36
Selection of Servomotor Size
Selection of Servomotor Size
Motions
Rotational Motion
Linear Motion
Horizontal Axis
Vertical Axis
Mechanical Configuration
Speed Diagram
Travel Distance (m)
Min. Starting Time (S)
Min. Braking Time (S)
Running Power (W)
Acceleration Power (W)
Load axis speed
(min
-1
)
Motor Speed (min
-1
)
Effective Load Torque at
Motor Shaft (N
m)
Required Starting Torque
(N
m)
Required Braking Torque
(N
m)
Effective Torque(N
m)
Effective Load Inertia at
Motor Shaft (kg
m
2
)
Rotational Motion
Linear Motion
Servomotor
R
=
2
Servomotor
Lead
:
P
B
Lead
:
P
B
Servomotor
Counterbalance
Speed
Speed
For motion of vertical axis
Torque
Torque
Cycle time
t
(
s
)
0
9.8
×
µ
M
P
B
P
B
2
π
N
M
(
J
M
+
J
L
)
2
<Inertia for motor shaft>
At gear input side
Solid cylinder
= 7.87
×
10
3
(kg/m
3
)
= 2.70
×
10
3
(kg/m
3
)
8
1
L (m)
At gear output side
V
V
T
p
T
L
T
S
t
a
t
c
t
m
t
e
t
d
V
M
C
N
R
N
N
=
N
M
=
N
R
V
P
B
2
t
a
+ 2
t
c
+
t
d
Where
t
a
=
t
d
,
P
B
: Ball screw lead (m)
M
: Mass of linear-motion unit (kg)
M
C
: Mass of counterbalance (kg)
M
µ
M
1/R
1/R
1/R
60
V
N
=
V
P
B
J
L3
J
L3
J
L2
J
L1
J
L1
J
L1
J
L3
J
L2
J
L2
T
T
L
=
T
L
=
J
L
=
J
L1
+
J
L2
+
J
L3
J
L1
=
(M + M
C
)
J
L1
=
M
2
π
R
9.8
×
( M – M
C
)P
B
T
L
=
2
P
B
2
π
R
J
K
=
M
K
D
2
or
J
K
=
L
D
4
J
L2
=
J
K
J
L3
=
J
K
R
2
t
am
=
2
π
N
M
(
J
M
+
J
L
)
t
dm
=
2
π
N
M
T
L
60
P
0
=
2
π
60
N
M
P
a
=
J
L
t
a
2
π
N
M
(
J
M
+
J
L
)
60
×
t
a
T
P
=
+
T
L
2
π
N
M
(
J
M
+
J
L
)
60
×
t
d
T
S
=
–
T
L
T
P
2
t
a
+
T
L
2
t
c
+
T
S
2
t
d
T
rms
=
t
T
P
2
t
a
+
T
L
2
(
t
c
+
t
e
)
+
T
S
2
t
d
T
rms
=
t
D (m)
Formulas for Selecting Servomotor Capacity
R
= (
tm – ta)
60
V
32
: Mass (kg)
: Density (kg/m
3
)
Iron
Aluminum
M
K
Load axis speed (min
-1
)
Load speed (m/min)
Effective load torque
at motor shaft (N
m)
Friction coefficient
N
:
V
:
T
:
µ
:
:Gear ratio
:Combined efficiency
:Servomotor maximum
torque (N
m)
1/R
T
M
R
2
π
R
2
π
R
π
60 (
T
M
–
T
L
)
60 (
T
M
+
T
L
)
