This study is concerned with a cam type gravity compensation mechanism. A new type interior cam mechanism is introduced as an alternative gravity-balancing mechanism for robot arms. Cam profile of the mechanism is derived from static balancing condition of an unbalanced rotating arm which is combined with an interior cam. Configurational drawing and mechanical structure of the mechanism are presented. Finally, application of mechanisms on parallelogram version of 2R robot manipulator is given. (C) 2008 Elsevier Ltd. All rights reserved.