128
to eliminate the sinusoidal error additional poles are introduced into
the I.M. system corresponding to the 4 Hz signal. The response is given
in Figure 7-17. Notice that the steady-state error is now virtually
zero. Figure 7-18 is presented simply to show the poor performance which
results from using an I.M. system consisting of just integrators.
Figures 7-19 through 7-21 illustrate the effects of applying both a
reference and a disturbance signal. First, poles at only the
frequencies of the reference and disturbance signals are included in the
I.M. system. The resulting response is shown in Figure 7-19. Since the
steady-state error in joint 2 has a large dc offset, integrators are
then incorporated into the I.M. system. The response is shown in Figure
7-20. Notice that the dc error has been eliminated, however a ripple at
a frequency of 6 Hz is present. The I.M. system is then modified to
accommodate for the 6 Hz signal and the response is given in Figure
7-21.
This concludes the tests of the rigid-link manipulator. In the
next section we consider a manipulator with flexible links.