A novel gravity compensation mechanism for orthogonal DoFs with coupled springs

A novel gravity compensation mechanism for orthogonal DoFs (degrees of freedom) comprised of springs, wires, and pulleys is proposed and validated on a previously developed humanoid waist. The mechanism utilizes two groups of springs coupled with wires and pulleys to counterbalance gravitational potential energy in a coupling way. It provides high versatility for existing robotic systems and high freedom in design without being restricted by the location of the springs. Nine implementation methods are illustrated based on the location of the springs and the placement of the spring-side pulleys. The mechanism was validated on a fixed-base humanoid waist with adjustable springs for different load demands. A current consumption experiment was conducted to quantify the compensation rate based on motor current, showing a static compensation rate of ≥ 90% at maximum tilt angles. A path repetition experiment showed that the Euclidean distance between reference and measured paths was reduced by 57.8% with gravity compensation. These results indicate that the mechanism effectively reduces actuator burden and improves robot performance. • Novel spring coupling for gravity compensation in pitch and roll rotations. • Nine theoretical types of implementations according to spring and pulley locations. • Application to a fixed-base humanoid waist with adjustable spring configuration. • Significant reduction in motor current consumption and improvement in path accuracy.