Appeal No. 1998-1078 Page 3
Application No. 08/442,532
the zero-crossing points "a" and "b" of the sinusoidal FG
signal. Such coincidence delays the change of the speed of
the motor in response to an input of a speed control signal,
i.e., the speed control reaction is delayed. When the
brushless motor is used to drive a video tape recorder, for
example, the delay causes undesirable phenomena such as color
slippage and disturbance in the displayed image.
The appellants' invention aims to prevent the reaction
delay of a brushless motor by setting the relative positions
of the stator core, the magnetized poles of the rotor magnet,
the FG magnetized portion, and the FG pattern in a
circumferential direction so that the minimum point "c" of the
torque ripple shown in Fig. 3(a) of the appellants'
specification occurs at a different time than a point of an
output signal from the FG pattern that functions as a trigger
for rotation control. In other words, points "a" and "b"
shown in Figs. 3(b) and (c), which are used as trigger points
for rotational control, occur at a different time from the
minimum point "c" of the motor torque ripple. Preferably, the
relative positions are set so that the maximum point of torque
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