RTC
®
5 PC Interface Board
Rev. 1.9 e
8 Advanced Functions for Scan Head and Laser Control
182
Then, Processing-on-the-fly correction must be acti-
vated via set_fly_rot
(1)
. The parameter
Resolution
[in counts per revolution] must thereby be specified.
The inverse of this parameter defines the rotation [in
number of revolutions] of the current output position
in the image field corresponding to one counting unit
(see below).
The set_fly_rot command resets the encoder counter
Encoder0 to zero.
Thereafter, the output value is calculated from the
current output position via a linear transformation
(rotation around the specified rotation center, where
rotation angle / 360° = current Encoder0 counter
value /
Resolution
). This correction is performed
every 10 µs
(2)
.
Determining the
Resolution
Parameter
If the angular position of the workpiece is to be regis-
tered via an incremental encoder, then a calibration
must be performed to determine a value for the
Resolution
parameter:
Read the counter start value (via get_encoder)
and begin the rotation (any desired number of
full rotations)
Count the number of revolutions.
Stop the rotation and read the counter end value
(via get_encoder)
(3)
.
The parameter
Resolution
[i.e. the counts per
revolution] can then be calculated as follows:
Resolution
= (counter end value – counter start
value) / number of revolutions
Note that the number of counts per revolution is
equal to the number of encoder signal edges per
revolution i.e. four times the number of encoder
increments per revolution (see page 216).
If the workpiece rotates at a constant speed [in
number of revolutions per second] and an encoder
simulation was activated via simulate_encoder, then
the
Resolution
parameter can be calculated as
follows:
Resolution
= (1000000 counts/second) /
It might be necessary to adjust the sign of
Resolution
to the direction of rotary movement.
Correction via McBSP Interface
If angle-position values for Processing-on-the-fly
correction of rotary movement are forwarded via the
McBSP interface, then Processing-on-the-fly
correction must be activated via set_fly_rot_pos.
Here, the required
Resolution
parameter has the
same meaning as with set_fly_rot and can be simi-
larly determined (see above), with the difference that
McBSP input values are queried via read_mcbsp
(while counter values are queried via get_encoder).
Notes
• As with using McBSP input values to compensate
linear motions, McBSP input values get copied to
internal memory location 0 (see notes on
page 180).
(1) See footnote
(2)
on page 179.
(2) The encoder counters are 32-bit counters (for signed 32-bit
values). If the maximum (minimum) count is reached, then
counting will continue with the minimum (maximum) count.
(3) Alternatively, the counter start and end values can be stored in
a buffer on the RTC
®
5 via the list command store_encoder
and then retrieved from there via the control command
read_encoder.
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