Gripping Orthotic (Cable-Driven Finger Exoskeleton)

Problem Definition

This project focused on designing and building a wearable, cable-driven orthotic to assist with finger flexion and gripping. In a team setting, we developed a 1-finger proof-of-concept device that converts a passive elastic return system and a single tendon-like cable into controlled grasping motion. The goal was to create a simplified, ergonomic assistive system capable of enabling grip without requiring active finger muscle force from the user.

The final design uses 3D-printed phalanx segments, a cable-driven actuation system, and elastic bands to replicate finger extension and flexion. A wrist-mounted anchor serves as the structural base for both the elastic return system and the motorized cable routing concept.

Design

The finger was modeled as a simplified multi-link system representing the MCP, PIP, and DIP joints. We designed custom 3D-printed phalanxes and a wrist mount that anchors both the elastic return system and the cable routing

The design prioritized simplicity, wearability, and low friction cable motion. Iterations focused on improving alignment between joints and ensuring consistent cable tension across all finger segments.

Prototype and System Function

The prototype was fabricated using PLA 3D-printed parts, braided nylon fishing line for the cable, and elastic bands for passive return. Although a motorized wrist-mounted actuator was planned, the final prototype used manual cable actuation for testing.

The system successfully demonstrated assisted gripping by curling the finger around a stress ball using cable tension, with full extension restored by the elastic band when released.

Modeling and Simulation

A simplified kinematic model was used to represent the finger as a linked chain of rigid segments with joint angles at the MCP, PIP, and DIP. A quasi-static tension model was used to describe the relationship between cable force and joint torque, prioritizing cable tension as the dominant input.

A Simscape Multibody simulation validated that a single MCP-driven torque input could produce coordinated multi-joint flexion when combined with elastic spring elements at each joint.

Results and Conclusions

This project reinforced how simplified biomechanical modeling and cable-driven actuation can be used to design effective wearable assistive devices. It also highlighted the importance of reducing complex dynamics into dominant physical behaviors for practical prototyping.

Skills

Mechanical Design and Prototyping

  • CAD of wearable systems
  • 3D printing
  • Ergonomic joint design
  • Cable-driven mechanisms

Biomechanics and Kinematics

  • Multi-link finger modeling
  • Joint kinematics
  • Quasi-static torque analysis

Data and Analysis

  • Simscape Multibody
  • Spring-damped joint modeling
  • Cable-actuated system simulation

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