Hardware Reference
In-Depth Information
2
1.5
1
0.5
0
0
0.5
1
1.5
2
2
Step input
Output
Response to 1st step
Response to 2nd step
1.5
1
0.5
0
0
0.5
1
1.5
2
Time (ms)
Figure 2.35: Cancelation of residual vibration by preshaping.
in the lower plot are the oscillatory responses to two step functions, and the
solid line shows the resultant. The output of the system to the staircase input
is vibration free after the second impulse is applied. It is obvious that values
of the relative amplitudes of impulses and phase between them, i.e., the values
of K and ∆T must be chosen exactly to achieve vibration-free response. Any
change in these values fails to suppress the vibration completely. Accurate
knowledge of the resonant mode is essential to make this method effective.
Command shaping method described above is very sensitive to parameter
variation, and it is not suitable for application in HDD where the designer does
not enjoy the freedom of selecting the sampling interval (T
S
). The separation of
impulses in the input shaper (∆T ) may not be an integer multiple of sampling
interval (T
S
). Use of input shaper with more impulses can resolve these issues.
