Setting of rotation time
Even if the torque that is required by the load in the rotation movement is small, the internal parts
could become damaged depending on the inertia of the load.
Therefore, select an appropriate model for your application by taking the load’s moment of inertia, kinetic
energy, and rotation time into consideration. (A chart that depicts the moments of inertia and the rotation
time is provided to facilitate the selection process.)
Moment of inertia
Moment of inertia is the tendency of a still object to resist rotation, or, conversely, the tendency of a
rotating object to resist stopping.
When the actuator moves an object (load), inertia (kinetic energy) is generated in the object.
The actuator stops at the rotation end, but due to inertia, a large shock (kinetic energy) is applied to the
rotary table. The kinetic energy can be calculated using the formula below.
2
2
1
I
E
E: Kinetic energy [
J
]
I: Moment of inertia [
2
m
kg
]
ω: Angular speed [
s
rad
]
There is a threshold of kinetic energy that a rotary actuator allows. Therefore, by finding the moment of
inertia, it is possible to find the threshold value of the rotation time.
The basic formula for finding the moment of inertia is shown below.
2
r
m
I
m
: Weight
[ kg ]
r : Center of gravity of load and distance of rotational axis [ m ]
This represents the moment of inertia for a shaft with mass m, which is located at distance r from the shaft.
The formula for finding the moment of inertia depends on the shape of the object.
A table of formulae for calculating moment of inertia is shown on the following page.
- 28 -
Fig. 10
[m]
m
[kg]
