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Influence of Motion Restrictions in an Ankle Exoskeleton on Gait Kinematics and Stability in Straight Walking

Miha Dezman, Charlotte Marquardt, Adnan Ugur, Tamim Asfour

TL;DR

This study investigates how ankle exoskeletons with adjustable degrees of freedom (DoF) influence gait kinematics and stability during straight walking. In a pilot trial with six participants, the authors compare Exo1DoF, Exo2DoF, and Exo3DoF configurations against NoExo, measuring ankle angles, stride parameters, cuff rotation, and trunk stability. Results show that increasing DoF generally improves kinematic similarity to unassisted walking and reduces cuff rotation, with the largest gains when moving from 1 to 2 DoF and the best overall performance achieved with 3 DoF. However, added mass and a rigid sole introduce drawbacks, and stability does not fully return to NoExo values; future work will pursue lighter designs and integration with a knee joint to enhance overall gait restoration.

Abstract

Exoskeleton devices impose kinematic constraints on a user's motion and affect their stability due to added mass but also due to the simplified mechanical design. This paper investigates how these constraints resulting from simplified mechanical designs impact the gait kinematics and stability of users by wearing an ankle exoskeleton with changeable degree of freedom (DoF). The exoskeleton used in this paper allows one, two, or three DoF at the ankle, simulating different levels of mechanical complexity. This effect was evaluated in a pilot study consisting of six participants walking on a straight path. The results show that increasing the exoskeleton DoF results in an improvement of several metrics, including kinematics and gait parameters. The transition from 1 DoF to 2 DoF is shown to have a larger effect than the transition from 2 DoF to 3 DoF for an ankle exoskeleton. However, an exoskeleton with 3 DoF at the ankle featured the best results. Increasing the number of DoF resulted in stability values closer the values when walking without the exoskeleton, despite the added weight of the exoskeleton.

Influence of Motion Restrictions in an Ankle Exoskeleton on Gait Kinematics and Stability in Straight Walking

TL;DR

This study investigates how ankle exoskeletons with adjustable degrees of freedom (DoF) influence gait kinematics and stability during straight walking. In a pilot trial with six participants, the authors compare Exo1DoF, Exo2DoF, and Exo3DoF configurations against NoExo, measuring ankle angles, stride parameters, cuff rotation, and trunk stability. Results show that increasing DoF generally improves kinematic similarity to unassisted walking and reduces cuff rotation, with the largest gains when moving from 1 to 2 DoF and the best overall performance achieved with 3 DoF. However, added mass and a rigid sole introduce drawbacks, and stability does not fully return to NoExo values; future work will pursue lighter designs and integration with a knee joint to enhance overall gait restoration.

Abstract

Exoskeleton devices impose kinematic constraints on a user's motion and affect their stability due to added mass but also due to the simplified mechanical design. This paper investigates how these constraints resulting from simplified mechanical designs impact the gait kinematics and stability of users by wearing an ankle exoskeleton with changeable degree of freedom (DoF). The exoskeleton used in this paper allows one, two, or three DoF at the ankle, simulating different levels of mechanical complexity. This effect was evaluated in a pilot study consisting of six participants walking on a straight path. The results show that increasing the exoskeleton DoF results in an improvement of several metrics, including kinematics and gait parameters. The transition from 1 DoF to 2 DoF is shown to have a larger effect than the transition from 2 DoF to 3 DoF for an ankle exoskeleton. However, an exoskeleton with 3 DoF at the ankle featured the best results. Increasing the number of DoF resulted in stability values closer the values when walking without the exoskeleton, despite the added weight of the exoskeleton.
Paper Structure (14 sections, 13 figures, 1 table)

This paper contains 14 sections, 13 figures, 1 table.

Table of Contents

  1. Introduction
  2. Materials and Methods
  3. Exoskeleton and restriction
  4. User Study
  5. Stride Segmentation
  6. Gait Parameters
  7. Kinematics
  8. Stability
  9. Results and Analysis
  10. Angle and
  11. Gait parameters
  12. Stability evaluation
  13. Discussion
  14. Conclusion

Figures (13)

  • Figure 1: Left: Shank and foot sections of the exoskeleton. Right: The exoskeleton during the three rotations: PFDF, INEV, and IRER of the ankle joint, as well as the forefoot rotation of the foot frame. (adapted from Dezman2024Ankle)
  • Figure 2: The three exoskeleton configurations: Exo3DoF, Exo2DoF, and Exo1DoF. The kinematic structure comprises various joint types: a hinge joint represented by " ", a ball joint " ", a hinge joint with angle measurement " ", and an adjustable translation joint " ". The explanations for each callout are provided in the text. (adapted from Dezman2024Ankle)
  • Figure 3: A participant without and with the ankle exoskeleton in its three configurations. The parts added to fix certain are marked in red.
  • Figure 4: marker positions on the exoskeleton and the user. Red markers are attached on the user. Blue markers are attached on the exoskeleton cuff. Green markers are attached on the exoskeleton.
  • Figure 5: Top left: heel switch activation and detected strides in green. Bottom: an example of two segmented strides of the left leg. Top right: the stride length and width definition.
  • ...and 8 more figures