**4. Application scenario 2: contour tracing in two dimensions**

The contour tracing task was conducted to verify the proposed method in realizing fast and accurate trajectory motion control under internal and external uncertainties [25]. Robotic contour tracing (contour following) is a useful technique in manufacturing tasks such as welding and sealing. Fast and accurate contour tracing under uncertainty from both a robot system and external environment is quite challenging. In this study, the task was confined in two dimensions. The experimental testbed is shown in **Figure 7**. The target is a closed curve with irregular contour pattern (2.5 mm width) printed on a paper which is placed on a stage. External disturbance is exerted on the stage to simulate environmental uncertainty. The same parallel-link robot was deployed as the main robot to execute the fast, coarse global motion. A two-DOF compensation module was configured at the end effector of the main robot. The same VGA camera was globally configured to realize the motion planning for the main robot's coarse positioning.
