
B–65142E/04
4. SELECTING A MOTORDESCRIPTIONS FOR THE α series
37
Generate an operation cycle which includes rapid traverse. Write the
time–speed graph and time–torque graph as shown below.
In a common cutting machine, the frequency of positioning in rapid
traverse will cause no problems. In a special machine tool which
frequently executes rapid traverse, however, the motor must be checked
to see whether it is overheated by the current required for acceleration or
deceleration.
t
1
t
2
t
3
to
t
1
Ta+Tm
Tm
To
Tm–Ta
to
t
1
t
2
t
1
t
3
Time
Speed
Torque
Time
From the time–torque graph, obtain the root–mean–square value of
torques applied to the motor during the single operation cycle. Check
whether the value is smaller than or equal to the rated torque (condition
3).
Trms +
(Ta ) Tm)
2
t
1
) Tm
2
t
2
) (Ta–Tm)
2
t
1
) To
2
t
3
t
O
Ǹ
Ta : Acceleration torque
Tm : Friction torque
To : Torque when stopped
If Trms is smaller than or equal to 90% of the rated torque at stall (Ts), the
motor is judged to be usable.
(A margin including the overall thermal efficiency is considered.)
Example)
When an α3/3000 (Ts = 31 (kgf⋅cm) = 3.0 (Nm)) is used under the
following conditions: Ta = 12.1 (Nm), Tm = To = 0.9 (Nm), t1 = 0.1
(s), t2 = 1.8 (s), t3 = 7.0 (s)
Trms +
(12.1 ) 0.9)
2
0.1 ) 0.9
2
1.8 ) (12.1–0.9)
2
0.1 ) 0.9
2
7
t
O
Ǹ
+ 20.2(Nm) t Ts 0.9 + 2.9 0.9 + 2.61(Nm)
The α3/3000 can be used for operation. (Condition 3)
4.1.3
Calculating the
Root–mean–square
Value of the Torques
Calculating the
frequency of positioning
in rapid traverse