Mitsubishi Electric FR-A700 Technical Manual page 282

Using the parameters, the travel per command pulse
can be set separately to set the travel per command
pulse without a fraction.
[Pr. 420]
s
=
Pf [Pr. 421]
In addition, the relationship between the motor speed
and internal command pulse frequency is as follows:
[Pr. 420]
fo = Pf
[Pr. 421]
fo :internal command pulse frequency [pps]
No :motor speed [r/min]
Set the electronic gear in the range of 1/50 to 20.
Note that too small a value will decrease the speed
command and too large a value will increase the
speed ripples.
[Setting example 1]
The travel per pulse is
system where the ball screw pitch PB = 10(mm) and the
reduction ratio 1/n = 1 and the electronic gear ratio is
s = 10 (mm) when the number of feedback pulses Pf =
4000 (pulse/rev). According to the following formula:
[Pr. 420]
s
=
Pf [Pr. 421]
[Pr. 420]
=
[Pr. 421]
4000
= 0.01
Therefore, set [Pr. 420 = 4], [Pr. 421 = 1].
[Setting example 2]
Find the internal command pulse frequency of the
dedicated motor rated speed. Note that the command
pulse scaling factor [Pr. 420/Pr. 421 = 1] .
Assuming that the number of encoder pulses is 2048
(pulses/rev) (feedback pulse Pf = 2048
fo = 2048
(multiplication)
= 204800
Therefore, the internal command pulse frequency is
204800 (pps).
The relationship between position resolution
overall accuracy is as follows. Since overall accuracy
(positioning accuracy of machine) is the sum of
electrical error and mechanical error, normally take
measures to prevent the electrical system error from
affecting the overall error. As a guideline, refer to the
following relationship.
1 1
( to )
5 10
:positioning accuracy
No
60
= 0.01(mm) in a drive
Pf
s
4
10 1
4),
4 No [Pr. 421]
60 [Pr. 420]
<Stopping characteristic of motor>
When parameters are used to run the motor, the
command pulse frequency and motor speed have the
relationship as shown in the chart on page 308, and
as the
accumulated in the deviation counter of the inverter.
These pulses are called droop pulses ( ), and the
relationship between command frequency (fo) and
position loop gain (Kp: [Pr. 422]) is as represented by
the following formula.
fo
=
Kp
204800
=
= 8192 [pulse]
When the initial value of Kp is 25s
( ) are 8192 pulses.
Since the inverter has droop pulses during running, a
stop settling time (ts) is needed from when the
command has zeroed until the motor stops. Set the
operation pattern in consideration of the stop settling
time.
ts = 3
When the initial value of Kp is 25s
time (ts) is 0.12s.
Positioning accuracy
following formula.
=(5 to 10)
(2) Position command acceleration/
deceleration time constant [Pr. 424]
When the electronic gear ratio is large (about 10 or
more times) and the speed is low, rotation will not be
smooth, resulting in pulse-wise rotation. At such a
time, set this parameter to smooth the rotation.
When acceleration/deceleration time cannot be
provided for the command pulses, a sudden change
in command pulse frequency may cause an
overshoot or error excess alarm. At such a time, set
and
this parameter to provide acceleration/deceleration
time.
Normally set 0.
316
PARAMETER
motor speed decreases,
[pulse]
[pulse] (rated motor speed)
25
-1
1
[s]
Kp
-1
is represented as the
[mm]
pulses are
, the droop pulses
, the stop setting