Comparison of Grasping Performance of Tendon and Linkage Transmission Systems in an Electric-Powered Low-Cost Hand Prosthesis

The popularization of fused deposition modeling (FDM) technology and open-source microcontrollers has permitted the explosion of electric hand prostheses that can be designed, shared, built, and operated at a low cost, under the Do It Yourself premise. Patients with limb reductions at the transcarpal or transradial level are best candidates to benefit from them. They manage the gross location with the remaining limb, while the built-in motors offer the possibility of controlling each finger independently. The number of mobile joints along the finger and the type of transmission can determine the quality of the grasp. Moreover, there is a need of objective procedures to assess the functionality of complete prototypes at reasonable effort. This work makes a critical review of the different transmission systems that can be found in most low-cost finger designs: linkage and tendon mechanisms. Mechanical performance has been analyzed using a standardized model of the index finger. Furthermore, robotic grasp quality metrics (GQM) have been used to evaluate by simulation the functionality of complete devices. Neither finger transmission design appeared clearly advantageous in the range of flexion studied. The evaluation of the complete devices gave slightly better quality grades for the linkage-driven model. Instead, tendon-driven model achieved a greater quantity of successful grasps. In the current state of art, some other aspects may have led to a dominant situation of the tendon-driven hands: fewer number of parts to be printed, easier assembly for a nonexpert user, advantageous in pursuit of lightweight devices.