Determining natural arm configuration along a reaching trajectory

Abstract

Owing to the flexibility and redundancy of neuromuscular and skeletal systems, humans can trace the same hand trajectory in space with various arm configurations. However, the joint trajectories of typical unrestrained movements tend to be consistent both within and across subjects. In this paper we propose a method to solve the 3-D inverse kinematics problem based on minimizing the magnitude of total work done by joint torques. We examined the fit of the joint-space trajectories against those observed from human performance in a variety of movement paths in 3-D workspace. The results showed that the joint-space trajectories produced by the method are in good agreement with the subjects' arm movements (r2>0.98), with the exception of shoulder adduction/abduction (where, in the worst case, r2 approximately 0.8). Comparison of humeral rotation predicted by our algorithm with other models showed that the correlation coefficient r2) between actual data and our predictions is extremely high (mostly >0.98, 11 out of 15 cases, with a few exceptions, 4 of 15, in the range of 0.8-0.9) and the slope of linear regression is much closer to one (<0.05 distortion in 12 out of 15 cases, with only one case >0.15). However, the discrepancy in shoulder adduction/abduction indicated that when only the hand path is known, additional constraint(s) may be required to generate a complete match with human performance.

Resolving the redundancy of a seven DOF wearable robotic system based on kinematic and dynamic constraint

“…In this context, the redundancy of the human arm movement can be resolved by optimizing the cost function at the dynamic level. For instance, [10] proposed to solve the 3D inverse kinematics based on minimizing the magnitude of total work done by joint torques for each time step. This dynamic criteria had generated satisfactory prediction of the joint space trajectory for the fundamental motions of the human arm, such as the shoulder adduction/abduction, the shoulder flexion/extension, the shoulder internal/external and the elbow flexion/extension.…”

“…Most of the related work resolved the redundancy at the kinematic level and focused on the desired hand posture given the kinematic constraint of a target location. Another line of research resolved the redundancy of the human arm based on dynamic constraints, such as the amount of work and energy consumption [10] [11]. In this context, the minimum-torque-change model is presented in [12] [13].…”

“…More recently in [11], it is shown that arm posture based on a particular target is affected by both the kinematics and dynamics, and their relative contribution might be variable depending on the task complexity. Kang et al [10] presented an inverse kinematic solution which defines the elbow rotation axis for natural arm movement by minimizing the total work done by joint torques for each time step. All criteria discovered thus far are important from an engineering point of view and they partially explain the human arm inverse kinematic mechanism.…”

“…In this paper, the redundancy of the human arm represented as swivel angle is resolved for the seamless integration between a human and a wearable robot, based on a new kinematic constraint combined with well known dynamic constraint [10]. The proposed algorithm focuses on the functional difference between robot and human manipulators by closely observing human behavior and linearly combines the kinematic and dynamic aspect of the human arm movement to improve the estimation result.…”

Biomimetic orthosis for the neurorehabilitation of the elbow and shoulder (BONES)

“…A coordinate for the last DOF of the wrist needs to be defined from the rotation matrix of the transformation. Using the swivel angle [44] as this final coordinate, a coordinate transformation from shoulder and elbow angles to wrist position and arm swivel can be defined as…”