
B-65232EN/03 DESCRIPTIONS FOR FANUC AC SERVO MOTOR β series 3.INSTRUCTIONS
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3.2 MACHINE MOVEMENT PER 1 REVOLUTION OF MOTOR
SHAFT
The machine movement per 1 revolution of motor shaft must be
determined at the first stage of machine design referring the load
torque, load inertia, rapid traverse speed, and relation between
minimum increment and resolution of the position sensor mounted on
the motor shaft. To determine this amount, the following conditions
should be taken into consideration.
• The machine movement per 1 revolution of motor shaft ("L")
must be such that the desired rapid traverse speed can be
obtained. For example, if the maximum motor speed is 1500 rpm
and the rapid traverse speed must be 12 m/min., the amount of
"L" must be 8 mm/rev. or higher.
• As the machine movement per 1 revolution of motor shaft is
reduced, both the load torque and the load inertia reflected to
motor shaft also decrease.
Therefore, to obtain large thrust, the amount of "L" should be the
lowest value at which the desired rapid traverse speed can be
obtained.
• Assuming that the accuracy of the reduction gear is ideal, it is
advantageous to make the machine movement per 1 rev. of motor
shaft as low as possible to obtain the highest accuracy in
mechanical servo operations. In addition, minimizing the
machine movement per 1 rev. of motor shaft can increase the
servo rigidity as seen from the machine's side, which can
contribute to system accuracy and minimize the influence of
external load changes.
• An optimum condition for the servo system is attained when the
motor rotor inertia is equal to the load inertia reflected to the
motor shaft. If the machine operation is characterized by
repeated acceleration/ deceleration (for example, in a machine
such as a punch press or print board drill), a heating problem
may occur due to the current caused by acceleration and
deceleration. Should this occur, specify the amount of machine
movement per motor rotation so as to satisfy the optimum
condition as much as possible.