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S y s t e m I n e r t i a
System inertia must be included in the selection of an MDrive and Planetary
Gearbox. Inertia is the resistance an object has relative to changes in velocity.
Inertia must be calculated and matched to the motor inertia. The Planetary
Gearbox ratio plays an important role in matching system inertia to motor
inertia. There are many variable factors that affect the inertia. Some of these
factors are:
The ratio of the system inertia to motor inertia should be between 1:1 and
10:1. With 1:1 being ideal, a 1:1 to 5:1 ratio is good while a ratio greater than
5:1 and up to 10:1 is the maximum.
T y p e o f S y s t e m
There are many systems and drives, from simple to complex, which react
differently and possess varied amounts of inertia. All of the moving compo-
nents of a given system will have some inertia factor which must be included
in the total inertia calculation. Some of these systems include:
Not only must the inertia of the system be calculated, but also any load that it
may be moving or carrying. The examples below illustrate some of the factors
that must be considered when calculating the inertia of a system.
L e a d S c r e w
In a system with a lead screw, the following must be considered:
Weight of
table
Weight of
screw
Friction of
guideways
The type of system being driven.
Weight and frictional forces of that system.
The load the system is moving or carrying.
❐ lead screw
❐ rack and pinion
❐ conveyor belt
❐ rotary table
❐ belt drive
❐ chain drive
❒ the weight and preload of the screw
❒ the weight of the lead screw nut
❒ the weight of a table or slide
❒ the friction caused by the table guideways
❒ the weight of any parts
Weight of
parts
Weight of
nut
Preload on
leadscrew
91
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