Upper-Limb Rehabilitation Robot

From mechanisms to a wearable prototype

Person wearing the assembled upper-limb robot with hand linkage, forearm support and elbow structure — The integrated prototype during a wearable demonstration. The hand, wrist and elbow modules form one supported assembly.

The completed system combines a linear-actuator hand linkage, a belt-driven wrist and a linear-actuator elbow mechanism. Mechanical supports, motor actuation and sensor input were assembled and tested together.

Outstanding Course Project Award. Developed as a Shanghai Jiao Tong University Design and Manufacturing II course project in Fall 2024; the report was completed in January 2025.

Original project report (PDF, Chinese)

Hand grasping through a four-bar linkage

A linear actuator drives a four-bar linkage to couple movement of the hand-back support and the first segments of the four fingers. Extension bends the linked supports into a grasping posture; retraction opens them. Link lengths and attachment positions were adjusted to fit the hand, with supports at the wrist, hand back and finger segments. A separate stop locates the thumb.

Two mechanism sketches showing the linear-actuator-driven four-bar hand linkage in different configurations — Hand mechanism concept: actuator translation becomes coupled bending through the four-bar linkage.

CAD model of the hand support, finger linkage and linear actuator — The hand CAD model locates the actuator, linked finger supports and wearable attachment points.

Wrist rotation: gears to a synchronous belt

The initial wrist concept used meshing gears. Manufacturing the required gear surfaces added cost and machining complexity, so the detailed design moved to a synchronous belt transmission. The belt-driven assembly connects wrist rotation with the hand module while simplifying fabrication and maintenance.

CAD view of the integrated hand and wrist assembly with the forearm support — Integrated hand and wrist CAD assembly after the transmission design iteration.

Elbow motion and adjustable support

A linear actuator mounted along the upper-arm structure drives forearm flexion and extension through a guide mechanism. The original straight-guide concept was revised to a curved guide to reduce variation in the actuator's pressure angle over the motion. The upper-arm support provides several adjustment positions for different arm lengths.

CAD elbow assembly showing a curved guide plate, forearm linkage and adjustable upper-arm support — Elbow module CAD: the curved guide shapes motion transmission, while the upper-arm support adjusts the wearable fit.

Linkage geometry, support alignment and manufacturability were treated together: the actuator supplies translation, the guide controls the motion path, and the adjustable support locates the mechanism against the arm.

Embedded actuation and bilateral input

The prototype uses a 12 V DC supply and an STM32 microcontroller for motor actuation and sensor communication. The implementation includes PWM initialization, DC motor port control and software I²C communication.

An IMU worn on the opposite hand supplies motion input. Movement of that hand commands corresponding wrist movement on the robot, connecting the wearable mechanism to a bilateral motion interface.

Fabrication, assembly and demonstration

3D printing produced end caps, supports and guide components. Laser cutting was used for larger elbow parts and linkage/guide components, while machining produced higher-strength connectors. Purchased actuators, motors and straps completed the assembly.

Assembled rehabilitation robot held horizontally with motor electronics and hand linkage visible — The completed prototype brings the actuator, hand mechanism and arm support into one assembly.

Bench assembly and electrical debugging of the rehabilitation robot — Prototype assembly and electrical debugging at the workbench.

Prototype testing and the wearable demonstration brought together simple grasping, wrist rotation and elbow flexion/extension. Fit adjustment and linkage alignment were practical integration concerns; the demonstrated motions focus on these three functions.

CAD illustrations, mechanism drawings and prototype photos are from the original project report. Open any image for a larger view; the linked report retains its original text and credits.