
B-65262EN/03 SPECIFICATIONS FOR THE αiS/αi SERIES 2.HOW TO USE SERVO MOTORS
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2.3.2 Allowable Axis Load for a Servo Motor
The allowable axis load on a motor shaft is given in the specifications
of the relevant motor in Part II and afterward. Using a motor under a
load higher than the allowable axial load may break the motor. When
designing a machine and connecting a motor to the machine, fully
consider the following points:
• The allowable radial load is determined, assuming that a radial
load is applied to the end of the shaft.
• Applying a load higher than the allowable axis load may break
the bearing. Applying a radial load higher than the allowable
radial load may break the shaft due to a fatigue failure.
• A radial load indicates the constant force continuously applied to
the shaft depending on the mounting method (such as belt
tension) and the force by the load torque (such as moment/pulley
radius).
• When a timing belt is used, the belt tension is critical
particularly. Too tight a belt causes a fault such as the broken
shaft. Belt tension must be controlled so as not to exceed the
limits calculated from the allowable radial load. Positioning the
pulley as close to the bearing as possible in design can prevent
possible faults such as the broken shaft.
• In some use conditions, the pulley diameter and gear size should
be considered. For example, when the model α4i is used with a
pulley or gear having a radius of 2.5 cm or less, the radial load at
the occurrence of a torque of 17.6 N⋅m (180 kgf⋅cm) will exceed
686 N⋅m (70 kgf). In this case, take measures such as supporting
the end of the motor shaft mechanically.
• If a motor may be used under a load higher than the allowable
axis load, the machine tool builder should examine the life by
referencing the shaft diameter, bearing, and other factors. Since
the standard single-row deep-groove ball bearing is used for the
motor bearing, a too high axial load cannot be used. To use a
worm or helical gear, in particular, use another bearing.
• The motor bearing is generally fixed with a C-snap ring, and
there is a small play in the axial direction. If the axial play
affects the positioning in the case of using a worm or helical gear,
fit it with another bearing.