Loading...

Design and Analysis of the Connection Mechanics in Robotic Exoskeletons to Improve the Kinematic Compliance with User’s Anatomy

Shafiei, Morteza | 2020

436 Viewed
  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 53355 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Behzadipour, Saeed
  7. Abstract:
  8. User comfort in wearable robots and precise limb tracking of the robots' links can be considered as general and significant indicators of the robots' performance. On the other hand, due to the kinematic mismatches between the human body and conventional wearable robots, which often occur due to various reasons such as the kinematic differences between the body and robot joints (e.g. the knee joint), it seems unlikely to achieve a robot in which user's limbs comfortably follow its link without tracking error. In this study, in order to evaluate and improve the performance of the robot, two performance indices: limbs tracking error index (TEI) and user discomfort index (DI) were introduced, and calculated based on a model of the robot, body and robot-body connection. In order to model and identify the parameters of the robot-body connection elements, a set of tests was performed on three participants. In addition to nonlinear behaviors such as hysteresis loops, the results showed that using a linear relationship (symmetric stiffness matrices for robot-body connection) to model the wrench-displacement of the connection leads to an error of less than 10%. By identifying the connection stiffness matrices and completing the initial model, the sensitivity of the performance indices to changes in their eigenvalues was investigated. It was observed that a decrease in some eigenvalues, especially in the shank connection (possibly due to intricacy of the knee joint), can improve both performance indices or one of them with a large improvement (up to 50% in the average of indices, relative to the nominal values). Also, the effect of added backlashes to the robot-body connection on the performance indices, as an alternative to the stiffness reduction, was investigated using the initial model. Rotational and translational backlashes added to the shank connection with directions close to the Y axis (axial direction) were found to have the greatest positive effect on the performance (about 60%) and consequently, in the same direction, cylindrical backlashes were found to be highly effective. Afterwards, a series of tests was performed which led to the modification and validation of the model. In the modified model, unlike the initial one, the weight force was considered and consequently the TEI and DI increased from 3.4° and 0.22J (for the initial model) to 6.3° and 0.39J, and therefore, the destructive effects of the weight force on the performance indices were observed to be almost equal to the kinematic mismatches effects. The modified model results showed different optimized parameters for some backlashes and their effectiveness. For instance, the shank translational backlash could not significantly improve the performance indices (unlike the initial model), but the shank rotational backlash in the axial direction still improved the performance by 22.3%. Collectively, using biomechanical modeling and identification of robot-body connection stiffness, the presence of backlash or stiffness reduction in the robot-body connection was confirmed as a solution to improve the wearable robot performance by both the initial and modified models. Also, the shank rotational backlashes in the directions close to the Y axis with a range of motion of ±15° were found as the optimal backlashes by both models
  9. Keywords:
  10. Exoskeleton ; Tracking Errors ; Kinematic Misalignment ; Performance Improvement ; User Discomfort

 Digital Object List

 Bookmark

No TOC