Thesis Defense - Mahsa Sarrafi Khosrowshah (MSME)

Mahsa Sarrafı Khosrowshah – M.Sc. Mechanical Engineering

Assist. Prof. Dr. Ramazan Unal – Advisor

Date: 10.08.2023

Time: 11:30

Location: AB4 B428

“DESIGN, DEVELOPMENT, AND FUNCTIONAL EVALUATION OF BIOMECHANICALLY

INSPIREDHAND AND WRIST PROSTHESES”

Assist. Prof. Dr. Ramazan Unal, Özyeğin University

Assist. Prof. Dr. Özkan Bebek, Özyeğin University

Assist. Prof. Dr. Elif Hocaoglu, Istanbul Medipol University

Abstract:

The first aspect of this study focuses on the limitations of existing hand prostheses. Passive prostheses, although common, are hindered by their inability to perform a wide range of tasks, thus necessitating more advanced alternatives. Robotic prostheses offer precise motions and adequate force capabilities but face operational time and motor control challenges. To overcome these limitations, a novel design for a body-powered hand prosthesis is proposed. This innovative design is inspired by the natural movements of the human hand and incorporates a three-dimensional trajectory for the thumb. Elastic elements enable the prosthesis to return to its natural position after the application of forces through tendons from the opposite shoulder. With 8 degrees of freedom in the fingers, the prosthesis is prototyped using a 3D printer with ABS material. Performance evaluations demonstrate that this prosthesis, weighing 168 g, enables users to perform a wide range of activities of daily living, including pinching, grasping, and power gripping, thus significantly improving the functional capabilities of the hand prosthesis.

The second aspect of this research focuses on the importance of a wrist joint for upper-limb amputees. A new, lightweight, and adjustable 2-DOF wrist joint is introduced specifically for transradial amputees. This wrist joint incorporates an innovative load-transferring mechanism, allowing modulation of joint stiffness to handle objects of varying weights. The use of a 3D printer with ABS material and a brushless DC motor for joint stiffness modulation results in a functional and practical wrist joint design. The successful functional evaluation of the RoboWrist under different load settings proves its efficacy in adapting to the diverse weight requirements of handled objects.

Lastly, this thesis delves into the critical aspect of precise finger positioning in hand prosthesis design. Proper finger positioning is essential to effectively apply the required pinching force during manual tasks, thereby improving the overall user experience. The proposed approach involves integrating three DC motors for accurate finger positioning before task performance. These motors control the flexion/extension movements of the index and triple fingers, while another motor facilitates the sliding movement of the thumb along a 3D trajectory on the palm. Additionally, the use of four-bar mechanisms further enhances finger joint actuation, maximizing the functionality of the proposed hand prosthesis. The design is validated through kinematic and structural analyses using ADAMS and ANSYS, setting the foundation for potential practical applications.

Bio:

A student with a fully funded scholarship in the M.Sc. program in mechanical engineering at Özyeğin University, Türkiye. Mahsa Sarrafi Khosrowshah Graduated from Islamic Azad University in Iran in 2017. She started her master’s program in mechanical engineering at Özyeğin University in 2020. She has worked in the Human-centered Design laboratory under the supervision of Assist. Prof. Dr. Ramazan Unal. Designing, developing, and evaluating body-powered hand and 2-DOF robotic wrist prostheses, in addition to designing and developing a pre-botic hand prosthesis, are her research experiences during her master’s. Her fields of interest are biomechanical, hand and wrist prostheses, upper-body prostheses, control, and design.