Example Of Servo Selection; Motor Selection Calculation - Mitsubishi Electric MELDAS MDS-B-SVJ2 Series Specifications And Instruction Manual

11-5 Example of servo selection

A servomotor is selected using a machining center with the following specifications as an example.
Specification item
Axis type
Movement direction
Table support method
Table movement friction coefficient
Ball screw diameter
Ball screw length
Ball screw lead
Deceleration ratio
Primary side gear inertia
Secondary side gear inertia
Motor/ball screw connection section
inertia
Weight of moving object installed on the
machine (table, etc.)
Weight of standard added object
(workpiece, etc.)
Rapid traverse rate
Target acceleration/deceleration time
constant
Rapid traverse positioning frequency
Motor brakes

11-5-1 Motor selection calculation

The selection calculation is carried out in order using the Z axis
as an example.
(1) Obtaining the load inertia
Calculate the motor shaft conversion load inertia separately
for the rotation load and linear movement load. Furthermore,
calculate the rotation load inertia separately for the primary
and secondary side.
• Primary side rotation load inertia: J
This is the primary side gear inertia.
J = 1.6 (kg·cm
R1
• Secondary rotation load inertia: J
This is the sum of the ball screw inertia J
side gear inertia.
The ball screw is generally calculated as a cylinder made of steel.
Refer to section "11-7 Load inertia calculation"
J = J + 8.1 =
R2 B
= 19.6 + 8.1 = 27.7 (kg·cm
• Total rotation load inertia: J
This is the sum of the primary side load inertia and secondary side load inertia. To convert the
secondary side load inertia to the motor shaft (primary side), multiply by the square of the
deceleration ratio.
2
J = J + ( 3 )
R R1
• Linear movement load inertia: J
The inertia is calculated when a standard workpiece, tool, etc., is attached. The conversion to the
motor shaft by the deceleration ratio is included in the travel increment per motor rotation. Refer to
section "11-7 Load inertia calculation".
ΔS
J = W · (
T
20π
Chapter 11 Selection
Unit
%
mm
mm
mm
2
kg·cm
2
kg·cm
2
kg·cm
kg
kg
mm/min
msec
times/min.
R1
2
)
R2
and secondary
B
π · ρ · L
4
D + 8.1 =
32
2
)
R
4
2 × J 9 × 27.7 = 1.6 + 12.3 = 13.9 (kg·cm
= 1.6 +
R2
T
10 × 2
2
) = (400 + 10) · (
20π × 3
X axis
Linear
Horizontal
Rolling
5
40
900
10
1
−
−
2.0
500
100
30000
120
20
Not available Not available
− 3
π × 7.80 × 10 × 100
32
2 2
) = 4.6 (kg·cm
11-15
Y axis Z axis
Linear Linear
Horizontal Vertical
Rolling Rolling
5 2
40 40
800 1000
10 10
1 2/3
−
1.6
−
8.1
−
2.0
400 400
100 10
30000 20000
120 120
20 20
Available
Deceleration ratio = 2/3
Secondary Primary side
side gear gear
2
8.1kg·cm
400kg
Servomotor
10kg Ball screw
φ40, 1000mm
Fig. 11-3 Z axis configuration
× 4 4
+ 8.1
2
)
)
2
1.6kg·cm