Comparison of various balance systems for energy conservation in a vertically articulated manipulator with three joints

It is important to conserve dissipated energy from machines in order to reduce global warming. This paper discusses energy conservation in a vertically articulated three-joint manipulator with a rotation–pivot–pivot structure. The amount of dissipated energy can be decreased by canceling out the gravity on the second and the third links of the manipulator using a mass balancer or a spring balancer. Mass balancers are designed optimally by diminishing the inertia matrix so that the amount of dissipated energy can be minimized. Three kinds of counterbalancer systems, which include a mass–mass balancer, a spring–mass balancer and a spring–spring balancer, are designed optimally. Energy is compared among the three types of counterbalancers mounted on a three-link manipulator in simulation. The simulation indicates that a spring–mass balancer is more practical because of the considerable energy conservation effect and simplicity in implementation. In order to confirm the simulation results, the dissipated energy is measured experimentally using a practical system of a directly-driven manipulator on which a suboptimal mass–mass balancer or a spring–mass balancer is mounted. As a result, the measured dissipated energy is approximately the same as the result obtained by simulation.