LIBRARY ı6ıul 0) - Cranfield University

movements, in which the robot and the table should move to achieve the required
relative position at the weld start point. The sequence of signals and their purpose
were already described in section 4.1.3.1.
Table 6.11 - Analogue signal connections in the control system
Robot
Output 7 ---rAM
Monitoring ' Signal ' Robot Interface Moving
& Control PC Conditioning (BDH 550) Table
0-iov
A! D Channel 1 0-100V Voltage sensor
A/D Channel 2 o- 1ov 0- 10H Current Sensor
A/D Channel 3 0-10v o- lov Position sensor
+SV
Channel4
t
D/A Channel 1 0- 5v 0- lov Analogue Input 1
(Setup voltage)
D/A Channel 2 0- SV 0-10v Analogue Input 2
1 (Wire feed speed))
A/D : Analogue to Digital Converter D/A: Digital to Analogue Converter
The digital codes issued by the robot controller could also be accessed by the
monitoring PC. This was made possible by running a special program in parallel with
the table control program, such that the state of the table controller inputs could be
checked repeatedly and an externally accessible variable could be continuously
updated. Each input was considered as corresponding to a bit in a binary number,
whose equivalent integer value was assigned to a global variable, which could be
accessed by the monitoring PC at any time via the serial link. The robot interface error
indication outputs were also connected to the table controller and relayed to the
monitoring PC in the same manner. By accessing the state of the table controller
inputs, the monitoring PC would have information on which stage the robot program
was at and on the error state of the welding power source.
In order to provide a means to manually stop the whole system in the event of
an uncontrollable situation, one dedicated robot output was used to trigger the
welding power source and another was connected directly to the table controller to
indicate if the robot was executing a welding movement. By pressing the robot built-
in emergency-stop button, all its outputs are reset, thus switching off the welding arc
and signaling the table controller to stop any movement.
Also, two digital outputs from the robot interface were connected to the table
controller to indicate a failure in the welding arc ignition or some hardware error in
the welding power source. In the event of one or both errors, the table controller
should stop any workpiece movement, send an error signal to the robot and move the
workpiece back in the direction of the approach vector, such that the robot could
continue moving until the end of the programmed weld without colliding with the
workpiece. At the end of the weld movement, the robot program would be aborted as
a result of the error signal issued by the table controller.
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