Chapter 7 EtherCAT Communication
7.3.4 Common conversion factor
User units and motor units internally controlled by the drive are often inconsistent. To facilitate the unification of
units, the CiA 402 device specification provides a set of conversion factors for converting user units and motor
units.
The default motor units of the M5-N drive are as follows:
• Motor displacement unit: p
• Motor speed unit: rpm
The actual units commonly used by users are as follows:
• Load displacement unit: mm
• Load speed unit: mm/s
7.3.4.1 Position factor (6093h)
The substantial meaning of position factor is: when the load displacement is 1 user unit, the corresponding motor
displacement (unit: p).
The position factor is composed of the numerator 6093-1h and the denominator 6093-2h. The proportional
relationship between load displacement (user unit) and motor displacement (motor unit) can be established
through the position factor:
Positionfactor 6093h =
Positionfactormolecule 6093−1h
Positionfactordenominator 6093−2h
Motordisplacement = Loaddisplacement(user)×Positionfactor
Loadfeedbackdisplacement (user) =
Motorfeedbackdisplacement
Positionfactor
Example
For ball screw:
• 1 user unit corresponding displacement: 0.001mm
• Lead screw: pB=5mm/r
• The user unit that drives the load movement per rotation of the load shaft: 5/0.001 = 5000
• Motor encoder resolution =2
n
, n bit encoder bits, absolute encoder bits are 23 bits, motor encoder resolution is
2
23
=8388608
• The machine reduction ratio of the motor shaft and the load side is m/n (the load shaft rotates n turns when the
motor rotates m turns) =1
Therefore, the position factor is calculated as follows:
Position factor:
Positionfactor =
Encoderresolution
Loadmovementperturn(commandunit)
×
m
n
=
8388608
5000
It shows that when the load displacement is 5000 user units (5mm), the motor displacement is 8388608 pulses
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