YASKAWA MOTIONPACK-110 Descriptive Information page 246

When starting and stopping are repeated very frequently, the thermal capacity may
sometimes become insufficient due to acceleration and deceleration torque, so that effective
torque must be calculated to check the capacity. When the operation is made with a pattern
as shown in Fig. 12.2, the effective torque T,,, required for the motor is given by
/T_ • t, +T_ • t2+ (TA- TL)2. t3 T,m,
[kg
m]
(4)
v
t f+ t2 + t3 + t4
The rated torque of themotor selected must be greater than T ....
As seen in equation (3), the motor selected must have a large starting torque and a
small value of GD 2 in order to reduce the acceleration time. That is, a motor with a large
power rating must be selected (power rating is obtained by dividing the equare value of the
rated torque of motor by motor inertia; servo performance becomes better as the power
rating increases). As reference, the load GD 2 (GD2L) can be calculated from the following
equations:
• GD 2 (GD2r) for table
GD2r = 0.101W _ [kg • m 2] ....................................... (5)
• GD 2 (GD2B) for ball screw
GDZB = 125_ P LDo _ ............................................................ (6)
where, P : Specific gravity of the material of ball screwEg/cm 3]
D L: Length of ball screw [m]
Do: Diameter of ball screw [m]
• GD 2 (GDZc) of coupling
Sum of values of GD 2 shown above is equal to the load GD 2. That _s,
GD2L =GD2r+_-_ GD2B + GDXc
D 1
where, -_-: reduction ratio
GD 2 for coupling is often ignored but it must always be included in calculation.
MOVING PART (TABLE)
<_ _>V FEED SCREW
OR,V,..O OR B--- l
I h J /-°°
_ _ l/1111111111Yl111_, " .
/l/ll/llllrl/A u J
DETECTOR
(TG+PG)
Fig. 12.1 Machine Configuration
D m
235