
4. SELECTING A MOTOR
B–65142E/04
DESCRIPTIONS FOR THE α series
28
This section describes the procedure for selecting a servo motor best
suited for a table with a horizontal axis (figure below).
fg
µ
Fc
W
W : Weight of movable parts (table and workpiece) = 1000 (kgf) =
98000 (N)
w : Weight of movable parts (table and workpiece) = 1000 (kg)
µ : Friction coefficient of the sliding surface = 0.05
η : Efficiency of the driving system (including a ball screw) = 0.9
fg : Gib fastening force (kgf) = 50 (kgf) = 490 (N)
Fc : Thrust counter force caused by the cutting force (kgf) = 100 (kgf)
= 980 (N)
Fcf : Force by which the table is pressed against the sliding surface,
caused by the moment of cutting force = 30 (kgf) = 294 (N)
Z
1
/Z
2
: Gear reduction ratio = 1/1
Db : Shaft diameter = 32 (mm) = 32 × 10
–3
(m)
Lb : Shaft length = 1000 (mm) = 1 (m)
P : Pitch = 8 (mm) = 8 × 10
–3
(m)
Ta : Acceleration torque (kgf⋅cm) (Nm)
Vm : Motor speed in rapid traverse = 3000 (min
–1
) = 50 (s
–1
)
ta : Acceleration time (s) = 0.10 (s)
J
M
: Motor inertia (kgf⋅cm⋅sec
2
) (kg·m
2
)
J
L
: Load inertia (kgf⋅cm⋅sec
2
) (kg·m
2
)
ks : Servo position loop gain = 30 (s
–1
)
4.1
CALCULATING
CONDITIONS FOR
SELECTING A
MOTOR
Sample mechanical
specifications of the
table and workpiece
Sample specifications of
the feed screw
(ball screw)
Sample specifications of
the operation of the
motor shaft