Design of gravity compensation mechanisms based on expansion of spring elongation

Gravity compensation mechanisms are essential for reducing energy losses in mechanical systems, with cable-pulley-spring units being a common implementation. Theoretical analysis of a classic unit reveals a fundamental trade-off: increasing spring elongation allows for reduced stiffness, which is particularly advantageous for systems requiring low spring stiffness and/or with limited motion ranges. However, systematic methods to achieve such elongation amplification remain underexplored. This study addresses this gap by proposing a spring elongation expansion method, derived from a reformulated elastic potential energy expression. Furthermore, the method is implemented through five proposed solutions, each corresponding to a novel mechanism. Each solution is systematically analyzed to establish kinematic and functional principles, supported by case studies and simulations. The proposed gear-based, X-type unit-based, and iris-based mechanisms achieve significant elongation improvements of 108.67%, 100.37%, and 83.87%, respectively. By synthesizing their parametric characteristics, this work provides a generalized design framework for high-performance gravity compensation systems, advancing energy-efficient mechanical design.