> > Yes I think this is possible (basically using the index hardware as a > latch to > catch the quick index pulse) but note that the actual home position will > vary > with the velocity when the index is detected (and with a servo thread > period > uncertainty) >
I assume that, the slower the latch speed is, the better the repeatability of the index detection right? This wouldn't happen using hardware encoder feedback because the 7i52S firmware would be much more fast, accurate and repeatable when resetting the position counter of the encoder? Anyway I just did the component and tested it several times reading the encoder feedback on the display of the drive. I'm getting really good results so I think when the time comes to test it with a dial indicator on the machine this should work well. At least, this is a lot better than only using the limit switch, which is not only affected by the servo thread period but also the mechanical variations that could occur. I'm attaching a video of the homing working so you can see. https://youtu.be/9s-UC-5ZIrU <https://youtu.be/9s-UC-5ZIrU> El sáb., 11 abr. 2020 a las 0:17, Peter C. Wallace (<p...@mesanet.com>) escribió: > On Fri, 10 Apr 2020, Leonardo Marsaglia wrote: > > > Date: Fri, 10 Apr 2020 22:08:05 -0300 > > From: Leonardo Marsaglia <ldmarsag...@gmail.com> > > Reply-To: "Enhanced Machine Controller (EMC)" > > <emc-users@lists.sourceforge.net> > > To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net > > > > Subject: Re: [Emc-users] Home use index problem (In step + dir mode) > > > > Sorry for not catch it earlier Peter. I thought no matter the feedback, > >when index was detected it will behave as a second home switch. > > > >I'm thinking now about making a custom component to use as limit switch > and > >drive it with the actual limit switch for home search and with the index > >pulse triggering for the final detection (latch velocity) of the home > >position. This way, I can home with the accuracy of the index pulse, but > >with the normal behaviour of only having the limit swtich. > > > >My idea is to use positive search vel and latch vel so when I hit home the > >following should happen: > > > >LinuxCNC will see that the switch is pushed, it will back off a little > >until the switch is released. After that it will return to move towards > the > >switch in latch velocity, that's when I intend to bypass the switch and > >instead use the index enable edge as the switch signal for the final home > >position. I suppose I can use the joint.#.homing-state to know when to > >bypass the switch easily. > > > >It seems very doable. I'll always have the limit switches in case of a > >problem. > > > Yes I think this is possible (basically using the index hardware as a > latch to > catch the quick index pulse) but note that the actual home position will > vary > with the velocity when the index is detected (and with a servo thread > period > uncertainty) > > > > > El vie., 10 abr. 2020 a las 21:16, Peter C. Wallace (<p...@mesanet.com>) > escribiяя: > > > On Fri, 10 Apr 2020, Leonardo Marsaglia wrote: > > > > > Date: Fri, 10 Apr 2020 20:32:23 -0300 > > > From: Leonardo Marsaglia <ldmarsag...@gmail.com> > > > Reply-To: "Enhanced Machine Controller (EMC)" > > > <emc-users@lists.sourceforge.net> > > > To: "Enhanced Machine Controller (EMC)" < > emc-users@lists.sourceforge.net > > > > > > Subject: Re: [Emc-users] Home use index problem (In step + dir mode) > > > > > > I'm playing with the homing at slow speeds so I can hit the home switch > > >always half a turn away from the index pulse more or less. > > > > > >One thing is happening is the following: > > > > > >If I let the mark (keyway in this case) of the motor at 3 o'clock and > then > > >I turn off LinuxCNC, whenever I home the axis again (with the switch and > > >index and home position and offset both in 0) the axis goes to this same > > >position after the home sequence stops. Does that make sense? > > > > > >I was hoping that with both the home offset and home position in 0 the > > >motor would stop near the index pulse with some overshoot may be. But > > >always there and not in the last position when the machine turned off. > By > > >the way I'm not using the POSITION_FILE option and I also tried to use > > >VOLATILE_HOME with the same results. > > > > > >Sorry for all the questions but this is the first machine I'm using > with a > > >proper homing sequence. > > > > As I tried to explain, you cannot really do homing to index without using > > the > > encoder as feedback, because only the encoder hardware has the suported > > ability > > to zero the position at the edge of index. > > > > > > > > > You can use homing with index if you use the drives encoder output > > >> for feedback, but this is a bit more work and more difficult > > >> to tune > > > > > > > > > Do you think is a good practice to use them as feedback? Because I'll > > > be coupling the servos to the ballscrews with a timing belt, so this > > might > > > not be that accurate as having the encoders mounted directly on the > > > ballscrews. In that case anyway I would be using the servos with analog > > > voltage for velocity command because I can't use them in speed mode > with > > > the speed reference being pulsed. > > This can also be done with step/dir, though tuning may be difficult > > if there is substantial lag between step --> motion > > > > > > > > Also there's the difference in diameter of the pulleys, but that can be > > > scaled so it would be no problem. > > > > > > By the way, I finally succeeded in using the home switch + index. I > think > > > it was me trying to imitate the sequence in a wrong way pushing the > > switch. > > > I'll try a little more to be sure. > > > > > > El vie., 10 abr. 2020 a las 19:23, Peter C. Wallace (<p...@mesanet.com > >) > > > escribiяяяя: > > > > > >> On Fri, 10 Apr 2020, Leonardo Marsaglia wrote: > > >> > > >> > Date: Fri, 10 Apr 2020 19:01:51 -0300 > > >> > From: Leonardo Marsaglia <ldmarsag...@gmail.com> > > >> > Reply-To: "Enhanced Machine Controller (EMC)" > > >> > <emc-users@lists.sourceforge.net> > > >> > To: "Enhanced Machine Controller (EMC)" < > > >> emc-users@lists.sourceforge.net> > > >> > Subject: Re: [Emc-users] Home use index problem (In step + dir mode) > > >> > > > >> >>> Do you have a home switch and is it working? > > >> > If you want to home to index only you must set HOME_SEARCH_VELOCITY > > to 0 > > >> > > > >> > > > >> >The home switch is working perfectly. I'm pushing it by hand because > > I'm > > >> >only testing in the desk but it works. If I only use home switch for > > >> homing > > >> >it works perfectly. The problem starts when I try to use the index > > pulse. > > >> > > > >> > > >> If you have homing setup for home switch + index, motions index-enable > > >> output > > >> should be set high when the home switch is tripped > > >> > > >> > > >> >If I set HOME_SEARCH_VELOCITY to 0 and try to home using index only, > > the > > >> >joint.0.index-enable pin turns to TRUE and when the motor trips the > > index > > >> >pulse it stops but I get the following error message and the homing > > >> aborts. > > >> >Always in the same position of the motor, so the index is detected. > > >> > > >> The following error is expected unfortunately since motion expects the > > >> position > > >> to have been zeroed on index detection, but the stepgen position is > not > > >> affected > > >> by the encoder index > > >> > > >> >>Do the servos have a emulated encopder output (you mentioned a Z > > >> signal, is > > >> >> that from the drive?) > > >> > > > >> > > > >> >Yes the drive has the encoder output pins for the A, /A, B, /B, Z > and > > /Z > > >> >signals. I'm only using the Z and /Z signals because I thought I > could > > >> home > > >> >with index independently of the feedback I was using. > > >> > > >> No, index handling is intimately entangled with the position feedback. > > >> This is because index detection effectively zeros the position > feedback > > >> at the instant of index detection so its is precise regardless of the > > >> detection > > >> speed. As I mentioned, there is firmware to support index detection > with > > >> the > > >> stepgen hardware, but it is not currently supported by the hostmot2 > > driver > > >> Also as you might expect, the stepgen index input pin is not an > encoder > > >> input > > >> rather, its part of the stepgen. > > >> > > >> You can use homing with index if you use the drives encoder output > > >> for feedback, but this is a bit more work and more difficult > > >> to tune > > >> > > >> > > >> Peter Wallace > > >> Mesa Electronics > > >> > > >> (\__/) > > >> (='.'=) This is Bunny. Copy and paste bunny into your > > >> (")_(") signature to help him gain world domination. > > >> > > >> > > >> > > >> _______________________________________________ > > >> Emc-users mailing list > > >> Emc-users@lists.sourceforge.net > > >> https://lists.sourceforge.net/lists/listinfo/emc-users > > >> > > > > > > > _______________________________________________ > > Emc-users mailing list > > Emc-users@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > Peter Wallace > > Mesa Electronics > > > > (\__/) > > (='.'=) This is Bunny. Copy and paste bunny into your > > (")_(") signature to help him gain world domination. > > _______________________________________________ > > Emc-users mailing list > > Emc-users@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > > Peter Wallace > Mesa Electronics > > (\__/) > (='.'=) This is Bunny. Copy and paste bunny into your > (")_(") signature to help him gain world domination. > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
