
4. SELECTING A MOTOR
B–65142E/04
DESCRIPTIONS FOR THE α series
30
D Allow for an increase in friction on the sliding surface (Fcf) caused by
the cutting resistance. The cutting resistance and the driving force
generally do not act through a common point as illustrated below.
When a large cutting resistance is applied, the moment increases the
load on the sliding surface.
When calculating the torque during cutting, allow for the friction
torque caused by the load.
Cutting force
Cutting force
Driving force
Driving force
D The feedrate may cause the friction torque to vary greatly. Obtain an
accurate value by closely examining variations in friction depending
on variations in speed, the mechanism for supporting the table (sliding
contact, rolling contact, static pressure, etc.), material of the sliding
surface, lubricating system, and other factors.
D The friction torque of a single machine varies widely due to
adjustment conditions, ambient temperature, and lubrication
conditions. Collect a great amount of measurement data of identical
models so that a correct load torque can be calculated. When adjusting
the gib fastening force and backlash, monitor the friction torque.
Avoid generating an unnecessarily great torque.
Unlike the load torque, an accurate load inertia can be obtained just by
calculation. The inertia of all objects moved by the revolution of a driving
motor forms the load inertia of the motor. It does not matter whether the
object is rotated or moved along a straight line. Calculate the inertia
values of individual moving objects separately, then add the values
together, according to a rule, to obtain the load inertia. The inertia of
almost all objects can be calculated according to the following basic rules:
D
b
L
b
Calculating the load
inertia
D Inertia of a cylindrical
object (ball screw, gear,
coupling, etc.)