Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Optimal Kinematic Synthesis and Prototype Development of Knee Exoskeleton

Shashank Mani Gautam, Ekta Singla, Ashish Singla

TL;DR

This work tackles maximizing the knee ROM in a one-DoF exoskeleton by optimizing a planar four-bar mechanism actuated by a linear actuator. An interior-point optimization handles nonlinear geometric constraints to derive link lengths that maximize the knee angle $\theta$, achieving $\theta=148^{\circ}$ (a $24.7\%$ gain over a reference design) while preserving a fixed actuator stroke $d_{min}=242$ mm. Kinematic modeling establishes the relationship among link lengths, knee angle, and actuator stroke; graphical simulation validates feasibility and exposes a local-feasible optimum. Gait analysis and a physical LAKE prototype further corroborate minimal misalignment and practical viability, suggesting this approach can yield more natural knee motion in rehabilitation devices without added DoF complexity.

Abstract

The range of rotation (RoR) in a knee exoskeleton is a critical factor in rehabilitation, as it directly influences joint mobility, muscle activation, and recovery outcomes. A well-designed RoR ensures that patients achieve near-natural knee kinematics, which is essential for restoring gait patterns and preventing compensatory movements. This paper presents optimal design of one degree of freedom knee exoskeleton. In kinematic analysis, the existing design being represented by nonlinear and nonconvex mathematical functions. To obtain feasible and optimum measurement of the links of knee exoskeleton, an optimization problem is formulated based on the kinematic analysis and average human's leg measurement. The optimized solution increases the range of motion of knee exoskeleton during sit to stand motion by $24 \%$ as compared with inspired design. Furthermore, misalignment study is conducted by comparing the trajectory of human's knee and exoskeleton's knee during sit to stand motion. The joint movement is calculated using marker and camera system. Finally, a prototype of the knee joint exoskeleton is being developed based on optimal dimensions which validate the maximum range of motion achieved during simulation.

Optimal Kinematic Synthesis and Prototype Development of Knee Exoskeleton

TL;DR

This work tackles maximizing the knee ROM in a one-DoF exoskeleton by optimizing a planar four-bar mechanism actuated by a linear actuator. An interior-point optimization handles nonlinear geometric constraints to derive link lengths that maximize the knee angle , achieving (a gain over a reference design) while preserving a fixed actuator stroke mm. Kinematic modeling establishes the relationship among link lengths, knee angle, and actuator stroke; graphical simulation validates feasibility and exposes a local-feasible optimum. Gait analysis and a physical LAKE prototype further corroborate minimal misalignment and practical viability, suggesting this approach can yield more natural knee motion in rehabilitation devices without added DoF complexity.

Abstract

The range of rotation (RoR) in a knee exoskeleton is a critical factor in rehabilitation, as it directly influences joint mobility, muscle activation, and recovery outcomes. A well-designed RoR ensures that patients achieve near-natural knee kinematics, which is essential for restoring gait patterns and preventing compensatory movements. This paper presents optimal design of one degree of freedom knee exoskeleton. In kinematic analysis, the existing design being represented by nonlinear and nonconvex mathematical functions. To obtain feasible and optimum measurement of the links of knee exoskeleton, an optimization problem is formulated based on the kinematic analysis and average human's leg measurement. The optimized solution increases the range of motion of knee exoskeleton during sit to stand motion by as compared with inspired design. Furthermore, misalignment study is conducted by comparing the trajectory of human's knee and exoskeleton's knee during sit to stand motion. The joint movement is calculated using marker and camera system. Finally, a prototype of the knee joint exoskeleton is being developed based on optimal dimensions which validate the maximum range of motion achieved during simulation.
Paper Structure (11 sections, 5 equations, 10 figures, 1 table)

This paper contains 11 sections, 5 equations, 10 figures, 1 table.

Table of Contents

  1. Introduction
  2. Kinematic Modeling
  3. Design Optimization
  4. Problem Formulation
  5. Design Variables
  6. Constraints
  7. Optimization Method and Results
  8. Graphical Simulation
  9. Gait Analysis
  10. Prototype Development
  11. Conclusion

Figures (10)

  • Figure 1: Linear Actuator based Knee Exoskeleton (LAKE)
  • Figure 3: (a) CAD model of optimized exoskeleton (b) Mannequin wearing exoskeleton on hospital bed
  • Figure 4: (a) Existence of local minima at optimal solution. (b) Variation of knee joint angle with respect to linear actuator's stroke length.
  • Figure 5: Graphical Simulation of optimal exoskeleton at (a) $\theta$ = $2^{\circ}$ (b) $\theta$ = $70^{\circ}$ (c) $\theta$ = $110^{\circ}$ (d) $\theta$ = $148^{\circ}$
  • Figure 6: Optimum dimension based knee exoskeleton
  • ...and 5 more figures