
B-65262EN/03 SPECIFICATIONS FOR THE αiS/αi SERIES 3.SELECTING A MOTOR
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3.2 SELECTING A MOTOR
Sample model for calculations for selecting a servo motor
The following subsections explain how to calculate conditions for
selecting a servo motor best suited for a table with a horizontal axis
with the following specifications.
Sample mechanical specifications of the table and workpiece
W : Weight of movable parts (table and workpiece)
=11760[N]=1200[kgf]
w : Mass of movable parts (table and workpiece) =1200[kg]
µ : Friction coefficient of the sliding surface =0.05
η : Efficiency of the driving system (including a ball screw) =0.9
F
g
: Gib fastening force (kgf) =490[N]=50[kgf]
F
c
: Thrust counter force caused by the cutting force (kgf)
=4900[N]=500[kgf]
F
cf
: Force by which the table is pressed against the sliding surface,
caused by the moment of cutting force =294[N]=30[kgf]
Z
1
/Z
2
: Gear reduction ratio = 1/1
T
f
: Friction torque applied to the motor shaft =0.8[N⋅m]=8[kgf⋅cm]
Sample specifications of the feed screw (ball screw)
D
b
: Shaft diameter =40×10
-3
[m]=40[mm]
L
b
: Shaft length =1[m]=1000[mm]
P : Pitch =20×10
-3
[m/rev]=20[mm/rev]
Sample specifications of the operation of the motor shaft
T
a
: Acceleration torque [N⋅m][kgf⋅cm]
V : Workpiece rapid traverse rate =60[m/min]
V
m
: Motor speed in rapid traverse [min
-1
]
t
a
: Acceleration time (s) =0.08[s]
J
M
: Motor inertia [kg⋅m
2
][kgf⋅cm⋅sec
2
]
J
L
: Load inertia [kg⋅m
2
][kgf⋅cm⋅sec
2
]
k
s
: Position loop gain =30[s
-1
]