Determining Drive Capacity; Load Drive Capacity - YASKAWA VS-626M5 Instruction Manual

15.3 Determining Drive Capacity

When controlling machine speed, an inverter drive must supply torque to accelerate and decelerate the drive
system (couplings, machine, and motor), as well as torque to match the characteristics of the machine that
makes up the motor load. Consider the following points when determining drive capacity.
D
D
D
The above equation shows the method for calculating load drive force and acceleration/deceleration motive
force.

15.3.1 Load Drive Capacity

The torque-speed characteristics of the load mechanism that uses the VS-626M5 are classified as listed
in Table 15.3. The methods of calculating load drive capacity that are described are typical examples.
Table 15.3
Load Characteristics
Fixed Torque Load Load torque over
speed is a fixed
load.
Usually a friction
load.
Fixed Output Load Required output
over speed is a
fixed load.
Reduced Output Load torque over-
Load speed is a variable
load.
Load has the inter-
mediate characteris-
tics of fixed output
load and fixed
torque load.
Make clear the ratings to be used (continuous rating, short-time rating, and repetitive rating) to suit
the load characteristics.
Consider the efficiency of the motive force transmission mechanism and the load dispersion, and select
a drive capacity greater than the motive force required by the load.
Select a capacity that can sufficiently provide the startup torque and maximum torque required by the
load. Use the following equation to select the drive capacity.
Drive load ≧ Motive force to drive the load mechanism + Motive force to accelerate and decel-
erate the load mechanism to the required speed
Typical Load Torque-Speed Characteristics
Load Examples
Conveyers
Cranes
Winches
Other friction loads
and gravity loads
Center drive low ten-
sion winders
Main axis of ma-
chine-tool
Veneer rotor relays V t l
15 -11
Speed-Torque Characteristics
Load torque is fixed regardless of speed.
Output is proportional to speed.
1.0
Load torque
Load output
0
1.0
Speed
Within fixed torque range:
Load torque is fixed regardless of speed.
Output is proportional to speed.
Within fixed output range:
Output required by load is fixed.
Load torque is inversely proportional to speed.
1.0
0.5
Load torque
Load output
2.0
1.0
0
Intermediate speed-torque and output charac-
teristics of fixed torque load and fixed output
load
1.0
Load torque
Load output
0
1.0
15.3 Determining Drive Capacity
Motor Capacity
Motor capacity is the
same as the maximum
speed load capacity.
Required rated output
when using a drive
with fixed torque
characteristics is as
follows:
Required output =
Load output x Fixed
1/2
output control ratio
Motor capacity is the
same as the maximum
speed load capacity.
15