Mitsubishi FR-A800

Position control under vector control and PM sensorless vector control
248
PARAMETERS
Relationship between the position resolution  and system accuracy
The system accuracy (the positioning accuracy of the machine) is the sum of electric deviation and mechanical deviation.
Normally try to prevent the total deviation from being affected by the electronic deviation. Refer to the following relationship
as a reference.
<Motor stop characteristics>
When running the motor by parameter settings, the relationship between the internal command pulse frequency and the
number of motor rotations will be as shown in Figure page 229. Pluses as much as the motor speed delay are accumulated
in the deviation counter. These pulses are called droop pulses (). The relationship between the command frequency (fo)
and position loop gain (Kp:Pr.422) is shown in the following formula.
The number of droop pulses () will be 8192 with the initial value Kp = 25 s
-1
.
Since the inverter has droop pulses during operation, a stop settling time (ts), which is the time between the zero command
output and the motor stop, is required. Set the operation pattern taking into the account the stop setting time.
The stop settling time (ts) will be 0.12 s for the initial value Kp=25 s
-1
.
The accuracy of positioning  will be (5 to 10)   = [mm]
[Setting example 1]
In a driving system whose ball screw pitch is PB=10 (mm) and the reduction ratio is 1/n=1, the electronic gear ratio is s=10
(mm) when  =0.01 (mm) and Pf=4000 (pulses/rev) is set as the number of feedback pulses. Based on this, use the
following formula:
Thus, set the parameters as follows: Pr.420="4", Pr.421="1".
[Setting example 2]
Find the internal command pulse frequency for the rated motor speed of the dedicated motor.
However, the command pulse ratio is Pr.420/Pr.421="1".
If the number of encoder pulses is 2048 (pulses/rev), (feedback pulse pf = 2048  4)
The internal command pulse will be 204800 (pps) in accordance with the above formula.

<(
1
to
1
)  : positioning accuracy
510
 =
fo
[pulse]  =
204800
[pulse] (with the rated motor speed)
Kp 25
ts = 3 
1
[s]
Kp

=
s

Pr.420
Pf Pr.421
Pr.420
=


Pf
Pr.421 s
=0.01
4000
=
4
10 1
fo = 2048  4 (multiplication) 
No.

Pr.421
60 Pr.420
= 204800