Re: homing. Delta printers usually home at the top of their travel. When I asked my CNC instructor about a delta mill he said the lack of rigidity would kill accuracy.
On Sat, Nov 7, 2015, 7:38 PM linden <[email protected]> wrote: > Thanks for taking the time to look at the pictures and read through my > chicken scratch notes. Now I know that Linuxcnc should be able to > control something like this and we have a potential solution for > homing. I will keep going. I really need a real Internet connection or > some card board to start pushing shapes around simulating to see how > they interact with each other. One dimension is not to bad but trying to > picture things in my head in 3 dimensions and 6 dof freedom is a bit > much for my little brain sometimes. lol > > I am having second thoughts about using the lower set of trucks and > additional links associated with them. The original idea and thought be > hide this approach was it would give me a larger translational working > area relative to overall tool hight and may help with rigidity. looking > at the videos suggested earlier about rigidity and with the abb picker I > am having second thought. I have also seen a Russian you tube model that > has given me some ideas. once I have modled and thought a bit more I > would like to pick your collective brains again. > > all the best, > > Linden > > On 15-11-07 06:30 PM, Philipp Burch wrote: > > Hi Linden! > > > > On 07.11.2015 00:55, linden wrote: > >> Hello All, > >> > >> I have progressed a little with the design and modeling of the machine I > >> asked for help simulating. It has evolved a little over the last few > >> weeks. have a look at the pdf attached for pictures Another month and I > >> will be back to the world of fast Internet and I should be able to try > >> some of the previous suggestions for simulation. > > Looks nice :) > > Since you have 6 actuators, your design will definitely be > > overconstrained if you only want 5 degrees of freedom. But I have the > > feeling that you could actually get 6 DOF by having the nominal angle in > > C about 60° (or even 90°) rotated in respect to the picture you > > attached. Since you can control the distance between all the joints on > > the center plate to their slides, this will allow you to rotate the tool > > plate as well. > > Even if you don't need rotation around C, I'd suggest to implement this > > angular offset, as it will most probably make the system more robust > > against torsional forces. Similar to how hexapods are done. > > > >> The big question is: > >> > >> Could linuxCNC something control this? or do I have 2 many variables > >> with no fixed base position? > > When you get the kinematics right (which I'd expect to be about midways > > between the complexity of a delta kins and a hexapod), this should be no > > problem. > > > >> A few other questions and thoughts I would like to pick your collective > >> brains on. > >> > >> How would you home something like this? > > As with a hexapod, forward kins are complicated and may have many > > (practically) invalid joint positions. I'd suggest to have the following > > homing switches: > > > > 1. One for every pole at the top end, which gets activated when the > > upper slide reaches the top limit. > > > > 2. One between every two slides on a pole which is closed when the > > slides are closer than the nominal position (shown in your PDF) and open > > otherwise. This must NOT be limit switches, as movement in both > > directions over the activation point must be possible. > > > > Additionally, it will help to have an approximation of the distance > > between every two slides on a pole. This could be done rather easily by > > using a linear potentiometer. > > > > You could then implement the homing about as follows, using coordinated > > movements in the XYZABC space (not on a joint basis): > > > > 1. When the system gets turned on, all you know is that it must be in > > some mechanically feasible position. So start by a linear move towards > > Z+, meaning that all slides run synchronously upwards. Stop as soon as > > one upper slide reaches the top homing switch. > > > > 2. Use the feedback from the pots as an initial guess of the slide > > distances for the kinematics. Using those, perform a move in the XY > > plane perpendicularly away from the joint which has it's top slide > > homed, i.e. moving approximately towards the center position. Stop as > > soon as the second upper slide hits the top homing switch. Since this > > movement will also adjust the distance of the slides on a pole, you may > > also detect one or the other homing switch edge of those. Use this > > information to correct the joint position guesses. > > > > 3. Do the same as in step 2, but this time with a movement perpendicular > > to the connecting line of the two homed poles. So you should eventually > > also reach the top homing switch of the third pole, meaning that all > > upper slides know their positions and the tool is roughly centered. > > > > 4. Move all slides down by a few millimeters to get some "working range" > > for the last step (i.e. coordinated move towards Z-). > > > > 5. Perform a movement to X0Y0A0B0C0, i.e. to the approximate nominal > > position with an aligned tool base. This is possible using the > > information form the pots. > > > > 6. Perform moves from C-30 to C30 (or less, depending on the accuracy of > > your potentiometer feedbacks), so that all homing switches of the lower > > slides see at least one edge. As soon as this happens, all joints are > homed. > > > > All this will require that the tool can rotate around a C axis (which in > > my terminology is perpendicular to the machine table, NOT aligned to the > > tool axis). This means that it will be required to have this angular > > offset of the tool base plate as described above. > > > >> I stile haven't simulated the movement digitally yet or built a complete > >> cardboard and drinking straw model, but i think i have finally settled > >> on approximate geometry any questions or comments are gladly welcome. > >> Has any one seen any thing like this before I am sure I am not the > >> first? Is there any grate big flaw with this logic that I have missed? > > At least from my feeling, I think that this should work with the > > mentioned adaptation. I'm not very familiar with complex machine > > kinematics, however. > > > > I find it a cool construction :) No idea if someone else already built > that. > > > > Good luck! > > > > Regards, > > Philipp > > > > > > > > > ------------------------------------------------------------------------------ > > > > > > _______________________________________________ > > Emc-users mailing list > > [email protected] > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > ------------------------------------------------------------------------------ > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
