Figure 7

Sensitivity of hand path and segment trajectories to applied perturbations. Here, error vector magnitudes are tuned to produce a straighter path by emphasis of shoulder over elbow. The remaining parameters in the controller are identical to those in Figure  5. Notice that the trajectories for each hand path speed in (b), (c) and (d) refer to the same path labels in (a); solid black line (no perturbations), blue line (sustained perturbations), red line (pulse perturbations), green line (trajectory planning motion). Finally, observe that the speed profiles are not identical for each motion even though the initial hand-target distance is identical in magnitude. Also, motion (d) completes sooner – it is caused the geometric configuration and changes in motor drive of the shoulder/elbow with respect to one another. For more information see Figure  10. For each hand speed plot, the sustained perturbation time is shown as a dark grey bar, while the pulse perturbation time is shown as a black bar.