I did a gantry system with LinuxCNC a few years back. The gantry was very stiff and self squaring when powered off. The gantry was 10-12 feet across and very heavy. It used used 2 - 1 KW servo drives driving two ball screws on each end of the gantry for the Y axis. In order to keep things simple I used step and direction on the servo drives and fed the same signals to both of the Y axis servo drives. It homes to a prox switch but since this is a waterjet, the home position really isn't all that important. That machine has been running for almost 3 years now everyday. It has never had any homing issues.
I keep hearing that Gantrykins has issues. If you wanted to stick with Trivkins I would try to implement something in hal probably with some custom components that did something like this: Gear both axes together at 1:1 and do some minor hal tricks to have both of them follow each other towards the home switches. Then detect which axis sees it's home switch first, then back that axis up a predetermined amount, continue to run the other axis until it's home switch is seen, then back that axis up a predetermined amount. If more precision is required, repeat the routine at a much lower speed. I think some hal logic and probably one or two custom components would be required, but it should not be very difficult. Once the homing is complete, shift the hal logic so that both axes are again locked/geared together. This would avoid gantrykins and the associated issues. The limit3 component can be used to drive an axis. That would be a good component to use as part of or morph into another custom component that could be part of this scheme. Running both drives into a hard stop might be workable if the homing speeds are low, but with big servo drives and a heavy gantry, probably not a good idea. Dave Cole On 5/22/2013 9:43 PM, Jon Elson wrote: > So, the issue of homing a dual-motor gantry comes up, again. > > This one is a stiff structure, and the customer says if the motors get > seriously out of synch, it will bend the slide rails. Well, at power-on, > the motors will be pretty well synched by mechanical forces. So, > there would be two ways to home it. One is to kill one servo amp > and allow just one of the servo amps to drive to the home position. > Then, enable the 2nd amp and home it. The machine builder would > need to be sure the home positions were such that with both at home > the gantry was not under stress. > > The other scheme would be some kind of simultaneous homing that > kept both encoders at the same relative offset during the whole > process. If the home switch was only on one side of the gantry, then > maybe there is a way to have both encoders home to their own index > pulses at the same time. (When properly set up, the two encoders > should arrive at their index positions nearly simultaneously.) > > Anybody have any ideas or especially experience with a system like > this? > > Jon > > ------------------------------------------------------------------------------ > Try New Relic Now& We'll Send You this Cool Shirt > New Relic is the only SaaS-based application performance monitoring service > that delivers powerful full stack analytics. Optimize and monitor your > browser, app,& servers with just a few lines of code. Try New Relic > and get this awesome Nerd Life shirt! http://p.sf.net/sfu/newrelic_d2d_may > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > > ------------------------------------------------------------------------------ Try New Relic Now & We'll Send You this Cool Shirt New Relic is the only SaaS-based application performance monitoring service that delivers powerful full stack analytics. Optimize and monitor your browser, app, & servers with just a few lines of code. Try New Relic and get this awesome Nerd Life shirt! http://p.sf.net/sfu/newrelic_d2d_may _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
