RTC
®
5 PC Interface Board
Rev. 1.9 e
9 Programming Peripheral Interfaces
215
9.3.3 Synchronization via Encoder
Signals
Intended Use
When processing moving workpieces, the laser scan
processes need to be adapted to the current work-
piece position.
To incorporate the current workpiece position, the
RTC
®
5 can evaluate signals of up to two user-
supplied incremental encoders. Though incremental
encoders generally do not (directly) register the
current workpiece position, they register the motion
of the transport system (conveyor belt, rotating plate,
etc.)
(1)
: For each transport motion, they provide
signals (depending on the direction of movement) to
the RTC
®
5 which can result in incrementing or decre-
menting of its two internal encoder counters. The
states of the RTC
®
5’s encoder counters thereby corre-
spond directly to the position of the workpiece
(2)
.
If workpieces are always processed at a constant
speed and an encoder is therefore not needed, then
the encoder signals can also be simulated via
simulate_encoder, so that both encoder counters
will also increment at a constant counting rate
without an external encoder signal. Of course, the
encoder simulation can also be used to achieve a
constant counting rate of the encoder counter for
laser scan processes that aren’t dependent on work-
piece motion.
The current counts of both encoder counters can be
queried via the control command get_encoder.
Alternatively, they 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. In addition, the RTC
®
5 automatically
evaluates the current counts if execution of the laser
scan processes is controlled as follows:
• For Processing-on-the-fly-applications (see
page 177), the coordinate values of all vector and
arc commands are transformed in accordance
with the encoder counters’ current counts (i.e. in
accordance with the current workpiece position).
•Via the list command wait_for_encoder_mode,
further execution of a list can be postponed until
the selected encoder counter (i.e. the workpiece
position) has overstepped or understepped a pre-
defined value.
• For external list starts, a track delay can be
defined via simulate_ext_start,
set_ext_start_delay or set_ext_start_delay_list
for postponing execution of a list start relative to
the triggering input signal or corresponding
command (see page 210).
• Encoder-speed-dependent automatic laser
control (see page 148) uses the current encoder
speed (counter pulses in the most recent 10 µs
interval) of an encoder counter to control a laser
signal parameter.
Inputs for External Encoder Signals
For receiving encoder signals, the
MARKING ON THE FLY connector provides two
encoder inputs (ENCODER X and ENCODER Y, see
page 51).
For linear movements of the parts to be processed, up
to two user-supplied incremental encoders (that
determine, independently from each other, the work-
piece’s motion in the X and Y directions) can be
connected to these inputs.
For rotational movements only one incremental
encoder is necessary. For Processing-on-the-fly appli-
cations, it must be connected to the ENCODER X
input.
Each encoder input is designed for a pair of stan-
dardized differential input signals (RS422).
(1) The actual workpiece position can also be forwarded via the
McBSP interface to the RTC
®
5 (see page 216).
(2) The encoder counters are 32-bit counters (for signed 32-bit
values). Upon reaching the maximum (minimum) counter
value, counting will continue with the minimum (maximum)
value. A counter reset will only occur if triggered by Processing-
on-the-fly-commands (see set_fly_x, set_fly_y, set_fly_rot).
set_control_mode (bit #9 = 1) can be used to precisely
synchronize the encoder reset with external start signals, thus
avoiding the 10 µs jitter (random time offset between the start
signal and the list start).
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