Mitsubishi Electric MELDAS MDS-B-SVJ2 Series, Технические характеристики и инструкция по эксплуатации

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Chapter 11 Selection
11-7
11-3 Selection of servomotor capacity
The following three elements are used to determine the servomotor capacity.
1. Load inertia ratio
2. Short time characteristics (acceleration/deceleration torque)
3. Continuous characteristics (continuous effective load torque)
Carry out appropriate measures, such as increasing the motor capacity, if any of the above conditions
is not fulfilled.
11-3-1 Load inertia ratio
Each servomotor has an appropriate load inertia ratio (load inertia/motor inertia). The control becomes
unstable when the load inertia ratio is too large, and parameter adjustment becomes difficult. It
becomes difficult to improve the surface precision in the feed axis, and the positioning time cannot be
shortened in the position axis because the settling time is longer.
If the load inertia ratio exceeds the recommended value in the servomotor list of specifications,
increase the motor capacity or change to a motor series with a large inertia. Note that the
recommended value for the load inertia ratio is strictly one guideline. This does not mean that
controlling a load with inertia exceeding the recommended value is impossible.
POINT
When selecting feed axis servomotors for NC unit machine tools, place
importance on the surface precision during machining. To do this, always
select a servomotor with a load inertia ratio within the recommended value.
Select the lowest value possible within that range.
11-3-2 Short time characteristics
In addition to the rated output, the servomotor has an output range that can only be used for short
times such as acceleration/deceleration. This range is expressed at the maximum torque. The
maximum torque differs for each motor even at the same capacity, so confirm the torque in section
"10-2 Servomotor".
The maximum torque affects the acceleration/deceleration time constant that can be driven. The linear
acceleration/deceleration time constant ta can be approximated from the machine specifications using
expression (11-2). Determine the maximum motor torque required from this expression, and select the
motor capacity. The same selection can also be made by using the simple motor capacity selection
diagrams on the last pages of this section (11-3).
ta =
(J
L
+ J
M
)
×
N
95.5
×
(0.8
×
T
MAX
−
T
L
)
(msec) .................................................. (11-2)
N : Motor reach speed (r/min)
J
L
: Motor shaft conversion load inertia (kg·cm
2
)
J
M
: Motor inertia (kg·cm
2
)
TMAX : Maximum motor torque (N·m)
T
L
: Motor shaft conversion load (friction, unbalance) torque (N·m)