8.5 Estimating the Moment of Inertia
8.5.1 Outline
8-16
8.5
Estimating the Moment of Inertia
This section describes how the moment of inertia is calculated.
The moment of inertia ratio that is calculated here is used in other tuning functions. You can
also estimate the moment of inertia during autotuning without a host reference. Refer to the fol-
lowing section for the procedure.
8.5.1
Outline
The moment of inertia during operation is automatically calculated by the SERVOPACK for
round-trip (forward and reverse) operation. A reference from the host controller is not used.
The moment of inertia ratio (i.e., the ratio of the load moment of inertia to the motor moment of
inertia) is a basic parameter for adjusting gains. It must be set as accurately as possible.
Although the load moment of inertia can be calculated from the weight and structure of the
mechanisms, doing so is very troublesome and calculating it accurately can be very difficult
with the complex mechanical structures that are used these days. With moment of inertia esti-
mation, you can get an accurate load moment of inertia simply by operating the motor in the
actual system in forward and reverse a few times.
The motor is operated with the following specifications.
•
Maximum speed:
±
1,000 min
-1
(can be changed)
•
Acceleration rate:
±
20,000 min
-1
/s (can be changed)
•
Travel distance:
±
2.5 rotations max. (can be changed)
8.5.2
Restrictions
The following restrictions apply to estimating the moment of inertia.
Systems for which Execution Cannot Be Performed
•
When the machine system can move only in one direction
•
When the range of motion is 0.5 rotations or less
Systems for Which Adjustments Cannot Be Made
Accurately
•
When a suitable range of motion is not possible
•
When the moment of inertia changes within the set operating range
•
When the machine has high dynamic friction
•
When the rigidity of the machine is low and vibration occurs when positioning is performed
•
When the position integration function is used
•
When proportional control is used
Note: Execute moment of inertia estimation after jogging to
a position that ensures a suitable range of motion.
SERVOPACK
Travel distance
Servomotor
Travel distance
Responses
References
Movement
speed
