172 Computed-Torque Control 1 =ATAN2(y, x)-ATAN2 (a 2 sin 2 , a 1 +a 2 cos 2 ) (6) Figure 4.2.1: Two-link planar elbow arm. Figure 4.2.2: Desired Cartesian trajectory. Copyright © 2004 by Marcel Dekker, Inc.