We present a hybrid spring system called CoiLeaf spring that offers superior space utilization and energy-storage performance by employing a combination of compression coil springs and leaf springs. The concept of this spring was verified in the design space of a compact variable gravity compensator (CVGC) developed by our group. Initially, we defined the space available for spring utilization in the CVGC as the Γ-space and allocated it to two design spaces for compression coil springs and leaf springs. Next, we derived the design constraints for the springs and optimized the compression coil spring on the basis of these constraints. Then, we selected a commercially available spring that was the closest to the optimized one. By contrast, the custom-fabricated leaf spring was optimally designed to maximize energy storage. Thereafter, we used Python scripting to construct the optimization process by linking finite element analysis software with mathematical computing software. Finally, we fabricated the proposed CoiLeaf spring. The energy storage capacity of the CoiLeaf spring system was experimentally measured as 11.38 J. Compared to the general systems utilized in the Γ-space, the maximum energy-storage capacity of the proposed CoiLeaf spring system was 5.47 times higher.

Funding Information
* The Samsung Research Funding & Incubation Center of Samsung Electronics under Project Number SRFC-IT1903-02