Appeal No. 1998-1078 Page 2
Application No. 08/442,532
the drive coils and an FG magnetized portion that opposes the
FG pattern.
The rotational speed and position of a conventional
brushless motor are controlled as follows. The FG pattern
outputs the sinusoidal FG signal shown in Fig. 7(b) of the
appellants' specification. The sinusoidal FG signal is
converted into the pulse-like FG signal shown in Fig. 7(c) of
the specification. The pulse-like FG signal's leading edge
point "a" or point "b" shown in Fig. 7(c) can serve as a
trigger point for rotational control. Alternatively, the
sinusoidal FG signal's zero-crossing point "a" or zero-
crossing point "b" shown in Fig. 7(b) can be used as the
trigger point.
The torque ripple of the motor is shown in Fig. 7(a).
When the period of the ripple equals the period of the
FG signal, or an even number multiple thereof, the minimum
point "c" of the motor torque due to the torque ripple
coincides with the leading edge "a" or the trailing edge "b"
of the pulse-like FG signal, and therefore also coincides with
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