In this article, we propose a compact variable gravity compensation (CVGC) mechanism with a geometrically optimized lever shape. The CVGC mechanism can be used to generate gravity compensation torque by employing a cam and lever mechanism and can also amplify the gravity compensation torque by varying the pivot point of the lever. Among these advantages, we aimed to maximize the variable ratio of torque generation with an optimized lever. First, the mechanism concept and details of the CVGC mechanism are explained. Next, the conceptual benefit of using a curved lever instead of the original lever is explained. Afterward, the modeling and mechanics of the testbed using a curved lever are presented for force analysis. Based on these mechanics and B-spline curve representation, the methodology for optimizing the curved lever and cam profile design is presented. Finally, the performance of variable gravity compensation using the optimized lever is verified through experiments that compare the designed and measured gravity compensation torque. As we had hoped, the verification test shows that using the optimized curved lever improves the variable ratio from 5.27 to 14.43.

Funding Information
* The Samsung Research Funding and Incubation Center of Samsung Electronics under Project SRFC-IT1903-02
* The Chung-Ang University Graduate Research Scholarship in 2019