  A new kind of six degree-of-freedom teaching manipulator without actuators is
designed, for recording and conveniently setting a trajectory of an industrial
robot. The device requires good gravity balance and operating force performance
to ensure being controlled easily and fluently. In this paper, we propose a
process for modeling the manipulator and then the model is used to formulate a
multi-objective optimization problem to optimize the design of the testing
manipulator. Three objectives, including total mass of the device, gravity
balancing and operating force performance are analyzed and defined. A popular
non-dominated sorting genetic algorithm (NSGA-II-CDP) is used to solve the
optimization problem. The obtained solutions all outperform the design of a
human expert. To extract design knowledge, an innovization study is performed
to establish meaningful implicit relationship between the objective space and
the decision space, which can be reused by the designer in future design
process.
