170
3 PARAMETERS FOR POSITIONING CONTROL
3.3 Fixed Parameters
For example, suppose that the servomotor was connected to the ball screw.
Because the travel value (
S) of machine per motor rotation is [mm]/[inch] unit, the travel value (positioning address) set in
the program is commanded in [mm]/[inch] unit. However, the servomotor is positioning controlled by the servo amplifier in
pulse unit.
Therefore, AP/AL is set so that the following expression of relations may be materialized in order to convert the travel value of
[mm]/[inch] unit set in the program into a pulse.
Number of pulses per motor rotation = AP
Travel value of machine per motor rotation = AL
(There is a range which can be set in the numerical value set as AP/AL, so it is necessary to make the setting range of AP/AL
the value calculated from the above expression (reduced) of relations.)
Example of the real setting is shown below. Refer to the Number of pulses/travel value at linear servo use for the setting at
linear servo. (
Page 171 Number of pulses/travel value at linear servo use)
■
For ball screw
When the ball screw pitch is 20 [mm], the servomotor is HG-KR (4194304 [pulse/rev]) and direct connection (No reduction
gear) is set.
First, find how many millimeters the load (machine) will travel (AL) when the servomotor runs for one rotation (AP).
AP (Number of pulses per motor rotation) = 4194304 [pulse]
AL (Travel value of machine per rotation) = Ball screw pitch
Reduction ratio = 20 [mm]
Substitute this for the above expression (1).
Although it becomes above, when a control unit is set to [mm] unit, the minimum unit of the command value in a program is
0.1 [
m] and converted from 20 [mm] (20.0000 [mm]) to 20000.0 [
m].
The travel value per motor rotation in this example is 0.0000047 [mm].
For example, when ordering the travel value of 19 [mm], it becomes 3984588.8 [pulse] and the fraction of 0.8 [pulse]. At this
time, the Motion CPU orders the travel value of 3984588 [pulse] to the servomotor and the fraction is memorized in the Motion
CPU. Positioning is performed by seasoning the travel value with this fraction at the next positioning.
Electronic
gear
=
AP
AL
. . . . . (1)
AP
AL
=
4194304 [pulse]
20 [mm]
AP
AL
=
4194304 [pulse]
20000.0 [
μ
m]
Summary of Contents for MELSEC iQ-R16MTCPU
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