Abstract: The displacement analysis of the general spatial 7R mechanism is one of he most difficult tasks in the kinematic analysis of spatial mechanisms. In the paper published in 1980 by J. Duffy and C. Crane, the input-output equation for this mechanism was shown to be 32nd degree. Recently J. Duffy began to believe that the proper order of the input output equation should be lower. In the present paper the input-output equation without any unwanted roots has been worked out to be 16th degree by using a complex number method, which is much simpler in computer programming than the others. A numerical. Verification shows that the real roots are agreed with those obtained by J. Duffy.

Key words: feedforward compensation controller, hydraulic drive unit(HDU), Position control system, Hydraulic drive legged robot