ERROR IN JOINT 2 (DEGREES) ERROR IN JOINT 1 (DEGREES) ,-6.00 -3.00 0.00 3.00 6.00 -3.00 -1.50 0.00 1.50 3.00 131 (a) Tracking error Figure 7-14 Manipulator's response: ref. = 0; dist. = 2.0 Hz sinusoid with amplitude of 50 N; I.M. frequency = 0 Hz