Calculating inertia moment
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Object form
Mass, inertia,
gravity center
Object form
Mass, inertia,
gravity center
Rhombus pillar
Hexagonal pillar
Isosceles triangle
pillar
Right triangle pillar
Example of specific gravity
The following tables show reference values for specific gravity. Confirm the specific gravity for the
material of the drive load.
Material
Specific gravity
[
×
10
3
kg / m
3
]
Material
Specific gravity
[
×
10
3
kg / m
3
]
Material
Specific gravity
[
×
10
3
kg / m
3
]
SUS304
7.93
Aluminum
2.70
Epoxy resin
1.90
S45C
7.86
Duralumin
2.80
ABS
1.10
SS400
7.85
Silicon
2.30
Silicon resin
1.80
Cast iron
7.19
Quartz glass
2.20
Polyurethane rubber
1.25
Copper
8.92
Teflon
2.20
Brass
8.50
Fluorocarbon resin
2.20
(2) Both centerlines of rotation and gravity are not the same:
The following formula calculates the inertia moment when the rotary center is different from the gravity
center.
I
: Inertia moment when the gravity center axis does not match
the rotational axis [kg·m
2
]
I
g
: Inertia moment when the gravity center axis matches the
rotational axis [kg·m
2
]
Calculate according to the shape by using formula (1).
m
: Mass [kg]
F
: Distance between rotary center and gravity center [m]
(3) Inertia moment of linear motion objects
The inertia moment, converted to FHA-C actuator axis, of a linear motion object driven by a screw, etc.,
is calculated using the formula below:
I
: Inertia moment of a linear motion object converted to actuator axis [kg·m
2
]
m
: Mass [kg]
P
: Linear travel per actuator revolution [m/rev]
Rotary
center
Gravity
center
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
=
