Static balancer of a 4-DOF manipulator with multi-DOF gravity compensators

This paper proposes a Gravity compensator (GC) for a humanlike four Degrees-of-freedom (4-DOF) manipulator in that three 2-DOF and two 3-DOF unit GCs are used. The equivalent mapping analyses show that various types of multi-DOF GCs can be classified into their own type of DOF regardless of the order of successive rotations and selection of reference frames. Therefore, the selection of multi-DOF GCs has become simple. A method for the placement of unit GCs is proposed. For the 4-DOF manipulator sixteen combinations of unit GCs are obtained and various designs (mapping matrices) can be further developed for an each combination considering locations of unit GCs. The 5-GC combination is chosen among various designs. The placement of the unit GCs is conducted for the 5-GC combination, and its performance is evaluated with a numerical simulation. The case study showed that most of the unit GCs are applicable to the 4-DOF manipulator and the same placement of unit GCs is achieved for all applicable unit GCs.