**6. Conclusions**

In this article, we present the mechanical design, control, and performance evaluation of the wheelchair exoskeleton for physical assistance. The design takes advantage of non-backdrivable mechanisms and holds the output position of the exoskeleton without energy consumption. Furthermore, an overall structure of the exoskeleton system offers compatible kinematics and provides a safer ROM that generates a variety of unconstrained motions for active assistance.

The experiments performed evaluated the system's response to shoulder extension/flexion, shoulder internal/external rotation, and elbow extension/flexion for two different ADLs. The statistical analysis of the joint angle trajectories shows that the proposed system and the implementation of PD-based control method are appropriate for performing several essential tasks. Upon the data presented, it is expected that the system will be able to support the tetraplegia users in different ADLs, such as drinking/eating, which helps them in maintaining an independent lifestyle.

**Supplementary Materials:** The following are available at https://www.mdpi.com/2076-3417/11/1 3/5865/s1.

**Author Contributions:** Conceptualization, M.A.G., S.B., M.T. and L.N.S.A.S.; methodology, M.A.G.; software, M.T., S.H.B. and M.M.; validation, M.A.G.; formal analysis, M.A.G.; investigation, M.A.G.; writing—original draft preparation, M.A.G.; writing—review and editing, M.A.G., S.B., M.T., L.N.S.A.S. and T.B.M.; supervision, S.B. and T.B.M., T.B. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work has been supported by AAU EXOTIC project.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** The experiments presented in this study were the part of system testing thus did not require consent statement.

**Data Availability Statement:** Data is contained within the article.

**Conflicts of Interest:** The authors declare no conflict of interest.
