I don't know how fast you are moving this machine, but years ago I retrofit a large water jet that had two motors on the Y axis. The gantry weighs probably 1000 lbs since it carries 4 jet heads and the Z axis is manual but built into the gantry. The entire machine is massive. The vertical legs that carry the gantry overhead about 8 feet off the ground, are 10" square steel tubes which are flanged, bolted, and grouted to the concrete floor. The columns are also knee braced to the floor with more square steel tubing, grout and bolts.
Everything was ball screw driven and we replaced all of the ball screws and the square rail linear bearings at the same time. I put 1 KW brushless AC servo drives on all of the screws via direct drive as was the original arrangement. I used Automation Direct servos. The gantry was stiff enough that it would "self square" when unpowered. Because of that I was able to use step and direction servo drives (they were also able to do analog velocity) and drive them via an lpt port. The gantry has never gone out of square for a couple of reasons. I oversized the motors which was a minor cost increase. The original motors were 750 watts, the replacements were 1 KW. If one of the Y axis motors loses position, it shuts down the the machine, shutting down the parallel motor at the same time, preventing any serious racking. My thought regarding this retrofit was to try the simplest retrofit approach first and that was using the step and direction option for the drives. If that did not work well I was going to go analog and then deal with homing issues for the two different axes. This water jet has been running now for almost 4 years everyday in a production environment without problems. It has a chain conveyor bed and feed system so it can run almost nonstop. The machine has been running 8-10 hrs per day recently but for a while it was running 16-20 hrs per day. To give you an idea of how hard they run this machine. Some of the servo drive cables, which run in cable chains, have been replaced twice already. Even though the cables are secured in the cable chains the constant motion of the machine simply wears though the cable insulation. I'd do the same thing again but I would use a hardware based step generator instead of an LPT port, even though the existing setup has been reliable. The machine runs fast since it is cutting a very lightweight material (foam) so it can hit speeds of 5-600 ipm on long straight cuts. Dave On 6/13/2014 10:16 AM, Todd Zuercher wrote: > Except for the sum of the backlash of each pinion, plus any twist of the > connection between them. > > ----- Original Message ----- > From: "andy pugh" <bodge...@gmail.com> > To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net> > Sent: Friday, June 13, 2014 6:04:37 AM > Subject: Re: [Emc-users] Ball Screw Drive? > > On 12 June 2014 01:34, Todd Zuercher > <zuerc...@embarqmail.com> wrote: >> I was considering just putting a ball screw on just one side of the gantry >> and leaving the racks and pinions alone (still connected). I know it kind >> of still leaves the far side to flop around > In that scenario the free-wheeling rack-and-pinion pair would keep > things square, so it isn't such a strange idea. > > ------------------------------------------------------------------------------ HPCC Systems Open Source Big Data Platform from LexisNexis Risk Solutions Find What Matters Most in Your Big Data with HPCC Systems Open Source. Fast. Scalable. Simple. Ideal for Dirty Data. Leverages Graph Analysis for Fast Processing & Easy Data Exploration http://p.sf.net/sfu/hpccsystems _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
