I am working on a continuous production line, more in specific where vynil is produced. At some point they have implemented a 'positioning frame', which is in fact a roller that can turn some degrees to the left or right of its central mounting position.By turning the roller the vynil can be guided to a requested position.
For the automatic positioning a cognex camera is used as sensor for the actual position of the vynil (the Cognex recognizes the edge of the vynil).
There is a drive with integrated position controller that positions the roller.
The position setpoint is generated in the central Siemens S7 plc.
There a PI controller has as setpoint of 0 and as actual value the distance from the edge of the vynil to the Cognex 'zero position'. The Cognex camera itself can also be positioned (independent of the guiding roller) to have another position setpoint for the vynil.
The position setpoint from the PI controller in the plc is sent to the drive of the guiding roller as a position setpoint of an absolute positioning.
The described system was already implemented before on another part of the production line. We have copied this system to our new part, but we have quite some overshoot when a new position is requested for the vynil.
We can off course tweak the PI values of the PLC PI controller,
but I wanted to get some opinions about this whole positioning system.
I am in fact more thinking about doing relative positioning in the drive and using only p-factor in the plc. We may not forget that there is not a fixed direct relationship between the angle of the guiding roll and the position the vynil will take. Moving the guiding roller to a certain extent will guide the vynil also in a certain direction, but it can not be exactly calculated. That is probably why the other company used PI controller in the plc. Need to say also that there is not an isochronous communication between plc and Cognex and drive. It is Profinet, should be rather fast, but not clocked.
So how about my idea of relative positioning in spite of the actual absolute positioning, and only proportional factor.
For the automatic positioning a cognex camera is used as sensor for the actual position of the vynil (the Cognex recognizes the edge of the vynil).
There is a drive with integrated position controller that positions the roller.
The position setpoint is generated in the central Siemens S7 plc.
There a PI controller has as setpoint of 0 and as actual value the distance from the edge of the vynil to the Cognex 'zero position'. The Cognex camera itself can also be positioned (independent of the guiding roller) to have another position setpoint for the vynil.
The position setpoint from the PI controller in the plc is sent to the drive of the guiding roller as a position setpoint of an absolute positioning.
The described system was already implemented before on another part of the production line. We have copied this system to our new part, but we have quite some overshoot when a new position is requested for the vynil.
We can off course tweak the PI values of the PLC PI controller,
but I wanted to get some opinions about this whole positioning system.
I am in fact more thinking about doing relative positioning in the drive and using only p-factor in the plc. We may not forget that there is not a fixed direct relationship between the angle of the guiding roll and the position the vynil will take. Moving the guiding roller to a certain extent will guide the vynil also in a certain direction, but it can not be exactly calculated. That is probably why the other company used PI controller in the plc. Need to say also that there is not an isochronous communication between plc and Cognex and drive. It is Profinet, should be rather fast, but not clocked.
So how about my idea of relative positioning in spite of the actual absolute positioning, and only proportional factor.