Yes, the possibility of muck and rubbish on the tip had crossed my mind, but I have to admit I was thinking more along the lines of initial set up and calibration than ongoing checking, so the chances are that the hot end will be very clean at that point. If the software for calibrating is done with the safeguards I envisage, it will only be microstepping, at slow speeds, so in theory, the bed plate should not be at risk, but that was one of the reasons I was thinking of a metal plate for the calibration work, but cost might be a factor here.
The maybe spurious thought of finding true centre was that with the way delta geometry works, if the centre truly is centre, it should help the accuracy of all the other points around it, all other things being hopefully accurate.
In repect of upper limits and switches, I would not be doing away with the switches, they are the protection against driving fast into a hard limit, which is not a good idea, but I was thinking that if the hard limit was a few steps above the soft limit, that might help with the setting up accuracy, and make subsequent calibration easier, the soft limit is the signal to the system to stop under normal operation, but for calibration, the soft limit would be the signal to carefully find the hard limit, which in theory would mean that the centre really would be the centre, as long as the mechanical accuracy and lengths etc were correct,
Yes, some basic measurement of the Z height will have to be put into the softeware in order to do even basic calibration, to save time, but if it was possible to say something along the lines of
Home X,Y,Z
Check X hard limit
Check y Hard Limit
Check Z Hard limit
which would drive X steps past the soft limit, which should in effect hit the top mechanical block
Home to soft limits
Position down by Z height - plate thickness - 5mm and stop
Visual check for basic looks good. press a continue option
Slow power and speed step down at appropriate distance till contact with plate. That gives accurate height offset from soft limit.
Validate that, however is deemed appropriate, by up down steps a good few times, then check it again
Check for plate level position at each mast base, to see if the plate is anywhere near level, if not, provide feedback for adjustment, which can be done with system live, by moving base till it contacts the hot end,
Recheck centre height and then tower heights if changes have been made, as they could (will) all be different.
Now the bed is level, (might take a couple of more of adjustments to get it right) check for accuracy moving over the bed and determine the adjustment to the code to ensure level printing across all sections of the bed. Again, this can all be automatic, with the data being saved on board, or stored for display to the user for entry into the final software information.
When completed, either store, or update firmware or as needed, then remove the calibration plate, and the entire unit should in theory be very accurately set up, and the user has had to do very little in comparison to the procedure at present, if what I've been reading is correct, and hopefully, the printing will be accurate across the entire print area.
If the only requirement is to clean the hot end tip and put the plate on the print station to check everything is OK, that has to be a bonus before starting a large or complex print job, just to make sure a belt has not slipped, or stretched, or a bearing has gone slack, or is worn.
That's my thinking on that one, and for some systems it could save some pain. On the Delta Pi for example, there are no lower limit switches, so the calibration has to be accurate in order to prevent head crashes into the print bed, and this was my way of trying to arrive at an automatic way to determine the correct values for the critical items. There is no way to have a lower limit switch system, because of the geometry of the Delta, so the whole calibration concept and accurate geometry of the towers is much more important.
That's my take on the Delta and I still like the idea. though I have to admit to having some interest in a modified version of the H system, as that can do the X & Y coordinates on a large bed with effectively 2 motors.
Steve
The maybe spurious thought of finding true centre was that with the way delta geometry works, if the centre truly is centre, it should help the accuracy of all the other points around it, all other things being hopefully accurate.
In repect of upper limits and switches, I would not be doing away with the switches, they are the protection against driving fast into a hard limit, which is not a good idea, but I was thinking that if the hard limit was a few steps above the soft limit, that might help with the setting up accuracy, and make subsequent calibration easier, the soft limit is the signal to the system to stop under normal operation, but for calibration, the soft limit would be the signal to carefully find the hard limit, which in theory would mean that the centre really would be the centre, as long as the mechanical accuracy and lengths etc were correct,
Yes, some basic measurement of the Z height will have to be put into the softeware in order to do even basic calibration, to save time, but if it was possible to say something along the lines of
Home X,Y,Z
Check X hard limit
Check y Hard Limit
Check Z Hard limit
which would drive X steps past the soft limit, which should in effect hit the top mechanical block
Home to soft limits
Position down by Z height - plate thickness - 5mm and stop
Visual check for basic looks good. press a continue option
Slow power and speed step down at appropriate distance till contact with plate. That gives accurate height offset from soft limit.
Validate that, however is deemed appropriate, by up down steps a good few times, then check it again
Check for plate level position at each mast base, to see if the plate is anywhere near level, if not, provide feedback for adjustment, which can be done with system live, by moving base till it contacts the hot end,
Recheck centre height and then tower heights if changes have been made, as they could (will) all be different.
Now the bed is level, (might take a couple of more of adjustments to get it right) check for accuracy moving over the bed and determine the adjustment to the code to ensure level printing across all sections of the bed. Again, this can all be automatic, with the data being saved on board, or stored for display to the user for entry into the final software information.
When completed, either store, or update firmware or as needed, then remove the calibration plate, and the entire unit should in theory be very accurately set up, and the user has had to do very little in comparison to the procedure at present, if what I've been reading is correct, and hopefully, the printing will be accurate across the entire print area.
If the only requirement is to clean the hot end tip and put the plate on the print station to check everything is OK, that has to be a bonus before starting a large or complex print job, just to make sure a belt has not slipped, or stretched, or a bearing has gone slack, or is worn.
That's my thinking on that one, and for some systems it could save some pain. On the Delta Pi for example, there are no lower limit switches, so the calibration has to be accurate in order to prevent head crashes into the print bed, and this was my way of trying to arrive at an automatic way to determine the correct values for the critical items. There is no way to have a lower limit switch system, because of the geometry of the Delta, so the whole calibration concept and accurate geometry of the towers is much more important.
That's my take on the Delta and I still like the idea
Steve