Omron TJ2-MC64 - PROGRAMMING Programming Manual page 309

Examples and tips
The parameter end_pos, which defines the values in the CAM table,
depends on external conditions of the system. Therefore a program that
runs in another task or even a controlling device using FINS communication,
can change it while the main program that links two axis runs. Suppose that
these changes in conditions, which result in a change of the end_pos
parameter, happen most of the time when the axes are not linked, i.e. when
the CAMBOX command is not executed. Suppose furthermore that very
rarely the condition changes when the axes are linked. The change of the
end_pos parameter triggers the recalculation of the CAM table while the
CAMBOX command is executed. The consequence is that the part of the
demanded position of the slave axis follows the profile before the change,
and the other part follows the profile after the change. In the end this leads to
a discontinuation of the profile, which causes an indefinite speed of the axis
and ends up with this error: the WDOG goes off, and all axes stop.
The scenario above is hard to analyze when you do not know what happens.
The only thing that the user sees is that the slave axis has an error once
every few hours or even less often. But the oscilloscope can clearly show
where the problem is. In order to be able to use the oscilloscope, all desired
parameters must be captured at the time of an error. This can be achieved
by arranging the application programs in a certain way. The good
programming practice suggests to have a separate start-up program that is
set to run automatically on power-up of the system and checks the integrity
of the system, whether all the expected devices are connected and
initialized. It is recommended to let the start-up program, when it is finished,
start only one program that takes care of the safety and integrity of the
application and execution of all other application programs. This program is
usually referred to as a SHELL program. For more information on designing
a SHELL program, see section 5.2.1.
Suppose that program is designed in a way the it contains a following
fraction of code:
'When there is an error, we stop all programs. No new
'oscilloscope captures are done. And we have stored in
'the selected TABLES the last data trace in which the
'error has occurred. Therefore, we can recover this
'trace and analyze it.
loop:
PROGRAMMING MANUAL 303