4-Bar Linkage mechanical knee prostheric

Hi Everybody!
This project comes as a remix of Incept 3D's Leg prosthetic.

Disclaimer: This prosthetic leg design is an experimental prototype and is provided as-is for educational and developmental purposes only. It is not certified, approved, or tested for clinical, medical, or long-term use.

Here are main improvements of the new model compared to the original:

1. New hole sizes for Metric system heat threaded Inserts.
2. Main leg component is now a more avaliable M12 Screw and Nut.
3. Spring mechanism to lock the M12 Screw in place.
4. Many TPU parts to get around wide tolerances due to printing imperfections and to dampen the movement and provide a more comfortable experience.
5. Thicker and more robust foot.
6. Flexible foot on the fingers' level.
7. Different shaft lengths for different heights.

4-Bar linkage:

Description:
The 4-bar linkage uses four connected bars arranged in a parallelogram structure to mimic the natural motion of a human knee. ([1] S. Phoengsongkhro et al., "Development of four-bar polycentric knee joint with stance-phase knee flexion," Sci. Rep., vol. 12, no. 1, p. 18338, Oct. 2022.)

Advantages:

The mechanism relies solely on bearings, thus no friction between the 3d printed parts. The retraction during swing allows for better ground clearance and reduced risk of tripping. It also enables more natural gait patterns compared to single-axis knees. The mechanism is stable at stance, comfortable swing phase, closer to anatomical motion, and adaptable to walking speeds.

Disadvantages:
The main disadvantages of the 4-bar linkage are the maximal angle of rotation of 90° as well as requiring tight bearing tolerances for a precise alignment to avoid twisting the whole assembly. It is also high-profile, having 3 moving bars required to be as thin and strong as possible, as well as being compact at the same time. The lower leg doesn‘t touch the ground when sitting due to the mechanism’s retracting motion.
 

IMPORTANT NOTES:
ONLY BUY 2x90mm SHOULDER SCREWS and 2x45mm SHOULDER SCREWS for this model

PAUSE THE PRINT for the leg's inner shaft TO INSERT THE TPU DAMPERS AND M12 NUT

Bill Of Materials:

Important parts Images:

1-Shoulder screws

2- Micro Steel Deep Groove Ball Bearings 688ZZ (4PCS) - EA026

Please refer to the original Incept 3D model for the build instructions!
There are only some minor changes as the TPU parts to be glued as shown in the pictures (blue parts are out of TPU and are to be glued)
 

Build Photos: