Mitsubishi Electric FR-A800, Instruction Manual

Page: 357 / 1042

Parameters Position control under vector control and PM sensorless vector control
FR-A800 5 - 177
5.5.7 Electronic gear setting
Set the gear ratio between the machine gear and motor gear.
Gear ratio calculation (Pr. 420, Pr. 421)
The position resolution (travel distance per pulse
Δ
l [mm]) is the travel distance per motor rotation
Δ
s
[mm] and the feedback pulse of the detector.
It is determined by Pf [pulse/rev] and represented with the following formula.
Δ
l: Travel distance per pulse [mm]
Δ
s: Travel distance in one motor rotation [mm]
Pf: Number of feedback pulses [pulse/rev] (the number of pulses after the number encoder
pulses is quadruplicated)
The travel distance in 1 command pulse can be separately specified with a parameter and so an in-
teger can be set as the travel distance in 1 command pulse.
The following formula shows the relationship between the motor speed and internal command pulse
frequency.
fo: Internal command pulse frequency [pps]
No: Motor rotation speed [r/min]
Pr. Name
Initial
value
Setting
range
Description
420
B001
Command pulse scaling
factor numerator
(electronic gear
numerator)
1 1 to 32767
Set the electronic gear.
Pr. 420 is the numerator and Pr. 421 is the
denominator.
421
B002
Command pulse
multiplication
denominator (electronic
gear denominator)
1 1 to 32767
424
B005
Position command
acceleration/deceleration
time constant
0 s 0 to 50 s
Use it when the rotation is not smooth because the
electronic gear ratio is large (10 times or larger) and
the rotation speed is slow.
Δ
l =
Δ
s
Pf
Δ
l =
Δ
s
×
Pr. 420
Pf Pr. 421
fo ×
Pr. 420
= Pf ×
No
Pr. 421 60
NOTE Set the electronic gear ratio in the range of 1/50 to 20. Note that, if the setting value is too small,
the speed command will also be too small; while if it is too large, the speed ripple will be too large.
Vector Vector Vector PM PM PM