 ). The baseline controller promotes joint transparency, corrects for non-coordinated scapulohumeral rhythm through an impedance control law (spring-damper corrective assistance), and compensates for the robot weight through positive feedback that is computed inverse dynamics recursive algorithm (weight counterbalance assistance).…”

Asymmetric Bimanual ADL Training With Underactuated Exoskeleton Using Independent Joint Control and Visual Guidance

“…For example, adjusting robot assistance for different individual joints with task-space impedance control [9][10][11] may be difficult. Besides, some research attempting to control individual joint assistance, like the inverse kinematics (IK) method with joint coordination constraints [12], has difficulty assigning joint constraints for specific joint coordination patterns in different ADL tasks.…”

“…Third, some task-space control focused on correcting patients' motion errors. For instance, the joint position control with IK [12][13][14] and the task-space adaptive control, like the Barrier composite energy function scheme [19], followed the preset task-space trajectories by accurately tracking generated joint trajectories. However, this provides insufficient motion error in both task and joint space for motor learning [15].…”