Absolute Quadrature Interface - Balluff BML Información Básica

Interfaces for BML Magnetic Encoder System
2
Interfaces (continued)
2.5

Absolute quadrature interface

If the sensor is supplied with voltage that is
isolated from the processing electronics, the
GND for this voltage must be connected to the
GND of the processing electronics.
The absolute quadrature interface uses the incremental
digital A/B interface with Z-signal to send the absolute
position when power is turned on. This gives a
conventional incremental controller absolute functionality.
No changes to the controller are necessary. No homing
move is necessary and the absolute position is always
available.
The absolute quadrature interface is compatible with the
digital incremental A/B/Z interface. The user must select
the desired resolution and minimum edge separation (see
Tab. 2-4 on page 24) which is appropriate for the
controller. This will give the maximum travel speed or rpm's
for rotary applications. The relationship can be seen in the
respective tables in the sensor user's guide.Tab. 2-4 on
page 24 shows and example.
The sensor evaluates the signals as per Fig. 2-26 on
page 23 and determines from that the s_AB position.
14 english
Switch-on behavior
s_AB
s_act
s_act
1
s_AB
0
A
B
Z
Ub
t0 t1 t2 t3
Fig. 2-9: Switch-on behavior
The exact timing at switch-on is described in Fig. 2-9: The
sensor carries out a move corresponding to s_act. When
power is turned on at time t0 all outputs are high
impedance. At time t1, after the switch-on delay, the
outputs are low impedance and the start delay t
begins. It lasts until time t2. Now the virtual homing move
VH begins. A Z-pulse is output between t2 and t3. The
controller must use this to set its internal position counter
to zero. Beginning with t3 the measuring system generates
A/B increments until the incremental position s_AB has
reached the physical position of the sensor head s_act, at
time t4. From this point on the controller knows the
physical position. Between t2 and t4 all edges are output
with the minimum edge separation. Then the measuring
system outputs normal increments which follow the
physical movement s_act.
The time for VH (t ) is normally several milliseconds and is
VH
determined as follows:
Measuring length [µm] × minimum edge
separation [µs]
t [µs] =
VH
Resolution [µm/Inc]
Edge separation and resolution are defined in
the user's guide for the sensor.
Up to time t4 no controlled movement is permitted.
The time duration can be reduced by running the function
Preset at the beginning of the measuring range.
Each time the null point is crossed a Z-pulse is output.
t
t
t
t
t4
t
VHstart_delay