Dne 3.11.2011 7:21, piše Tom Easterday: > On Nov 2, 2011, at 5:50 PM, Jon Elson wrote: >> On 11/02/2011 12:07 PM, Tom Easterday wrote: >>> Pleas tell me how you home an axis with 2 joints to an index pulse? >>> >>> >> The way commercial machines like big gantry boring mills do it is they >> have a swivel joint in the gantry. So, each tower of the gantry can move >> independently without any binding. The beam across the gantry has a swivel >> at one end, and a slotted bearing at the other. They may have limit >> switches >> on the slotted bearing so if the machine gets seriously out of square, it >> trips the E-stop. In this manner, the two linear joints can move relatively >> together toward home, and then each homes to its own home switch >> and index pulse. Once homed, then the CNC program always keeps >> them parallel. > I would like to see a picture or video, that sounds interesting. But, let me > me rephrase my question… > > Using gantrykins with a gantry that cannot be out of square more than about > 3/4", how can we home the 2-jointed Y axis? > > We cannot move in World Mode before homing. We cannot move in Joint Mode > without racking. We cannot understand how to select one encoder to find > index pulse on. Can we home to one of the two index pulses or is this > impossible? > > -Tom > > If you have stepper then if one stepper lost step you have trouble. To avoid that I think the only option is to have encoder disc on each side and then compare reading pulses from them. As you can tolerate 3/4 (18mm) then encoder can be homemade as it need only one or two slot's (like butterfly for example). And let's do EMC to compare both encoders. If they go out of sync 2 or more pulses then STOP is trigered. and all the programming (i hope) can be done in HAL.
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