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11.2 Reference Information for Servomotor Capacity Selection
11.2.1 Formulas Required to Select the Servomotor Capacity
11.2
Reference Information for Servomotor Capacity Selection
11.2.1 Formulas Required to Select the Servomotor Capacity
Type of Motion
Machine Configura-
tion
Speed Diagram
Travel distance (m)
Load Shaft Speed
-1
(min
)
Motor Shaft Speed
-1
(min
)
Load Torque Calcu-
lated at Motor Shaft
(Nm)
Load Moment of Iner-
tia Calculated at
Motor Shaft (kgm
Minimum Starting
Time (s)
11-4
Rotary Motion
Servomotor
N : Load shaft speed (min
V : Load speed (m/min)
T : Load torque calculated at load
shaft (Nm)
μ : Friction coefficient
T
L
2
)
Linear Motion
Section
Solid Cylinder
Rotary Motion
Hollow Cylinder
Section
D
D
0
(m) (m)
Moment of Inertia of Rotary Motion Section Calculated at Motor Shaft
Rotary motion section at gear input shaft
Horizontal Axis
N
R
Servomotor
1/R
-1
P
: Ball screw lead (m)
)
B
M: Linear motion section mass
(kg)
M
: Counterweight mass (kg)
c
Motor speed
Torque
V
T
p
T
L
0
T
t
s
a
One cycle, (S)
t
2t
t
V
+
+
a
c
d
=
R
60
2
N
N
T
=
T
=
R η
L
J
= J
L
–
J
L1
J
=
K
L (m)
(m)
D
L (m)
J
=
K
1
J
=
J
L2
K
2π
t
=
am
Linear Motion
V
M
R
μ
Counter-
weight
Lead:
P
B
1/R
1/R: Gear ratio
η : Mechanical efficiency
T
: Servomotor instantaneous
pM
maximum torque (Nm)
Motor speed
Torque
Vertical axis
t
t
d
c
t
t
m
e
t
V
t
t
t
t
= If... ,
=
(
-
)
R...
a
d
m
a
60
V
N =
P
B
= N R
M
μ
9.8 ×
M P
B
T
=
η
2π R
L
+ J
+ J
L1
L2
L3
2
P
(
)
B
=
M
J
=
L1
2π
R
π
1
2
J
M
D
OR
=
L
K
k
8
32
M
: Solid cylinder mass (kg)
k
: Density (kg/m
3
)...Iron
...Aluminum
1
2
2
J
M
(
D
+
D
)
OR
=
k
K
0
i
8
32
Rotary motion section at gear output shaft
N
(
J
+
J
)
M
M
L
T
T
60 (
-
)
PM
L
Continued on next page.
Vertical Axis
Servomotor
M
c
1/R
M
V
Lead:
P
B
9.8 × (
M M
-
)
P
c
B
2π R η
2
P
(
)
B
( +
M M
)
c
2π
R
4
D
3
3
= 7.87 × 10
(kg/m
)
3
3
= 2.70 × 10
(kg/m
)
π
4
4
L
(
D
-
D
)
0
i
J
K
J
=
L3
2
R
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