Page 171 - Mechatronic Systems Modelling and Simulation with HDLs

160 7 MECHATRONICS

Graph0
[V] : t(s)
Control voltage
2.8
2.4
[V]
2.0
1.6
[A] : t(s)
1.0
Controlled current
0.5
[A] 0.0
−0.5
−1.0 [rad/sec]: t(s)
60.0 Velocity
40.0
[rad/sec] 20.0
0.0
[#track]: t(s)
25000.0 Track
20000.0
[#track] 15000.0
10000.0
5000.0
0.0
−5000.0
0.0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 0.011 0.012 0.013 0.014 0.015 0.016 0.017 0.018 0.019
t(s)
Figure 7.17 Simulation results for long seek over 20 000 tracks. From top to bottom: digital
output of firmware controller, controlled current, velocity of rotational actuator and track-number

be combined with a model of the test equipment, which allows test program devel-
opment to be initiated long before silicon is available.
The support of application engineering is mostly about analyzing the system
to explain spurious behaviour, which in turn allows solutions to be devised and
implemented. This includes fault modelling for the components of any domain.
One might easily include, amongst many others:

• Head assembly resonances of certain frequencies (mechanics)
• On-resistances of power transistors higher than specified (analogue electronics)
• Timing problems in the serial communication between motion-control and disk
controller (digital electronics)
This facilitates the assessment of the influence of the respective fault on system
behaviour, which in turn can be compared to the behaviour observed in field.

7.5.7 Conclusion

The section has given an overview on state of the art disk drive technology and
indicates how this translates into requirements for disk electronics. Moreover, it
has shown how system modelling and simulation can support a related electronics
product throughout its entire life-cycle. In that vein, the multi-domain nature of
the system increases both the need for a systematic solution and the problems
associated with modelling and simulation at the same time.