Mitsubishi Electric MELDAS MDS-B-SVJ2 Series, Specifications And Instruction Manual

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Chapter 11 Selection
11-2
11-1 Outline
11-1-1 Servomotor
It important to select a servomotor matched to the purpose of the machine that will be installed. If the
servomotor and machine to be installed do not match, the motor performance cannot be fully realized,
and it will also be difficult to adjust the parameters. Be sure to understand the servomotor
characteristics in this chapter to select the correct motor.
(1) Motor inertia
The servomotor series is mainly categorized according to the motor inertia size. The features in
Table 11-1 are provided according to the motor inertia size.
Table 11-1 Motor inertia
Motor model Medium inertia motor Low inertia motor
Motor type HC
†
, HA
†
N, HC-SF HC
†
R, HC-RF, HA-FF, HC-MF
Inertia The flange size is large.
The inertia is comparatively large. The flange size is small.
The inertia is small.
Acceleration/deceleration The acceleration/deceleration time
constant does not change much even for
a low inertia load.
The effect of the motor inertia is large.
Acceleration/deceleration is possible
with a short time constant in respect to
low inertia loads.
The effect of the motor inertia is small.
Installation The motor size in respect to the output
capacity is large, and the installation
space is large. The motor size in respect to the output
capacity is small, and the installation
space is smaller.
Disturbance characteristics The effect of disturbance is small. The effect of disturbance is large.
Speed fluctuation The effect of the torque ripple and
cogging torque is small, and speed
fluctuation does not occur easily. The effect of the torque ripple and
cogging torque is large, and speed
fluctuation occurs easily.
Suitability Suitable for high precision interpolation
control
Suitable for high speed high frequency
positioning
Select a medium inertia motor when interpolation precision is required, or for machines having a
large load inertia. Select a low inertia motor when a shorter positioning time is required by
machines having a small amount of inertia. In general, use HC
†
and HA
†
N motors for axis
control of machine tools, and use HC
†
R, HC-SF, HC-RF, HA-FF and HC-MF motors for machine
tool auxiliary axes, peripheral axes, and general industrial machine positioning.
The servomotor has an optimum load inertia scale. If the load inertia exceeds the optimum range,
the control becomes unstable and the servo parameters become difficult to adjust. When the load
inertia is too large, decelerate with the gears (The motor axis conversion load inertia is
proportional to the square of the deceleration ratio.), or change to a motor with a large inertia.
POINT
The HC-MF motor has the lowest inertia. This series pursues low inertia motor
performance. To realize the proper acceleration/deceleration performance of
the low inertia motor, set the load inertia to within five times of the motor inertia.
If the load inertia ratio increases, the control stability will deteriorate, and in the
end the positioning will take longer.