Lenze DSD - Manual (Page 321)

Lenze · Drive Solution Designer · Manual · DMS 4.2 EN · 12/2013 · TD23
321
11 Drive Dimensioning
11.2 Motor selection
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11.2.8 Load-matching factor
The load-matching factor is an important assessment criterion for speed- or angle controlled dy-
namic acceleration drives.
• The load-matching factor is the ratio of the load moment of inertia (reduced to the motor shaft)
to the moment of inertia of the motor:
• The load-matching factor k
J
is an important indicator for:
• The acceleration capability
• The control quality for speed- or angle-controlled drives
• The stability limits of the control for speed- or angle-controlled drives
• A high k
J
factor is uncritical for torque-controlled systems.
• With a low k
J
factor, the load is not very dominant and the motor has a significant effect on the
acceleration capability of the drive.
• Increasing the motor size is the wrong thing to do, as this might quickly result in making it
impossible to achieve the required dynamic performance.
• The solution for this is an increase of the gearbox ratio within the realms of possibility (ob-
serve the maximum speed for the motor and gearbox drive), or alternatively the use of low-
inertia motors (e. g. synchronous motors, 120-Hz motors).
The DSD automatically calculates the occurring load-matching factors, i.e. the mismatch of the mo-
ments of inertia.
• The calculated values are displayed and logged as preview values in the different masks and af-
ter definition of the components also as actual values.
• Depending on the application, the load-matching factor k
J
is fixedly determined in the DSD:
• In the case of applications with a horizontal direction of movement, k
J
= 20 is preset.
• In the case of applications with a vertical direction of movement (angle of tilt > 45°), k
J
= 50
is preset.
• In the case of open-loop speed-controlled winding drives, k
J
= 500 is preset as limit value. The
load-matching factor is only relevant for closed-loop speed-controlled winders.
• If the load-matching factor k
J
< 0.5, the drive is no longer optimally adjusted.
• In this case, the motor and no longer the load is dominant (see diagram [11-6] ).
• For acceleration drives it is then favourable to select another ratio or a motor with low inertia.

Note!
Load-matching factors k
J
< 0.5 are only unfavourable for acceleration drives, but not for
quasi-stationary drives (acceleration torques in this connection are not dominant).
• For instance in the case of drives in materials handling technology, the load-matching
factor k
J
can be clearly lower than 0.5. This is uncritical.
k
J
J
L
i
2
J
M
⋅
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