
B-65262EN/03 SPECIFICATIONS FOR THE αiS/αi SERIES 3.SELECTING A MOTOR
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[Selection condition 4] Acceleration torque
- Acceleration can be made with a desired time constant.
Since the load torque generally helps deceleration, if
acceleration can be executed with a desired time constant,
deceleration can be made with the same time constant, through
both acceleration and deceleration should be considered in
principle. Calculate the acceleration torque and check that the
torque required for acceleration is within the intermittent
operating zone of the motor.
[Selection condition 5] Root-mean-square value of torque
- The root-mean-square value of torque in a cycle must be
sufficiently greater than the stall torque.
A motor gets hot in proportion to the square of the torque. For a
servo motor for which the load condition always changes, the
calculated root-mean-square value of torque in a cycle must be
sufficiently greater than the stall torque.
Pay attention, in particular, when the cutting load,
acceleration/deceleration condition, and other load conditions
variously change in a cycle.
When the desired frequency of positioning in rapid traverse
becomes greater, the ratio of the time during which the
acceleration/deceleration torque is being applied to the entire
operation time increases and the root-mean-square value of
torque increases. In this case, increasing the
acceleration/deceleration time constant is effective to decrease
the root-mean-square value of torque.
[Selection condition 6] Percentage duty cycle and ON time with the maximum
cutting torque
- The time during which the table can be moved with the
maximum cutting torque (percentage duty cycle and ON
time) must be within a desired range.
The continuously applied torque such as the cutting load may
exceed the stall torque. In this case, use overload duty curves to
check how the ratio (percentage duty cycle) of the load applying
time to the no-load applying time and the time during which the
load is being applied (ON time) change.
[Selection condition 7] Dynamic brake stop distance
- The stop distance when the dynamic brake is applied at an
emergency stop must be within a desired range.
If the stop distance is not within the desired range, the machine
may cause a collision at an emergency stop.
The following sections explain the procedure for selecting a motor
sequentially for each selection condition. Determine whether each
selection condition above is satisfied.