We propose a concept for a gravity compensator designed for prismatic joints. The compensator depends on the suspension of linear springs together with transmission mechanisms to achieve constant application of force along the sliding span of the joint. We introduce the use of self-locking worm gears to ensure isolation of spring forces. A 2-DoF system which consists of a revolute and a prismatic joints is investigated with the proposed compensator. We introduce the use of pin-slot mechanism to transform rotational motion of the revolute joint into linear wire displacement. We introduce a design methodology of the compensator and selection of parameters to achieve static balancing. The results of simulation show complete compensation of gravity force leading to zero actuator effort.