Reference Point Function - Balluff BML-S1A-Q/A-M-0-S184/KA Serie Manual De Instrucciones

BML-S1A_-Q/A_ _ _-M_ _ _-_0-S184/KA_ _
Linear Position Encoder
3 Function and characteristics (cont.)
3.5

Reference point function

The reference position is always
required as the starting point for the
count for each incremental
displacement system.
How the reference position is
determined depends on the sensor
type, the tape and on the controller.
– In the simplest system the
sensing head with the sinusoidal
and cosinusoidal sensors can
count only the magnetic periods.
The tape contains only one track
with magnetic north and south
poles (Fig. 3-3).
In this case the displacement
measuring system does not
know the absolute position.
This is determined by the
controller by adding the counted
increments. First however the
reference position must be
determined by a homing move to
the reference switch.
– A sensing head with an additio-
nal reference point sensor can
output a reference point signal as
soon as it reaches the
magnetically encoded reference
point on the second track of the
tape (Fig. 3-4). Then a reference
switch is not needed.
– In another sensing head version
a reference point signal is
output with each magnetic pole.
This signal is repeated every
millimeter (pole-periodic
reference pulse).
The tape does not require a
second track with a magnetically
encoded reference point. In this
case an external reference switch
needs to be placed at the
selected reference position.
The controller precisely evaluates
the reference position when the
switch and the reference point
signal of the sensing head are
active. The accuracy requirement
for this reference switch is not
especially great.
– The sensor head with an
additional reference point sensor
can also be combined with
a magnetic tape having fixed
periodic reference points
(Fig. 3-4). Here the reference
points are integrated across the
entire length of the tape at
certain constant intervals, such
as every 10 cm.
To obtain the exact position, the
homing move must be made
over the entire length of the tape
up to the external reference
switch, which selects the correct
reference pulse from the sensor
head (AND-operation).
.
Fig. 3-3: Displacement measuring system with or without pole-periodic reference point function
Reference point sensor
Reference points at unequal distances
based on mathematical algorithm
Fig. 3-4: Displacement system with reference point function
– For the magnetic tape with
distance-coded reference points
(Fig. 3-4) the reference points are
arranged according to a
mathematical algorithm.
This makes it possible to know
the absolute position as soon
has you have passed over two
reference points.
This type of magnetic tape
requires no external reference
switch.
Explanations for Fig. 3-4:
To make the principle apparent,
the reference points are shown
separately (green and red),
although they are physically
identical (for details, see user's
guide for tape at www.balluff.de).
Tape without reference
point/with pole-periodic
Incremental
reference point
sensors
Tape with one
reference point
Magnetic reference point
Tape with fixed periodic
referenced points
Magnetic reference points
Tape with distance coded
reference points
Base reference points at
equal distances
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