Journal
IEEE TRANSACTIONS ON MEDICAL ROBOTICS AND BIONICS
Volume 3, Issue 4, Pages 970-979Publisher
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
DOI: 10.1109/TMRB.2021.3123528
Keywords
Kinematic compatibility; exoskeleton; misalignments; wrist; impedance
Categories
Funding
- National Science Foundation [1943712]
- American Heart Association [17SDG33690002]
- Div Of Chem, Bioeng, Env, & Transp Sys
- Directorate For Engineering [1943712] Funding Source: National Science Foundation
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The study introduces a low-impedance 2-DOF wrist exoskeleton UDW with different design strategies to achieve kinematic compatibility, and develops two versions for experimental comparison. Results show that UDW-NC with passive joints is more robust to misalignments compared to UDW-C, but it has greater Coulomb friction and less accurate torque transfer.
We present the UDiffWrist (UDW), a low-impedance 2-DOF wrist exoskeleton featuring a cable-differential transmission. To investigate the effect of different design strategies for achieving kinematic compatibility, we developed two versions of this robot: One version (UDW-C) achieves kinematic compatibility only in the case of perfect alignment between human and robot joints. The second version (UDW-NC) connects the human and robot via passive joints to achieve kinematic compatibility regardless of alignment between human and robot joints. Through characterization experiments, we found that the UDW-NC was more robust to misalignments than the UDW-C: the increase in maximum interaction torque associated with misalignments was greater for the UDW-C than the UDW-NC robot (p = 0.003). However, the UDW-NC displayed greater Coulomb friction (p < 0.001). Further, Coulomb friction increased more for the UDW-NC than the UDW-C in the presence of misalignments between the human and robot axes (p < 0.001). We also found that torque transfer was more accurate in the UDW-C than in the UDW-NC. These results suggest that for the small (10 deg) 2-DOF wrist movements considered, the advantages of the UDW-NC in terms of kinematic compatibility are likely overshadowed by the negative effects in friction and torque transfer accuracy.
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