Appendix 2 Calculations of moment of inertia
- Appendix 2-2 -
Shape of object
Mass, inertia,
position of center of gravity
Shape of object
Mass, inertia,
position of center of gravity
Rhombic prism
Regular hexagon prism
Equilateral triangular
prism
Right-angled triangular
prism
◆
Example of specific gravity
The following table shows informative values of specific gravity. Please check actual specific gravities of
materials individually.
Material
Specific gravity
Material
Specific gravity
Material
Specific gravity
SUS304
7.93
Aluminum
2.70
Epoxy resin
1.90
S45C
7.86
Duralumin
2.80
ABS
1.10
SS400
7.85
Silicone
2.30
Silicone resin
1.80
Cast iron
7.19
Quartz glass
2.20
Urethane rubber
1.25
Copper
8.92
Teflon
2.20
Brass
8.50
Fluorine resin
2.20
(2) When center of revolution and line of center of gravity do not match
Moment of inertia when axis of center of gravity and axis of revolution of an inertia field do not match is
calculated by the following formula.
I: Moment of inertia when axis of center of gravity and axis of
revolution do not match (kgm
2
)
Ig: Moment of inertia when axis of center of gravity and axis of
revolution match (kgm
2
)
Calculated by formula shown in (1) in accordance with shape.
m: Mass (kg)
F: Distance between axis of revolution and axis of center of gravity (m)
(3) Moment of inertia of linear motion object
The moment of inertia converted into an FHA-C actuator axis of a linear motion object driven by a screw
is calculated by the following formula.
I: Moment of inertia converted into actuator axis of a linear motion object (kgm
2
)
m: Mass (kg)
P: Amount of linear movement per revolution of actuator (m/rev)
Axis of
revolution
Axis of center
of gravity
F
ρ
ABC
2
1
m
=
+
=
2
2
C
3
2
2
B
m
12
1
Ix
+
=
2
2
C
3
2
A
m
12
1
Iy
+
=
2
B
A
m
12
1
Iz
2
2
3
C
G
=
G
z
x
y
B
A
C
G
1
z
x
y
B
A
G
2
C
ABC
ρ
2
1
m
=
(
)
2
2
C
B
m
36
1
Ix
+
=
+
=
2
2
C
3
2
A
m
12
1
Iy
3
C
G
1
=
+
=
2
2
B
3
2
A
m
12
1
Iz
3
B
G
2
=
z
x
y
C
A
B
ρ
ABC
2
1
m
=
(
)
2
2
C
B
m
24
1
Ix
+
=
(
)
2
2
2A
C
m
24
1
Iy
+
=
(
)
2
2
2A
B
m
24
1
Iz
+
=
z
x
y
B
B
√
3
A
2
B
m
12
5
Ix
=
+
=
2
2
B
2
5
A
m
12
1
Iy
+
=
2
2
B
2
5
A
m
12
1
Iz
ρ
AB
2
3
3
2
=
m
2
mF
Ig
I
+
=
2
2
P
m
I
π
=
