Specifications
11– 6
11.SELECTION
11-5 Capacity selection
As a first step, temporarily select the servo motor capacity by calculating the load conditions. Next,
determine the command pattern, calculate required torques according to the following equations,
and confirm that the servo motor of the initially selected capacity may be used for operation.
(1) Initial selection of servo motor capacity
After calculating the load torque (TL) and load inertia moment (JL), select a servo motor which
will satisfy the following two relationships:
Servo motor's rated torque > TL
Servo motor JM > JL/m
m=3 : High duty (more than 100 times/min.)
Settling time 40ms or less
m=5 : Middle duty (60 to 100 times/min.)
Settling time 100ms or less
m= permissible load inertia moment : Low duty (less than 60 times/min.)
Settling time more than 100ms
Find the acceleration and deceleration torques and continuous effective load torque as described
in (2) to make a final selection. For high-duty positioning, the JL value should be as small as
possible. If positioning is infrequent as in line control, the JL value may be slightly larger than in
the above conditions.
(2) Acceleration and deceleration torques
The following equations are used to calculate the acceleration and deceleration torques in the
following operation pattern:
(3) Torques required for operation
Torques required for the servo motor are the highest during acceleration. If any of the torques
obtained with Equations 11-9 to 11-13 exceeds the maximum servo motor torque, the servo
motor speed cannot be increased as commanded. Confirm that the calculated value is lower
than the servo motor's maximum torque. Since a friction load is normally applied during
deceleration, only the acceleration torque needs to be considered.
Command pulse
frequency
Servo motor speed
[pps][r/min]
f
0
0
Nofo
Time
Time
Command
Servo motor
speed
Tpsa Tpsd
Ta
Td
Deceleration
torque
Acceleration
torque
• Acceleration torque Ta =
(JL+JM) • No
9.55 x 10
4
1
Tpsa
•
........................................................................ (11-9)
• Deceleration torque Tb =
(JL+JM) • No
9.55 x 10
4
1
Tpsd
•
...................................................................... (11-10)