
B-65222EN/03 CONFIGURATIONS AND SELECTION 2.SELECTION METHODS
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2.1.4 Overload Duty Characteristic
A linear motor can be used intermittently, even out of its rated
continuous operating area, when the maximum force is not exceeded.
The overload duty characteristic represents the duty ratio (%) and "on
time" for which the motor runs under a given overload condition. The
conditions for the "on time" and "off time" of the motor can be
calculated as follows:
<1> Obtain the overload ratio using the following expression:
Overload ratio = load force ( rated continuous force
Then, the duty ratio (%) and on time of the motor can be
determined from the overload ratio and overload duty cycle
characteristic curves (shown on the next and subsequent pages).
Example:
To run the 1500A/4 (no cooling) with a load force of 360 N
at very low speed for one minute:
Overload ratio = 360 ÷ 300 = 1.2 (120%)
because the rated continuous force of the 1500A/4 is 300 N.
From the overload duty characteristic curve for the 1500A/4
with no cooling, the duty ratio (%) is determined to be 68%
when the motor runs with an overload ratio of 120% for one
minute.
<2> Obtain the off time of the motor using the following expression.
Off time = on time × (100 ÷ duty ratio (%) - 1)
Example:
From the value obtained in the example in <1>:
Off time=1×(100÷68-1)
0.47 minutes (about 28 seconds)
Therefore, it is necessary to keep the motor stopped for at
least 28 seconds after it runs for one minute under the
conditions described above.