Chapter 9 Order guide
69
9.1 Capacity selection
Servo capacity is relative to the load inertia, the load torque, the orienting precision and
max. speed required which are taken into account by the following steps:
1） Calculation of inertia and torque of load, torque of acceleration and deceleration
① Calculation of torque
The load torque is caused by the friction and cutting force of the driver.
2πM = FL
M ── Torque of motor shaft
F ── Force required for moving the mechanical parts in linear direction
L ── Distance of moving mechanically for a revolution (2 π rad) of
motor
2πM is the work done by the motor torque M in a revolution, while FL is the
work done by force F moving an object for L distance.
Practically, due to the factors of transmission efficiency and friction coefficient,
the torque required by ball screw overcoming the external load force P for
uniform velocity movement is shown as following diagram:
With pre-fastened
double nuts
Servo
motor
Ball screw
， －Tooth number
An example for servo feeding drive system
Calculate it by the following equation:
M
1
＝（K
π
2
F
0 spa
h
＋
1
2
P
πη
sp
h
＋M
B
）
2
1
Z
Z
Ｍ
1
—— Drive torque for uniform velocity movement
K
π
2
F
0 spa
h
—— Pre-fastened torque of double nuts ball screw（N•mm）
F
a0
——Pre-fastened force, it generally amounts to one third of the
Chapter 9 Order guide
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