Peter Nachtwey
Member
Let me start by saying I already know how. I was wondering how others would solve this problem.
Assume you have a machine control application that requires a motion controller and a light curtain. The machine executes the same sequences of steps or state every cycle or part. Also assume there are many simple moves that must be made so there are many states.
What do you do when someone breaks the light curtain? Obviously the motion must stop, the real question is how do you restart the state machine or step sequencer? SFCs, sequential function charts go from one step to another when a transition is satisfied. This doesn't seem adequate to solve this problem. Do SFCs have the concept of interrupts? I have the IEC 61131-3 specifications and I don't see interrupts mentioned. Maybe they are just an extenstion.
When the light curtain breaks the current state machine or SFC must be stopped but how do you restart the sequence? From what I have seen this is not possible without starting over. Ideally it would be best if the state machine or SFC could be restarted at the current step or actually back at the last motion command so the motion command will be re-issued. This need to go back to the last motion command means that and interrupt is not going to work because an interrupt will restart where it was interrupted which is probably waiting for the in position bit to be set which will never happen now that the motion is stopped.
What I am looking for are really clean/simple solutions. I don't want to taint the ideas with mine so I will keep mine to myself right now. I am a little concerned that my solution will require unfamiliar concepts.
Assume you have a machine control application that requires a motion controller and a light curtain. The machine executes the same sequences of steps or state every cycle or part. Also assume there are many simple moves that must be made so there are many states.
What do you do when someone breaks the light curtain? Obviously the motion must stop, the real question is how do you restart the state machine or step sequencer? SFCs, sequential function charts go from one step to another when a transition is satisfied. This doesn't seem adequate to solve this problem. Do SFCs have the concept of interrupts? I have the IEC 61131-3 specifications and I don't see interrupts mentioned. Maybe they are just an extenstion.
When the light curtain breaks the current state machine or SFC must be stopped but how do you restart the sequence? From what I have seen this is not possible without starting over. Ideally it would be best if the state machine or SFC could be restarted at the current step or actually back at the last motion command so the motion command will be re-issued. This need to go back to the last motion command means that and interrupt is not going to work because an interrupt will restart where it was interrupted which is probably waiting for the in position bit to be set which will never happen now that the motion is stopped.
What I am looking for are really clean/simple solutions. I don't want to taint the ideas with mine so I will keep mine to myself right now. I am a little concerned that my solution will require unfamiliar concepts.