4 . P o s i t i o n i n g U n i ts
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4-3
△
l
: Linear movement of the working object obtained by
each feedback pulse
P
f
: Feedback pulses, i.e. pulses sent from 1 revolution of
the encoder inside the servo motor. The value is usually
fixed.
f
B
f
P
n
1
P
P
S
×
=
Δ
=
Δ
l
The positioning resolution (mm/pulse)
0
Δ
l
will be determined by the equipment parameters,
which is the linear movement of the working object generated by each instruction pulse sent.
×
0
f
Electronic gear ratio
f
P
=
×
=
=
f
0
0
P
Δ S
f
Δ S
Δ
l
Electronic gear ratio
When the electronic gear ratio
＞
1,
U
ℓ
0
＞
U
ℓ
, which means the positioning resolution is
degrading.
Example 1:
Assume we know that the feedback pulses are 4,000ppr and want the rotation speed of the
motor to be 3,000rpm when the instruction pulses are at 100KPPS. How should we set up the
electronic gear ratio?
[Solution]
3,000rpm = 3,000 revolutions per minute = 50 revolutions per second
ƒ
0
× electronic gear ratio = 4,000ppr × 50 revolutions per second
@
Electronic gear ratio
= 2 (200KPPS / 100KPPS = 2).
Example 2:
Assume the feedback pulses P
f
are at 4,000ppr, the screw pitch P
B
= 10mm and the
deceleration ratio 1/n = 1, what is the electronic gear ratio when the positioning resolution =
0.01mm/pulse?
[Solution]
Electronic gear ratio =
1 pulse sent by the instruction (pulse
ƒ
0
) will be converted into 4 pulses by the electronic gear
and the servo motor will rotate for 4 steps (1 step = 10/4,000mm) with a screw rotation of
0.01mm.
4.1.1.2 The Position Controller
The position controller estimates how many pulses, along with the pulse frequency that are required
by the equipment parameters (speed and distance) to set up in the servo motor system and send
